Evaluation report. X-ray tomographic image guided radiotherapy systems CEP10071

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1 Evaluation report X-ray tomographic image guided radiotherapy systems CEP10071 March 2010

2 Contents 2 Summary... 3 Introduction... 6 Product description... 9 Methods Technical performance Purchasing Acknowledgements Glossary References Appendix 1: Supplier contact details Appendix 2: Clinical protocols Appendix 3: Imaging dose calibration Appendix 4: Imaging dose data Appendix 5: Hounsfield number accuracy Appendix 6: CATphan image quality spatial resolution Appendix 7: CATphan image quality CTP404 module Appendix 8: Evaluation phase 1 summary of results Appendix 9: User survey questionnaire Author and report information... 84

3 Summary 3 The product X-ray tomographic IGRT systems are designed to acquire images of the 3D treatment target either immediately prior to or during radiotherapy treatment delivery. This report describes the evaluation of three different tomographic IGRT systems currently in use in the UK: Varian OBI v1.5 Elekta Synergy v4.2 TomoTherapy Hi-Art v3.2 Objective This document forms part of a national evaluation of X-ray tomographic IGRT systems, specifically those funded by the Department of Health Cancer Equipment Programmes. The purpose of the evaluation was to investigate whether these systems are able to provide accurate image guidance for radiotherapy. This report compares the performance and functionality of the systems assessed from both a technical and a user perspective. Field of use Image guidance systems of this type are used to assist with and improve the delivery of radiotherapy. They produce 3D images of patients whilst they are set up in the treatment position. Associated image registration capabilities allow the error in positioning to be quantified through comparison with a reference CT image of the patient acquired at the planning stage. If this is found to be above a specified action level, these errors can be corrected via movement of the patient support system or re-positioning of the patient. National guidance As image guidance is a relatively new and developing technology there is little national or international guidance governing 3D CT-based in-room image guidance systems. The National Radiotherapy Advisory Group in its 2007 report to the UK government [1] recommended that all replacement and newly installed machines are capable of image guided four-dimensional (4D) adaptive radiotherapy. Methods The evaluation was carried out in accordance with the CEP protocol [2], developed by a team in Leeds in consultation with equipment suppliers, users, professional bodies, and recognised experts in the field. The evaluation included several phantom-based technical studies assessing image alignment, image dose and image quality with a total of ten sites contributing data.

4 Summary 4 A user survey was conducted through a web-based questionnaire, with recruitment of users of tomographic IGRT performed through the Society of Radiographers. Technical performance All systems assessed had accurate alignment between the tomographic image to the treatment isocentre (within 1mm). The automatic couch correction features of all systems accurately re-positioned the treatment isocentre to within 1.5mm following translational shifts. Rotational accuracies were not measured. Imaging doses measured for typical clinical protocols ranged from 1.4 mgy per scan for a low dose head protocol to 25 mgy for the highest exposure pelvis protocol. These are comparable or lower than the maximum dose associated with most megavoltage planar portal imaging protocols. All systems were able to differentiate the contrast between muscle and fat as evident from images taken of a male pelvic phantom and, from this point of view; all were able to provide 3D soft tissue anatomical information. There were differences observed in the measured image quality parameters on each of the three systems and these were shown to vary with image dose. It was not possible, in this evaluation, to determine whether these differences affect the systems ability to perform image guidance. Operational considerations Tomographic IGRT systems are still relatively new. Few centres who responded to the user survey have had them installed for more than two or three years. As a result, the role of tomographic IGRT is still developing. This is further indicated by the variety of clinical applications and verification strategies used. Users were generally happy with the technical features of their systems. These systems may require additional in-room space, cable ducting and desk space for the IGRT workstation in the control area. The exact requirements will depend on the particular system and should be confirmed early in the purchase process so any refurbishment costs can be included in the business plan. CEP verdict All three systems evaluated fulfil the basic requirements of IGRT. They are capable of imaging 3D volumes within a patient with some definition of soft tissue and they

5 Summary 5 each have the ability to automatically correct for translational discrepancies in patient position based on comparison with a reference CT scan. Alignment of scans with treatment isocentre and automatic correction of the treatment delivery is achievable within 1.5 mm. Imaging doses are relatively low when compared to the dose from the treatment itself and are equal to or less than the dose associated with conventional megavoltage planar portal imaging. Following IRMER regulations, doses from imaging should still be justified on an individual basis. Tomographic IGRT is still relatively new and research and development are ongoing. While the results from this evaluation suggest tomographic IGRT is promising, clinical trials will likely be required to identify the disease sites where it can best be used and optimise the functionalities for each site.

6 Introduction 6 Background In the UK, over 50% of cancer patients will have radiotherapy as part of their treatment [1]. This treatment modality involves the delivery of a high dose of radiation to the tumour, whilst minimising the irradiation of surrounding healthy tissue. Many significant developments have taken place in the field of Radiotherapy over the past three or four decades primarily due to several key technological advancements. The first major landmark was the introduction of computed tomography (CT) with direct applications within treatment planning. This new imaging technique, coupled with improvements in computer processing capabilities and speed, meant computer planning systems rapidly developed to allow individualised patient planning in 3 dimensions (3D). This was followed by the introduction of multi-leaf collimators, which resulted in an increase in the conformality of the dose distribution achievable around the treatment target. More sophisticated methods of planning and beam delivery are now available in the form of intensity modulated radiotherapy, IMRT, in which the intensity of the radiation is varied during radiation beam delivery. This enables better sparing of organs at risk and the possibility of escalating the dose to the target without compromising surrounding healthy tissue. In many cases IMRT plans are produced using inverse planning techniques. This involves assigning dose constraints to each defined target volume or organ at risk with the system automatically calculating the beam parameters needed to deliver the optimal plan. These benefits can only be fully realised if the radiation distribution is assured to be delivered where it is planned in relation to patient structures. Image-guided radiotherapy (IGRT) uses imaging techniques to improve the accuracy of radiotherapy delivery to the target tumour, allowing more accurate and precise targeting of the treatment volume and avoidance of organs at risk (OAR). This may lead to a reduction in the radiation-induced complications and side effects that are caused by irradiation of normal tissues. It may also allow an increased dose to be delivered to the target tissues, thereby maximising the chances of successful control or eradication of the tumour. The term IGRT is ill-defined and may have a variety of meanings in different contexts. Here IGRT refers to the ability: to visualise the anatomical target and OAR s in 3D to identify changes in position, shape and size of target anatomy relative to that seen when the treatment was planned to quantify the variation in position of the anatomical target between the planned and initial setup treatment images

7 Introduction 7 to correct any patient misalignment by changing the relative geometry of the treatment machine (couch, gantry) before the treatment is delivered. This technology is being rapidly deployed throughout the world and while there is, as yet, little clinical trial evidence of its effect on outcomes, it has great potential to improve radiotherapy delivery for a significant proportion of patients [3]. IGRT can involve almost any imaging modality, but a common implementation is to have a CT- like scanner closely integrated with the linear accelerator (linac). For the purposes of this project, these systems have been termed X-ray tomographic IGRT systems. Scope The Department of Health Cancer Equipment Programmes invested 5m in IGRT supplementary equipment to eight linear accelerators in operation within the NHS (Varian and Elekta), plus the provision of one integrated IGRT solution (TomoTherapy). This funding was conditional on recipient NHS trusts participating in a national evaluation of the technology, the purpose being to verify that these systems are able to achieve accurate image guidance and to compare their performance and functionality both from a technical and a user perspective. This document presents the findings of that evaluation. The project comprised two phases. Phase 1 concerned the development of an evaluation protocol, published separately [2] and phase 2 was the implementation of this protocol at several test sites, as reported in this document. Specifications of tomographic IGRT systems available in the UK are provided in a separate market review (CEP10072).

8 Introduction 8 National guidance As IGRT is a relatively new and developing technology, there is little national or international guidance governing 3D CT-based in-room image guidance systems. The following is an excerpt from the National Radiotherapy Advisory Group in its 2007 report to the UK government [1]: NRAG: A 3D based environment for imaging, planning and radiotherapy delivery is the current baseline for linacs. However, 4D radiotherapy takes into account tumour volume in three dimensions but also takes into account changes with time (the 4th dimension). Adaptive therapy also allows the treatment set-up and dose delivered to be verified and then changed as necessary during a course of treatment. NRAG advises that image guided four-dimensional (4D) adaptive radiotherapy is the future standard of care for radical radiotherapy treatment that the NHS should aspire to. NRAG therefore recommends that all replacement and newly installed machines are capable of image guided four-dimensional (4D) adaptive radiotherapy. There is evidence (set out in the technology report) that these processes will become more time-efficient as the technology becomes standard practice. Outside of the UK there are work in progress guidelines for the use of IGRT from the American Society for Therapeutic Radiology and Oncology (ASTRO) and the American College of Radiology (ACR) [4] and also from the Advanced Technology QA consortium, based at Washington University School of Medicine in the United States [5]. The ACR have also published practice guidelines for IGRT [6].

9 Product description 9 Equipment overview X-ray tomographic IGRT systems are designed to acquire images of the 3D treatment target either immediately prior to or during radiotherapy treatment delivery. The systems enable these images to be compared with the CT reference images used for planning the patient s treatment. The supporting document, CEP10070 [2] provides a framework and detailed protocol for the technical evaluation of all X-ray tomographic IGRT systems, including in-room kilovoltage CT (kvct) [7], kilovoltage and megavoltage cone beam CT (kv-cbct, MV-CBCT) [8, 9] and megavoltage CT (MVCT) [10]. This specific report describes the evaluation of two types of tomographic IGRT system; kv-cbct and MVCT. KV-CBCT systems have an additional kv X-ray imaging system mounted onto the gantry of the MV treatment machine, producing kv cone beam CT images. This is a method used by a number of different manufacturers [11-12]. MVCT is, at present, unique to the one manufacturer and employs the technology of standard helical kvct but uses an MV fan beam [14]. MV-CBCT systems use the electronic portal imaging device (EPID) which is mounted on the gantry of conventional MV treatment machines. These acquire a 2D projection image through the patient from the MV treatment beam but can be engineered to rotate around the patient while acquiring a series of projection images. The images can be reconstructed into 3D datasets with image intensity related to the electron density. At the time this study was initiated, no such systems were available in the UK market and are therefore not covered in this evaluation. Additionally, kvct systems which are essentially a CT scanner located in the treatment room with a couch that allows direct transfer of the patient between the kvct scanner and the MV treatment machine were also not evaluated in this study. Systems evaluated Three systems were evaluated for this report: Varian OBI v1.5 Elekta Synergy v4.2 TomoTherapy Hi-Art v3.2 Varian On-Board Imager (OBI) v1.5 The Varian OBI is a kv-cone beam CT system integrated onto the Varian Clinac series of linacs. The system consists of an X-ray tube and amorphous silicon flat panel detector, both of which are mounted on robotic arms to the linac gantry system. The imaging direction is perpendicular to the treatment beam axis. For the tube this is such that the X-ray source is at 1000 mm from the machine s isocentre. For 2D imaging the source to detector distance is variable but for CBCT it is fixed at the

10 Product description 10 default setting of 1500 mm. Re-calibration for other source to detector distances is possible, but the default is usually adopted. Image acquisition is controlled by the on board imager computer from the linac control room. The system can be set to acquire both static gantry radiographic or fluorographic images as well as CBCT. In CBCT mode the robotic arms extend automatically to the required position prior to imaging and can be retracted back to their folded position once imaging is complete. There are two principal fields of view in the trans-axial plane called full fan and half fan. In full fan mode the maximum field of view is 24 cm, while in half fan mode the collimation and detector are shifted laterally to allow a field of view up to 50 cm diameter 1 and a half cone beam is used resulting in only half of the field of view being irradiated in any one projection. Collimation in the long axis is continuously variable and can be set by the operator with the maximum lengths achievable being dependent upon the fan mode and slice thickness. During image acquisition approximately 650 2D projection images are acquired while the gantry rotates through 360º, taking approximately 1 minute. In full fan mode, it is possible to reduce the number of projection images to approximately 360, by reducing the gantry rotation range to only 200º. This is an effective way of reducing patient dose and increasing image acquisition speed. Scans can be acquired with or without a bow tie filter [13] (with separate filters available depending on whether operating in full fan or half fan mode). The direction of gantry rotation can be either clock-wise or anti-clockwise. The direction defaults to that with a start angle nearest the gantry angle immediately prior to the start of image acquisition. There are six standard pre-defined CBCT modes with three different tube voltages; 100 kv for those involving the head, 110 kv for the thorax and 125 kv for pelvic acquisitions. These modes have standard exposure settings ranging from 72 mas (low dose head protocol) to 720 mas (high quality head protocol and pelvis spotlight mode). By varying the combination of tube current and pulse length, it is possible to create user customised image acquisition modes at non-standard exposures. Once acquired, the projections are stored on a separate computer system which reconstructs the CBCT slices and sends them to the OBI computer for display. Images can be reconstructed on pixel matrices of 128 x 128, 256 x 256, 384 x 384 or 512 x 512. The pixel size depends on the field of view and the size of the pixel matrix. Slice separation can be selected with a choice of 1 to 5 mm in 0.5 mm increments and 10 mm. However, the default setting when used in a pre-defined 1 Note that these FOVs apply for the default source to detector distance of 1500 mm.

11 Product description 11 clinical mode is a pixel matrix of 384 x 384 with 2.5 mm slice thickness. There is a choice of two image reconstruction filters, sharp and standard which affect the characteristics of the noise in the reconstructed images. Image registration of the CBCT image with a reference image is also performed on the OBI computer. Image registration can be performed either manually or automatically and is restricted to rigid body transformations and rotations. Assuming a standard Varian couch, the degrees of freedom for the registration are the three perpendicular translation directions, (lateral, vertical and longitudinal) and one rotation about the vertical axis corresponding to an isocentric couch rotation. Correction of patient position is achieved by translation of the couch in lateral, vertical and longitudinal directions as well as isocentric couch rotation and all can be performed automatically and remotely from outside the room, including yaw. There are no in-built facilities for correcting rotations about the horizontal two axes, pitch and roll. Elekta Synergy x-ray volumetric imager (XVI) v4.2 The Elekta Synergy system is a kv-cone beam CT system integrated onto an Elekta Precise linear accelerator. The system consists of an X-ray tube and amorphous silicon flat panel detector both of which are mounted with a view direction that is perpendicular to the treatment beam axis. The tube is deployed manually for imaging while the detector unfolds from its stored position against the face of the gantry under motorised control. The configuration of the system has the X-ray source at 1000 mm from the machine s isocentre while the X-ray source to imager distance is fixed at 1536 mm. Image acquisition is controlled by the XVI computer from the linear accelerator control room. The system can be set to acquire static gantry, radiographic or fluorographic images as well as CBCT. There are three principal fields of view in the trans-axial plane called small, medium and large. The small field of view has a diameter of approximately 25 cm with the detector centred on the source-isocentre axis. The large field of view has a diameter of approximately 50 cm and requires a half fan offset of the detector and corresponding offset collimation of the radiation field. The medium field of view has a diameter of approximately 40 cm and is a compromise between the improved image quality of the small field of view and an increased field of view to sufficiently image the majority of patients. Collimation for the small, medium and large fields of view is achieved by a set of removable lead collimator inserts with fixed aperture sizes. These have to be interchanged manually when swapping between fields of view. Collimation in the long axis is also achieved using the removable collimators with a choice of 3 to 4 lengths depending on the field of view (S, M, L). These are labelled 2, 10, 15 and 20 but are approximately 3.5, 13.6, 17.6 and 27.7 cm (giving corresponding cone angles of 1.0º, 3.9º, 5.0º and 7.9º) and can be set by the operator.

12 Product description 12 During image acquisition approximately 630 2D projection images are acquired while the gantry rotates through 360º, taking approximately 2 minutes. The direction of gantry rotation can be either clockwise or anti-clockwise. The tube voltage for image acquisition can be chosen from a range of 70 kv to 150 kv and the exposure level can be chosen using discrete combinations of tube current and pulse length. The range of exposure levels is from 0.1mAs/pulse to 80mAs/pulse. Details of image acquisition such as tube voltage, current, pulse length, gantry start and stop are chosen using predefined clinical presets. Once acquired the image is reconstructed on the XVI computer. Image reconstruction size, position and voxel size are controlled using reconstruction presets. Standard reconstruction presets provided with the system have three resolutions, described as small medium and large corresponding to 0.5 mm 3, 1 mm 3 and 2 mm 3. Voxel sizes are isotropic hence slice thickness is linked to the in-plane resolution. The image viewing application allows slices to be viewed as an average of slices on either side to simulate thicker slices. The flexibility to adjust image reconstruction, filter parameters and scatter correction exists, but is not usually adjusted from the default values by the user. Image registration of the CBCT image with a reference image is also performed on the XVI computer. Image registration can be performed either manually or automatically using one of two algorithms. The Bone algorithm uses the chamfer matching algorithm [15] and the Grey algorithm uses correlation ratio [16, 17]. Image registration is rigid body with six degrees of freedom. These are the 3 perpendicular translation directions, lateral, vertical and longitudinal, and 3 rotations about the three major axes. Correction of patient position is achieved by translation of the couch in lateral, vertical and longitudinal directions, as well as isocentric couch rotation, and all can be performed automatically and remotely from outside the room. There are no in-built facilities for correcting rotations. However, additional equipment, such as the Hexapod robotic couch, may be purchased to correct rotations about the three axes. TomoTherapy Hi-Art v3.2 The TomoTherapy Hi-Art system is a fully integrated IMRT/IGRT system. The megavoltage treatment delivery system is delivered using a helical fan beam with a continuous couch feed similar to a diagnostic CT scanner. The design of the TomoTherapy Hi-Art system is optimised for the delivery of complex IMRT treatments, the IMRT capabilities replacing the features of conventional linear accelerator systems such as electron beams and non-coplanar beam arrangements. Imaging is performed using an X-ray beam generated from the same linear accelerator system as the treatment beam; the 6MV beam is de-tuned to 3.48 MeV

13 Product description 13 peak (average of kev) for imaging purposes [18]. The beam is collimated by 264 dynamic multi-leaf collimators to a width of 1 cm and length sufficient to give a maximum transverse field width of 38.4 cm at isocentre. Maximum field length is 160 cm, achieved by continuous translation of the treatment couch through the isocentre as the radiation is delivered. The image is acquired using an arc shaped Xenon gas detector which rotates with the source. The source to detector distance is 145 cm and the source to axis distance is 85 cm. The default pitch settings of the helical acquisition are 1.0, 1.6 and 2.4 which correspond to slice widths of 2 mm, 4 mm and 6 mm. These are given the terms 'fine', 'normal' and 'coarse'. The beam on time to acquire a single slice is 5s with an initial 16s overhead at the start of the procedure. Images are reconstructed with an in-plane matrix of 512 x 512 for the 38.4 cm width field of view giving rise to a pixel spacing of 0.75 mm. Rigid body image registration of the MVCT with the reference kvct can be performed manually or automatically using a mutual information based algorithm [14]. Image registration provides the three perpendicular translations (lateral, vertical and longitudinal) and three rotations about the three major axes, required to correct the patient. Vertical, longitudinal and lateral couch movements can be performed remotely from the control area. Correction for rotation about the longitudinal axis ('roll') can also be performed automatically and remotely by correcting the gantry position of the treatment prescription. There are no facilities for correcting rotations about the other two axes, 'pitch' and 'yaw'. MVCT images acquired before a treatment is administered can be used in the Planned Adaptive module to recalculate the dose to the patient from that particular fraction. This enables any positional corrections or variations in patient anatomy that may be present, (for example tumour shrinkage), to be taken into account. Once recalculated, a dose difference map can be generated, allowing the effect of these anatomy or positional changes on the plan to be assessed. If desired, regions of interest (ROIs) can be re-contoured to allow the analysis of DVHs for these deformed structures. In addition, hotspots and coldspots within a particular structure can be isolated and segmented out as separate ROIs, thus local top up or reduction of dose can be performed. The MVCT data can then be exported to the planning system incorporating any modifications or additions to the ROIs and a new plan can be generated.

14 Methods 14 User evaluation A web based user survey (appendix 9) based on previous KCARE survey forms and designed in consultation with the Society of Radiographers was used to gather user feed back on tomographic IGRT systems. Where possible, the survey used multiple choice answers and rating scales to ensure focussed responses, but provision was also made for more general comments. Technical evaluation The objective of the technical evaluation was to test each of the IGRT systems to assess their capability in delivering accurate image guidance. A secondary objective was to perform a subset of the tests on more than one system of the same type to determine the variation across multiple systems from the same manufacturer where possible. To achieve these objectives the evaluation examined three key aspects of performance: image alignment, image dose and image quality. Image alignment For image guidance, geometrical accuracy of the image is as important as the ability to see an object in the image. In this context, geometrical accuracy can be divided into a number of components: initial spatial registration of the image data to the treatment delivery system spatial integrity of the data within the image volume image registration of the IGRT image to the pre-treatment planning scan the correction of any patient misalignment. The initial spatial registration identifies the position of the image volume with respect to the position of the isocentre of the megavoltage beam delivery system; often this is in a different plane with a defined offset. This measures the radiation isocentre which is a better representation of the delivered treatment centre and is quicker than measurement of the physical isocentre. To assess this alignment, for CT based imaging a kv-mv coincidence test has been devised specifically for this evaluation [2, 19]. For an integrated CT-treatment machine, as is the case with TomoTherapy, the imaging and treatment beams are one and the same and are therefore assumed to be registered. Once the imaged volume has been registered to the isocentre of the treatment delivery system it is also necessary to know that all points within an imaged volume are in the correct position relative to each other and that there are no rotations of the volume. By using structures in an image quality test phantom, image scaling, rotation and skew have been measured. While these do not demonstrate spatial integrity of the data over the whole imaged volume, they do at least demonstrate the integrity of a sample of points. Since image reconstruction relies on correct knowledge of the

15 Methods 15 projection data geometry, identification of these few points goes some way to demonstrating the integrity of the whole volume. In this evaluation, image registration of the IGRT image to the pre-treatment planning scan has been performed manually using visualisation. Although automatic image registration algorithms are provided on some IGRT systems and have the potential to reduce time spent on image registration and reduce intra-observer variability, the performance of these is not easily measured and is the subject of current research [20]. It therefore was not considered to be within the scope of this report to evaluate the performance of the automatic image registration algorithms. To demonstrate the ability to measure and correct for the misalignment of a patient, an image-shift-verify test has been employed using a geometric phantom. The ability to correct the patient position is usually restricted to three orthogonal axes of translation (plus one axis of rotation for some systems) and these are evaluated in this report. However, it is acknowledged that it does not demonstrate that the treatment dose is delivered to the correct target. This test only verifies corrections performed by a translation or rotation shift of the phantom using the patient support system and does not verify corrections made by adjusting treatment delivery parameters. Image dose The X-ray dose produced by the imaging equipment, which affects normal tissue as well as tumour, is an important parameter which affects the usability of these systems, as in some circumstances a high image dose may prohibit the repeated use of such systems for daily online image guidance. The associated image dose has therefore been measured on each system for a selection of clinically relevant imaging protocols. Image quality As an indicator of a system s ability to image soft tissue, the image quality must be sufficiently good to resolve contrast between muscle and fat. It is accepted that the inter-dependence of contrast, resolution and dose is a complex relationship which limits the size of an object that can be seen at the same level of contrast. This is further complicated by the ability to change the reconstruction filters on some systems which can have large effects on this relationship. It is beyond the scope of this evaluation to perform tests that comprehensively characterise the imaging system. Instead, basic image quality measures of contrast, noise and resolution have been measured on each system using a selection of clinically relevant imaging protocols. The additional imaging of an anthropomorphic phantom has also been included to enable the image quality of a clinically realistic object to be visually assessed and allow subjective comparison between different systems.

16 Methods 16 Participating centres The technical evaluation was carried out in two stages; the first, performed between February and May 2008, took place at the DH funded evaluation sites. In addition some evaluation work was performed at other sites with similar systems. These sites formed part of an informal research network which permitted the testing of the evaluation protocol. In this document these have been called the test sites. Due to significant changes in software and system upgrades in the subsequent period, a follow-up evaluation was carried out in February 2010 using the most up to date clinical systems currently available in the UK. The main body of this evaluation report presents the data acquired during this second wave of evaluations. Results from the first round of evaluations are given in appendix 8. This data provides an indication of the variation in performance that exists between multiple systems from the same manufacturer and highlights the degree of standardisation between them. Table 1. List of participating sites Phase 1. Evaluation sites Guy's and St Thomas NHS Foundation Trust Maidstone and Tunbridge Wells NHS Trust Poole Hospital NHS Trust Southampton University Hospitals NHST Ipswich Hospital NHS Trust University Hospital Birmingham NHSFT Royal Free Hampstead NHS Trust Cambridge University Hospitals NHS Foundation Trust Phase 1. Test sites Ipswich Hospital NHS Trust Equipment Elekta Synergy Varian OBI Elekta Synergy Elekta Synergy Varian OBI Elekta Synergy Varian OBI TomoTherapy Hi-Art Equipment Varian OBI

17 Methods 17 Cambridge University Hospitals NHS Foundation Trust Leeds Teaching Hospitals NHS Trust Phase 2. Test sites Clatterbridge Centre for Oncology NHS Foundation Trust Cambridge University Hospitals NHS Foundation Trust Leeds Teaching Hospitals NHS Trust TomoTherapy Hi-Art Elekta Synergy Equipment Varian OBI TomoTherapy Hi-Art Elekta Synergy Test 1: Registration of image volume to treatment isocentre Overview The purpose of this test is to assess whether the centre of the imaging volume is registered to the treatment isocentre to within ± 1 mm in all directions. This is particularly critical if the system is to be used as guidance for intra-cranial stereotactic treatments such as SRS and SBRT. A greater tolerance of ± 2 mm may be acceptable for other clinical sites [51]. The design of this test is not suitable for systems where the imaging beam is the same as the treatment beam and therefore share the same focal spot and machine isocentre The test relies on a phantom that can be imaged with both the imaging device and the treatment device. The MODUS Penta-Guide Quasar Phantom [2, 19] was chosen for this task. Its design is such that the megavoltage treatment isocentre is inferred from an anterior-posterior and lateral portal image, however this method does not measure the MV treatment beam isocentre sufficiently accurately to determine whether the IGRT system is suitable for treatments which require high levels of accuracy and precision, e.g. stereotactic cranial irradiation and SBRT. The method as detailed in [19] is summarised below. Materials 1. Modus QUASAR Penta-Guide phantom (Modus Medical Inc, Ontario, Canada) [21] 2. Analysis software [2, 19]. For further details contact the authors. Method 1. The Pentaguide phantom was scanned at high resolution on a CT scanner and a simple plan was created with a single isocentre positioned at the geometric centre of the central air-cavity within the Penta-Guide phantom.

18 Methods Eight,12cm x 12cm square beams were created at gantry angles of 0, 90, 180 and 270, two at each gantry angle with opposing head angles (e.g. 90 and 270 ). 10 cgy was set for each beam to provide sufficient quality MV images for automated image analysis. 3. The DICOM images, DICOM-RT structure and plan data were sent and imported into the IGRT system(s) under evaluation and the plan data was sent to the treatment delivery system. 4. The phantom was aligned to the room lasers of the IGRT system ensuring that the phantom was level. 5. Eight MV images were acquired for the beams defined in the treatment plan. 6. The phantom was then scanned using the CBCT system with a standard field of view. 7. Analysis software was used to determine the shift of the centre of the Pentaguide phantom with the MV isocentre. 8. The IGRT system was then used to determine the shift required to align the central air-cavity in the CBCT image of the Pentaguide phantom with the aircavity in the CT images of the treatment plan. 9. The vector (lateral, longitudinal and vertical) difference between the phantom centre measured with the MV-imaging system with that of the kv-imaging system was then calculated. Test 2: Image-shift-verify test Overview This test demonstrates the ability of an IGRT system to perform a basic correction of patient misalignment to within ±2 mm. This is achieved through imaging a misaligned object, performing an image registration to determine the misalignment and correcting the misalignment. Verification of the correction is then achieved by a further image and image registration procedure. This test was performed using the geometric Pentaguide phantom as used in test 1. Materials 1. Modus QUASAR Penta-Guide phantom (Modus Medical Inc, Ontario, Canada) [21]. Method 1. The Pentaguide Phantom was scanned at high resolution on a CT scanner and a basic plan was created with the treatment isocentre at the centre of the phantom. 2. The DICOM images, DICOM-RT structure and plan data was imported into the IGRT system under evaluation. 3. Using external lasers on the IGRT system, the phantom was aligned to a set of offset markers on the surface of the phantom and a standard IGRT image was acquired.

19 Methods Manual image registration was then performed and the required registration shifts as displayed by the IGRT system were recorded. 5. The phantom position was then corrected as far as possible by movement of the patient support system using automated methods where available and manual movement when this was not possible. 6. A repeat image was then acquired followed by another image registration to enable residual errors to be quantified. 7. This process was performed as described at each of the evaluation sites and repeated three times at each of the test sites to give an indication of system reproducibility. Test 3: Imaging dose Overview Using a standard method, this test enables the dose in air and the dose (to water) in two CTDI phantoms to be measured for a range of scanner settings and clinical protocols. Currently no standards exist for the measurement of concomitant dose associated with IGRT procedures and there is no consensus as to what measurements should be made or what information should be reported. For standard diagnostic CT scanning procedures, a 10 cm long CTDI chamber is used, which due to the elongated sensitive volume, enables all scatter contribution to be collected during the imaging of a single slice. Measurements are made both at the centre and at the periphery of a CTDI phantom. Resultant doses are then expressed as a weighted CTDI w (1/3 x central measurement + 2/3 x peripheral measurement). However, CBCT systems do not have narrow beam geometry thus it is no longer instructive to measure over 10 cm. The situation is further complicated by the fact that for larger fields of view, there is an offset between the tube and the panel thus resulting in a complex dose profile in the transverse plane. Consequently, for this evaluation, dose is sampled at a single point within the field using a Farmer chamber inside a CTDI phantom and measurements are acquired at an intermediate position (~7 cm from the centre) in addition to the standard central and peripheral positions. Materials 1. Two computed tomography dose index (CTDI) phantoms (head and body, 16 cm and 32 cm diameters) (ImPACT, London, UK) [22] 2. A Farmer chamber with calibration traceable to NPL standard at the appropriate beam quality obtained by measuring the half-value thickness. 3. Calibrated electrometer. Method This protocol closely follows the methods employed by Song et al [23]. 1. For in air dose measurements, the ion chamber was suspended over the end of the couch and positioned at isocentre.

20 Methods For scan protocols involving smaller FOV imaging fields, dose measurements were made in two 16cm diameter CTDI phantoms. These phantoms were positioned back to back with the ion chamber positioned longitudinally offset by approximately 1.5 cm to ensure that measurements were not affected by the join between phantoms. The CTDI phantoms were aligned such that the midline of the phantom coincided with the imaging isocentre. 3. For scan protocols involving larger FOV imaging fields, dose measurements were made in two 32 cm diameter CTDI phantoms set up in the same way. 4. On the Elekta Synergy system, 6 standard clinical protocols were measured using the S20 collimator for the head protocols and M10, M15 and M20 for the pelvic acquisitions. On the Varian OBI system, the five manufacturer supplied standard clinical protocols were measured and on the TomoTherapy Hi-Art, measurements were made for each of the three pitch settings (fine, medium and coarse). 5. In all cases, measurements were made at the centre and periphery of the CTDI phantom. For the larger FOV protocols, a further measurement was acquired at an intermediate position (~7 cm from the centre). For further details of the image acquisition settings adopted see appendix 2. Test 4: Pseudo-clinical image quality This test is intended to assess image quality using an anthropomorphic phantom which has realistic soft-tissue organs in order to simulate a clinical scenario as closely as possible. Materials 1. Virtually Human Male Pelvis Phantom, CIRS (Norfolk, Virginia ) [24]) Method 1. The anthropomorphic phantom was aligned centrally to the isocentre. 2. An image of the phantom was acquired on each of the test systems using typical clinical protocols for prostate IGRT, for specific acquisition and reconstruction settings, see Appendix The images were then displayed in each of the sagittal, coronal and transverse planes ready for visual inspection. Test 5: Image quality Overview This test is intended to measure various indicators of image quality for 3D images measured for a selection of acquisition and reconstruction settings representative of clinical practice. As there are no standard ways of measuring image quality over the whole volume, this method measures image quality at specific points in the FOV

21 Methods 21 using a standard image quality phantom [25], thus enabling the following image quality indicators to be measured: contrast to noise ratio, Hounsfield number accuracy, axial plane resolution (lp/cm), modulation transfer function, slice sensitivity, uniformity and spatial integrity. Materials 1. CATphan 504 (The Phantom Laboratory, Salem, NY, USA) [25]. 2. Image analysis capability either on the system under test, or a separate Dicom viewer such as ImageJ [26] or IQWorks [27]. Method 1. The phantom was positioned at the isocentre of the imaging volume. On the upper surface of the CATphan there are five alignment markers to indicate the position of the centre of each module. In each case, the CATphan was aligned longitudinally with the 2nd marker (CTP528). Care was taken to ensure that the CATphan was aligned laterally and vertically with the room lasers and to avoid any tilt of the phantom. 2. The phantom was then scanned on each system using the acquisition parameters dictated by each system s respective clinical protocol; see Appendix 2 for further details. Image analysis 1. Contrast-to-noise ratio (CNR): Contrast-to-noise ratio gives an indication of the ability of a system to distinguish the difference between two materials in the presence of image noise. It is given by the ratio of the difference in mean grey level between two objects (contrast) by the standard deviation of the noise. Using the image analysis function, the mean and standard deviation of the mean pixel values occurring within square ROIs (approx 7mm x 7mm) placed on each of the 8 contrast inserts of the CTP404 module was measured and thus CNRs were calculated for each insert relative to polystyrene using the equation below, where mat indicates the material of the ROI, x is the mean of the pixels in the ROI and s is the standard deviation of the pixel values in the ROI. CNR mat = ( xmat x polystyrene ) 2 2 ( s + s ) mat polystyrene 2. Hounsfield number accuracy: The mean pixel values found during the analysis above are related to the Hounsfield numbers for each of the inserts. To convert the raw image data into actual Hounsfield numbers, it is necessary to apply a scaling factor, Rescale slope and an offset equal to the Rescale

22 Methods 22 intercept [28]. Using the Dicom header files, these factors were determined and applied to the data thus enabling the Hounsfield numbers to be calculated. Through comparison with the actual values specified by the phantom supplier, the Hounsfield number accuracy was determined by taking the difference between the two. 3. Uniformity: Uniformity is a measure of a system s ability to produce a uniform image across the field of view of an object with uniform density. To calculate uniformity, five adjacent trans-axial image slices sampled from a large uniform region of the CTP468 module were selected within each image set. For each of these slices, a central ROI of size 10mm x 10mm, was chosen with four other identical ROIs placed 45 mm above, below, left and right of the central ROI. Two definitions were used to calculate the overall uniformity as defined below, where max and min refer to the maximum and minimum pixel value averaged over each ROI respectively, Ave(peripheral) is the average pixel value within all peripheral ROIs and Centre relates to the mean pixel value occurring within all central ROIs. ( Max Min) U1 = ( Max + Min) / 2 U 2 = Ave( peripheral) Centre Centre 4. Axial plane resolution: The ability of the system to resolve two lines of high contrast placed close together was quantified by recording the greatest number of line pairs within the CTP528 module that were fully resolved when the images were viewed at similar magnification and window settings. 5. Spatial integrity: To assess the system s ability to accurately represent the object imaged without scaling, rotation or distortion, the four rods spaced at the corners of a 50 mm square within the CTP404 module of the CATphan were used. Linearity was quantified by recording the side length with the greatest deviation from 50 mm and the aspect ratio was recorded as the maximum ratio of perpendicular side to length. 6. Slice sensitivity: Slice sensitivity is a measure of slice width. This was assessed by measuring the full width at half maximum (FWHM) across the wire ramps present in the CTP404 module of the CATphan. This was performed using the image analysis software IQworks [27]. 7. Low contrast visibility: Within the central region of the CTP404 module of the CATphan, there are acrylic spheres with diameters ranging between 2 mm and 10 mm. To assess low contrast visibility, the images were assessed to see if any of the spheres were visible.

23 Technical performance 23 Test 1: Registration of image volume to treatment isocentre This test was only performed on Elekta Synergy v4.2 and Varian OBIv1.5, being unnecessary for TomoTherapy Hi-Art as previously discussed. The test was also performed at each of the phase 1 evaluation centres; see Table 21, Appendix 8. The resultant vector (magnitude) has also been calculated. Table 2. kv/mv alignment (mm) Elekta Synergy v4.2 Lateral Longitudinal Vertical Magnitude Varian OBI v1.5 Lateral Longitudinal Vertical Magnitude Test 2: Image-shift verify test This test has demonstrated the ability of all systems to perform a basic correction of patient misalignment to within ±1.5mm using a geometric phantom. Both the Elekta Synergy system and the TomoTherapy Hi-Art system were able to position the phantom to within 0.6mm as shown in table 3. Despite the Varian OBI recording a maximum residual error of 1mm, the digital display for this system only reads to the nearest mm therefore residual errors up to 1.5mm may have occurred. The image matching was performed by current users of each of the systems with previous experience. Table 3. Residual errors after image-shift-verify test (mm) Elekta Synergy v4.2 Lateral Long Vertical Set Set Set Varian OBI v1.5 Lateral Long Vertical Set Set Set

24 Technical performance 24 TomoTherapy Hi Art v3.2 Lateral Long Vertical Set Set Set Test 3: Imaging dose Tables 4-5 display the resultant doses that are representative of each scan protocol. The values reported correspond to the average measurement made across central and periphery positions in the head phantom, and between central, periphery and mid-periphery positions in the body phantom. The comprehensive list of measurements is provided in appendix 4. Dose measurements are accurate to within ±10%. Table 4. Elekta Synergy v4.2 dose measurements in mgy Protocol 1 Low head Protocol 2 Med Head Protocol 3 High Head Head Protocol 4 Pelvis M10 Protocol 5 Pelvis M15 Protocol 6 Pelvis M20 Body Air Table 5. Varian OBI v1.5 dose measurements in mgy Low Dose Head Standard Dose Head High Quality Head Pelvis Pelvis Spotlight Head Body In Air Table 6. TomoTherapy Hi-Art v3.2 dose measurements in mgy Coarse Medium Fine Head Body In Air

25 Technical performance 25 Test 4: Pseudo-clinical image quality Figures 1-3 display the images of the VHMP as acquired on each of the systems using typical clinical pelvic protocols. Elekta Synergy v4.2: There is clear differentiation between the muscle and fat soft tissues. In the transaxial images there is a degree of streak artefact which increases with the longitudinal field of view. Some shading artefacts are present, an example being the shadowing visible between some of the pelvic bones, demonstrating non uniformity of the CT number within the imaged volume. There is also some evidence of a circular artefact which is likely to be related to the interface between regions exposed throughout the 360 scan and those regions only exposed through 180 (this artefact was also observed within the CATphan images). Varian OBI v1.5: There is clear differentiation between the muscle and fat soft tissues. In the transaxial images there are some streak artefacts originating from high density objects within the image i.e. bones and surface markers. In the sagittal and coronal sections the noise characteristics are elongated in the longitudinal direction due to the slice thickness (2.5mm). The spotlight protocol gives acceptable images as long as the image of the skin surface is not required. For this protocol, a prominent shading artefact between the brighter centre of the image and the darker outer region is visible; however this is not likely to affect image guidance of the central prostate. TomoTherapy Hi-Art v3.2: There is clear differentiation between the muscle and fat soft tissues. The CT number uniformity across the image is free from shading and streaking artefacts. However, this absence makes the stochastic noise more apparent and in the sagittal and coronal sections the noise characteristics are elongated in the longitudinal direction due to the slice thickness. This is increasingly noticeable as the pitch increases. There is also an artefact extending along the longitudinal rotation axis of the system which again is predominantly visible in the sagittal and coronal views.

26 Technical performance 26 Figure 1. Elekta Synergy v4.2 VHMP images displayed in the transverse, sagittal and coronal planes for a) M10, b) M15 and c) M20 collimators a) b)

27 Technical performance 27 c)

28 Technical performance 28 Figure 2. Varian OBI v1.5 VHMP images displayed in the transverse, sagittal and coronal planes for a) pelvis and b) pelvis spotlight protocol a) b)

29 Technical performance 29 Figure 3. TomoTherapy Hi-Art v3.2 VHMP images displayed in the transverse, sagittal and coronal planes for a) coarse b) normal and c) fine pitches a) b)

30 Technical performance 30 c)

31 Technical performance 31 Test 5: Image quality Tables 7-9 list the various image quality parameters that were measured on each system for their respective clinical protocols. The full data set regarding Hounsfield number accuracy can be found in Appendix 5 and example images taken from both the CTP404 module of the CATphan and the CTP528 module of the CATphan are displayed in Appendix 6 and 7. A summary of the image quality data for each system is presented below. TomoTherapy Hi-Art v3.2 The spatial integrity of the images was found to be good in all cases; linearity was below 1% and the maximum aspect ratio was On visual inspection, although the images appeared uniform the presence of a brighter region occurring at the centre of the imaged volume resulted in relatively high uniformity values (of the order of 5%). This artefact was noticeable in all image sets. The noise present within the polystyrene ROI and hence the CNR for polystyrene did not vary significantly with pitch. Spatial resolution was also constant with pitch at 3 lp/cm resolved. Estimates of the Hounsfield numbers of each of the density inserts were within 13%. No variation with pitch was observed. Elekta Synergy v4.2 The spatial integrity of the images was found to be good in all cases; linearity was below 1% and the maximum aspect ratio was For all protocols investigated, the slice sensitivity was overestimated by an average of 0.7mm. The head protocols produced the most uniform images with uniformity figures ranging between 1.8% and 3.2%. Using the pelvis protocols with the panel offset to produce the medium field of view, resulted in a loss of uniformity with a ring artefact becoming more dominant at ~5cm from the centre of the image. This led to the uniformity figures increasing up to a maximum of 4.9%, corresponding to the protocol with the largest field length (M20). This artefact is not visible in the VHMP images and may only be present in CATphan images. Increased exposure and therefore increased dose for a given protocol resulted in an expected reduction in noise and thus a higher CNR. Spatial resolution remained at 3 lp/cm for all protocols assessed. The Synergy system overestimated the Hounsfield numbers for all the density inserts with a maximum error of 123%. Although the accuracy increased significantly with image dose, even the highest exposure protocols (corresponding to the pelvis) still

32 Technical performance 32 suffered large errors ranging between 29% and 63% depending upon the insert density. Varian OBI v1.5 The spatial integrity of the images was found to be good in all cases; linearity was below 0.7% and the maximum aspect ratio was The slice width was estimated to within 0.15mm for all protocols tested except the low dose head protocol which underestimated it by 0.6mm, however, it is likely that this may indicate an error in the actual measurement. The Varian OBI system accurately estimated the Hounsfield numbers of each of the density inserts to within 6%. Discounting the first clinical protocol, the calculated Hounsfield numbers from the low dose head protocol (2.8 mgy) and the half fan pelvis protocol showed excellent agreement with the true values, with maximum variations of 2% and no further variations with imaging protocol were observed. Spatial resolution was very good with 7lp/cm resolvable for all clinical protocols assessed except for the pelvis protocol for which a maximum of 6lp/cm were resolved. This was the only protocol which utilises the half fan mode. Uniformity was also relatively constant across each imaging protocol with a maximum value of 2.8%. However, a distinct ring artefact was present within the images using the half fan pelvis protocol which resulted in poorer uniformity (3.9%). This artefact is not visible in the VHMP images and may only be present in CATphan images. Surprisingly, the noise was slightly higher for the standard dose head when compared with the low dose head protocol resulting in a lower CNR. This result suggests that despite the increase in dose by a factor of two no additional benefit in image quality is gained from using the standard head protocol over the lower dose protocol.

33 Technical performance 33 Table 7. Varian OBI v1.5: comparison of image quality parameters as measured using different imaging protocols Low Dose Head Standard Dose Head High Quality Head Dose (mgy) CNR for polystyrene Noise for polystyrene CT Slice Uniformity Number Resolution Linearity Aspect sensitivity % Error lp/cm % ratio (mm) Min Max U1. U % 6% (0.30) % -2% (0.25) % -2% (0.23) Pelvis % 5% (0.33) Pelvis Spotlight % -2% (0.21) Notes: Noise defined as the standard deviation of the polystyrene density insert. Two different definitions of uniformity used.

34 Technical performance 34 Table 8. Synergy XVI: comparison of image quality parameters as measured using different imaging protocols Low Dose Head Med Dose Head High Dose Head Pelvis M10 Pelvis M15 Pelvis M20 Noise for CT number Slice Uniformity Dose CNR for Resolution Linearity Aspect polystyren Error sensitivity % (mgy) polystyrene e lp/cm % ratio Min Max (mm) U1. U % (0.25) % % 92% (0.41) % 81% (0.64) % 61% (0.16) % 63% (0.22) % 56% (0.33) Notes: Noise defined as the standard deviation of the polystyrene density insert. Two different definitions of uniformity used.

35 Technical performance 35 Table 9. TomoTherapy Hi-Art v3.2: comparison of image quality parameters as measured using different imaging protocols Protocol CT Noise for Slice Uniformity Dose CNR for number Resolution Linearity Aspect polystyrene sensitivity % (mgy) polystyrene Error lp/cm % ratio (mm) Min Max U1. U2. Coarse % 13% Normal % 12% Fine % 13% Notes: Noise defined as the standard deviation of the polystyrene density insert. Two different definitions of uniformity used.

36 Technical performance 36 Discussion In this evaluation the ability of the systems to accurately assess and correct patient misalignment has been measured with a well defined geometric phantom. However, these measurements represent an upper limit on the clinical performance achievable as many factors come into play when assessing misalignments on real patients. These include the patient s size, shape and the definition of the target anatomy or its surrogates in addition to any motion occurring during image acquisition. Image quality, as determined by the calibration of the system, exposure settings and reconstruction settings, also plays a major role. Finally the visualisation tools and image registration algorithms are important in facilitating the measurement of misalignments. These technologies are relatively new and research has tended to focus on the measurement of patient motion and correction strategies. As such, there has been less research on quantifying realistic limits of IGRT accuracy or optimisation of these systems in performing specific image guidance tasks. The answer to the question what image quality is required to perform a specific image guidance task? is difficult. All three systems evaluated are able to differentiate the contrast between muscle and fat as evident from the VHMP phantom images and, from this point of view, all are able to provide 3D soft tissue anatomical information that would not otherwise have been obtainable. Therefore, it is true that they are all able to localise mobile soft tissue targets better than, for instance megavoltage portal images. However, there are clear differences in image quality between the three systems with different contrast to noise ratios, trans-axial plane resolution, slice sensitivity and image acquisition dose. These factors may all affect the degree of accuracy to which a particular target can be localised. Without further research, it is not possible to determine whether the observed image quality is either sufficient or optimal for a specific image guidance task for example to localise the prostate to within 3mm. In the following discussion, various factors affecting image quality and therefore the potential accuracy and their impact on the measurements performed in this evaluation are discussed in greater depth. As has been confirmed for all systems, an increase in exposure results in an increase in image quality as defined by contrast to noise ratio. However, according to IRMER legislation [29] patient doses should be kept as low as reasonably practicable (ALARP). It is therefore important that images are optimised and decisions made as to what level of image quality is acceptable for the clinical purpose, especially for techniques in which there is potential for multiple irradiations. Essentially this results in compromises being made or justification being presented in terms of the potential clinical benefit. Where image alignment is guided by high contrast structures such as bone-soft

37 Technical performance 37 tissue interfaces then the image dose can be reduced significantly by reducing the acquisition exposure parameters without significant impact on the image guidance accuracy [19, 30]. The Varian OBI and Elekta Synergy systems both have the flexibility to reduce the dose by lowering the tube current and exposure time. Furthermore, image dose can be reduced by lowering the tube voltage where applicable for example in the head and neck region, where there is inherently good contrast. This means that the associated reduction in contrast to noise is unlikely to significantly affect image matching. Image dose can be reduced in the TomoTherapy Hi-Art by increasing the slice thickness, but this compromises the spatial resolution in the longitudinal direction. Patient size affects the image quality for a given image acquisition dose. A larger patient size or section of anatomy will lead to greater attenuation and therefore reduced signal at the detector. The reduced signal will lead to a reduction in the signal to noise ratio and consequent reduction in contrast to noise ratio. A large patient size also leads to greater patient scatter which is a particular problem for the cone beam CT systems. The relationship between imaging beam quality, contrast, signal to noise ratio and scatter is complex [31, 32]. The contrast to noise ratio is a relatively crude measure of an imaging system s ability to image clinical anatomy. The low contrast detail that can be seen in an image is a function of both the modulation transfer function, which is qualitatively measured by the line pair test object in the CATphan, and the frequency components of the image noise, not measured here [33, 34]. It is possible to reconstruct an image from the same projection data twice with different reconstruction filters to give two images with very different visual characteristics. One may have a high contrast to noise ratio i.e. low image noise with good visibility of large low contrast objects, whereas the other image may have a lower contrast to noise ratio with greater image noise, but with finer detail visible in the image. Similarly, contrast to noise ratio is also dependent on the reconstructed image voxel size i.e. trans-axial plane pixel size and/or slice width. A set of projection images reconstructed with a large voxel size will have lower levels of noise and therefore a higher contrast to noise ratio while an image reconstructed with a small voxel size will have higher noise and therefore a lower contrast to noise ratio. However, the small voxel size will allow smaller objects to be resolved as long as the imaging dose is sufficient to reduce the image noise to an acceptable level. Further advantages of reconstructing with larger voxel sizes include the speed of reconstruction, speed of automatic image registration and both disk and memory storage requirements of the hardware. For these reasons the choice of optimal reconstruction filters and voxel size is complex.

38 Technical performance 38 The standard settings of both reconstruction filters, trans-axial plane pixel size and slice width are quite different when comparing the Varian OBI and Elekta systems, however, both have provided a degree of user flexibility as to the choice of reconstruction filters and the voxel size that can be employed. In the absence of good quality research in this area most users are reluctant to deviate from the manufacturers default settings. In this evaluation it was proposed that the two CBCT systems were compared by attempting to match the acquisition and reconstruction parameters to provide comparable images. This proved to be technically challenging and so image quality was assessed with standard clinical protocols, thus the data provided in this report can be used as a national reference for the comparison of similar measurements both on new installations and developments of existing systems, or for the comparison of new IGRT systems. The CATphan, which is designed for measurements of image quality on multislice helical CT scanners, is not particularly well suited to CBCT systems where noise, resolution and image uniformity may vary throughout the imaged volume. The phantom is also less than ideal for other reasons; the contrast, of the low contrast visibility objects, is too low for a reasonable measurement on these CBCT systems and are not visible at all on the TomoTherapy Hi-Art system and the resolution test object is good for assessment of the trans-axial plane but for a reconstruction where voxel size is isotropic the test object needs to be truly 3D in nature [20]. To address these problems, there is a need for better phantoms, however, in the absence of such, the CATphan was chosen as it is typically supplied by the manufacturer with the purchase of the Varian and Elekta CBCT systems. The accuracy of the IGRT systems CT number was assessed in this evaluation; however, the Elekta Synergy system does not specify its accuracy, which is reflected in the results presented in this report. CT number accuracy is also likely to be affected by non-cylindrical geometries, particularly in regions of rapidly changing surface contours and heterogeneities. This is likely to be a particular problem for CBCT systems where the scatter conditions will vary from the calibration conditions [35, 36]. Image artefacts also affect the CT number accuracy and these are evident in the VHMP images. Ensuring CT number accuracy is a challenge [37, 38], particularly for the CBCT systems in their current state of development. However, it is not necessarily a requirement of IGRT where the task is to assess positional alignment and this may be Elekta s reasoning for not specifying the accuracy of this parameter. Despite this, image registration algorithms used in the image guidance systems and those that might be employed for future adaptive radiotherapy techniques [39-43] are likely to perform better if the CT number corresponds more closely to the reference CT images.

39 Technical performance 39 The effect of patient movement during image acquisition will be different on each of the systems. The presence of a transient movement of bowel gas in the rectum when imaging the prostate, may only affect one or two slices on the slice based Hi-Art system, while such movement on a CBCT system can cause a severe loss in definition of the surrounding anatomy. The Hi-Art system will suffer from the well reported distortion of slice based systems when imaging in the presence of respiratory movement [44], although its 5s per slice acquisition time is likely to give results more typical of slow CT [45]. For the CBCT systems, respiratory motion will be averaged during the acquisition leading to a blurring of the motion, again similar to slow CT. The advantage of the CBCT system is that the reconstruction can be binned into phases and reconstructed to produce a 4D-CBCT without significant extra dose. Furthermore, this can be achieved by tracking movement within the projection images and without requiring an external surrogate of respiratory phase [46]. The release of functionality for 4D-CBCT reconstruction is expected in the near future on the two CBCT systems evaluated in this report. The measurements of dose reported here are only indicative of the dose. When considering patient dose, the patient s size, shape and the presence of inhomogeneities need also be considered. On a CBCT system, a factor of 2 might be expected for the difference in dose due to patient size between a paediatric and large adult [47, 48] and the dose to bone will be approximately 2.5 times that of the soft tissue [48-50] for kv systems. For MV systems, the dose difference due to patient size will be less as will the increase in dose to bone.

40 Operational considerations 40 Clinical impact There is little evidence in the literature to date on the direct patient benefit of using IGRT. The equipment allows visualisation of soft tissues and there are many publications reporting the movement and deformation of these tissues allowing treatment margins to be calculated with greater confidence. Image guidance enables a greater accuracy of treatment delivery to these tissues and therefore enables treatment margins to be reduced. However, well designed trials are required to determine if these margins can be reduced without compromising tumour coverage, particularly when the uncertainty of delineation of the target is taken into account. Reduction of margins should lead to lower rates of normal tissue toxicity but could also enable increases in delivered dose with expected increases in local tumour control. Alternative technologies The most common imaging technique used in the past was megavoltage (MV) radiograph, electronic portal imaging device (EPID) and planar kilovoltage (kv) imaging. Due to the advances in imaging technologies over the past decade, such as conformal radiotherapy and IMRT, where dose distributions become more complex and dose gradients become steeper, the focus is now to improve the ability to localize the target for treatment with millimetre accuracy. Several new enhanced methods of imaging are currently being introduced to improve treatment guidance and verification. The emerging technologies of IGRT imaging techniques are: Cone beam computed tomography (CBCT) and megavoltage CT, the subject of this evaluation, as well as in room kvct and MV CBCT Optical Tracking Uses virtual simulation (camera), real-time image guidance using surface landmarks attached to the skin Ultrasound Imaging Provides anatomical information using high frequency sound waves. It has minimal side-effects and allows real-time imaging Implanted fiducial markers Uses markers that are implanted in the body, but very few types of cancer are accessible for this method. User evaluation A user survey was carried out using a web-based questionnaire. 10 confirmed results were received for 3D IGRT systems (eg CT or CBCT). Figure 4 shows the distribution of responses by IGRT system and figure 5 shows the year systems were installed.

41 Operational considerations 41 Figure 4. User response by supplier Siemens CTVision 0% Siemens MVision 0% Tomotherapy HiArt (CTrue) 0% Varian OBI Advanced Imaging 45% Elekta Synergy 55% Figure 5. Year of installation 40% 35% 30% Proportion of responses 25% 20% 15% 10% 5% 0% Year of installation The users were asked to rate a variety of features of their IGRT system. The ratings are presented in figures 4 to 12. As can be seen from the graphs, the users were generally happy with the technical features of the system, but scored the ease of use and user manual slightly lower.

42 Operational considerations 42 Figure 6. Overall ease of use 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good Figure 7. Speed of use 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good

43 Operational considerations 43 Figure 8. Image quality 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good Figure 9. Image registration 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good

44 Operational considerations 44 Figure 10. Ease of image correction 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good Figure 11. Reliability 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good

45 Operational considerations 45 Figure 12. Information and usefulness of the user manual 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Very poor Poor OK Good Very good Clinical applications Responders were asked for which clinical applications they used tomographic IGRT. One responder used tomographic IGRT for breast therapy and a small number of centres used tomographic IGRT for a few patients for limb, paediatric or palliative radiotherapy. A small number of centres used tomographic IGRT for some spine radiotherapy patients, while several centres used tomographic IGRT for some thorax and mediastinum radiotherapy patients. The only patient groups for which tomographic IGRT was used for many patients were the head and neck group and the pelvis patient group. Verification strategies A number of different verification strategies were used by different centres. Table 10 shows the responses for each strategy. Centres may use multiple strategies and were permitted to select as many answers as were appropriate. Table 10. Verification strategies used Verification strategy Off-line verification (images analysed after treatment and corrections applied at a subsequent treatment) On-line verification (images analysed immediately and correction applied before the treatment) Number of responses 5 9

46 Operational considerations 46 Interfractional verification (compare setup between fractions) 6 Infrafractional verification (compare accuracy during a single fraction) 3 Real-time treatment verification (compare accuracy as the radiation is being delivered) 0 Registration strategies One responder used manual registration. Automatic registration using bone was most common, being used by more than twice as many responders as automatic registration using soft-tissue only. Training The number of staff provided training varied greatly between responses. Typically a number of radiographers were trained (between 2 and 12) and at least one physicist was trained at each centre. Technicians and clinicians were also trained at some centres, but the number varied considerably from centre to centre. Instructions for use The IGRT system should be provided with instructions for use. These may be hardcopy or softcopy. Due to the complex nature of IGRT, in addition to these documents, staff should be trained on the use of IGRT features of the system. Initial training will most likely be provided by the supplier of the equipment. Service requirements The addition of IGRT will increase the power consumption of the radiotherapy system by a small amount. Access conduits may be needed for control and data transfer to and from the IGRT system. If the IGRT system is being added as an upgrade to an existing linac the availability of cabling space should be confirmed and if it is not present then the additional work and cost should be considered in the business plan. Some IGRT systems use imaging units which are separate to the linac. This may require a larger treatment room and this should be considered during the preparation of a business case. The use of IGRT will require additional time per patient. This will have an impact on throughput and workflow which should be considered when introducing IGRT.

47 Operational considerations 47 Connectivity The IGRT system will need to connect to the treatment planning system (TPS) used. Confirmation that the specific IGRT system to be purchased can fully and appropriately interact with the local TPS should be sought during the purchase process. Image analysis may be conducted on the IGRT workstation. Alternatively, additional workstations may be provided or the data may be accessible from a generic PC. The particular options available should be confirmed during the purchase process. Consumables The consumable used in the application of this technology is electrical, but this is quite small when considered against the power requirements for running the radiotherapy system. Maintenance and servicing There are no user-serviceable parts in the system. All servicing must be performed by certified qualified personnel. A maintenance contract is recommended for this equipment. No reliability problems have been identified in the published literature or during the interviews with device users. Calibration and quality control Routine quality assurance will need to be undertaken. Daily tests will likely be performed by a radiographer, while weekly and monthly tests will likely be performed by specialist technical staff, such as medical physicists. Daily tests would be expected to take around 10 to 20 minutes, weekly tests around 30 minutes and monthly tests up to half a day. Staff requirements Specific staffing levels for IGRT equipment vary from centre to centre. Typically 2 or 3 radiography staff might be involved in delivering the treatment, with an additional 2 or 3 staff checking and preparing the treatment prescriptions. During implementation of IGRT, additional time will be required from specialist staff such as clinical oncologists and medical physicists.

48 Purchasing 48 Purchasing procedures The Trust Operational Purchasing Procedures Manual provides details of the procurement process [52]. European Union procurement rules apply to public bodies, including the NHS, for all contracts worth more than 90,319 (from January 1 st 2008) [53]. The purpose of these rules is to open up the public procurement market and ensure the free movement of goods and services within the EU. In the majority of cases, a competition is required and decisions should be based on best value. NHS Supply Chain ( a ten year contract operated by DHL on behalf of the NHS Business Services Authority, offers OJEU compliant national contracts or framework agreements for a range of products, goods and services. Use of these agreements is not compulsory and NHS organisations may opt to follow local procedures. Purchasing options In the case of the Elekta Synergy and Varian OBI systems the image guided units can be purchased for retrospective fitting to specific Elekta and Varian treatment units. Certain pre-conditions on the specification of the linac will apply. Otherwise, the IGRT systems can be purchased as add-on components to the linac purchase. In the case of the TomoTherapy Hi-Art system the IGRT components are integral to the treatment unit and as a result can only be purchased along with the treatment unit. Since this evaluation has been performed Siemens Medical Systems have introduced other X-ray tomographic IGRT systems to the market; the MVision system which is based on megavoltage cone beam CT imaging in addition to CTVision. Sustainable procurement The UK Government launched its current strategy for sustainable development, Securing the Future [54] in March The strategy describes four priorities in progressing sustainable development: sustainable production and consumption working towards achieving more with less natural resource protection and environmental enhancement protecting the natural resources and habitats upon which we depend sustainable communities creating places where people want to live and work, now and in the future climate change and energy confronting a significant global threat.

49 Purchasing 49 The strategy highlights the key role of public procurement in delivering sustainability. End-of-life disposal Consideration should be given to the likely financial and environmental costs of disposal at the end of the product s life. Where appropriate, suppliers of equipment placed on the market after the 13 th August 2005 should be able to demonstrate compliance with the UK Waste Electrical and Electronic Equipment (WEEE) regulations (2006) [55]. The WEEE regulations place responsibility for financing the cost of collection and disposal on the producer. Electrical and electronic equipment is exempt from the WEEE regulations where it is deemed to be contaminated at the point at which the equipment is scheduled for disposal by the final user. However, if it is subsequently decontaminated such that it no longer poses an infection risk, it is again covered by the WEEE regulations, and there may be potential to dispose of the unit through the normal WEEE recovery channels.

50 Acknowledgements 50 We should like to thank the following for their contribution to this evaluation report. Liz Adams, Medical Physicist, Cambridge University Hospitals NHS Foundation Trust Charlotte Beardmore, The Society and College of Radiographers Dan Emmens, Medical Physicist, Ipswich Hospital NHS Trust Jamie Fairfoul, Medical Physicist, Cambridge University Hospitals NHS Foundation Trust Hayley James, Medical Physicist, Ipswich Hospital NHS Trust Philip Mayles, Clatterbridge Centre for Oncology Donna Routsis, Addenbrooke's Hospital, Cambridge John Shakeshaft, Clatterbridge Centre for Oncology Tim Wood, Leeds Teaching Hospitals NHS Trust Leeds Teaching Hospitals NHS Trust Christie Hospital NHS Foundation Trust UCL, St Luc, Brussels Guy's and St Thomas NHS Foundation Trust Maidstone and Tunbridge Wells NHS Trust Poole Hospital NHS Trust Southampton University Hospitals NHST Ipswich Hospital NHS Trust The Royal Wolverhampton Hospitals NHST University Hospital Birmingham NHSFT Royal Free Hampstead NHS Trust Cambridge University Hospitals NHS Foundation Trust Elekta AB Siemens Healthcare TomoTheraphy Incorporated Varian Medical Systems Inc

51 Glossary 51 BTF CATphan CBCT CNR CT Bow tie filter - A filter that is inserted in front of the source to compensate for variations in path length and subsequent differential attenuation along the beams trajectory. A test phantom used for measuring image quality characteristics of 3D X-ray imaging systems. Cone beam computed tomography - Similar to CT, but instead of using a linear fan beam, a cone shaped X-ray beam is used and captured by a 2D array of detectors. Contrast to noise ratio - The difference in the mean grey level between two objects (contrast) divided by the standard deviation of the noise. The measure gives an indication of the ability of a system to distinguish the difference between two materials in the presence of image noise. Computed tomography - Method of X-ray imaging in which a series of 2D projection images acquired around a single axis of rotation are reconstructed to produce a 3D image data set consisting of a set of axial slices. CTDI phantom A standard Perspex phantom used for measuring CT dose that can be configured for estimates of head (16cm diameter) and body (32cm diameter). CT/HU number A relative scale relating the grey level of the pixel in an image to the linear attenuation of the object imaged. For Hounsfield Units (HU), air = and water = 0. DH Department of Health EPID Flexmap FOV IGRT Image acquisition Electronic portal imaging device - A digital imaging system which uses an amorphous silicon flat panel detector. A pre-measured lookup table used during image reconstruction to correct for shifts in alignment of the kv source and detector due to kv source arm and detector arm flex. Field of view - region over which data is acquired and reconstructed to display an image. Usually refers to the dimensions in the trans-axial imaging plane. Image guided radiotherapy - The process by which some form of imaging is performed during a patient s radiotherapy treatment and this additional information is used to either apply corrections to patient position, or to instigate plan modifications, with the overall aim being to improve treatment accuracy. The process of acquiring an IGRT image.

52 Glossary 52 Image review The process of reviewing an IGRT image. This involves comparison of the IGRT image with a reference CT scan and maybe performed on- of off-line IMRT Intensity modulated radiotherapy - A form of conformal radiotherapy that utilises several intensity modulated beams to yield a highly conformal dose distribution, which can be of a concave shape. IRMER Ionising Radiations (Medical Exposures) Regulations 2000 Isocentre The unique point in space around which all the major components of the Linear accelerator rotates. This point also defines the frame of reference of the imaging system. kv-cbct Kilovoltage cone beam CT - Cone beam CT performed utilising kv energy photons produced by an X-ray tube. Lat Lateral - Direction along the minor axis of the couch system, the x- axis (often also described as East/West and anatomically as left/right). Long MV-CBCT MVCT NPS Offline Offline review Online Online correction Longitudinal - Direction along the major axis of the couch system, the y-axis (often also described as North/South and anatomically as superior/inferior,). Megavoltage cone beam CT - Cone beam CT performed utilising MV energy photons produced by the linear accelerator and imaged using an electronic portal imaging device. Megavoltage computed tomography Noise power spectrum - This gives the powers of the spectrum of spatial frequencies found in an image sample. For offline correction strategies, reaction to an image is delayed to a subsequent fraction. The correction applied can vary between being a straightforward translation of the patient couch system to the initiation of a complete re-plan. The process of image review performed after treatment delivery with the aim of assessing systematic errors in patient position. Any measured systematic error is used to correct subsequent fractions of treatment delivery Online correction strategies involve images being acquired, assessed and any adjustments to patient positioning are applied immediately, prior to the patient being treated. The process of image review and if necessary the correction of patient position performed line immediately prior to treatment delivery

53 Glossary 53 Pentaguide Pitch QA ROI Roll SBRT Slice sensitivity Spatial Integrity Spatial resolution SRS Uniformity Vert VHMPP Yaw A test phantom for measuring geometrical alignment of 3D X-ray imaging systems Pitch - Rotation around the lateral axis (x) Quality assurance - A planned and systematic approach to monitoring, assessing and improving the quality of services provided on a continuous basis. Region of interest - An area or volume in which data is preferentially selected. Roll - Rotation around the longitudinal axis (y) Stereotactic body radiation therapy - Highly precise radiation therapy which delivers a high dose to the target volume within a small number of treatment fractions. A measurement of slice thickness. The term has been inherited from assessment of CT scanners which are slice based and is not ideal for cone beam CT X-ray imaging systems. The ability of a system to accurately represent the object imaged without scaling, rotation or distortion. The ability of the system to resolve two lines of high contrast placed closely together. Stereotactic radiosurgery - A highly precise form of radiation therapy used primarily to treat tumours and other abnormalities of the brain. The uniformity of image grey-level across the field of view of the image of an object with uniform density. Vertical - Direction perpendicular to the horizontal plane of the couch, the z-axis (often described anatomically as posterior/anterior). Virtually Human Male Pelvic Phantom - An anthropomorphic phantom of a male pelvis modelled using data from the Virtual Human project (National Institute for Health, US). The phantom is rigid and has materials that mimic both bone and soft tissues with differing radiological properties such as muscle and fat. Yaw - Rotation around the vertical axis (z)

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58 Appendix 1: Supplier contact details 58 Table 11. Supplier details Manufacturer System Supplier Elekta AB, Box 7593, Stockholm SE Varian Medical Systems, Inc Corporate Headquarters Hansen Way Palo Alto, CA TomoTherapy Incorporated 1240 Deming Way Madison, WI USA Tel: Fax: Synergy OBI Hi-Art UK Sales and Service Elekta Limited, Linac House, Fleming Way, Crawley, West Sussex RH10 9RR UK Sales/Service enquiries: Tel: Fax: Varian Medical Systems UK Ltd. Crawley, West Sussex, UK Tel: TomoTherapy Europe GmbH Park Lane Culliganlaan 2A 1831 Diegem, Belgium Tel: +32 (0) Fax: +32 (0) /02

59 Appendix 2: Clinical protocols 59 Table 12. Elekta Synergy v4.2 clinical image acquisition and reconstruction parameters Imaging Parameters Protocol 1 Low head Protocol 2 Med Head Protocol 3 High Head Protocol 4, 5 & 6 Pelvis kvp ma ms Ave No. Frames Exposure (mas) Bow Tie Filter No No No Yes Collimator S20 S20 S20 M10, M15 & M20 Slice Thickness (mm) In-plane dimensions (mm) x x x x 1.0 Table 13. Varian OBI v 1.5 clinical image acquisition and reconstruction parameters Imaging Parameters Low Dose Head Standard Dose Head High Quality Head Pelvis Pelvis Spotlight kvp ma ms Ave No. Frames Exposure Fan type Full Full Full Half Full Slice Thickness (mm) In-plane dimensions (mm) x x x x x 0.65

60 Appendix 2: Clinical protocols 60 Table 14. TomoTherapy Hi-Art v 3.2 clinical image acquisition and reconstruction parameters Imaging Parameters kvp Field Length Slice Thickness (mm) In-plane dimensions (mm) Fine Normal Coarse 3.5 MeV peak Up to 300 slices x x x 0.75

61 Appendix 3: Imaging dose calibration 61 Initial calibration Cone beam CT systems On the Elekta Synergy and Varian OBI systems, dose measurements were made using a Farmer chamber with a calibration factor traceable to national standards. A single HVL measurement was made of the beam quality of the Elekta Synergy system to enable suitable calibration factors to be determined. A measurement of HVL was not performed on the Varian OBI as part of this evaluation; however, it was assumed that this would not vary from that of the Elekta Synergy by more than1.5 mm [23]. This results in a further uncertainty in the calibration factor of a few % which is an acceptable degree of error for dose measurements of this type. TomoTherapy Hi-Art The TomoTherapy Hi-Art measurements were performed using a Standard Imaging A1SL chamber. The absorbed dose to water calibration factor used was the NPL alanine-derived factor as obtained for the clinical treatment beam (~6MeV peak). The University of Wisconsin 60 Co absorbed dose to water factor for the same chamber only varied by ~1.2%. Thus as the imaging beam for TomoTherapy lies somewhere between these two energies the use of the NPL derived factor introduces a maximum error of ~1%.

62 Appendix 4: Image dose data 62 All dose measurements are given in mgy. To remove variations due to differences in the number of frames (projection images) or output levels, a normalised dose per 100mAs has also been presented in brackets for the Elekta Synergy and Varian OBI systems, however, this is not applicable for the TomoTherapy Hi-Art as output cannot be expressed in terms of mas. Table 15. Elekta Synergy v4.2 dose measurements (mgy) 2 x Body Protocol 1 Low head Protocol 2 Med Head Protocol 3 High Head Protocol 4 Pelvis M10 Protocol 5 Pelvis M15 Protocol 6 Pelvis M20 Centre 9.9 (1.2) 11.3 (1.4) 12.9 (1.6) Top 16.0 (1.9) 17.0 (2.1) 17.5 (2.1) Mid Top 12.1 (1.5) 13.6 (1.7) 15.2 (1.9) Mid Bottom (1.7) Bottom (2.1) 2 x Head Protocol 1 Low head Protocol 2 Med Head Protocol 3 High Head Protocol 4 Pelvis M10 Protocol 5 Pelvis M15 Protocol 6 Pelvis M20 Centre 1.2 (3.3) 4.8 (3.3) 9.6 (3.3) Top 1.4 (3.8) 5.5 (3.8) 11.0 (3.3) Bottom 1.5 (4.0) 5.8 (4.0) 11.6 (4.0) In Air Protocol 1 Low head Protocol 2 Med Head Protocol 3 High Head Protocol 4 Pelvis M10 Protocol 5 Pelvis M15 Protocol 6 Pelvis M20 Isocentre 1.5 (4.1) 5.9 (4.1) 11.7 (4.1) 37.8 (4.6) 38.2 (4.7) 38.6 (4.7)

63 Appendix 4: Image dose data 63 Table 16. Varian OBI v1.5 dose measurements (mgy) 2 x Body Low Dose Head Standard Dose Head High Quality Head Pelvis Pelvis Spotlight Centre 19.8 (2.9) 17.9 (2.5) Top 29.0 (4.3) 1.6 (0.2) Mid Top 23.7 (3.5) 7.7 (1.1) Mid Bottom 23.4 (3.4) 31.1 (4.3) Bottom 28.7 (4.2) 42.6 (5.9) 2 x Head Low Dose Head Standard Dose Head High Quality Head Centre 3.0 (4.2) 6.1 (4.2) 30.4 (4.2) Top 1.0 (1.3) 1.9 (1.3) 9.6 (1.3) Bottom 4.3 (6.0) 8.7 (6.0) 43.5 (6.0) Pelvis Pelvis Spotlight In Air Low Dose Head Standard Dose Head High Quality Head Pelvis Pelvis Spotlight Isocentre 5.2 (7.3) 10.5 (7.3) 52.4 (7.3) 78.9 (11.6) 42.9 (6.0) Table 17. TomoTherapy Hi-Art v3.2 dose measurements (mgy) 2 x Body Fine Medium Coarse Centre Periphery Mid x Head Fine Medium Coarse Centre Periphery In Air Fine Medium Coarse Isocentre

64 Appendix 5: Hounsfield number accuracy 64 Table 18. Varian OBI v1.5 measured Hounsfield numbers. Percentage difference from expected given in brackets Low Dose Head Standard Dose Head High Quality Head Pelvis Pelvis Spotlight Air -942 (6%) -993 (1%) -998 (0%) -998 (0%) -999 (0%) PMP -195 (1%) -195 (1%) -202 (0%) -192 (1%) -194 (1%) LDPE -97 (0%) -101 (0%) -108 (-1%) -97 (0%) -100 (0%) Poly -51 (-2%) -56 (-2%) -56 (-2%) -50 (2%) -54 (-2%) Acrylic 91 (-3%) 106 (-1%) 102 (-2%) 126 (1%) 106 (-1%) Delrin 303 (-4%) 328 (-1%) 322 (-2%) 356 (2%) 325 (-2%) Teflon 928 (-6%) 980 (-1%) 982 (-1%) 1037 (5%) 985 (-1%) Table 19. Elekta Synergy v4.2 measured Hounsfield numbers. Percentage difference from expected given in brackets Low head Med Head High Head Pelvis M10 Pelvis M15 Pelvis M20 Air 230 (123%) -78 (92%) -191 (81%) -386 (61%) -375 (63%) -438 (56%) PMP 734 (93%) 544 (74%) 440 (64%) 235 (44%) 235 (44%) 251 (56%) LDPE 795 (90%) 618 (72%) 522 (62%) 296 (40%) 296 (40%) 311 (41%) Poly (86%) (69%) (60%) 339 (37%) 339 (37%) 365 (40%) Acrylic 945 (83%) 786 (67%) 695 (58%) 476 (36%) 466 (35%) 520 (40%) Delrin 1084 (74%) 942 (60%) 855 (52%) 638 (30%) 628 (29%) 703 (36%) Teflon (45%) (40%) (33%) (12%) 1080 (9%) (26%)

65 Appendix 5: Hounsfield number accuracy 65 Table 20. TomoTherapy Hi-Art v3.2 measured Hounsfield numbers. Percentage difference from expected given in brackets Fine Medium Coarse Air -914 (9%) -913 (9%) -908 (9%) PMP -93 (11%) -98 (10%) -104 (10%) LDPE -16 (8%) -5 (10%) 2 (10%) Poly 49 (8%) 39 (7%) 45 (8%) Acrylic 168 (5%) 162 (4%) 168 (5%) Delrin 384 (4%) 368 (3%) 390 (5%) Teflon 860 (13%) 866 (12%) 856 (13%)

66 Appendix 6: CATphan image quality - spatial resolution 66 Figure 13. Varian OBI v1.5 images of the CTP528 module of a CATphan. Images have been displayed at the same window and level settings Low dose head Standard dose head High quality head Pelvis Pelvis spotlight

67 Appendix 6: CATphan image quality - spatial resolution 67 Figure 14. Elekta Synergy v4.2 images of the CTP528 module of a CATphan. Images have been displayed at the same window and level settings Low dose head Medium dose head High dose head M10 M15 M20

68 Appendix 6: CATphan image quality - spatial resolution 68 Figure 15. TomoTherapy Hi-Art v3.2 images of the CTP528 module of a CATphan. Images have been displayed at the same window and level settings Coarse pitch Normal pitch Fine pitch

69 Appendix 7: CATphan image quality - low contrast visibility 69 Figure 16. Varian OBI v1.5 images of the CTP404 module of a CATphan. Images have been displayed at the same window and level settings Low dose head Standard dose head High quality head Pelvis Pelvis spotlight

70 Appendix 7: CATphan image quality - low contrast visibility 70 Figure 17. Elekta Synergy v4.2 images of the CTP404 module of a CATphan. Images have been displayed at the same window and level settings Low dose head Medium dose head High dose head M10 M15 M20

71 Appendix 7: CATphan image quality - low contrast visibility 71 Figure 18. TomoTherapy images of the CTP404 module of a CATphan. Images have been displayed at the same window and level settings Coarse pitch Normal pitch Fine pitch

72 Appendix 8: Evaluation phase 1 summary of results 72 Test 1: Registration of image volume to treatment isocentre Table 21. kv/mv alignment (mm) Elekta Synergy v 4.2 Varian OBI v 1.4 Site Site Site Site Site Site Site Site Mean 0.56 Mean 0.87 Max 0.85 Max 0.94 Test 2: Image-shift verify test Table 22. Residual errors after image-shift-verify test (mm) Elekta Synergy v 4.2 Site Lateral Long Vertical Magnitude Varian OBI v1.4 Site Lat Long Vertical Magnitude TomoTherapy Hi-Art v3.1 Measurement not performed

73 Appendix 8: Evaluation phase 1 summary of results 73 Image dose and Image quality Table 23. Image acquisition and reconstruction parameters as used for the investigation of image dose and image quality at the phase 1 evaluation and test sites Elekta Synergy v4.2 Varian OBI v1.4 TomoTherapy Hi-Art v3.1 Collimation S10 Full-Fan, FOV=24 cm, Length =13.6 cm Length = 9.4 cm Pitch = 1 Bow Tie No Yes N/A kv/mv 120 kv 125 kv 3.5 MV ma & ms 40 ma, 25 ms; High dose (40mA,10ms) N/A Reconstruction High resolution (0.5 mm x 0.5 mm) 0.5 mm x 0.5 mm 0.75 mm x 0.75 mm Slice thickness 1 mm 1 mm 1 mm Note: It should be noted that the Elekta Synergy does not permit the reconstruction of rectangular voxels. Consequently, 0.5 mm slices were reconstructed initially which were then compressed on DICOM export to increase slice thickness to the desired 1mm. Test 3: Image dose Table 24. Dose measurements made in air and in a single full body CTDI phantom. Results displayed as mean (standard deviation) Normalised dose (mgy/100mas) Centre Periphery In air Elekta Synergy 1.9 (0.1) 4.5 (0.1) 6.5 (0.1) Varian OBI 1.9 (0.2) 3.6 (0.2) 10.7 (0.6) TomoTherapy Hi-Art N/A N/A N/A Note: This is not applicable as the output for TomoTherapy Hi-Art cannot be expressed in terms of mas.

74 Appendix 8: Evaluation phase 1 summary of results 74 Figure 19. CT number accuracy for each density insert within the CTP404 module of a CATphan for each of the phase 1 evaluation sites, defined as measured CT number minus nominal (centres 1-5 Elekta Synergy, centres 6-8 Varian OBI and centre 9 TomoTherapy Hi-Art) 800 CT number accuracy Air PMP LDPE Polystyrene Acrylic Delrin Teflon Evaluation centre

75 Appendix 8: Evaluation phase 1 summary of results 75 Test 4: Image quality* Dose (mgy) CNR for polystyrene Noise for polystyrene Resolution lp/cm Linearity % Aspect ratio Slice sensitivity (mm) Uniformity % U1. U2. Elekta Synergy Site Site Site Site Site Varian OBI Site Site Site TomoTherapy Hi-Art Site Notes: * It should be noted that the Elekta Synergy images were attained without a bow tie filter in contrast to the Varian OBI images which were also acquired at effectively double the mas. Noise defined as the standard deviation of the polystyrene density insert. Two different definitions of uniformity used. Angled wire not visible in MV-CT images of CATphan, therefore measurement not made

76 Appendix 9: User survey questionnaire

77 Appendix 9: User survey questionnaire

78 Appendix 9: User survey questionnaire

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