Ini$al Performance Test Results on an Elekta MR-Linac

Transcription

1 Ini$al Performance Test Results on an Elekta MR-Linac Eric Paulson, PhD DABR Radia$on Oncology, Radiology, and Biophysics Froedtert and Medical College of Wisconsin Milwaukee, Wisconsin, United States April 7, 2017

2 Disclosures Advancing a Healthier Wisconsin ( / ) Elekta Instruments, AB

3 Why MRI in Radia$on Oncology? Pancreas Planning CT MRI Pillars of success in RT: Accurate delinea$on of disease extent Op$mal alignment of the treatment beam to the target kv CBCT MRI MR Simula$on: Consistent, true GTV More accurate CTV Esophagus MR-guided RT: Reduce inter-, intra-frac$onal varia$ons Biologically adap$ve, dose-escalated RT

4 Challenges Facing MR-guided RT Decoupling the magne$c field from RT components: Minimizing magne$c interference Decoupling the RT components from MRI acquisi$on: Minimizing radiofrequency interference Beam transmission through the MRI Influence of Lorentz force on secondary electrons

5 MR-gRT Implementa$ons MRI on Rails (PMH) Rota$ng Bi-Planar (CCI, Alberta) ViewRay (Wash U, UW Madison, UCLA, etc) Rota$ng Bi-Planar (Australia)

6 Elekta/Philips MR-Linac Philips 1.5T MRI: Ac$ve shielding reduces magne$c interference Faraday cage integrated into cryostat Split solenoid with transmission through the cyrostat Windows designed into gradient, RF coils Elekta Linac: 7MV FFF beam (transverse to B0) Rigid ring mounted gantry with slip rings 160-leaf MLC in S-I orienta$on 7mm projected leaf width at isocenter 142cm SAD 22cm max field size in along S-I EPID for portal imaging, QA

7 MR-Linac Vault at MCW Modified exis$ng 3 rd floor vault Floor built up 3 to provide gantry clearance: Maze with ramp (MCW) Ver$cal lig (MDA)

8 Pre-Acceptance Measurements Magnet ramped up: 3/4/2017 Philips Calibra$ons: 3/5/2017 3/6/2017 AAPM Abstract Deadline: 3/9/2017 Magnet ramped down: 3/11/2017

9 Magne$c Field vs Gantry Rota$on Passive shimmed at gantry = 0 deg: 4.1 Hz RMS Average of all angles: 10 Hz RMS (gantry posi$on can affect magne$c field homogeneity) Paulson, et al, AAPM 2017 (submiked)

10 Magne$c Field vs Gantry Rota$on (+Shimming) Average of all angles: 4.8 Hz RMS Conclusion: Perform shimming at each gantry angle prior to beam-on Paulson, et al, AAPM 2017 (submiked)

11 Gradient Linearity over 50cm FOV Axial Sagikal Coronal Es$mated within 1mm at 20cm radius from isocenter Paulson, et al, AAPM 2017 (submiked)

12 With/Without Radia$on Radia$on Off Radia$on On Difference Paulson, et al, AAPM 2017 (submiked)

13 ACR MRI Phantom QA Meets required tolerances for ACR Accredita$on using protocol from diagnos$c 1.5T Philips Ingenia Paulson, et al, AAPM 2017 (submiked)

14 Mo$on Es$ma$on Accuracy Matched programmed peak-to-peak displacement, trajectory, and frequency Paulson, et al, AAPM 2017 (submiked)

15 On-Board EPID Image Quality All required features on Las Vegas phantom were visible Paulson, et al, AAPM 2017 (submiked)

16 Magne$c Field On Beam Profiles Magne$c Field Off Symmetry within 0.3% (without magne$c field) Paulson, et al, AAPM 2017 (submiked)

17 End-To-End Test (1/2) CT Sim MIM Monaco Mosaiq TSM Integrity

18 CT Sim MIM Monaco Mosaiq TSM End-To-End Test (2/2) Date: 16/03/2017 ArcCHECK QA of Dose Distribution Hospital Name: QA File Parameter ArcCHECK Plan Patient Name : MRLINAC, CIRS Patient ID : MRLINAC06 Plan Date : 3/16/2017 SSD : SDD : Depth : Energy : 0 Angle : Relative Comparison Difference (%) Distance (mm) Threshold (%) Meas Uncertainty : Yes Summary (Gamma Analysis) Total Points Passed Failed % Passed : 3.0 : 3.0 : 5 : 272 : 261 : 11 : 96 *DTA/Gamma is using 2D Mode Dose Values in cgy CAX Norm Sel Max ArcCHECK Plan ArcCHECK Plan % Diff DTA(mm) NA 0.00 NA Coords (y,x) cm Notes 0,0 1, , \ \MRLINA... ArcCHECK-Plan 96% Set1 Set2 CAX Offset X=1 Y=-1 Integrity % X(mm) ArcCheck response affected by concurrent imaging while measuring

19 Summary MR-gRT extends the advantages of MRI into the RT treatment room, facilita$ng high precision, biologically-adap$ve, dose-escalated radiotherapy The Elekta MR-Linac is one of several implementa$ons pioneering MR-gRT, each uniquely addressing the design challenges of integra$ng MRI and RT devices Based on pre-acceptance measurements: MR image quality and geometric accuracy does not appear to have been compromised by integra$on of a linac Dosimetry effects in the presence of a magne$c field are as expected, and can be calculated and managed in treatment planning

20 Acknowledgements Nikolai Mickevicius X. Allen Li, PhD Ergun Ahunbay, PhD Xingfeng Chen, PhD Slade Klawikowski, PhD Ray Thomas (Elekta) Scok Kotlarz (Philips)