Optical Guidance Sanford L. Meeks July 22, 2010
Optical Tracking Optical tracking is a means of determining in real-time the position of a patient relative to the treatment unit. Markerbased systems track the positions of either active or passive infrared markers attached to the patient as a surrogate for actual patient position. Markerless systems track the reflection of light from the surface of the patient. The position of the point of reflection is determined using a camera system. Active markers Passive markers Camera
Calibration Camera has been correlated with linac isocenter to correlate virtual space with real space.
Clinical Applications of Optical Tracking 1. Markers are indexed to patient
Clinical Applications of Optical Tracking 2. Markers are identified in CT scan relative to treatment isocenter.
Clinical Applications of Optical Tracking 3. Markers are tracked using camera system. CCD Camera Control Computer Fiducial Array Optical guidance to track patient position using passive markers and a bite-plate system.
Clinical Applications of Optical Tracking 3. Markers are tracked using camera system.
4. Misalignments are corrected.
Optical Tracking Extracranial Targets Tracking surface alone may be inadequate Target motion relative to surface anatomy Imaging coupled with optical tracking Ultrasound X-Ray
Varian SonArray High-resolution infrared camera Detects passive and active fiducials Computer with Spatial Digitizer linked to Camera Image Processing and Localizing Software Optically tracked ultrasound system
Correlation of US with Planning CT
BrainLab ExacTrac asi detectors infrared camera Floor mounted stereoscopic kv X-ray tubes X-Ray Registration process: Either bony anatomy (automated) or implanted fiducial markers Patient tracked optically using reflective body markers
Observed positions Marker Alignment Expected positions Manual alignment Table Offsets Expected positions Observed positions Manual alignment Patient aligned and tracked using optical guidance
Gating with Marker-Based System (BrainLab Exactrac) Because optical tracking gives real-time feedback, it is also useful for generating respiratory gating signal. Gated x-ray verification is performed using implanted fiducials. Can verify at any time, including during treatment
Once the breathing signal is obtained the user selects the level of the breathing pattern for which x-rays are to be obtained X-Ray Level
Markerless Tracking Use of projection of patterned or structured light onto the scene. Use image feature correspondence in stereo images to track surface. Images from: Siebert et al, Human body 3D imaging by speckle texture projection photogrammetry, Sensor Review 20:3, p 218, 2000. Waldron ACMP 2009
Markerless Tracking RT Vision sensor system arranged in pods, each is capable of stereo vision. A pod contains 1 stereo pair of cameras and a speckle pattern projector. A texture camera, white flash, and speckle flash projector are also present. Speckle flash Stereo camera pair Speckle projector Texture camera Speckle Pattern Waldron ACMP 2009
Commercial Systems Company Varian BrainLab Accuray CMS Nomos Resonant Medical Medical Intelligence VisionRT External tracking, +ultrasound, gating External tracking + x-ray, gating External tracking + x-ray Ultrasound Ultrasound Ultrasound External tracking Surface tracking
TG147: QA for non-radiographic localization and positioning systems Disclaimer: This task group is still under review and has not been published (a work in progress)
Installation Machine isocenter and in-room laser accuracy (per customer ATP / TG40) Linac interference with localization system Localization system interference Linac (and collision space) Establish Localization Volume (Volume of View) Establish Tracking volume (VOV for Tracking) System Performance
Installation Machine isocenter and in-room laser accuracy (per customer ATP / TG40) Recommend the use of a Winston/Lutz film process for establishing machine isocenter / laser QA documentation prior to installation of add-on equipment
System Performance Calibration Procedures Overall Localization Accuracy (End to End Test) System Drift Reproducibility Tracking Accuracy Response Time (latency)
Target Localization Accuracy and Overall Positional Accuracy (End to End Test)
Localization on Treatment Planning System
Setup of Patient under Optical Guidance
Resulting Film: Measure of Total Accuracy of System Results: Z: 0.49 mm to T X: 0.35 mm to A Y: 0.50 mm High Overall error = 0.789mm