A complementary dual-modality verification for tumor tracking on a gimbaled linac system |
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Authors: | Kenneth Poels Tom Depuydt Dirk Verellen Benedikt Engels Christine Collen Steffen Heinrich Michael Duchateau Truus Reynders Katrien Leysen Marlies Boussaer Femke Steenbeke Koen Tournel Thierry Gevaert Guy Storme Mark De Ridder |
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Institution: | 1. Department of Radiotherapy, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Belgium;2. BrainLAB AG, Feldkirchen, Germany |
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Abstract: | Background and purposeFor dynamic tracking of moving tumors, robust intra-fraction verification was required, to assure that tumor motion was properly managed during the course of radiotherapy. A dual-modality verification system, consisting of an on-board orthogonal kV and planar MV imaging device, was validated and applied retrospectively to patient data.Methods and materialsReal-time tumor tracking (RTTT) was managed by applying PAN and TILT angular corrections to the therapeutic beam using a gimbaled linac. In this study, orthogonal X-ray imaging and MV EPID fluoroscopy was acquired simultaneously. The tracking beam position was derived from respectively real-time gimbals log files and the detected field outline on EPID. For both imaging modalities, the moving target was localized by detection of an implanted fiducial. The dual-modality tracking verification was validated against a high-precision optical camera in phantom experiments and applied to clinical tracking data from a liver and two lung cancer patients.ResultsBoth verification modalities showed a high accuracy (<0.3 mm) during validation on phantom. Marker detection on EPID was influenced by low image contrast. For the clinical cases, gimbaled tracking showed a 90th percentile error (E90) of 3.45 (liver), 2.44 (lung A) and 3.40 mm (lung B) based on EPID fluoroscopy and good agreement with XR-log file data by an E90 of 3.13, 1.92 and 3.33 mm, respectively, during beam on.ConclusionDual-modality verification was successfully implemented, offering the possibility of detailed reporting on RTTT performance. |
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Keywords: | Dynamic tumor tracking Intra-fraction treatment verification kV/MV fluoroscopy |
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