Anne Vestergaard1, Shaista Hafeez2, Ludvig P Muren3, Simeon Nill4, Morten Høyer5, Vibeke N Hansen4, Caroline Grønborg3, Erik M Pedersen6, Jørgen B Petersen3, Robert Huddart2, Uwe Oelfke4. 1. Department of Medical Physics, Aarhus University/Aarhus University Hospital, Denmark; Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom. Electronic address: annveste@rm.dk. 2. Academic Urology Unit, The Institute of Cancer Research, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 3. Department of Medical Physics, Aarhus University/Aarhus University Hospital, Denmark. 4. Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom. 5. Department of Oncology, AarhusUniversity/Aarhus University Hospital, Denmark. 6. Department of Radiology, Aarhus University/Aarhus University Hospital, Denmark.
Abstract
BACKGROUND AND PURPOSE: Adaptive radiotherapy (ART) using plan selection is being introduced clinically for bladder cancer, but the challenge of how to compensate for intra-fractional motion remains. The purpose of this study was to assess target coverage with respect to intra-fractional motion and the potential for normal tissue sparing in MRI-guided ART (MRIGART) using isotropic (MRIGARTiso), an-isotropic (MRIGARTanIso) and population-based margins (MRIGARTpop). MATERIALS AND METHODS: Nine bladder cancer patients treated in a phase II trial of plan selection underwent 6-7 weekly repeat MRI series, each with volumetric scans acquired over a 10 min period. Adaptive re-planning on the 0 min MRI scans was performed using density override, simulating a hypo-fractionated schedule. Target coverage was evaluated on the 10 min scan to quantify the impact of intra-fractional motion. RESULTS: MRIGARTanIso reduced the course-averaged PTV by median 304 cc compared to plan selection. Bladder shifts affected target coverage in individual fractions for all strategies. Two patients had a v95% of the bladder below 98% for MRIGARTiso. MRIGARTiso decreased the bowel V25 with 15-46 cc compared to MRIGARTpop. CONCLUSION: Online re-optimised ART has a considerable normal tissue sparing potential. MRIGART with online corrections for target shift during a treatment fraction should be considered in ART for bladder cancer.
BACKGROUND AND PURPOSE: Adaptive radiotherapy (ART) using plan selection is being introduced clinically for bladder cancer, but the challenge of how to compensate for intra-fractional motion remains. The purpose of this study was to assess target coverage with respect to intra-fractional motion and the potential for normal tissue sparing in MRI-guided ART (MRIGART) using isotropic (MRIGARTiso), an-isotropic (MRIGARTanIso) and population-based margins (MRIGARTpop). MATERIALS AND METHODS: Nine bladder cancer patients treated in a phase II trial of plan selection underwent 6-7 weekly repeat MRI series, each with volumetric scans acquired over a 10 min period. Adaptive re-planning on the 0 min MRI scans was performed using density override, simulating a hypo-fractionated schedule. Target coverage was evaluated on the 10 min scan to quantify the impact of intra-fractional motion. RESULTS: MRIGARTanIso reduced the course-averaged PTV by median 304 cc compared to plan selection. Bladder shifts affected target coverage in individual fractions for all strategies. Two patients had a v95% of the bladder below 98% for MRIGARTiso. MRIGARTiso decreased the bowel V25 with 15-46 cc compared to MRIGARTpop. CONCLUSION: Online re-optimised ART has a considerable normal tissue sparing potential. MRIGART with online corrections for target shift during a treatment fraction should be considered in ART for bladder cancer.
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