156 Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) has been implemented at our institution since 2014. We report on the initial clinical experience and patient selection in treating prostate cancer utilizing the first commercially-implemented MR-IGRT system. Methods: A total of 13 patients with prostate cancer have been treated with intensity-modulated radiation therapy (IMRT) using an MR-IGRT system. Of those treated, 6 patients received definitive radiation therapy (RT) for low, intermediate or high risk prostate cancer, 5 patients were treated with salvage RT after biochemical failure following surgery, and 1 patient was treated for the boost portion of definitive RT. Results: Patients were selected for MR-IGRT based on various clinical decisions. Four patients had co-morbidities requiring anticoagulation for which fiducial marker placement was contraindicated and soft tissue visualization via MR imaging was thought to be beneficial for daily set-up. Three patients were referred from outside institutions with concerns of radiation dose to the small bowel, and daily MR monitoring of bowel anatomy could be performed with plans for treatment adaptation if anatomy changed. One patient had received prior RT for rectal cancer and dose to organs at risk was of concern. The remainder of patients were post-operative salvage cases selected based on physician concern of accurate and reproducible daily localization with fiducial markers alone. Daily volumetric MR was monitored with the ability for treatment adaptation should small bowel dose increase, and no treatment changes were required. For all cases, onboard sagittal cine MR was visually monitored for bladder and target motion, and qualitative evaluation demonstrated no significant intra-fraction motion. Conclusions: MR-IGRT provides unique advantages when fiducial markers are contraindicated or when daily visualization of dose to the small bowel or other organs at risk is required to monitor and potentially prevent normal tissue toxicity. Clinical trials are in development to formally evaluate MR-IGRT for the treatment of intact and salvage prostate cancer.
Multiparametric prostate MRI-based intensity-modulated radiation therapy guided by prostatic calcifications
