ReIGNITE RT Boost: An international study testing the accuracy and feasibility of using restriction spectrum imaging (RSI) MRI to guide intraprostatic tumor target volume for radiotherapy boost

In a phase III randomized trial, adding a radiation boost to visible tumor(s) on MRI improved prostate cancer disease-free and metastasis-free survival without additional toxicity. However, radiation oncologists’ ability to identify prostate tumors is critical and represents a major barrier to widely adopting intraprostatic tumor radiotherapy boost for patients. We previously developed a quantitative diffusion MRI biomarker for prostate cancer, called the Restriction Spectrum Imaging restriction score (RSIrs), that has been shown to improve radiologist identification of clinically significant prostate cancer. 42 radiation oncologists (participants) from multiple, international institutions contoured prostate tumors on 40 patient cases using standard MRI with or without RSIrs map, producing 1646 target volumes. Use of RSIrs maps significantly improved all evaluated accuracy metrics, including participants’ percent overlap with consensus expert target volume (73% vs. 42%, p<0.001). A mixed effects model confirmed that RSIrs maps were the main variable driving the improvement in all metrics. System Usability Scores indicated RSIrs maps significantly improved the contouring experience (72 vs. 58, p<0.002). The expert-defined tumor was completely missed 158 times on standard MRI alone and only 19 times with RSIrs maps. RSIrs maps improve the accuracy of target delineation for prostate tumor boost. Patient Summary Adding an extra boost of radiation to tumor(s) visible on MRI has been shown to prevent cancer recurrence and cancer spread beyond the prostate without adding additional side effects; however, drawing the prostate tumor on MRI is difficult, and most radiation oncologists have not been trained to do this. We have developed an advanced MRI technique (RSIrs maps) that increases tumor visibility. We found that RSIrs maps improve radiation oncologists’ accuracy in targeting prostate tumors. ### Competing Interest Statement AJL reports consulting for MIM Software. MEH reports honoraria from Multimodal Imaging Services Corporation and research funding from GE Healthcare. AMD is a Founder of and holds equity in CorTechs Labs, Inc, and serves on its Scientific Advisory Board. He is a member of the Scientific Advisory Board of Human Longevity, Inc. and receives funding through research agreements with GE Healthcare. The terms of these arrangements have been reviewed and approved by the University of California San Diego in accordance with its conflict-of-interest policies. TMS reports honoraria from Multimodal Imaging Services Corporation, Varian Medical Systems, and WebMD; he has an equity interest in CorTechs Labs, Inc. and also serves on its Scientific Advisory Board; he has received in-kind research support from GE Healthcare via a research agreement with the University of California San Diego. These companies might potentially benefit from the research results. The terms of this arrangement have been reviewed and approved by the University of California San Diego in accordance with its conflict-of-interest policies. ### Funding Statement This work was supported, in part, by the National Institutes of Health (NIH/NIBIB K08 EB026503, NIH/NCI U54CA132384, U54CA132379, UL1TR001442), the American Society for Radiation Oncology (ASTRO), the Prostate Cancer Foundation, the Radiological Society of North America (RSNA), the American College of Radiation Oncology (ACRO), and the Grillo-Marxuach Family Fellowship at the Moores Cancer Center of UC San Diego. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All patient information, images, participant information and study related communications were approved by the UC San Diego Institutional Review Board I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. 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