Online adaptive radiotherapy potentially reduces toxicity for high-risk prostate cancer treatment

•By allowing tighter PTV margins, MR-guided adaptive RT may reduce dose to the surrounding tissues compared to standard RT for high-risk prostate cancer patients.•Individual fraction doses were accumulated on the varying patient anatomy over the treatment course for both standard RT and MR-guided adaptive RT.•The observed reductions in dose to healthy tissues translates to potentially reduced risk of acute gastro-intestinal toxicity and late bladder toxicity.