Hypofractionated SBRT to 36.25 Gy in 5 fractions (fraction dose 7.25 Gy) for low- and intermediate risk prostate cancer is standard of care. Using higher fraction doses that might be beneficial for disease control is not safe in all patients, unless adaptive treatment is performed. In this clinical trial the feasibility of online MR-guided SBRT fraction dose adaptation (between 7 and 8 Gy) for prostate cancer will be investigated. A fraction dose to the planning target volume (PTV) will be adapted to organs-at-risk (OAR) geometry (position, shape and volume) on online planning MRI scans of the treatment day (geometry-of-the-day). Thus the investigators hope to maximize treatment individualization.
The purpose of this study is to evaluate a technical feasibility of MR-guided SBRT fraction dose adaptation for low-risk, intermediate-risk and low-volume metastatic prostate cancer. .