Online Adaptive Stereotactic Body Radiotherapy for Localized Prostate Cancer

Inclusion Criteria: * histologically confirmed localized prostate cancer * planned treatment is SBRT according to standard of care and consists of definitive CT or MRI online adaptive SBRT of the prostate according to the PACE trial which includes a total dose to clinical target volume 1 (CTV1, i.e. prostate and proximal 1 cm of the seminal vesicle) of 40.0 Gy in 5 weekly fractions (single dose of 8.0 Gy) and total dose to planning target volume 1 (PTV1) of 37.5 Gy in 5 weekly fractions (single dose of 7.5 Gy) with a compromise for bowel sparing allowed. For patients with unfavorable intermediate to very high-risk disease (according to NCCN guidelines) a total dose to the planning target volume 2 (PTV2, i.e. proximal 1-2 cm of the seminal vesicle) of 32.5 Gy in 5 weekly fractions (single dose of 6.5 Gy) will be delivered. * intermediate to (very) high risk localized prostate cancer (≤ cT3a and Gleason score ≤ 9 and/or PSA ≤ 20 ng/ml) * prostate volume \> 60 cc and/or IPSS \> 12; Exclusion Criteria: * Very high risk localized prostate cancer with indication for ADT and ARPI (i.e. Gleason ≥ 8 and cT3a) * Involvement of seminal vesicles (cT3b) * Contraindications against definitive CT or MRI-adaptive radiotherapy of the prostate, e.g. inflammatory bowel disease (IBD); previous radiotherapy in the pelvis, previous local radiotherapy of the prostate, contraindication for MRI or CT; * Patients with severe genitourinary symptoms (e.g. recent urinary retention ≥ grade 3 according CTCAE v.5.0); * Lymph node metastases or distant metastases (i.e. no localised prostate cancer); * Participation in a clinical trial which might influence the results of this project.