The purpose of the study was to evaluate the relationship among planning target volumes (PTVs) and organs at risk (OARs) based on four different radiotherapy treatment plans for high-risk prostate cancer patients. CT scans were obtained in supine position with knee and ankle support (KAS) and in prone position with belly-board (BB) both with full bladder (FB) and empty bladder (EB). Overlapping volumes of the delineated PTVs and OARs on four different setup combinations (KAS-FB; BB-FB; KAS-EB; BB-EB) were analyzed according to the patient position, bladder filling and circumference of abdomen (CA). Overlapping (∩) was significantly smaller with FB than with EB at the bowels and bladder: PTVpel∩bladder: p=0.0069, PTVpvs∩bladder: p<0.001, PTVp∩bladder: p<0.001, PTVpel∩bowels: p=0.0055. Comparison according to small and large CA resulted in significantly smaller overlapping of PTVs and OARs for large CA patients at: KAS-FB: PTVpel∩rectum: p=0.0255, PTVpvs∩rectum: p=0.0179, PTVp∩rectum: p=0.0386, PTVpel∩bladder: p=0.0355. KAS-EB: PTVpvs∩bladder: p=0.0184, PTVp∩bladder: p=0.0107. BB-EB: PTVpvs∩bladder: p=0.0464, PTVp∩bladder: p=0.0077. The exception was PTVpel∩rectum at KAS-FB where the overlapping were smaller for small CA (p=0.0255). According to our results we recommend to deliver radiotherapy treatment for high-risk prostate cancer patients in supine position with KAS immobilization and full bladder. The overlapping volumes of PTVs and OARs were smaller practically at all patients with larger circumference of abdomen.