Patient positioning variations to reduce dose to normal tissues during 3D conformal radiotherapy for high-risk prostate cancer

Background and purpose: The goal of this work was to assess optimal treatment positioning of 3D conformal radiotherapy (3DCRT) for high-risk prostate cancer patients. Patients and methods: Treatment plans of 25 patients in different patient positions were evaluated: with knee and ankle support (KAS) in the supine position and with a belly board (BB) in the prone position both with full (FB) and empty bladder (EB). Planning target volumes (PTVs) for pelvis, prostate and vesicles, prostate, and organs at risk (OARs) were delineated. Dose and overlapping volumes were evaluated. Results: Overlapping volumes were significantly smaller with a FB than with an EB. No significant differences were found in overlapping volumes with respect to patient fixation systems, but the percentage values of dose to the OARs showed significantly better results employing KAS than a BB. A FB reduced the dose volumes to the OARs. Comparison with respect to circumference of abdomen (CA) showed significantly smaller overlapping at large CA in most of the cases. Conclusion: Supine position is suggested with KAS combined with a FB (especially in cases of larger CA) when using 3DCRT with planning technique modification for high-risk prostate cancer patients to reduce the dose of OARs, based on our results. (orig.)