Prostate cancer radiotherapy in kidney transplant candidates: a planning framework for defining and optimizing transplant-specific organs at risk.

Purpose: Kidney transplant candidates increasingly present with localized or locally advanced prostate cancer. While radiotherapy is frequently indicated, current planning guidelines do not account for the surgical constraints of future kidney transplantation. This study proposes a practical planning framework by defining transplant-specific organs at risk (OARs) and evaluating the dosimetric impact of their systematic optimization during prostate cancer radiotherapy. Materials and methods: Through multidisciplinary collaboration between radiation oncologists and transplant surgeons, transplantation-critical structures were identified and delineated, including the bladder dome, ureters, and Results: In prostate-only treatments, active optimization of transplant-specific OARs resulted in a threefold or greater reduction in mean dose to the bladder dome, without compromising target coverage or increasing doses to conventional OARs. Similar dose reductions were observed for ureters and Conclusion: This work establishes a planning framework for integrating kidney transplantation constraints into prostate cancer radiotherapy. Prostate-only radiotherapy allows effective sparing of transplant-critical structures through active optimization, whereas pelvic nodal irradiation inevitably exposes these structures to high doses despite optimization. These findings support transplant-oriented treatment planning and careful selection of pelvic irradiation in kidney transplant candidates.