ESTRO 2025 - Abstract Book

S1513

Clinical – Mixed sites & palliation

ESTRO 2025

2164

Digital Poster External beam radiotherapy for synchronous prostate and rectal cancer. Maxim Van den Kieboom 1 , Reinhilde Weytjens 1,2 , Piet Ost 1 , Piet Dirix 1 , Frederik Vandaele 1 , Carole Mercier 1 , Guido Buelens 1 , Sabine Vanderkam 1 , Ines Joye 1,2 1 Radiation Oncology, Iridium Netwerk, Wilrijk, Belgium. 2 Centre for Oncological Research (CORE)-IPPON, University of Antwerp, Antwerpen, Belgium Purpose/Objective: Radiation therapy is frequently applied for prostate and rectal cancer. However, management of synchronous prostate and rectal cancer is challenging as reports on the optimal curative treatment for this dual pathology are scarce. We report outcome of patients with synchronous prostate and rectal cancer who were treated according to Lavan et al. Material/Methods: Medical files of patients with synchronous prostate and rectal cancer undergoing curative radiation therapy between 01/06/2017 and 31/12/2023 were retrospectively reviewed. All patients were multidisciplinary discussed at the digestive and urological tumour boards. Patients undergoing surgery only were excluded. The study was approved by the ethical committee and the need for an informed consent was waived. Outcome data were updated in November 2024. Results: Ten patients were identified (Table 1). Median follow-up was 30.8 months from the start of radiation therapy (range 10.4 - 84.9 months). VMAT was applied in all patients. Pelvic doses of 45-50 Gy (25 fractions) were prescribed. Prostate total doses ranged from 66 to 74 Gy (33 to 37 fractions). Concomitant 5-FU and capecitabine were applied in 6 and 3 patients, respectively. One patient was treated according to a modified RAPIDO regimen, in which a total dose of 25 Gy in 5 fractions was delivered on pelvis posterior and prostate. Total mesorectal excision (TME) and abdominoperineal resection (APR) were performed in 5 and 2 patients, respectively. Three patients obtained a clinical complete response of whom two remain disease-free at 14 and 47 months. One patient had a pathological complete response after APR. Four patients developed grade 3 toxicity (Table 2). One patient experienced urinary retention necessitating a TURP 3 months after radiation therapy. Three patients experienced grade 3 rectal side effects (proctitis in 2 and rectal fistula in 1). Prostate cancer was controlled in 8 out of 10 patients, with 2 patients developing bone metastases during follow-up. Rectal cancer was controlled in 8 out of 10 patients with 2 patients developing metastatic disease combined with a local recurrence in 1.