ESTRO 2025 - Abstract Book

S1888

Clinical - Urology

ESTRO 2025

485

Digital Poster Safety of prostate SBRT treated with an empty bladder (EMPTY-RT): A prospective phase 2 trial. Simran Gulati, Suman Ghosh, Shivani Sable, Reena Phurailatpam, Ritesh Mhatre, Mihir Solanki, Maneesh Singh, Parth Verma, Pallavi Singh, Sakshi Dubey, Priyamvada Maitre, Vedang Murthy Radiation Oncology, Tata Memorial Hospital, Mumbai, India Purpose/Objective: The full bladder protocol used traditionally for prostate SBRT can pose challenges, including patient discomfort and bladder volume variability, which may lead to inconsistencies in prostate positioning and treatment delivery. This study aimed to evaluate the feasibility, safety, and clinical outcomes of prostate SBRT with an empty bladder protocol. Material/Methods: This is a phase II single arm prospective study (CTRI/2023/08/056231) in patients with prostate cancer planned for 5 fraction SBRT to the prostate with or without pelvic lymph nodes. Patients were simulated and treated at every fraction with an empty bladder immediately after voiding. Daily image-guided radiotherapy was implemented using online cone-beam computed tomography (CBCT). The primary objective was to assess the acute gastrointestinal (GI) and genitourinary (GU) toxicities (CTCAE v5.0) and to compare it with a similar cohort of patients undergoing SBRT with a full bladder in the ongoing PRIME trial. [1] The secondary objectives were to determine the patients’ concerns with a full bladder treatment using a 10-item survey, to assess the feasibility of planning SBRT with an empty bladder and to evaluate bladder volume variability on CBCTs. Results: Of the 68 patients enrolled, 62 were treated with an empty bladder to either the prostate only (61.3%) or whole pelvic RT; delivered either on alternate days (67.5%) or once-weekly and were eligible for analysis. Six patients (8.8 %) did not meet the empty bladder dose constraints and were treated with a full bladder. While 1 patient (2.6%) had Gr 3 GU toxicity, acute grade 2 GU toxicity was seen in 30% patients (vs 31.2% in PRIME). Acute Grade 2 GI toxicity were observed in 6.4% (15% in PRIME) with no grade 3 GI toxicity. The median empty bladder volume at simulation was 73cc (IQR:56-107) and ranged from 59cc to 69cc during treatment (Fig 1). On univariable analysis, no significant association was found between simulation bladder volume and clinical factors such as age at diagnosis, tumor stage, IPSS, median PTV volume. Total 44% patients reported significant urge to void during treatment with a full bladder and 68% preferred no bladder filling.

Conclusion: This is the first prospective trial of an empty bladder protocol during prostate SBRT. Results indicated no inadvertent increase in acute GU and GI and toxicity compared to full bladder treatment. The empty bladder