ESTRO 2021 Abstract Book

S684

ESTRO 2021

modulated arc therapy (VMAT) following RC has an acceptable toxicity profile. Materials and Methods This is a multicentric prospective phase two study requiring 76 patients. Eligible patients were patients with MIBC, treated with RC and presenting with ≥1 of the following characteristics: · Pathological (p)T3 stage + presence of lymphovascular invasion on pathological examination · pT4 stage · <10 lymph nodes removed · positive lymph nodes · positive surgical margins A median dose of 50 Gy in 25 fractions was prescribed to the pelvic lymph node regions with inclusion of the operative bladder bed in case of a positive surgical margin. All patients were treated with VMAT. Kaplan-Meier statistics were used to calculate 2-years locoregional control and MIBC-specific survival. Results We included 76 patients (58 males and 18 females). The median follow up was 12 months (0-72 months). Median age at inclusion was 70 years (34-87 years). Only 43% of the patients received NAC. The majority of patients had a stage ≥(y)pT3 (80%) and positive lymph node status (67%) at RC. There was only 1 patient who stopped EBRT early after 15 fractions due to tumor progression . Eight patients (11%) required hospitalization during radiotherapy. Reasons for hospitalization were: infection (N=4), intestinal sub-obstruction (N=1), nausea-diarrhea (N=1), leakage of the neobladder requiring surgery (N=1) and removal of a transurethral catheter (N=1). An overview of other acute and late toxicity is presented in table 1. Two-years locoregional control was 87% (figure 1A) and 2-years MIBC-specific survival was 65% (figure 1B). Table 1. Overview on acute and late toxicity not requiring hospitalization. For urinary toxicity only patients with a neobladder were evaluated. Numbers represent percentages.

Figure 1.