Determinants of late genitourinary toxicity after definitive radiotherapy with or without intraprostatic simultaneous integrated boost in patients with prior transurethral resection of the prostate.

backgroundPatients with prior transurethral resection of the prostate (TURP) are considered at increased risk of genitourinary (GU) toxicity following radiotherapy (RT). However, the safety of focal dose escalation using simultaneous integrated boost (SIB) in this surgically altered prostate remains insufficiently defined. This study evaluated late GU toxicity in prostate cancer (PCa) patients with prior TURP treated with definitive RT, compared outcomes between SIB and non-SIB approaches, and identified clinical predictors of late GU toxicity. MATERIALS AND

methodsWe performed a retrospective analysis of a prospectively maintained institutional database including PCa patients with prior TURP treated with definitive external beam RT between October 2012 and March 2023. Patients received conventionally fractionated RT, with 78 Gy in 39 fractions delivered to the prostate in the non-SIB group and an intraprostatic SIB up to 86 Gy in 39 fractions in the SIB group. Late GU toxicity was graded according to CTCAE version 5.0. Time-to-event outcomes were estimated using Kaplan-Meier analysis, and logistic regression models were used to identify predictors of late grade ≥ 2 and grade ≥ 3 GU toxicity.

resultsA total of 201 patients were included, of whom 98 (48.8%) received intraprostatic SIB and 103 (51.2%) received standard-dose RT. After a median follow-up of 9.5 years (IQR 8.3-10.7), the overall incidence of late grade ≥ 2 and grade ≥ 3 GU toxicity was 18.0% and 11.9%, respectively. The estimated 5‑year incidence of grade ≥ 2 GU toxicity was 41.8% in the SIB group and 28.5% in the non-SIB group (p = 0.13), while corresponding grade ≥ 3 toxicity rates were 13.8% and 12.1%, respectively (p = 0.98). Acute grade ≥ 2 GU toxicity occurred less frequently with SIB than without SIB (35.7% vs. 51.9%, p = 0.03). Acute grade ≥ 2 gastrointestinal toxicity was also less frequent in the SIB group (5.1% vs. 17.5%, p = 0.006), whereas late grade ≥ 2 gastrointestinal toxicity was comparable between groups (4.1% vs. 5.8%, p = 0.57). On multivariable analysis, anticoagulant use (OR 2.65, 95% CI 1.39-5.09; p = 0.03), acute grade ≥ 2 GU toxicity (OR 3.36, 95% CI 1.66-6.80; p < 0.001), and multiple TURP procedures (OR 2.28, 95% CI 1.04-5.90; p = 0.04) independently predicted late grade ≥ 2 GU toxicity. Multiple TURP procedures were the only independent predictor of grade ≥ 3 toxicity (OR 3.93, 95% CI 1.93-9.23; p < 0.001).

conclusionsIn patients with prior TURP treated with definitive RT, no statistically significant association was observed between intraprostatic SIB and late GU toxicity. Multiple TURP procedures were associated with greater late GU morbidity. However, clinically relevant excess toxicity with SIB cannot be excluded, and these findings should not be interpreted as evidence of equivalence or definitive safety.