Main Session
Sep
29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement
3341 - Late Genitourinary Toxicity after Definitive Radiotherapy with or without Simultaneous Integrated Boost In Post-TURP Prostate Cancer: A Competing-Risk Study
Presenter(s)
Huseyin Cem Onal, MD - Baskent University Faculty of Medicine, Adana, Yuregir
H. C. Onal1,2, O. C. C. Guler3, G. Erbay4, I. G. Balci4, A. Elmali1, B. Demirhan5, and M. N. Yavuz1; 1Baskent University Faculty of Medicine, Department of Radiation Oncology, Ankara, Turkey, 2Baskent University, Faculty of Medicine, Adana Turgut Noyan Research and Treatment Center, Department of Radiation Oncology, Adana, Turkey, 3Baskent University Faculty of Medicine, Adana Dr Turgut Noyan Research and Treatment Center, Department of Radiation Oncology, Adana, Turkey, 4Baskent University, Faculty of Medicine, Adana Turgut Noyan Research and Treatment Center, Department of Radiology, Adana, Turkey, 5Iskenderun Gelisim Hospital, Division of Radiation Oncology, Hatay, Turkey
Purpose/Objective(s):
Patients with prostate cancer (PCa) and prior transurethral resection of the prostate (TURP) have an elevated risk of late genitourinary (GU) toxicity after radiotherapy, raising concerns regarding the safety of focal dose escalation. Evidence specifically addressing simultaneous integrated boost (SIB) in this surgically altered population remains limited. We evaluated late GU toxicity after definitive radiotherapy with or without SIB in post-TURP PCa patients using competing-risk methodology.Materials/Methods:
We analyzed 201 PCa patients with a history of TURP treated with conventionally fractionated radiotherapy between 2012 and 2023, including 98 patients treated with SIB and 103 without SIB. All patients received 78 Gy in 39 fractions to the prostate, with selected patients receiving SIB up to 86 Gy to intraprostatic lesions. Late GU toxicity was graded according to CTCAE v5.0. Cumulative incidence functions were estimated with death treated as a competing event and compared using Gray’s test. Predictors of late Grade =2 and Grade =3 GU toxicity were assessed using prespecified Fine–Gray competing-risk regression models.Results:
Baseline clinicopathologic characteristics were well balanced between treatment groups. Most patients were high-risk (59.7%), 74.8% received androgen deprivation therapy, and 13.1% had undergone two or more TURP procedures. After a median follow-up of 117.8 months, late Grade =2 GU toxicity occurred in 37 patients (18.0%), with no significant difference between the SIB and non-SIB groups (20.4% vs 15.7%, p=0.45). The most frequent Grade 2 toxicities were hematuria, urinary obstruction, and incontinence. Late Grade =3 GU toxicity was observed in 24 patients (11.9%), with comparable rates between SIB and non-SIB cohorts (11.2% vs 12.6%, p=0.83). Median time to onset of Grade =2 toxicity was similar between groups. At 5 years, cumulative incidence of Grade =2 GU toxicity was 39.1% with SIB and 31.2% without SIB (p=0.31), while corresponding Grade =3 rates were 13.8% and 14.5%, respectively (p=0.81). On competing-risk regression, the number of prior TURP procedures emerged as the strongest independent predictor of late Grade =2 GU toxicity (SHR 3.65, 95% CI 2.04–6.54, p<0.001), whereas SIB use was not associated with increased toxicity. For Grade =3 toxicity, no covariate demonstrated a statistically significant association. Toxicity-specific analyses showed that cardiac disease and anticoagulant use predicted hematuria, while repeated TURP procedures predicted urinary obstruction; SIB was not associated with any toxicity endpoint.Conclusion:
In PCa patients with prior TURP, focal dose escalation using SIB does not increase the risk, severity, or timing of late GU toxicity. Late GU morbidity is driven predominantly by cumulative surgical injury rather than radiation dose escalation, supporting selective and individualized use of SIB in appropriately chosen post-TURP patients.