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ASTRO 2023: Predicting Late Toxicity From External-Beam Radiotherapy for Prostate Cancer

By: Julia Fiederlein Cipriano, MS
Posted: Wednesday, October 18, 2023

A post hoc analysis of the RTOG 0126 trial revealed that the conditional risk of late toxicity decreased as patients with localized prostate cancer proceeded further from the completion of external-beam radiotherapy, according to Gregory S. Alexander, MD, of Thomas Jefferson University, Philadelphia, and colleagues. Their findings were presented during the 2023 American Society for Radiation Oncology (ASTRO) Annual Meeting (Abstract 283).

“The majority of grade 2 or higher gastrointestinal and genitourinary toxicities occur in the first 2 years of treatment,” the investigators commented. “Patients who have not had [such toxicities] within the first 5 years are likely to remain toxicity-free.”

The trial randomly assigned patients with intermediate-risk disease to receive either standard or dose-escalated radiotherapy alone. In this analysis, the investigators focused on 1,499 of these individuals; follow-up data were provided for a median of 8.4 years. The conditional cumulative 5-year risks of late grade 2 or higher gastrointestinal toxicity at enrollment, 2 years, and 5 years of grade 2 or higher gastrointestinal toxicity–free survivorship were 14.7%, 6.2%, and 1.8%, respectively. With regard to late grade 2 or higher genitourinary toxicity, the cumulative 5-year risks were 7.9%, 4.7%, and 2.7%, respectively.

Dose-escalated radiotherapy (hazard ratio [HR] = 1.401; P = .0066), acute gastrointestinal toxicity (HR = 1.962; P < .0001), and Black race (HR = 0.630; P < .0463) were initially found to be predictive of late gastrointestinal toxicity. Based on a multivariable analysis, after 2 years of grade 2 or higher gastrointestinal toxicity–free survivorship, acute gastrointestinal toxicity alone remained indicative (HR = 2.015; P < .0048). At enrollment, dose-escalated radiotherapy (HR = 1.616; P < .0023), intensity-modulated radiotherapy (HR = 0.559; P = .0017), and urinary frequency at baseline (HR = 1.377; P < .0498) appeared to be predictive of late genitourinary toxicity.

Disclosure: Dr. Alexander reported no conflicts of interest.

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