Combined Brachytherapy and Ultra-Hypofractionated Radiotherapy for Intermediate-Risk Prostate Cancer: Comparison of Toxicity Outcomes Using a High-Dose Rate (HDR) vs. Low-Dose Rate (LDR) Brachytherapy Boost

Abstract

<h3>Purpose/Objective(s)</h3> Combined brachytherapy and external beam radiotherapy is an accepted treatment for unfavorable intermediate-risk and high-risk prostate cancer. We compared genitourinary and gastrointestinal toxicity of low-dose-rate (LDR) and high-dose-rate (HDR) brachytherapy boost when combined with ultra-hypofractionated external beam radiation therapy (UH-EBRT) for prostate cancer. <h3>Materials/Methods</h3> 99 intermediate-risk prostate cancer patients underwent UH-EBRT (5 Gy x 5) combined with brachytherapy HDR (n=59) or LDR (n=40) boost. HDR brachytherapy consisted of 15 Gy using Iridium-192, and LDR brachytherapy consisted of Palladium-103 seed implantation (prescription dose=100 Gy). Median baseline IPSS was 5 for both cohorts. Median follow-up was 29.3 months. Toxicity assessment included Common Terminology Criteria for Adverse Events (CTCAE) version 4.0, International Prostate Symptom Score (IPSS), and bowel symptom assessment. Cumulative incidences were calculated for toxicity outcomes. Fisher exact tests were used to evaluate associations. <h3>Results</h3> Overall incidence of grade 2 genitourinary toxicity at 12 and 24 months was 21% and 29%, respectively. The incidence of grade 2 genitourinary toxicity at 12 and 24 months was higher for LDR cohort compared with HDR cohort (45% versus 5.1%, and 55% versus 11%; p<0.001). No grade ≥3 or 4 toxicities were observed. On MVA, only treatment regimen (LDR versus HDR) was significantly associated with grade ≥2 genitourinary toxicity (p<0.001). Two patients had grade 2 rectal toxicity in each cohort. No grade ≥ 3 or 4 toxicities were observed. <h3>Conclusion</h3> Both LDR and HDR brachytherapy combined with UH-EBRT were associated with favorable toxicity profiles, but significantly less grade 2+ genitourinary toxicity was observed in patients receiving HDR compared with LDR brachytherapy.