Low-Dose-Rate Brachytherapy Combined With Ultrahypofractionated Radiation Therapy for Clinically Localized, Intermediate-Risk Prostate Cancer: Results From a Prospective Trial

Abstract

To report early toxicity and tumor control outcomes of Pd-103 brachytherapy with ultrahypofractionated stereotactic radiation therapy (RT) for intermediate-risk prostate cancer. This prospective trial included 40 patients with intermediate-risk prostate cancer who underwent low-dose-rate (Pd-103) brachytherapy (prescription dose, 100 Gy), followed 1 month later with ultrahypofractionated stereotactic RT (25 Gy in 5 fractions) to the prostate and seminal vesicles. The primary endpoint was the rate of grade 2+ genitourinary toxicity at 12 months using Common Terminology Criteria for Adverse Events v 4.0. Secondary endpoints included patient-reported quality-of-life metrics (International Prostate Scoring System [IPSS], International Index of Erectile Function, and Expanded Prostate Cancer Index Composite-bowel). Biochemical failure was defined as prostate-specific antigen nadir +2 ng/mL. Posttreatment biopsies were performed at between 24 and 36 months; median follow-up was 36 months. The rate of grade 2 urinary toxicity at 12 months was 25% with no grade 3 urinary toxicity noted. Mean IPSS at baseline and 12 and 24 months was 5, 10, and 6.2, respectively. Mean change in IPSS from baseline at 12 months was +5.5 (interquartile range, 1-9.75) and +1.05 (interquartile range, -3 to 3.25) at 24 months. Grade 2 bowel toxicity was 5% at 12 months with no grade 3 bowel toxicity noted. Mean Expanded Prostate Cancer Index Composite-bowel domain scores at baseline and 12 months were 92.8 and 90.3, respectively. Of patients who were potent (International Index of Erectile Function ≥21) at baseline, 75% remained potent at 12 months. Of 40 patients, 28 underwent posttreatment prostate biopsy (PPB), which was negative (n = 20) or demonstrated severe treatment effect (n = 8). No patient had a positive PPB or developed biochemical failure during the follow-up period. One patient without a PPB developed osseous metastases at 18 months posttreatment in the absence of biochemical failure. Low-dose-rate brachytherapy in combination with ultrahypofractionated stereotactic RT was safe and effective for intermediate-risk prostate cancer in early results of this trial.