HDR brachytherapy monotherapy for large-volume prostate glands

Summary: Traditionally, caution is advised in managing prostate cancer (PC) with high-dose-rate brachytherapy (HDR-BT) in large volume glands. This study aims to evaluate the toxicities of HDR-BT in large volume prostates. Retrospective registry study of men with clinical stage I–IIC PC and prostate volume >50 cc who received HDR-BT monotherapy. Ultrasound-guided HDR-BT monotherapy was delivered in two fractions to 27 Gy using an iridium-192 source. The primary objective was to measure genitourinary (GU)/gastrointestinal (GI) physician reported toxicity using Common Terminology Criteria for Adverse Events (CTCAE) and health reported quality of life (HRQOL) using Expanded Prostate Cancer Index Composite Short Form (EPIC-26). Data were collected at baseline and post-treatment (acute [months 1-6] and late [months 7-30]). Descriptive statistics for patient, tumor, and treatment characteristics were calculated. Univariable logistic regression models assessed the association between GU and GI toxicities, accounting for demographic and clinical factors (prostate volume, age, baseline international prostate symptom score, pre-treatment GU medications, benign prostatic hyperplasia). EPIC-26 score HRQOL changes were assessed according to the minimally important difference (MID) per the PROSTQA consortium. Multiple imputation addressed missing data which was combined following Rubin’s rule. Thirty-nine patients were analyzed. Mean prostate volume 56.3 cc (maximum: 78.1 cc). Severe toxicity was rare with no acute or late grade 3 GI and no late grade 3 GU adverse events. One patient experienced acute grade 3 GU toxicity due to hospitalization secondary to hematuria and urinary retention. The table details acute and late CTCAE toxicities. Logistic regression analysis indicated that clinical values were not significantly associated with increased rates of GU or GI toxicity. Mean EPIC-26 urinary incontinence pre-treatment score was 87.8, compared to 92.2 at 1–6 months and 87.5 at 7–30 months post-treatment. Mean urinary irritation/obstruction pre-treatment score was 87, compared to 85.1 at 1-6 months, and 87.2 at 7-30 months post-treatment. Mean sexual pre-treatment score was 59.3, compared to 46.8 at 1–6 months, and 50.8 at 7–30 months post-treatment. Mean bowel pre-treatment score was 89.1, compared to 89.3 at 1–6 months, and 94.6 at 7–30 months post-treatment. Changes in EPIC-26 scores for GU and GI domains did not meet criteria for MID except for temporary decrease in sexual domain. In this retrospective registry study describing HDR-BT for large-volume prostates, treatment was reasonably well-tolerated with favorable acute and late patient-reported and physician-graded toxicities. This study suggests the relative safety of HDR brachytherapy treatments in patients with large-volume prostates. Nathan Zubin, BS (Co-Author) - Temple University Hospital System; Alexander Lukez, MD (Presenting Author) - Fox Chase Cancer Center; Li Zhang, PhD (Co-Author) - Fox Chase Cancer Center; Eric Horwitz, MD (Co-Author) - Fox Chase Cancer Center; Mark Hallman, MD (Co-Author) - Fox Chase Cancer Center; Iavor Veltchev, PhD (Co-Author) - Fox Chase Cancer Center; Jessica Wong, MD (Co-Author) - Fox Chase Cancer Center