Patient-reported outcomes after Low-dose-rate versus High-dose-rate brachytherapy boost in combination with external beam radiation for intermediate and high risk prostate cancer

PURPOSE: Addition of a brachytherapy boost to external beam radiation therapy (EBRT) reduces prostate cancer (PCa) recurrence at the expense of genitourinary (GU) toxicity. Whether brachytherapy boost technique, specifically low-dose-rate (LDR-BT) versus high-dose-rate (HDR-BT), impacts treatment-related toxicity is unclear. METHODS: Between 2012-2018, 106 men with intermediate/high risk PCa underwent EBRT (37.5-45 Gy in 1.8-2.5 Gy/fraction) plus brachytherapy boost, either with LDR-BT (110 Gy I-125 or 100 Gy Pd-103; n = 51) or HDR-BT (15 Gy x1 Ir-192; n = 55). Patient-reported outcomes (PRO) were assessed by International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index Composite (EPIC-CP) surveys at 3-6-month intervals for up to three years following treatment, with higher scores indicating more severe toxicity. Provider-reported GU and gastrointestinal (GI) toxicity was graded per CTCAE v5.0 at each follow-up. Linear mixed models comparing PROs between LDR-BT versus HDR-BT were fitted. Stepwise multivariable analysis (MVA) was performed to account for age, gland size, androgen deprivation therapy use, and alpha-blocker medication use. Incidence rates of grade 2 + GU/GI toxicity was compared using Fisher's exact test. RESULTS: Use of LDR-BT was associated with greater change in IPSS (p = 0.003) and EPIC-CP urinary irritative score (p = 0.002) compared with HDR-BT, but effect size diminished over time (LDR-BT versus HDR-BT: baseline to 6-/24-month mean IPSS change, + 6.4/+ 1.4 versus + 2.7/-3.0, respectively; mean EPIC-CP irritative/obstructive change, + 2.5/+ 0.1 versus + 0.9/+ 0.1, respectively). Results remained significant on MVA. Post-treatment grade 2 + GU toxicity was significantly higher in the LDR-BT group (67.5% versus 42.9% for LDR-BT and HDR-BT, respectively; p < 0.001). There were no differences between groups in incontinence, bowel function, and erectile function, or grade 2 + GI toxicity. CONCLUSION: Compared with LDR-BT, HDR-BT was associated with lower acute patient-and provider-reported GU toxicity. (C) 2021 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.