Impact of high-dose rate and low-dose rate brachytherapy boost on toxicity, functional and cancer outcomes in patients receiving external beam radiation therapy for prostate cancer: a national population-based study

Abstract

Purpose: External beam radiotherapy (EBRT) with brachytherapy boost reduces cancer recurrence in patients diagnosed with prostate cancer compared to EBRT monotherapy. However, randomised controlled trials or large-scale observational studies have not compared brachytherapy boost types directly. Methods and materials: This observational cohort study used linked national cancer registry data, radiotherapy data, administrative hospital data and mortality records of 54,642 patients diagnosed with intermediate-risk, high-risk and locally advanced prostate cancer in England. The records of 11,676 patients were also linked to results from a national patient survey collected at least 18 months after diagnosis. Competing risk regression analyses were used to compare gastrointestinal (GI) toxicity, genitourinary (GU) toxicity, skeletal-related events (SREs), and prostate cancer-specific mortality (PCSM) at five years with adjustment for patient and tumour characteristics. Linear regression was used to compare EPIC-26 domain scores (scale from 0 to 100, higher scores indicating better function). Results: 5-year GI toxicity was significantly increased after LDR-BB (32.3%) compared to HDR-BB (16.7%) or EBRT monotherapy (18.7%). 5-year GU toxicity was significantly increased after both LDR-BB (15.8%) and HDR-BB (16.6%), compared to EBRT monotherapy (10.4%). These toxicity patterns were matched by the mean patient-reported bowel function scores (LDR-BB: 77.3, HDR-BB: 85.8, and EBRT monotherapy: 84.4) and the mean patient-reported urinary obstruction/irritation function scores (LDR-BB: 72.2, HDR-BB: 78.9, and EBRT monotherapy: 83.8). 5-year incidences of SREs and PCSM were significantly lower after HDR-BB (2.4% and 2.7%, respectively) compared to EBRT monotherapy (2.8% and 3.5%, respectively). Conclusions: LDR-BB has worse GI and GU toxicity and HDR-BB has worse GU toxicity compared to EBRT monotherapy. HDR-BB has a lower incidence of SREs and PCSM than EBRT monotherapy.