Five-year outcomes from a prospective comparative effectiveness study evaluating external-beam radiotherapy with or without low-dose-rate brachytherapy boost for localized prostate cancer

Background: To inform patients who are in the process of selecting prostate cancer treatment, the authors compared disease-specific function after external-beam radiotherapy (EBRT) alone versus EBRT plus a low-dose-rate (LDR) brachytherapy boost (EBRT-LDR). Methods: For this prospective study, men who had localized prostate cancer in 2011 and 2012 were enrolled. Assessments at baseline, 0.5, 1, 3, and 5 years included the patient-reported Expanded Prostate Index Composite, the 36-item Medical Outcomes Study Short-Form Health Survey, and treatment-related regret. Regression models were adjusted for baseline function and for patient and treatment characteristics. The minimum clinically important difference in scores on the Expanded Prostate Index Composite 26-item instrument was from 5 to 7 for urinary irritation and from 4 to 6 for bowel function. Results: Six-hundred ninety-five men met inclusion criteria and received either EBRT (n = 583) or EBRT-LDR (n = 112). Patients in the EBRT-LDR group were younger (median age, 66 years [interquartile range [IQR], 60-71 years] vs 69 years [IQR, 64-74 years]; P <.001), were less likely to receive pelvic radiotherapy (10% vs 18%; P =.040), and had higher baseline 36-item Medical Outcomes Study Short-Form Health Survey physical function scores (median score, 95 [IQR, 86-100] vs 90 [IQR, 70-100]; P <.001). Over a 3-year period, compared with EBRT, EBRT-LDR was associated with worse urinary irritative scores (adjusted mean difference at 3 years, −5.4; 95% CI, −9.3, −1.6) and bowel function scores (−4.1; 95% CI, −7.6, −0.5). The differences were no longer clinically meaningful at 5 years (difference in urinary irritative scores: −4.5; 95% CI, −8.4, −0.5; difference in bowel function scores: −2.1; 95% CI, −5.7, −1.4). However, men who received EBRT-LDR were more likely to report moderate or big problems with urinary function bother (adjusted odds ratio, 3.5; 95% CI, 1.5-8.2) and frequent urination (adjusted odds ratio, 2.6; 95% CI, 1.2-5.6) through 5 years. There were no differences in survival or treatment-related regret between treatment groups. Conclusions: Compared with EBRT alone, EBRT-LDR was associated with clinically meaningful worse urinary irritative and bowel function over 3 years after treatment and more urinary bother at 5 years. Lay Summary: In men with prostate cancer who received external-beam radiation therapy (EBRT) with or without a brachytherapy boost (EBRT-LDR), EBRT-LDR was associated with clinically worse urinary irritation and bowel function through 3 years but resolved after 5 years. Men who received EBRT-LDR continued to report moderate-to-big problems with urinary function bother and frequent urination through 5 years. There was no difference in treatment-related regret or survival between patients who received EBRT and those who received EBRT-LDR. These intermediate-term estimates of function may facilitate counseling for men who are selecting treatment.