Patient-Reported Outcomes (PROs) Comparing Pencil Beam Scanning (PBS) and Double Scatter/Uniform Scanning Proton Beam Therapy for Localized Prostate Cancer (PC): Analysis of PCG 001-09

Abstract

The use of proton beam therapy (PBT) for treatment of prostate cancer (PC) is controversial. ASTRO recommends against use of PBT for PC outside of a clinical trial or prospective registry. A pivotal randomized controlled trial comparing PBT and photon-based treatment is underway. However, PBT delivery has evolved from “conventional” PBT techniques (uniform scanning/double scatter [US/DS]) to PBS technology since this trial was first activated. Although PBS is thought to be the most conformal method for PBT delivery, it is unknown whether differences in toxicity outcomes characterize the 2 techniques. PROs are widely recognized as the gold standard for subjective symptom reporting. This analysis compares PRO changes associated with PBS and US/DS techniques for localized PC in a prospective multicenter registry study. We evaluated PROs (bowel, urinary, and sexual QOL) with the expanded prostate cancer index composite (EPIC) instrument for men with low-to-intermediate-risk PC enrolled in PCG 001-09 (NCT01255748). The analysis was limited to men treated with PBT to the prostate ± seminal vesicles with conventionally fractionated radiation using US/DS or PBS techniques. PROs were assessed at baseline and 3, 6, and 12 mo, with changes at these time periods evaluated. Mean changes from baseline in the EPIC domains were tested using repeated measures models. The proportions of men with minimally important differences (MIDs) in each domain were assessed using repeated measures logistic models. A total of 1,164 men completed EPIC at baseline; 280 (24%) received PBS and 884 (76%) received US/DS. Completion rates were 67.9% at 3 mo, 67.6% at 6 mo, and 63.9% at 12 mo. Average QOL declines from baseline to 12 mo were significantly higher in PBS than in US/DS for urinary QOL (P<0.05), whereas declines in average bowel QOL (P=0.96) and sexual QOL (P=0.09) were not significantly different. Among men responding to EPIC at all 4 time points (n=480), the percentages reporting a 1 MID decline at 12 mo for PBS and US/DS were 33.73% and 27.96%, respectively, for urinary QOL (P=0.21); 47.31% and 41.82%, respectively, for bowel QOL (P=0.35); and 36.71% and 31.07%, respectively, for sexual QOL (P=0.97). Corresponding 2-MID declines were observed in 26.51% and 13.71% for urinary QOL (P<0.01), 33.33% and 29.87% for bowel QOL (P=0.48); and 16.46% and 16.67% for sexual QOL (P=0.81). This is the first comparative evaluation of PROs following 2 different PBT delivery techniques for men with PC. The results of this analysis, demonstrating increased urinary bother scores following PBS, warrant further investigation and highlight the urgent need for prospective evaluation of PBT for PC.