Multi-institutional Prospective Evaluation of Bowel Quality of Life After Prostate External Beam Radiation Therapy Identifies Patient and Treatment Factors Associated With Patient-Reported Outcomes: The PROSTQA Experience

Purpose To evaluate patients treated with external beam radiation therapy as part of the multicenter Prostate Cancer Outcomes and Satisfaction with Treatment Quality Assessment (PROSTQA), to identify factors associated with posttreatment patient-reported bowel health-related quality of life (HRQOL). Methods and Materials Pretreatment characteristics and treatment details among 292 men were evaluated using a general linear mixed model for their association with measured HRQOL by the Expanded Prostate Cancer Index Composite instrument through 2 years after enrollment. Results Bowel HRQOL had a median score of 100 (interquartile range 91.7-100) pretreatment and 95.8 (interquartile range 83.3-100) at 2 years, representing new moderate/big problems in 11% for urgency, 7% for frequency, 4% for bloody stools, and 8% for an overall bowel problems. Baseline bowel score was the strongest predictor for all 2-year endpoints. In multivariable models, a volume of rectum ≥25% treated to 70 Gy (V70) yielded a clinically significant 9.3-point lower bowel score (95% confidence interval [CI] 16.8-1.7, P =.015) and predicted increased risks for moderate to big fecal incontinence ( P =.0008). No other radiation therapy treatment-related variables influenced moderate to big changes in rectal HRQOL. However, on multivariate analyses V70 ≥25% was associated with increases in small, moderate, or big problems with the following: incontinence (3.9-fold; 95% CI 1.1-13.4, P =.03), rectal bleeding (3.6-fold; 95% CI 1.3-10.2, P =.018), and bowel urgency (2.9-fold; 95% CI 1.1-7.6, P =.026). Aspirin use correlated with a clinically significant 4.7-point lower bowel summary score (95% CI 9.0-0.4, P =.03) and an increase in small, moderate, or big problems with bloody stools (2.8-fold; 95% CI 1.2-6.4, P =.018). Intensity modulated radiation therapy was associated with higher radiation therapy doses to the prostate and lower doses to the rectum but did not independently correlate with bowel HRQOL. Conclusion After contemporary dose-escalated external beam radiation therapy up to 11% of patients have newly identified moderate/big problems with bowel HRQOL 2 years after treatment. Bowel HRQOL is related to baseline function, rectal V70, and aspirin use. Finally, our findings validate the commonly utilized cut-point of rectal V70 ≥25% as having significant impact on patient-reported outcomes.