The burden of overtreatment: comparison of toxicity between single and combined modality radiation therapy among low risk prostate cancer patients.

INTRODUCTION: To compare radiation related toxicities among men with low risk prostate cancer treated with single or multimodal radiation therapy. MATERIALS AND METHODS: The SEER-Medicare linked database was used to assess the relationship between treatment type and toxicity among men with low risk prostate cancer treated with brachytherapy (BT), external beam radiation therapy (EBRT), or combined therapy between 2004 and 2007. Inverse probability of treatment weighting was utilized to minimize selection bias and control for confounding. Multivariate logistic regression models were used to explore the relationship between treatment and outcomes. RESULTS: Overall 1915 (43.9%), 1893 (43.4%), and 555 (12.7%) patients were treated with EBRT, BT, and combined therapy, respectively. In univariate analyses, combined modality radiation was more toxic than BT alone for GU incontinence (56.76% versus 49.08%), GU obstruction (21.26% versus 19.70%), and erectile dysfunction (22.52% versus 22.24%) (p < 0.01, all comparisons). Compared to EBRT alone, combined modality radiation was more toxic for GI bleeding (7.21% versus 6.21%), GU incontinence (56.76% versus 29.24%), GU obstruction (21.26% versus 14.15%), and erectile dysfunction (22.52% versus 15.35%) (p < 0.01, all comparisons). Among the most frequent radiation toxicity events, the probability of treatment associated toxicity was highest for patients receiving combined modality treatment and lowest for the group treated with EBRT. After multivariate adjustment, EBRT alone demonstrated protective effects against GU obstruction (OR 0.56 [CI 0.50-0.63]), GI bleeding (OR 0.57 [CI 0.48-0.67]), GU incontinence (OR 0.39 [CI 0.36-0.43]), and erectile dysfunction (OR 0.68 [CI 0.61-0.76]) when compared to combined therapy. CONCLUSIONS: The use of combined modality radiation therapy in low risk prostate cancer patients is discordant with clinical guidelines and associated with a significantly increased burden of associated toxicity when compared to EBRT monotherapy. Prudent patient selection and judicious use of combined therapy among men with low risk prostate cancer represents a targetable area to reduce the burden of overtreatment.