Determinants of the combined use of external beam radiation therapy and brachytherapy for low-risk localized prostate cancer.

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e16039 Background: Prostate cancer treatment patterns have been shown to vary by physician and patient characteristics. For low-risk localized prostate cancer patients, we examined the association between their region of residence and their radiation oncologists’ practice affiliations with medical schools on the likelihood they would receive both external beam radiation therapy (EBRT) and brachytherapy (BT) – a treatment regimen that is at variance with clinical guidelines and has not been shown to improve survival or other patient centered outcomes. Methods: Using the Surveillance, Epidemiology and End Results – Medicare linked database and the American Medical Association Physician Masterfile, we conducted a retrospective cohort study of 4,479 patients aged 66 years or older who were diagnosed between 2004-2007 with low-risk localized prostate cancer, and the 401 radiation oncologists who saw them. Multilevel regression analyses were used to evaluate the influence of patients’ region of residence and radiation oncologists’ practice affiliations with medical schools on the combined use of EBRT and BT on patients within 6 months of diagnosis. Results: Overall, 231 (5.2%) patients received combined EBRT and BT. After adjusting for patient, tumor and radiation oncologist characteristics, patients who saw radiation oncologists with no practice affiliation with medical schools were significantly more likely to receive combined EBRT and BT (odds ratio [OR], 3.14; 95% confidence interval [95% CI], 1.50-6.59, p = 0.003). Regional variations were also observed; the odds of receiving combined therapy for patients residing in California (OR, 0.1; 95% CI, 0.03-0.33, p<0.0001) were significantly less than those in Georgia (OR, 1.0; referent). Conclusions: Low-risk localized prostate cancer patients residing in Georgia were significantly more likely to receive combined EBRT and BT when compared to those in other SEER Regions. Radiation oncologists without practice affiliations with medical schools were significantly more likely to treat patients with combined therapy; such treatment patterns are not consistent with clinical guidelines and unlikely to have significant survival benefit.