OBJECTIVES: The relationship between provider volume and cancer control has not been studied in the setting of definitive radiotherapy. We examined the effect of annual and cumulative provider volume on the rate of use of secondary therapies after definitive external-beam radiotherapy (EBRT) for localized prostate cancer. METHODS: The cohort consisted of 3907 patients treated with definitive radiotherapy without neoadjuvant or adjuvant hormonal therapy (delivered within 12 mo of EBRT) between 1989 and 2000. Overall median follow-up was 6.2 yr versus 3.8 yr in event-free patients. All were treated by 72 radiation oncologists, with an average annual provider volume of 14 cases (median: 10.4; range: 1-39) and an average cumulative volume of 138 (median: 105; mean: 138). Secondary treatment was defined as hormonal therapy after definitive EBRT. Age and comorbidities represented covariates in Cox regression analyses. RESULTS: Of all patients, 731 (18.7%) received secondary therapy. The median failure-free survival was not reached (mean: 11.2 yr). At 5 and 10 yr, secondary therapy-free survival rates were 79.5% and 61.3%, respectively. Annual (p=0.007) and cumulative (p=0.003) provider volumes were independent predictors of failure-free survival. After adjustment for covariates, cubic splines demonstrated lower rates of secondary therapy for annual provider volume > 10 cases and for cumulative provider volume > 200 cases. CONCLUSIONS: Our data suggest that to minimize the rates of secondary therapy, EBRT should ideally be delivered by high-volume providers with an annual or cumulative volume in excess of, respectively, 10 or 200 cases.
