The effect of overall treatment time on local control in patients with adenocarcinoma of the prostate treated with radiation therapy.

Studies of patients treated with radiation therapy for squamous cell carcinoma of the head and neck have demonstrated that when all other variables are constant, protraction of the overall treatment time leads to a decreased probability of local control. Few data exist on the effect of overall treatment time on local control following irradiation of tumors that are generally thought to be slowly proliferating, such as adenocarcinoma of the prostate. This analysis was undertaken to determine the time-dose relationships for local control of prostatic adenocarcinoma at the University of Florida. All patients were treated at least 5 years prior to the date of analysis. For patients with Stage A2 disease, a tumor dose of 6500 cGy in 7 to 7.5 weeks to 7000 cGy in 8 weeks resulted in local control in 17/17 patients (100%). For patients with Stage B1 disease, the local control rate was 14/16 (88%) with an overall treatment time of less than or equal to 8 weeks versus 1/3 in patients who received split-course treatment in greater than 8 weeks (p = .097). For patients with Stage B2, C1, and C2 disease who received greater than or equal to 6500 cGy, the 5-year rate of local control was lower when overall treatment time was protracted beyond 8 weeks. Results were as follows: B2 (62 patients), less than or equal to 8 weeks, 88%, versus greater than 8 weeks, 55%, p = .002; C1 (87 patients), less than or equal to 8 weeks, 88%, versus greater than 8 weeks, 73%, p = .052; Cs (33 patients), less than or equal to 8 weeks, 81%, versus greater than 8 weeks, 65%, p = .056. Stratification by tumor grade of patients with Stage B1, B2, C1, and C2 disease who received greater than or equal to 6500 cGy demonstrated significantly lower local control rates for all grade categories when the overall treatment time was protracted beyond 8 weeks. Five-year local control rates (life-table method) for overall treatment time less than or equal to 8 weeks versus greater than 8 weeks were as follows: well differentiated, 93% versus 73% (p = .003); moderately differentiated, 86% versus 69% (p = .017); and poorly differentiated, 75% versus 59% (p = .046). These data suggest that tumor repopulation during excessively protracted treatment may be a clinically significant factor in patients with adenocarcinoma of the prostate.