Dose selection for prostate cancer patients based on dose comparison and dose response studies

Purpose: To better define the appropriate dose for individual prostate canc er patients treated with three-dimensional conformal radiation therapy (3D CRT). Methods and Materials: Six hundred eighteen patients treated with 3D CRT be tween 4/89 and 4/97 with a median follow-up of 53 months are the subject of this study. The bNED outcomes were assessed by the American Society for Th erapeutic Radiology and Oncology (ASTRO) definition. The patients were grou ped into three groups by prostate-specific antigen (PSA) level (<10 ng/ml, 10-19.9 ng/ml, and 20+ ng/ml) and further subgrouped into six subgroups by favorable (T1, 2A and Gleason score less than or equal to 6 and no perineur al invasion) and unfavorable characteristics (one or more of T2B, T3, Gleas on 7-10, perineural invasion). Dose comparisons for bNED studies were made for each of the six subgroups by dividing patients at 76 Gy for all subgrou ps except the favorable <10 ng/ml subgroup, which was divided at 72.5 Gy. F ive-year bNED rates were compared for the median dose of each dose comparis on subgroup. Dose response functions were plotted based on 5-year bNED rate s for the six patient groupings, with the data from each of the six subgrou ps divided into three dose groups. The 5-year bNED rate was also estimated using the dose response function and compares 73 Gy with 78 Gy. Results: Dose comparisons show a significant difference in 5-year bNED rate s for three of the six subgroups but not for the favorable <10 ng/ml, the f avorable 10-19.9 ng/ml, or the unfavorable greater than or equal to 20 ng/m l subgroups. The significant differences ranged from 22% to 40% improvement in 5-year bNED with higher dose. Dose response functions show significant differences in 5-year bNED rates comparing 73 Gy and 78 Gy for four of the six subgroups. Again, no difference was observed for the favorable <10 ng/m l group or the unfavorable greater than or equal to 20 ng/ml group. The sig nificant differences observed in 5-year bNED ranged from 15% to 43%. Conclusions: Dose response varies by patient subgroup, and appropriate dose can be estimated for up to six subdivisions of prostate cancer patients. T he appropriate use of high dose with 3D CRT results in 5-year cure rates th at equal or exceed other treatments. The national practice must be upgraded to allow the safe administration of 75-80 Gy with 3D CRT. (C) 2000 Elsevie r Science Inc.