TECHNICAL AND TUMOR-RELATED FACTORS AFFECTING OUTCOME OF DEFINITIVE IRRADIATION FOR LOCALIZED CARCINOMA OF THE PROSTATE

Purpose: The influence of some tumor-related and technical factors on therapeutic outcome is analyzed in 738 patients with histologically confirmed carcinoma of the prostate treated with definitive irradiation. Methods and Materials: This is a retrospective study of the records of the Radiation Oncology Center. The information was coded on computer-compatible forms and analyzed with multiple cross-reference checks to ensure data reliability. Detailed analysis of portal films and dose distribution isodose curves was carried out in 310 patients on whom this information was readily available. All patients were followed-up for a minimum of 3 years (median observation, 6.5 years). Results: Disease-free survival rates in Stages A2 (T1b) and B (T2) were 76% at 5 years and 62% at 10 years; in Stage C (T3) it was 57% at 5 years and 38% at 10 years. Overall, prostate recurrence rates were: 8% for Stage A2, 17% for Stage B, 28% for Stage C, and 46% for Stage D1 (T4). The 10-year actuarial local failure rate by stage was 20% in Stage A2 (T1b), 24% in Stage B (T2), 40% in Stage C (T3), and 70% in Stage D1 (T4) tumors. When the inferior margin of the portals was at or caudal to the ischial tuberosity, the actuarial 5-year pelvic failure rate was 0% for Stage A2 (T1b), 18% for Stage B (T2), and 20% for Stage C (T3), in contrast to 60% for Stage A2 (T1b), 27% for Stage B (T2), and 38% for Stage C (T3) when the inferior margin was cephalad to the ischial tuberosity (p = 0.05 in Stage C). Local tumor control was comparable in Stages A2 (T1b) and B (T2) when either small fields limited to the prostate and periprostatic tissues were used or, in addition, the pelvic lymph nodes were irradiated (85% and 80%, respectively). In Stage C (T3) there was significantly better pelvic tumor control (80% of 274 patients) when all of the pelvic (including common iliac) lymph nodes were treated compared with 65% in a group of 137 patients on whom the lymph nodes were irradiated with smaller fields (14 X 14 cm) (p = 0.01). In Stage C (T3), 30 patients treated with doses less than 6000 cGy had a 50% overall pelvic failure rate compared with 35% in 20 patients receiving 6500 cGy and 24% in 362 patients treated with 7000 cGy (p = 0.01). Pelvic tumor control or failure was closely associated with development of distant metastasis. In patients with pelvic tumor control, the distant metastasis rate was 18% for stages A2 (T1b) and B (T2) and 30% for stage C (T3), in contrast to 30% (p = 0.02) and 65% (p < 0.01), respectively, when prostate/pelvic failure was detected. Conclusion: Volume treated and dose of irradiation are important factors influencing local/pelvic recurrence rate in carcinoma of the prostate, particularly in stage C tumors. With recent advances in three-dimensional treatment planning and conformal radiation therapy techniques, it is imperative to determine optimal volumes and doses of irradiation to be delivered to these patients while minimizing morbidity to enhance the role of irradiation in the management of localized carcinoma of the prostate.