POTENCY PROBABILITY FOLLOWING CONFORMAL MEGAVOLTAGE RADIOTHERAPY USING CONVENTIONAL DOSES FOR LOCALIZED PROSTATE-CANCER

Purpose: Impotence is; a familiar sequela of definitive external beam radiation therapy (EBRT) for localized prostate cancer; however, nerve -sparing radical prostatectomy (NSRP) has offered potency rates as hig h as 70% for selected for patients in several large series. To the aut hors' knowledge, age and stage-matched comparisons between the effects of EBRT and NSRP upon the normal age trend of impotence have not been performed. Herein, we report the change in potency over time in an FB RT-treated population, determine the significantly predisposing health factors affecting potency in this population, and compare age and sta ge-matched potency rates with those of normal males and prostatectomy patients. Methods and Materials: Our results are obtained from a retro spective study of 114 patients ranging in age from 52 to 85 (mean, 68) who were diagnosed with clinical stages A-C C (T1-T4N0M0) prostate ca ncer and then treated conformally with megavoltage x-rays to 6500-7000 cGy (180-200 cGy per fraction) using the four-field box technique. In formation concerning pre-RT potency, medical and surgical history, and medications was documented for each patient as was time of post-RT ch ange in potency during regular follow-up. The median followup time was 18.5 months. Results: The actuarial probability of potency for all pa tients gradually decreased throughout post-RT followup. At months 1, 1 2, 24, and 36, potency rates were 98, 92, 75, and 66%, respectively. F or those patients who became impotent, the median time to impotence wa s 14 months. Factors identified from logistic regression analysis as s ignificant predictors of post-EBRT impotence include pre-EBRT partial potency (p < 0.001), vascular disease (p < 0.001), and diabetes (p = 0 .003). Next, an actuarial plot of potency probability to patient age f or the EBRT-treated population was compared to that obtained from the Massachusetts Male Aging Study of normal males. The two curves were no t significantly different (logrank test, p = 0.741) between ages 50 an d 65. Finally, potency probability after follow-up of 1 year or more i n FBRT-treated patients was stratified by age and substratified by cli nical stage and then compared to similarly stratified potencies for pa tients treated with NSRP. The prostatectomy data were derived from the pooled data of six large (total n, 952), independent series conducted at academic centers. For patients older than 70 years, 79.1% of EBRT patients and 32.9% of NSRP patients remained potent after treatment. F or patients with stage B2 disease, 75.0% of EBRT patients and 49.3% of NSRP patients remained potent after treatment. Overall EBRT patient p otency was 76.1% vs. 66.2% for NSRP patients. Conclusions: 1) By 36 mo nths after completion of EBRT for localized prostate cancer, fully one -third of all patients becomes impotent; however, for patients younger than 70 years, the probability of impotence does not depart significa ntly from that for normal males. 2) In the EBRT-treated population, pr e-EBRT partial potency, vascular disease, and diabetes are the most si gnificant predispositions to the development of impotence. Patients wi th these predispositions, though, do not become impotent significantly earlier than other patients. 3) When comparing age and stage-stratifi ed potency rates for EBRT and NSRP patients, potency is roughly equal for both modalities for most age and stage groups; however, for patien ts older than 70 years or with stage B2 disease, EBRT offers notably h igher posttreatment potency rates than NSRP. Thus, for the treatment o f localized prostate cancer, EBRT may not affect the normal age trend of impotence in younger patients and may induce impotence less frequen tly than NSRP in older patients or in patients with later stage diseas e. (C) 1997 Elsevier Science Inc.