Long term tolerance of high dose three-dimensions conformal radiotherapy in patients with localized prostate carcinoma

BACKGROUND. The current study was undertaken to evaluate the incidence and predictors of late toxicity in patients with localized prostate carcinoma t reated with high dose three-dimensional conformal radiotherapy (3D-CRT). METHODS. A total of 743 patients with prostate carcinoma classified as T1c- T3 were treated with 3D-CRT that targeted the prostate and seminal vesicles . A minimum tumor dose of 64.8 gray (Gy) was given to 96 patients (13%), 70 .2 Gy to 266 patients (365), 75.6 Gy to 320 patients (43%), and 81.0 Gy to 61 patients (8%). The median follow-up time was 42 months (range, 18-109 mo nths). Late toxicity was graded according to the Radiation Therapy Oncology Group morbidity scoring scale. RESULTS. Late gastrointestinal (GI) and urinary (GU) toxicities were absent or minimal (Grade 0 or 1) in 90% of patients. The 5-year actuarial likelih ood of the development of Grade 2 and 3 late GI toxicities was 11% and 0.75 %, respectively. A multivariate analysis identified doses 75.6 Gy (P < 0.00 1), history of diabetes mellitus (P = 0.01), and the presence of acute GI s ymptoms during treatment (P = 0.02) as independent predictors of Grade grea ter than or equal to 2 late GI toxicity. The 5-year actuarial likelihood of the development of Grade 2 and 3 late GU toxicities was 10% and 3%, respec tively Doses greater than or equal to 75.6 Gy (P = 0.008) and acute GU symp toms (P < 0.001) were independent predictors of Grade greater than or equal to 2 late GU toxicity. Among 544 patients who were potent before treatment (73% of all patients), 211 (39%) became impotent after 3D-CRT. The 5-year actuarial risk of potency loss was 60%. Doses greater than or equal to 75.6 Gy (P < 0.001) and the use of neoadjuvant androgen deprivation (P = 0.01) were independent predictors of posttreatment erectile dysfunction. CONCLUSIONS. The incidence of severe late complications after high dose SD- CRT was minimal. Radiation doses greater than or equal to 75.6 Gy and the p resence of acute treatment-related symptoms during SD-CRT correlated with a higher incidence of Grade greater than or equal to 2 late GI and GU toxici ties. In addition to higher doses, the use of androgen deprivation therapy increased the likelihood of permanent impotence in these patients. Intensit y-modulated radiotherapy, which makes it possible to enhance the conformali ty of the dose distribution, has recently been implemented in an attempt to reduce the incidence of moderate grade toxicities in patients receiving hi gh dose SD-CRT. Cancer 1999;85:2460-8, (C) 1999 American Cancer Society.