Limitations of reduced-field irradiated volume and technique in conventional radiation therapy of prostate cancer: Implications for conformal 3-D treatment

In order to define technical limitations of conventional external beam irra diation for clinically localized prostate cancer, we evaluated the impact o f several reduced-field treatment factors, such as reduced-field (RF) irrad iated volume, RF technique, photon energy of treatment, and dose on surviva l endpoints and local control in a retrospective series. Several survival e ndpoints, such as disease-specific survival, freedom from relapse survival, biochemical no-evidence of disease (bNED) survival, and local control were associated with several treatment variables using univariate and multivari ate analyses in 329 patients. Reduced-field technique appeared to predict s urvival outcome, with patients treated by bilateral 120 degrees arcs faring less well than those treated by full 360 degrees rotational fields. The ir radiated volume of the reduced-field was also significantly associated with survival outcome, with patients treated with smaller volumes faring less w ell. Local failure rates also appeared increased, although not statisticall y, in patients treated with smaller RF sizes. In an attempt to explain thes e detected deficiencies, dose-volume histograms for prostate coverage were created for a small sample of patients. The deficiencies related to small r educed-field volume appeared to be largely attributable to poor dosimetric coverage of the prostate. These results underscore the limitations of conve ntional external beam treatment for prostate carcinoma when conventional te chniques are employed, particularly if small reduced fields are used, and f urther supports the development of improved treatment techniques, such as c onformal irradiation, as alternatives. (C) 2000 Wiley-Liss, Inc.