Comparison of a conformal nonaxial boost with a four-field boost technique in the treatment of adenocarcinoma of the prostate.

PURPOSE: A comparative study of a standard four-field boost technique and a customized nonaxial external beam technique for the treatment of adenocarcinoma of the prostate was performed to quantify rectal and bladder sparing. METHODS AND MATERIALS: Sixteen patients with localized carcinoma of the prostate who underwent simulation and treatment planning computed tomography formed the basis of this study. The prostate, seminal vesicles, lymph node, pelvic bones, rectum, bladder, and skin volumes were contoured from the CT slices to the three-dimensional treatment planning system. Each patient was planned for both standard four-field and nonaxial techniques to a boost treatment dose of 24 Gy to the prostate. Isodose plans were chosen on the basis of adequate tumor coverage and normal tissue sparing.
RESULTS: The volumes of the prostate, rectum, and bladder ranged from 46-148 cc, 25-196 cc, and 50-378 cc, respectively. Data analysis demonstrated a statistically significant reduction (p < 0.01) in normal tissue irradiation with the nonaxial external beam technique at dose levels of 15 and 20 Gy.
CONCLUSION: The nonaxial four-field external beam technique appears to be superior to the standard four-field approach in reducing the volume of high dose irradiation to the adjacent rectum and bladder.