2090 Five-field conformal radiation therapy of prostate carcinoma: Optimization technique and correlation with decreased acute side effects

Abstract

Purpose/Objective: We developed a novel noncoplanar 5-field conformal radiation therapy technique for the treatment of prostate carcinoma. We evaluated this technique via dose-volume histograms (DVH) of the clinical target volume (CTV) and surrounding structures, as well as the acute effects experienced by patients while on treatment. Materials and Methods: The traditional four-field box technique with AP/PA and bilateral fields was modified by splitting the anterior field into AP and anterior-inferior-oblique (AIO) fields. AIO field required 90 deg.couch rotation and 25-35 deg.gantry rotation to reduce irradiation of the bladder. Patients were placed in the supine position with half-body immobilization with Vac-Lok. The apex of the prostate was determined with urethrogram. The optimal gantry angle of the AIO field was confirmed on the plan check simulation to exclude both testicles. Treatment planning for 22 patients was performed using helical CT scanning and PTI 3-D planning system with 18 MV photons. Uniformed margins of 1.5 cm around CTV were used, with the inferior border defined by the urethrograms. Treatments were deliverd on Clinac 2100 C/D with multileaf collimator. Rectum, bladder, femoral heads, and CTV dose-volume histograms were computed for five-, and four-fields technique for evaluation. Twenty-two patients with histological confirmed adenocarcinoma of the prostate completed radiation treatment with the 5-field technique. Seven patients were with stage T1C disease, four with T2A, four with T2B, four with T2C and three with T3. Median age was 72 (range:60-83). Radiation dose was 66.6 Gy for T1C - T2B; 70.2 Gy for T2C or higher. Median Gleason score was 7 (range: 5 -7). Eight patients received neoadjuvant hormonal therapy. The acute effects of irradiation among 22 patients treated with the 5-field technique were reported according to the RTOG G-U morbidity score. Results: In comparison with the four-field dose distribution, our novel noncoplanar technique substantially reduced the radiation doses from anterior and posterior fields. With a minimum target coverage of 100% of prescribed dose, the dose uniformity within the CTV was (8 {+-} 2)%. Median bladder dose reduction of 8% (Max=14.9%, Min=1.3%) in a sample group of thirteen patients was found to be statistically significant (p<0.0001). Rectum and femoral doses were generally not improved. Median changes of -0.6% (rectum) and 0.5% (femoral heads) were not significant. All 22 patients tolerated the treatment very well, with one patient requiring a treatment break of only three days. Thirteen (59%) patients reported an acute RTOG GU score of 0, five (23%) reported a score of 1, and four (18%) reported a score of 2. There was no grade 3 or 4 morbidity. Conclusion: The five-field three dimensional conformal radiation therapy technique resulted in homogeneous dose to the clinical target volume with more than 80% of patients requiring no medical management of side effects of radiation.