Comparison of multileaf collimator and customized blocks for 3-D conformal radiotherapy of prostate cancer with six-field technique

Abstract

The recent technological advances in radiation oncology gave us the opportunity to increase the doses given to the tumor tissues while reducing the doses of normal tissues. The shaping of the conformal fields may be achieved by using lead customized (C) blocks, multileaf collimators (MLC) or intensity modulated beams. In this study, in order to minimize the doses of normal tissues, we compared the different conformal treatment techniques and shapes for the radiotherapy in the case of prostate cancer. Dose volume histograms of the six patients' treatment plans generated with multileaf collimation technique and the customized blocks are presented. Six patients with localized prostatic carcinoma who have been treated with conformal irradiation between January 2001 and September 2002 were evaluated retrospectively. They were all chosen to assess the differences between customized blocks and MLC configuration in the definitive radiation therapy of prostate cancer with six-field technique. A total dose of 68.4 -72 Gy to the prostate and seminal vesicles were given to all of the patients with a fractionation of 1.8 Gy/daily. The dose calculation and dose volume histograms were used to compare the resulting dose distributions. The dose was calculated using the pencil beam algorithm in the Theraplan plus treatment planning system. The dose volume histograms for blocks and multileaf collimation technique were compared in terms of normal tissue volume for rectum, bladder and femoral heads and it was assumed that, although there were small discrepancies between the plans and all of the doses were under the critical dosages stated for rectum, bladder and femoral heads for each technique, the doses given to the critical organs were higher with the MLC technique. Regarding the late toxicity and the critical organ doses, each of these shaping methods is suitable for the definitive irradiation of prostate carcinoma with six-field technique.