Comparison of Dose Distribution between Intensity Modulated Radiation Therapy and Dynamic Arc Therapy in and out-of- Field for Prostate Cancer Treatment

Abstract

AIM: The aim of this study is to compare intensity modulated radiation therapy (IMRT) and dynamic conformal arc therapy (DAT) for prostate cancer treatments. METHODS: Doses received by in-field and out-of-field organs were estimated for both techniques. We have selected ten patients with prostate cancer and we simulated their treatment using IMRT and DAT. A 6-beams (6MV) ballistic was used for the IMRT treatment, whereas a 4-arc (6MV) ballistic was used for the DAT. Dose volume histograms (DVHs) were computed. For both techniques, Planning Target Volume (PTV), Planning Organ at Risk Volume (PRV) and Remaining Volume at Risk (RVR), as well as estimates of the dose out-of-field for thirteen anatomical sites were analyzed and compared. The out-of-field dose evaluation was performed using experimental data from previous work. RESULTS: The mean absolute RVR volume, included between 2-45 Gy for IMRT, was about 1500 cm3 larger than with DAT. On the other hand, IMRT significantly increased the irradiated volume of the rectum wall in the dose range 2 to 60 Gy and also significantly increased the irradiated volume of the bladder wall. However, IMRT significantly reduced the dose to the femoral heads, as compared to the DAT. For both techniques, the dose to the PTV remained similar. For the thirteen out-of-fields anatomical sites evaluated, IMRT provided doses about 5% higher than DAT. CONCLUSIONS: DAT improves the dosimetric parameters of the prostate cancer treatment by reducing the doses not only to the PRV’ s but also to the RVR while keeping the same PTV coverage.