Assessing the Out-of-Field Dose Calculation Accuracy by Eclipse Treatment Planning System in Sliding Window IMRT of Prostate Cancer Patients

Background: The objective of this study was to evaluate out-of-field dose distribution calculation accuracy by the Anisotropic Analytical Algorithm (AAA), version ۱۳.۰.۲۶, in Eclipse TPS, (Varian Medical Systems, Palo Alto, Ca, USA) for sliding window IMRT delivery technique in prostate cancer patients. Materials and Methods: Prostate IMRT plans with nine coplanar were calculated with the AAA Eclipse treatment planning system. To assess the accuracy of dose calculation predicted by the Eclipse in normal tissue and OARS located out of radiation field areas, including the rectum, bladder, right and left head of the femur, absolute organ dose value, and dose distribution were measured using the Delta۴+ IMRT phantom. Results: In the out-of-field areas, underestimation of -۰.۶۶% in organs near the field edge to -۳۹.۶۳% in organs far from the field edge (۲.۵ and ۷.۳ cm respectively) occurred in the TPS calculations. The percentage of dose deviation for the femoral heads was ۹۵.۷ on average while for the organ closer to the target (rectum) it was ۷۹.۸۱. Conclusions: AAA dosimetry algorithm (used in Eclipse TPS) showed poor dose calculation in areas beyond the treatment fields border where underestimation varies with the distance from the field edges. A significant underestimation was found for the AAA algorithm in the sliding window IMRT technique (P-value <۰.۰۵).

Keywords:

Out-of-field dose , dose calculation accuracy , TPS , IMRT , Prostate cancer