Poster — Thur Eve — 72: Improving Dose Homogeneity for TBI Using Irregular Surface Compensation Approach

In a first step toward the implementation of irregular surface compensation for Total Body Irradiation (TBI), we have evaluated the ability of the Eclipse™ AAA to accurately predict dose distributions in water at extended SSD for a 6 MV beam (Hussain et al., 2010 JACMP,in press). As an extension of this work dose distribution calculations in a Rando® at extended SSD (185 cm) with and without the use of irregular surface compensation were performed. Calculations using surface compensation showed a significant improvement on dose uniformity across Rando® reducing dose heterogeneity on the lung region from ±10% to ±2%. In order to validate these dose calculations, TLD measurements were performed at the head thorax and abdominal regions of Rando®. An opposed beam pair (AP‐PA) with a large field (56×43 cm2) was set to cover the head and neck down to the lower chest. The open and surface compensated beams were delivered at gantry zero with Rando® set at 185 cm SSD. 2200 MU and 400 MU were needed to deliver a 100 cGy dose to the midplane in Rando® for the compensated and open deliveries respectively. The agreement between measurements and calculations for the open beam was within ±3% except in the lung region where up to 4.9% dose overestimation was observed. For the irregular surface compensation delivery, an overall dose calculation/measurement agreement was within ±3%. These results indicate the potential clinical use of the irregular surface compensation for TBI at extended SSD.