SU‐F‐T‐524: Investigation of the Dosimertric Benefits of Interchangeable Source Size of a Novel Rotating Gamma System

Abstract

Purpose:Tremendous technological developments were made for conformal therapy techniques with linear accelerators, while less attention was paid to cobalt‐60 units. The aim of the current study is to explore the dosimetric benefits of a novel rotating gamma ray system enhanced with interchangeable source sizes and multi‐leaf collimator (MLC).Material and Methods:CybeRT is a novel rotating gamma ray machine with a ring gantry that ensures an iso‐center accuracy of less than 0.3 mm. The new machine has a 70cm source axial distance allowing for improved penumbra compared to conventional machines. MCBEAM was used to simulate Cobalt‐60 beams from the CybeRT head, while the MCPLAN code was used for modeling the MLC and for phantom/patient dose calculation. The CybeRT collimation will incorporate a system allowing for interchanging source sizes. In this work we have created phase space files for 1cm and 2cm source sizes. Evaluation of the system was done by comparing CybeRT beams with the 6MV beams in a water phantom and in patient geometry. Treatment plans were compared based on isodose distributions and dose volume histograms.Results:Profiles for the 1cm source were comparable to that from 6MV in the order of 6mm for 10×10 cm2 field size at the depth of maximum dose. This could ascribe to Cobalt‐60 beams producing lowerenergy secondary electrons. Although, the 2cm source have a larger penumbra however it could be still used for large targets with proportionally increased dose rate. For large lung targets, the difference between cobalt and 6MV plans is clinically insignificant. Our preliminary results showed that interchanging source sizes will allow cobalt beams for volumetric arc therapy of both small lesions and large tumors.Conclusion:The CybeRT system will be a cost effective machine capable of performing advanced radiation therapy treatments of both small tumors and large target volumes.