1. Retroactive Calculation of TLD and Film Dose in Anthropomorphic Phantom as Assessment of Updated TPS Performance H. Alkhatib 1, S. Oves 1, B. Tsang 1, W. Neglia 1, P. Sobash 2 1 South Carolina Oncology Associates, Columbia, SC 2 Medical University of South Carolina, Charleston, SC Summary Abstract Materials and Methods Pinnacle Version 9.2 and 9.6 Results: Dose Points Results: Film Profiles CT images and IMRT plan of a RPC anthropomorphic head phantom, previously calculated by Pinnacle 3 version 9.0, was re-computed using Pinnacle 3 9.2 and 9.6. The dosimeters within the phantom include four TLD capsules representing a primary PTV, two TLD capsules representing a secondary PTV, and two TLD capsules representing an organ at risk. Also included were three sheets of film arranged into axial and sagittal planes. Performance of the updated TPS version was assessed by recalculating point doses and dose profiles corresponding to TLD and film position respectively and then comparing the results to reported values by the RPC The purpose of this study is to demonstrate a quick and comprehensive method verifying the accuracy of an updated treatment planning system. In this method, the dose model of the newer TPS version is tested by re-computing dose distribution to a previously irradiated anthropomorphic phantom used by third-parties to verify stated dose deliveries. The test itself can be achieved by the user recalculating dose to positions corresponding to point detectors and dose profiles corresponding to film positions within the phantom. This data can then be compared to previously reported measured values. Anthropomorphic Phantom TLD Positions The graph compares dose values reported by the RPC to calculated values by Pinnacle 3 versions 9.0, 9.2, and 9.6. This work shows the difference in dose calculation in an RPC head phantom between Pinnacle 3 versions 9.0. 9.2, and 9.6 for a dynamic arc treatment setup. Additionally, this study illustrates a method for the user to gain confidence in the performance of a software upgrade which is particularly helpful when time is limited. The above graphs shows a comparison of Pinnacle 3 9.0, and 9.6 dose profiles within the RPC head phantom. Anthropomorphic Phantom Film Profiles Above is a CT reconstruction of the RPC head phantom. The colored points represent positions of TLD pairs within the phantom Above is a CT reconstruction of the RPC head phantom. The rectangular planes represent film positions. Philips Pinnacle 3 version 9.2 released in 2012 lists improved small field accuracy as one of its new features. The new features of version 9.6, released in 2013, does not include an update in beam modeling or dose algorithm. However, it is the recommendation of the AAPM that that all TPS be commissioned after software updates 1. For both the 9.2 and 9.6 versions, the treatment plans were copied from that of 9.0 to ensure that dose calculations were only affected by the updated beam modeling. The plan itself is a 2-arc sliding window IMRT configuration optimized to deliver 6.6 Gy to an area of the phantom labeled as ‘primary PTV’ by the RPC. 1. Fraass, et al. “AAPM Radiation Therapy Committee Task Group 53,” Med. Phys. 25 (10), (1998).