SU-E-T-533: Evaluating Effective Source Position Corrections during Modeling with Pinnacle Version 9.2 Software for Flattening Free (FFF) Small Field Treatments.

Abstract

Advanced treatment delivery techniques require more robust treatment planning system (TPS) models for accurate dose planning and computation. As stereotactic body radiation therapy (SBRT) and volumetric-modulated arc therapy (VMAT) treatments become more prevalent, the ability of the TPS to accurately calculate dose delivered from small fields becomes of greater importance. An additional level of complexity in photon beam modeling is added with the inclusion of flattening filter free (FFF) treatment beams, due to steep in field dose gradients and non uniform penumbra regions. The purpose of this work is to examine the ability of ADAC/Pinnacle TPS to accurately model and calculate dose from small field FFF treatment beams. Photon beam data was first modeled using Pinnacle v9.0. Flattened and FFF beam models were generated for 6MV and 10MV energies. Models were fine-tuned using a 5×5 cm2 field as the standard field in order to place more emphasis on the accuracy of the model for the small fields. An upgrade to Pinnacle v9.2 allowed for comparison between version 9.0 and version 9.2. Accurately modeling small fields using Pinnacle v9.0 proved difficult, particularly in the lower penumbra region. An asymmetry appeared in the small field models for both the flattened and FFF models. The Pinnacle v9.2 upgrade eliminated the small field asymmetries, and allowed for more accurate penumbra region calculations. Preliminary results have shown that Pinnacle v9.2 is capable of developing accurate beam models when an emphasis is placed on the small fields. In addition, patient specific dosimetric information for version 9.0 and version 9.2 was also calculated and examined for prostate, head & neck, and lung treatments. Pinnacle v9.2 showed improved accuracy in small field FFF dose modeling over version 9.0. Comparison of patient dosimetric information reflected the improvement in the small field modeling.