SU‐F‐T‐22: Clinical Implications When Using TG‐186 (ACE) Heterogeneity Software

Abstract

Purpose:The purpose of this study is to compare dosimetric calculations using traditional TG‐43 formalism and Oncentra Brachy Advanced Collapsed cone Engine (ACE) TG‐186 calculation algorithm in clinical setting.Methods:We analyzed dosimetry of four patients treated with accelerated partial breast irradiation using a multi‐channel intracavitary device (SAVI). All patients were treated to 34 Gy in 10 fractions using a high‐dose‐rate (192) Ir source. The plans were designed and treated using the TG‐43 model. ACE was used to assess the effect heterogeneity correction on various dosimetric parameters. Mass density was estimated using Hounsfield units.Results:Compared to TG‐43 formalism, ACE estimated lower doses to targets and organs at risk. The mean difference was 19.8% (range 15.3–24.1%) for PTV_eval V200, 12.0% (range 9.7–17.7%) for PTV_eval V150, 4.3% (range 3.3–6.5%) for PTV_eval D95, 3.3% (range 1.4–5.4%) for PTV_eval D90, 5.4% (range 2.9–9.9%) for maximum rib dose, and 5.7% (2.4–7.4%) for maximum skin dose. There was no correlation between the magnitude of the difference and the PTV_eval volume, air volume, or tissue‐applicator conformance.Conclusion:Based on our preliminary study, the TG‐43 algorithm appears to overestimate the dose to targets and organs at risk when compared to the ACE TG‐186 software. We hypothesize that air adjacent to the SAVI struts contributes to lack of scatter thereby contributing a significant difference in dose calculation when using ACE. We believe that ACE calculation provides a more realistic isodose distribution than TG‐43. We plan to further investigate the impact of heterogeneity correction on brachytherapy planning for a wide variety of clinical scenarios, include skin, cervix/uterus, prostate, and lung