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

Authors


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

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