Validation of a freely available Eclipse script for automatic calculation of EQD2 dose distribution in external beam...

To validate a script designed to streamline equivalent dose in 2 Gy fractions (EQD2) calculations for external beam radiotherapy. The VarianESAPI-EQD2Converter script for EQD2 calculation was evaluated for the Eclipse v. 16.1 treatment planning system. Seven anatomical sites were included (head and neck, lung, liver, breast, prostate, abdomen, and brain), and 3 cases per site were randomly selected from our clinical database. For each plan, the values of the D2%, D50% and D98% metrics of the planning target volume (PTV), and D2%, D50%, and D0.1cc of the organs-at-risk (OARs) were retrieved and converted into EQD2 values using the EQD2 formula ("true values"). Then, the script was executed for each plan following these 2 approaches: (1) the alpha-beta values of the PTV and OARs were simultaneously entered (approach 1); (2) only the external patient contour ("body") structure was considered, and the script was run several times by entering the alpha-beta values of the PTV and OARs each time. Validation of the script was performed by comparing the EQD2 values computed by the script for the Dx%/D0.1cc metrics with the respective true values. A 2-tailed t-test statistical analysis was done (alpha = 0.05). Nonstatistically significant differences were found between the 2 approaches, but unacceptably high differences (up to 57.5%) were found using approach 1. By contrast, low absolute differences (mostly < 0.5%) were found with approach 2. The VarianESAPI-EQD2Converter script with approach 2 is a reliable method to automate the EQD2 calculation process for Eclipse users.