Purpose: The quality of planned dose distributions in lung SBRT was evaluated by characterizing dose distributions for conformity, homogeneity, and gradient parameters using an in-house script. The goal of this study was to establish size-dependent recommendation for achievable values of these plan quality metrics
Methods: Sixty-nine patients (73 lesions) treated with lung SBRT during the period 2017- 2020 were retrospectively reviewed for this study. Included patients had been treated on the Varian Edge and have a prescription of 50-60 Gy in 5 fractions. All cases were classified based on the lesion size into four groups, very small (V<5cc), small (5
Results: Our recommendations for the acceptable values for the plan quality metrics, HI, GI, CI and PCI is shown in table 1 of the supporting documents. These are based on clinically approved plans, after removing statistical outliers that we would not have approved if the metrics had been calculated. Additionally, we observed that a sharper dose fall-off and a more homogeneous plan were found using 6FFF compared to 10FFF energy.
Conclusion: Using various dosimetric indices to characterize dose distributions in lung SBRT is a powerful tool to assess plan quality. The plan recommendations are now being used in our clinics. We recommend that these values be calculated for all plans, utilizing a script or program so as to improve clinical workflow. Our retrospective analysis identified 9 out of 73 plans that would have been rejected. Also, we recommend using the 6FFF beam for lung SBRT treatment planning based on our institutional data evaluation.