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Session: Therapy General ePoster Viewing [Return to Session]

A Retrospective Study to Establish Recommendations for Plan Quality Metrics in Linac Lung SBRT

S Taghizadehghahremanloo, F Akbari*, D Pearson, University of Toledo, Toledo, OH


PO-GePV-T-262 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

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 (530cc). Plans were generated in RayStation treatment planning system using the collapsed cone algorithm with a computation grid size of 2 mm. Plans were retrospectively evaluated using dosimetric indices from respective RTOG and ICRU protocols.

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.



    Plan Quality, Lung SBRT


    TH- External Beam- Photons: General (most aspects)

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