Purpose: Dose indices are effective variables that may serve as predictors in determining the plan quality for Stereotactic Radiosurgery (SRS) and Stereotactic Radiotherapy (SRT) treatments of brain lesions. The purpose of this study is to provide recommendations for dose indices versus target volumes based upon an institutional retrospective analysis of Linac based VMAT brain SRS/SRT treatments utilizing the Edge Radiosurgery System (Varian Medical Systems Inc, Palo Alto, CA). This study compares the dose indices of VMAT brain SRS/SRT treatments of patients treated at The University of Toledo Medical Center against previously established institutional guidelines for dose indices of this kind of treatment based upon Dynamic Conformal-Arc (DCA) radiotherapy.
Methods: One hundred and forty patients with approved treatment plans planned in RayStation V.8A (184.108.40.206) TPS treated with VMAT SRS/SRT on Varian EDGE radiosurgery system using 6FFF with single brain metasis were randomly selected. Plans were grouped into three categories based upon lesion volume; small (0.10-2.0 cc , n=80), medium (2-10 cc, n=35), large (10-40 cc, n=24 ). Gradient Indices (GI), RTOG conformity indices (CI(RTOG)), and Paddick Conformity Indices (CI), were computed for each plan using a script developed in house and calculated via a collapsed cone dose calculation algorithm V.4.1 with a 1mm dose grid resolution. Plan indices for each plan were tabulated.
Results: For patients presenting with small brain lesions (n=80), medium lesions (n=36), and (n=24) large lesions the recommendations suggested for plan quality metrics are presented in Table 1 of supporting documents.
Conclusion: This study provides recommendations based upon an institutional retrospective analysis for plan indices versus lesion volumes for VMAT brain SRS/SRT Linac based treatments; serving as a guide to assessbrain VMAT SRS/SRT plan quality. We recommend plan quality metrics be calculated for patients, preferably using scripts to allow this to be accepted into the clinical workflow.