Room: Stars at Night Ballroom 1
Purpose: To implement and evaluate an in-house developed geometry optimization (GO) software which provides the optimal lesion clustering, isocenter placement and collimator angle of each arc for cranial multi-lesions VMAT SRS planning.
Methods: An Eclipse-plugin program was developed to facilitate the setup of SRS arcs for clinically-challenging multiple metastases cases. A mixed, unsupervised exhaustive and k-mean clustering method was used to group lesions and place isocenters. The sum of squared Euclidean Distance (SSED) and customizable maximum dimension of lesionsâ€™ projection contours on beamsâ€™ eye view in x and y direction from the arc trajectory were used as supervised parameters to determinate the optimal number of isocenters. Collimator angle resulting in the minimal sum of mlc opening area from all gantry angles of each arc was selected as the optimal angle. Eight clinical VMAT SRS cases with a total of 51 lesions treated during 2016 with 3 or more isocenters were selected for testing of the GO software. Paddick gradient index (GI), conformity index (CI), local brain volume receiving 12Gy (local V12Gy) around each lesion were compared between clinical plans and GO plans.
Results: In three out of the 8 cases, the number of isocenters were reduced in the GO plan. For three cases the GO plans had the same number of isocenters as the clinical plans but had different lesion grouping. The GO plans had significantly lower GI (4.3Â±0.9 vs 4.5Â±1.0, p<0.0001), CI (1.2Â±0.2 vs 1.2Â±0.1, p=0.0007) and local V12Gy (5.3Â±4.7 vs 5.6Â±4.7 in c.c., p<0.0001) than the clinical plans. The GO plans had slightly higher mean normal brain dose but not statistically significant. Volume of normal brain receiving â‰¥6 Gy was lower in the GO plans.
Conclusion: This geometry optimization software does improve planning efficiency and provides improved plan quality for multiple cranial metastasis VMAT SRS planning.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by the MSK Cancer Center Support Grant/Core Grant (P30 CA008748)