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Dosimetric Comparison of Original Gamma Knife Plans and Optimized Gamma Knife Plans for Metastatic Brain Tumors

B Delacruz1*, E Calugaru2, B Garcia1, J Chang2, A Goenka2, (1) Hofstra University, Hempstead, NY, (2) Northwell Health, Lake Success, NY

Presentations

PO-GePV-T-389 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Patients with metastatic brain tumors may be treated with stereotactic radio surgery (SRS) using GammaKnife (GK)-based platform or a linear accelerator (LINAC)-based platform. Recently, Leksell GammaPlan (LGP) was updated to provide an optimization algorithm in addition to preexisting treatment planning tools. Our objective was to compare older, completed GK plans with newer “optimized” GK plans to establish if there were improvements on plan parameters, namely, Gradient Index (GI), and Selectivity Index (SI).

Methods: We reviewed our institutional database to identify patients with brain metastases treated by GK for SRS with varying lesion sizes to see if there were any significant differences in how the optimization algorithm would treat large lesions (>5 cc), what we defined as very small (<2 cc), small (2-3 cc) and medium-sized lesions (3-4 cc). All were treated with a 900 cGy x3 fractionation scheme. Optimization was performed on these plans while maintaining at least 99.51% coverage of the lesion volume and prescribing to the 50% isodose line.

Results: 30 patients with metastatic brain tumors were identified. 15 had large lesions, 5 had medium-sized lesions, 5 had small lesions, and 5 had very small lesions. The GI improved for the very small on average by 0.492 (14.88%), the small on average by 0.482 (16.27%), the medium on average by 0.37 (12.66%), and the large by 0.176 (6.63%). The SI improved for the very small on average by 0.144 (25.71%), the small on average by 0.096 (12.83%), the medium on average by 0.132 (22.92%). However, the large on average lowered by 0.017 (-2.05%).

Conclusion: Utilizing this new optimization algorithm may be associated with improvement in dose falloff and local control of the tumor volume. Our data suggests that for lesions of all sizes, optimization significantly improves all parameters in question for GK treatment planning quality.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: intracranial stereotactic/SBRT

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