SU-F-T-608: Forward Treatment Planning Techniques On Leksell Gamma Knife for the Normalization Effect Reduction

Abstract

Purpose: In the Gamma Knife forward treatment planning, we use multiple shots for large targets to cover the targets and for irregular target shapes to achieve better target conformity. However, the normalization effect can be found when multiple shots are used during treatment planning, which can cause a decrease in the coverage of high value isodose lines within targets. In this study, we aim to evaluate the performance of forward treatment planning techniques for the normalization effect reduction. Methods: We can change the shot positions and the shot weightings to reduce the normalization effect for both models of Leksell Gamma Knife with and without the new collimation system during treatment planning. The new collimation system of Leksell Gamma Knife Perfexion, which contains 8 movable sectors, can provide us another method to reduce the normalization effect by using composite shots during treatment planning. Results: We proposed different forward treatment planning techniques that can achieve the normalization effect reduction. The normalization effect reduction can increase the coverage of high value isodose lines within targets, so the mean dose to targets would increase and the high‐dose regions within targets can be more uniform. Conclusion: Due to an increase in the mean dose to targets from the normalization effect reduction, we can decrease the prescribed dose or set the prescribed dose at higher isodose line, and then lower the risk of complications.