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In Gamma Knife forward treatment planning, normalization effect may be observed when multiple shots are used for treating large lesions. This effect can reduce the proportion of coverage of high‐value isodose lines within targets. The aim of this study was to evaluate the performance of forward treatment planning techniques using the Leksell Gamma Knife for the normalization effect reduction. We adjusted the shot positions and weightings to optimize the dose distribution and reduce the overlap of high‐value isodose lines from each shot, thereby mitigating the normalization effect during treatment planning. The new collimation system, Leksell Gamma Knife Perfexion, which contains eight movable sectors, provides an additional means to reduce the normalization effect by using composite shots. We propose different techniques in forward treatment planning that can reduce the normalization effect. Reducing the normalization effect increases the coverage proportion of higher isodose lines within targets, making the high‐dose region within targets more uniform and increasing the mean dose to targets. Because of the increase in the mean dose to the target after reducing the normalization effect, we can set the prescribed marginal dose at a higher isodose level and reduce the maximum dose, thereby lowering the risk of complications.

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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.

Purpose: To analyze and compare the characteristics of dose distributions for Leksell Gamma Knife Perfexion (LGK-PFX) and CyberKnife (CK) in treating arteriovenous malformations (AVMs). Subjects and Methods: Twenty-four patients with AVMs who received CK radiosurgery at a prescribed dose (PD) of 16-25 Gy in a single fraction were selected. A LGK-PFX treatment plan with the same PD was designed for each patient. Dosimetric values for both systems were compared with respect to the conformity index (CI); selectivity index (SI); gradient index (GI) of 75, 50, and 25% of the PD; heterogeneity index; volume of the brain tissue covered by doses of 10 and 12 Gy; maximum dose delivered to the brainstem; and beam-on time. Results: The CIs of LGK-PFX and CK were 0.744 ± 0.075 and 0.759 ± 0.071 (p = 0.385), respectively. The SIs of LGK-PFX and CK were 0.764 ± 0.081 and 0.780 ± 0.076 (p = 0.424), respectively. The GI_75%, GI_50%, and GI_25% values of LGK-PFX and CK were 1.028 ± 0.123 and 2.439 ± 0.338 (p < 0.001), 3.169 ± 0.265 and 4.972 ± 0.852 (p < 0.001), and 8.650 ± 0.914 and 14.261 ± 2.476 (p < 0.001), respectively. Volumes of the brain tissue covered by 10 Gy and 12 Gy for LGK-PFX and CK (p < 0.001) exhibited a significant difference. Conclusions: LGK-PFX and CK exhibited similar dose conformity. LGK-PFX showed superior normal tissue sparing.