A Study and Automatic Solution for Multishot Treatment Planning for the γ-Knife

Abstract

It is recognized that multiple-shot radiosurgery using the Leksell Gamma Knife (LGK) can result in larger penumbra dose and less target dose homogeneity compared with a single shot treatment. In addition, the number of shots used increases significantly with increasing volume, which makes planning and optimization time consuming and complex. Although such complexity may not affect the accuracy of treatment delivery itself, it is difficult to assess the dosimetrical merits of a given plan. To deal with this complicated process, we have studied shot-related effects and target shape as separate issues. Shot-related effects include homogeneity, penumbra, shot weight, and prescription isodose line “shift.” Target shape is analyzed using morphological tools. Target volume and shape, as represented by the three-dimensional (3-D) medial axis transform or skeleton, are used to determine optimal shot positions, sizes, and number. These parameters are determined from successive 3-D skeletons of the unplanned target volume. Essentially, target shape is replicated by the arrangement of shots compromising the 3-D skeleton, forcing a conformal dose distribution. This planning process has been automated for multishot treatment. A clinical case in 3-D demonstrates this approach as a replacement for manual planning when a plan with multiple shots is required.