Comparison of radiation field irradiated by different focusing modes of γ-knife

Objective: To compare the single-shot fields irradiated by three focusing modes of γ-knife and explore the approaches for improving the quality of stereotactic radiosurgery. Methods: GAFCHROMIC^® EBT³ mode flushing-free film was used to measure the single-shot fields irradiated by multi-source static focusing modes, multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode of γ-knife. Also the uniformity and penumbra of the single-shot fields were compared. Results: The 2D dose distribution of the single-shot fields irradiated by three focusing modes of γ-knife was different. In the axis (x, y, z), the rang of penumbra axial length ratios of multi-source static focusing modes, multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode were 0.13-0.48, 0.17-0.33 and 0.28-0.54, in the diagonal direction of the wings plane (NSD, PSD), were 0.31-0.39, 0.38-0.43 and 0.54-0.72, respectively; the penumbra axial length ratio of single-source double-axis rotating focusing mode was bigger than in multi-source static focusing modes and multi-source single-axis rotating focusing mode. On the no-wings plane, the area ratios of 80% dose curve enveloped and 50% dose curve enveloped (A_80%/A_50%) were 0.40, 0.47 and 0.19, on the wings plane, were 0.61, 0.53 and 0.35, respectively. The field uniformity of multi-source static focusing modes and multi-source single-axis rotating focusing mode were superior to single-source double-axis rotating focusing mode. Conclusions: Considering dose distribution of the single-shot fields, the multi-source static focusing modes devices and the multi-source single-axis rotating focusing mode devices should be preferred, when important tissues and organs are adjacent to the target areas. Compared with single-source double-axis rotating focusing mode, both multi-source static focusing modes and multi-source single-axis rotating focusing mode could make more target areas to be surrounded by high dose region. (authors)