用PENELOPE检验Leksell GammaKnife信源信道的简化模型
A simplified model of the source channel of the Leksell GammaKnife tested with PENELOPE
摘要：
已经使用代码PENMENTAL PE进行了蒙特卡罗模拟，以测试Leksell伽玛刀$^{\circledR}$的源通道几何形状的简化模型。详细分析了辐射通过治疗头盔的特性。我们已经发现，只有从源发射的初级粒子的极角小于3 $^{\rm o}$相对于射束轴是相关的伽玛刀的剂量测定。在$(x,y,z=236 {\rm mm})$处到达输出头盔准直器的光子轨迹在一侧显示出$ρ=(x^2+y^2)^{1/2}$与其极角$θ$之间的强相关性，在另一侧显示出$\tan^{-1}(y/x)$与其方位角$ϕ$之间的强相关性。这使我们能够提出一个简化的模型，将整个源通道作为一个数学准直器。这种简化模型产生的剂量与全几何形状的剂量非常一致。在最大剂量区域，18和14 mm头盔的两种计算方法之间的相对差异在3%以内，8和4 mm头盔的相对差异在10%以内。此外，简化的模型允许在计算时间的大幅减少（大于15倍）。
英文摘要：
Monte Carlo simulations using the code PENELOPE have been performed to test a simplified model of the source channel geometry of the Leksell GammaKnife$^{\circledR}$. The characteristics of the radiation passing through the treatment helmets are analysed in detail. We have found that only primary particles emitted from the source with polar angles smaller than 3$^{\rm o}$ with respect to the beam axis are relevant for the dosimetry of the Gamma Knife. The photons trajectories reaching the output helmet collimators at $(x,y,z=236 {\rm mm})$, show strong correlations between $ρ=(x^2+y^2)^{1/2}$ and their polar angle $θ$, on one side, and between $\tan^{-1}(y/x)$ and their azimuthal angle $ϕ$, on the other. This enables us to propose a simplified model which treats the full source channel as a mathematical collimator. This simplified model produces doses in excellent agreement with those found for the full geometry. In the region of maximal dose, the relative differences between both calculations are within 3%, for the 18 and 14 mm helmets, and 10%, for the 8 and 4 mm ones. Besides, the simplified model permits a strong reduction (larger than a factor 15) in the computational time.
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