Incorporating dynamic collimator motion in Monte Carlo simulations: an application in modelling a dynamic wedge
Incorporating dynamic collimator motion in Monte Carlo simulations: an application in modelling a dynamic wedge
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DOI：
10.1088/0031-9155/46/2/302
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发表时间：
2001-02-01
影响因子：
3.5
通讯作者：
Liu, HH
中科院分区：
文献类型：
--
作者：
Verhaegen, F;Liu, HH
在放射治疗中，采用动态准直和强度调制的新治疗模式增加了剂量计算的复杂性，因为必须将新的维度（时间）并入传统的三维问题中。在这项工作中，我们研究了两类采样技术，将动态准直器运动的Monte Carlo模拟。最初评估的方法建模增强动态楔形（EDW）从瓦里安加速器（瓦里安医疗系统，帕莱阿尔托，美国）。在位置概率采样或PPS方法中，计算准直器位置的累积概率分布函数（CPDF），然后可以在模拟期间对其进行采样。在静态分量模拟或SCS方法中，动态场以步进方式由多个静态场近似。根据准直器位置的概率分布函数（PDF）计算每个分量场模拟的粒子权重或粒子数量。根据EDW的分段治疗表（STT）计算CPDF和PDF。在此计算中必须应用输出校正因子，以说明影响监测室读数的背散射辐射。从PPS方法（与步进射击运动）与SCS方法的相空间数据的比较显示出良好的一致性。PPS方法的准确性进一步验证了测量和计算的剂量分布之间的协议。与SCS方法相比，从操作角度来看，PPS方法更加自动化和高效。PPS方法的原理可以扩展到模拟其他动态运动，特别是使用多叶准直器的强度调制光束。
In radiation therapy, new treatment modalities employing dynamic collimation and intensity modulation increase the complexity of dose calculation because a new dimension, time, has to be incorporated into the traditional three-dimensional problem. In this work, we investigated two classes of sampling technique to incorporate dynamic collimator motion in Monte Carlo simulation. The methods were initially evaluated for modelling enhanced dynamic wedges (EDWs) from Varian accelerators (Varian Medical Systems, Pale Alto, USA). In the position-probability- sampling or PPS method, a cumulative probability distribution function (CPDF) was computed for the collimator position, which could then be sampled during simulations. In the static-component-simulation or SCS method, a dynamic field is approximated by multiple static fields in a step-shoot fashion. The weights of the particles or the number of particles simulated for each component field are computed from the probability distribution function (PDF) of the collimator position. The CPDF and PDF were computed from the segmented treatment tables (STTs) for the EDWs. An output correction factor had to be applied in this calculation to account for the backscattered radiation affecting monitor chamber readings. Comparison of the phase-space data from the PPS method (with the step-shoot motion) with those from the SCS method showed excellent agreement. The accuracy of the PPS method was further verified from the agreement between the measured and calculated dose distributions. Compared to the SCS method, the PPS method is more automated and efficient from an operational point of view. The principle of the PPS method can be extended to simulate other dynamic motions, and in particular, intensity-modulated beams using multileaf collimators.