The application of Monte Carlo (MC) simulation in the context of Medical Linear Accelerator (LinAc) treatment planning has increased in recent decades owing to its accuracy in dose calculations. The Multileaf Collimator (MLC), a component of the LinAc heads, plays an essential role by allowing the precise customization of the treatment beam's shape, effectively targeting the tumor area while minimizing radiation exposure to surrounding healthy structures. During a jaws static treatment, this MLC configuration varies for each angular position of the accelerator gantry, while the rest of the LinAc geometry remains static. To address the operation of the accelerator during the treatment planning avoiding the need of computationally intensive and repetitive simulations, phase-space files (PSF) are widely employed in LinAc MC calculations. This study aims to introduce and validate a methodology for the computational generation of PSFs specifically defined just below the MLC. These PSFs will assume the appropriate shape corresponding to the angle at which the accelerator gantry is positioned during treatment. The core of this methodology involves the creation of a comprehensive database containing precalculated probability functions derived from MC. In order to validate the methodology, simulated dose values of a LinAc emitting a 6 MV photon beam have been employed. The results have been tested against experimental data, and compared with the results from complete simulations, yielding PSFs of varying shapes. Finally, this study reveals that the results obtained by comparing organ dose values computed from the generated PSFs to those from the reference PSF are statistically compatible. This innovative method not only offers a valuable tool for optimizing LinAc treatment planning but also underscores the importance of accurate dose calculations in the field of radiation therapy.

中文翻译：

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一种用于计算生成蒙特卡罗模拟相空间文件的方法，应用于医疗直线加速器的治疗计划


近几十年来，由于剂量计算的准确性，蒙特卡罗 (MC) 模拟在医疗直线加速器 (LinAc) 治疗计划中的应用有所增加。多叶准直器 (MLC) 是 LinAc 头的一个组件，通过精确定制治疗光束的形状，有效瞄准肿瘤区域，同时最大限度地减少对周围健康结构的辐射暴露，发挥着重要作用。在钳口静态治疗期间，这种 MLC 配置会随着加速器机架的每个角度位置而变化，而 LinAc 几何结构的其余部分保持静态。为了解决治疗计划期间加速器的运行问题，避免计算密集型和重复模拟的需要，相空间文件 (PSF) 在 LinAc MC 计算中被广泛采用。本研究旨在介绍并验证一种在 MLC 下专门定义的 PSF 计算生成方法。这些 PSF 将呈现与治疗期间加速器机架定位的角度相对应的适当形状。该方法的核心涉及创建一个综合数据库，其中包含从 MC 导出的预先计算的概率函数。为了验证该方法，采用了发射 6 MV 光子束的 LinAc 的模拟剂量值。结果已根据实验数据进行了测试，并与完整模拟的结果进行了比较，产生了不同形状的 PSF。最后，本研究表明，通过将生成的 PSF 计算的器官剂量值与参考 PSF 计算的器官剂量值进行比较，获得的结果在统计上是一致的。 这种创新方法不仅为优化 LinAc 治疗计划提供了宝贵的工具，而且强调了精确剂量计算在放射治疗领域的重要性。