Carina Medical LLC, Lexington, Kentucky, USA.
Department of Radiation Medicine, University of Kentucky School of Medicine, Lexington, Kentucky, USA.
J Appl Clin Med Phys. 2022 May;23(5):e13556. doi: 10.1002/acm2.13556. Epub 2022 Feb 9.
Monte Carlo (MC) independent dose calculations are often based on phase-space files (PSF), as they can accurately represent particle characteristics. PSF generally are large and create a bottleneck in computation time. In addition, the number of independent particles is limited by the PSF, preventing further reduction of statistical uncertainty. The purpose of this study is to develop and validate a virtual source model (VSM) to address these limitations. Particles from existing PSF for the Varian TrueBeam medical linear accelerator 6X, 6XFFF, 10X, and 10XFFF beam configurations were tallied, analyzed, and used to generate a dual-source photon VSM that includes electron contamination. The particle density distribution, kinetic energy spectrum, particle direction, and the correlations between characteristics were computed. The VSM models for each beam configuration were validated with water phantom measurements as well as clinical test cases against the original PSF. The new VSM requires 67 MB of disk space for each beam configuration, compared to 50 GB for the PSF from which they are based and effectively remove the bottleneck set by the PSF. At 3% MC uncertainty, the VSM approach reduces the calculation time by a factor of 14 on our server. MC doses obtained using the VSM approach were compared against PSF-generated doses in clinical test cases and measurements in a water phantom using a gamma index analysis. For all tests, the VSMs were in excellent agreement with PSF doses and measurements (>90% passing voxels between doses and measurements). Results of this study indicate the successful derivation and implementation of a VSM model for Varian Linac that significantly saves computation time without sacrificing accuracy for independent dose calculation.
蒙特卡罗（MC）独立剂量计算通常基于相空间文件（PSF），因为它们可以准确地表示粒子特性。PSF 通常较大，成为计算时间的瓶颈。此外，独立粒子的数量受到 PSF 的限制，从而阻止了统计不确定性的进一步降低。本研究的目的是开发和验证虚拟源模型（VSM）以解决这些限制。从瓦里安 TrueBeam 医用线性加速器 6X、6XFFF、10X 和 10XFFF 光束配置的现有 PSF 中对粒子进行了计数、分析，并用于生成包括电子污染的双源光子 VSM。计算了粒子密度分布、动能谱、粒子方向以及特征之间的相关性。使用水模测量值以及针对原始 PSF 的临床案例对每个光束配置的 VSM 模型进行了验证。与基于它们的 50GB PSF 相比，新的 VSM 为每个光束配置仅需要 67MB 的磁盘空间，从而有效地消除了 PSF 设置的瓶颈。在 MC 不确定性为 3%的情况下，VSM 方法将我们服务器上的计算时间缩短了 14 倍。使用 VSM 方法获得的 MC 剂量与临床案例中的 PSF 生成剂量以及水模中的测量值（剂量和测量值之间的通过像素大于 90%）进行了比较。在所有测试中，VSM 与 PSF 剂量和测量值非常吻合（剂量和测量值之间的通过像素大于 90%）。这项研究的结果表明，成功地为瓦里安直线加速器开发和实施了 VSM 模型，该模型在不牺牲独立剂量计算准确性的情况下，大大节省了计算时间。
