Medical Physics Department, University Hospital Rijeka, Rijeka, Croatia.
Department of Medical Physics and Biophysics, Faculty of Medicine, University of Rijeka, Rijeka, Croatia.
Radiol Oncol. 2020 Sep 16;54(4):495-504. doi: 10.2478/raon-2020-0051.
Introduction Advanced, Monte Carlo (MC) based dose calculation algorithms, determine absorbed dose as dose to medium-in-medium (Dm,m) or dose to water-in-medium (Dw,m). Some earlier studies identified the differences in the absorbed doses related to the calculation mode, especially in the bone density equivalent (BDE) media. Since the calculation algorithms built in the treatment planning systems (TPS) should be dosimetrically verified before their use, we analyzed dose differences between two calculation modes for the Elekta Monaco TPS. We compared them with experimentally determined values, aiming to define a supplement to the existing TPS verification methodology. Materials and methods In our study, we used a 6 MV photon beam from a linear accelerator. To evaluate the accuracy of the TPS calculation approaches, measurements with a Farmer type chamber in a semi-anthropomorphic phantom were compared to those obtained by two calculation options. The comparison was made for three parts of the phantom having different densities, with a focus on the BDE part. Results Measured and calculated doses were in agreement for water and lung equivalent density materials, regardless of the calculation mode. However, in the BDE part of the phantom, mean dose differences between the calculation options ranged from 5.7 to 8.3%, depending on the method used. In the BDE part of the phantom, neither of the two calculation options were consistent with experimentally determined absorbed doses. Conclusions Based on our findings, we proposed a supplement to the current methodology for the verification of commercial MC based TPS by performing additional measurements in BDE material.
介绍 高级蒙特卡罗（MC）剂量计算算法将介质中的吸收剂量定义为介质中剂量（Dm，m）或水中剂量（Dw，m）。一些早期的研究确定了与计算模式相关的吸收剂量差异，特别是在骨密度等效（BDE）介质中。由于在使用之前应验证治疗计划系统（TPS）中内置的计算算法是否符合剂量学要求，因此我们分析了 Elekta Monaco TPS 两种计算模式之间的剂量差异。我们将其与实验确定的值进行了比较，旨在为现有 TPS 验证方法学定义补充内容。 材料与方法 在我们的研究中，我们使用了来自线性加速器的 6 MV 光子束。为了评估 TPS 计算方法的准确性，我们将在半拟人模型中的 Farmer 型腔室中的测量值与两种计算选项获得的测量值进行了比较。比较是针对具有不同密度的三个模型部分进行的，重点是 BDE 部分。 结果 对于水和肺等效密度材料，无论计算模式如何，测量值和计算值之间的剂量均一致。但是，在模型的 BDE 部分，两种计算方案之间的平均剂量差异在 5.7%至 8.3%之间，具体取决于所使用的方法。在模型的 BDE 部分，两种计算方案均与实验确定的吸收剂量不一致。 结论 根据我们的发现，我们提出了一种补充当前商业 MC 基于 TPS 验证方法学的方法，即在 BDE 材料中进行额外的测量。
