Multisource modeling of flattening filter free (FFF) beam and the optimization of model parameters
Multisource modeling of flattening filter free (FFF) beam and the optimization of model parameters
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DOI：
10.1118/1.3560426
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发表时间：
2011-04-01
期刊：
影响因子：
3.8
通讯作者：
Suh, Tae-Suk
中科院分区：
文献类型：
--
作者：
Cho, Woong;Kielar, Kayla N.;Suh, Tae-Suk
目的：随着放射肿瘤学中引入无平坦滤波器 (FFF) 直线加速器，需要适用于当前治疗计划系统的 FFF 光束的新分析源模型。在这项工作中，设计了FFF光束的多源模型以及相关模型参数的优化。方法：该模型基于Yang等人提出的三源模型。 [“用于计算头部散射因子的三源模型”，Med。物理。 29, 2024-2033 (2002)]。将光子注量的离轴比 (OAR) 引入到主要源项中以生成锥形轮廓。源模型的参数是使用线搜索优化技术根据测量的头部散射因子确定的。光子注量的 OAR 是通过使用相同的优化技术从 40 x 40 cm(2) 场尺寸的测量剂量分布确定的，但开发了一种获取 OAR 梯度项的新方法以提高优化过程的速度。改进的模型通过 TrueBeam (TM) STx 直线加速器在 6 和 10 MV 下测量的 3 x 3 至 40 x 40 cm(2) 射野尺寸的剂量分布进行了验证。此外，还计算了临床使用的辐射场的平面剂量分布，并与使用伽马指数方法使用 2D 阵列探测器进行的测量进行比较。结果：在 6 和 10 MV 光束下，计算曲线的所有剂量值与测量剂量曲线的一致性在 0.5% 以内，但较大射野尺寸的一些低剂量区域除外。对于大视场尺寸，在靠近视场边缘的下半影区域中可以看到略微高估了 1%-4%。当伽马指数方法的标准选择为 3%/3 mm 时，平面剂量计算显示出相当的通过率 (>98%)。结论：开发的源模型显示测量的剂量分布和计算的剂量分布之间具有良好的一致性。该模型可轻松应用于使用 FFF 光束的任何其他直线加速器，因为所需数据仅包括测量的 PDD、剂量分布和各种射野尺寸的输出因子，这些数据在传统光束调试过程中很容易获得。 (C) 2011 年美国医学物理学家协会。 [DOI：10.1118/1.3560426]
Purpose: With the introduction of flattening filter free (FFF) linear accelerators to radiation oncology, new analytical source models for a FFF beam applicable to current treatment planning systems is needed. In this work, a multisource model for the FFF beam and the optimization of involved model parameters were designed.Methods: The model is based on a previous three source model proposed by Yang et al. ["A three-source model for the calculation of head scatter factors," Med. Phys. 29, 2024-2033 (2002)]. An off axis ratio (OAR) of photon fluence was introduced to the primary source term to generate cone shaped profiles. The parameters of the source model were determined from measured head scatter factors using a line search optimization technique. The OAR of the photon fluence was determined from a measured dose profile of a 40 x 40 cm(2) field size with the same optimization technique, but a new method to acquire gradient terms for OARs was developed to enhance the speed of the optimization process. The improved model was validated with measured dose profiles from 3 x 3 to 40 x 40 cm(2) field sizes at 6 and 10 MV from a TrueBeam (TM) STx linear accelerator. Furthermore, planar dose distributions for clinically used radiation fields were also calculated and compared to measurements using a 2D array detector using the gamma index method.Results: All dose values for the calculated profiles agreed with the measured dose profiles within 0.5% at 6 and 10 MV beams, except for some low dose regions for larger field sizes. A slight overestimation was seen in the lower penumbra region near the field edge for the large field sizes by 1%-4%. The planar dose calculations showed comparable passing rates (>98%) when the criterion of the gamma index method was selected to be 3%/3 mm.Conclusions: The developed source model showed good agreements between measured and calculated dose distributions. The model is easily applicable to any other linear accelerator using FFF beams as the required data include only the measured PDD, dose profiles, and output factors for various field sizes, which are easily acquired during conventional beam commissioning process. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3560426]