蒙特卡罗法计算 INTRABEAM 电子近距离放疗源的相对 TG-43 剂量学参数。

Monte Carlo calculation of the relative TG-43 dosimetry parameters for the INTRABEAM electronic brachytherapy source.

机构信息

Medical Physics Unit, McGill University and Cedars Cancer Center, Montreal, Canada.

出版信息

Phys Med Biol. 2020 Dec 22;65(24):245041. doi: 10.1088/1361-6560/abc6f1.

Abstract

The INTRABEAM system (Carl Zeiss Meditec AG, Jena, Germany) is an electronic brachytherapy (eBT) device designed for intraoperative radiotherapy applications. To date, the INTRABEAM x-ray source has not been characterized according to the AAPM TG-43 specifications for brachytherapy sources. This restricts its modelling in commercial treatment planning systems (TPSs), with the consequence that the doses to organs at risk are unknown. The aim of this work is to characterize the INTRABEAM source according to the TG-43 brachytherapy dosimetry protocol. The dose distribution in water around the source was determined with Monte Carlo (MC) calculations. For the validation of the MC model, depth dose calculations along the source longitudinal axis were compared with measurements using a soft x-ray ionization chamber (PTW 34013) and two synthetic diamond detectors (microDiamond PTW TN60019). In our results, the measurements in water agreed with the MC model calculations within uncertainties. The use of the microDiamond detector yielded better agreement with MC calculations, within estimated uncertainties, compared to the ionization chamber at points of steeper dose gradients. The radial dose function showed a steep fall-off close to the INTRABEAM source ([Formula: see text]10 mm) with a gradient higher than that of commonly used brachytherapy radionuclides (Ir, I and Pd), with values of 2.510, 1.645 and 1.232 at 4, 6 and 8 mm, respectively. The radial dose function partially flattens at larger distances with a fall-off comparable to that of the Xoft Axxent® (iCAD, Inc., Nashua, NH) eBT system. The simulated 2D polar anisotropy close to the bare probe walls showed deviations from unity of up to 55% at 10 mm and 155°. This work presents the MC calculated TG-43 parameters for the INTRABEAM, which constitute the necessary data for the characterization of the source as required by a TPS used in clinical dose calculations.

摘要

INTRABEAM 系统（德国卡尔蔡司 Meditec 公司）是一种专为术中放射治疗应用而设计的电子近距离放射治疗（eBT）设备。迄今为止，INTRABEAM X 射线源尚未根据 AAPM TG-43 规范对近距离放射治疗源进行特征描述。这限制了其在商业治疗计划系统（TPS）中的建模，因此，风险器官的剂量是未知的。这项工作的目的是根据 TG-43 近距离放射治疗剂量学协议对 INTRABEAM 源进行特征描述。通过蒙特卡罗（MC）计算确定了源周围水中的剂量分布。为了验证 MC 模型，沿源纵轴的深度剂量计算与使用软 X 射线电离室（PTW 34013）和两个合成金刚石探测器（microDiamond PTW TN60019）进行的测量进行了比较。在我们的结果中，水测量结果与 MC 模型计算结果在不确定度范围内一致。与电离室相比，在剂量梯度较陡的位置，microDiamond 探测器的使用与 MC 计算结果具有更好的一致性，在估计的不确定度范围内。径向剂量函数在靠近 INTRABEAM 源（[公式：见文本]10 毫米）处急剧下降，梯度高于常用的近距离放射治疗放射性核素（Ir、I 和 Pd），在 4、6 和 8 毫米处分别为 2.510、1.645 和 1.232。在较大距离处，径向剂量函数部分变平，下降幅度与 Xoft Axxent®（iCAD，Inc.，Nashua，NH）eBT 系统相当。在靠近裸探头壁的地方模拟的二维极向各向异性在 10 毫米和 155°处偏离 unity 高达 55%。这项工作展示了 INTRABEAM 的 MC 计算的 TG-43 参数，这些参数构成了 TPS 进行临床剂量计算所需的源特征描述的必要数据。