一种结合剂量点核（DPK）的扩散-泄漏模型，用于扩散性α粒子发射体放射治疗（DaRT）的剂量测定。

Khan Ahtesham Ullah, Jollota Sean, DeWerd Larry A

Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA.

Med Phys. 2024 May;51(5):3725-3733. doi: 10.1002/mp.16960. Epub 2024 Jan 29.

BACKGROUND

Diffusing alpha-emitters radiation therapy (DaRT) is a novel brachytherapy technique that leverages the diffusive flow of Ra progeny within the tumor volume over the course of the treatment. Cell killing is achieved by the emitted alpha particles that have a short range in tissue and high linear energy transfer. The current proposed absorbed dose calculation method for DaRT is based on a diffusion-leakage (DL) model that neglects absorbed dose from beta particles.

PURPOSE

This work aimed to couple the DL model with dose point kernels (DPKs) to account for dose from beta particles as well as to consider the non-local deposition of energy.

METHODS

The DaRT seed was modeled using COMSOL multiphysics and the DL model was implemented to extract the spatial information of the diffusing daughters. Using Monte-Carlo (MC) methods, DPKs were generated for Pb, Bi, and their progenies since they were considered to be the dominant beta emitters in the Ra radioactive decay chain. A convolution operation was performed between the integrated number densities of the diffusing daughters and DPKs to calculate the total absorbed dose over a 30-day treatment period. Both high-diffusion and low-diffusion cases were considered.

RESULTS

The calculated DPKs showed non-negligible energy deposition over several millimeters from the source location. An absorbed dose >10 Gy was deposited within a 1.8 mm radial distance for the low diffusion case and a 2.2 mm radial distance for the high diffusion case. When the DPK method was compared with the local energy deposition method that solely considered dose from alpha particles, differences above 1 Gy were found within 1.3 and 1.8 mm radial distances from the surface of the source for the low diffusion and high diffusion cases, respectively.

CONCLUSIONS

The proposed method enhances the accuracy of the dose calculation method used for the DaRT technique.

背景

扩散性α粒子发射体放射治疗（DaRT）是一种新型近距离放射治疗技术，在治疗过程中利用镭子代产物在肿瘤体积内的扩散流。细胞杀伤是通过发射的α粒子实现的，这些α粒子在组织中的射程短且线能量转移高。目前针对DaRT提出的吸收剂量计算方法基于扩散-泄漏（DL）模型，该模型忽略了β粒子的吸收剂量。

目的

这项工作旨在将DL模型与剂量点核（DPK）相结合，以考虑β粒子的剂量以及能量的非局部沉积。

方法

使用COMSOL多物理场对DaRT种子进行建模，并实施DL模型以提取扩散子代产物的空间信息。由于铅、铋及其子代产物被认为是镭放射性衰变链中的主要β发射体，因此使用蒙特卡罗（MC）方法为它们生成DPK。在扩散子代产物的积分数密度与DPK之间进行卷积运算，以计算30天治疗期内的总吸收剂量。同时考虑了高扩散和低扩散情况。

结果

计算得到的DPK显示，在距源位置数毫米范围内，能量沉积不可忽略。对于低扩散情况，在径向距离1.8毫米内沉积的吸收剂量>10 Gy；对于高扩散情况，在径向距离2.2毫米内沉积的吸收剂量>10 Gy。当将DPK方法与仅考虑α粒子剂量的局部能量沉积方法进行比较时，对于低扩散和高扩散情况，分别在距源表面径向距离1.3毫米和1.8毫米内发现了超过1 Gy的差异。