State Key Laboratory of Radiation Medicine and Protection, Suzhou 215123, People's Republic of China.
School of Radiation Medicine and Protection, Soochow University, Suzhou 215123, People's Republic of China.
Phys Med Biol. 2023 Aug 14;68(17). doi: 10.1088/1361-6560/acec2b.
In clinical proton therapy, the spread-out Bragg peak (SOBP) is commonly used to fit the target shape. Dose depositions at microscopic sites vary, even with a consistent absorbed dose (D) in SOBP. In the present study, monolayer mesh-type cell population models were developed for microdosimetric assessment at different SOBP depths.Normal human bronchial epithelial (BEAS-2B) and hepatocytes (L-O2) mesh-type cell models were constructed based on fluorescence tomography images of normal human cells. Particle transport simulation in cell populations was performed coupled with Monte Carlo software PHITS. The relationship between microdosimetry and macrodosimetry of SOBP at different depths was described by analyzing the microdosimetric indicators such as specific energyz,specific energy distributionfz,D,and relative standard deviationσz/z¯within cells. Additionally, the microdosimetric distributions characteristics and their contributing factors were also discussed.The microscopic dose distribution is strongly influenced by cellular size, shape, and material. The mean specific energyz¯of nucleus and cytoplasm in the cell population is greater than the overall absorbed dose of the cell population model (Dp), with a maximumz¯/Dpof 1.1. The cellular dose distribution is different between the BEAS-2B mesh-type model and its concentric ellipsoid geometry-type model, which difference inz¯is about 10.3% for the nucleus and about 7.5% for the cytoplasm with the SOBP depth of 15 cm. WhenD= 2 Gy, the maximumzof L-O2 nucleus reaches 2.8 Gy andσz/z¯is 5.1% at the mid-depth SOBP (16-18 cm); while the maximumzof the BEAS-2B nucleus reaches 2.2 Gy with only 2.7% ofσz/z¯.The significant variation of microdosimetric distributions of SOBP different depths indicates the necessity to use mesh-type cell population models, which have the potential to be compared with biological results and build the bio-physical model.
在临床质子治疗中，扩展布拉格峰（SOBP）常用于拟合靶区形状。即使在 SOBP 中具有一致的吸收剂量（D），微观位置的剂量沉积也会有所不同。本研究开发了用于不同 SOBP 深度的微剂量评估的单层网格型细胞群体模型。基于正常人体细胞的荧光断层成像图像，构建了正常人类支气管上皮（BEAS-2B）和肝细胞（L-O2）的网格型细胞模型。使用 PHITS 蒙特卡罗软件进行细胞群体中的粒子输运模拟。通过分析细胞内的微剂量指标，如比释动能z、比释动能分布fz、D 和相对标准偏差σz/¯z，描述了不同深度 SOBP 的宏观剂量和微观剂量的关系。此外，还讨论了微剂量分布特征及其影响因素。微观剂量分布受细胞大小、形状和材料的强烈影响。细胞群体中核和细胞质的平均比释动能z¯大于细胞群体模型的总吸收剂量（Dp），最大z¯/Dp为 1.1。BEAS-2B 网格型模型与其同心椭球几何型模型的细胞剂量分布不同，当 SOBP 深度为 15cm 时，核的 z¯差异约为 10.3%，细胞质的 z¯差异约为 7.5%。当 D=2Gy 时，L-O2 核的最大 z 达到 2.8Gy，σz/¯z 为 5.1%，位于中深度 SOBP（16-18cm）；而 BEAS-2B 核的最大 z 达到 2.2Gy，仅为 2.7%的σz/¯z。SOBP 不同深度的微剂量分布的显著变化表明需要使用网格型细胞群体模型，这有可能与生物学结果进行比较，并构建生物物理模型。
