基于蒙特卡罗模拟的^(9)C重离子衰变产物对细胞损伤的分析

Monte Carlo simulation⁃based analysis of cell damage by^(9)C⁃ion decay products

目的探究^(9)C重离子治疗中因自身衰变产生的缓发粒子对细胞产生的辐射损伤和在单个V79中国仓鼠肺细胞模型上的微观剂量以及引起的生物学效应。方法采用蒙特卡罗程序模拟多种能量(3~10 MeV)α粒子在细胞(细胞半径R_(C)=10μm,细胞核半径R_(N)=5μm)中的输运后细胞核内吸收剂量结果,并与医学内照射剂量(MIRD)方法S值(S_(N←N),S_(N←Cy),S_(N←CS))进行比较,证明该方法的可行性,最后使用蒙特卡罗方法模拟计算^(9)C重离子分别在V79细胞模型表面、细胞质内以及细胞核3种位置处衰变生成的缓发粒子(α粒子和质子)在靶中输运能量沉积情况及细胞生存率。结果蒙特卡罗模拟结果与MIRD方法S值进行比较,靶源组合从细胞核到细胞核S_(N←N)值的差异为1.91%~4.95%,细胞质到细胞核S_(N←Cy)为1.48%~5.11%,细胞表面到细胞核S_(N←CS)差异为-1.99%~0.80%,证明蒙特卡罗计算值与MIRD方法S值吻合较好(差异值均<6%)。当一个^(9)C离子在V79细胞模型表面衰变产生次级粒子进入细胞,细胞核内平均吸收剂量为10^(-2) Gy数量级,计算细胞生存率约为88%;衰变在细胞质中进行,计算细胞生存率约为80%;当碳离子直接进入细胞核中衰变,α粒子射程短并将大部分能量沉积在细胞中(细胞核内平均剂量0.1 Gy数量级),造成细胞损伤较大,细胞存活的概率约为53%。结论^(9)C离子自身衰变发射次级带电粒子,其中α粒子进入细胞核时对细胞造成的损伤较大,生物学效应明显。

Objective To explore the radiological damage to cells induced by the delayed particles of^(9)C⁃ions for heavy ion therapy,as well as the microdosimetric distribution and biological effects of these particles on a single model of V7^(9)Chinese hamster lung cells.Methods The Monte Carlo program was employed to simulate the endonuclear absorbed doses ofαparticles with various energies(3-10 MeV)transported in cells(cell radius R_(C)=10μm,nucleus radius R_(N)=5μm).Then,the result were compared with the S values(S_(N←N),S_(N←Cy),and S_(N←CS))derived using the medical internal radiation dose(MIRD)method to demonstrate the feasibility of Monte Carlo simulations.Finally,the energy deposition of the delayed particles of^(9)C⁃ions generated at three sites(i.e.,on the surface and in the cytoplasm and nucleus of the V79 cell model)during their transport in targets was simulated,and the result ing cell surviving fraction was analyzed.Results Monte Carlo and MIRD method yielded differences in S values of 1.91%-4.95%for S_(N←N)(nucleus to nucleus),1.48%-5.11%for S_(N←Cy)(cytoplasm to nucleus),and-1.99%to 0.80%for S_(N←CS)(surface to nucleus),indicating highly consistent S values derived using both method(differences<6%).When a^(9)C⁃ion decayed on the surface of the V79 cell model and the produced secondary particles entered the cell,the average endonuclear absorbed dose was 10^(-2) Gy orders of magnitude,with a cell surviving fraction of about 88%.In the case where decay occurred in the cytoplasm,the cell surviving fraction was about 80%.However,when the^(9)C ion decayed in the nucleus,αparticles had short ranges and deposited most of their energy in the cell(mean endonuclear absorbed dose:0.1 Gy).In this case,severe cell damage was induced,with the cell surviving fraction reducing to about 53%.Conclusions^(9)C⁃ions emit secondary charged particles due to decay,among whichαparticles cause great damage to cells when entering the nucleus and trigger evident biological effects.