实验细胞直线加速器照射方法与剂量学探讨

Irradiation method of experimental cell on linear accelerator and dosimetry study

目的:探讨不同深度、不同照射方式及空腔效应在离体细胞照射中的影响,为选择合适的照射方式以减少照射剂量不确定性提供参考。方法:培养皿中分别加入不同深度的培养液,上盖1 cm厚补偿物,下加4 cm固体水,模拟机架0°照射无旁向散射时不同深度的培养液对细胞剂量的影响。获取此摆位情况下的CT图像;培养皿置于一注有等高培养液大培养皿中,同前加入补偿物和固体水,模拟机架0°照射时增加旁向散射对细胞剂量影响,同样获取CT图像。将前一步的补偿物和散射体,改为上加4 cm厚固体水,下放1 cm厚有机玻璃体膜板,获取此摆位情况下的CT图像,模拟机架180°照射时增加旁向散射对细胞剂量影响;去掉外周培养皿,模拟机架180°照射时无旁向散射对细胞剂量影响。基于获取的CT图像做计划,分析剂量分布,剂量分布结果均以相对剂量(%)表述。结果:2.5、5.0、7.2 mm深度处培养皿底壁的剂量最大偏差分别为5.5%、4.2%、6.5%。机架为0°照射无旁向散射,剂量最大偏差为14.7%,平均剂量为96.6%;增加旁向散射后剂量最大偏差4.9%,平均剂量97.1%。机架为180°照射无旁向散射,剂量最大偏差为10.5%,平均剂量为98.6%;增加旁向散射后最大剂量偏差3.1%,平均剂量99.1%。结论:180°机架照射比0°照射受照细胞剂量偏差更小且均匀性更好。增加旁向散射可以明显改善外侧培养液和培养皿壁部的剂量分布。

Objective To explore the effect of culture medium of different depths, irradiation methods and cavity effect on the irradiation of experimental cell, and to minimize the uncertainty of exposure dose by providing reference for choosing the optimal irradiation method. Methods The culture medium of different depths was added into different culture dishes, with 1 cm of compensation on the cover and 4 cm of solid water on the bottom, and then, the irradiation at a gantry angle of 0° without side scattering was carried out for investigating the effect of the culture medium of different depths on the cell irradiation and obtaining the CT image. After the culture dish was placed into a larger culture dish with the same depth of culture medium to simulate the side scattering and the compensation and solid water were added as in previous treatment, the effect of the irradiation at a gantry angle of 0° with side scattering on cell irradiation was discussed and the CT image was obtained. The effect of the irradiation at a gantry angle of 180° with side scattering on cell irradiation was analyzed and CT image was obtained by replacing the previous compensation and solid water with 4 cm of solid water on the cover and 1 cm of organic vitreous membrane on the bottom. After removing the peripheral culture medium, we analyzed the effect of the irradiation a gantry angle of 180° without side scattering on cell irradiation. Based on those obtained CT images, treatment plans were designed and the dose distributions which were expressed in relative doses（%） were compared. Results The maximum dose deviation was 5.5%, 4.2%, and 6.5% for 2.5, 5.0,and 7.2 mm of culture medium, respectively. The maximum dose deviation and mean dose were 14.7% and 96.6% for the irradiation at a gantry angle of 0° without side scattering, and 4.9% and 97.1% for that with side scattering. Furthermore, the maximum dose deviation and mean dose were 10.5% and 98.6% for the irradiation at a gantry angle of 180° without side scattering, and 3.1% and 99.1% for that with side scattering. Conclusion For experimental cell irradiation, irradiation at a gantry angle of 180° has a smaller dose deviation and a better homogeneity than the irradiation a gantry angle of 0°, and adding side scattering can dramatically improve the dose distribution of lateral culture medium and adherent culture.