模拟IMRT模式的生物效应研究初探

Preliminary study of radiobiological effects in intensity modulated radiation therapy model

目的模拟临床调强适形放疗的照射模式对人大肠癌细胞系HT-29进行生物效应变化的初步研究.方法采用指数生长期的HT-29细胞制成单细胞悬液,于接种后12 h内进行不同模式和剂量的照射.分成3个照射组:(1)急速照射组(包括0、1、2、3、5、7、10Gy共7个剂量点),剂量点的照射完成时间为0～5 min,剂量率为6 Gy/min;(2)IMRT照射模式组(包括15 min完成照射组及30min完成照射组),剂量率同上,每组所含照射剂量点同急速照射组,其中15min和30min照射组指各剂量点完成照射时间分别是15 min和30min.采用成克隆分析法计算存活分数,运用多靶单击数学模型拟合曲线,求出Do、Dq等参数值.结果急速照射组、15 min照射组和30 min照射组的Dq值分别为1.54、1.74和1.72Gy;Do值分别为0.82、0.89和1.00Gy;SF2分别为0.448、0.548和0.558.结论 IMRT模式下随分次照射时间的延长,相对剂量率降低,从而导致生物效应下降.

Objective To investigate the radiobiological effects of HT-29 cell line irradiated by mimic clinical intensity modulated radiation therapy （IMRT） model. Methods Single cell suspension solution of HT-29 cell line was prepared with exponential growth phase cell, then irradiated by two different models 12 hours after seeding： 1.acute irradiation model： the cells were irradiated at0, 1, 2, 3, 5, 7, 10 Gy dose level by 6 MV X ray, 6 Gy/min, with each dose delivered within 0 to 5 minutes,2. IMRT model; two subgroups in this model, 15 minute group and 30 minute group, with the same dose level and dose rate as acute irradiation model, were delivered to each subgroup within 15 minutes and 30 minutes with a pulse manner. The cell-survival curves were plotted by classical colony forming assay. The values of Dq, Do and SF2 in three groups were calculated according to the“single-hit multi-target model”. Results The values of Dq, Do and SF2 were 1.54 Gy, 0.82 Gy and 0.448 in acute irradiation group, 1.74 Gy, 0.89 Gy and 0.548 in 15 minute irradiation group, 1.72 Gy,1.00 Gy and 0.558 in 30 minute irradiation group, respectively. Conclusions This study shows that prolonged fraction delivery time, as that of IMRT model, would decrease the radiobiological effects.