鼻咽鳞癌CNE1、CNE2细胞系IMRT模式离体照射生物效应研究

In Vitro Study of the Radiobiological Effects of Nasopharyngeal Carcinoma Cell Lines CNE1 and CNE2 in IMRT Model

目的观察适形调强放射治疗(IMRT)模式单次剂量输出时间延长对鼻咽鳞癌CNE1、CNE2细胞放射生物效应的影响,以便为临床制定个体化IMRT计划提供一些理论依据。方法分别急速照射指数生长期的CNE1细胞、CNE2细胞9个剂量点,采用克隆分析法计算细胞存活分数,运用单靶多击和线性二次方程数学(LQ)模型拟合曲线,求出2种细胞放射生物学参数。将指数生长期的CNE-1细胞、CNE-2细胞分成3个组:①EBRT组;②IMRT模式15min照射组;③IMRT模式30min照射组(单次剂量输出时间延长至15min和30min)。每组照射总剂量为6Gy,1次/天,2Gy/次,连续照射3天,采用克隆分析法计算细胞的存活分数。结果急速照射1次后的各点细胞存活率以单靶多击模型拟合曲线,得出CNE1细胞D0值为0.88Gy,Dq值为0.47Gy,N值为3.5,CNE2细胞D0值0.60Gy,Dq值为0.36Gy,N值为4.0;以LQ模型拟合曲线,得出CNE1细胞α值为0.16Gy-1,β值为0.089Gy-2,α/β值为1.8Gy,CNE2细胞α值为0.97Gy-1,β值为0.086Gy-2,α/β值为11.3Gy。CNE1细胞EBRT组细胞存活率为7.21%,IMRT模式15min照射组为8.85%,IMRT模式30min照射组为9.92%,IMRT模式组随着单次剂量时间延长到15min和30min,细胞存活率较EBRT组明显增加,t检验有显著差异(P<0.05)。CNE2细胞EBRT组为0.190%,IMRT模式15min照射组为0.204%,IMRT模式30min照射组细胞存活率为0.207%,t检验无显著差异(P>0.05)。结论鼻咽高分化鳞癌CNE1细胞具有较低的α/β值及较大的D0、Dq值,相对于鼻咽低分化鳞癌CNE2细胞具有较强的亚致死性修复(SLDR)能力。SLDR能力在单次剂量延长的放疗中对细胞存活起重要作用。IMRT模式单次剂量输出时间延长将使CNE1细胞存活率增加明显,而CNE2细胞增加不明显。

Objective To investigate the impact of prolonged fraction delivery time by modeling intensity modulated radiation therapy （IMRT） on radiobiological effects of human nasopharyngeal carcinoma cell lines CNE1 and CNE2 ,to provide radiobiological basis for individual IMRT optimization for this disease. Methods Cell lines CNE1 and CNE2 prepared with exponential growth phase were irradiated acutely at 9 dose levels. The cell survival was calculated by classical colony forming assay, then was fitted by using standard linear-quadratic （LQ） model and single hit multi target model to get the values of radiobiological parameters. Each of the two cell lines was then irradiated on three models ：①EBRT model （ the ceils were irradiated continuly by 6 MV X-ray） ;②15 min IMRT model;③30min IMRT model. （the same dose as the EBRT in 15 minutes and 30 minutes with a pulse manner）. The total doses of each group were 6 Gy with a fraction dose of 2 Gy in 3days. The cell survival of three models was calculated by classical colony forming assay. Results The values of Dq,D0 and N of CNE1 were 1.54 Gy ,0.82Gy ,. 5 and the values of CNE2 were 0.60 Gy,0.36 Gy,4.0 respectively by using single hit multi target model. The values of α,β,α/β of CNE1 were 0.16 Gy^-1 ,0. 089 Gy^-2, 1.8Gy and the values of α,β α/β of CNE2 were 0.97 Gy^-1 ,0.086 Gy^-2, 11.3 Gy, respectively by using standard LQ model. The CNE1 cell survival percentage in EBRT model, 15min IMRT model and 30min IMRT model was 7.21,8.85,9.92 respectively. The survival percentage of CNE1 irradiated by modeling IMRT with the fraction delivery time prolonged to 15 min and 30 min was significantly higher than that of conventional EBRT with paired t-test（ P 〈0.05 ）. The CNE2 cell survival percentage by EBRT model, 15 min IMRT model and 30min IMRT model was 0. 190,0.204,0.207 respectively, and had no significant differences between different models （ P 〉 0.05 ）. Conclusion Well differentiated nasopharyngeal SqCa cell CNE1 with a lower α/β and higher DO ,Dq has a relatively large capacity for sub-lethal damage repair（ SLDR ） than poorly differentiated nasopharyngeal SqCa cell CNE 2 . The capability of SLDR was the predominant factor determining the cell kill - ing decrease , the prolonged fraction delivery time modeling IMRT significantly increased the cell survival in CNE1 but not in CNE2.