摘要
目的 研究细胞在不同半修复时间 (T1/ 2 )和照射间隔时间条件下 ,由于亚致死性损伤(SLD)修复所需在线性二次模型 (LQ模型 )中引入的修正因子 (MF)的变化趋势。方法 根据LQ模型 ,应用Thames的不完全修复模型 (IR模型 )和Brenner的G因子模型在不同T1/ 2 和不同照射间隔下 ,计算两次高剂量率外照射和单次低剂量率近距离治疗时的MF。并分析两种模型计算结果的差别及根据G因子模型分析引入MF后二次项的变化特点。结果 当T1/ 2 在 0 .5～ 1.0h范围内时 ,因SLD修复引入的MF变化不大 ;对于这一范围的T1/ 2 ,当照射间隔时间 >6h时 ,SLD基本完全修复。IR模型和G因子模型计算低剂量率连续照射的MF结果完全一致 ,但对高剂量率分次照射的计算结果在短T1/ 2 时结果相差较大。在相同剂量和照射间隔时间条件下MF和剂量平方的乘积与照射次数呈线性关系。结论 因SLD修复引入的MF与T1/ 2 、照射间隔时间的关系较为复杂。在T1/ 2 较短的情况下IR模型不能用于高剂量率分次照射。根据G因子的计算结果提示当T1/ 2 很短时 ,应考虑照射时间内发生的修复。对于短T1/ 2
Objective The present work is designed to quantify the relationship between the sublethal damage (SLD) repair modify factor and the half repair time (T 1/2 ) as well as fraction interval.Methods Using the linear quadratic model (LQ model), the magnitude of the modify factor (MF) of the dose square term due to sublethal damage repair was calculated for varying T 1/2 between 0.01 and 6h, both for external beam radiotherapy (EBRT) and low dose rate continuous brachytherapy. The results of G factor and incomplete repair model (IR model) were compared. Also calculation was performed for two 2?Gy fractionation with interval ranging from 0.1 to 24.0 hour for some T 1/2 respectively. The trend of the product of the MF and the square of dose was analyzed for EBRT schedule consisted of same fraction dose and same intervals.Results The MF changed with T 1/2 and fraction interval. For fraction interval longer than 6 hour and T 1/2 between 0.5～1.0 hour, the change of the MF is small. The results that calculated from the G factor and IR model have significant difference for very short T 1/2 in EBRT. When plot to the number of fractions, the product of the MF and the square of dose is a straight line, which slop changing with T 1/2 and fraction interval.Conclusions The effectiveness of SLD repair was changed with T 1/2 and fraction interval. The very short T 1/2 may have importance on the biological effectiveness of radiation to tissue and tumor. The original h() function of IR model cannot reflect the influence of very short T 1/2 .
出处
《中华放射肿瘤学杂志》
CSCD
北大核心
2000年第1期53-57,共5页
Chinese Journal of Radiation Oncology
