Establishment of a dose-conversion model for use in high-dose-per-fraction radiotherapy

用单细胞、球体和小鼠肿瘤研究了线性二次(LQ)公式在评估单一高剂量和低分割剂量之间的生物等效性方面的可靠性。单次剂量2~26Gy4~12Gy2~5次。从细胞存活曲线得到α/β比值，并利用该比值和LQ公式计算出各次分割剂量的当量单次剂量。然后将它们与实际确定的相当于低分馏剂量的单次剂量进行比较。在所有实验中，根据LQ公式计算的低分馏剂量的等量单次剂量比实际测量的生物等量单次剂量低10-40%。使用LQ公式将低分馏辐射剂量转换为单剂量，低估了低分馏辐射的影响。在直接比较2到5个部分的时间表时，当细胞存活率与实际辐射剂量作图时，各自的剂量-反应曲线几乎重叠。然而，当细胞存活率与使用α/β比率计算的体外EMT6细胞的生物有效剂量(BED)绘制曲线图时，曲线倾向于通过增加分数向下移动。因此，床是不合适的。使用多靶点模型，在高剂量时，配伍有所改善，但剂量转换仍不理想。其他生物模型目前正在研究中。

The reliability of the linear-quadratic (LQ) formalism in assessing biological equivalence between single high and hypofractionated radiation doses were investigated using single cells, spheroids and murine tumors. Single doses of 2-26Gy and 2-5 fractions of 4-12Gy were used. The α/β ratio was obtained from the cell survival curves, and using it and the LQ formalism, equivalent single doses for the hypofractionated doses were calculated. They were then compared with actually-determined equivalent single doses for the hypofractionated doses. In all experiments, equivalent single doses for hypofractionated doses calculated from the LQ formalism were lower than the actually-measured biologically-equivalent single doses by 10-40%. Conversion of hypofractionated radiation doses to single doses using the LQ formalism underestimated the effect of hypofractionated radiation. In direct comparison of the 2- to 5-fraction schedules, respective dose-response curves almost overlapped when cell survival was plotted against actual radiation doses. However, the curves tended to shift downwards by increasing the fraction number when cell survival was plotted against biologically effective doses (BED) calculated using an α/β ratio for in vitro EMT6 cells. Thus, BED was inappropriate. Using the multi-target model, the compatibility improved at high doses, but still dose conversion was not perfect. Other biological models are now being investigated.