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

以单细胞、球体和小鼠肿瘤为研究对象，考察了线性二次元（LQ）形式评价单次高剂量和低分次辐射剂量生物等效性的可靠性。采用2-26Gy单次剂量和4-12Gy 2-5次剂量。从细胞存活曲线中得到α/β比值，并结合LQ公式，计算出减少剂量的等效单次剂量。然后将它们与实际确定的低分割剂量的等效单剂量进行比较。在所有实验中，根据LQ公式计算的低分割剂量的等效单次剂量比实际测量的生物等效单次剂量低10-40%。使用LQ形式将低分割辐射剂量转换为单剂量低估了低分割辐射的影响。在直接比较2- 5组分方案时，当绘制细胞存活与实际辐射剂量时，各自的剂量-反应曲线几乎重叠。然而，当使用α/β比计算体外EMT6细胞的生物有效剂量（BED）来绘制细胞存活率时，随着分数的增加，曲线倾向于向下移动。因此，BED是不合适的。采用多靶点模型，在高剂量下相容性得到改善，但剂量转换仍不完善。其他的生物模型正在研究中。

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.