Abe Y, Urano M, Kenton L A, Kahn J, Willet C G
Edwin L. Steele Laboratory, Department of Radiation Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114.
Int J Radiat Oncol Biol Phys. 1991 Nov;21(6):1529-34. doi: 10.1016/0360-3016(91)90329-3.
Radiation response of a spontaneous mouse fibrosarcoma, FSa-II, to various fractionated doses was studied in vivo together with single dose cell survival curves. Early generation isotransplants were used. Animals were C3Hf/Sed mice derived from our defined flora mouse colony. Lung colony and TD50 assays were used to determine cell survival. Surviving fractions were determined following fractionated irradiations of 1.0 to 5.0 Gy each per fraction with interfractional time intervals of 4 hr. The alpha/beta ratio based on fractionated irradiations was 8.8 Gy for aerobic FSa-II tumor cells and flexure dose was less than 1.3 Gy. Multiple fractions of 5.0 Gy each given with 4, 12, and 24 hr intervals showed an increase in survival with increasing interfractional time interval, suggesting a rapid repopulation of tumor cells between fractions; namely, cell doubling time was shortened between fractions after the first 5.0 Gy doses. These results indicated that tumor cell repopulation is a critical factor in the fractionated radiotherapy. Linear-quadratic model was fitted to single dose survival data. Single dose survival curve of aerobic FSa-II tumor cells following lung colony assays which allowed determination of minimal survival of approximately 3.0 x 10(-3) showed that alpha, beta, and alpha/beta ratios were 0.25 Gy-1, 0.048 Gy-2, and 8.47 Gy, respectively. Single dose survival curve of the same aerobic cells determined by both lung colony and TD50 assays to a survival level of approximately 3.0 x 10(-6) demonstrated that alpha, beta, and alpha/beta ratios were 0.375, 0.0127, and 29.5, respectively. Similar determination for hypoxic FSa-II tumor cells showed that alpha, beta values were smaller whereas the alpha/beta ratio was much larger than for aerobic cells. The oxygen enhancement ratio calculated by the alpha/beta ratios was greater than 3.0.
在体内研究了自发小鼠纤维肉瘤FSa-II对不同分割剂量的辐射反应，并绘制了单剂量细胞存活曲线。使用早期传代的同基因移植瘤。动物为源自我们特定菌群小鼠群落的C3Hf/Sed小鼠。采用肺集落和TD50测定法来确定细胞存活情况。在每次分割剂量为1.0至5.0 Gy、分割间期为4小时的分次照射后，测定存活分数。基于分次照射的α/β比值，需氧的FSa-II肿瘤细胞为8.8 Gy，挠曲剂量小于1.3 Gy。每次给予5.0 Gy的多个分割剂量，间隔时间分别为4、12和24小时，结果显示随着分割间期的增加，存活率上升，这表明在分割之间肿瘤细胞迅速再增殖；也就是说，在首次给予5.0 Gy剂量后，分割之间的细胞倍增时间缩短。这些结果表明，肿瘤细胞再增殖是分次放射治疗中的一个关键因素。将线性二次模型拟合至单剂量存活数据。通过肺集落测定法得到的需氧FSa-II肿瘤细胞单剂量存活曲线显示，其最小存活数约为3.0×10⁻³，α、β和α/β比值分别为0.25 Gy⁻¹、0.048 Gy⁻²和8.47 Gy。通过肺集落和TD50测定法将相同需氧细胞的单剂量存活曲线测定至存活水平约为3.0×10⁻⁶，结果显示α、β和α/β比值分别为0.375、0.0127和29.5。对缺氧的FSa-II肿瘤细胞进行类似测定显示，α、β值较小，而α/β比值比需氧细胞大得多。通过α/β比值计算得到的氧增强比大于3.0。
