Afzal S M, Tenforde T S, Kavanau K S, Curtis S B
Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Radiat Res. 1991 Aug;127(2):230-3.
Measurements were made of clonogenic cell survival in rat rhabdomyosarcoma tumors as a function of time following in situ irradiation with single or fractionated doses of 225-kVp X rays or with 557-MeV/u neon ions in the distal position of a 4-cm extended-peak ionization region. Single doses of 20 Gy of X rays or 7 Gy of peak neon ions reduced the initial surviving fraction to approximately 0.025 for each modality. Daily fractionated doses (four fractions in 3 days) of either peak neon ions (1.75 Gy per fraction) or X rays (6 Gy per fraction) achieved a cell survival of approximately 0.02-0.03 after the fourth dose of radiation. In the single-dose experiments, significant 5- and 10-fold decreases in the fraction of clonogenic cells were observed between the third and fourth days after irradiation with peak neon ions and X rays, respectively. After the sixth day postirradiation, the residual clonogenic cells exhibited a rapid burst of proliferation leading to doubling times for the surviving cell fractions of approximately 1.5 days. Radiation-induced growth delay was consistent with the cellular repopulation dynamics. In the fractionated-dose experiments with both radiation modalities, a large delayed decrease in cell survival was observed at 1-3 days after completion of the fractionated-dose schedule. Cellular repopulation was consistent with postirradiation tumor volume regression and regrowth for both radiation modalities. The extent of decrease in survival following the four-fraction radiation schedule was approximately two times greater in X-irradiated than in neon-ion-irradiated tumors that produced the same survival level immediately after the fourth dose. Mechanisms underlying the marked reduction in cell survival 3-4 days postirradiation are discussed, including the possible role of a toxic host cell response against the irradiated tumor cells.
对大鼠横纹肌肉瘤肿瘤中的克隆形成细胞存活率进行了测量，测量结果是在原位照射后随时间变化的函数，照射采用单次或分次剂量的225 kVp X射线，或在4厘米扩展峰电离区域的远端位置采用557 MeV/u的氖离子。单次剂量20 Gy的X射线或7 Gy的峰氖离子，每种照射方式都将初始存活分数降低至约0.025。每日分次剂量（3天内分4次）的峰氖离子（每次1.75 Gy）或X射线（每次6 Gy），在第四次照射后细胞存活率约为0.02 - 0.03。在单剂量实验中，分别在用峰氖离子和X射线照射后的第三天和第四天，观察到克隆形成细胞分数显著下降了5倍和10倍。照射后第六天，残留的克隆形成细胞呈现出快速的增殖爆发，导致存活细胞分数的倍增时间约为1.5天。辐射诱导的生长延迟与细胞再增殖动力学一致。在两种辐射方式的分次剂量实验中，在分次剂量方案完成后的1 - 3天观察到细胞存活率大幅延迟下降。两种辐射方式下，细胞再增殖与照射后肿瘤体积的消退和再生长一致。在产生相同的第四次照射后存活水平的情况下，接受X射线照射的肿瘤在四次分次照射方案后的存活下降程度比接受氖离子照射的肿瘤大约两倍。讨论了照射后3 - 4天细胞存活率显著降低的潜在机制，包括有毒宿主细胞对受照射肿瘤细胞反应的可能作用。
