Raaphorst G P, Ng C E, Smith D, Niedbala M
Medical Physics Department, Ottawa Regional Cancer Centre, Ottawa, Ontario, Canada.
Int J Radiat Oncol Biol Phys. 2000 Nov 1;48(4):1139-44. doi: 10.1016/s0360-3016(00)00727-6.
Pulsed-dose-rate (PDR) brachytherapy as a substitute for continuous low-dose-rate (LDR) brachytherapy has a number of clinical advantages. However, early results show that some cells can exhibit an adaptive response to radiation and in PDR where many pulses are given such an adaptive response may play an important role in the outcome.
Nine human cell lines (two normal fibroblast and seven tumor) were evaluated for an adaptive response. Cells were given either a single adapting dose before a challenge dose or given PDR sequences for which the average dose rate matched the LDR dose rate. Response was assessed using the colony survival assay.
Five of the nine cell lines showed an adapting response to single small doses of radiation. Three of these cell lines were further investigated for adapting response to PDR and two of the three lines (one ovarian carcinoma and one glioma) showed an adaptive response which was dependent on pulse size and interval.
The data show that an adaptive response can occur in human cells and that it can vary among cell lines. In addition, PDR sequences also produced an adaptive response which could have an affect on PDR therapy if such a response is found in tissues.
脉冲剂量率（PDR）近距离放射治疗作为连续低剂量率（LDR）近距离放射治疗的替代方法具有许多临床优势。然而，早期结果表明，一些细胞对辐射可表现出适应性反应，在给予多次脉冲的PDR治疗中，这种适应性反应可能在治疗结果中起重要作用。
评估了九种人类细胞系（两种正常成纤维细胞系和七种肿瘤细胞系）的适应性反应。细胞在给予挑战剂量之前先给予单次适应性剂量，或给予平均剂量率与LDR剂量率匹配的PDR序列。使用集落存活试验评估反应。
九种细胞系中有五种对单次小剂量辐射表现出适应性反应。对其中三种细胞系进一步研究其对PDR的适应性反应，这三种细胞系中的两种（一种卵巢癌细胞系和一种神经胶质瘤细胞系）表现出依赖于脉冲大小和间隔的适应性反应。
数据表明人类细胞中可发生适应性反应，且不同细胞系之间存在差异。此外，如果在组织中发现这种反应，PDR序列也会产生适应性反应，这可能会影响PDR治疗。
