Chen C Z, Huang Y, Hall E J, Brenner D J
Center for Radiological Research, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Int J Radiat Oncol Biol Phys. 1997 Jan 1;37(1):137-43. doi: 10.1016/s0360-3016(96)00461-0.
Pulsed dose rate (PDR) brachytherapy as a substitute for continuous low dose rate (CLDR) has the potential to be a useful option in brachytherapy. However, the frequency and duration of pulses that will produce results practically equivalent to CLDR is still an open and important question. This study was designed to compare the survival of human tumor cells, cultured in vitro, and exposed to continuous or pulsed irradiation where the pulse frequency was varied.
Three different human carcinoma cells, derived from cervical and breast cancers, were exposed to CLDR gamma rays, or to pulsed irradiations with the same overall dose rate. Pulsed regimens used were 3.8 min every hour, 7.6 min every 2 h, 11.4 min every 3 h, 15.2 min every 4 h, 22.8 min every 6 h, and 45.6 min every 12 h. For each comparison between CLDR and PDR, the overall dose and the overall time were the same. Experimental design was such that significant differences in biological effectiveness, if present, would be detected.
For the cell lines investigated, hourly pulses resulted in cell survival indistinguishable from CLDR. However, as the pulse interval was increased, cell survival progressively decreased compared with CLDR, and the pulsed regimes were no longer equivalent to continuous low dose rate.
This study provides some evidence to support the suggestion that a 10-min pulse, repeated every 1 to 2 h, would be functionally equivalent to a continuous low dose rate irradiation, at least in terms of early responding endpoints. Longer intervals between pulses might result in loss of equivalence in some cases.
脉冲剂量率（PDR）近距离放射治疗作为连续低剂量率（CLDR）的替代方法，有可能成为近距离放射治疗中一种有用的选择。然而，产生与CLDR实际等效结果的脉冲频率和持续时间仍是一个尚未解决的重要问题。本研究旨在比较体外培养的人类肿瘤细胞在连续或脉冲照射（脉冲频率不同）下的存活率。
三种源自宫颈癌和乳腺癌的不同人类癌细胞系，分别接受CLDR伽马射线照射，或相同总剂量率的脉冲照射。所采用的脉冲方案为每小时3.8分钟、每2小时7.6分钟、每3小时11.4分钟、每4小时15.2分钟、每6小时22.8分钟以及每12小时45.6分钟。在CLDR和PDR的每次比较中，总剂量和总时间均相同。实验设计确保若存在生物学效应的显著差异，能够被检测到。
对于所研究的细胞系，每小时的脉冲照射导致的细胞存活率与CLDR难以区分。然而，随着脉冲间隔增加，与CLDR相比细胞存活率逐渐降低，且脉冲方案不再等同于连续低剂量率。
本研究提供了一些证据支持以下建议，即至少就早期反应终点而言，每1至2小时重复一次的10分钟脉冲在功能上等同于连续低剂量率照射。在某些情况下，更长的脉冲间隔可能导致等效性丧失。
