192Ir近距离照射的剂量率效应研究

目的对１９２Ｉｒ高剂量率近距离治疗机在近距离放射治疗中的剂量率效应进行了实验室观察和探讨。方法分别在不同剂量率条件下（平均剂量率为４６．２９Ｇｙ／ｈ或５．７９Ｇｙ／ｈ）进行全腹或全胸１９２Ｉｒ近距离照射。观察指标为存活隐窝细胞数（小肠）和ＬＤ５０值（肺）。结果随平均剂量率的降低和照射时间的延长，早反应组织小肠和晚反应组织肺癌生物效应也会随之下降。不同剂量率照射后小肠的ＥＤ１０剂量之差为２．４６Ｇｙ［（１５．４１－１２．９５）Ｇｙ］，等效剂量降低了１６．０％；肺的ＬＤ５０剂量之差为４．２５Ｇｙ［（１３．２５－９．００）Ｇｙ］，等效剂量降低了３２．１％。结论在进行近距离放射治疗过程中，随剂量率的不同存在着对晚反应组织可能过量或肿瘤剂量不足的潜在生物学问题，该点应予注意。

Dose rate effect of 192Ir high dose rate brachyirradiation

Objective To investigate the dose rate effect of 192Ir high dose rate (HDR) brachyirradiation in mice. Methods Whole abdomen or thorax was irradiated with different dose rates (46.29 Gy/h or 5.79Gy/h). The end points for early response tissue (small intestine) and late response tissue (lung) were number of surviving crypt stem cells and LD50 value. Results The isoeffect dose for early and late response tissues decreased with decay of dose rate. The ED10 difference for intestinal mucosa was 2.46 Gy and LD50 value for lung tissue was 4.25 Gy under different dose rates. The isoeffect dose decreased about 16.0% for intestine and 32.1% for lung, respectively. Conclusions The results show that in HDR afterloading, there is a critical radiobiological potential for overdosing with respect to late complications or underdosing with respect to late complications or underdosing with respect to tumor sterilization under differet dose rate conditions.