低剂量率下高线性能量转移碳离子束辐照人类唾液腺细胞的存活效应

The Clonogenic Surviving Effect of Human Salivary Gland Cells Exposed to High-linear Energy Transfer Carbon Ion Beams at Low Dose Rate

利用日本千叶重离子医用加速器HIMAC提供的碳离子束,对人类唾液腺细胞(HSG)在剂量率为0.5Gy/h的低剂量率条件下进行了辐照,运用标准的克隆形成法得到了3种不同剂量平均线性能量转移(LET)碳离子束辐照HSG细胞的剂量存活效应.与先前HSG细胞在治癌剂量率(1￣5Gy/min)下对相近剂量平均LET碳离子束辐照的剂量存活效应数据相比,HSG细胞对高LET碳离子束辐射表现出明显的剂量率效应.为在相同条件下得到碳离子束对HSG细胞的相对生物学效应(RBE),利用60Co-#射线在剂量率为0.5Gy/h的条件下辐照了HSG细胞,得到该细胞系对低LET射线响应的剂量存活效应.与先前在治癌剂量率下得到的RBE值相比,低剂量率条件下得到的RBE值总体减小.由实验发现的剂量率效应及低剂量率条件下RBE值的减小,表明由高LET碳离子束造成的辐射损伤在低剂量率条件下也存在着显著的修复效应.据此,对辐射造成细胞致死的原因进行了探讨.

Human salivary gland cells （HSG） were irradiated with carbon ion beams supplied by the Heavy Ion Medical Accelerator in Chiba （HIMAC）, Japan at a low dose rate of 0.5 Gy/h. Clonogenic survival effects of HSG cells after exposure to carbon beams with three different dose-averaged LETs were obtained by means of standard colony-forming assay. Compared to the previous surviving data acquired for carbon beams with similar dose-averaged LETs at therapeutic dose rates （1-5 Gy/min）, HSG cells show an obvious dose-rate sparing effect. To derive relative biological effectiveness （RBE） of the carbon beams for HSG cells under the same dose-rate condition, the dose surviving effect of HSG cells irradiated with ^60Co γ-rays was measured as well at the dose rate of 0.5 Gy/h. The RBE values obtained at the low dose rate are totally reduced in contrast with those determined at the preceding therapeutic dose rates. The dose-rate sparing effect and the reduction in RBE at the low dose rate imply that the radiation-induced damage by high-LET carbon ion beams at low dose rates could be repaired to a great extent. Based on the important findings, the essential reason of cell lethality by radiation was discussed.