Reduction in life span of normal human fibroblasts exposed to very low-dose-rate charged particles

We studied the effect of in vitro life span in normal human fibroblasts exposed to chronic low-dose radiation in heavy-ion radiation field. Cells were cultured in the CO2 incubator, which was set in the irradiation room for biological study of heavy ions in the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences (NIRS), and exposed to scattered radiations produced with heavy-ion beams throughout the life span of the cell population. Absorbed dose, which was measured using a thermoluminescence dosimeter (TLD) and a Si-semiconductor detector, was to be 1.4 mGy per day when operating the HIMAC machine for biological experiments. The total population doubling number of the exposed cells reduced to 79-93% of non-exposed control cells. On the other hand, the life span of low-dose 137Cs gamma-ray exposed cell population (~1 mGy / day), which was cultured in the CO2 incubator set in the gamma-ray irradiation room in NIRS, prolonged to 104-106% of non-exposed control. There is evidence that the exposure of chronic low-dose radiation in heavy-ion radiation field promotes the life-span reduction in cellular level