Cellular response in normal human cells exposed to chronically low-dose radiation in heavy-ion radiation field

We have been studying the biological effects in normal human fibroblasts exposed to chronically low-dose radiation in a heavy-ion radiation field. The cells were cultured in a CO₂ incubator, which was placed in the irradiation room for biological study of the heavy ions in the Heavy Ion Medical Accelerator in Chiba (HIMAC), at the National Institute of Radiological Sciences (NIRS). We measured the absorbed dose, which was determined by a thermoluminescence dosimeter (TLD) and a Si-semiconductor detector, to be 1.4 mGy per day when operating the HIMAC machine. The total population doubling number (tPDN) of the exposed cells reduced to 77-94% of the non-exposed control cells. Furthermore, the shortening of the speed of the telomere length in the exposed cells was much higher than that in the non-exposed cells at the 26th passage, during which period the exposed cells were accumulated at 0.22 Gy. These findings show that the acceleration of senescence in normal human cells occurs by the chronically low-dose irradiation in a heavy-ion radiation field.