Micronucleus frequencies and clonogenic cell survival in TK6 cells exposed to changing dose rates under controlled temperature conditions

Purpose: In most exposure scenarios the dose rate of exposure is not constant. Despite this, very little information exists on the possible biological effects of exposing cells to radiation under the conditions of a changing dose rate. The current study highlights interesting effects following exposure under these conditions. Materials and methods: We constructed a new exposure facility that allows exposing cells inside an incubator and used it to irradiate human lymphoblastoid TK6 cells both after a moderate (0.48 Gy) and a high (1.1 Gy) dose, where the change in dose rate was, respectively, ≈ 17-fold (2.2-37 mGy/min) and ≈ 39-fold (2.7-106 mGy/min). Clonogenic survival and micronuclei (MN) induction were the chosen endpoints. Results: The obtained results confirm the outcome of our first study that TK6 cells exposed to a decreasing dose rate express more MN than cells exposed to an increasing or constant dose rate. The effect was not seen after the moderate dose of 0.48 Gy or detectable at the level of clonogenic cell survival. Conclusions: We speculate that the high level of MN is probably related to a delayed elimination of damaged cells by interphase death, as opposed to mechanisms relating to DNA damage and repair.