Effect of dose-rate on induction of neoplastic transformation in vitro by low doses of 232 MeV protons

Purpose: To determine the effect of dose-rate on induction of neoplastic transformation in vitro by low doses of 232 MeV protons. Materials and methods: The experimental system used was the human hybrid cell assay. The dose-rates examined were 50 cGy/min and 20 cGy/h. The dose-rate 20 cGy/h was chosen as this is in the range of the maximum dose-rate that can be experienced in an unshielded space environment following a solar flare. At low dose-rate (LDR), doses from 0.5–100 cGy were studied. At high dose rate (HDR), the dose range was 0.5–200 cGy. Results: The data indicated no significant differences between the two dose-rates at doses up to 100 cGy. Conclusion: For the endpoint of neoplastic transformation in vitro, high dose-rate data may be sufficient to estimate low dose-rate effects (20 cGy/h) in the dose range up to 100 cGy from 232 MeV protons. The data are of relevance to risk estimation for space travel. (authors)