RADIOISOTOPES

High LET radiation is highly expected to control hypoxic fraction in tumor tissue that shows radiation resistance to low LET radiation, because oxygen effect decreases with increasing LET. Due to the availability of various ions and LETs, HIMAC has produced many outcomes from basic to clinical studies. In the basic studies, the mechanism of decreasing oxygen effect with increasing LET was experimentally examined based on the previously proposed “oxygen in the track” model. In addition, in vitro cellular and in vivo transplanted tumor studies demonstrated the LET dependent feature of DNA damage produced under hypoxic condition. For the effort to connect basic studies to clinical trials, measurement of LET dependence of OER (Oxygen Enhancement Ratio) was extended to various oxygen concentrations to mimic oxygen environment in tumors. Finally clinical research using carbon ions for cervical cancer patients demonstrated the effective control of hypoxic fraction.