Oxygen enhancement ratio measured for heavy ions at different LET in various oxygen concentrations

Hypoxia is one of the most common causes for tumor radioresistance and metastasis. High LET irradiation is expected to reduce these problems. However, although the dependence of the oxygen enhancement ratio (OER) from LET has been previously measured at the Lawrence Berkeley Laboratory (USA) and HIMAC (Japan), no data are available for intermediate oxygen concentrations, especially between 0.1% and 2%, where the OER sharply increases after X-rays.Here we report the first measurements of the OER and relative biological effectiveness (RBE), for different LET, ions (carbon, nitrogen, oxygen and lithium) at different oxygen concentrations: normoxic (air), hypoxic (0.5%O2) and anoxic (0% O2).The carbon irradiation gave an OER value of 1.8+/-0.1 in anoxia, while for photon irradiation it results in a value of 2.4+/-0.1. In hypoxia, the OER values decrease to 1.29+/-0.07 and to 1.5+/-0.1 for carbon and photon irradiation respectively.OER values decrease with increasing LET. The values found were from 1.8+/-0.1 for carbon 100 keV/mm to 1.30+/-0.04 for nitrogen 160 keV/mm. A clear influence of atomic number could not be seen in this atomic number range.About the RBE results, in anoxia the RBE value increases with increasing LET. The range of values found was from 3.1+/-0.2 for carbon 100 keV/mm to 4.4+/-0.2 for nitrogen 160 keV/mm while does not change in normoxic condition: 2.6+/-0.2 to 2.4+/-0.2. Experiments to measure the full OER-LET curves at intermediate oxygen concentrations at HIMAC within the program of the IOL "Radiation Quality".The 10th International Symposium on Chromosomal Aberration