The Effect of Oxygen on Impairment of the Proliferative Capacity of Human Cells in Culture by Ionizing Radiations of Different LET

Abstract

SummaryOxygen-enhancement ratios (OER) have been determined for the inhibition of clone-formation by cultured cells of human origin irradiated with α-particles and deuterons of different energies, fast neutrons and 250 kvp x-rays. The results of experiments with mono-energetic charged particles, whereby narrow distributions of linear energy transfer (LET) are obtained, show that the OER decreases with increasing LET from about 2·6 at a LET∞ of 5·6 kev/μ of unit density tissue to a value of 2·05 at 61 kev/μ, followed by a more rapid decrease to 1·0 at 165 kev/μ. With fast neutrons, produced by bombarding Be with 16 mev deuterons, an OER of 1·6 was obtained and with 250 kvp x-rays the OER was 2·7.The relation between the relative biological effectiveness (RBE), the OER and the LET is discussed.