The bromine enhancement ratio in mammalian cells in vitro and experimental mouse tumours.

Human kidney cells in culture and cells of mouse sarcoma-180 were allowed to incorporate bromine into their DNA. Cultured cells with and without incorporated BUdR were irradiated with electromagnetic radiations ranging in energy from 12 keV X-rays to 60Co gamma-rays to find out whether or not there exists any energy dependence of the bromine dose enhancement ratio BER. Such a dependence should show in the immediate neighbourhood of the K-absorption edge of bromine (13.5 keV). Any influence of the Auger effect triggered in bromine by external irradiation should show by a significant increase of the BER for energies rising from slightly below to slightly above the bromine K-edge. Values of D37, D0 and the extrapolation numbers of the cell survival curves served as biological endpoints. Measured values of BER ranged from 1.12-2.00 without any significant dependence energy. A weakly pronounced peak was found for 50 kV X-rays of 26 keV mean energy. Sarcoma-180 were irradiated with 14 kEV X-rays and 60C gamma-rays. BUdR was administered i.v., i.p. and directly into the tumours in quantities of up to 1 ml of a 10(-3) M solution. Tumour regression caused by the irradiations served as a measure of the radiation effects with and without incorporated BUdR. No significant dose enhancement effect of bromine was observed in this case. Within error limits, the combination of BUdR with 14 keV X-rays proved more effective than BUdR combined with 60Co gamma-rays.