The Effectiveness of Fast Neutrons Compared with Low LET Radiation on Cell Survival Measured in the Mouse Jejunum

HORNSEY, SHIRLEY. The Effectiveness of Fast Neutrons Compared with Low LET Radiation on Cell Survival Measured in the Mouse Jejunum. Radiat. Res. 55, 58-68 (1973). Cell survival curves have been established from mouse jejunum after irradiation with 6-MeV neutrons at 50-100 rads/min from the Hammersmith Cyclotron, 7-MeV electrons at 6 krad/min, and 7-MV x-rays at 100 rads/min given in single doses or two fractions. After an initial shoulder region all curves show an exponential region between surviving fractions of 10-l-10-8. The LD5o(5) values for all types of irradiation fall at a cell surviving fraction of 10-2. The relative sensitivities of these radiations obtained from a comparison of Do values are for neutrons relative to 7-MV x-rays at 100 rad/min 2.0; for neutrons relative to 7-MeV electrons at 6 krad/min 1.5; for 7-MeV electrons at 6 krad/min to 7-MV x-rays at 100 rad/min 1.3. The relative sensitivities obtained from a comparison of DQ values are similarly 4.7, 3.6, and 1.3. Thus, the effect of a change in dose rate in the low LET radiation has almost as big an effect on Do as a change in LET but the effect on shoulder size is much less than is seen with a change in LET.