Lung tumour induction in mice after X-rays and neutrons
Coggle, J.E.
International Journal of Radiation Biology and Related Studies in Physics Chemistry and Medicine 53(4): 585-597
1988
ISSN/ISBN: 0020-7616 PMID: 3258294 Document Number: 309082
Dose-response curves were determined for pulmonary adenomas and adenocarcinomas in mice after single acute doses of 200 kVp X-rays and cyclotron neutrons (.hivin.E = 7.5 MeV). A serial-killing experiment established that the radiation induction of chromosome aberrations. The validity of the concept of PLD neous cancers. The dose versus incidence (I) of tumours in male and female mice for X-ray doses between 0.25 and 7.5 Gy is 'bell-shaped' and best fitted with a purely quadratic induction and exponential inactivation terms, i.e. I = A + BD2 e-.alpha.D. In contrast, the tumour dose-response aftrer 0.1-4.0 Gy of neutrons is best fitted by I = A + BD e-.alpha.D and is steeply liner .ltoreq. 1 Gy, peaks between 1 and 3 Gy and sharply declines at 4.0 Gy. The data for the female mice .ltoreq. 1 Gy neutrons are best fitted to the square root of the dose. A major objective of the experiments was to derive neutron RBE values. Because of the differences between the X-ray (quadratic) and neutron (linear) curves, the RBEn will vary inversely with decreasing X-ray dose. The RBE values at 1 Gy of X-rays derived from the B coefficients in the above equations are 7.4 .+-. 3.2 (male and female); 8.6 .+-. 3.6 (female) and 4.7 .+-. 1.8 (male). These are high values and imply even higher values at the doses of interest to radiation protection. If, however, one restricts the analysis to the initial, induction side of the response (.ltoreq. 1 Gy neutrons, .ltoreq. 3 Gy X-rays) then good linear fits are obtainable for both radiations and indicte neutron RBE values of 7.4 .+-. 2.3 for female mice and 4.5 .+-. 1.8 for males, and these are independent of dose level.