Cell Death (Apoptosis) in the Mouse Small Intestine after Low Doses: Effects of Dose-rate, 14·7 MeV Neutrons, and 600 MeV (Maximum Energy) Neutrons

Abstract

The production of dead (apoptotic) cells by low doses of γ-rays was independent of dose-rate between 0·27 and 450 cGy per min. The r.b.e. for doses of 14·7 MeV neutrons between 1 and 15 cGy was about 4, and for neutrons generated by bombarding a beryllium target with 600 MeV protons the r.b.e. was about 2·7. The dose–incidence curves for all three radiation types reached a plateau at about 3–4 dead cells per crypt section, and this occurred at about 20–40 cGy of γ-rays. These curves are compatible with exponential survival of the cell population at risk (D₀ of 24 cGy for γ-rays, 6 cGy for 14·7 MeV neutrons and 9 cGy for 600 MeV neutrons). Since the dose-response is exponential there is no indication of much higher r.b.e. values at very low doses, a point of concern in radiation protection. The spatial distribution of dead cells in the crypt was similar after doses of γ-rays or neutrons, indicating that the same population of target cells was affected in both cases.