Flow cytometric evaluation of the effects of 2.3 MeV neutrons and 240 kV X rays on mouse spermatogenic S-phase cells using bromodeoxyuridine incorporation.

A sensitive flow cytometric assay has been developed to assess the effect of X rays or neutrons on the DNA-synthesizing ability of mouse testis cells. The dose to reduce the labelling index (LI) to 50% (ED50) was 25 cGy for X rays and 5 cGy for neutrons, giving a relative biological effectiveness (RBE) of 5.0. A significant reduction of the LI was seen at X-ray doses as low as 10 cGy. Neutron treatment resulted in an exponential decrease in functional S-phase cells while the X-ray response was biphasic. The sensitivity and rapidity of the assay would be suitable for use in biological dosimetry.