Hacker-Klom, U. B., Köhnlein, W., Kronholz, H. L. and Göhde, W. The Relative Biological Effectiveness of Low Doses of 14 MeV Neutrons in Steady-State Murine Spermatogenesis as Determined by Flow Cytometry.

The relative biological effectiveness of 14 MeV neutrons in the low-dose range ≤1 Gy has been determined in differentiating and differentiated spermatogonia. Male NMRI mice were exposed to single doses of 2 cGy to 3 Gy of ⁶⁰Co γ rays or neutrons. The ratios of testicular S-phase cells, 4c primary spermatocytes, and elongated spermatids were quantified by DNA flow cytometry 2 to 70 days after irradiation and were found to decrease. Histological samples and testis weight were analyzed in parallel. Doses of 2–5 cGy neutrons and 10–50 cGy γ rays significantly (P < 0.05) decreased the proportions of S-phase cells, spermatocytes and elongated spermatids at 4, 14 and 28 days postirradiation. For S-phase cells, the biphasic shape of the cell survival curves was described with a D₅₀ of 5 cGy neutrons. The D₅₀ for ⁶⁰Co γ rays and the relative biological effectiveness could not be determined. The relative biological effectiveness of neutrons at 50% reductions of testis weight, primary spermatocytes, and elongated spermatids were 2.5, 10.0 and 6.1, respectively. This in vivo assay is interesting because of its sensitivity at dose ranges that are relevant for exposures in the environment, the workplace and radiotherapy.