RELATIVE BIOLOGICAL EFFECTIVENESS OF TRITIUM FOR INDUCTION OF MYELOID-LEUKEMIA IN CBA H MICE/

To help resolve uncertainties as to the most appropriate weighting fac tor for tritium beta rays, a large experiment was carried out to measu re the relative biological effectiveness (RBE) of tritiated water comp ared to X rays for the induction of myeloid leukemia in male mice of t he CBA/H strain. The study was designed to estimate the lifetime incid ence of myeloid leukemia in seven groups of about 750 mice each; radia tion exposures were approximately 0, 1, 2 and 3 Gy both for tritiated water and for X rays. The lifetime incidence of leukemia in these mice increased from 0.13% in the control group to 6-8% in groups exposed t o higher radiation doses. The results were fitted to various equations relating leukemia incidence to radiation dose, using both the raw dat a and data corrected for cumulative mouse-days at risk. The calculated RBE values for tritium beta rays compared to X rays ranged from 1.0 /- 0.5 to 1.3 +/- 0.3. A best estimate of the RBE for this experiment was about 1.2 +/- 0.3. A w(R) value of 1 would thus appear to be more appropriate than a w(R) Of 2 for tritium beta rays. (C) 1995 by Radiat ion Research Society