Radiation Damage to Mouse Testis Cells from [99mTc] Pertechnetate

The radiation dose and the biologic damage to mouse testis from intravenously administered [99mTc] pertechnetate were studied. The dose was measured for penetrating radiations from Tc-99m, using calibrated thermoluminescent dosimeters and calculations from the uptake of the nuclide in the testis, and was found to be 4.9 rada per mCi of Tc-99. The biologic damage was measured by the decrease in the number of sperm heads in the testis, counted both by hemacytometer and by Coulter counter. In preliminary experiments using external gamma radiation from Cs-137, the number of sperm heads reached a minimum 29 days after irradiation. Twenty-nine days after injection of 5.8 mCi of Tc-99m, which gives 28 rads to the testis, the number of sperm hads decreased to 70% of control. The biologic effect corresponds to that seen after 40 rads of gamma radiation from Cs-137. The damage to mouse testis cells from internally administered Tc-99m as measured in an in vivo system appears to be at least as significant as that from external gamma irradiation, if not more so.