Radiotoxicity of thallium-201 in mouse testes: inadequacy of conventional dosimetry.

When TI-201 is concentrated in mouse testes, the low-energy Auger electrons following its electron-capture decay are found to be much more effective in causing loss of testicular weight and reduction of sperm heads than the energetic beta particles from similarly distributed TI-204. These results are contrary to expectations based on conventional dosimetry of tissue-incorporated radionuclides, and point to possible underestimation of risks by the currently adopted dosimetric procedures, especially in the case of radionuclides decaying by electron capture and internal conversion.