AUGER-ELECTRON EMITTERS AS TOOLS FOR ELUCIDATING THE LOCATION OF PRIMARY RADIOSENSITIVE TARGETS

The radiotoxicity of the Auger emitter Cr-51 was investigated using th e well established mouse testis model. Spermatogonial cell survival se rved as the experimental endpoint. In the sodium chromate form, about 85% of the intracellular Cr-51 activity was found in the cytoplasm of the testicular cells while the remaining activity was localised in the cell nucleus. The spermhead survival data yielded a D37 value of 1.95 Gy. This is in contrast to the 0.68 Gy obtained in earlier studies wi th cytoplasmically localised I-125, a prolific emitter of Auger electr ons. The relatively low biological effectiveness of Cr-51 compared wit h similarly localised I-125 is due to the very low energy nature of th e Auger electrons emitted in the decay of Cr-51 which have a maximum r ange of about 0.65 mum. Theoretical dose profiles for cytoplasmic and nuclear localisation of Cr-51 in the cell shows that the dose to the n uclear membrane is not affected by the subcellular distribution of the radionuclide. These considerations imply that the primary radiosensit ive targets are not necessarily limited to the surface of the cell nuc leus.