In vivo effects of iron-55 and iron-59 on mouse testes: biophysical dosimetry of Auger electrons.

When the Auger-electron emitter, 55Fe, and the beta-emitter, 59Fe, are similarly distributed in the testes of mice, the conventionally calculated average radiation dose to the organ from 55Fe is about 2.6 times more effective in reducing the sperm-head count than the dose from 59Fe. This finding emphasizes the ability of low-energy Auger electrons to damage radiosensitive targets of cells through localized irradiation. The observed efficacy is understandable in terms of dosimetric models based on intracellular distribution studies of the radionuclides.