Radionuclides that emit Auger electrons are widely used in nuclear medicine (e.g.,${}^{99{\rm m}}{\rm Tc},\ {}^{123}{\rm I},\ {}^{201}{\rm Tl}$) and biomedical research (e.g.,${}^{51}{\rm Cr},\ {}^{125}{\rm I}$), and they are present in the environment (e.g.,${}^{40}{\rm K},\ {}^{55}{\rm Fe}$). Depending on the subcellular distribution of the radionuclide, the biological effects caused by tissue-incorporated Auger emitters can be as severe as those from high-LET α particles. However, the recently adopted recommendations of the International Commission on Radiological Protection (ICRP) provide no guidance with regard to calculating the equivalent dose for these radionuclides. The present work, using spermatogenesis in mouse testis as the experimental model, shows that the lethality of the prolific Auger emitter125 I is linearly dependent on the fraction of the radioactivity in the organ that is bound to DNA. This suggests that the equivalent dose for Auger emitters may have a similar linear dependence. Accordingly, a formalism for calculating the equivalent dose for Auger emitters is advanced within the ICRP framework.

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