Cellular radiation dosimetry and its implications for estimation of radiation risks. Illustrative results with...

Radiation absorbed doses at the cellular level were calculated for routine, human lung perfusion examinations after the intravenous injection of technetium 99m-labeled microspheres or macroaggregated albumin. In such studies, more than 90% of these particles are trapped in the precapillary arterioles of the lung, resulting in an extremely inhomogeneous distribution of radionuclide. We used a computer program that accounted for the inhomogeneity of radiopharmaceutical distribution and calculated the dose to individual lung cells. Absorbed doses to individual lung cells were found to vary by a factor of about 30,000. We believe that such findings call for a reevaluation of the justification for dosimetry at the organ level and an examination of the implications of absorbed doses calculated at the cellular level for the estimation of radiation risks.