Cellular radiation dosimetry and its implications for estimation of radiation risks. Illustrative results with technetium 99m-labeled microspheres and macroaggregates.

Abstract

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.