Cellular radiation dosimetry and its implications for estimation of radiation risks. Illustrative results with technetium 99m-labeled microspheres and macroaggregates
G. M. Makrigiorgos, S. J. Adelstein and A. I. Kassis
Department of Radiology, Harvard Medical School, Boston, Mass.
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.
