The microlesion concept and dosimetry of HZE particles in space radiation safety

Projected space program activities include the possibility that a substantial number of workers may be exposed to primary cosmic radiation while performing tasks in high orbit. Most of the biologically-effective energy deposition by the high-Z, high-energy (HZE) component of this radiation is due to iron nuclei. A dosimetric procedure is needed whereby the unique biological features of this type of radiation can be accounted for. The microlesion concept is examined as a possible means of quantitatively estimating the biological damage due to HZE particles and translating this damage into a measure of dose. A microlesion is defined as the biological damage done to several cells in the track of a single HZE particle, including the mutagenic effects on laterally located cells exposed to long-range secondary electrons. Quantitative LET and energy thresholds are considered in defining the microlesion, and published biological evidence for the expected effects are critically examined. That a single particle can damage several cells in a row along its track is clearly established, but unequivocal evidence that cells positioned laterally may also be damaged is lacking. Microlesion doses are estimated for specific organs at risk in specific radiation fields in space