Biological detection of reduction in dose at the surface of volume sources containing beta emitters

Dosimetry theory related to volume sources containing uniformly distributed beta-emitting radionuclides predicts a rapid drop in dose at the outer surface to approximately one half of the maximum dose within the volume. The purpose of this study was to determine if this reduction in surface dose could be observed using a measurable biological endpoint. In this study rats were injected with radiocolloids of either 198Au, 113In-m or 99Tc-m, to produce liver irradiation from their decay, or their livers were treated with external X-irradiation. After irradiation, a portion of the liver was surgically removed to stimulate cell division in the liver remnant revealing radiation damage in the form of chromosomal aberrations. The percentages of dividing cells with bridges were scored in the outer edges (0.45 mm) of the tissue sections and were compared to levels obtained from the central portion of the liver lobe. No significant difference was observed with X-irradiation or from 99Tc-m irradiation. However, irradiation with 198-Au and 113In-m (which emit large numbers of energetic electrons) produced significantly fewer aberrations in the outer layer when compared to the central portion. These differences in the distribution of biological damage allowed us to detect the predicted dose reduction at the surface of volume sources containing beta emitters.