Radiation Doses from 51Cr-Bleomycin

Extensive studies were made of long-term whole-body retention, plasma concentration, urinary excretion and organ retention of51 Cr in rats after intravenous injection of 51Cr-bleomycin. A similar but less extensive investigation was performed on rabbits, and whole-body retention, plasma concentration and urinary excretion was also followed in patients given 51Cr-bleomycin for diagnostic purposes. From an analysis of the collected information it followed that integrated whole-body and organ retention, corrected for radioactive decay, is similar in man and rabbit, and higher by a factor of about 2 in the rat. Doses to organs and whole body in man were calculated using the MIRD methodology and assuming conservatively that the kinetic data derived in rats are applicable to man. The organ and whole-body MIRD doses after 51Cr-bleomycin administration are comparable to those after 67Ga-citrate and the effective dose equivalent from a diagnostic amount of 740 MBq of the 51Cr complex amounts to about 6 mSv. However, the subcellular distribution in the liver of51 Cr, administered in the form of 51Cr-bleomycin, indicated a significant enrichment of 51Cr in the nuclei and in the DNA over mean concentrations in the liver cells. Also, the quality factor for Auger electrons, emitted by51 Cr, when assessed on the basis of the Q vs. LET relationship, as proposed by ICRP, was substantially higher than unity. Doses calculated for cell nuclei and the DNA in the liver cells were higher than the cell-averaged values by a factor 2.5 and 5, respectively, and the corresponding dose equivalents by a factor of 9 and 24. The effective dose equivalent, estimated on the basis of dose equivalents to cell nuclei and the DNA, amounted to 33 and 83 mSv per examination (740 MBq of 51Cr-bleomycin), respectively.