BIOLOGICAL HAZARDS AND TOXICITY OF RADIOACTIVE ISOTOPES

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Abstract
The effects of large dosages of radioisotopes resemble to a marked extent those of total-body irradiation, with modifications dependent on tissue distribution. Permissible exposure levels are determined by late or chronic radiation changes, of which malignant changes have quite properly attracted major attention. There is no evidence to indicate that radiation dosages to tissue corresponding to estab-lished"permissible" external dosages (0.3 to 0.6 rep per week) will result in increased incidence of malignant disease detectable in a population of moderate size For such calculations it is necessary to estimate maximum local tissue dosage, rather than the mean value for an organ or structure, and to make use of factors recognizing the greater effectiveness of ionization in areas where it is dense (e.g., alpha-particle ionization). It is suggested that a more conservative figure is desirable where a large population may be affected, and the basis for using larger doses in clinical investigation, diagnosis, and therapy is discussed. Bone tumor induction by Sr89 has been studied extensively in mice. The data are consistent with the view that each given quantity of radiation to bone confers a given probability of bone tumor formation that may occur at any time following a "latent period." The latent period increases gradually with the dosage. It is not known at present whether a threshold exists for such effects.