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Radioiodine dosimetry
230
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34. Radioiodine Dosimetry J. R. JOHNSON Health Sciences Division, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario, KOJ lJ0, Canada The estimation of individual doses for radiation protection purposes from a radioiodine intake requires a knowledge of the distribution and retention of the radioiodine (primarily in the thyroid), and a knowledge of the average energy deposited in each organ per radioactive decay. In addition, the dose distribution on a sub-organ scale and sub-cellular scale may be required to understand the observed effects for organically bound radioiodines, particularly for lz51 and lz91. This presentation reviews the state of our knowledge in these areas for euthyroid subjects. It includes a description of the change in the thyroid mess and iodine concentration with age, the effects of stable dietary iodine on distribution and retention and the prophylactic use of stable iodine in accidents. The effect on the calculated thyroid dose using different methods of calculating the absorbed fraction of energy per decay and from using actual thyroid mass rather than an assumed one are also discussed.
35. Radiotoxicology
of Iodine*
DAVID M. TAYLOR Kernforschungszentrum Karlsruhe, Institute Heidelberg, Federal Republic of Germany
for Genetics and for Toxicology, and University
of
Thirty radioisotopes of iodine, ranging in mass number from 116 to 141, have been identified. These nuclides decay, with half-lives of from 0.5 second to 1.57 x 10’years, by the emission of beta particles, positrons, gamma rays, Auger electrons or neutrons. Only those isotopes with mass numbers between 123 and 135 are of major radiotoxicological interest. Since radiotoxicity depends on the radiation characteristics, physical half-life, chemical and metabolic properties of the radionculide, which may enter the body by inhalation, ingestion or by injection, a broad spectrum of radiotoxicity might be expected for the different radioiodines and radioiodinated compounds. However, toxicological data are available for only a few radioiodine isotopes and compounds. Exposure of animals or man to inorganic 13’1 or lz51 may result in the induction of benign or malignant thyroid tumours or depression of thyroid function; Bq for Bq lz51 is less toxic than 13’I. However, the shorter lived radioiodines i3*I, 1331, and ‘35I appear to be 10-100 times more toxic than i3’I alone. Adrenal, pituitary and ovarian tumours, as well as parathyroid hypofunction and other biochemical disturbances, have been reported in animals but not, so far, in man. Gonad doses from i3iI up to at least 800mGy do not appear to cause in man an increased incidence of congenital abnormalities or spontaneous abortions. Little information is available about the radiotoxicity of radioiodine containing organic compounds. The DNA precursor, iododeoxyuridine when labelled with ‘*$I becomes incorporated into the cell nucleus and produces severe and often irreparable damage due to the emission of Auger electrons. The risk estimate for the induction of thyroid carcinoma or adenoma by inorganic i3iI is considered to be 10-20.10-6 persons Gy-‘y-l, but is probably up to 100 times larger for persons exposed to mixtures of short-lived radioiodines.
36. Receptor-Mediated Hormones*
Cytotoxicity
of
Iodine-125
Labeled
W. D. BLOOMER, W. H. MCLAUGHLIN, R. R. WEICHSELBAUM, D. E. SEITZ, R. N. HANSON and S. J. ADELSTEIN Departments of Radiation Therapy and Radiology, Harvard Medical School, and the Department of Chemistry, Northeastern University, Boston, Massachusetts, U.S.A. Although sex steroid hormones are transported to all parts of the body via the blood stream, they stimulate only specific target cells containing receptors. In such cells, a hormone-receptor complex is * Accepted for publication as Original article in the Inr. J. Nucl. Med. Biol.
Around
the Nuclrar
World
34. Radioiodine Dosimetry J. R. JOHNSON Health Sciences Division, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario, KOJ lJ0, Canada The estimation of individual doses for radiation protection purposes from a radioiodine intake requires a knowledge of the distribution and retention of the radioiodine (primarily in the thyroid), and a knowledge of the average energy deposited in each organ per radioactive decay. In addition, the dose distribution on a sub-organ scale and sub-cellular scale may be required to understand the observed effects for organically bound radioiodines, particularly for lz51 and lz91. This presentation reviews the state of our knowledge in these areas for euthyroid subjects. It includes a description of the change in the thyroid mess and iodine concentration with age, the effects of stable dietary iodine on distribution and retention and the prophylactic use of stable iodine in accidents. The effect on the calculated thyroid dose using different methods of calculating the absorbed fraction of energy per decay and from using actual thyroid mass rather than an assumed one are also discussed.
35. Radiotoxicology
of Iodine*
DAVID M. TAYLOR Kernforschungszentrum Karlsruhe, Institute Heidelberg, Federal Republic of Germany
for Genetics and for Toxicology, and University
of
Thirty radioisotopes of iodine, ranging in mass number from 116 to 141, have been identified. These nuclides decay, with half-lives of from 0.5 second to 1.57 x 10’years, by the emission of beta particles, positrons, gamma rays, Auger electrons or neutrons. Only those isotopes with mass numbers between 123 and 135 are of major radiotoxicological interest. Since radiotoxicity depends on the radiation characteristics, physical half-life, chemical and metabolic properties of the radionculide, which may enter the body by inhalation, ingestion or by injection, a broad spectrum of radiotoxicity might be expected for the different radioiodines and radioiodinated compounds. However, toxicological data are available for only a few radioiodine isotopes and compounds. Exposure of animals or man to inorganic 13’1 or lz51 may result in the induction of benign or malignant thyroid tumours or depression of thyroid function; Bq for Bq lz51 is less toxic than 13’I. However, the shorter lived radioiodines i3*I, 1331, and ‘35I appear to be 10-100 times more toxic than i3’I alone. Adrenal, pituitary and ovarian tumours, as well as parathyroid hypofunction and other biochemical disturbances, have been reported in animals but not, so far, in man. Gonad doses from i3iI up to at least 800mGy do not appear to cause in man an increased incidence of congenital abnormalities or spontaneous abortions. Little information is available about the radiotoxicity of radioiodine containing organic compounds. The DNA precursor, iododeoxyuridine when labelled with ‘*$I becomes incorporated into the cell nucleus and produces severe and often irreparable damage due to the emission of Auger electrons. The risk estimate for the induction of thyroid carcinoma or adenoma by inorganic i3iI is considered to be 10-20.10-6 persons Gy-‘y-l, but is probably up to 100 times larger for persons exposed to mixtures of short-lived radioiodines.
36. Receptor-Mediated Hormones*
Cytotoxicity
of
Iodine-125
Labeled
W. D. BLOOMER, W. H. MCLAUGHLIN, R. R. WEICHSELBAUM, D. E. SEITZ, R. N. HANSON and S. J. ADELSTEIN Departments of Radiation Therapy and Radiology, Harvard Medical School, and the Department of Chemistry, Northeastern University, Boston, Massachusetts, U.S.A. Although sex steroid hormones are transported to all parts of the body via the blood stream, they stimulate only specific target cells containing receptors. In such cells, a hormone-receptor complex is * Accepted for publication as Original article in the Inr. J. Nucl. Med. Biol.