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Title: Radioactive iodine therapy in cats with hyperthyroidism

Abstract

Eleven cats with hyperthyroidism were treated with radioactive iodine (/sup 131/I). Previous unsuccessful treatments for hyperthyroidism included hemithyroidectomy (2 cats) and an antithyroid drug (7 cats). Two cats had no prior treatment. Thyroid scans, using technetium 99m, showed enlargement and increased radionuclide accumulation in 1 thyroid lobe in 5 cats and in both lobes in 6 cats. Serum thyroxine concentrations were high and ranged from 4.7 to 18 micrograms/dl. Radioactive iodine tracer studies were used to determine peak radioactive iodine uptake (RAIU) and effective and biological half-lives. Activity of /sup 131/I administered was calculated from peak RAIU, effective half-life, and estimated thyroid gland weight. Activity of /sup 131/I administered ranged from 1.0 to 5.9 mCi. The treatment goal was to deliver 20,000 rad to hyperactive thyroid tissue. However, retrospective calculations based on peak RAIU and effective half-life obtained during the treatment period showed that radiation doses actually ranged from 7,100 to 64,900 rad. Complete ablation of the hyperfunctioning thyroid tissue and a return to euthyroidism were seen in 7 cats. Partial responses were seen in 2 cats, and 2 cats became hypothyroid. It was concluded that /sup 131/I ablation of thyroid tumors was a reasonable alternative in the treatment ofmore » hyperthyroidism in cats. The optimal method of dosimetry remains to be determined.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Department of Radiological Sciences, School of Veterinary Medicine, University of California, Davis
OSTI Identifier:
6830928
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Am. Vet. Med. Assoc.; (United States); Journal Volume: 184:5
Country of Publication:
United States
Language:
English
Subject:
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; 62 RADIOLOGY AND NUCLEAR MEDICINE; HYPERTHYROIDISM; RADIOTHERAPY; CATS; DOSE-RESPONSE RELATIONSHIPS; IODINE 131; ANIMALS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; DAYS LIVING RADIOISOTOPES; DISEASES; ENDOCRINE DISEASES; INTERMEDIATE MASS NUCLEI; IODINE ISOTOPES; ISOTOPES; MAMMALS; MEDICINE; NUCLEAR MEDICINE; NUCLEI; ODD-EVEN NUCLEI; RADIOISOTOPES; RADIOLOGY; THERAPY; VERTEBRATES 560162* -- Radionuclide Effects, Kinetics, & Toxicology-- Animals, Plants, Microorganisms, & Cells; 550604 -- Medicine-- Unsealed Radionuclides in Therapy-- (1980-)

Citation Formats

Turrel, J.M., Feldman, E.C., Hays, M., and Hornof, W.J.. Radioactive iodine therapy in cats with hyperthyroidism. United States: N. p., 1984. Web.
Turrel, J.M., Feldman, E.C., Hays, M., & Hornof, W.J.. Radioactive iodine therapy in cats with hyperthyroidism. United States.
Turrel, J.M., Feldman, E.C., Hays, M., and Hornof, W.J.. 1984. "Radioactive iodine therapy in cats with hyperthyroidism". United States. doi:.
@article{osti_6830928,
title = {Radioactive iodine therapy in cats with hyperthyroidism},
author = {Turrel, J.M. and Feldman, E.C. and Hays, M. and Hornof, W.J.},
abstractNote = {Eleven cats with hyperthyroidism were treated with radioactive iodine (/sup 131/I). Previous unsuccessful treatments for hyperthyroidism included hemithyroidectomy (2 cats) and an antithyroid drug (7 cats). Two cats had no prior treatment. Thyroid scans, using technetium 99m, showed enlargement and increased radionuclide accumulation in 1 thyroid lobe in 5 cats and in both lobes in 6 cats. Serum thyroxine concentrations were high and ranged from 4.7 to 18 micrograms/dl. Radioactive iodine tracer studies were used to determine peak radioactive iodine uptake (RAIU) and effective and biological half-lives. Activity of /sup 131/I administered was calculated from peak RAIU, effective half-life, and estimated thyroid gland weight. Activity of /sup 131/I administered ranged from 1.0 to 5.9 mCi. The treatment goal was to deliver 20,000 rad to hyperactive thyroid tissue. However, retrospective calculations based on peak RAIU and effective half-life obtained during the treatment period showed that radiation doses actually ranged from 7,100 to 64,900 rad. Complete ablation of the hyperfunctioning thyroid tissue and a return to euthyroidism were seen in 7 cats. Partial responses were seen in 2 cats, and 2 cats became hypothyroid. It was concluded that /sup 131/I ablation of thyroid tumors was a reasonable alternative in the treatment of hyperthyroidism in cats. The optimal method of dosimetry remains to be determined.},
doi = {},
journal = {J. Am. Vet. Med. Assoc.; (United States)},
number = ,
volume = 184:5,
place = {United States},
year = 1984,
month = 3
}
  • Thirty-one cats with hyperthyroidism were given one dose of radioactive iodine (131I) IV. Serum thyroxine (T4) concentrations were measured before treatment in all cats, at 12-hour intervals after treatment in 10 cats, and at 48-hour intervals after treatment in 21 cats. Serum T4 concentrations also were measured one month after /sup 131/I therapy in 29 cats. Activity of 131I administered was 1.5 to 6.13 mCi, resulting in a dose of 20,000 rads to the thyroid. Serum T4 concentrations before /sup 131/I administration were 5.3 to 51.0 micrograms/dl, with a median T4 concentration of 11.0 micrograms/dl. Serum T4 decreased most rapidlymore » during the first 3 to 6 days after treatment. Sixteen cats (55%) had normal serum thyroxine concentrations by day 4 after 131I administration, and 23 cats (74%) were euthyroxinemic by day 8 after treatment. One month after administration of 131I, the 29 cats evaluated were clinically improved, and 24 (83%) of the 29 cats evaluated had normal serum T4 concentrations, 3 cats (10%) remained hyperthyroxinemic, and 2 cats (7%) were hypothyroxinemic. Therefore, administration of 131I was a safe and effective method to quickly decrease serum T4 concentrations in hyperthyroid cats.« less
  • A review of 542 hyperthyroid patients treated by I/sup 131/ at the Toronto General Hospital between 1950 and 1955 is presented. This group included 403 patients with diffuse hyperplastic goitre and 139 patients with toxic nodular goitre. The method for assessing the initial dose of I/sup 131/ is described. In general, patients with toxic nodular goitres received much larger doses. Of the diffuse hyperplastic group 72% were cured with one dose, the remainder requiring two or more doses. A greater percentage of the toxic nodular group required only one dose. No cases of complete resistance to 1/sup 131/ therapy weremore » encountered. Permanent hypothyroidism was produced in 16.3% of those so treated, but in 6.5% it was very mild. The incidence of clinical hypothyroidism was much lower in the toxic nodular group than in the diffuse hyperplastic group. There was a continuing incidence of late hypothyroidism, occurring years after therapy; some of these patients had undergone a transient period of hypothyroidism shortly after treatment, then recovered for some years. Factors possibly related to the response to treatment and to the development of hypothyroidism have been analyzed. Recurrent hyperthyroidism after thyroidectomy was associated with a significant increase in the incidence of post-I/sup 131/ hypothyroidism, while pretreatment with artithyroid drugs seemed to reduce radiosensitivity in the diffuse group. No late recurrences of hyperthyroidism were noted. Twenty-one deaths occurred within two years of therapy. In most, there was no obvious relation to therapy, while in none was there a clear-out cause-and-effect relationship to I/sup 131/ therapy. Nevertheless, elderly or very ill patients should be treated only after they have been rendered euthyroid by antithyroid drugs. Fertility has not been affected by I/sup 131/ therapy, but the use of this isotope in pregnancy is contraindicated because of the possible ill effects on the fetas. The possibility of genetic effects appears to be negligible, as judged by the gonadal radiation doses received in I/sup 131/ therapy. The fear of carcinoma of the thyroid likewise appears to be receding if the therapy is utilized only in adults. Leukemia has been reported in 14 instances. However, the statistical import is not clear, since the total number of cases of leukemia and of persons treated by I/sup 131/ is not known. It may be that there is a slight increase in the incidence of leukemia following radioactive treatment, comparable to that possibly induced by certain diagnostic radiological procedures, but this is insufficient to warrant any change in policy regarding the use of I/sup 131/ After consideration of these hypothetical dangers, it is concluded that the use of radioactive iodine is a safe, effective form of therapy for adult, nonpregnant hyperthyroid patients, and is to be preferred to surgical thyroidectomy. 108 references. (auth)« less