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Confidence in the release criteria utilized by the facility:
Cats undergoing radioiodine therapy are hospitalized following that therapy for a variable period of time to allow for the excretion of the majority of the radioiodine prior to their release to the client. The collected radioactive waste material is generally “held for decay” by the radioactive materials license holder. These requirements are regulated by federal codes but usually implemented by more local government agencies, generally at the State government level. Interestingly, these federal regulations are not specific to the use of radioiodine for the treatment of hyperthyroidism in cats. Indeed the regulations were written before cats were recognized as developing hyperthyroidism. Rather, the regulations were written with the general goal of ensuring that those licensed to use radioactive materials of any kind, did so with limits imposed upon them to ensure against inappropriate radiation exposure to members of the general public. Specifically, the federal codes are designed to preclude the general public from receiving greater than 0.1 rem/year as the result of the actions of radioactive materials license holders. Since clients with hyperthyroid cats are members of the general public, this is the major motivation for requiring hospitalization following radioiodine therapy.
The development of standardized release criteria based on the measured radiation exposure emitted from the cat seems at first glance to be straightforward. However, the dramatic effect of varying proximity between the person and the cat (the source of the radiation) needs to be taken into consideration. Radiation exposure follows the “inverse square law”. This means that as the distance between a person and a source of radiation is doubled, the exposure level is decreased by a factor of 4. At what location relative to the cat should one measure the exposure level when determining release criteria? Obviously one should attempt to reproduce the anticipated proximity between the cat and the people with whom the cat lives.
Different release criteria can therefore be chosen based on different anticipated proximities to the cat. Currently state regulatory agencies in different states have interpreted the federal codes differently. This has lead to different release criteria for facilities performing the same procedure in different states.
Anxious clients will often encourage the release of their cats following the radioiodine therapy before they have reached the release criteria established by the authoritative regulatory agency. Referring veterinarians should have confidence that the release criteria used by a facility providing radioiodine therapy have been developed with the best interest of the patient and the client in mind.

A recent decision by the California State Department of Health supports the earlier release of cats following radioiodine therapy for hyperthyroidism. Cats can now be discharged in as little as 3 days following radioiodine therapy!

Confidence in the follow-up care provided:
The results of the radioiodine therapy manifest themselves over a period of several weeks to months. A familiarity with the management of these patients and the assurance of ongoing communication with the client and referring veterinarian should be expected from the facility providing radioiodine therapy.
Advanced Veterinary Medical Imaging has been providing radioiodine therapy to patients in southern California since 1986. Both telephone and written follow-up with referring veterinarians and client’s is a major part of our commitment to providing the best care possible for these patients.

Finally it is of paramount importance to note the following:

Licensing by a federal or state agency to provide radioiodine therapy to cats with hyperthyroidism is NOT a guarantee of proficiency in this procedure.

Referring veterinarians should thoroughly familiarize themselves with the methods used by facilities they refer patients to for radioiodine therapy.

References:

1 Peterson ME, Becker DV, Hurley JR, et al. Spontaneous hyperthyroidism in the cat. American College of Veterinary Internal Medicine Scientific Proceedings, Seattle, July 1979. (abstract).
2 Holzworth J, Theran P, Carpenter JL et al. Hyperthyroidism in the cat: ten cases. J Am Vet Med Assoc 1980 Feb 15;176(4):345-53.
3 Peterson ME, Kintzer PP, Cavanagh PG, et al. Feline hyperthyroidism: pretreatment clinical and laboratory evaluation of 131 cases. J Am Vet Med Assoc 1983 Jul 1;183(1):103-10.
4 Peterson ME, Graves TK, Cavanagh I. Serum thyroid hormone concentrations fluctuate in cats with hyperthyroidism. J Vet Intern Med 1987 Jul-Sep;1(3):142-6.
5 Peterson ME, Graves TK, Gamble DA. Triiodothyronine [T3] suppression test--An aid in the diagnosis of mild hyperthyroidism in cats. J Vet Intern Med Sep/Oct’90 4[5]:233-238.
6 Peterson ME, Broussard JD, Gamble DA. Use of the thyrotropin releasing hormone stimulation test to diagnose mild hyperthyroidism in cats. J Vet Intern Med 1994 Jul-Aug;8(4):279-86.
7 Peterson ME, Melian C, Nichols R. Measurement of serum concentrations of free thyroxine, total thyroxine, and total triiodothyronine in cats with hyperthyroidism and cats with nonthyroidal disease. J Am Vet Med Assoc 2001 Feb 15;218(4):529-36.
8 Kintzer PP, Peterson ME. Thyroid scintigraphy in small animals. Semin Vet Med Surg (Small Anim) 1991 May 6[2]:131-9.
9 Turrel JM, Feldman EC, Hays M et al. Radioactive iodine therapy in cats with hyperthyroidism. J Am Vet Med Assoc 1984 Mar 1;184(5):554-9.
10 Meric SM, Rubin SI. Serum thyroxine concentrations following fixed-dose radioactive iodine treatment in hyperthyroid cats: 62 cases (1986-1989). J Am Vet Med Assoc. 1990 Sep 1;197(5):621-3.
11 C. T. Mooney. Radioactive iodine therapy for feline hyperthyroidism: Efficacy and administration routes J Small Anim Pract 35[6]:289-294 Jun’94.
12 Malik R, Lamb WA, Church DB. Treatment of feline hyperthyroidism using orally administered radioiodine: a study of 40 consecutive cases. Aust Vet J 1994 Aug;71(8):270.
13 Theon AP, Van Vechten MK, Feldman E. Prospective randomized comparison of intravenous versus subcutaneous administration of radioiodine for treatment of hyperthyroidism in cats. Am J Vet Res 1994 Dec;55(12):1734-8.
14 Peterson ME, Becker DV. Radioiodine treatment of 524 cats with hyperthyroidism. J Am Vet Med Assoc 1995 Dec 1;207(11):1422-8.
15 Broome MR, Turrel JM, Hays MT. Predictive value of tracer studies for 131I treatment in hyperthyroid cats. Am J Vet Res 1988, 49; 193-197.
16 Hays MT, Broome MR, Turrel JM. A multicompartmental model for iodide, thyroxine, and triiodothyronine metabolism in normal and spontaneously hyperthyroid cats. Endocrinology. 1988 Jun;122(6):2444-61.
17 Broome MR, Hays MT, Turrel JM. Peripheral metabolism of thyroid hormones and iodide metabolism in healthy and hyperthyroid cats. Am J Vet Res 1987, 48; 1286-1289.
18 Hays MT, Turrel JM, Broome MR. Assessing degree of hyperthyroidism in cats. J Am Vet Med Assoc 1988 Jan 1;192(1):7.
19 Peterson ME, Keene B, Ferguson DC, Pipers FS. Electrocardiographic findings in 45 cats with hyperthyroidism. J Am Vet Med Assoc 1982 Apr 15;180(8):934-7.
20 Kienle RD, Bruyette D, Pion PD. Effects of thyroid hormone and thyroid dysfunction on the cardiovascular system. Vet Clin North Am Small Anim Pract 1994 May;24(3):495-507.
21 Fox PR, Peterson ME, Broussard JD. Electrocardiographic and radiographic changes in cats with hyperthyroidism: comparison of populations evaluated during 1992-1993 vs. 1979-1982. J Am Anim Hosp Assoc 1999 Jan-Feb;35(1):27-31.