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MODULE 7

Recommended Guidelines for Evaluation of Thyroid Disease in Person Potentially Exposed to Environmental Radioiodine

by the Hanford Thyroid Disease Study

OBJECTIVES

After studying this module, the reader will be able to

• discuss guidelines from the Hanford Thyroid Disease Study for the evaluation of thyroid disease in people exposed to environmental iodine-131
• name the initial diagnostic procedure for evaluation of a thyroid nodule

Background

Atmospheric Releases of Radioactive Iodine from the Hanford Nuclear Reservation

In February 1986, the Department of Energy released 19,000 pages of documents, some previously classified, that detailed the environmental records of past emissions at Hanford. Among the most serious problems disclosed in these documents were the airborne releases of iodine-131. The most current information from the Hanford Environmental Dose Reconstruction (HEDR) Project estimates that approximately 737,000 curies of iodine-131 were released from the Hanford Nuclear Site in the 1940s and 1950s.

This information, as well as the current information from two large ongoing scientific studies investigating these emissions, has led to widespread public concern about effects of these releases on the health of people who have lived in the region around Hanford. In particular, questions have arisen from both the public and the medical community as to the types of thyroid problems which may have resulted from these exposures, as well as which type of screening evaluations is recommended.

The purposes of these physician guidelines are to give the medical community some background about radiation-induced thyroid disease, provide recommendations for clinical evaluation of thyroid disease, and to summarize the two major ongoing scientific studies.

Radiation-Induced Thyroid Disease

The primary evidence linking exposure to ionizing radiation with the subsequent development of thyroid disease results from studies of individuals exposed to head and neck radiation in childhood, as well as from studies of Japanese atomic bomb survivors. The treatments during childhood were formerly given to children for benign diseases of the head and neck. Examples of the indications for head and neck radiation treatments included: presumed enlargement of the thymus gland, tonsillar enlargement, acne, cervical adenitis (such as with individuals having tuberculosis), and fungal infections of the scalp.

The type of radiation utilized for such treatments during childhood was external gamma radiation. These external beam treatments were generally directed toward the head and neck and were often given on multiple occasions.

Since the 1950s, it has become apparent that such treatments increased the risk of developing both benign and malignant thyroid tumors. There is also evidence which shows that such exposures increase the risk of hypothyroidism.

The radioactive material released from the Hanford Nuclear Site that is of greatest concern in the context of thyroid disease is iodine-131. The radiation exposure described in the preceding paragraphs is from external gamma rays or X-rays. Most of the radiation dose for iodine-131, however, is due to beta radiation from iodine-131, which is concentrated in the thyroid gland.

Much less information is available in the scientific literature to suggest that iodine-131 exposure produces thyroid tumors in human beings. The available information is primarily from patients with hyperthyroidism who are treated with iodine-131. This information shows that at high doses of iodine-131 the thyroid gland can be ablated, resulting in hypothyroidism. There is little information to indicate that such iodine-131 treatments increase the risk of developing thyroid tumors. However, this has been clearly shown in animal studies. It has also been suggested from recent studies of persons exposed to atmospheric nuclear testing at the Nevada Test Site that iodine-131 may cause an increased risk of developing thyroid neoplasms.

While there has been a dramatic increase in childhood thyroid cancer in persons exposed to fallout from the Chernobyl accident, it is not yet certain which type of radiation or combination of radiation types have caused these cancers.

As a result of the above information, it can be stated with confidence that thyroid tumors, both benign and malignant, and hypothyroidism can result from exposure to external radiation. Regarding radioactive iodine exposure, while it is certain that hypothyroidism can result from sufficient doses of iodine-131, the question of benign or malignant thyroid tumor development after iodine-131 exposure remains uncertain.

Approach to the Evaluation Of Thyroid Disease and Recommendations to Persons Potentially Exposed to Environmental Radioiodine

We recommend the following approach for individuals having any concerns that they may have a thyroid problem or concern that they may have been exposed to radioactive iodine releases from Hanford. The first recommendation is that they see their personal or family physician or other health care provider for an evaluation. This applies not only to persons who may have symptoms or may feel ill, but also to individuals who are asymptomatic, but who are concerned that they may have a thyroid problem.

Second, some individuals may feel that if their health care provider is not an expert in radiation issues, they will not be able to evaluate thyroid problems that might have resulted from Hanford emissions. It is our belief and recommendation to both the public and the medical community that the evaluation of thyroid disease is the same regardless of whether the thyroid problem might have been caused by radiation exposure or might be totally unrelated to such exposure. Therefore, it is not necessary to consider a health care provider's expertise in health physics or radiation issues when deciding whom to see for a thyroid evaluation.

Third, we recommend to the medical community that consultants in endocrinology or internal medicine be liberally utilized, either for interpretation of abnormal screening results or for more experienced thyroid examinations.

Clinical Evaluation Of Thyroid Disease

The following is the recommended minimum evaluation for an individual concerned about the possibility of a thyroid problem. Incorporated into these recommendations is a complete history and physical examination, given that many symptoms and signs of thyroid dysfunction overlap with other medical problems.

A.	Complete history with elaboration of residence history; prior endocrine, thyroid, or parathyroid problems; prior history of childhood head and neck radiation treatments; prior thyroid diagnostic tests; and a prior history of thyroid or neck surgery.
B.	Complete physical examination, including careful thyroid examination.
C.	Laboratory to include free thyroxine index (total thyroxine level and T3 resin uptake) and TSH level.
D.	Thyroid nuclear scans or thyroid ultrasound scans are NOT recommended as routine initial screening diagnostic tests. However, they may be utilized as an additional evaluation once a thyroid problem is clinically suspected.
E.	Although there is some variation in the diagnostic evaluation of a thyroid nodule, the initial diagnostic procedure is fine needle aspiration biopsy of the thyroid nodule.
F.	In individuals who have a normal screening evaluation for thyroid disease, it is recommended that they be rescreened on a yearly basis, or less often as indicated by the health care provider. This would be particularly true in those individuals who have reason to believe that they may have been exposed to environmental radioactive iodine.
G.	Follow-up of abnormal screening evaluation: as noted, above, liberal use of consultants in endocrinology or internal medicine is recommended.

Studies