Ask the Doctor Childhood and Neck Irradiation
It was first appreciated approximately 25 years ago that childhood exposure to external beam radiation in the head and neck region was associated with a significant increased risk of thyroid nodules and thyroid cancer. Similar exposures in adults have not been clearly associated with an increased risk, although there is one study from China in which health care workers using radiation equipment had a 2-fold increased risk of thyroid cancer.
The most common indications for radiation treatments in childhood were enlargement of the thymus gland, tonsilitis, glandular inflammation of various kinds, and acne. Other exposures were for treatment of ringworm of the scalp, various benign tumors, bronchitis, hearing loss, and head and neck malignancies.
The risk of thyroid cancer in such patients is estimated to be 53-fold higher than the non-irradiated population. On recall studies, a third of patients with a history of childhood radiation exposure were found to have thyroid nodules, and about a third of the nodules proved to be malignant. In one registry of patients in the Chicago area who were exposed to radiation in childhood, 12% have been diagnosed with thyroid cancer.
Radiation exposure to nuclear fallout from atomic bomb explosions or from nuclear reactor accidents is also associated with increased risk of thyroid cancer. There is currently an epidemic of childhood thyroid cancer in the region surrounding Chernobyl.
In view of these statistics, all patients with a history of childhood head or neck irradiation require careful and lifelong assessment of their thyroid for nodularity. Most physicians recommend a baseline thyroid ultrasound (although some prefer a thyroid scan). Any significant nodule requires a fine needle aspiration biopsy to assess the possibility of malignancy. Careful annual physical exams are essential, and depending upon the baseline ultrasound and the ability of the physician to examine the thyroid, follow-up thyroid ultrasounds may be recommended. In general , physicians are more aggressive in evaluating nodularity in a patient with a history of childhood neck irradiation; fine needle aspiration biopsy is more likely to be used to evaluate multiple nodules in a nodular goiter.
If the biopsy demonstrates that a nodule or nodules are suspicious or malignant, then most surgeons will do a near total thyroidectomy to remove all irradiated thyroid tissue. In patients with a history of external radiation during childhood, the types of thyroid cancer are similar to those in non-irradiated patients. In general these cancers do not behave more aggressively than those of non-irradiated patients, and therefore the majority of young patients with differentiated thyroid cancer have a good prognosis.