Researchers in Israel studied the long-term effects of low-dose radiation in treating children with tinea capitis, a fungal infection of the scalp more commonly called ringworm of the scalp. It may begin as a small sore and may resemble a pimple before becoming patchy, flaky or scaly. The infection site may become swollen, tender or red and it may cause patches of hair to fall out.

Today, the condition is treated with oral antifungals and radiation is no longer used. However, researchers wanted to look at the effect of ionizing radiation on the thyroid gland, the tissue that sits just below the Adam's apple in the neck. The thyroid secretes hormones that regulate a person's metabolism, the physical and chemical processes necessary to maintain life. Numerous studies have shown that thyroid is sensitive to the effects of ionizing radiation, especially in children. The American Cancer Society estimates that about 33,500 people in the United States will be diagnosed with thyroid cancer in 2007.

The scientists studied 10,834 people who received radiation treatments in the 1950s and compared them to two groups who were not treated. They identified 159 cases of thyroid cancer. The risk of developing the cancer increased with the level of radiation received in childhood, but decreased with the more time that elapsed after radiation exposure. The risks were significantly increased 10 to 19 years after exposure, peaking at 20 to 30 years, but decreased dramatically 40 years after exposure.

The results agree with risk factors documented in many studies of radiation's effect on thyroid cancer. Researchers said further studies are needed on whether genetic factors make certain ethnic groups, particularly Jewish people, more susceptible to the radiation effects.

The study was published in a recent issue of the Journal of Clinical Endocrinology and Metabolism.

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