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Radiation-induced thyroid disease 

Radiation-induced thyroid disease
Chapter:
Radiation-induced thyroid disease
Author(s):

Furio Pacini

, Rossella Elisei

, and Aldo Pinchera

DOI:
10.1093/med/9780199235292.003.3124
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date: 12 December 2017

Radiation is a mitogen which may cause damage to the cell DNA. When sufficiently severe, the damage may result in cell death. When the damage is less severe, the consequences to the cell depend upon the gene and cell system that are affected. The thyroid gland is particularly sensitive to the effects of radiation and the evidence that radiation may damage the thyroid gland is overwhelming. Both external and internal radiation have been associated with thyroid diseases (cancer and hypothyroidism, with or without thyroid autoimmunity) both in vitro and in vivo. External radiation to the thyroid was first recognized as a cause of thyroid carcinoma in the 1950s, when cases were found in individuals who had been given radiotherapy during childhood for an enlarged thymus (1). Since then, numerous studies have confirmed and extended this initial observation.

Radioactive isotopes are used in several situations in humans. They are given in very large doses in the treatment of thyroid cancer, when the dose used is intended to kill all thyroid cancer cells, and in smaller doses in the treatment of thyrotoxicosis, with the intent to produce hypothyroidism. In these conditions the radiation doses are sufficiently high to kill the cells, thus no unwanted secondary thyroid disease occurs. Low doses of iodine isotopes are also used as tracers for diagnostic evaluation of the thyroid gland. In this situation, no cell killing is observed and there is the theoretical possibility for thyroid cell damage. However, no convincing evidence of subsequent thyroid disorders has so far been provided.

Many animal studies have shown that radio-iodine is carcinogenic to the thyroid. Some of the earlier data suggested that internal radiation by radio-iodine was less effective than external radiation, but according to one more recent study in rats (2), the carcinogenic potential of 131I and X-rays appears to be the same. In both cases, the dose–response relationship seems to be linear, indicating that low doses also carry a risk. Iodine-131 is 20–30% as effective as external X- or χ‎-rays.

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