Thyroid hormone administration in irradiated patients

Endocrine Late Effects in Childhood Cancer Survivors

Endocrine complications are highly prevalent in childhood cancer survivors. Approximately 50% of survivors will experience at least one hormonal disorder over the course of their lives. Endocrine complications often are observed in survivors previously treated with radiation to the head, neck, or pelvis. We provide an overview the most common endocrine late effects seen in survivors, including hypothalamic-pituitary dysfunction, primary thyroid dysfunction, obesity, diabetes mellitus, metabolic syndrome, and decreased bone mineral density. Primary gonadal injury is discussed elsewhere in this series. Given a variable latency interval, a systematic approach where individuals are periodically screened on the basis of their risk factors can help to improve health outcomes by prompt diagnosis and treatment of evolving endocrinopathies. These recommendations must be revised in the future given changes and improvements in cancer treatment over time.

Endocrine intervention during irradiation does not prevent damage to the thyroid gland

Radiation to the head-neck region may damage the thyroid gland, leading to hypothyroidism or thyroid carcinoma. Outcomes of radiation protection by lowering plasma thyroid-stimulating hormone (TSH) have thus far been ambiguous. Our aim was to evaluate the radioprotective effect of inhibiting the thyroid gland's activity during x-radiation. For this purpose, of 80 5-week old Wistar rats, 64 received cervical irradiation with 15 Gy (single dose). During irradiation, endocrine intervention was done, using thyroxine (T(4)), T(4) plus iodine, or iodine alone compared to placebo. During the endocrine interventions and follow-up, TSH and T(4) concentrations were measured periodically. Histologic examination of thyroid, pituitary gland, or the hypothalamus and any suspect lymph nodes, lungs, and liver was performed after 6 and 54 weeks. It was found that during the endocrine intervention, plasma levels of TSH were lower in rats given T(4) and higher in rats given iodine. After 6 and 54 weeks, no significant reduction in hypothyroidism or thyroid carcinoma was found between the different groups of rats given any endocrine intervention or no intervention. In conclusion, the administration of T(4), iodine or the combination during x-irradiation does not protect against radiation-induced thyroid damage.

Endocrine late effects from multi-modality treatment of neuroblastoma

Thyroid dysfunction has been reported after 131I-MIBG-treatment for neuroblastoma. In this study, we have evaluated all endocrine functions from patients who were given multi-modality treatment including 131I-MIBG. Twenty-five neuroblastoma survivors who were off therapy for a median period of 6.0 years (range 1.3-11.1) were evaluated and their median age was 8.1 years (range 2.2-14.7). All patients had received 131I-MIBG, 16 chemotherapy, and 16 surgery. Fourteen patients (56%) had permanently elevated thyrotropin levels and 9 received thyroxine. Two patients had a small thyroid volume while 6 had thyroid nodules or cysts. Two boys showed hypergonadotropic hypogonadism. Growth was retarded in 39% of children. Mean Target Height Standard Deviation Score of patients with thyrotropin elevation was lower than those without (P=0.019). Children treated for neuroblastoma with 131I-MIBG, chemotherapy and surgery were seen to be at risk from developing irreversible thyroid function loss, thyroid nodules, hypergonadotropic hypogonadism, and growth retardation. We recommend that during follow-up of neuroblastoma children, special attention should be paid to their endocrine state.

Hypothyroidism after external radiotherapy for head and neck cancer

PURPOSE

To study the development of thyroid hypofunction in patients with head and neck cancers admitted for external radiotherapy.

METHODS AND MATERIALS

Between November 1990 and July 1996, thyroid function was measured in 264 consecutive patients, where the entire thyroid gland or part of it was included in the target volume. The time to development of hypothyroidism (HT) was calculated from the start of the radiotherapy.

RESULTS

The median follow-up period was 19 months. Seventeen patients (6%) developed elevated serum thyroid-stimulating hormone levels with depressed (free) thyroxine levels (i.e., clinical HT). Elevated serum thyroid-stimulating hormone level with normal (free) thyroxine levels (i.e., chemical HT) developed in 57 (22%). The median time to clinical HT was 15 months (range: 7 to 32). The median time to chemical HT was also 15 months (range: 2 to 28). The actuarial risk of developing clinical or chemical HT 3 years after treatment was 15 and 40%, respectively. The incidence of chemical HT was significantly higher (p = 0.041) when the whole thyroid was included in the target volume compared to patients where only part of the thyroid was irradiated. The same trend was seen as regards clinical HT (p = 0.063). For those 20 patients who underwent laryngectomy, there was an increased risk of both chemical and clinical HT (p = 0.011 and 0.019, respectively). Increasing age was associated with an increased risk of chemical HT (p = 0.001), but not of clinical HT (p = 0.553). Sex, tumor site, radiation dose, and combination of radiotherapy and chemotherapy were not significant factors for thyroid hypofunction.

CONCLUSION

Depressed thyroid function is common after external radiotherapy for cancers of the head and neck. Routine testing for possible thyroid hypofunction should be included in the follow-up procedures, even many years after end of radiotherapy.

Radiation and thyroid disease

External irradiation of the thyroid causes the subsequent development of thyroid malignancies at an approximate rate of 5 per rad per million people per year. There is no certain lower threshold, but possibly doses above 3000 rads are less effective. The tumours produced are primarily differentiated malignancies typical of non-irradiated patients, and the clinical course is similar. Most radiation-associated malignancies followed treatment given for enlarged thymic glands, enlargement of the tonsils or adenoids, and acne. Currently patients are seen with radiation-associated thyroid disease following treatment of malignant tumours in the neck. Diagnostic manoeuvres are similar to those used in non-irradiated individuals, but multinodularity is probably an indication for operation. Because of the high incidence of multicentricity, we prefer near-total thyroidectomy if cancer is found. Prophylactic thyroid hormone administration is of uncertain value in preventing the development of tumours. X-ray to the thyroid also can induce other histologic abnormalities, including a high incidence of adenomas and hypothyroidism, and is associated with an increased incidence of autoimmune thyroid disease and possibly the development of exophthalmos and Graves' disease. In contrast to the obvious effects of external irradiation, 131I diagnostic tests and treatments have not been associated with a clearly increased incidence of thyroid malignancy.