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Thyroid tumors following thymus irradiation.
Journal of the National Cancer Institute
|June 1, 1985
Summary
Infant X-ray therapy for enlarged thymuses significantly increased thyroid cancer and benign tumor risk, persisting for over 40 years. Radiation exposure elevated risks substantially, particularly in females.
Area of Science:
- Radiation Oncology
- Epidemiology
- Endocrinology
Background:
- Infant thymic irradiation was a historical medical practice.
- Long-term health effects of childhood radiation exposure require ongoing study.
Purpose of the Study:
- To assess the long-term incidence of thyroid tumors after infant X-ray treatment for thymic enlargement.
- To evaluate the relationship between radiation dose and thyroid tumor risk.
Main Methods:
- A cohort study followed 2,650 individuals treated with X-rays and 4,800 sibling controls for an average of 29 years.
- Mail questionnaires were used for follow-up, achieving an 88% response rate.
- Thyroid radiation doses ranged from 5 to over 1,000 rad.
Main Results:
- The irradiated group showed significantly higher rates of thyroid cancer (30 vs. 1) and benign adenomas (59 vs. 8) compared to controls.
- Relative risks were approximately 45 for thyroid cancer and 15 for benign adenomas.
- Excess risk was observed for at least 40 years post-irradiation, with higher risks in females.
Conclusions:
- Infant thymic irradiation is a significant risk factor for both malignant and benign thyroid tumors.
- The risk of thyroid tumors persists for decades after exposure.
- Dose-response relationships and sex-specific risks were identified.