Radiation induced thyroid neoplasms 1920 to 1987: a vanishing problem?

Area of Science:

• Oncology
• Endocrinology
• Public Health

Background:

• Therapeutic radiation for benign conditions historically exposed millions of children, with an estimated 7% developing thyroid cancer after a significant latency period.
• Thyroid stimulating hormone, linked to radiation-induced hypothyroidism, is a suspected causative factor in animal models.
• This led to widespread, costly screening programs for high-risk individuals.

Purpose of the Study:

• To investigate the incidence of radiation-induced thyroid neoplasms (RITN) in light of declining pediatric irradiation rates over the past two decades.
• To evaluate the continued necessity of intensive screening protocols for patients with a history of head and neck irradiation.

Main Methods:

• Retrospective analysis of 227 patients with thyroid malignancies treated between 1974 and 1987.
• Identification of patients with a history of prior head and neck irradiation.
• Analysis of latency periods and thyroid function test results.

Main Results:

• Eleven percent (26 of 227) of patients with thyroid malignancies had a history of head and neck irradiation.
• The mean latency period from irradiation to diagnosis was 25.4 years.
• A significant decrease in RITN incidence was observed since 1970 compared to the 1940-1970 period.
• None of the irradiated patients presented with abnormal thyroid function tests.

Conclusions:

• The incidence of radiation-induced thyroid neoplasms appears to be decreasing, suggesting that extensive screening programs for high-risk populations may no longer be cost-effective or warranted.
• Routine thyroid hormone replacement therapy is not recommended for previously irradiated patients with chemically induced hypothyroidism.