Thyroid Cancer Following Childhood Low-Dose Radiation Exposure: A Pooled Analysis of Nine Cohorts

J Clin Endocrinol Metab. 2017 Jul 1;102(7):2575-2583. doi: 10.1210/jc.2016-3529.


Context: The increased use of diagnostic and therapeutic procedures that involve radiation raises concerns about radiation effects, particularly in children and the radiosensitive thyroid gland.

Objectives: Evaluation of relative risk (RR) trends for thyroid radiation doses <0.2 gray (Gy); evidence of a threshold dose; and possible modifiers of the dose-response, e.g., sex, age at exposure, time since exposure.

Design and setting: Pooled data from nine cohort studies of childhood external radiation exposure and thyroid cancer with individualized dose estimates, ≥1000 irradiated subjects or ≥10 thyroid cancer cases, with data limited to individuals receiving doses <0.2 Gy.

Participants: Cohorts included the following: childhood cancer survivors (n = 2); children treated for benign diseases (n = 6); and children who survived the atomic bombings in Japan (n = 1). There were 252 cases and 2,588,559 person-years in irradiated individuals and 142 cases and 1,865,957 person-years in nonirradiated individuals.

Intervention: There were no interventions.

Main outcome measure: Incident thyroid cancers.

Results: For both <0.2 and <0.1 Gy, RRs increased with thyroid dose (P < 0.01), without significant departure from linearity (P = 0.77 and P = 0.66, respectively). Estimates of threshold dose ranged from 0.0 to 0.03 Gy, with an upper 95% confidence bound of 0.04 Gy. The increasing dose-response trend persisted >45 years after exposure, was greater at younger age at exposure and younger attained age, and was similar by sex and number of treatments.

Conclusions: Our analyses reaffirmed linearity of the dose response as the most plausible relationship for "as low as reasonably achievable" assessments for pediatric low-dose radiation-associated thyroid cancer risk.

Publication types

  • Evaluation Study

MeSH terms

  • Adolescent
  • Age Factors
  • Child
  • Child, Preschool
  • Cohort Studies
  • Dose-Response Relationship, Radiation
  • Female
  • Humans
  • Male
  • Neoplasms, Radiation-Induced / diagnosis*
  • Neoplasms, Radiation-Induced / epidemiology*
  • Prognosis
  • Radiation Exposure / adverse effects*
  • Risk Assessment
  • Sex Factors
  • Survival Rate
  • Thyroid Neoplasms / epidemiology*
  • Thyroid Neoplasms / etiology*