Article review date
August 2024
Article publication date
July 2024
Summary
This meta-analysis of cohort studiesevaluated the current evidence on the association between occupational exposure to ionising radiation and risk of thyroid cancer. A total of six studies published between 2006 and 2021, which had a total of 420,543 participants, 6,322 cases and a mean follow-up period of 23 years, were included in the analysis. Data on radiation exposure levels (in Gray (Gy) or mSv) were available for almost all studies; whereas the information on thyroid cancer was largely based on clinical (i.e., histopathological) diagnosis except two studies which had self-reported diagnosis. The associations between ionising radiation exposure (i.e., personal or estimated thyroid doses) and thyroid cancer were examined in terms of risk ratio (RR) with 95% confidence interval (CI). Quality assessment of the included studies was also conducted according to the Newcastle-Ottawa Scale (NOS). The results showed that the five included studies had reported the occupational radiation exposure doses (individual doses or estimated thyroid doses), which ranged from 10.4 to 500 mGy or <0.20 to 7.2 mSv. Occupational radiation exposure was associated with the risk of thyroid cancer (RR=1.61, 95% CI: 1.27‑2.04). Sex-wise sensitivity analysis further showed that males with the history of occupational radiation exposure (compared to females) tend to be at a slightly higher risk of developing thyroid cancer (RR=1.74, 95% CI: 1.61‑1.87 vs. RR=1.30, 95% CI: 1.15‑1.48). Overall, the evidence from the meta-analysis indicates that occupational exposure to ionising radiation was associated with the risk of thyroid cancer.
Published in
Oncology Letters
Link to study
Occupational radiation exposure and risk of thyroid cancer: A meta‑analysis of cohort studies
Commentary by ARPANSA
The meta-analysis provides the latest risk estimate of thyroid cancer risk among occupationally exposed human populations to ionising radiation. These findings are consistent with those of a previous pooled analysis of seven studies (Ron et al, 1995); however, contrary to those reported in a previous case-control study (Fincham et al, 2000). Similarly, the findings that males tend to have higher risk of developing thyroid cancer is contrary to the findings of a latest study (Khoramian et al., 2024) reporting higher thyroid cancer risk among females (compared to males) undergoing head CT imaging. No similar data are available to compare these findings in the Australian context. A key limitation of the current meta-analysis is that the available data in the included studies did not allow a detailed subgroup analysis of the occupation type, dose‑effect and time‑effect relationship. Further, the meta-analysis doesn't provide any information on the exposure contrast, so it is difficult to determine whether the exposure metrics that were used in the meta-analysis from the different studies were appropriate. Though quality of a majority of the included studies in the meta-analysis was high, they had a considerable heterogeneity (I2=84%) resulting in between-study variance.
In Australia, The Code for Radiation Protection in Planned Exposure Situations sets out the requirements for the protection of occupationally exposed persons in all planned exposure situations. All Australian jurisdictions have uniform annual limits (20 mSv) for occupational exposure to ionising radiation. In addition to the dose limits, optimisation of radiation protection and safety involves practising ‘as low as reasonably achievable (ALARA) considering economic and societal factors.
