Thyroid Ultrasound Examination
Outline of the Thyroid Ultrasound Examination (TUE)
Purpose
One of the health problems caused by the Chornobyl (Chernobyl) nuclear power plant accident was thyroid cancer in children caused by internal exposure from radioactive iodine. Although the exposure level in Fukushima Prefecture caused by the nuclear accident in 2011 is considered to be much lower than in Chornobyl, we launched a Thyroid Ultrasound Examination program to address long-term health concerns by understanding the condition of children's thyroid glands.
Eligible persons and Progress of the TUE
| Survey category | Implementation Period | Eligible persons |
|---|---|---|
| Preliminary Baseline Survey (the first-round survey) Aiming to check the baseline condition of participants thyroid glands |
From October 2011 through March 2014 | Fukushima Prefecture residents who were born between April 2, 1992 and April 1, 2011, i.e., in the range of 0 to 18 years old as of March 11, 2011. |
| First Full-Scale Survey (the second-round survey) For comparison with the Preliminary Baseline Survey |
From April 2014 through March 2016 | Fukushima Prefecture residents who were born between April 2, 1992 and April 1, 2012 |
| Second Full-Scale Survey (the third-round survey) and after | Eligible participants are invited to receive thyroid examinations every two years until the age of 20, and then every five years thereafter at the age of 25, 30, and so on. (The interval before the Age 25 Survey should not be more than 5 years.) | |
Due to the COVID-19 pandemic, the Fourth Full-Scale Survey (the fifth-round survey) will be conducted over 3 years from 2020 through 2022.
Method
| Primary examination | Ultrasonography |
|---|---|
| Confirmatory examination | Advanced ultrasonography, urine, and blood test Fine-needle aspiration cytology (FNAC) is conducted, if needed. |
Diagnostic criteria of Primary Examination
| Grade | Criteria | Next step | |
|---|---|---|---|
| A | No abnormal findings | ||
| A1 | No cysts or nodules | Undergo another primary examination 2 (or 5) years later | |
| A2 | Nodule(s) with a diameter of 5.0 mm or less* or cyst(s) with a diameter of 20.0 mm or less | ||
| B | Nodule(s) with a diameter of 5.1 mm or more or cyst(s) with a diameter of 20.1 mm or more | Undergo a confirmatory examination | |
| C | Cases considered as requiring detailed examination** | Undergo a confirmatory examination immediately | |
* Some nodules that are 5.0 mm or less in diameter may be judged as Grade B based on ultrasound images.
** Cases in which thyroid nodules are suspected to have infiltrated non-thyroidal tissues or a large lymph node metastasis (Large N) of 3 cm or more is observed
Implementation criteria of FNAC in Confirmatory Examination
Nodules are treated in accordance with the Guidebook on Thyroid Ultrasound Diagnosis (edited by the Japan Association of Breast and Thyroid Sonology).
* Nodule without cystic characteristics
** FNAC: Fine-needle aspiration cytology
Implementation status
Preliminary Baseline Survey (the first-round survey) As of March 31, 2018
- Implementation period: October 2011 - March 2014
- Eligible persons: 367,637
- Primary examination participants: 300,472
- Grade A1 or A2 cases: 298,178
- Grade B cases: 2,293
- Confirmatory examination participants: 2,130
- Participants with finalized results: 2,091
- FNAC participants: 547
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 116 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
First Full-Scale Survey (the second-round survey) As of March 31, 2021
- Implementation period: April 2014 - March 2016
- Eligible persons: 381,237
- Primary examination participants: 270,552
- Grade A1 or A2 cases: 268,322
- Grade B cases: 2,230
- Confirmatory examination participants: 1,877
- Participants with finalized results: 1,834
- FNAC participants: 207
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 71 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
Second Full-Scale Survey (the third-round survey) As of March 31, 2021
- Implementation period: May 2016 - March 2018
- Eligible persons: 336,667
- Primary examination participants: 217,922
- Grade A1 or A2 cases: 216,420
- Grade B cases: 1,502
- Confirmatory examination participants: 1,104
- Participants with finalized results: 1,068
- FNAC participants: 79
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 31 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
Third Full-Scale Survey (the fourth-round survey) As of June 30, 2022
- Implementation period: April 2018 - March 2020
- Eligible persons: 294,228
- Primary examination participants: 183,410
- Grade A1 or A2 cases: 182,016
- Grade B cases: 1,394
- Confirmatory examination participants: 1,036
- Participants with finalized results: 1,016
- FNAC participants: 91
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 39 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
Fourth Full-Scall Survey (the fifth-round survey) As of December 31, 2024
- Implementation period: April 2020 - March 2023
- Eligible persons: 252,936
- Primary examination participants: 113,959
- Grade A1 or A2 cases: 112,613
- Grade B cases: 1,346
- Confirmatory examination participants: 1,116
- Participants with finalized results: 1,101
- FNAC participants: 101
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 50 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
Fifth Full-Scall Survey (the sixth-round survey) As of March 31, 2025
- Implementation period: April 2023 - March 2025
- Eligible persons: 211,929
- Primary examination participants: 68,921
- Those who completed the processes of preliminary examination and with finalized results: 68,439
- Grade A1 or A2 cases: 67,469
- Grade B cases: 970
- Confirmatory examination participants: 670
- Participants with finalized results: 608
- FNAC participants: 34
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 15 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
Survey for Age 25 As of March 31, 2025
- Implementation period: May 2017 -
- Eligible persons*: 169,956
- Primary examination participants: 13,840
- Those who completed the processes of preliminary examination and with finalized results: 13,775
- Grade A1 or A2 cases: 13,003
- Grade B cases: 772
- Confirmatory examination participants: 604
- Participants with finalized results: 592
- FNAC participants: 54
Results
Results of Primary Examination
Results of Confirmatory Examination
Age distribution of 26 persons diagnosed through cytology, etc. as having nodule that is malignant or suspected to be malignant
* Those who become 25 during each fiscal year (those born between FY1992 and FY1999)
Survey for Age 30 As of March 31, 2025
- Implementation period: April 2022 -
- Eligible persons*: 66,542
- Primary examination participants: 4,193
- Those who completed the processes of preliminary examination and with finalized results: 4,054
- Grade A1 or A2 cases: 3,699
- Grade B cases: 355
- Confirmatory examination participants: 229
- Participants with finalized results: 218
- FNAC participants: 23
Results
Results of Primary Examination
Results of Confirmatory Examination
* Those who become 30 during each fiscal year (those born between FY1992 and FY1994)
Evaluation of Results
Evaluation of Findings from the Preliminary Baseline Survey (first round) through the Full-Scale Survey (fifth Round)
"No association between thyroid cancer and radiation exposure was identified in the Preliminary Baseline Survey through the fifth-round Full-Scale Survey."
"Given that more multifaceted and multilayered analyses became possible compared with what was done through the fourth-round Survey, the conclusions can now be stated with even greater confidence."
Main reasons for this evaluation
- Concerning the relationship between radiation dose and the detection rate of malignancy or suspicion of malignancy from the Preliminary Baseline Survey through the fifth-round Full-Scale Survey, no consistent dose–response relationship was observed.
Evaluation of Results from the Preliminary Baseline Survey (first round) through the Full-Scale Survey (fourth round)
"No association between thyroid cancer and radiation exposure was identified in the Preliminary Baseline Survey through the fourth-round Full-Scale Survey."
Main reasons for this evaluation
- Concerning the relationship between radiation dose and the detection rate of malignancy or suspicion of malignancy, no consistent dose–response relationship was observed.
Source: Extracted from Material 3-2, the 49th Meeting of the Fukushima Prefectural Oversight Committee for the Fukushima Health Management Survey, November 2023.
Evaluation of the Results from the Second-Round Full-Scale Survey
"At this point, no association has been identified between radiation exposure and thyroid cancers detected in the second-round Full-Scale Survey."
Main reasons for this evaluation
- In the analysis of the relationship between the estimated thyroid absorbed dose calculated by UNSCEAR* and the detection rate of thyroid cancer, no consistent relationship (dose–response relationship), such as an increase in detection rate with higher doses, was observed.
* UNSCEAR: United Nations Scientific Committee on the Effects of Atomic Radiation
Source: Extracted from documents 1-1 and 1-2 from the 36th Meeting of the Fukushima Prefectural Oversight Committee for the Fukushima Health Management Survey, October 2019.
Evaluation of the Results from the Preliminary Baseline Survey
"Concerning thyroid cancers detected to date, comprehensive analysis indicates that they are unlikely to be attributable to the effects of radiation."
Main reasons for this evaluation
- Exposure doses due to the accident at Fukushima Daiichi were generally lower than those of the Chernobyl accident.
- The period of time (one to four years) from exposure is too short for the usual evolution of radiation-related thyroid cancers.
- Cancers have not been detected in those who were age five or younger at the time of the accident.
- There are no substantial regional differences in detection rates.
Source: Extracted from the Interim Summary of the Fukushima Prefectural Oversight Committee for the Fukushima Health Management Survey, March 2016.