A 11 year-old-girl might have been exposed to a high dose of radiation in 2011 due to the Fukushima Daiichi nuclear accident.
The National Institute of Radiological Sciences says it learned of the possibility at a meeting two months after the nuclear accident.
But the institute says it didn't disclose the story because the data was not trustworthy. It adds the meeting was just an opportunity to share information among its officials and that it didn't get a request to do anything from the central government.
The girl was checked for radiation exposure immediately after the accident. It's reported she was playing outside on the day it happened.
An official estimated at that time she received the equivalent dose of about 100 millisieverts in her thyroid gland.
Equivalent dose is an indicator used to gauge how much radiation a specific organ has been exposed to.
People are said to face an increased risk of thyroid cancer after absorbing radioactive iodine released in a nuclear accident.
Guidelines established by authorities prior to the accident said that anyone receiving 100 millisieverts or more of radiation should be given iodine tablets to block the absorption by the thyroid.
But a lot of the tablets were never administered, and the scale of people's radiation exposure is not yet known due to a lack of large-scale studies.
The government surveyed 1,080 children living within 30 kilometers of the Fukushima Daiichi nuclear plant immediately after the accident.
The highest reading for thyroid radiation exposure was reported to be 35 millisieverts.