Dozens of workers at the Fukushima nuclear plant have been found to have received high doses of radiation to their thyroid glands, according to data submitted to the World Health Organization.

Tests for 522 workers found doses greater than 100 millisieverts on the thyroid glands of 178 individuals doing recovery work at the crippled plant. Those workers are at risk of thyroid cancer, the report from Tokyo Electric Power Co. revealed.

The highest recorded dose was 11,800 millisieverts, found in the thyroid gland of an individual aged between 30 to 39 years old, while two other workers had an exposure of more than 10,000 millisieverts to their thyroid glands, Tepco said. The levels are considered to be a lethal dose when received as full-body exposure but that dose on thyroid glands can have limited impact on that organ, the WHO said.

The individual whose thyroid gland received 11,800 millisieverts had a whole-body radiation dose of 678.8 millisieverts. He had not developed symptoms of ill-health and remains employed in a non-nuclear job, the report said.

Reports on radiation doses found on workers remain shrouded, with Tepco refusing to release data directly to individuals involved, Asahi Shimbun reports.

The company said it was monitoring whole-body radiation doses instead because there are no dose limits for thyroid gland data. Tepco also said it plans to offer free thyroid gland ultrasound tests to workers with 50 millisieverts or higher whole-body radiation doses.