Thyroid cancer in local children and adolescents following the Fukushima nuclear disaster was probably caused by radiation released in the accident, four researchers said Tuesday in a report.

Annual thyroid cancer incidence rates in Fukushima Prefecture from March 2011 through late last year were 20 to 50 times the national level, said a team led by Toshihide Tsuda, professor of environmental epidemiology at Okayama University. The findings were published in the electronic edition of the journal of the International Society for Environmental Epidemiology.

The finding, based on screenings of around 370,000 Fukushima residents aged 18 or younger at the time of the accident, “is unlikely to be explained by a screening surge,” the researchers said, pointing to radiation exposure as a factor behind the rise in thyroid cancer cases.

But their conclusion is refuted by other epidemiology experts, including Shoichiro Tsugane of the National Cancer Center, who said the results are premature.

“Unless radiation exposure data are checked, any specific relationship between a cancer incidence and radiation cannot be identified,” said Tsugane, director of the Research Center for Cancer Prevention and Screening. He said there is a global trend of over-diagnosis of thyroid cancer.

As of late August, the Fukushima Prefecture Government identified 104 thyroid cancer cases in the prefecture.

But the prefectural government and many experts have doubted whether these cases are related to the nuclear disaster, as the amount of radioactive iodine released during the crisis was smaller than that following the 1986 Chernobyl nuclear accident.