In a study that began in April 2014 to check the impact of the 2011 Fukushima reactor meltdowns, 30 children have so far been diagnosed with thyroid cancer and 27 others are suspected of having the disease, according to a prefectural government panel.

Most of them were thought to be problem-free when their thyroid glands were checked during the first round of the study conducted over a three-year period through March 2014, the panel said Monday.

The first survey covered about 300,000 people who were under the age of 18 and living in Fukushima Prefecture when the nuclear disaster was triggered by the 3/11 earthquake and tsunami.

The number of children diagnosed with thyroid cancer in the second round was up from 16 as reported at the previous panel meeting in February.

Hokuto Hoshi, head of the panel and a senior member of the Fukushima Medical Association, maintained his earlier view of the correlation between the cancer figures and radiation, saying based on expertise acquired so far, it is “unlikely” that the disease was caused by radiation exposure.

Hoshi also said: “Concerns have been growing among Fukushima residents with the increase in the number of cancer patients. We’d like to further conduct an in-depth study.”

When the results of the first and the ongoing second round of the heath study are combined, the number of children diagnosed with thyroid cancer totals 131, and 41 others are suspected of having it.

According to Fukushima Medical University and other entities involved in the health checks, the 57 children in the second round of the survey either confirmed or suspected to have thyroid cancer were age 5 to 18 when the crisis started, and the sizes of their tumors ranged from 5.3 mm to 35.6 mm.

The examiners were able to estimate how much external radiation exposure 31 of those children had over the four months immediately after the catastrophe started, with the maximum being 2.1 millisieverts. Eleven of the children were exposed to less than 1 millisievert.