To be selected for the basic survey, individuals had to be either a registered resident of Fukushima Prefecture during the period of 11 March to 1 July (including those evacuated or transferred to residence registration in another prefecture); a resident of Fukushima Prefecture who was registered in another prefecture during the period of 11 March to 1 July; a resident of another prefecture who commuted to Fukushima Prefecture during the period of 11 March to 1 July; or a resident of another prefecture who temporarily stayed in Fukushima Prefecture during the period of 11 March to 25 March. David Brenner, director of the Center for Radiological Research at Columbia University, adds that the study makes no effort to trace the exposure of patients.
– For four years, nearly all kids living in Japan's Fukushima prefecture have received ultrasounds to gauge the effects of the nuclear disaster there in March 2011. Now a research team says the alarming results are in: Children living near the nuclear plant have thyroid cancer rates that are 20 to 50 times higher than those found in children elsewhere, the AP reports. Per a study being published in the November issue of Epidemiology, of the 370,000 or so kids 18 and under in the Fukushima region who received thyroid exams since the disaster, 137 of them have suspected or confirmed cases of thyroid cancer, a number that rose by 25 from last year, the AP notes. "This is more than expected and emerging faster than expected," lead author Toshihide Tsuda tells the AP. Thyroid cancer cases in children outside the prefecture are estimated to be around one or two out of every million kids per year. Children's thyroids are particularly vulnerable to cancer—radioactive iodine released during nuclear meltdowns can cause it—because they're growing so quickly, NPR notes. Tsuda and his team claim that the numbers aren't simply the result of a "screening effect"—in which more routine checkups like the ones in Fukushima have simply found tumors earlier and more often—as the Japanese government has suggested. Other experts, however, aren't so sure how accurate Tsuda's study is and note the complexity of studying such an issue. The director for Columbia University's Center for Radiological Research, for example, tells NPR that just tying certain geographic areas to higher cancer rates doesn't prove anything without looking at individual radiation exposure, a claim that's echoed in a report by the World Health Organization.(The residents of the Japanese town of Nahara are finally allowed back—but many don't want to go.)