The head of the Transportation Security Administration has backed off a public commitment to conduct a new independent study of X-ray body scanners used at airport security lanes around the country.

Earlier this month, a ProPublica/PBS NewsHour investigation found that the TSA had glossed over research that the X-ray scanners could lead to a small number of cancer cases. The scanners emit low levels of ionizing radiation, which has been shown to damage DNA. In addition, several safety reviewers who initially advised the government on the scanners said they had concerns about the machines being used, as they are today, on millions of airline passengers.

At a Senate hearing after the story ran, TSA Administrator John Pistole agreed to a request by Sen. Susan Collins, R-Maine, to conduct a new independent study of the health effects of the X-ray scanners, also known as backscatters.

But at a Senate hearing of a different committee last week, Pistole said he had since received a draft report on the machines by the Department of Homeland Security’s inspector general, or IG, that might render the independent study unnecessary. . .

“I hope the Obama administration is not backing away from an independent study of the health effects of these radiation-emitting machines,” Collins said in a statement to ProPublica. “What I asked for — and what the administrator committed to — was an independent study on the health effects of [the] machines, not just a study on whether TSA is doing an adequate job of inspecting, maintaining and operating” them.