Scientists still can’t agree over whether the dose of radiation delivered by X-ray backscatter machines is significantly higher than the government says. This is despite months of public debate between the White House, the U.S. Food and Drug Administration, and independent scientists.

In April, four scientists at the University of California, San Francisco, wrote a public letter to the White House warning that the government may have underestimated the dosage of ionizing radiation delivered to a person’s skin from a backscatter machine by one or two orders of magnitude.