Beyond the issue of radiation dosage, the other issue here is the effectiveness of such machine in detecting hidden objects underneath one's clothing. This question came up recently upon the publication of a new study that showed (mainly via simulation), that depending on the type of material and where it is hidden on the body, such objects can missed in such a body scan. This new study was covered and reported here.
According to the report, the reasons contraband might not be detected are because of the X-ray exposure level produced by the scanner combined with how a substance such as plastic explosives are placed on a persons body. Those factors can prevent the material from being detected by the scanner, the study says. In addition, “because front and back views are obtained (in a scan), low Z (metal) materials can only be reliably detected if they are packed outside the sides of the body, or with hard edges, while high Z materials are well seen when placed in front or back of the body, but not the sides.”
You may read the actual paper at the link listed at the bottom of this blog entry. Of course, the TSA has a standard response to something like this:
Nonetheless, the TSA says, “Advanced imaging technology is a proven, highly-effective tool that safely detects both metallic and non-metallic items concealed on the body that could be used to threaten the security of airplanes.”
“TSA employs many layers of security that work collaboratively to form a system that gives us the best chance to detect and disrupt the evolving threats we face,” the agency’s statement says.
That is a non-statement that doesn't address the scientific study. A proper rebuttal would be to send a rebuttal paper to address the specific result of the paper. That's the only way the scientific result can be disputed, not by basically saying "it is effective because I said so". That might work in politics, but it doesn't work at all in science. And this is a scientific issue. The TSA should commission a study to either verify or dispute this work, not issue some bland, generic replies that really didn't say anything worthy.
 L. Kaufman and J.W. Carlson J. Transp. Secur. DOI 10.1007/s12198-010-0059-7 (a copy of the paper is available, at this moment, here).