Thank you for the opportunity to provide input.
Page 7, first bullet, Lines 205 - 209 and page 28, Section 5.1 (lines 1053 - 1074)
Drive through portal systems are available for use where a high throughput is required to avoid excessive delays going through a check point such as at a border crossing. When the dose to the driver is constrained to the same limit and with equivalent engineered safety interlocks used for screening members of the general public a drive through configurations might be justifiable. The situation described in the draft appears to be based on vehicle screening products which operate on stationary vehicles or which control the motion of the vehicles being screened. We agree that in either of those situations leaving the driver in place does not seem appropriate.
Page 8, lines 231 - 234, definition of backscatter detection system
Backscatter detection systems operate in the same x-ray energy range as medical diagnostic x-ray systems. While these are low energies compared to emissions from particle accelerators they are not generally thought of as low energy or soft x-rays. Backscatter systems conforming to ANSI 2009 have a minimum of 1 mm AL equivalent filtration which eliminates soft x-rays.
Page 8, lines 240 - 244, definition of transmission detection system
This definition may not be adequately specific. Backscatter detection systems emit sufficiently penetrating x-ray to produce a transmission image in addition to the backscatter image. The potential quality of a transmission image varies depending on the specific system parameters.
Page 13, section 3.1, lines 452 – 456 also page 22, section 4.4, lines 797 – 799
The draft document says, “Furthermore, the exposure will be predominately to the skin, because the energies used do not significantly penetrate the body.” And “For backscatter security systems, the exposure will be predominately to the skin, because the energies used do not significantly penetrate the body.”
These statements are inaccurate. Full-body security x-ray systems emit x-rays and filter out the lowest energy x-rays (soft x-rays) which might not penetrate significantly. X-rays emitted from full-body security x-ray systems currently available will penetrate the body and there will be some x-rays transmitted through the body. A portion of the exposure does result in internal organ doses. There are commercially available products which operate at higher peak tube potential and the exposure from those systems will not be predominately to the skin. We recommend the use of effective dose as the constraint for dose per screening and annual dose.