Nov. 05, 2010
Center for Study of Responsive Law
1530 P Street, NW
Washington, DC 20005
Dear Ms. Carroll:
Thank you for sharing your concerns in your letter dated July 29, 2010. Dr. Shuren asked me to respond to your concerns. In your letter to Dr. Shuren you asked, “In your capacity as the director of the FDA's CDRH, do you agree with the TSA statement that the X-ray scanners are safe for all air travelers? Do you believe that a more prudent approach for public health would be to convene an independent panel of experts to study the potential health impacts posed by these X-ray scanners?”
Several independent panels of experts have evaluated these products. The dose from one screening with a general-use full-body x-ray security screening system presents a miniscule risk to any individual being scanned. General-use x-ray security systems may be operated without limiting the number of individuals screened or, in most cases, the number of screenings an individual can have in a year.1 Any individual member of the general public would have to be screened more than 1,000 times in one year to exceed the annual dose limit set in the national safety standard2. The annual dose limit is based on the National Council of Radiation Protection and Measurements3 (NCRP) recommendations for the annual effective dose limit for individual members of the general public4,5. NCRP’s dose limitation recommendations for the general public were made with the understanding that the general public includes special populations, such as children, who are more sensitive to radiation than the rest of the population.
Regarding the sources of information you mention in your letter:
- The University of California – San Francisco letter has been answered jointly by the Food and Drug Administration (FDA) and the Transportation Security Administration (TSA). [Response to University of California - San Francisco Regarding Their Letter of Concern, October 12, 2010]
- In his March 17, 2010 presentation, in addition to the remarks you attributed to him, Dr. Brenner also said, “The individual risks associated with x-ray backscatter scanners are probably extremely small.” Furthermore, the NCRP’s report on collective dose6 stated, “The summation of trivial average risks over very large populations or time periods into a single value produces a distorted image of risk, completely out of perspective with risks accepted every day, both voluntarily and involuntarily.” Dr. Brenner seems to be doing just that in the remarks you cited. We understand that NCRP commentaries are reviewed by all program area committee7 members as well as other subject-area experts and those comments are resolved before a vote is conducted. At least 10 of the 13 NCRP board members must approve a commentary before it is issued as an NCRP8 publication. Dr. Brenner had many distinguished colleagues that participated in the review and vote to approve NCRP Commentary No. 16 before it was published in 2003. NCRP posted a press release regarding Commentary No. 16 on May 26, 20109.
Under the law CDRH is directed to protect the public health and safety from electronic product radiation. Public health is protected when general-use x-ray security systems that comply with the applicable national radiation safety standard10 are used in accordance with the requirements of use in that standard. Using a general-use system as just described will result in effective doses to individuals below the annual dose limits recommended by NCRP for the general public. In fact the dose limit per screening is far below the negligible individual dose set by NCRP11. If you have any further questions or concerns, please contact Daniel Kassiday of my staff.
John L. McCrohan
Deputy Director for Technical and
Office of Communication, Education, and
Center for Devices and Radiological Health
Food and Drug Administration
1NCRP Commentary No. 16 Screening of Humans for Security Purposes Using Ionizing Radiation Scanning Systems. (2003)
2ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation. This standard limits the dose per screening to 0.25 µSv (25 µrem) reference effective dose. The annual dose limit is 250 µSv (25,000 µrem) over a 12 month period.
3NCRP was founded in 1964 by the U.S. Congress to “cooperate with the International Commission on Radiological Protection, the Federal Radiation Council, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units and measurements and with radiation protection.”
4NCRP report no. 116 Limitation of exposure to ionizing radiation (1993); pages 45-47, 56;
5NCRP Statement 10, Recent Applications of the NCRP Public Dose Limit Recommendation for Ionizing Radiation (2004)
6NCRP Report No. 121 Principles and Application of Collective Dose in Radiation Protection (1995), page 58
7NCRP website current program, http://www.ncrponline.org/Current_Prog/Current_Program.html
8NCRP website, http://www.ncrponline.org/Members/Members.html; There are 100 voting members that are elected to six-year terms with the terms of approximately 14 members expiring each year. They are selected on the basis of their scientific expertise. The current board members are found at http://www.ncrponline.org/Members/Officers-BOD.html.
10ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation.
11NCRP report no. 116 Limitation of exposure to ionizing radiation (1993); pages 51 - 52