Monday, November 22, 2010

Review of the TSA X-ray backscatter body scanner safety report: hide your kids, hide your wife

I am a biochemist working in the field of biophysics. Specifically, the lab I work in (as well as many others) has spent the better part of the last decade working on the molecular mechanism of how mutations in the breast cancer susceptibility gene, BRCA2, result in cancer. The result of that work is that we now better understand that people who have a deficient BRCA2 gene are hypersensitive to DNA damage, which can be caused by a number of factors including: UV exposure, oxidative stress, improper chromosomal replication and segregation, and radiation exposure. The image below shows what happens to a chromosome of a normal cell when it is exposed to radiation. It most cases, this damage is repaired; however, at high doses or when there is a genetic defect, the cells either die or become cancerous.

Quite some time ago, I posted a short educational video that describes how BRCA1 and BRCA2 mutations cause cancer. In short, when a person who has a mutation in one of these genes is exposed to environmental factors that cause DNA damage, they simply don't repair the damage with the same efficiency as the general population. Over the course of their lifetime, the incremental exposures to relative small and seemingly safe doses of ionizing radiation (which is everything from UV light to X-rays to gamma radiation) statistically accumulate damage (or the effects of damage and improper repair) until the probability of developing cancer becomes almost certain. This is because BRCA1 and BRCA2 are both part of a molecular process that is very similar to the spell-check on your word processor (in oncology parlance, these genes are known as caretakers of the genome for this specific reason). When these genes don't work, mutations accumulate faster and eventually results in cancer.

Its because of my interest in this aspect of cancer biology that I felt compelled to review the safety reports released on the TSA website here. However, my interest is not only professional, but also personal. My grandmother died of breast cancer in 2005 after being in remission for 20+ years. While she was never tested for either BRCA1 or BRCA2, her family history indicates that there is a strong probability of one of these mutations running in my family. Including my grandmother, at least four of her siblings developed cancer: two died of breast cancer, one developed a rare form of leukemia and another died of skin cancer. All of her female siblings had cancer, and its noteworthy that her mother died of a very young age (maybe 30's or early 40's) of an unknown (to me) cause. For these reasons, I fear that inadequate safety evaluation of these machines could unduly expose my family (and myself) to levels of radiation that might be harmful should this high familial cancer rate in fact be hereditary.

Last spring, a group of scientists at the University of California at San Francisco (UCSF) including John Sedat Ph.D., David Agard Ph.D., Robert Stroud, Ph.D. and Marc Shuman, M.D. sent a letter of concern to the TSA regarding the implementation of their 'Advanced Imaging Technology', or body scanners as a routine method of security screening in US airports. Of specific concern is the scanner that uses X-ray back-scattering. In the letter they raise some interesting points, which I've quoted below:
  • "Our overriding concern is the extent to which the safety of this scanning device has been adequately demonstrated. This can only be determined by a meeting of an impartial panel of experts that would include medical physicists and radiation biologists at which all of the available relevant data is reviewed."
  • "The X-ray dose from these devices has often been compared in the media to the cosmic ray exposure inherent to airplane travel or that of a chest X-ray. However, this comparison is very misleading: both the air travel cosmic ray exposure and chest X-rays have much higher X-ray energies and the health consequences are appropriately understood in terms of the whole body volume dose. In contrast, these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/vol, possibly by one to two orders of magnitude, the real dose to the skin is now high."
  • "In addition, it appears that real independent safety data do not exist."
  • "There is good reason to believe that these scanners will increase the risk of cancer to children and other vulnerable populations. We are unanimous in believing that the potential health consequences need to be rigorously studied before these scanners are adopted."
In order to really understand these concerns, I think its important to consider the type of radiation used in these scanners, which the TSA has described as 'soft' and 'safe'. First, we need to clarify the definition of 'soft' vs 'hard' X-rays. The TSA has been stating that the X-rays used in the back scatter machines use 'soft' X-rays, which are defined as radiation between 0.12-12 keV (or kilo electron volts) and are generally stopped, or absorbed, by soft tissue or low density matter. 'Hard' X-rays are between 12-128 keV and are absorbed by dense matter like bone. According to the TSA safety documents, AIT uses an 50 keV source that emits a broad spectra (see adjacent graph from here). Essentially, this means that the X-ray source used in the Rapiscan system is the same as those used for mammograms and some dental X-rays, and uses BOTH 'soft' and 'hard' X-rays. Its very disturbing that the TSA has been misleading on this point. Here is the real catch: the softer the X-ray, the more its absorbed by the body, and the higher the biologically relevant dose! This means, that this radiation is potentially worse than an a higher energy medical chest X-ray.

With that being said, because the scanners have both a radiation source AND a detector in the front AND back of the person in the scanner, it is actually possible for the hardware to conduct a classic, through-the-body X-ray. The TSA claims that the machines are not currently being used in that way; however, based on the limited engineering schematics released in the safety documents, they could be certainly be easily reconfigured to do so by altering the aluminum-plate (or equivalent) filter or by changing the software. So the hardware has the capability to output quite high doses of radiation, however a biological dose is a function of the time of exposure as well as the proximity to the source and the power of the power of the source. Unfortunately, it is difficult to determine which zones in the scanner are 'hottest' because that information is masked in the document. An excerpt of the safety evaluation from Johns Hopkins is shown below to give you sense of how much other information is being withheld. Ultimately my point is this: even though the dose may actually be low, these machines are capable of much higher radiation output through device failure or both unauthorized or authorized reconfiguration of either hardware or software.


Which brings me to how the scanner works. Essentially, it appears that an X-ray beam is rastered across the body, which highlights the importance of one of the specific concerns raised by the UCSF scientists... what happens if the machine fails, or gets stuck, during a raster. How much radiation would a person's eye, hand, testicle, stomach, etc be exposed to during such a failure. What is the failure rate of these machines? What is the failure rate in an operational environment? Who services the machine? What is the decay rate of the filter? What is the decay rate of the shielding material? What is the variability in the power of the X-ray source during the manufacturing process? This last question may seem trivial; however, the Johns Hopkins Applied Physics Laboratory noted significant differences in their test models, which were supposed to be precisely up to spec. Its also interesting to note that the Johns Hopkins Applied Physics Laboratory criticized other reports from NIST (the National Institute of Standards and Technology) and a group called Medical and Health Physics Consulting for testing the machine while one of the two X-ray sources was disabled (citations at the bottom of the page).

These questions have not been answered to any satisfaction and the UCSF scientists, all esteemed in their fields and members of the National Academy of Sciences have been dismissed based on a couple of reports seemingly hastily put together by mid-level government technicians or engineers. The documents that I have reviewed thus far either have NO AUTHOR CREDITS or are NOT authored by anyone with either a Ph.D. or a M.D., raising serious concerns of the extent of the expertise of the individuals and organizations evaluating these machines with respect to biological safety. Yet, the FDA and TSA continue to dismiss some of the most talented scientists in the country...

With respect to errors in the safety reports and/or misleading information about them, the statement that one scan is equivalent to 2-3 minutes of your flight is VERY misleading. Most cosmic radiation is composed of high energy particles that passes right through our body and the plane itself without being absorbed. The spectrum that is dangerous is known as ionizing radiation and most of that is absorbed by the hull of the airplane. So relating non-absorbing cosmic radiation to tissue absorbing man-made radiation is simply misleading and wrong. Of course these are related and there is over-lap, but we have to compare apples to apples.

Furthermore, when making this comparison, the TSA and FDA are calculating that the dose is absorbed throughout the body. According the simulations performed by NIST, the relative absorption of the radiation is ~20-35-fold higher in the skin, breast, testes and thymus than the brain, or 7-12-fold higher than bone marrow. So a total body dose is misleading, because there is differential absorption in some tissues. Of particular concern is radiation exposure to the testes, which could result in infertility or birth defects, and breasts for women who might carry a BRCA1 or BRCA2 mutation. Even more alarming is that because the radiation energy is the same for all adults, children or infants, the relative absorbed dose is twice as high for small children and infants because they have a smaller body mass (both total and tissue specific) to distribute the dose. Alarmingly, the radiation dose to an infant's testes and skeleton is 60-fold higher than the absorbed dose to an adult brain!

There also appears to be unit conversion error in the Appendix of the report, which was recently cited by the FDA in response to the UCSF scientist's letter of concern, which might mean that the relative skin dose is 1000-fold higher than the report indicates (pg Appendix B, pg ii, units of microSv are used in an example calculation, when it appears that units of milliSv should have been used). I attempted to contact the author, Frank Cerra, to query whether this was a computational mistake or an unexplained conversion; however, none of his web-published email addresses are valid and there was no answer by phone. I cannot rule out that a conversion factor was used that was not described in the methods, and would welcome confirmation or rebuttal of this observation.

Finally, I would like to comment on the safety of the TSA officers (TSO) who will be operating these machines, and will be constant 'bystanders' with respect to the radiation exposure. The range of exposure estimates is a function of where an officer stands during their duty, what percentage of that duty is spent in the same location and how often the machine is running. A TSO could be exposed to as much as 86-1408 mrem per year (assuming 8 hours per day, 40 hours a week, 50 weeks per year and between 30-100% duty and 25-100% occupancy, as defined by the Johns Hopkins report), which is between 86%-1410% of the safe exposure of 100 mrem. At the high end, if for example a TSO is standing at the entrance of the scanner when it is running at maximum capacity, then that officer could hit their radiation exposure limit in as few as 20 working days (assuming an 8 hour shift). While we may not be very happy with our TSOs at the moment as the face of these policies, we need to keep in mind that they really should be wearing radiation badges in order to know their specific exposure (especially for those officers who may also have to receive radiation exposure for medical reasons).

As far as I'm concerned, the jury is still out on whether these machines are safe or even could be made safe for this application. Until then, I suggest keeping your family out of these machines and as vile as it is, either submit to a physical search or just don't fly.

Safety reports that should be considered invalid due to the fact that one of the two X-ray sources was disabled during testing:
  1. Medical and Health Physics Consulting, Radiation Report on Rapiscan Systems Secure 1000 (March 21, 2006).
  2. Medical and Health Physics Consulting, Radiation Report on Rapiscan Systems Secure 1000 (June 5, 2008).
  3. Medical and Health Physics Consulting, Supplement to Report dated June 5, 2008 (October 28, 2008).
  4. National Institute of Standards and Technology Assessment of Radiation Safety and Compliance with ANSI N43.17-2002 Rapiscan Dual Secure 1000 Personnel Scanner (July 9, 2008).

UPDATE

Just to clarify, I am not a radiation biologist, radiologist, health physicist, etc... my expertise is actually in single molecule biophysics and the biochemistry of DNA repair. This article is simply my review of the safety reports published by the TSA on their website, and not the result of any independent evaluation or experimentation. Also, all views and comments are my opinion (professional and unprofessional) and are not endorsed or representative of the University of California or any affiliated departments or colleges.

UPDATE 2

Thanks Anthony for clarifying how to interpret the data from Appendix B. There DOES NOT appear to be a 1000-fold unit conversion error.

73 comments:

Debbie said...

Well written and detailed. I hope you do not mind, but I have sent a link out to your outline. FINALLY some factual information from someone in the field and not an opinion poll from persons with other agendas.

Thanks you.
Computer Engineer

Jen said...

Thank you! I would love to see more information on the actual safety of these machines. This was a well done piece. Do you mind if I quote/cite you in my own blog?

Steve M said...

I'm finally impressed that someone who knows all about these machines and what they do (who doesn't work for the government) can in regular persons speach explain the problems. My Wife is an X-Ray technologist at a Trauma 1 center in Milwaukee, so I know the precautions they have to take around all types of x-rays including fluoroscopy (live x-ray). I'm certain, like you said, that the TSA are not wearing exposure badges.

Again, thank you, I found this very interesting and look forward to reading more about the BRCA1 and 2 mutation research.

Henry Cate said...

So the backscatter is a bad idea.

How do we get TSA to stop using it?

The only two options I can come up with is to tell my favorite airlines I won't be flying and to plead with my representatives.

Any other suggestions?

kaolin fire said...

Thank you for this.

Andrea said...

Yes, thank you so much for your analysis! I am shouting this from the rooftops to anyone who will listen! Go to Noagendashow.com for more information and listen to the podcasts and live shows where they discuss this issue in detail!

E.N. & S.D. said...

Thank you so much for the well-written analysis. Our family has a long and strong history of cancer, your information is quite helpful!

Thanks again,
Registered Dietitian/Personal Trainer

Jason said...

Feel free to re-post or cite. Mind you, all of this information was released by the TSA, but in a very technical, uninteresting and somewhat dense format. I'm just pointing out what I consider to be some shortcomings of their evaluations, which made good talking points like "2-3 minutes of radiation exposure during your flight" or "less radiation than a cell phone call", but in the end fail to seriously evaluate the cancer risk associated with these scanners.

In the end, we need independent, peer-reviewed evaluation.

Le Merveilleux Chef said...

Thanks Jason! A lot of people are just assuming that these things are properly evaluated and just submitting to the scans without protest. I know the next time I fly, I will definitely opt out...not that the alternative is going to be more pleasant :(

Andrew said...

Wow, I am bowled over!

I would not trust the official reports about the safety of the devices now, even if clarified. A totally new and completely government-disconnected analysis, with 100% open methods, data, and analysis, would be required for me to accept a claim of "safe".

Hearsay: The TSOs may have been issued film badges to measure received doses, but then the badges were canceled. What's more, I do not believe the TSOs are even allowed to wear a self-procured film badge for personal monitoring interest.

If true, this may perhaps be one among very many reasons the TSA has had a high TSO turnover rate. TSOs start resigning as they learn more about the full measure of their jobs.

Jason said...

TSA never actually tested whether the scanners are safe for their specific application (although I suppose airline passengers are now the test subjects). The long-term risks of exposing millions of people are unknown, and while they really could be trivial there are reasons to be concerned that these risks could be significant enough to undermine the justification of their use. When the TSA says these scanners are "safe", what they really mean is: we ran a few tests and they meet the specific regulatory (ANSI N43.17) limits for general radiation exposure to the public.

Loren Pechtel said...

There's a problem here:

A TSO could be exposed to as much as 86-1408 mrem per year (assuming 8 hours per day, 40 hours a week, 50 weeks per year and between 30-100% duty and 25-100% occupancy, as defined by the Johns Hopkins report), which is between 86%-141% of the safe exposure of 100 mrem.

Either that should be 140.8 mrem or 1410%. I strongly suspect the latter.

Brad Parsons said...

This is OUTSTANDING. While we wait for the UCSF faculty rebuttal, this review seems to be the best out there calling into question the safety of the full body scanners. Thank you!

krelnik said...

Thank you for an excellent post, and I agree there are concerns about the use of backscatter x-rays by TSA. But I think there is an important point you missed.

Quoting: "Of specific concern is the scanner that uses X-ray back-scattering."

Note the wording of that phrase. TSA uses two different types of backscatter machines. One uses x-rays, and is the subject of this post. The other uses "millimeter wave technology" (aka "microwaves") which is an entirely different kettle of fish.

Now I can't find any statistics on the relative deployments of these two machines. However, I travelled about 35,000 miles by air last year and it looks like I'll be close to that in 2010. Airports I've personally been through during this time included ATL, JFK, BOS, ACY, LAX, IAD, BWI, IAH, LAS, MKE, MSN, RNO, PHX, FLL, ROC and SEA.

Just based on my admittedly anecdotal personal experience, and the photos of the machines on the TSA website, the x-ray style machines are FAR less prevalent than the millimeter wave machines. I've been asked to step through a millimeter wave machine four or five times at four different airports. I've NEVER been asked to step through the x-ray variety.

Here's what the TSA's X-ray backscatter machines look like.

Here's what the most common millimeter wave backscatter machine looks like. This is the one I've seen in nearly every airport I've seen the new scanning procedures.

Even googling those photos, it is far easier to find photos of the millimeter scanners than it is to find one of the x-ray variety.

Here's a blog post from the TSA that explains the difference as well, and shows a picture of a different type of X-ray backscatter machine (which I have personally never seen).

Bottom line: I believe that there is in fact a potential risk here, and thank you for pointing it out.

But depending on which airport you go through, the risk may be nil due to the relative deployments of the two types of machines.

Warner Losh said...

In the article, you state a worker could receive between 86 and 1406 mrem of radiation. Later, you say this is between 86% and 141% of the safe dose of 100mrem per year. Looks like the 1406 should be 140.6 or 141 instead.

Great article.

Cory said...

Extremely important questions.
TSA needs to focus on undercover and police work to discover and root out those who should not have the freedom to fly. They need to stop spending on technology and personal inspection that restrict ordinary passengers' freedom to fly.

Nor do we consider the cost in anxiety, time, and inconvenience of the current TSA practices. Never mind the possible health risks of the very expensive backscatter X-ray machines.

Douglas said...

It's great that you're thinking of these things and bringing this issue to public awareness, but it's important to keep things in perspective. First- my disclaimer: I am not a radiation safety officer or physicist. As a radiologist, I do have a pretty good background on the subject of radiation interactions with tissues. I've gotta look up allowable limits and government regulations just like the next guy.

The biological effects of radiation are caused by a number of factors, and the issue gets very complex very quickly. One parameter of an exposure (such as kEv) cannot be used by itself to predict the absorbed dose. If you'd like to know more, read on. If you don't want any details, here's the punchline: I do NOT think these scanners (maintained properly and operating within their reported specs) are of great concern.

For any given photon, the energy is proportional to acceleration potential (kEv) as well as "flow rate" of photons (milliAmps), and duration of exposure (seconds). The product of "flow rate" and "exposure time" is referred to as mAs (milliamp-seconds). Putting it all together, for a given radiation your exposure is basically proportionate to kEv (x) mAs.

Unfortunately, there's a LOT more to it. Things like Distance from the source also play a huge role, as exposure drops off at a rate of "radius squared"- so doubling your distance from the source would cut exposure by a factor of 4. Tripling, by a factor of 9, etc. So a TSA agent standing 6 feet away from the machine experiences much less radiation than someone inside the scanner.

Shielding is yet another major factor to consider. Those low kEv photons won't make it through a thin lead curtain, while very high kEv beams penetrate better. Oddly, photons with high kEv don't necessarily Deposit their energy in tissue- like a bullet that goes completely through a person versus a big slug that stays inside (depositing all it's energy). Additionally, not all tissue is as sensitive to the effects of radiation. This is reflected in a weighting coefficient in calculations. Age is important too, as infants and children are more sensitive than adults. They also have a longer life ahead of them to actually experience potential long term consequences of an inappropriate dose.

Now, to answer a few questions: The exposure you get from a flight IS higher than the scanner, because it's not just Gamma rays that you receive, it's a whole spectrum of radiation. And no, the body of the airplane doesn't block it.

Just for fun, I'm expressing the Reported Dose from a typical body scan in an adult (2.6 microRem) in terms of Time Spent in Denver. The answer? Atmospheric annual exposure in Denver (Not including Radon!) = 1.8 mRem or about 1,800 microRem per year. Calculate: (1800 microRem/ year) x (1 year/365 days) x (1 day/24 hrs) = 0.2 microRem per Hour for just standing around in Denver. So the scanner gives you about half of a day in Denver- now you've got something to think about during your layover. ;)

Anthony said...

You wrote, "There also appears to be unit conversion error in the Appendix of the report, which was recently cited by the FDA in response to the UCSF scientist's letter of concern, which might mean that the relative skin dose is 1000-fold higher than the report indicates (pg Appendix B, pg ii, units of microSv are used in an example calculation, when it appears that units of milliSv should have been used)."

I don't understand this point. Are you saying that the 1uSv = 1 uR for photons is an incorrect conversion? Or are you saying the weighted effective dose parameter is wrong?

On page 13 of the document, the author cites the effective adult dose conversion factor as 0.246 uSv/uR, but in the appendix, he uses 0.00246 uSv/uR. But if this is the discrepancy you're noting, he's off by a factor of 100, not 1000, and in each set of calculations, the numbers are consistent. That is, using 0.246 uSv/uR you get 2.36 uRem per dose, just as the table on page 13 indicates.

Isara said...

Thanks to Krelnik above to a comparison of the two different types of machines. For the record, the x-Ray backscatter machines are in use at San Diego International Airport. I have been through them a couple of times, but I'll be sure to avoid that line from now on (it's usually shorter and I'm not body shy, and they didn't seem to care about the iPhone I forgot to take out of my pocket - go figure)

Jason said...

Douglas, thanks for weighing in on this. Your right, radiation biology gets VERY complex VERY fast. I'd like to know if you could weigh in on how frequently 'soft' x-rays of this kind are used, if at all, in the medical field? To my knowledge they aren't, but I'd welcome some information here.

I'd also like to clarify a few points. The spectrum of x-rays that are used in the scanner would in fact be absorbed primarily by the hull of the aircraft, as would other low energy ionizing radiation (e.g. UV light). What you've pointed out so well with your bullet analogy, and what I may have failed to do in the post, is stress that the other radiation on the higher end (high energy x-rays, gamma rays and cosmic rays) mostly pass right through the plane and the passenger without being absorbed, and therefore posing only a very small biological risk. Those that do, are randomly absorbed throughout the entire volume of the body as opposed to being disproportionally deposited into the skin, thymus and testes.

I'm certain your calculation is accurate; however, should know that comparing the biological impact of alpha radiation isn't the same as the biological effect of x-rays... alpha radiation is very weak, and can be absorbed by a sheet of paper or even our dead outer layer of skin cells. This is the same mistake that the TSA is making, assuming that all radiation has the same biological effect and working backwards from background levels of the radiation that disproportionally don't do us harm. Generally speaking, I feel like the science and medical communities have an excellent handle on the biological effects of specific types of ionizing radiation like UV light, high energy x-rays and gamma rays; however, because low energy x-rays haven't been used for many medical or industrial applications (that I know of), they haven't been examined with the same scrutiny.

I don't know about you, but I'd rather err on the side of skepticism and wait for hard experimental data... and when we have it (or when its released, or publicized) then I'll be first to change my tune if its compelling and validated.

Again, thanks for weighing in... I've been dying to talk to a radiologist about this... could you tell us how powerful the x-ray machines are that your office/hospital uses and what the thickness of the Al-equivalent filter is so we can have a grounded comparison to the specs on these scanners.

Jason said...

Thats really interesting that you've only encountered millimeter scanners Krelnik.

One of my coworkers is a card carrying physicists and an expert in optics, and he was telling me that one of his former colleagues is just beginning to do experiments with millimeter waves (aka terahertz radiation). What is a bit scary is that he also said that the technology is so new that they can create and detect the terahertz radiation, but optics to manipulate these wavelengths simply don't exist yet and are still being actively developed.

A quick wikipedia check states that terahertz waves were 'technically challenging' until the mid-1990's and that a portable, compact device for generating them wasn't developed until 2007. Its a little unsettling that the technology is so new that we don't even have optics for it, but we're using it on people; however, because this radiation is on the far IR end on the spectrum (like the remote control on your TV, or Wii), I don't have too much concern for the biological/cancer impact.

It is worth point out though that for many years we used to size kid's feet using x-ray machines in shoe stores simply because the technology was new enough that we still didn't understand the long term consequences of exposure.

Jason said...

Thanks Warner Losh, you're right, I made a typo in the post. This is why we have the peer review process in science, and why I was concerned about the units in the FDA/NIST report. It happens much more frequently than we would like. I've corrected the main text now.

M(r)s MD/PhD Candidate said...

Thanks for taking the time to go through this data! I've shared your post on facebook, but the sexism of the title bothers me. You study radiation, I study history and culture, so I noticed that "hide your wife" assumes that the reader is male and heterosexual (or a lesbian living in a state that allows marriage equality). "Spouse" would be a less condescending and sex/gender-neutral term. But as I said, from one PhD student to another, I really do appreciate you taking the time to help those of us out who couldn't understand the government reports.

Angela the Magnificent said...

M(r)s, I'm obviously not the author, but I suspect that the title of the article specifically calls out "wives" and children because of his concern over breast cancer, and that one of the reports mentioned children. So for a lesbian couple, I think each wife would have to be looking out for the other : ) Although it certainly seems that men could be at some risk as well.

Paula said...

Mr/s PhD Candidate -- way to totally miss the point! Relax, it's just a humorous figure of speech! I'm a feminist and I thought it was funny. Talk about straining at gnats . . .

Eric said...

Thanks for posting this as it verifies my concernes. The basic fact is that there is no safe dose of ionizing radiation. While you can't avoid it in going about your life it doesn't mean you should be intentionally exposing people to more.

I think it is even scarrier that these devices are being used in a wholly non-medical setting and the operators have no understanding of the possible danger. Quotes from operators and other TSO show that they don't even understand the basic differences between ionizing and non ionizing radiation. What policy is in place to notify passengers if they do receive a non trivial dose?

The fact that they could be used for a through x-ray is also a concern that has been bothering me for a while. If you presume that backscatter was chosen because of ability to spot threats and not because of who benefits; the ability to do spot checks for the future "butt bomber" now or in the future with a software upgrade make these devices far more capable than their mmW counterparts. Once they have the buy-in from the public they can reveal the feature, claiming only a 5% increase in radiation.

The other option is just as scary. The devices were chose becau of who benefits and the risk to the public has been downplayed to increase profits.

Cara said...

Thanks so much for this. I wholeheartedly agree that an independent, peer-reviewed process is an absolute must.

M(r)s MD/PhD Candidate--"hide yo kids, hide yo wife" is a pop culture reference which is particularly applicable.

Lisa said...

Is there a peer-reviewed study on these machines? Because right now I'm seeing a lot of opinions by people who may or may not have any evidence backing them up.

In particular, I'm interested in any studies from Europe, where they've been using full body scanners for at least three years.

Thank you.

Jason said...

Anthony, sorry if you didn't see your comment go up. I think the long quote may have triggered Blogger's spam filter.

Actually, it would appear that you have found a different conversion error, though I'm not quite sure yet whether that error propagates to any of the critical numbers provided by the report.

The error I refer to in the post is in bullet three on page ii of Appendix B. The author multiplies 9.6 uR x 0.00554 uSv/uR = 0.0532 uSv to calculate the skin dose. The second number appears to come from the table in the first screen print on page iii of Appendix B, where the simulated skin dose is 0.005543 mGy. Since 1 mGy = 1 mSv.

And as your point out, he used a weighting coefficient of 1 uSv = 1 uR, so in order to calculate the actual skin dose, it seems to me that the author multiplied the number from the table on page iii by 9.6 uR to get his answer.

I believe that he should have converted 0.00554 mGy = 0.00554 mSv = 5.54 uSv. So the final answer should have been 53.2 uSv/uR x 9.6 uR = 53 uSv per scan. If I'm right, then that error propagates to the final bullet, which was quoted by the FDA in their dismissive response to the UCSF scientists.

How does that look to you?

Cancer Bitch said...

Thanks for this. I'm going to re-read it carefully when I have time. Do you have any info about UVB rays and cancer? I'm undergoing phototherapy 3 times a week in order to combat the itching caused by polycythemia vera. It has worked to stop the itching but I wonder at what cost.
Sincerely,
Cancer Bitch http://cancerbitch.blogspot.com

C.S.Magor said...

Great post! I'm always looking for molecular biologists who can write, if you are interested in doing some scientific editing - DM me: @csmagor on Twitter.

Neil Fraser said...

It seems that the Terac-25 disaster happened too long ago and people are forgetting the lessons which were learned. Safety-critical systems need mechanical safety interlocks and closed-loop controllers. Software is not enough.

As a software engineer, I'm not stepping into one of these scanners until the code has been peer reviewed.

Douglas said...

@Jason, to clarify a few more points:

I'd like to know if you could weigh in on how frequently 'soft' x-rays of this kind are used, if at all, in the medical field?

The designation "soft" versus "hard" radiation is a colloquialism. It refers to the penetrance of a given beam through material, and has no significance on the relevant topic: biological effect and energy deposited. To directly answer your question, yes, we use "soft" x-rays every day. Mammograms are a good example where use a low kEv beam (around 20 kEv). In general, low energy photons are used when we want better contrast between soft tissues.

The spectrum of x-rays that are used in the scanner would in fact be absorbed primarily by the hull of the aircraft

Absolutely false. Beam attenuation is measured experimentally, and expressed in terms of Half Value Layers (HVL), or "how thick something has to be in order to block half of the incident radiation". If you use two HVLs, they would block 75% (ie: each subsequent HVL blocks half of the radiation that passed through the first HVL). Aluminum (I'm assuming most airplanes are still made of aluminum), has a HVL of approximately 8mm for a 50 kEv photon. So an 8 mm thick plate of aluminum attenuates only 50% of the incident 50 kEv x-ray beam. Referring to my prior post, your mAs in a flight is very high because your exposure is constant throughout the flight (time of exposure is high). So even if only 25% of the incoming 50 kEv radiation passed through the hull, your exposure is still much higher than your short exposure in the body scanner. If you're an electronics geek, think of aluminum as a Low Pass Filter for radiation, selectively allowing more of the higher energy beam. Remember, you're exposed to an entire spectrum of radiation in flight, not just 50 kEv, so you'll receive proportionately more 60 kEv photons than 50, and more 50 than 30, etc.

comparing the biological impact of alpha radiation isn't the same as the biological effect of x-rays

I was not referring to alpha or beta emissions in my post, and neither the TSA nor the NRC (Nuclear Regulatory Commission) made this mistake in their assessments either. The type of radiation is accounted for in all exposure assessments, as well as the target organ of that radiation exposure.

because low energy x-rays haven't been used for many medical or industrial applications (that I know of), they haven't been examined with the same scrutiny.

On the contrary, our use and understanding of what you're calling "low energy x-rays" is fairly extensive. Mammography is probably The Single Most regulated and standardized sub-specialty within Radiology, and also one of the more common procedures. Google the Mammography Quality Standards Act (or MQSA) for a glimpse of what I'm talking about.

I'd rather err on the side of skepticism and wait for hard experimental data... and when we have it (or when its released, or publicized) then I'll be first to change my tune if its compelling and validated.

I'm never one to discourage a healthy dose of skepticism. Question Everything, as they say. I'm not trying to sway your opinion one way or another, but as I originally said, it's important to keep these concerns in perspective. The relevant question here is: Do Body Scanners (operating within their specified limits) give a biologically relevant dose of radiation? My conclusion is simply- No, they don't.


@MD/PhD Candidate- take it easy, life is too short to fret about gender role assignment in some dude's Web Blog.

Eric said...

Douglas

Would you agree that there is no true safe dose of ionizing radiation? Every dose should be balanced against the risks?

Then these devices are an unnecessary risk when a non ionizing technology exists to perform the same function.

Ralph said...

Cincinnati/Northern Kentucky (CVG) airport seems to have predominately the X-ray variety, judging by the photos.

Douglas said...

@Eric:


Would you agree that there is no true safe dose of ionizing radiation? Every dose should be balanced against the risks?


I think that what you're getting at is that the Benefit of every dose should be balanced against the Risk of that dose. And yes, I'd agree to that completely (It's called the ALARA Principle). I'd also state that the Risk of a very low dose exposure is outweighed by the Benefit of safer airline transportation.

As you imply, you DO have a no-radiation alternative, which is the pat-down. Screening very large numbers of people in this way might be difficult, which is why the scanners were developed. However, if you're uncomfortable with a small dose of ionizing radiation, you should exercise your right to opt-out and get the pat-down.

The whole point here is to NOT spread misinformation. Jason's well written comments on the subject are a good starting point to have this kind of public dialog.

As a person who works with radiation, I like it when my patients ask about their exposure for various exams. It means that you're asking the right questions, and engaged in your healthcare.

Eric said...

@Douglas

"I'd also state that the Risk of a very low dose exposure is outweighed by the Benefit of safer airline transportation. "

The first of two presumptions is that there is a benefit to these scans, in fact many in the security realm have said that there is no measurable improvement in safety or loss of security because of these devices. Without clear and documented benefit to safety we are essentially using the flying public as guinea pigs in a huge, and possibly dangerous, experiment.

The second presumption in your argument is that the risk of the devices, in an operating environment, are bounded enough to make an educated decision to risk. The devices are known to carry a much larger xray source than needed, as a cost saving measure, and has moving parts. These are operated in a non-medical setting and the operators are not
equipped to identify or deal with failure conditions.

All of this rest on the presumption that the TSA even has the authority to conduct such invasive searches on all domestic passengers as part of their legal mandate.

Eric said...

Correction to my last post.

"The first of two presumptions is that there is a benefit to these scans, in fact many in the security realm have said that there is no measurable improvement in safety or loss of security because of these devices."

I meant to say that some indicated that there could even be a loss of security because of the devices.

Wimpie said...

Even if the government is right about the risk, if I keep out of the scanners I improve my odds of staying alive by 50%.

http://WeWontFly.com

kwilinski said...

The "hide your wife, hide your kids" title is a joke, coming from the popular, viral Youtube video and subsequent songs and copycat videos which spread awhile back.

torilife said...

Thank you. I finally have information I can use. Aloha -Tori Life

Jason said...

@Douglas pt1

Again, thanks for your comments! This is exactly the kind of intelligent technical dialogue that I was hoping to promote!

I think that some of the discrepancies between our analysis appears to stem from an inconsistent use of the 'soft' and 'hard' x-rays, and based on your response it sounds like there isn't a strict definition in the field either. In my post, I define soft x-rays as those below 12 kEv and hard x-rays above (admittedly, this definition was based on Wikipedia). I used the terminology only because that is what the TSA was using in its statements regarding the safety of the scanners.

Thanks for clearing up the point about the types of x-rays that are used in mammograms. I was under the impression that they were in the 50keV range, so learning that they are an even lower energy , and specifically in the mid-range of these scanner's output (30keV) is interesting and I think it drives home the point that TSA has been misleading in their statements in which they assert that the scanners are different from medical x-rays.

You said, "The designation "soft" versus "hard" radiation is a colloquialism. It refers to the penetrance of a given beam through material, and has no significance on the relevant topic: biological effect and energy deposited."

I disagree. It is exactly the point of the relevant topic. The greater the penetrence (i.e. the 'harder' or more powerful an x-ray is) the less it is absorbed by soft tissue, and the 'softer' or lower energy the x-ray is, the more it is absorbed by soft tissue(and therefore the potential for biological harm is greater). This is part of the reason that NICE (a patient advocacy group that provides guidance and quality standards to the NHS in the UK) recommends MRI screening for BRCA patients instead of mammograms.

Jason said...

@Douglas pt2

With regard to the to the radiation absorbed by the airplane hull. If we assume the hull is a 4mm Al plate, then greater than 90% of the X-rays below 30keV and essentially 100% below 20keV would be absorbed by the airplane hull. In reality, airplane hulls are composed of an aluminum alloy for which I can't find any real x-ray shielding data on, and it could be higher or lower depending on the total composition. At any rate, a 4mm Al equivalent is a pretty good approximation.

Here is a graph of x-ray transmission by Al thickness. The scanner has a filter that would be nearly equivalent to curve (I) and a 4mm thick airplane hull would be somewhere around curve (J) or (K). Therefore, the difference between these curves is what I'm referring to when I say most of the equivalent radiation output of the scanner would be absorbed by the plane hull.

http://www.johncaunt.com/pages/detectors/images/fig53.jpg

Its important that I am emphasizing the specific absorption of the x-rays being generated by the scanner, not all x-rays in the spectrum. You are absolutely right that the higher energy x-rays are not absorbed by the plane hull at all, but most of those x-rays would also not be absorbed by biological tissue (though some would).

Naturally time and intensity are also critical parameters. I'm not sure what the intensity of natural x-rays in the 1-50 keV range after airplane shielding would be, but that would be critical to calculate both the total body dose as well as doses to specific organs like the skin. My point is, and always has been, that we have to compare apples to apples, and the 2-minute equivalent is comparing apples to oranges.

You also said: "I was not referring to alpha or beta emissions in my post, and neither the TSA nor the NRC (Nuclear Regulatory Commission) made this mistake in their assessments either."

Apologies! I misread your last paragraph in your comment as calculating the atmospheric radiation from radon, which you actually were specifically excluding. My bad. There is no question that the total radiation exposure from a scan is low as demonstrated by your calculation as well as the TSA. But again, your calculation is based on total atmospheric radiation exposure, not the exposure to this specific spectrum of x-rays. In the end, what I would like to see is a direct comparison (ideally measured) between the skin dose from a scan and the skin dose from atmospheric exposure specifically in the 5-50 keV x-ray spectra.

Abstractly, I think comparing these scanners to UV flash photography is a fair assessment. I recently read an account of a teenage model who didn't realize that the photographer was using a UV flash, and she ended up be hospitalized for severe sunburn and was temporarily blinded by the damage done to her eyes. Of course, you might get a worse sunburn laying on the beach without sunscreen for a day, but that doesn't mean that a UV flash bulb is safe, especially when it improperly used.

As a radiologist, you use radiation in a controlled environment with trained staff and extensive oversight (I would hope). But putting these machines in the field, operated by people who don't have degrees in radiation or health physics or medicine and scanning hundreds of millions of people a year by an organization known to be bureaucratically heavy handed is a very different thing. I mean, what could go wrong?

Douglas said...

@Jason:
"soft versus hard" radiation is not a technical or physically relevant parameter. That's what I meant when I said it's a colloquialism. Nobody walks around talking about "soft versus hard" x-rays. We talk about kEv and mAs.

A low kEv backscatter with a low mAs has a low amount of deposited energy. Lower kEv photons tend to deposit a higher percentage of their energy in tissue. In other words, more photons of the original beam will be attenuated. This obviously does not mean that a higher biological Dose is achieved (ie: a tiny exposure won't result in a large dose, no matter how much of the tiny exposure is absorbed).

It seems that the industry or press has been popularizing terms like "hard" and "soft" in order to make the process appear more acceptable (or maybe more understandable?) to the layperson. IMHO, pseudo-technical terms like that just confuse the issue. People are smart enough to figure it out, and when they do, they start wondering why they were being misled (as happened here). Let's cut the the chase, and avoid those terms completely.

I'll say it again: Body Scans do not expose people to a harmful dose of radiation.

Someone said something about the size of the generator. The size of the generator isn't really relevant. Furthermore, I'm not sure if the poster means the size of the focal spot, a larger anode, the potential voltage, wattage, or whatever else a "bigger generator" implies. A 50kEv photon is produced when an electron is accelerated at the target with a potential of 50kEv. Other relevant parameters are the amperage (number of electrons accelerated per unit of time) and duration of exposure (seconds).

More relevant info: the vast majority (almost all) of imaging equipment uses an automatic exposure meter with a cut-off when sufficient photons are collected to make an image, with a fail-safe mechanism that's a standard timer. This keeps the mAs part of the equation under control. Basically, increased amperage across the generator circuit results in higher exposure, thereby triggering the auto exposure to shut it off.

Honestly, you can run the calculation any way you'd like, but you'll reach the same inevitable conclusion that you'll get more biologically relevant radiation dose from your flight than you will from the body scanner.

@Eric: judging by your tone, you seem to want to "argue" your point or believe that The Man is conducting experiments on the populous. You're probably right. In fact, I bet you're Always Right. It's all a big conspiracy. Also, I've not encountered any literature that states that body scans "decrease airport security", but admittedly, I'm not a security expert. I'm sure everyone would be interested in that reference. I don't have the time or inclination to "argue" with you. Read a book. Try Walter Huda's review book on radiation physics for a start.

Eric said...

@Douglas,

Are you privy to the technical specs of the device? If not you are also speculating as to the interlocks that are used. You have no idea how the device will work and degrade in an operating environment or how a failure will affect those being screened.

You admit that ionizing radiation should only be used when the benefit outweigh the risks, but then ignore that same rule by presuming that there is a safety benefit. Even if we presume that the human risk is minimal according the specs, the device must have a significant security advantage compared to the non-ionizing alternatives.

David said...

You seem to equate cell absorption of a wavelength to DNA damage. While I don't have knowledge for X-rays, this is quite clearly not true for the UV spectrum, where certain wavelengths increase the odds of cancer, but others break down collagen when absorbed, leading to wrinkles. If you know of a source that shows absorption of these wavelengths leads primarily to DNA damage, I'd be interested.

Anthony said...

Hopefully, this comment won't get spam-filtered.

@Douglas, re: conversion factors

I don't think that's how that table is meant to be read. In the text on the first page of Appendix B, the author explains that the monte carlo simulations calculated dose in mGy for a 1 mR exposure. At least, that's how I'm interpreting his description.

Thus, 0.0054 mGy = 0.0054 mSv skin dose for 1 mR exposure. Since the actual exposure is claimed to be 9.6 uR, the actual skin dose would be 9.6 uR * 0.0054 mSv/mR or 9.6 uR * 0.0054 uSv/uR = 0.0532 uSv, as the example says.

vincenzio said...

@krelnik - On the few occasions I've had to fly recently, the X-Ray machine has been the one to which I've been subjected. I have never even seen the clear cage mm-wave variety until I saw your linked photo.

Eric said...

A friend of mine posted this to his facebook page - your description is quite thoughtful, and I'd add, accurate in the details concerning the types of X-rays (I should add that my field is high energy astrophysicics, so I study X-rays from quite a different perspective).

You, and your readers, may be interested in a facebook discussion that I and several colleagues had on this subject a week or two ago. It is archived at http://rohrblog.posterous.com/radiation-risks-are-airport-body-x-ray-scanne. For the record, I was astrophysicist #4.

http://rohrblog.posterous.com/radiation-risks-are-airport-body-x-ray-scanne.

Pete said...

I believe it is incorrect to say that "Most cosmic radiation is composed of high energy particles that passes right through our body, the plane and even most of the earth itself without being absorbed or even detected."

This is true for neutrinos, but not for most other radiation and cosmic particles which will decay or be deposited in the earth.

Jason said...

@Pete, you're right, I was thinking primarily of neutrinos when I wrote that line. I've made a correction.

"About 89% of incoming cosmic ray particles are simple protons (hydrogen nuclei), nearly 10% are helium nuclei (alpha particles), and slightly under 1% of cosmic ray nuclei are those of the heavier elements." -Wikipedia

X-rays are photons.

Eric said...

@Eric - there are now two erics in this discussion

FYI the round booths are for the millimeter wave scanners, not the X-ray scanners.

Eric said...

@Douglas

http://www.nytimes.com/roomfordebate/2010/11/22/do-body-scanners-make-us-safer/a-waste-of-money-and-time

The scanners and enhanced pat downs are a waste of time and money that could be used on real security.

Allie said...

Thank you for translating TSA techno-babble into something lay people can understand.

I find it particularly disturbing that so many people, including TSO's, are being irradiated on a daily basis with their alternative being sexually manhandled. Finding out that the TSA lied, while not a shock, is highly concerning as they are putting the general public at risk as well as their typically under-educated officers.

I plan to cite your article on a blog of my own later this week.
http://allisondduncan.com

Pete said...

@Jason

Thanks for correcting it, this is better. Your paragraph could do with a quick edit to tidy the language.

Next it would be good to find some information about the flux spectra of cosmic radiation at 38,000 feet compared with ground level. I had a brief look, but found little in the short time I had. I feel as though your argument is correct but I am uncomfortable to not know what the numbers are to demonstrate this.

w said...

It would seem that the safety of these devices operated by unqualified personnel is inviting disaster. Is the TSA trying to detect covertly placed explosives or intentionally expose the public to ionizing radiation? Would it not make better sense to use bomb sniffing dogs walking around the concourses of the airports and the cargo processing areas? The TSA has already stated that the underwear bomb and shoe bomb would not have been detected by these devices. Kick out the TSA and hire the security folks from El Al ASAP.
Bill

Sumana said...

Mr. Bell, I strongly appreciate the work you've done in translating this documentation. And other scientists and experts in the comment threads, thank you for talking this out as well. We need open peer review of this data.

I agree with Neil Fraser (mentioned the Therac-25 in my blog post quoting you, Mr. Bell).

Oh, and M(r)s MD/PhD Candidate, good on you for pointing out the offputting title. Other people in the thread explained the reference -- I had not heard of it. To those other folks in the comments: (a) "Lighten up/it's just a joke"? Take your own advice and lighten up when someone makes a good-faith bug report. And (b) if I think of a funny jokey reference, and then I realize it'll come across wrong or sexist or offputting to people who don't get the reference, I come up with something else and it's just as good or better. Just takes practice, like science.

Again, Mr. Bell, thanks for writing and sharing this.

-Sumana Harihareswara

arshad said...

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Jason said...

@David.

Most ionizing radiation, including x-rays, indirectly damage DNA by creating reactive oxygen species in the cell. Naturally, proteins like collagen are also damaged by this process; however, many proteins are pretty much in a constant flux in the cell, so damaging them may be stressful, but not necessarily cancer-inducing.

The damage to DNA is a different story. The response to DNA damage is complex with respect to the type of damage, the genetic, cellular, physiological makeup, etc; however, the main point is that if the damage is greater than the cell can repair, it will die (which actually is a good thing in the context of cancer prevention). If the damage is repaired and the cell survives, there is an error rate that can be highly variable, and if the error rate is high enough, then cancer becomes increasingly probable. Therefore, if a cell has suffered DNA damage, there is a probability of mutating the DNA in that particular cell and some of these mutations could result, over time, in cancer.

What you refer to as wavelength is really a function of the energy of the x-rays and their relative transmission through various materials. All ionizing radiation is relatively 'bad' for biological tissue; however, the probability of that radiation being absorbed by the tissue is function of thickness, density, radiation energy and time of exposure. There is a certain amount that most people can tolerate without increasing their relative risk of cancer; however, it is becoming increasingly appreciated that that tolerable dose is not the same throughout the population. I hope this answers your question.

Phelps said...

These monstrosities are the shoe-fitting fluoroscopes of our time. In 50 years, our descendants are going to look at us like we were idiots for even considering this.

Jeremy said...

Jason, I've recently done a write-up of the effects of EMF on the human body. Just ignore the rest of the site, as the sorts of things being alleged are unprovable (for now)... but I'd appreciate your remarks. You can click the Leave Feedback button on that page.

http://areyoutargeted.com/fighting-back/public-relations/making-your-case/eh-and-health/

Pixiepurls said...

Nearly all of my grandparents have died of cancer, this was of particular interest to me and thank you for the information.

Bill McGonigle said...

Jason,

Thanks for the write-up, and it's great to see the comments section refining it.

When your post reaches a reasonable state of equilibrium, I'd encourage you to bring it full-circle and bring the data back to Wikipedia, where it can be further expanded/refined and gain a larger audience.

Littlebear said...

"In addition, it appears that real independent safety data do not exist."
O.o, seriously? now that's kind of dangerous to do something not tested.

Craigs said...

We get hit by radiation when we fly too. Hide your kids, hide your wife....hahaha :)

http://www.hps.org/publicinformation/ate/q444.html

Jenny said...

@Eric: I agree with your assertion that the risks (which still sound very much uncertain and arguable) outweigh the benefits, primarily because I think the only benefit to this is the public's irrational belief that these scanners make them safer. I also agree that we could spend our money differently and get a much more effective security system. This is a very interesting article about how airport security is done at Ben Hurion in Israel: http://www.thestar.com/news/world/article/744199---israelification-high-security-little-bother

@Jason & @Douglas: THANK YOU for the thoughtful and respectful dialog on the science of the matter. I wish more of our public debate could be this way. I appreciated reading your discussion here.

nola said...

@Douglas - Dr. David Brenner, head of the Center for Radiological Research at Columbia University, doesnt share your confidence on the safety risk of these devices. read his quotes and link to more here:

http://www.npr.org/blogs/health/2010/11/12/131275949/protests-mount-over-safety-and-privacy-of-airport-scanners

...sorry but if its not good enough for him, its not good enough for me.

also, on Safety Benefits -- there is no data to indicate these scanners create a safer flight (see security expert Bruce Schneier's editorial). so if the decision entails "possible safety risk" paired with "no security benefit", the risk evaluation must always end in a decision of "not worth it".

Debbie said...

Thank you to everyone for a thoughtful discussion of the facts..refreshing.

While opinions stated by myself are certainly antipodal in nature, as a computer engineer, I realize the failure rate in equipment can be high. It is the reason we have qualified licensed individuals to monitor such equipment to prevent any exposures that would damage someone.

Your outline and the subsequent comments are went the equipment is working perfectly. Adding the technological side to the formula, weighted by non-qualified personnel running them, increases the potential dangers you so nicely outline.

Peer review seems like a no-brainier and qualified comparisons to other countries and their findings seems like a obvious solution. Yes those obvious protections are not being implemented. The question of why. We have so much safety build into our society, it seems blind to suddenly ignore them without proper studies.

That indicator seems to bring us upon a subject that is neither scientific or technical. Rather it dances upon the subjects of politics and monetary gain.

I too am not a medical doctor or scientist. I am a computer engineer who works directly with hardware on a regular basis. I know what can go wrong with equipment over time and/or software bugs in non-predicted situations. All combined with the potential of the evidence you present here and being one of those individuals who has survived skin cancer I will not be entering any one of the machines any time soon by choice.

The even scary issue is, if the technically is going to be applied to the population unknowingly, in the form of roaming trucks, as has been announced in recent news broadcasts.

One wonders if the science is of any concern to those who implement it. Does our health and all the work you do, do find out why cancer does what it does in the body..have any value in this day and age. Sadly, if feels like there are other priorities.

Again, I thank you again for the wonderful discussion and outline. It helped to make my own personal decision of opt-out, regardless of of possible objections of mainstream TSA officials. The risks do not outweigh the benefits.

I would be interested in more information you could find out on this subject, as time goes on.

Debbie
Computer and Software Engineer

Debbie said...

@ Nola, I agree with you. If it not good enough for Dr. Bremer, it is not good enough for me.

Combined with another radilogist in the field who also, although more bluntly, has said:

“…..As a radiographer I know about the dangers of radiation. These machines use soft radiation. Does anyone realize what this means? Soft radiation is unfiltered, thus it is absorbed by the body unlike hard or filtered radiation used by x-ray machines in the medical field which penetrate the body. And the Govt wants to douse its citizens for 10 seconds with radiation far more dangerous than what a patient would receive in an imaging dept, where exposure times = milliseconds?

At what kVp are these machines operating and what would be the final mAs of such body scans? What about total body dose? Can any of these Govt Goons or official tell me that? I'll only go thru a scanner if I can wear a dosimeter, just pray I don't get an ALARA letter.

Anyone who allows themselves to be body scanned in such a way is crazy. I'd rather walk to my destination.
- Anne-Marie, Atl, GA....."


That is 2, plus this discussion. Seem like a obvious decision, based on health alone. But the health discussion does assume one great item, that the equipment works perfectly all the. time.

As a software engineer who works with hardware on a regular basis, I know the problems of technical equipment, left in non-certified hands, is a formula for disaster.

Equipment breaks. After all, the essentials of function is based on software and the ability of the programmer to predict all situations. While any engineer is good,we are not perfect. The possibility of malfunction, especially left in the hands of unqualified staff is not a matter of IF but WHEN. With this knowledge I will not be getting into any scanner willingly, any time soon.

Computer/Software Engineer

As a computer engineer

Debbie said...

@Jeremy.
Fascinating read on your own article.

Mz M. said...

Thank you, awesome blog post. I'm passing this on.

My first thought, before I read your blog was: let the TSA employee lawsuits began. Very shortly there's going to be a rash of TSA grunts with all sorts of cancer. THEN maybe they'll get rid of these dangerous machines.

Eric said...

I have a few more questions for anyone.

Does anyone know any other precedent where untrained personnel are using xray equipment on human subjects?

Does anyone know a precedent in the past that was not later recalled for safety reasons?


Even if you make the presumption that out of the factory these devices are safe the novel use of technology with a horrible safety record when used outside of the medical field should give anyone skepticism*. The sheer number of domestic travelers a year ( Over half a billion domestic travelers a year ) should give people pause before we start mass radiating the public.

*Yes, I know, even within the medical community the use and abuse of xray technology is also problematic. Things like CT scans are used far too often because they are cheap diagnostic tools and previous exposures are usually not even taken into account unless the patient is informed on the topic.

Debbie said...

@ERIC, The only precedent I know of was the famous chemical sniffer system that was in test a few years back. I do not recall the exact numbers, but after several hundred where purchased they were dropped because the system broke down on a regular basis.

I believe they were called
Explosives trace-detection portal machine.

From my limited read, TSA spent approximately $29.6 million only to abandon them because of numerous break downs.

There is minor article here. You may be able to find more with google. I just remembered reading about them and the technical challenges they had after only a few months of use.

http://blog.tsa.gov/2009/05/explosive-trace-detection.html