You couldn't roll out a medical device like this, but foist it on the public at large and suddenly the testing requirements are very lax.
Field testing is essential. You can't just use a model that the manufacturer "kindly" provides for free. (To do proper Consumer Reports, you have to buy a unit on the open market incognito.) And you can't test for wear-and-tear malfunction by using a brand-new model.
Which doesn't mention who provided the unit, and seems content to test it in black-box mode, focused on the externalities and not the actual hardware or software internals.
What about possibly buggy software updates?
iPhone apps get more auditing trying to release a new version than this thing.
# "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."
"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 lab technicians. 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. Yet, the FDA and TSA continue to dismiss some of the most talented scientists in the country..."
"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%-141% 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)."
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).
> Though usually omitted from public sources about H-bombs, including all of the sources I managed to find this morning with a bit of Googling, I remember hearing somewhere, years ago, that there is an extra component between the primary and the secondary that slows down hard X-rays to soft X-rays, because in the form of hard X-rays they would otherwise just go through the secondary without significantly interacting with it.
Here's my take on the post from a radiation physics point of view.
I'm not convinced that these pose a great radiation risk. I would be mostly concerned about people with genetic conditions, who could not normally undergo x-rays, but then again flying itself might be worse from a radiation point of view. I'm much more concerned about the civil liberties issue.
Firstly, I'll say one thing: there is no such thing as a truly safe radiation dose.
The problem with this statement is that there is very poor data for low dose, long term exposure. And as you can imagine, it's not exactly easy to set up controlled experiments. The generally accepted model is the linear, no threshold model, which agrees with his statement. But there is some evidence for a threshold limit (below which cancer doesn't occur) and slight evidence that small amounts of radiation is actually beneficial (hormesis).
At a fundamental level, the main effect we need to be concerned with is high energy particles smashing into a piece of DNA and doing just the right amount of damage to cause the cell concerned to start doing something it shouldn't.
Actually, for photons (x-rays/gamma rays), most damage is done by so called indirect damage, where the photon creates a free radical (in this case OH.), which then interacts with DNA.
it's worth remembering that one hit that gives you cancer or leukaemia is enough to kill you. Just one. Even though most interactions won't kill you, it only takes one good one to finish you off.
This is just plain hyperbole. You almost certainly need multiple radiation interactions to produce DNA damage that will result in fatal cancer. Most DNA damage is repaired by the cell, most persistent DNA damage is benign, and most cancer is killed off by the body. That's not even to say anything about the fact that once a cancer gets to the point of discoverability that most are survivable (you still don't want cancer though!).
I remember hearing somewhere, years ago, that there is an extra component between the primary and the secondary that slows down hard X-rays to soft X-rays
This was in reference to the hydrogen bomb. You can not (generally) change the energy of x-rays. You can "harden" an x-ray beam energy distribution by filtering out the lower energy x-rays, but not the other way around. I assume he really meant neutrons.
The main mistake he (and others) makes is seeming to not understand the nature of radiation dose and how that relates to the body. Dose is simply the amount of energy deposited by radiation per unit mass. It can be thought of as a density like quantity. The related term equivalent dose is used for setting radiation exposure limits and takes into account the biological effects of different radiation types (and energies) and different tolerances of organs and tissues.
When people see that low energy radiation is mostly absorbed near the bodies surface, this seems to concern them a lot. What is more important is what the actual dose is. From a general carcinogenesis point of view, it's actually considered better that the dose is not to the entire body
What's generally not understood is that limit of dose to a specific part of the body (e.g. skin) is higher than the limit of the total body dose. This is because your body is better at dealing with localized damage, than it is with systemic damage.
>>But there is some evidence for a threshold limit (below which cancer doesn't occur) and slight evidence that small amounts of radiation is actually beneficial (hormesis).
Interesting, but one question.
That part about a threshold sounds a bit strange?
Are you ignoring alpha (because you have to ingest/breath it) -- or do mean that there can't be unrepairable DNA damage from a single alpha particle?
According to my radiobiology text (Hall), "mammalian cells on average experience over 100,000 DNA lesions per day as a result of replication errors, chemical decay of their bases, attack by reactive oxygen species, or exposure to ionizing radiation. However, the mutation rate in mammalian cells is quite low owing to the development of DNA repair pathways that handle each type of damage."
Basically the threshold hypothesis assumes that the body can successfully repair up to a point, beyond which the risk of cancer increases with the increasing number DNA lesions.
Alphas (and other charged particles heavier than electrons) act in a slightly different way. They can do more direct DNA damage. They can also occur externally, from cosmic rays or accelerator beams. I only addressed photons because we were talking about the body scanners.
Not disagreeing with the math or anything... but does anyone see the stomach and lungs and stuff are? I mean, since we don't have a true global source of x-rays there's bound to be some shadowing (ass cheeks for an example), and all the stuff going on in the chest looks like a combination of shadowing, artifacts, and human mind gone wild?
If we can only see the shin bones cause there's like half a centimeter of flesh there, how can we see the lungs without seeing the rib cage???
I would imagine it has to do with variable penetration and/or a form of constructive interference or resonance, due to factors I couldn't specifically identify offhand.
Um... you could go into the scanner wearing a radiation-measuring device on you that sends data live to your server. I even doubt that would be illegal, although you'll probably end up on a couple lists.
Taking the manufacturer's word for it isn't even good enough for software or gas mileage; we rely on third-party benchmarking.
And where's the independent safety auditing to check for hardware dose limiting in case of faulty software, for example?
http://en.wikipedia.org/wiki/Therac-25
You couldn't roll out a medical device like this, but foist it on the public at large and suddenly the testing requirements are very lax.
Field testing is essential. You can't just use a model that the manufacturer "kindly" provides for free. (To do proper Consumer Reports, you have to buy a unit on the open market incognito.) And you can't test for wear-and-tear malfunction by using a brand-new model.
I found this report:
http://publicintelligence.net/nist-rapiscan-secure-1000-reda...
Which doesn't mention who provided the unit, and seems content to test it in black-box mode, focused on the externalities and not the actual hardware or software internals.
What about possibly buggy software updates?
iPhone apps get more auditing trying to release a new version than this thing.