Leading scientists say backscatter X-ray may be far more dangerous than thought

http://www.npr.org/assets/news/2010/05/17/concern.pdf

by zacharyvoase • 16 years ago

91 48 16 years ago

sstone• 16 years ago

The document was linked here before but is very detailed and interesting, even naming specific issues:

A) The large population of older travelers, >65 years of age, is particularly at risk from the mutagenic effects of the X-rays based on the known biology of melanocyte aging.

B) A fraction of the female population is especially sensitive to mutagenesis provoking radiation leading to breast cancer. Notably, because these women, who have defects in DNA repair mechanisms, are particularly prone to cancer, X-ray mammograms are not performed on them. The dose to breast tissue beneath the skin represents a similar risk.

C) Blood (white blood cells) perfusing the skin is also at risk.

D) The population of immunocompromised individuals--HIV and cancer patients (see above) is likely to be at risk for cancer induction by the high skin dose.

E) The risk of radiation emission to children and adolescents does not appear to have been fully evaluated.

F) The policy towards pregnant women needs to be defined once the theoretical risks to the fetus are determined.

G) Because of the proximity of the testicles to skin, this tissue is at risk for sperm mutagenesis.

H) Have the effects of the radiation on the cornea and thymus been determined?

pygy_3• 16 years ago

I've been told by an engineer friend of mine that the radiation dose these scanners deliver was dwarfed by the in-flight cosmic irradiation.

He didn't give me numbers, though. It would be nice if a radiotherapist (or another expert) could chime in on this topic.

----------------------------

edit: answering my own question: he's wrong.

from [1] :

>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.

> Other experiments, or dose rate measurements with the neutron dosimeter, consisting of LR-115 track detector and boron foil BN-1 or 10B converter, were performed on five intercontinental flights.

> Comparison of the dose rates of the non-neutron component (low LET) and the neutron one (high LET) of the radiation field at the aircraft flight level showed that the neutron component carried about 50% of the total dose.

> The dose rate measurements on the flights from the Middle Europe to the South and Middle America, then to Korea and Japan, showed that the flights over or near the equator region carried less dose rate; this was in accordance with the known geomagnetic latitude effect.

[1] http://www.sciencedirect.com/science?_ob=ArticleURL&_udi...

tomjen38• 16 years ago

Maybe, but unless they remove radiation, they give out too much for what they are worth.

Cancer machines are bad for you, say no to cancer machines.

aperiodic• 16 years ago

The health risks can't just be quantified by the overall radiation dose. It depends on how that dose is deposited in the subject. The letter raises the concern that the since almost all the radiation is absorbed by the skin, the dose to your first centimeter or two of epidermal tissue may be fairly high. If the calculations that concluded the devices were safe assumed that the radiation was evenly distributed throughout the body, then the safety of the devices could be suspect.

fluidcruft• 16 years ago

The PR video/slideshow at the last checkpoint I went through said that the dose was safe because it was equivalent to being in the airplane for 3 hours. This presumably was meant to be comforting, but in my mind I was computing a 3hours:3sec ratio and trying to remember if time-dose averaging was appropriate (I work in MR, and it's been a while since my ionizing radiation course). I was not asked to go through the machine, but I would have refused simply because of the flippant tone of the 3hrs in the air claim.

uvdiv• 16 years ago

No, actually your data validates him. Maybe you are confusing 'm' with 'μ', that is, milli- (10^-3) with micro- (10^-6)?

>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.

1.64 mSv (milliSieverts) / 500 hours = 3.28 μSv/hour. A 3-hour flight is 10 μSv.

For comparison, the FDA letter [1] linked in another comment here cites the effective dose of the backscatter x-rays as 0.25 μSv.

The cosmic ray dose from a 3 hour flight is 40 times that of the backscatter x-ray. Pretty much "dwarfs it".

(Note that while the FDA letter says the effective dose is 0.25 μSv, the footnote there (11) says that RapiScan is <=0.05 μSv. Not sure how to parse this -- maybe the 0.25 μSv is a regulatory definition, not the real dose. An NPR article [2] I cited earlier claimed 0.02 μSv, consistent with that <=0.05 μSv figure.

While I'm in these parentheses, NOAA has a table [3] of cosmic ray doses as a function of altitude. Pretty much consistent with your source -- 3 μSv/hr at 30,000 ft, 6 μSv/hr at 40,000 ft).

[1] http://www.fda.gov/Radiation-EmittingProducts/RadiationEmitt...

[2] http://www.npr.org/templates/story/story.php?storyId=1268330...

[3] http://www.swpc.noaa.gov/info/RadHaz.html

jrockway• 16 years ago

That's fine though. Society has already determined that 3000 people dying in a terrorist attack is much scarier than 500,000 people that die every year from heart disease. Otherwise we'd be spending money on encouraging a heart-healthy lifestyle rather than preventing someone from bringing a toothpaste-bomb onto a plane.

It's clear that if we can save 200 business travelers and vacationers from incineration, it's worth killing off a few senior citizens. Won't someone please think of the children?

(Hey, this isn't my policy. If someone asked me, "is it worth hurting someone to possibly save someone else", I would have said no. But nobody ever asks me about these things!)

AngryParsley4• 16 years ago

That letter is from April. The FDA wrote a response last month: http://www.fda.gov/Radiation-EmittingProducts/RadiationEmitt...

The recommended limit for annual dose to the skin for the general public is 50,000 µSv. The dose to the skin from one screening would be approximately 0.56 µSv when the effective dose for that same screening would be 0.25 µSv. Therefore the dose to skin for the example screening is at least 89,000 times lower than the annual limit.

Most of the concerns in the letter are addressed. It's easy to spread FUD, but these devices are likely safe. Other organizations and governments have evaluated their safety independently.

eiji• 16 years ago

"Most" of the concerns ...

... are "likely" safe.

It's a tiny line between FUD and alertness. I prefer people bring this stuff up every now and then to remind all of us to never stop questioning things.

AngryParsley4• 16 years ago

It's so easy to get caught up in the halo/horn effect and try to make every fact about backscatter machines bad. But the truth is complicated. It requires weighing all evidence, not just looking at evidence that agrees with your current views.

89,000 times lower than the annual limit.

I'm not a fan of the TSA or backscatter machines, but facts are not up for debate. If backscatter machines cause cancer, it would be very surprising and it would tell us something new about physics and/or biology.

Also, if you worried about every risk that was as low as backscatter machines, you simply wouldn't be able to function in society. 5 minutes in a car is a 1 in 5 million chance of death.

tomjen38• 16 years ago

It does not matter if they are safe (which they aren't), it matters that they be removed.

A little fud now and then is a good thing.

chroma• 16 years ago

If you're willing to say anything to make the other side look bad, why should anyone give you credence?

Yzupnick• 16 years ago

> A little fud now and then is a good thing

This, my friend, is the problem with politics and science today.(And probably all of human history, but I was going for affect.)

Retric• 16 years ago

There is some evidence that extremely low radiation do not increase your cancer risk. However, if you realize that a pilot already receives increased radiation by flying several hours a day and could average 2+ of these scanning’s a day for 30+ years you are probably adding a significant risk (compared to getting a pat down).

As to passenger safety the annual dosage delivered in a short period of time is not safe. So take someone with say, a bad sun burn or a recent CAT scan and walking though those things is probably a bad idea.

Also due to poor training / incompetence some people are going to be sent through these things several times and or be required to stand there while someone get's distracted.

PS: The corresponding annual effective dose... and 500 mrem for the more exposed routes. (Bottollier-Depois JF et al. Assessing exposure to cosmic radiation during long-haul flights. Radiat Res 153(5 Pt. 1):526-32; 2000.)

loewenskind2• 16 years ago

>It's easy to spread FUD, but these devices are likely safe.

We have two facts here:

* These machines should not be in use as they do nothing to help security and they are ripe for abuse (and have already been abused in their short time of being used)

* The public is not ever going to be bothered enough by privacy concerns to actually do something about it. They would, however, do a great deal if they felt their lives depended on it.

Taking these two facts into account, if a leading scientist says these things may be dangerous I would tend to take his word for it without digging into it. That sounds bad but how else can one deal with people who value convenience over what is right?

tptacek• 16 years ago

I accidentally upvoted you. There is the truth and there is falsity. None of our principles, including the one that says minimum wage security workers shouldn't be looking at us naked, mean anything if we can't look each other in the eyes and articulate them truthfully.

It is falsity that is allowing people to convince airport authorities that these machines make sense. If you want to get into the bullshitting arms race, know a priori that you will lose; those people are much better at it than you are, and they have more to gain or lose.

gammarator• 16 years ago

Thanks for pointing to this very thorough response which addresses the concerns of the letter. I don't think the authors of the letter are spreading FUD, however: they're asking for more information about the means by which the dose is being calculated and pointing out potential health consequences of the lower-energy beam in skin absorption:

<em>if the key data (flux-integrated photons per unit values) were available, it would be straightforward to accurately model the dose being deposited in the skin and adjacent tissues using available computer codes.</em>

This looks like science to me, not FUD.

jcromartie• 16 years ago

Just as a general policy, I don't willingly step into superfluous machines intended to irradiate me.

chopsueyar2• 16 years ago

Why, what are you hiding?

Dylanlacey• 16 years ago

And THAT is the magic, but ultimately farsical response that opponents often have to defend against.

Not saying you're not being frivolous, but it's annoying how often people take the easy route.

pjscott2• 16 years ago

The airplane itself is much less superfluous, but irradiates you far more than the backscatter machines. Are you sure you're not just putting a sort of halo of evilness around the backscatter machines because you dislike them for other reasons?

(Full disclosure: I'm not particularly bothered by backscatter machines as such, but I vehemently object to the paranoid, theatrical, and statistically silly approach to security that has provided the impetus for their installation.)

catch23• 16 years ago

what's your source that the radiation emitted from sitting in the airplane cabin is higher than a cat scan machine?

carson• 16 years ago

I found the most interesting part of this to be the end when they list one of the concerns as Software. For those who want a point of reference of what could go wrong check out the Therac-25 story http://en.wikipedia.org/wiki/Therac-25

_ouxp• 16 years ago

I had the exact same thought.

"Because this device can scan a human in a few seconds, the X-ray beam is very intense. Any glitch in power at any point in the hardware (or more importantly in software) that stops the device could cause an intense radiation dose to a single spot on the skin."

DanielBMarkham• 16 years ago

I believe what's happening is the use of the radiation concerns is a proxy for the underlying problem: regularly taking naked pictures of the population in the name of security.

I don't think anybody can effectively argue that the whole enterprise is in dire need of grownups -- too easy to get screwed the next time there is an attack. But you could argue that radiation is a key factor, or just wave your arms around and yell a lot. With enough arm-waving, smoke, and mirrors you can make the case that the population is deeply concerned about radiation effects -- regardless of the science -- so "something must be done". "Something must be done" is what got us here in the first place, perhaps "something must be done" is what can get us out.

alex_c• 16 years ago

The problem, of course, is that you are not solving the underlying problem... you are, at best, potentially treating one isolated symptom, and you are doing so by deflecting the conversation from the real problem as well as potentially compromising some scientific integrity along the way.

Tamerlin• 16 years ago

More to the point, it's the government engaging in pornography, illegal search, and sexual assault combined with radiation overdoses in the name of FALSE security.

We already know that they don't work, and they don't even pretend to address any of the real security vulnerabilities. They'll only deter idiot terrorists, not real ones.

DanI-S• 16 years ago

Airport security is ridiculous. What do we do when the first bright terrorist figures out they can blow up 500 people in the line for the scanner?

pjscott2• 16 years ago

We'll faint dead away!

Seriously? We could implement pipelined multi-stage inspections, like a security line to get into another security line, and hire more TSA people to make sure everyone is spread out. And have bomb-sniffing dogs everywhere. This would be silly, but I wouldn't put it past the TSA to actually do it.

Leading scientists say backscatter X-ray may be far more dangerous than thought

Related Stories