The Backscatter Machines Safety Debate

[Beth]

There may not be a monitoring program in place. In Congressman Dennis Kucinich's letter to Transportation Security Administration Chief John Pistole, dated Nov 24, 2020, he asked the TSA to set up a monitoring program for the safety of the TSA employees and the airline passengers.

Yes, it would make sense to do that. I'm sure that the machines have some sort of scheduled maintenance recommended, but a monitoring program for the safety of the individuals working with the machines would be a good idea.

I'd like to know what the range of radiation being released is for each model that has been sold to the govt and put into use.

Specifically I'd like to know the lower limits, upper limits, and typical usage limits for several areas around the machine. That is where its targeted (the airline passenger), near the operator (TSA employee) and several areas where bystanders could be waiting (airline passengers waiting at the checkpoint). How far away does one have to be so they get no effects of the radiation at all?

It's possible that some of this information may be available on technical specification sheets* that may be on the vendor's web sites -- but it would also be nice if this information was available on an independent 3rd party's web site.


*Its on my list of things I intend to google for ..

The problem with technical spec sheets is they are hard to understand unless you put a lot of time and effort into it. They're great for professionals who know what information is being provided and what it means, not so much for lay people without professional expertise.

 

[Kaylee]

Actually, probably not. The evidence suggests that low doses of radiation either have no effect at all, or could even be beneficial. See, for example, figure 9 and table 4 in "Radiation and Reason" by Wade Allison. (I think it's still available free, if not the references for those parts are:
Preston, Dale L. et al (2004) Effect of Recent Changes in Atomic Bomb Survivor Dosimetry on Cancer Mortality Risk Estimates. Radiat. Res. 162, 377–389.

Henriksen, Thormod and Maillie, H. David (2003) Radiation & Health. Taylor & Francis.)

Parts of Wade Allison's book is available on line at Google Books and at a web site set up for the book. However, AFAIK, the pages with figure 9 and table 4 are not available on-line.

How am I as a non-scientist suppose to evaluate whether Wade Allison has credibility? He appears to have excellent professional credentials, including being a professor of physics at Oxford University, but I have learned at the JREF that is not necc. enough. For example Rupert Sheldrake has degrees from Harvard and Cambridge Universities. However, his work cannot be replicated by others and his grasp of statistics is faulty (per others, I don't know enough about statistics to say).

Allison's book is probably self-published (the title page of his book says Published by Wade Allison Publishing). That's not necc. a bad thing, but it does eliminate at least one level of scrutiny that I know other authors have to go through. On his book's web site, there doesn't appear to be any reviews by peers or even science editors. Most of the reviews appear to be user comments on other web sites.

While attempting to find your other sources on line, I found this:

Health Risks from Exposure to Low Levels of Ionizing Radiation:
BEIR VII Phase 2

On page 10 the committee says why they disagree with studies that claimed that at low doses ionizing radiation is not harmful or may even be beneficial:

the committee reviewed articles arguing that a threshold or decrease in effect does exist at low doses. Those reports claimed that at very low doses, ionizing radiation does not harm human health or may even be beneficial. The reports were found either to be based on ecologic studies or to cite findings not representative of the overall body of data.

Ecologic studies assess broad regional associations, and in some cases, such studies have suggested that the incidence of cancer is much higher or lower than the numbers observed with more precise epidemiologic studies. When the complete body of research on this question is considered, a consensus view emerges. This view says that the health risks of ionizing radiation, although small at low doses, are a function of dose.

Both the epidemiologic data and the biological data are consistent with a linear model at doses where associations can be measured.

Committee members biographies are available on pages 379 - 384.

BTW, for those interested I recommend reading the Executive Summary of the book on pages 11 - 18. I read the public summary also. IIRC, the two summaries are mostly repetitive, but there was some interesting info that wasn't. So if you have time, you may want to read the first 11 pages also.

 

[Kaylee]

Yes, it would make sense to do that. I'm sure that the machines have some sort of scheduled maintenance recommended, but a monitoring program for the safety of the individuals working with the machines would be a good idea.

I agree and its clearly the responsibilty of the TSA to set one up. They should be on public record as to what their monitoring program is and how they are implementing it.

The problem with technical spec sheets is they are hard to understand unless you put a lot of time and effort into it. They're great for professionals who know what information is being provided and what it means, not so much for lay people without professional expertise.

I agree. It would be nice if the mass media helped close the information gap.

 

[Kaylee]

The company really is named Rapiscan? That is hilarious.

I believe it's mean to be pronounced rapi[d]-scan, not rape-i-scan; but the latter is definitely funnier.

Proof that some companies should spend more money on marketing consultants. I personally think that the first pronunciation is more appropriate but I bet Rapiscan's management doesn't.

You get a dose of radiation just from flying in an airplane.

That's a popular comparison that's been going around. Here's another POV*:

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!

* Point of View (POV) or actual fact? {shrug} One of the reasons I started this thread, I'm hoping that I'll get a better idea of which statements about x-rays floating around these days are backed up by evidence and which ones aren't.

 

[Kaylee]

1)<snip> as dosimeters have a quite high error at small doses.

Why is that? Is it because dosimeters can really only measure radiation dosage absorbed in matter and we are looking to see how much radiation has been absorbed by human tissue? Are they any other reasons?

 

[Drachasor]

Right. They are saying it hasn't been studied and we don't know how safe or dangerous it actually is. I'm not particularly comfortable with the idea of exposing millions of citizens, some of them quite frequently, to radiation when no one appears to know what the actual effect of it might be. It is also disquieting that the actual levels of radiation are not being measured and the results publicly released.

I haven't looked into it, but is there any information being released on maintenance and calibration of these machines? If one malfunctions by emitting too much radiation, will operators be able to tell and shut it down until it's fixed?

No, they are literally arguing over how miniscule the danger is. Is it tiny, tiny or tiny, tiny, tiny? That sort of thing.

Acting like they are saying there is any significant danger is the same fallacy creationists use to say evolution might not be true because scientists argue over small details of the theory.


Compare it to x-ray scanners at the doctor's office and you'll see just how trivial this stuff is. Even with the figures cited, the radiation here is nothing.

 

[Kaylee]

No, they are literally arguing over how miniscule the danger is. Is it tiny, tiny or tiny, tiny, tiny? That sort of thing.

Acting like they are saying there is any significant danger is the same fallacy creationists use to say evolution might not be true because scientists argue over small details of the theory.


Compare it to x-ray scanners at the doctor's office and you'll see just how trivial this stuff is. Even with the figures cited, the radiation here is nothing.

If I understood the links, numbers and dosage units correctly, if the average person flies 50 times a year they may increase their chances of getting cancer by 1%.

But, the risks are not the same for everyone as the scientists affiliated with the University of California (SF) and Brenner from Columbia University have explained. (Links in the OP)

I haven't heard any counter arguments that, say, someone with a history of cancer would probably have a much higher risk of future problems if they were to go through a backscatter machine. Brenner said their chances of getting cancer increased to 1 out of 20.

And since most radiologists agree that the more exposure the more risk -- the odds of someone with a history of cancer (whether family or personal) would go up the more they fly.

And the blogger brought up a good point that TSA employees may exceed the maximum amount of radiation exposure recommended for people who work with radiation.

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).

I haven't worked through his numbers. I suspect he's wrong about the safe annual amount being 100 mrem, I believe it would be 5,000 mrem (based on pg 5 in this link). I think he got the 100 mrem from the amount that the ICRP recommends that members of the general public limit themselves to from airplane flights.

But I'd like to hear an opposing view point, backed up with facts, as to why a TSA employee would not end up exceeding a "safe" amount of radiation exposure.

Translating "safe" to mean acceptable risks.

 

[Drachasor]

If I understood the links, numbers and dosage units correctly, if the average person flies 50 times a year they may increase their chances of getting cancer by 1%.

That's the high end and assumes 50 flights a year every year for someone's entire life, I believe. However, there is a fair bit of evidence that low levels of radiation actually make you healthier and don't increase cancer risk, so the likelihood of the 1% bit is not very high. Also, a 1% increase in a chance to get cancer which might be something like 5%, only results in a 5.05% chance of getting cancer.

I haven't heard any counter arguments that, say, someone with a history of cancer would probably have a much higher risk of future problems if they were to go through a backscatter machine. Brenner said their chances of getting cancer increased to 1 out of 20.

AFAIK, it is not true that someone with a history of cancer would have a much higher risk of future problems. It IS true that someone whose cells are bad at repairing DNA damage, would have a higher risk. That's a completely different thing from having a previous cancer.

And the blogger brought up a good point that TSA employees may exceed the maximum amount of radiation exposure recommended for people who work with radiation.

Well, I think John's Hopkins would have tested that, but I am not sure, I admit. Since they aren't standing in the scanner, their exposure is going to be far tinier than the tiny amount the people scanned get.

I haven't worked through his numbers. I suspect he's wrong about the safe annual amount being 100 mrem, I believe it would be 5,000 mrem (based on pg 5 in this link). I think he got the 100 mrem from the amount that the ICRP recommends that members of the general public limit themselves to from airplane flights.

But I'd like to hear an opposing view point, backed up with facts, as to why a TSA employee would not end up exceeding a "safe" amount of radiation exposure.

Translating "safe" to mean acceptable risks.

I'll take a look at it later, gotta get lunch now.

I do think it is a bit silly they are using x-ray machines at all. The radio-based ones would have zero harmful radiation. That said, I think people need to calm done about this being very dangerous. Worst case scenario they are dangerous if used for one's whole life, so there are easily years to study them and come to a firm conclusion.

 

[Beth]

No, they are literally arguing over how miniscule the danger is. Is it tiny, tiny or tiny, tiny, tiny? That sort of thing.

This appears to be a non sequitor. My question regarding the operators ability to determine if the machine malfunctions had nothing to do the size of the risk under normal operation.

Acting like they are saying there is any significant danger is the same fallacy creationists use to say evolution might not be true because scientists argue over small details of the theory.

I am not particularly worried as I don't travel much. But I can understand frequent travelers being skittish about it. It's not that I think it's dangerous. It's that I think the actual effects are pretty much unknown at this point.

Compare it to x-ray scanners at the doctor's office and you'll see just how trivial this stuff is. Even with the figures cited, the radiation here is nothing.

As I said earlier, I am concerned when apparently respectable experts in the field are claiming that we don't really know the effects of this particular type of radiation and that the type of radiation can potentially majorly impact the effect. Comparing it to the dose that is typical for X-rays doesn't mean much since it's a different type of radiation.

 

[Drachasor]

As I said earlier, I am concerned when apparently respectable experts in the field are claiming that we don't really know the effects of this particular type of radiation and that the type of radiation can potentially majorly impact the effect. Comparing it to the dose that is typical for X-rays doesn't mean much since it's a different type of radiation.

Again, you are misreading them. This is just like someone looking at two experts arguing about punctuated equilibrium and then saying it casts doubt on evolution. And no, it isn't different from an X-Ray scanner in Hospital except for the amount of radiation released and how the machine processes the information.

Compare:

Do experts disagree on the frequency and importance of punctuated equilibrium? Yes.
Do they disagree on the existence of evolution? No.

Do experts disagree on the exact effect of the radiation? Yes.
Do they disagree on whether it poses a significant health risk? No.

People are exaggerating the scale of disagreement.

 

[Beth]

Again, you are misreading them. This is just like someone looking at two experts arguing about punctuated equilibrium and then saying it casts doubt on evolution. And no, it isn't different from an X-Ray scanner in Hospital except for the amount of radiation released and how the machine processes the information.

Compare:

Do experts disagree on the frequency and importance of punctuated equilibrium? Yes.
Do they disagree on the existence of evolution? No.

Do experts disagree on the exact effect of the radiation? Yes.

Do they disagree on whether it poses a significant health risk? No.

People are exaggerating the scale of disagreement.

My perception is that experts disagree on what the exact health risk this TSA usage poses. Mostly what I gather is they don't know and don't have the information they need to make an accurate assessment.

 

[Drachasor]

My perception is that experts disagree on what the exact health risk this TSA usage poses. Mostly what I gather is they don't know and don't have the information they need to make an accurate assessment.

They disagree on the exact health risk. Evolutionary Biologists disagree on the exact details of evolution.

Disagreement doesn't mean anyone thinks there's a significant danger.

 

[Kaylee]

If I understood the links, numbers and dosage units correctly, if the average person flies 50 times a year they may increase their chances of getting cancer by 1%.

That's the high end and assumes 50 flights a year every year for someone's entire life, I believe.

I think my calculations were wrong yesterday. I got a different number today. (In my defense, I know very little about this area -- even the units for measuring radiation doses are brand new to me.)

For now, let's assume that the radiation dose per use is .02 mSv
(using the manufacturer’s figures as quoted from NPR article, link and quote in the OP)

and

that 1 out of 100 people will get cancer from a one-time exposure of 0.1 Sv of low-LET radiation above background.

(statistic worked up by The National Research Council’s Committee on the Biological Effects of Ionizing Radiation (BEIR) in their book, available on line:
Health Risks from Exposure to Low Levels of Ionizing Low Levels of Ionizing Radiation: BEIR VII Phase 2 Their study was summarized on page 7 and they go into more detail in Chapt. 12. )

My grasp of radiation units is still a little shaky, but I believe that

.02 mSv is equal to 2 mrem
.1 Sv is equal to 10, 000 mrems

(At low levels of LET, the mrem and Sv units are apparently interchangeable)

Using the manufacturers figures, an “average” airline passenger could use the backscatter machine 5,000 times before he would have a 1% risk of getting cancer as a direct result.

BUT
it appears that was not my only mistake yesterday.

It seems that I shouldn't use the manufacturer’s number of .02 mSv.

For everyone’s convenience, I’m requoting the University of California (SF) scientist’s reasoning as to why that figure is unrealistic:

Here's it is again from an NPR article that was also in the OP:

The San Francisco group thinks both the machine's manufacturer, Rapiscan, and government officials have miscalculated the dose that the X-ray scanners deliver to the skin — where nearly all the radiation is concentrated.

The stated dose — about .02 microsieverts, a medical unit of radiation — is averaged over the whole body, members of the UCSF group said in interviews. But they maintain that if the dose is calculated as what gets deposited in the skin, the number would be higher, though how much higher is unclear.

and from a blogger:

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!

This all sounds very reasonable to me. If anyone disagrees with the UCSF scientists or the above blogger, could you please post and explain why?


I'd also appreciate it if someone can confirm if the way the blogger uses the word "fold" in "the radiation is ~20-35-fold higher" means that a base number is suppose to be raised somewhere between the power of 20 and the power of 35. And if that is the case, any suggestions on how to find the base number?

Thanks!

Another issue is that only average numbers have been mentioned. I think the range of numbers in the dataset is very important also when formulating a health policy on deciding whether to use x-ray machines on people for security purposes. In other words when averaging numbers, its possible that all the numbers can be close to the mean average or they can be wildly apart. What is the general case in radiation studies? Has anyone seen those numbers?

 

[Kaylee]

<snip>

However, there is a fair bit of evidence that low levels of radiation actually make you healthier and don't increase cancer risk, <snip>

We're getting into the Radiation Hormesis Hypothesis vs the Linear No- Threshold model (every level of radiation exposure has risk)

I've haven't been able to find any support for it. The National Council of Research (NRC) doesn't think that the studies that support radiation hormesis holds up. See my post #22 from yesterday.

I looked some more today and basically my findings are that national and international agencies think that policies should be formulated using the linear no-threshold model. For example:

Consensus reports by the United States National Research Council and the National Council on Radiation Protection and Measurements and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) have upheld that insufficient human data on radiation hormesis exists to supplant the Linear no-threshold model (LNT). Therefore, the LNT continues to be the model generally used by regulatory agencies for human radiation exposure.

More quotes of the same nature are in the wiki article.

Cuddles also mentioned the radiation hormesis hypothesis yesterday (albeit not by name). I couldn't find his sources on line. If there are sources on-line that support the theory -- for humans outside of the lab -- I'd like to read them.

Also, a 1% increase in a chance to get cancer which might be something like 5%, only results in a 5.05% chance of getting cancer.

AFAIK, in the examples that the National Research Council (NRC) worked up, the possibility of getting cancer due to exposure to low-LET radiation above background was independent of the original probability of getting cancer. So the probabilities should be added ( 6%). But ... I already posted how my calculations yesterday were in error and how one of the recalculations today is probably useless because the backscatter machine manufacturer's assumption of a .02 mSV dose per use is probably wrong.

So, at this point, I have no idea what the amount of the backscatter machines' radiation exposure is.

AFAIK, it is not true that someone with a history of cancer would have a much higher risk of future problems. It IS true that someone whose cells are bad at repairing DNA damage, would have a higher risk. That's a completely different thing from having a previous cancer.

OK, makes sense. But I think I can infer that you agree that the average risk does not pertain to certain groups of people -- such as those who have BRC1 and BRC2 genes (some of the genes responsible for cells being bad at repairing DNA damage), and perhaps you even agree that it also doesn't pertain to children and infants -- as well as some of the other groups mentioned by the UCSF scientists in their letter of concern (mentioned and linked to in the OP).

Its unlikely that most people would know the reason why cancer runs in their family. Is it due to genes that produce cells that are poor at repairing DNA damage or is it due to another reason? As its not practical for most people to get the tests to find out, it would probably make sense for people in that situation to avoid backscatter machines.

I do think it is a bit silly they are using x-ray machines at all.

I agree with you on that.

 

[Kaylee]

My perception is that experts disagree on what the exact health risk this TSA usage poses.

That's my perception also. Brenner of Columbia University is a good example.
If he thinks its safe, why did he say he wouldn't have signed off on a report about guidelines for scanners if he had known that the intent was to use x-ray scanners on almost every traveler?

But the UCSF scientists aren't the only ones who are concerned. David Brenner, head of Columbia University's Center for Radiological Research, recently aired his worries before the Congressional Biomedical Caucus.

"There really is no other technology around where we're planning to X-ray such an enormous number of individuals," Brenner told the caucus and congressional staffers. "It's really unprecedented in the radiation world."

Brenner's name carries some clout, because he served on a small group of experts convened in 2002 by the National Council on Radiation Protection and Measurements to write guidelines for the security scanners. He now says he wouldn't have signed the report if he had known the X-ray scanners were going to be used on virtually every air traveler.

IMHO, another reason to be concerned about this is that airports are not the only place where the government intends to use x-ray scanners. They are currently being used in vans to surveil traffic and in Florida courthouses. We have every reason to believe that the govt. intends to expand their use of this technology. How widely this technology is used is an important consideration in determining how safe the technology is.

 

[69dodge]

I'd also appreciate it if someone can confirm if the way the blogger uses the word "fold" in "the radiation is ~20-35-fold higher" means that a base number is suppose to be raised somewhere between the power of 20 and the power of 35.

I'm pretty sure "-fold" just means "times", i.e., "20 to 35 times as high".

 

[Drachasor]

I'm pretty sure "-fold" just means "times", i.e., "20 to 35 times as high".

Correct, but we have to remember the base numbers are thousands of times lower than an x-ray scanner at a hospital (I think about 2000). While 20 or even 50 times more radiation seems like a lot, it isn't that much in the overall scheme of things.

"X-rays are a relatively safe method of investigation and the radiation exposure is relatively low, depending upon the study. Experimental and epidemiological data, currently do not support the proposition that there is a threshold dose of radiation below which there is no increased risk of cancer.[26] However, this is under increasing doubt.[27] Diagnostic X-rays account for 14% of the total annual radiation exposure from man-made and natural sources worldwide.[28] It is estimated that the additional radiation will increase a person's cumulative risk of getting cancer by age 75 by 0.6–1.8%.[29] The amount of absorbed radiation depends upon the type of X-ray test and the body part involved.[30] CT and fluoroscopy entail higher doses of radiation than do plain X-rays.

To place the increased risk in perspective, a plain chest X-ray or dental X-ray will expose a person to the same amount from background radiation that we are exposed to (depending upon location) everyday over 10 days.[31] Each such X-ray would add less than 1 per 1,000,000 to the lifetime cancer risk. An abdominal or chest CT would be the equivalent to 2–3 years of background radiation, increasing the lifetime cancer risk between 1 per 10,000 and 1 per 1,000.[31] For instance, the effective dose to the torso from a CT scan of the chest of a 14 year old girl is about 5mSv.[32] These numbers are very small compared to the roughly 40% chance of developing any cancer during our lifetime.[33] It should be noted that the accurate estimation of effective doses due to CT is difficult. For instance, the estimation uncertainty range is about ±19% to ±32% for adult head scans depending upon the method used.[34]" (From wikipedia).

So even the overall influence of all x-rays someone is likely to have gotten over 70-odd years, the increase is small. Backscatter X-rays are much, much weaker, however you measure them. Even if they are used for 10 years while further research is done, they aren't going to cause remotely significant harm.

 

[Kaylee]

I'm pretty sure "-fold" just means "times", i.e., "20 to 35 times as high".

Correct,

Thanks!

I may post more on other points in this thread but I have to run to my appt. now.