Are CT Scans More Dangerous Than We Thought?

[Necrosis]

There seem to be two key assumptions: CT scan radiation is comparable to A-Bomb radiation, and that this graph:

http://radiology.rsnajnls.org/cgi/content-nw/full/232/3/735/F1

is supposed to be linear through zero.


I'd like to hear someone knowledgeable comment on the first assumption... I might take a crack at the second one; that graph doesn't seem to support the linear through zero.

I agree, it looks like, to me, that it is capping off...as for the first assumption, I'm not sure I can give you a knowledgeable answer as I don't know that much about the bodies reaction to repeated doses of radiation as compared to one large dose of radiation.

 

[geometer]

my bad, interposed percentage figures, I meant .08% which is from the original post. And for such a potentially dangerous illness, I find that significant.

As I mentioned earlier, this is a population risk, not an individual risk. This means that in a population of 10,000 individuals, exposure at this level could be expected to result in as many as 8 additional deaths over what would normally be expected. It doesn't mean that your individual risk has increased by .08%

 

[Necrosis]

As I mentioned earlier, this is a population risk, not an individual risk. This means that in a population of 10,000 individuals, exposure at this level could be expected to result in as many as 8 additional deaths over what would normally be expected. It doesn't mean that your individual risk has increased by .08%

I never meant to state that it was an individual risk, and If I did, I am sorry, but 8 more people is still 8 more people. :Shrug:

 

[Tsu]

If you're that concerned about radiation, stay away from the following:
Airplanes
Microwaves
Tobacco
Televisions
Smoke detectors
Lantern mantles
Building materials
Luminous watches and dials
Water
Rocks
Sunshine
Other people

All of these things give off radiation. Oh. And NEVER permit yourself to have ANY medical x-rays or you will DIE in 50 years or so. Of course it will probably be less if you have to have mammograms - but obviously none of you are concerned with such issues. Guess none of you have wives...

 

[Necrosis]

If you're that concerned about radiation, stay away from the following:
Airplanes
Microwaves
Tobacco
Televisions
Smoke detectors
Lantern mantles
Building materials
Luminous watches and dials
Water
Rocks
Sunshine
Other people

All of these things give off radiation. Oh. And NEVER permit yourself to have ANY medical x-rays or you will DIE in 50 years or so. Of course it will probably be less if you have to have mammograms - but obviously none of you are concerned with such issues. Guess none of you have wives...

POSTED BY ME
Well, I don't know what problem you have with me, but let me make this perfectly clear for you and any other person who loves to interpret words as what they don't mean but could mean;

I would want to know the risk, even if it meant all that would happen is my hair would stand on end. I do know that driving has more chance of me dying in an accident than me dying through cancer from a CT scan, hell, more so for me because I race at the strip and am an aggressive driver whose blinkers don't currently work. I could choke on my SOUP tonight and die. I do not care about the death or how the death occurs, it is statistically proven that you WILL die. My problem is that only 7% of people that get a CT scan are informed of the risks when it may mean something more to a cancer survivor or a family member of a cancer victim or likewise. I PERSONALLY like to know the knowledge associated with damn near everything I can or that pertains to me, it's a tall drink, but I eventually want to order another one.

Why don't you look up and link what the lifetime expectency of a Marine while deployed in the field is, because I was in the Marines, and I was in the field and I went through that. My father was a S.E.A.L. and he had an even smaller lifetime expectency while in the field. I look at chances and odds because to ignore them is pre-mature death, but to disregard them is the same.

Appearantly you don't like to read everything...and yes I do have a wife.

 

[Necrosis]

Necrosis,

My gut reaction is honed by working at a job where, rightly, I must be sensitive to people suffering from medical conditions. Of course this is PF reality, so I will take the original comment with a grain of NaCl. I appreciate your going out of your way to explain its content.

I originally had associated "Necrosis" with "brain dead." I am a Unitarian - no doubt some Satanists in that crowd. Back to the Thread?

No problem.

Do you know something about repeated doses of radiation as compared to a single large dose? When the small doses eventually add up to almost the same (we'll call it the same for this question) amount as the large dose?

 

[Loren Booda]

I think that question had been touched upon earlier, but not answered definitively by our "experts."

The local radio station has a commercial that warns of household radiation danger. Apparently radon ("the second leading cause of lung cancer") builds up in basements in geographical regions where this particular decay product is generated. The choice may be between an energy "tight" house and a house safe from radiation.

 

[Tsu]

Appearantly you don't like to read everything...and yes I do have a wife.

No, I read it.
I'm glad you have a wife. We wives are nice to have around.

My point was, there is radiation everywhere. You said you wanted to know the risks of everything you do. I was merely trying help you avoid having to take those risks by pointing out a few things to avoid.

Radiation dose is cumulative. You are 'allowed' just so much in your lifetime and it's dependent upon your age. I'll have to brush up on my radiation protection terms and formulas (a few things have changed since I studied it ) but IIRC, the maximum permissable dose (MPD) is calculated by your age minus 18, then multiply by 5. This will give your MPD in RADs (radiation absorbed dose). I believe 1 RAD = 1 Roentgen = 1 rem (radiation equivalent man).

The body is a remarkable machine with amazing powers of regeneration. Did you know that every 7 years you have a brand new liver? We are continually making new cells and repairing damaged ones. The only parts of the body that don't regenerate are the eyes and reproductive organs. We take GREAT care to protect those.

There is no doubt that medical radiation is the source of most absorbed dose, and you should always discuss your concerns of risks with your physician before any scheduled medical exam. However, if you fall and break your hip, or get into a big car wreck, I doubt that the risks of radiation will be first and foremost in your mind.

Now, since the title of this thread is 'Danger in CT scans', I felt that it was important to point out that mammograms are higher dose exams than many CT scans. What I found interesting was that no one seems to want to comment on that. Are you not concerned about the massive dose your women are receiving on an annual basis? Possibly your women aren't old enough to worry about that yet, but it is certainly something that I am concerned about - and I work in the profession! Wouldn't that be enough to get your attention?

So, to those of you who may be doing research in the field or if you really want to help to make a difference - PLEASE FIND A WAY OF IMAGING THE BREASTS WITHOUT RADIATION! I have huge concerns that the very method we are using to detect breast cancer is also CAUSING some of those cancers. I don't have these concerns about CT scans as much because they are done in the 120KV range instead of the more damaging 20-30KV range. BUT - you DON'T want to go to one of those Body Imaging places in the local mall to have your annual screening CT scans. Most of the medical community are STRONGLY against those places. They are a source of needless radiation and the exams are generally useless.

 

[russ_watters]

...PLEASE FIND A WAY OF IMAGING THE BREASTS WITHOUT RADIATION!

Must...resist...sexual...inuendo.

Seriously though, Necrosis, you are taking this waaaay to personally. I'm no one - I'm not worth the effort to flame. If you disagree with something I said, say why you disagree or ignore me. Life's too short to get upset about it.

Regarding you desire to know the risk in everything, what we're trying to convey to you is two-fold:

1. There are risks everywhere and it is impossible to know what they all are all the time. To want to know every risk will lead to risk-reward analysis controlling your entire life.
2. Rest assured, when you go for that CT scan, someone (who knows more than you or me about the subject) has analyzed the risks and determined that it the benefit outweighs the risk of the scan.

 

[Integral]

2. Rest assured, when you go for that CT scan, someone (who knows more than you or me about the subject) has analyzed the risks and determined that it the benefit outweighs the risk of the scan.

Unfortunately, Russ, I am not so sure this is true. The Medical "professionals" must justify and pay for expensive equipment Tsu's comments reinforce my believe that profits come before long term patient safety in the US medical system.

Unfortunately my mother in law (whom I never had the chance to meet) and a very dear aunt of mine died of breast cancer way to young, both were faithful in their mammograms and Hormon Replacement. Both of which are questionable medical practices which may in the long run shorten the life of the patient while padding the wallet of the medical professionals.

Fortunately my wife was astute enough to make a connection and has not bought into the common concept of what is good for the doctors wallet is good for me.

 

[Loren Booda]

How effective are sonograms in breast imaging?

 

[imabug]

How effective are sonograms in breast imaging?

Ultrasound in breast imaging is good a characterizing soft tissue masses, but you can't see small calcifications that are characteristic of many types of breast cancer. Good specificity for some things, lacking in sensitivity.

Mammography on the other hand has very good sensitivity at detecting many things, but is not very specific. You can detect that something is there, but you can't always determine whether it is malignant or not.

Ultrasound is commonly used as an adjunct to mammography imaging, particularly to characterize soft tissue masses seen in mammograms. Ultrasound will never replace mammography because the resolution is too coarse.

 

[imabug]

You are 'allowed' just so much in your lifetime and it's dependent upon your age. I'll have to brush up on my radiation protection terms and formulas (a few things have changed since I studied it ) but IIRC, the maximum permissable dose (MPD) is calculated by your age minus 18, then multiply by 5. This will give your MPD in RADs (radiation absorbed dose).

this is only true from a regulatory stand point. MPD limits come from the NRC and FDA based on recommendations from bodies such as NCRP and ICRP. As such, they are always subject to change. And don't expect anyone to arrest or fine you for exceeding your MPD. Don't expect to suddenly keel over and die or contract some form of cancer either.

I believe 1 RAD = 1 Roentgen = 1 rem (radiation equivalent man).

applies at diagnostic energies only (<150 kVp) and only for x-ray/gamma radiation.

Now, since the title of this thread is 'Danger in CT scans', I felt that it was important to point out that mammograms are higher dose exams than many CT scans. What I found interesting was that no one seems to want to comment on that. Are you not concerned about the massive dose your women are receiving on an annual basis? Possibly your women aren't old enough to worry about that yet, but it is certainly something that I am concerned about - and I work in the profession! Wouldn't that be enough to get your attention?

In the USA, MQSA regulations limit the maximum mean glandular dose to 3 mSv (300 mrem) per exposure. The majority of mammography units typically achieve about half this value. Digital mammography units, once regulators get a feel for how they behave and stop treating them like film/screen mammo units, i believe will be able to provide acceptable mammograms at even less exposure.

 

[imabug]

I was recently reading pop sci and it revealed the following stats

For one full ct scan

• 1,300: Radiation dose in millirems

• 
  a typical average dose for a body CT.
  

  [*].08%: increase in risk of death from cancer

It is usually not very meaningful to talk about risk as a straight percentage without referring to the amount of dose. A typical value for increased cancer risk that I see is about 4%/sievert (Sv) or 0.04%/mrem. Very important to remember that this is for a population (as someone else pointed out earlier).

Also

• 3.75%: increase in risk of death from cancer if you have a full body CT scan annualy from age 25

• 
  why anyone would want to have an annual full body CT scan is beyond me. Totally unecessary radiation exposure and expense.
  

  [*] 300: Average annual radiation dose from natural sources a year in millirems

  normally quoted value. dose from natural background sources varies quite a bit with location and altitude. People living in Denver CO get quite a bit more than this, and they seem to be doing just fine.
  

  [*] $16 billion Estimated annual cost of unecessary diagonstic imagine

  I would question how they determine something is unnecessary
  

  [*]7%: Percentage of patients infromed of the risks of their CT scans

Sad, but not very surprising. Consent forms generally don't get too specific on radiation risks and many places use a single generic consent form to cover just about everything done in the hospital. And it's like fine print. Nobody ever reads it anyway.

That said, there's nothing keeping a patient from asking the technologist, radiologist or staff physicist about radiation risks. most (at least the ones I know anyway) are more than happy to do discuss it with the patient.

 

[imabug]

Unfortunately, Russ, I am not so sure this is true. The Medical "professionals" must justify and pay for expensive equipment Tsu's comments reinforce my believe that profits come before long term patient safety in the US medical system.

In many hospitals (the ones I've worked at anyway), requests for CT scans are generally protocolled before being scheduled. The request is filled out by the requesting physician with a description of the patient's history and signs/symptoms. This is then reviewed by the radiologist or resident or sometimes the lead technologist to determine if the type of scan requested is suitable, whether to order a contrast enhanced scan. If there are any questions with regard to suitability, the radiologist or resident generally calls the referring physician and discusses the case.

I haven't worked everywhere yet, so I can't say that this is how everyone works, but I think it's a fairly common procedure.

studies that are scheduled just to generate revenue to pay for a scanner usually don't make it past this point (I wouldn't even expect it to make it past the insurer). And if they do, that would definitely be fraud. if Medicare/Medicaid is involved as a payor and the gov't finds out it would also be grounds for a hospital/clinic to lose their Medicare/Medicaid provider status which no one is going to risk because of the money involved.

 

[Loren Booda]

Has anyone mentioned MRIs for mammography?

 

[Tsu]

Unfortunately, Russ, I am not so sure this is true. The Medical "professionals" must justify and pay for expensive equipment Tsu's comments reinforce my believe that profits come before long term patient safety in the US medical system.

Actually, Integral, I don't really think it is so much about the money-making aspects with CT (not nearly as much as with mammography - that has almost become an industry all by itself!). With CT, I believe it is more of a CYA kind of a thing. Doctors are almost FORCED to order every conceivable test in the book just to avoid being sued. Medical lawsuits have also almost become an industry all by themselves. Not to mention physicians who come out of med. school being completely unable to clinically diagnose their way out of a box! I actually had an ER physician look at an abdomen xray and, seeing a collection of gallstones in the gallbladder, he pointed them out and said to me "See? I knew he had KIDNEY stones!" When I told him they were gallstones, he said "Oh. Yeah. I guess if they were kidney stones they would be in a little line going down the ureter." (ON WHAT PLANET WOULD THAT BE, DOCTOR?) I had to leave the ER at that point or I would have screamed to all of the patients "GO HOME! THIS DOCTOR DOESN'T KNOW WHAT HE'S DOING!" It's unbelievably frustrating to be stuck in these kinds of situations all of the time. I have been SO less than impressed with what medical schools are turning out these days. Whoops. I digress AGAIN... But you guys really got me where I LIVE with this thread...

Imabug! Thanks for jumping in here! As a medical physicist, you are in a position to help push my agenda for non-radiation breast imaging. Wanna help? Are you a radiation physicist? Do you know Tim Kasson?

 

[Tsu]

Has anyone mentioned MRIs for mammography?

Yes, I mentioned in an earlier post that I think MR is the way of the future for breast imaging. We are doing MR on breasts now, but usually only AFTER a mammogram and/or ultrasound has been done. MR is extremely sensitive to soft tissue differences and yields extremely diagnostic images. IIRC, they've been able to detect breast cancers where mammograms have not. They are not currently used as a screening tool, however, because of the time and cost factors.

Oh, Imabug...! That's where YOU come in...! Can you build me a MR Breast Imager that can perform breast exams in 15 minutes and is as (or MORE! ) cost effective as mammography? Pretty please? :shy:

 

[Tsu]

Must...resist...sexual...inuendo.

Pervert.

 

[imabug]

Imabug! Thanks for jumping in here! As a medical physicist, you are in a position to help push my agenda for non-radiation breast imaging. Wanna help?

anyone who comes up with an imaging method that's as sensitive as x-ray mammography, specific as MRI, cheap and fast will probably have it made. very challenging task.

there are several breast imaging techniques out there that use non-ionizing radiation. MRI and ultrasound are two. optical imaging is another one, but I don't really see it going very far. electrical impedance tomography is another one. I've even heard of some people trying to develop microwave imaging. I don't see any of these being anything more than adjuncts to x-ray mammography though.

x-ray mammography is currently the gold standard in breast imaging because it has excellent low contrast and resolution (15-20 line pairs/mm or < 0.03 mm), fast and easy to do so you can screen a lot of people and relatively cheap. beat those and you'll have a winner.

Are you a radiation physicist? Do you know Tim Kasson?

I'm a diagnostic medical physicst specializing in diagnostic x-ray and nuclear medicine. I'm afraid I don't know Tim Kasson.

 

[Tsu]

In the USA, MQSA regulations limit the maximum mean glandular dose to 3 mSv (300 mrem) per exposure. The majority of mammography units typically achieve about half this value. Digital mammography units, once regulators get a feel for how they behave and stop treating them like film/screen mammo units, i believe will be able to provide acceptable mammograms at even less exposure.

DR/CR is, no doubt, the future of radiology. But even so, aren't we still dealing with the extremely low KV ranges? 20-30? Can you convince me that those 'soft' rays are not CAUSING the very cancers we are trying to detect?

(Hey, guys! Sorry I hijacked this thread. We'll get back to CT in a minute. OK? I tried to start a thread about mammography about a year ago, but no one would touch it. This is a subject that has been eating at me for 20 years and it IS (somewhat ) relative to the topic...)

anyone who comes up with an imaging method that's as sensitive as x-ray mammography, specific as MRI, cheap and fast will probably have it made. very challenging task.

Are you up for it?

More to the point, how can this get pushed to the forefront in R&D? I've written to most of the major producers of mammography equipment trying to nudge them along, but...

BACK TO CT!

I'm really questioning that 1,300mr dose for an average CT scan. I thought it was about half that. In fact... Yeah! Pervect showed that on page one. I'll try to check my scanner tonight and get a few dose readouts.

Here's the interesting thing about CT dose. (Imabug, correct me if things have changed!) If you have a chest CT, you'll receive a dose of 500mr along the length of the chest scan. (NOW think about a dose of 300mr to each BREAST in an annual screening mammogram! - sorry - had to throw that in... ) If you have a chest AND abdomen CT at the same time, you'll still receive a dose of... 500mr! - but it's along the length of the chest and the abdomen. They aren't added together to get a dose of 1000mr. However, it is still cumulative. Two chest CT's in one week will yield a dose of 1000mr.

 

[imabug]

DR/CR is, no doubt, the future of radiology. But even so, aren't we still dealing with the extremely low KV ranges? 20-30? Can you convince me that those 'soft' rays are not CAUSING the very cancers we are trying to detect?

I ran across a paper a while back discussing the cancer induction risks associated with screening mammography. As I recall, they were relatively low (not insignificant though). However, I think the benefits of finding a cancer early via screening mammograms vastly outweighs the slight increase in risk of developing a cancer years later because of screening mammography. it will probably take some time to dig it up, but I'll see if I can find a reference.

BACK TO CT!

I'm really questioning that 1,300mr dose for an average CT scan. I thought it was about half that. In fact... Yeah! Pervect showed that on page one. I'll try to check my scanner tonight and get a few dose readouts.

CT doses vary significantly from machine to machine, but anywhere from 10-30 mGy (1-3 rad) is probably typical. Body CT doses can range anywhere from 3-4 rad for older single slice machines to less than 1 rad for newer machines with automatic technique adjustments (these have software that adjust the x-ray technique throughout the scan to compensate for changing body thickness). A lot of places are starting to modify their CT protocols to lower patient dose, particularly for pediatric studies.

Here's the interesting thing about CT dose. (Imabug, correct me if things have changed!) If you have a chest CT, you'll receive a dose of 500mr along the length of the chest scan. (NOW think about a dose of 300mr to each BREAST in an annual screening mammogram! - sorry - had to throw that in... ) If you have a chest AND abdomen CT at the same time, you'll still receive a dose of... 500mr! - but it's along the length of the chest and the abdomen. They aren't added together to get a dose of 1000mr. However, it is still cumulative. Two chest CT's in one week will yield a dose of 1000mr.

yes, this is correct, but only if the slices don't overlap. doses quoted for CT scans are typically dose/slice, but having a 40 slice CT scan doesn't mean you get 40 times the dose.

Not very intuitive, but obvious if you know what dose represents.

Dose (in rad/Gray) is a unit of absorbed energy measured in J/kg. The dose from 1 CT slice might be 1.3 rad. The dose from 2 CT slices is still 1.3 rad. You've deposited twice the energy (2 slices vs 1 slice), but at the same time the total mass you've irradiated has doubled. The factors of 2 cancel out.

However, if you irradiate the same volume of tissue twice, you've deposited twice the energy, but the total mass of tissue you've irradiated stays the same. Therefore dose adds up.

 

[Math Is Hard]

So, to those of you who may be doing research in the field or if you really want to help to make a difference - PLEASE FIND A WAY OF IMAGING THE BREASTS WITHOUT RADIATION! I have huge concerns that the very method we are using to detect breast cancer is also CAUSING some of those cancers. I don't have these concerns about CT scans as much because they are done in the 120KV range instead of the more damaging 20-30KV range. BUT - you DON'T want to go to one of those Body Imaging places in the local mall to have your annual screening CT scans. Most of the medical community are STRONGLY against those places. They are a source of needless radiation and the exams are generally useless.

I am glad you weighed in on this thread, Tsu. Your comments have really made me think. I can't even imagine how difficult it would be to do a study on the correlation of mammograms and incidence of breast cancer. Women who are getting annual (or more frequent) mammograms are going to be in a group that has a greater risk for the disease, so choosing groups for a study would be very problematic, I'd think.
Interesting that you mentioned those "Body Imaging" places. I hear them advertised on the radio frequently and I was very curious as to what traditional radiologists had to say about them.

 

[imabug]

Interesting that you mentioned those "Body Imaging" places. I hear them advertised on the radio frequently and I was very curious as to what traditional radiologists had to say about them.

FDA's http://www.fda.gov/cdrh/ct/
American College of Radiology's http://www.acr.org/s_acr/doc.asp?CID=2192&DID=16014

The American College of Radiology (ACR) recognizes that an increasing number of computed tomography (CT) screening examinations are being performed in the United States. Much CT screening is targeted at specific diseases, such as lung scanning for cancer in current and former smokers, coronary artery calcium scoring as a predictor of cardiac events and CT colonography (virtual colonoscopy) for colon cancer. Early data suggest that these targeted examinations may be clinically valid. Large, prospective, multicenter trials are currently under way or in the planning phase to evaluate whether these screening exams reduce the rate of mortality.

The ACR, at this time, does not believe there is sufficient evidence to justify recommending total body CT screening for patients with no symptoms or a family history suggesting disease. To date, there is no evidence that total body CT screening is cost efficient or effective in prolonging life. In addition, the ACR is concerned that this procedure will lead to the discovery of numerous findings that will not ultimately affect patients' health but will result in unnecessary follow-up examinations and treatments and significant wasted expense.

The ACR will continue to monitor scientific studies concerning these procedures.

 

[Math Is Hard]

Thank you, imabug.

In addition, the ACR is concerned that this procedure will lead to the discovery of numerous findings that will not ultimately affect patients' health but will result in unnecessary follow-up examinations and treatments and significant wasted expense.

Sounds like the advice is: Don't borrow trouble.

 

[russ_watters]

Unfortunately, Russ, I am not so sure this is true. The Medical "professionals" must justify and pay for expensive equipment Tsu's comments reinforce my believe that profits come before long term patient safety in the US medical system.

Well, like Tsunami said, I think that's more about money and CYA than risk/reward. But I was talking as much about the science that went into designing these machines and the approvals that had to be gotten before they could ever use them. Its not just the doctor ordering the test that you are putting your trust in. But still, doctors are human, so there are times when doing your own homework is a good idea. But a standard test done in a standard way doesn't ring my warning bell (and trust me - I'm a very distrustful person).

Even I have a story about a doctor who wasn't motivated by a patients' best interest: My grandfather at an aneurism of the aorta about 15 years ago. Standard treatment at the time was to crack the chest and wrap some dacron around it. A surgeon in Allentown (where it was diagnosed) wanted to perform the surgery. He'd done 5 - 3 successful. This wasn't good enough for my mom, who started asking questions and researching and found that the best place to have this done was in Dallas, by a surgeon who had done hundreds. So that's where they went and my grandfather is still active today at 88.

I know some doctors are pushing yearly full-body scans for profit, but AFAIK, few reputable doctors' groups/medical journals say that's a good idea (though probably at least as much because of the unnecessary expense). We may yet get to the point where your yearly physical includes some type of full-body scan, but we're not there yet. A Star Trek style tricorder that can non-invasively diagnose anything would be the holy grail of diagnostic tools.

 

[Loren Booda]

In graduate school we were once asked to determine a lower limit for proton decay halflife by considering the effect of such radiation on ova production!

 

[imabug]

In graduate school we were once asked to determine a lower limit for proton decay halflife by considering the effect of such radiation on ova production!

interesting, although I'm not quite seeing the connection. how did you go about solving the problem?

 

[Tsu]

Hi. Wow. Did the ER kick our butts last night! I checked my scanner dose - an average chest scan runs a dose of 456mGy.cm. An abdomen is around 620 while a pelvis is around 600-650. Heads are less than 100. So your dose for a mammogram is higher than for most CT work.

WONDERFUL!

edit: on the other hand, what is the conversion factor from rems to Grays? I'm actually going to have to finally LEARN the new Rad Safety Speak!? Why the hell did they change everything anyway? I know. It was just to mess with the heads of all of us old dogs, right??

 

[Loren Booda]

imabug,

I'm sorry. If it does have a legitimate answer, I have long since forgotten it.