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Need input from Nag Ehgoeg
Topic Started: Mar 20 2013, 09:05 AM (261 Views)
Tristan da Cunha
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Science and Industry


Today I inadvertently walked in front of a room with a half open door in which a CT scan was being performed. I was probably 15 feet away from the scanner and spent about 45 seconds exposed to it. I would like to know the effects of this exposure upon: cancer risk, infertility implications, other effects, etc.

I googled it but there is a lot of conflicting information and I prefer to hear it from the mouth of Nag.

I would also like a brief discussion of radiation safety of fluoroscopic C-arms if there is time.
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Nag Ehgoeg
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The Devil's Advocate

There's a short and a long answer to your questions here:

Short answer:

Perfectly safe.

Long answer:

Probably perfectly safe.

...

...

What?

Oh, very well.

CT scanners (and also flourscopic c-arms) use x-radiation to create images of the structures inside the body. X-radiation (more commonly known as "x-rays") is a form of electromagnetic radiation - like visible light, ultra-violet radiation and radiowaves. X-rays have a short wave-length and a high frequency which allows them to knock electrons out of atoms -- ionising them. Thus x-rays are a form of ionising radiation.

Your body works by all your organs working together. Your organs work by all their tissues working together. Your tissues work by all of your cells working together. Your cells work by all of your atoms working together.

If one of your atoms becomes an ion (or if an ion has its charge increased (or decreased)), it can, on occasion, change the way its cell works. This can cause (among other things) cancer.

So, if you are exposed to x-rays from a CT scanner, the x-rays can ionise the atoms in your cells and cause cancer.

In theory.

In practise, your have ~7,000,000,000,000,000,000,000,000,000 atoms in your body. If a few of them have their charges changed, pretty much nothing will happen. You're exposed to background radiation from the sun (and the gases in the Earth) all the time and dozens of other things also cause cancer that are far more important than a few seconds of exposure to x-rays.

Additionally, as I said before, x-rays are a form of electromagnetic radiation -- they are a form of light. Imagine if you were in a dark room. Well, the room the CT scanner is in, is "dark". The CT scanner works like a torch, shinning x-rays into the darkness. When you turn on a torch in a dark room, the whole room gets a little brighter but the vast majority of the light goes where you shine the torch. Our CT scanner is shinning its light down at the patient being scanned but there's a little bit of radiation (which is called "scatter") that lights up the rest of the room, which is why the CT scanning room is lead lined, has a lockable door and a huge sign on the outside of the door that will say something like "RADIATION DO NOT ENTER". As a form of electromagnetic radiation, x-rays obey the inverse square law -- double your distance away from the x-rays and quarter your exposure, triple your distance and you're at a ninth of the dose. If you got a good look at where the patient was in relation to the scanner (right inside it, practically pressed up against it) compared to where you were (standing in the doorway fifteen feet away), you can take comfort in the fact that you did not get exposed to a lot of radiation (side note: Alot of Radiation).


I prepared a section of stochastic and deterministic effects of radiation, but when I give this speech to my students their eyes glaze over. I'll give you the cliff notes. A CT scanner will not cause you to go sterile, make your hair fall out or give you radiation sickness. It doesn't give nearly enough radiation for that (well... usually it won't). The only real risk associated with diagnostic levels of x-rays (CT scanners, x-ray machines, flourscopy of all shapes) is stochastic -- the more radiation your exposed to, the greater the chance you might get cancer. You have no need to worry about turning into the Hulk.

That said...

Until the results of an insanely interesting study involving mice comes back, all hospitals, everywhere in the world must comply to the "Linear No Threshold" model of radiation damage. This states that x-rays are damaging to all living things and there is no safe threshold for exposure. Any amount of exposure increases cancer risk and thus all industries that use radiation must limit human exposure as much as possible. I have no idea what legislation is relevant in the USA (but if this happened in the UK, let me know), but I assure you, the legislation is there.

By standing in that doorway, you have increased your risk of getting cancer. Without knowing what was being scanned (and for how long, and on what kind of CT scanner), I can't give you definitive numbers, but I'd say that one incident has given you somewhere between a one-in-a-billion extra chance of getting cancer to a one-in-a-thousand chance of getting cancer. This cancer chance is added to your normal risk of getting cancer at some point in your life (which is something like one-in-three, so now your have a 334.3/1000 chance of getting cancer instead of a 333.3/1000 chance) and it could take twenty years or more for your cancer to develop.

In the UK this is gross clinical negligence ("first do no harm"), the operators of the scanner could be punished (anything from a verbal warning to being struck off and never allowed to practise again) and you could be entitled to compensation (at least a formal apology, but I mean actual monetary compensation).

In the UK, it is standard practise to lock the door into the CT scanner, and there is no way in hell a competent operator in the UK would allow the scan to continue to 45 seconds with someone in the doorway. It boggles belief. It goes against all the training needed to operate a CT scanner (in the UK), and if this happened in the UK the hospital would already be taking statements in preparation for a lawsuit (and the operator would be ****ting bricks).

Now, you might be thinking "but Nag, didn't you just assure me it was perfectly safe?"

Smoking one cigarette will probably not give you cancer and kill you. But it could. By exposing you to ionising radiation unnecessarily, the people running the CT scanner have basically held you down and forced you to smoke a cigarette against your will. Judges (in the UK) do not look kindly on this. You'd probably survive and make a full recovery if I stabbed you with a kitchen knife, doesn't mean you can't sue me if I do.

So...

Cancer risk: Slightly increased. CT scanners use the most radiation of all diagnostic tools found in a hospital. If the x-ray department is a M-16, the CT scanner is a nuke. But on a more realistic scale, the x-ray department is a dust mite and the CT scanner is an ant.

Infertility: Unless you actually get cancer, there is no risk of infertility. If you get cancer,chances are it's the cancer treatment that will leave you infertile.

Other effects: You get to laugh your way to the bank if you can find a sleazy no-win-no-fee lawyer.

C-arms: Use x-radiation, just like CT scanners. Where CT scanners use high energy x-rays to form hundreds of 2D images that can be stuck together to make a 3D model (like a 3D printer), fluoroscopy use low energy x-rays and a huge "image intensifier" to create x-ray images in real time (so you could make an "x-ray video" if so inclined). C-arms are typically only used in operating theatres (as "over-couch tubes" are cheaper and safer -- but take up much more room and aren't portable).

Low energy radiation is not less dangerous than high energy (much like bullets, it's better to have a high energy bullet pass straight through you than to have a low energy bullet stuck inside you giving you cancer), but it's much more easily stopped (about 0.35mm of lead will stop anything a c-arm can output). So radiation safety is a lot easier with c-arms, you just need to wear a "lead apron" (which uses rubberised lead or a synthetic variant to absorb the x-rays). Whereas CT scanners need the big lead lined room (with the warning sign on the door, seriously, they're freaking huge warning signs -- most of them light up in bright red letters "DO NOT ENTER", how do you miss one of those?).

Anyway, I'm running late for my Role Playing Game group. If you have any questions or want me to go into more depth (or less depth) on anything, just reply here and I'll get back to you.
Edited by Nag Ehgoeg, Mar 22 2013, 06:52 PM.
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Tristan da Cunha
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Thanks brother. Timely radiological knowledge from Nag as always.

The machine that irradiated me was a portable CT scanner, basically wheeled up to a patient's room to get her a head CT,  which, if I understand correctly is one of the most radiation-intensive studies. The techs also brought a portable sign on wheels that said "warning, CT is progress" which they placed off to the side. This sign was at an angle so I missed seeing it. They also called out to me to warn me but there was so much noise and commotion in the area and I was concentrating on looking for something in a stack of papers that I failed to register what they were saying. Thus is the tale of my getting a blast from the CT.

I also get irradiated by a c-arm on a regular basis. I'll be needing to invest in a pair of radiation goggles if I don't want to develop cataracts soon.
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Nag Ehgoeg
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The Devil's Advocate

Portable CT scanners are awesome. I've only seen them in showrooms. The NHS generally considers them to be over-priced luxury items. From my understanding of how they work, the scan would be helical (instead of interval axial), which, yes, is one of the most radiation intensive studies (not the most but definitely closer to the one-in-a-thousand chance of cancer end of the scale). Pity, because if it hadn't been a portable head scan, interval axial scans of the head are actually one of the lowest doses. These scans can be paused, however. Providing they weren't using intravenous contrast (and the patient wasn't dying right then and there), they should have been able to stop the scan and start again once you were clear. Still sounds negligent to me.

The cells in your eye have a very slow rate of mitosis. On the one hand, this makes them less vulnerable to radiation (cells are more vulnerable when they are dividing (specifically, undergoing cleavage)). On the other, it makes them pretty much incapable of healing radiation damage. This sad fact prevents me from making a "the goggles do nothing" joke because your cataracts fear is justified (so long as you're measuring "soon" in "years and decades" not "days and weeks"). Kinda wish I had goggles (don't get goggles).

Consider also your thyroid. Like the eyes people (falsely) claim the thyroid is radio-sensitive. (It's not particularly.) It does (however) control a metric butt-load of vital bodily functions and it is not something you want damaged by radiation. Wrap a thyroid shield around your neck if there's one available (the UK is a lot stricter on radiation safety than the US, but I'm willing to bet the person operating the c-arm will have a thyroid shield around their neck).

Also, I know, (personally know) someone who works with a c-arm all day and developed a tumour on her lower leg - just below where her lead apron ends. The rest of that department has invested in shin-guards. This harrowing story aside, when you're working near a c-arm pick the right size lead coat. Most of them have clearly labelled sizes, and if you're wearing a "large" instead of a "medium" then you'll be carrying around a lot of extra weight (which is bad for your back - and if you're wearing a lead coat all day, I don't need to tell you what a pain in the ass the extra weight is). And if you pick a "small" instead of a "large" you'll find it doesn't cover your sides effectively (and will probably ride up a little to close to your testicles for peace of mind). Two piece suits spreads the weight much more comfortably than one piece aprons, but they're fitted for either male or female hips and they can be a pain to put on and take off. Lead coats should also give it's "lead thickness equivalent", the British Institute of Radiology recommends at least 0.35mm for c-arm work, so look for those magic numbers if you can see them (many prefer the comfort of the much lighter 0.2mm gauge, but I prefer the comfort of not getting cancer).

I've got to say, I'm much more interested in your c-arm doses of radiation. I might go back and (what's the opposite of "dumb-down"?) "smarten-up" my first post. What are you doing that's exposing you to all this radiation?
Edited by Nag Ehgoeg, Mar 22 2013, 06:59 PM.
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Rhadamanthus
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Nag Ehgoeg
Mar 22 2013, 06:51 PM
Still sounds negligent to me.
Yeah, I have to wonder what are the safety procedures outlined at TC's hospital. I can't believe that a poorly placed sign and shouting at him without confirming that he heard the warning would satisfy even the laxest safety protocol.
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Tristan da Cunha
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Nag Ehgoeg
Mar 22 2013, 06:51 PM
Portable CT scanners are awesome. I've only seen them in showrooms. The NHS generally considers them to be over-priced luxury items. From my understanding of how they work, the scan would be helical (instead of interval axial), which, yes, is one of the most radiation intensive studies (not the most but definitely closer to the one-in-a-thousand chance of cancer end of the scale). Pity, because if it hadn't been a portable head scan, interval axial scans of the head are actually one of the lowest doses. These scans can be paused, however. Providing they weren't using intravenous contrast (and the patient wasn't dying right then and there), they should have been able to stop the scan and start again once you were clear. Still sounds negligent to me.

The cells in your eye have a very slow rate of mitosis. On the one hand, this makes them less vulnerable to radiation (cells are more vulnerable when they are dividing (specifically, undergoing cleavage)). On the other, it makes them pretty much incapable of healing radiation damage. This sad fact prevents me from making a "the goggles do nothing" joke because your cataracts fear is justified (so long as you're measuring "soon" in "years and decades" not "days and weeks"). Kinda wish I had goggles (don't get goggles).

Consider also your thyroid. Like the eyes people (falsely) claim the thyroid is radio-sensitive. (It's not particularly.) It does (however) control a metric butt-load of vital bodily functions and it is not something you want damaged by radiation. Wrap a thyroid shield around your neck if there's one available (the UK is a lot stricter on radiation safety than the US, but I'm willing to bet the person operating the c-arm will have a thyroid shield around their neck).

Also, I know, (personally know) someone who works with a c-arm all day and developed a tumour on her lower leg - just below where her lead apron ends. The rest of that department has invested in shin-guards. This harrowing story aside, when you're working near a c-arm pick the right size lead coat. Most of them have clearly labelled sizes, and if you're wearing a "large" instead of a "medium" then you'll be carrying around a lot of extra weight (which is bad for your back - and if you're wearing a lead coat all day, I don't need to tell you what a pain in the ass the extra weight is). And if you pick a "small" instead of a "large" you'll find it doesn't cover your sides effectively (and will probably ride up a little to close to your testicles for peace of mind). Two piece suits spreads the weight much more comfortably than one piece aprons, but they're fitted for either male or female hips and they can be a pain to put on and take off. Lead coats should also give it's "lead thickness equivalent", the British Institute of Radiology recommends at least 0.35mm for c-arm work, so look for those magic numbers if you can see them (many prefer the comfort of the much lighter 0.2mm gauge, but I prefer the comfort of not getting cancer).

I've got to say, I'm much more interested in your c-arm doses of radiation. I might go back and (what's the opposite of "dumb-down"?) "smarten-up" my first post. What are you doing that's exposing you to all this radiation?
We do spine surgeries which require an inordinate amount of c-arm use (mostly due to surgeon timidity-- in the 3rd world where c-arm is not available spine surgeons go into a case astride humongous cojones and put in 20, 24, 30 screws and 3 foot titanium rods up and down people's spines freehand with no image guidance--obviously would not pass medico-legal muster in the 1st world)

Also we do some cranial work (depth electrodes, deep brain stimulation, etc) which use te c-arm from time to time for hardware placement verification.
Edited by Tristan da Cunha, Mar 27 2013, 03:18 PM.
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Sedulius
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XDDDDDDD I love you guys!
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