Radiology: Radiation Exposure

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Radiology: Radiation Exposure




Guest: Dr. Walter Huda – Radiology, MUSC

Host:  Dr. Linda Austin – Psychiatry, MUSC


Dr. Linda Austin:  I’m Dr. Linda Austin.  I’m interviewing Dr. Walter Huda, who is Professor of Radiology here at MUSC.  Dr. Huda is a physicist by training, and is responsible for teaching our residents and trainees about the physics of radiation.  Dr. Huda, I understand you’re an expert, also, on the effects of radiation on the human body.  People often worry about that.  How would you describe to, let’s say, the average person getting a chest film the impact of the radiation on their body?


Dr. Walter Huda:  Well, the point that I would make is that everybody is actually exposed to radiation all the time.  There is what we call natural background radiation.  There’s radioactivity in the soils around us.  There’s cosmic radiation that flies in from outer space.  There are naturally occurring radioactive materials that are actually in your body, and my body, all the time.  And we get a certain amount of this background radiation year in, year out.  In our homes, we also have radioactive gas called radon that we’re exposed to.  


So, if you had a chest x-ray, I would say that the radiation you receive is a very small fraction of the amount of radiation that you receive every year of your life.  You always have, and you always will.  The other thing I would say is, for example, if you flew from New York to Los Angeles, because you’re flying at 30,000 feet, you don’t get the protection from the air; at 30,000 feet, and you’ll be receiving a little bit more radiation because of that flight.  And, I would say your chest x-ray is comparable to the additional radiation that you get if you fly from New York over to Los Angeles.


Dr. Linda Austin:  That begs the question, though:  how dangerous is that background radiation?  Is there any thought that that might be associated with folks getting cancer?


Dr. Walter Huda:  The evidence that we have is relatively limited.  But we do know that there are places that have much higher levels of background radiation.  There’s a famous place in India called Kerala Province.  In that particular area, the background level is, maybe, ten times higher than it is here in Charleston, and, to the best of my knowledge, we have no real clear evidence that there is an additional risk from that background radiation exposure.


Dr. Linda Austin:  How about people who work, let’s say, in x-ray facilities, or work in these environments all the time?  Do they have any higher rates of cancer or other problems?


Dr. Walter Huda:  We certainly have regulatory limits.  I work in a radiation environment.  I always have.  I actually have Omni, a little badge, to monitor how much radiation I’ve been exposed to, and I’ve been monitored for the last 20 or 30 years.  And, by and large, with one or two exceptions, there’s no clear evidence that working in a radiation environment increases your risk of cancer or other types of disease.  The exceptions, I’m always a bit cagey about saying absolutely.  There are studies of people who worked in uranium mines that were exposed to radioactive gases, and they have an elevated incidence of lung cancer.  So, there are small numbers of radiation workers where there have been detrimental effects.  But, by and large, people like me, and people who work in the nuclear power industry, do not see elevated levels of disease in general. 


Dr. Linda Austin:  And, yet, I’ve heard, for example, that female medical students are reluctant to go into fields like vascular surgery, where one is exposed to interventional radiology procedures, because of their concerns on the impact of a pregnancy.  Can you comment on that?


Dr. Walter Huda:  Certainly, we have women who work in interventional radiology.  If somebody came to me and asked about the risks, I would say that the risks, if any, are too small to be detected.  I find it very interesting that pregnant radiation workers, or residents, or attendings who are pregnant can continue to work in interventional radiology where the radiation exposures are higher, but we take steps to protect the individual.  And we would then monitor not just the radiation worker, but also the fetus.  But, in general, technologists who work in nuclear medicine, who work in radiation oncology, radiologists who work in interventional radiology, even after they declare a pregnancy, can continue to work.  And the radiation risks associated with that exposure certainly are deemed to be acceptable, if they exist.


Dr. Linda Austin:  You mentioned the chest exam in particular.  How about other radiologic procedures?  Are there higher, or perhaps lower, risks associated with other procedures?


Dr. Walter Huda:  Oh, for sure.  Let me try to give you a sense of the relative doses.  A chest x-ray is actually a relatively low dose exam.  It is not the lowest.  If you have a dental x-ray, I would say the radiation exposure is almost trivial.  It would be very low, and the risks would be minute.  If you had a bone densitometry examination, again, the radiation doses are relatively low.  At the other extent, you might have a CT examination, a CAT scan.  The radiation dose of a chest CT is, maybe, a 100 times more than a conventional chest examination.  But, at the same time, you get much more information from a CT scan than a conventional chest x-ray.


Dr. Linda Austin:  Is there a limit, then?  Let’s imagine, for example, patients who have lung cancer and have to have repeated chest CT scans.  Are there limits on how many of those procedures they can have done?


Dr. Walter Huda:  No.  That’s an excellent question.  And let me explain to you the philosophy that we adopt in radiology.  I believe that the practice of medicine is about an individual.  And if you present, and you have some indication which warrants a radiological exam, implicit in that is a sort of risk/benefit analysis that is performed jointly between the radiologist and the referring physician so that you, as an individual, will benefit from the information that is being generated, and there may be a small risk. 


And I would say that if an exam is indicated, if someone has sat down and weighed the risks and the benefits, then, in all probability, it will be to your disadvantage not to proceed with a radiological exam.  So, every time you have a study, there should be this kind of weighing of the possible downsides and the possible benefits.  And if it’s an indicated exam, my advice would always be to proceed with the exam.


Dr. Linda Austin:  How about diagnostic modalities that do not use radiation?


Dr. Walter Huda:  Okay.  There are two common exams.  One is ultrasound imaging.  It’s quite often used for scanning pregnant patients.  In fact, I’m just about to become a grandfather.  And, my step daughter, who lives in Scotland, just sent me a nice ultrasound image.  She’s about two months pregnant.  And so, ultrasound is deemed to be relatively safe.  We certainly don’t know of any detrimental effects.  The other modality that doesn’t use the kind of radiation that x-rays do is magnetic resonance imaging, known as MR imaging.  That uses radio waves, but not x-rays that can potentially cause these detrimental effects.

Dr. Linda Austin:  Let’s talk for a moment, as we wrap up this podcast, about just what radiation is.  I recently read a very interesting book, Bill Bryson’s A Short History of Nearly Everything.  It went into when radiation was first discovered, what an extraordinary thing it was, but so poorly understood.  Can you describe, in laymen’s terms, what radiation is?

Dr. Walter Huda:  I’ll certainly try to do so.  I also read the book by Bill Bryson.  I’m a Bill Bryson fan.  I read anything he writes.  Let me try to explain what radiation is.  Radiation, according to a physicist, is a form of electromagnetic radiation.  And that means that you have oscillating entities called electric and magnetic fields.  If you go down to the seaside and look out, you will see the level of water bobbing up and down.  And I would say, hey, you have water that moves up and down, and it will oscillate at a certain rate.  Maybe it bobs up and down once per second, and I would say the frequency is one bobbing up and down per second. 

Electromagnetic radiation has electric and magnetic fields that bob up and down.  And there are different types of this electromagnetic radiation.  There are radio waves, which we use to transmit radio waves.  There’s radar.  There’s television.  There is visible light.  If you’re looking at something, electromagnetic radiation comes into your eyes and allows you to see.  And there are x-rays and other forms of radiation.  And the only real difference between these is the frequency of this bobbing up and down, that I’ve referred to; the waves. 

If you look at radio waves, the electric fields and magnetic fields bob up and down fairly slowly.  If you look at visible light, the electric fields bob up and down a little bit more quickly.  And for x-rays, they bob up and down much more frequently.  And if ask a physicist what we’ve learned about this electromagnetic radiation over the last couple of hundred years, the physicist would say that we’ve learned that they come along in little discreet packets, or bundles.  Physicists have a fancy term for that.  We call them photons. 

The point is that the energy of these little bundles of electromagnetic radiation is proportional to the frequency.  In other words what I’m really trying to say is that the energy of a radio wave is very low, and the energy of visible light is moderate.  And the energy of an x-ray that we use is relatively high.  So, high energy electromagnetic radiation, like x-rays, you can think of it as a speeding bullet.  It can get into a cell and cause serious damage, whereas lower frequency; visible light or radio waves, just doesn’t have that energy.

So, generally speaking, I would say if you take living tissue, which is made up of cells, and expose it to radiation, if you put in a lot of energy, you can kill the cells.  If you put in a little bit of energy, you can transform the cells, whereas visible light, infrared, TV, and radio waves just don’t have the energy.  They can’t smash apart biologically important molecules.

Dr. Linda Austin:  That’s really clear.  Thank you very much.

Dr. Walter Huda:  You’re welcome.

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