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Chest X-ray question

  1. Sep 16, 2016 #1
    If you have chest x-ray of the lungs.. how much of the x-ray radiation goes to other parts of the body (like the lower abdomen)? Or do the machines just focus the beam on the chest?
     
  2. jcsd
  3. Sep 16, 2016 #2

    Bystander

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    Google "x-ray shielding."
     
  4. Sep 16, 2016 #3
    I meant without using any x-ray shielding or apron.. what is the levels of scattered x-ray (how many photons say per square inch) that goes to other parts of the body if it's a chest x-ray?
     
  5. Sep 16, 2016 #4

    Choppy

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    An x-ray tube is encased in some kind of shielding material, with a "window" that allows the x-rays to escape through it only. Typically the imager will also be equipped with blades which allow technicians to define the shape and size of the aperture, so that they only irradiate the relevant portion of the body.

    The radiation dose (energy per unit mass) from a chest x-ray is typically on the order of 10-4 Gy to the skin on the entrance surface. The deeper you go, the less dose is received. And the details of the actual dose calculation will depend on the specific characteristics of the x-ray spectrum you produce, the size of the field, how far you are from the source, and the quality of the image that you want to produce. In the industry, often to characterize the dose output from a machine, a quantity called air kerma is specified - the amount of energy released per unit mass of air.

    Outside of the directly irradiated area, the patient will still receive some dose from scattered and leakage radiation. During a chest x-ray the dose to the testes on a male is roughly 4 orders of magnitude less than the dose to the directly irradiated area.

    In terms of radiation protection all of this is converted into the mSv unit, which is a way to assess relative risk accounting for the approximate sensitivity of the organs that are directly irradiated and details of the radiation type that is used (alpha particles, for example do more damage per unit dose than photons). A typical chest x-ray delivers about 0.1 mSv. For reference, most people receive a background radiation dose on the order of 2-3 mSv/year.
     
  6. Sep 25, 2016 #5

    rbelli1

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    Why? If the X-ray technician is not following proper safety protocol you should run the other way. If they are then it is irrelevant. It's kind of like asking "How long can I arc weld before I go blind? I mean if I'm not wearing welding goggles."

    BoB
     
  7. Sep 26, 2016 #6

    jim mcnamara

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    Here is some perspective. Based on this easy to understand chart (it is a comic BTW) there is radiation exposure from eating single banana. Note the amounts in xrays:

    https://xkcd.com/radiation/

    My point: @rbelli nailed it - there is risk of exposure with xrays and living on the Earth -- and unacceptable risk with idiots running xray equipment. Seems to me this whole thing is a no-brainer. The reason is people hear the word 'radiation' and go unreasonably non-linear.
     
  8. Sep 26, 2016 #7
    As Choppy mentioined above, a chest X-ray typically delivers a dose of 0.1 mSv. Non-radiation workers are allowed an exposure of 20 mSv/year; radiation workers 50 mSv. Deduct the 2-3 mSv/year that we get from the environment. That leaves us with 17-18 mSv/year of allowable exposure. From a clinical point of view, that means we can have as many as 170 chest X-rays in a year (17 per year divided by 0.1 per chest X-ray). The link by Jim shows a good chart.
     
  9. Sep 26, 2016 #8

    Choppy

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    I think some clarification is warranted here.

    First, in terms of allowed exposures - this is something that is going to depend on regional legislation. The ICRP and IAEA recommend that members of the general public be exposed to less than 1 mSv per year and this is the most commonly adopted value in most countries. And the general approach to protection is guided by the ALARA principle (as low as reasonably achievable, social and economic factors accounted for). So radiation facilities are typically designed to keep exposures well below (by orders of magnitude) this limit.

    The 20 mSv/yr typically applies to radiation or nuclear energy workers. There are details in the application though. In Canada a nuclear energy worker can be expose to a maximum of 50 mSv in any given year, but cannot receive more than 100 mSv over a period of 5 years.

    Second, the legal exposure limits apply to controllable sources of radiation, not to natural background. These are not cumulative.

    Third, there is a big difference between occupational /general public exposures and medical exposures. They are also not cumulative from a legal or radiation protection standpoint.

    Medical exposures are separate from other exposure limits. That is because there is a balance between the risks associated with radiation exposure and the benefits of accurate medical diagnosis and treatment. So a patient is not limited to ten chest x-rays (10 x 0.1 = 1 mSv) per year. Professionals who are qualified to order x-ray studies (or other radiation procedures) are trained to weigh these benefits on a case-by-case basis. So if a patient needs an eleventh chest x-ray in a year to accurately asses a flail chest that's keeping him from breathing, he's going to get it, regardless of the ~4x10^-3 % lifetime increased risk for developing cancer. That's not to mention how much radiation goes into patients for therapeutic purposes!
     
  10. Sep 27, 2016 #9
    I agree, Choppy. Nicely done.

    I would like to add, though, that there are labs that post in their X-ray rooms how often people can have a chest X-ray in a year, and one at least advertises that a person can have as many as 166 in a year. I presume that it is also a "simplified" approach to dispel fear from patients.
     
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