3 Cardinal Principles

The 3 Cardinal Principles are so fundimentally basic, yet so extremely important, that I can tell you with a high amount of certainty that you will see it on quizzes and tests...more than once.  You can guarantee that you will see it on the Limited Scope ARRT test.  So what are the 3 Cardinal Principles?

  1. Time
  2. Distance
  3. Shielding

Time - X-rays are a recognized carcinogen.  It would make sense to limit amount of time you are exposed to it.  This principle goes for the x-ray operator, the patient, and anybody else who happens to get exposed to ionizing radiation.  If you reduce your time exposed to a x-ray source by half, you reduce your dose by half.  Limit the time exposed.

Distance - Again, if something is potentially hazzardous, it would make sense to maintain your distance from it.  The further away you are from an x-ray source, the less dose you will receive.  The inverse square law, which we will learn about in the next module, tells us that every time you double your distance from the x-ray source, you effectively cut your exposure to 1/4 (one-fourth) of it's previous value.  If you measure an exposure of 4 R at 1 foot from a source, you would only measure 1 R at 2 feet.  Always maintain proper distance whenever possible, or better yet, remove yourself from possible exposure all together.

Shielding - If you must be in the vicinity of a x-ray source, shielding is your friend.  By using a high atomic number material like lead you can greatly reduce exposure, or even eliminate it.  For x-ray operators, shielding is incorporated in the control booth.  For those that must be in the room during exposure, shielding is in the protective aprons that you wear.   Portable shielding that can be moved in the room, eye protection, and hand protection are also examples.  For the patient use, there is gonadal shielding.  For the public, it may be in the lead lined walls containing the x-ray machine.  Bottom line, always shield when possible.


ALARA

ALARA stands for As Low As Reasonably Achievable.  This is another concept that is extremely important (hint, hint), and builds on the 3 Cardinal Principles.  ALARA simply states that if it is reasonable to protect yourself or others, then you should do it. 

It is reasonable to minimize time exposed to x-rays.  If you work in a facility which requires human holders to be in the x-ray room during exposures, make sure that the same individual is not performing that duty all the time.  Other ways to minimize time is happening right this moment.  Through education, an x-ray operator becomes more knowledgable and profficient.  Profficiency leads to reduced repeats during examinations, which results in reduced time exposed.  So ALARA can also be attributed to education.  It's reasonable to obtain education as a x-ray operator.

It is reasonable to maintain distance from a x-ray source...most of the time.  If you have to assist an exam by holding a patient, it is a difficult to maintain distance.  If, however, you have the ability to use restraining devices instead of physically holding, it is reasonable to do so.

It is reasonable to utilize shielding.  In fact, in some situations it is law.  There are laws regarding room construction that states there will be shielding in control booths.  There are laws regarding shielding within the walls of x-ray rooms when public doses may exceed regulatory levels.  Many states have laws on when gonadal shielding must be used.  The use of shielding is reasonable, unless the shielding (like gonadal shielding) will interfere with image aquisition.