Wednesday, February 1, 2017

Radiographic Positioning

I found this article on Radiographic Positioning and it highlights some interesting regulatory differences between the US and Canada.  For instance, the article states that the US Nuclear Regulatory Commission has whole-body dose limits of 5 rem per year for occupational personnel, however Health Canada limits radiation doses to personnel to a much lower 20 mSv (In Canada, the Sievert (Sv) has replaced the REM (rem) as the unit of dose equivalent.  One rem equals 10 mSv).

Permissible Dose Equivalent Limits of X-Radiation to Operators and Other Occupationally Exposed Personnel
Annual permissible dose equivalent limits
Applicable body
organ or tissue
Other workers and
members of the public
Whole body
20 mSv
1 mSv
Lens of the eye
150 mSv
15 mSv
500 mSv
50 mSv
500 mSv
50 mSv
All other organs
500 mSv
50 mSv
Table from Health Canada Safety Code

As mentioned in the article and as discussed in class we should always use the principle of ALARA when taking radiographs.  Increasing our distance from the primary beam, decreasing our exposure time, using positioning aids and using a properly developed technique chart can all help decrease the amount of radiation we are exposed to.  Clearly, wearing personal protective equipment will also reduce our exposure and I was surprised that according to the article, PPE is only suggested in the US!  The lead equivalent in the US (0.25mm minimum in most states) is also less than that required here (0.5mm minimum at 150kVp).  PPE should be handled and stored correctly, and I recommend checking the wear of your PPE every 6 months, rather than yearly.  You should check it sooner if the integrity is in question (for instance if someone left a gown folded rather than hung up).  Any piece should be replaced if more than 10% of the protective surface is damaged.

More information on radiation safety can be found in the WorkSafeBC Guidelines Part 7 Division 3

The positioning tutorial in the article is very good, although some of the photos are not ideal.  There are a few places where the positions deviate from what we discuss in lab, which I will review here.

The lateral views of the scapula that they discuss are somewhat different from how we demonstrate them.  Their second view is the superimposed view we perform but they do not consider the view where the scapula is dorsally displaced, which is the only exposure that allows an unobstructed view of the entire bone structure.  Assuming that the position does not cause the patient pain, it is the first choice of lateral views.  Note that in the image of the caudocranial view of the scapula, the caudal portion is cut off, even though the text correctly states to include the entire bone.

In its conclusion, the statement is made that first and foremost we should do what is best for the patient.  I think that you should first ensure that you and the rest of the staff are protected, then do what is right for your patient.  Of course, the two often go hand in hand.  A perfect example was this week: a struggling, stressed patient made it impossible to get good images.  To continue would have further stressed the patient and put you at more exposure to radiation.  As RVTs, we must advocate for our patient and ourselves.  We discussed the risks with the DVM and made a plan to defer the radiographs until we could sedate the patient.  This decreased the patient (and our) stress, allows for better images and avoids retakes.

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