Time of fluoroscopic procedures
» What is the most significant thing I can do to reduce X ray exposure to my patients during fluoroscopy?
While there are several factors under your control that have an effect on exposure, one of the most significant is the time that the X ray beam is on.
Good practice is to use the shortest fluoroscopic times that are consistent with the clinical requirements of the procedure. This can be aided by being aware of and making a record of the exposure time for each procedure. The use of pulsed fluoroscopy with the pulse rate set as low as practical for the specific type of clinical procedure provides a significant reduction in the absorbed dose, although not all equipment may follow this and it is desirable to understand your equipment. If the equipment has more than one mode of operation, the high-dose rate mode should be used with caution, only for the time in which a low-noise image is required.
» Can I estimate the exposure of a patient for a fluoroscopic procedure?
It can be complex, especially if the X ray beam is moved during the procedure. However, let’s consider a simple case in which the X ray beam was in the same location for five minutes. The absorbed dose to the skin in the beam can be obtained by multiplying the dose rate (mGy/min) by exposure time. For this example we will use a dose rate of 30 mGy/min. This is within the range of normal fluoroscopic dose rates but is subject to considerable variation with factors such as patient size, kV, and the magnification mode used.
Our estimate for this case will be an absorbed dose to the skin of 30x5=150 mGy.
» Can the exposure to a patient be reduced by factors other than time?
Yes.
There are several parameters that have an effect on the exposure rate (mGy/min). The basic exposure rate is set by the different factors, as discussed in a question related to moving of the X ray beam to different areas of the patient’s body. Some fluoroscopic equipment is designed for pulsed-mode operation. With the pulsed mode, it can be set to produce less than the conventional 25 or 30 images per second. This is likely to reduce the exposure rate in most equipment. But patient dose management is a complex topic and practitioners should know the operational capabilities of their X ray systems. The reduction of unnecessary cine series or number of frames per series, the proper use of collimation, the influence of C-arm angulations and position of the table and image detector (geometry), to avoid the use of “high quality” of cine modes, etc ... could have a substantial influence on patient (and staff) doses.
Collimation of the X ray beam to the smallest practical size and keeping the distance between the patient and image receptor as short as possible contribute to good exposure management.