Good practices in fluoroscopy
? Does the kV value that I select for fluoroscopy have an effect on the absorbed dose to tissues in the patient??
? Does using the automatic brightness control (ABC) ensure that I am delivering the lowest exposure to my patients??
? Does changing the field of view, or magnification mode, have an effect on the exposure to the patient??
? Does moving the X ray beam to different areas of the patient’s body during a procedure have an effect on the exposure to the patient??
??Why should we no longer shield patients routinely?
??Doesn’t shielding reassure my patients?
??Should I continue to wear protective apron at work?
??Does the kV value that I select for fluoroscopy have an effect on the absorbed dose to tissues in the patient?
Yes, in general, increasing the kV reduces the exposure of the patient and especially to the skin exposed by the beam. This is because the higher kV produces radiation beams with increased penetration through the patient’s body and less radiation is required at the entrance surface (*) to produce the necessary exposure to the image receptor. The other factor that must be considered in selecting the appropriate kV value is the effect on image contrast. In general, lower kV values produce increased image contrast. This can be especially significant in fluoroscopy when using iodine contrast media.
(*) The number of photons and the total energy carried by these photons per unit area. For a more rigorous definition and detailed discussion (energy fluence) see Conversion Coefficients for use in Radiological Protection against External Radiation and Dosimetry in Diagnostic Radiology: An International Code of Practice.
??Does using the automatic brightness control (ABC) ensure that I am delivering the lowest exposure to my patients?
Not in all cases.
While the ABC is useful for adjusting the exposure to produce a good image for different patient thicknesses and densities, the actual exposure depends on the exposure level that has been set by the manufacturer or the engineer who maintains the equipment. The optimum setting of the ABC exposure level is one that delivers only the exposure to the image receptor that is required to produce the necessary image quality in terms of the visual noise.
? Does changing the field of view, or magnification mode, have an effect on the exposure to the patient?
Yes with regard to the absorbed dose?and no with regards to the energy imparted.
Changing from a large field of view to an increased magnification increases the exposure required by the image intensifier tube. Therefore, the absorbed dose to tissues within the beam is also increased. Decreasing the field of view by a factor of two increases the dose rate by a factor of four. Attention has to be paid to magnification.
Example:
Field of view, diameter 25 cm Dose rate= 0.3 mGy/s
Field of view, diameter 17 cm Dose rate = 0.6 mGy/s
Field or view, diameter 12 cm Dose rate = 1.23 mGy/s.
However, since the X ray beam is covering a smaller area, the total energy imparted is about the same as with the larger field of view that produces a lower dose rate.
? Does moving the X ray beam to different areas of the patient’s body during a procedure have an effect on the exposure to the patient?
Yes.
Since the absorbed dose to a specific tissue is influenced by the number of photons impinging on the same area of the skin, moving the beam spreads the radiation over more of the patient’s body and reduces the absorbed dose to any one area of the skin.
The highest absorbed dose to a specific tissue occurs when the X ray beam is not moved but remains at the same location on the patient’s body during a procedure.
Special attention should be paid to avoiding overlapping image areas combined with projections through the body at relatively low angles of the X ray beam (obliquity, e.g. cranio caudal or caudio cranial projections).
In summary, moving the beam can help avoid radiation injuries to the skin. The PKA, and the total energy imparted, is not changed by moving the beam during a procedure. The total energy imparted to a given region of the body is related to the probability of radiation induced cancer.
? Why should we no longer shield patients routinely?
As with all areas of medical practice, the use of patient contact shielding should be evaluated from a risk–benefit perspective. Patient contact shielding was previously employed routinely during medical exposures to reduce the potential risks from radiation. However, with the advances in medical imaging technology over the past 70 years, the amount of radiation being delivered during X ray examination has dramatically decreased. Also, incorrect or unintended placement of shielding in relation to the anatomy of interest can obscure important details, leading to repeat exposures. The dose to internal organs outside of the field of exposure results from internal scattering within the patient, making radiation exposure savings from shielding negligible. When used with automatic exposure controls, shields that partially or fully cover detectors may increase radiation exposure to other organs and tissues. Therefore, currently, the risks from routine use of shielding are believed to outweigh benefits in imaging. Optimization is primarily achieved through careful consideration of other technical factors such as the collimation and appropriate exposure factors selection.?
? Doesn’t shielding reassure my patients?
Scientific evidence should be the basis for clinical practice. While there may be, based on past practice, an expectation for routine shielding, the best reassurance for your patients and caregivers is an appropriate explanation of the optimization steps that will be followed for their particular examination. This can include an explanation of factors that are behind the change in practice. However, there will be situations that require professional judgement based on the individual patient and circumstances that might warrant shielding. This includes psychological safety for patients or parents/caregivers, especially if shielding is placed remotely (not adjacent to) from the examined area.??