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Invited Commentary

¹ Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas

I appreciate the opportunity to comment on the excellent article by Schueler et al that appears in this issue of RadioGraphics. The authors present an investigation into the radiation exposure of interventional radiologists utilizing an experimental angiography suite. Multiple measurements of exposure were made at various distances from the "patient" during the simulation of a procedure, and the influences of patient size and the use of cones, wedge filters for imaging equalization, and beam-hardening copper filters were studied.

The authors found that operator exposure increased when (a) the input dose to the patient increased, (b) patient size increased, and (c) image equalization filters were used. Of these factors, patient size was the most important, thus representing another risk factor for the physician taking care of obese patients. We know from our basic radiologic physics training that increasing body mass will increase the amount of scatter radiation; however, this radiation has never been quantified in a systematic way until now. This scatter radiation is two to four times higher than the remainder of the background radiation and, in an obese patient, is the cause of the greatest amount of radiation exposure to the operator.

I found it interesting that when copper filters were used for beam filtration, the scatter increased in proportion to the "hardness" of the beam. The increase in scatter with the use of wedge filters was also curious. Both findings argue for the use of table controls to place the wedge filters with the beam off and utilizing stored images.

Lest there be criticism that this study made use of "laboratory" or "experimental" equipment without clinical relevance, it should be noted that the type of angiography suite used in the study is still used in many departments. Although the suite includes an image intensifier instead of the most up-to-date flat panel detector, personal correspondence with the manufacturer of this equipment (Siemens) indicated that the input radiation to a flat panel detector and that to an image intensifier are roughly the same. This fact is important to interventional radiologists because the input radiation has not changed even though the imaging chain has undergone radical changes and the dose to the radiologist is mostly due to scatter rather than to the imaging beam. However, with the newer generations of angiography equipment, the radiation pulse rate can be specified, which can indeed reduce the scatter radiation dose to which interventional radiologists are exposed. Moving objects in the vascular system (eg, catheters) will appear more strobe-like, but the total radiation will be significantly reduced.

Given that the radiation dose we strive to achieve is governed by the "ALARA" (as low as reasonably achievable) principle, we need to look closely at those aspects of the procedure that are controlled by the interventional radiologist: fluoroscopy time, fluoroscopy pulse rate, and use of extra shielding. Minimizing the time required to perform a procedure is not only the hallmark of efficiency but also decreases the dose to the patient and physician. The use of continuous fluoroscopy should be reserved for instances where there is clinical necessity, not merely "sightseeing." Finally, all available shielding should be used, particularly under-the-table skirts and shields that are suspended from the ceiling. It would be helpful in follow-up studies if the results of shielding could be taken into account and three-dimensional isodose curves calculated for the immediate vicinity of the angiography table. Doing so would allow the placement of additional shielding and the sequestering of personnel in areas in which they are not as exposed.

Much stress has been placed recently on the increased prevalence of radiation-induced illnesses, notably radiation burns, cataracts, and potential oncogenesis. This important article by Schueler et al describes the sources of scattered radiation so that we can lower operator exposure while maintaining the quality of our studies and interventions.

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