Fundamental study on diagnostic reference level quantities for endoscopic retrograde cholangiopancreatography using a C-arm fluoroscopy system

Abstract

The diagnostic reference level (DRL) is an effective tool for optimising protection in medical exposures to patients. However regarding air kerma at the patient entrance reference point (K a,r), one of the DRL quantities for endoscopic retrograde cholangiopancreatography (ERCP), manufacturers use a variety of the International Electrotechnical Commission and their own specific definitions of the reference point. The research question for this study was whether K a,r is appropriate as a DRL quantity for ERCP. The purpose of this study was to evaluate the difference between K a,r and air kerma incident on the patient’s skin surface (K a,e) at the different height of the patient couch for a C-arm system. Fluoroscopy and radiography were performed using a C-arm system (Ultimax-i, Canon Medical Systems, Japan) and a over-couch tube system (CUREVISTA Open, Fujifilm Healthcare, Japan). K a,e was measured by an ion chamber placed on the entrance surface of the phantom. Kerma-area product (P KA) and K a,r were measured by a built-in P KA meter and displayed on the fluoroscopy system. K a,e decreased while K a,r increased as the patient couch moved away from the focal spot. The uncertainty of the K a,e/K a,r ratio due to the different height of the patient couch was estimated to be 75%–94%. K a,r may not accurately represent K a,e. P KA was a robust DRL quantity that was independent of the patient couch height. We cautioned against optimising patient doses in ERCP with DRLs set in terms of K a,r without considering the patient couch height of the C-arm system. Therefore, we recommend that K a,r is an inappropriate DRL quantity in ERCP using the C-arm system.