Patient entrance reference point

The position at which the cumulative air kerma for interventional x-ray equipment is measured in order to reasonably represent the air kerma incident on the patient’s skin surface. For isocentric fluoroscopes (C-arms) the patient entrance reference point is defined (IEC 2010) as lying on the central axis of the x-ray beam 15cm from the isocentre in the direction of the focal spot. (ICRP Publication 135, 2017)

ICRP Glossary entry - May 2019