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

Previous Description

For isocentric fluoroscopic systems such as C-arm fluoroscopes, the patient entrance reference point is located along the central x-ray beam at a distance of 15 cm from the isocentre in the direction of the focal spot (IEC, 2010). The earlier version of this standard refers to this point as the ‘interventional reference point’ (IEC, 2000). The patient entrance reference point is close to the patient’s entrance skin surface when the heart is at the isocentre of the gantry. (From ICRP Publication 120, 2012)

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