Changes

Air kerma of the primary x-ray beam measured under specific conditions and expressed as the equivalent value at the patient entrance reference point (IEC, 2004; 2010). For C-arm fluoroscopic systems, the [[patient entrance reference point ]] is a point along the central ray of the x-ray beam, 15 cm back from the isocenter toward the focal spot. Reference air kerma does not include backscatter and is measured in units of Gy. It is a special case of the quantity with the ICRU notation K_a,i, and has the NCRP notation K_a,r.

Air kerma of the primary x-ray beam measured under specific conditions and expressed as the equivalent value at the patient entrance reference point (IEC, 2004, 2010). It is the air kerma accumulated at a specific point in space relative to the fluoroscopic gantry (see [[Patient entrance reference point]]) during a procedure. Reference air kerma does not include backscatter and is measured in units of Gy. It is a special case of the quantity with the ICRU notation K_a,i, and has the NCRP notation K_a,r (ICRU, 2005; NCRP, 2010). Reference air kerma is sometimes referred to as ‘reference dose’ or ‘cumulative air kerma’. Earlier publications used the term ‘cumulative dose’ and the abbreviation ‘CD’ for this quantity (Stecker et al., 2009).