Air kerma at the patient entrance reference point
The air kerma at a point in space located at a ﬁxed distance from the focal spot (see “Patient entrance reference point”) accumulated from a whole x-ray procedure expressed in Gy. The International Electrotechnical Commission (IEC 2010) refers to this quantity as ‘reference air kerma’. The US Food and Drug Administration uses the term ‘cumulative air kerma’. The International Commission on Radiation Units and Measurements (ICRU) has not deﬁned a symbol for this quantity. Ka,r is the notation introduced by the National Council on Radiation Protection and Measurements (NCRP) in Report No. 168 (NCRP 2010). In many medical publications the acronym used for this quantity is CAK. This quantity is referred to in older medical publications as ‘cumulative dose’ and has also been called ‘reference air kerma’ and ‘reference point air kerma’.
(Adapted from ICRP Publication 135, 2017)
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