Air-kerma, entrance surface
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The air kerma on the central x-ray beam axis at the point where the x-ray beam enters the patient. The contribution of backscatter radiation is included through backscatter factor (B), thus:
[math]K_e= B⋅K_i[/math]
The unit for entrance surface air kerma is the Gy. Entrance surface air kerma Ke can be calculated from incident air kerma [math]K_i[/math] using suitable backscatter factor B, or determined directly using small dosimeters (thermoluminescent or semiconductor) positioned at the representative point on the skin of the patients. (Adapted from ICRP Publication 117, 2010)
ICRP Glossary entry - May 2019
