CPB Ljubljana 2018 course book

Reference Air Kerma Rate / Source Strength

α,α (r=1m) in m Gy . h -1 at 1 m

Reference Air Kerma Rate K R

= K

air

r = 1m

r

The reference air kerma rate of a source is defined as the air kerma rate in air at a reference distance of one metre from the centre of the source, corrected for attenuation and scattering in air. This is the air kerma rate in vacuo . For rigid sources usually considered in the practice of brachytherapy (as distinct from malleable wire sources), the direction from the source centre to the reference point at one metre has to be at right angles to the long axis of the source.

In 1985, the ICRU Report 38 5 defined as an emission specification quantity for γ-rays emitting brachytherapy sources the reference air kerma rate .