CPB Ljubljana 2018 course book

Reference Air Kerma Rate / Source Strength

Air Kerma Strength S K

AAPM, North America

r

The American Association of Physicists in Medicine in their Report No. 21 by the AAPM Task Group No 32 introduced in 1987 the idea for the specification of brachytherapy sources in terms of strength. That is, the air-kerma strength , S K , defined as the product of the air kerma rate in free space at a measurement distance r from the source centre along the perpendicular bisector and the square of the distance r. The distance r must be chosen to be large enough so that the source can be treated as a point source and so that the finite dimensions of the detector used for the measurement have no influence on the result!