Introduction:This work deals with the dosimetry of small photon fields according to the German protocol DIN 6809-8(2014).It is especially applied for the fluence-modulated radiation therapy(IMRT and VMAT).Commonly used ionization chambers with chamber volume larger than 0.1 cm 3 are too large related to the field size of the small photon fields.For field sizes smaller than 5×5 cm 2 one has to use high spatial resolution detectors with very small dimensions such as pinpoint chambers,silicon diodes and diamond detectors,for which generally neither calibration factors nor other correction factors are given in this protocol.