The Clinac-18 linear accelerator. 10 MeV photon beam data

Measurements were carried out on a Clinac-18 linear accelerator in order to characterize the 10 MeV photon beam. Depth dose data and tissue-maximum-ratios were obtained for field sizes up to 35 x 35 cm2. Using a parabolic expression a least square fit to the tissue-maximum-ratios was performed. The radiation field flatness and the penumbra were found to be in good agreement with the tolerances recommended by the IEC standard (draft). The radiation field and the light field isocentre were determined as suggested by the IEC. The distance between both isocentres was less than 1 mm.