MEASUREMENT OF DYNAMIC WEDGE ANGLES AND BEAM PROFILES BY MEANS OF MRIFERROUS SULFATE GEL DOSIMETRY

The purpose of this study is to examine the possible value of measurin g the dose distribution in dynamic wedge photon beams using ferrous su lphate gel phantoms analysed by MRI. The wedge angles and dose profile s were measured for a field size of 70 x 70 mm(2) and for dynamic wedg e angles of 15 degrees, 30 degrees, 45 degrees and 60 degrees using a 15 MV photon beam generated from a Clinac 2100 CD (Varian). The dose p rofiles obtained from MRI ferrous sulphate gel were in good agreement with the dose measurements performed with a diode detector array. Also , the wedge angles determined from the MRI ferrous sulphate gel agreed well with the values obtained by using film dosimetry and with calcul ations by use of TMS (treatment planning system) (Helax, Uppsala, Swed en). The study demonstrated that MRI ferrous sulphate gel dosimetry is an adequate tool for measurements of some beam characteristics of dyn amic radiation fields.