Energy and dose rate dependence of BANG-2 polymer-gel dosimeter

The purpose of this study was to evaluate dependence of BANG-2 polymer-gel dosimeter sensitivity on different photon and electron energies as well as on different mean dose rates expressed as repetition rates for a standard c linically used linear accelerator. The sensitivity of the dosimeter was rep resented by the slope of calibration curve in the linear region measured fo r each modality. A calibration curve (in the linear region) based on five d osimeters (four irradiated and one background) was obtained for each photon and electron energy and different repetition rates. Dosimeter sensitivity dependence on energy was studied for 4, 6, and 18 MV x-ray photons and for nominal electron energies 9, 12, 16, and 20 MeV. Dosimeter sensitivity depe ndence on mean dose rate was separately studied for electron and photon bea ms with the use of repetition rates 80, 160, 240, 320, and 400 MU min(-1). Evaluation of dosimeters was performed on Siemens MAGNETOM EXPERT IT scanne r in the head coil. A multiecho sequence with 16 equidistant echoes was use d for the evaluation of irradiated polymer-gel dosimeters. The parameters o f the sequence were as follows: TR 2000 ms, TE 22.5-360.0 ms, slice thickne ss 5 mm, FOV 255 mm, one acquisition. There was observed a trend in polymer -gel dosimeter sensitivity dependence on the quality index of high energy x -ray beams used and on mean electron energy absorbed in the center of the d osimeter. Polymer-gel dosimeter sensitivity was decreasing with increasing photon or electron energy. There was observed no trend in polymer-get dosim eter sensitivity dependence on mean dose rate expressed as a repetition rat e for both photon and electron beams. (C) 2001 American Association of Phys icists in Medicine.