WALL-CORRECTION AND ABSORBED-DOSE CONVERSION FACTORS FOR FRICKE DOSIMETRY - MONTE-CARLO CALCULATIONS AND MEASUREMENTS

For megavoltage radiotherapy photon beams, EGS4 Monte Carlo calculatio ns show, and experimental measurements confirm with an accuracy of 0.2 %, that glass or quartz-walled vials used in Fricke dosimetry increase the dose in the Fricke solution. This is mainly caused by increased e lectron scattering from the glass which increases the dose to the Fric ke solution. The dose perturbation is shown to vary from nothing in a Co-60 beam up to 2% in a 24-MV beam. For plastic vials of similar shap es, calculations demonstrate that the effect is in the opposite direct ion and even at high energies it is much less (0.2% to 0.5%).