CORRECTION FACTORS FOR PARALLEL-PLATE CHAMBERS USED IN PLASTIC PHANTOMS IN ELECTRON DOSIMETRY

In electron beam dosimetry using parallel-plate chambers solid phantom s are sometimes necessary. To obtain the dose to water from the ioniza tion obtained in the solid phantom, fluence correction factors and per turbation factors have to be applied. In this study fluence factors in a perturbation free geometry have been determined experimentally for common phantom materials. Wall perturbation factors for simulated Atti x, NACP, and Roos chambers have also been determined for the same mate rials. Comparative Monte Carlo calculations have been performed using the EGS4 Monte Carte code. Comparison with data in newly published pro tocols such as IAEA and IPEMB shows an agreement with the results obta ined in this paper to within 1%, demonstrating that the data published in these protocols may be used with reasonable accuracy if recommende d phantoms are used. The results also show that if unsuitable phantom materials are used, the wall perturbation factors may differ for diffe rent chambers and for different phantom materials by more than 3% and perturbation factors have to be considered in order to obtain a high a ccuracy in the dose determination.