MEASUREMENTS OF THE ELECTRON DOSE DISTRIBUTION NEAR INHOMOGENEITIES USING A PLASTIC SCINTILLATION DETECTOR

Purpose: Accurate measurement of the electron dose distribution near a n inhomogeneity is difficult with traditional dosimeters which themsel ves perturb the electron field. We tested the performance of a new hig h resolution, water-equivalent plastic scintillation detector which ha s ideal properties for this application. Methods and Materials: A plas tic scintillation detector with a 1 mm diameter, 3 mm long cylindrical sensitive volume was used to measure the dose distributions behind st andard benchmark inhomogeneities in water phantoms. The plastic scinti llator material is more water equivalent than polystyrene in terms of its mass collision stopping power and mass scattering power. Measureme nts were performed for beams of electrons having initial energies of 6 and 18 MeV at depths from 0.2-4.2 cm behind the inhomogeneities. Resu lts: The detector reveals hot and cold spots behind heterogeneities at resolutions equivalent to typical film digitizer spot sizes. Plots of the dose distributions behind air, aluminum, lead, and formulations f or cortical and inner bone-equivalent materials are presented. Conclus ion: The plastic scintillation detector is suited for measuring the el ectron dose distribution near an inhomogeneity.