Thermoplastic Mask Influence with High Energy Electron Radiotherapy Evaluated by the Fricke Xylenol Gel Chemical Dosimeter

A thermoplastic mask is used to immobilize the patient head during radiotherapy. It also enhances the absorbed dose distribution improving the radiotherapic treatment. In this work we investigate the influence of the thermoplastic material in the phantom surface and in the target volume region. For the measurements a Fricke Xylenol Gel dosimeter, based on Fe (II) to Fe (III) oxidation, was used and their values compared with those from a 0.055 cm3 PTW/Markus Parallel Plate Ionization Chamber. From the results we could infer the absorbed dose distribution as a function of depth in the water phantom from the surface up to the build-up depth for electron beam energies of 5, 8 and 10 MeV. The results show that using the mask, the surface dose distribution is not significantly alterated, and we therefore conclude that the mask is recommended and useful in head and neck cancer treatments.