RESUMO
Hot spots and cold spots always appear in the matched region of electron-photon fields. The degree of this kind of dose heterogeneity depends on the physical characteristic of a treatment unit and the energy of electrons. In this paper, a set of dosimetric parameters have been measured on electron rays and x rays for the Elekta Precise treatment unit and the Elekta Synergy treatment unit, respectively. The hot spots and cold spots in the region of perpendicular electron-photon matching fields have been analysed quantitatively. The method to extend penumbra for photon beam profiles was proposed for improving the dose uniformity in the matched regions. And the dose profiles in the matched regions for different treatment units were compared. The results showed that there were stronger hot spots and cold spots for treatment unit with smaller penumbra for photon beams either under the condition of unmodified photon beam profile or the condition of modified photon beam profile.