Verification of doses in electron beam radiotherapy

Entrance doses measured in 50 patients treated by electron beams were compared with planned values as the percentage difference between the given dose and its planned value. Electron beams of energy 6, 9, 12, 15, 18 and 22 MeV were generated by the Clinac 2300 C/D linear accelerator (Varian). Semiconductor EDE-5 diodes connected to a DPD-510 (Scanditronix) electrometer were applied for entrance dose measurements. In our investigations, the mean values of doses administered agreed well with the values of planned doses. The observed relatively large discrepancies in a few patients (up to 12%) should be carefully investigated.