Radiation leakage through electron applicators on Clinac-1800 accelerators

Radiation leakage through electron applicators by 6-, 9-, 12-, 16-, and 20-MeV electron beams from Varian Clinac-1800 has been measured with films. High levels of leakage were found under the corners of applicators and the touch-plate mounting port holes. The radiation leakage, relative to the central-axis dose at dmax, was found to be up to 13% on the patient plane [100-cm source-to-film distance (SFD)] and up to 35% beneath the corners of applicators (96-cm SFD). Up to 18% radiation leakage was measured beneath the touch plate near the mounting port holes (96-cm SFD). The extent of radiation leakage in all electron beams was investigated and some simple shielding solutions to reduce the leakage are suggested.