The peripheral dose outside the applicator in electron beams of an Elekta linear accelerator.

Abstract

Peripheral doses out of field could have short and long terms biological effects on patients treated with electron beams. In this study, peripheral dose outside the applicator was measured using the 6, 10 and 18MeV beams of an Elekta synergy linac. For these beams dose profiles were measured using EBT3 film at various depths within a solid water phantom. Measurements were performed using 6 × 6, 10 × 10, 14 × 14 and 20 × 20cm2 applicators at gantryangles of 0°, 10° and 20° and depths of 0, 0.5, 1cm and depth of Dmax (maximum dose) for each energy. The peripheral dose profiles were normalized to the distance of 2cm from the edge of each field. The largest peak of the peripheral dose was observed for 18MeV 3cm from the outer edge of the applicator. Peak dose increased with increasing energy. Peak dose at 18MeV electron beam was 1.6% at the surface of phantom and at the distance of 2cm from the outer edge of the applicator when the applicator of 20 × 20cm2 was used. Peak dose at 6MeV electron beam was 1.15% at the same distance in the same applicator size. It was found that the peak dose decreased with increasing depth and increased with increase in field size. Also, the peak dose moved towards CAX with increase in gantry angle.In general dose to tissue out of field could be reduced using appropriate shielding for each applicator and beam energy.