Surface dose measurements with GafChromic EBT film for 6 and 18MV photon beams

Abstract 

The aim of this study was to determine the surface doses using GafChromic EBT films and compare them with plane-parallel ionization chamber measurements for 6 and 18MV high energy photon beams. The measurements were made in a water equivalent solid phantom in the build-up region of the 6 and 18MV photon beams at 100cm SSD for various field sizes. Markus type plane-parallel ion chamber with fixed-separation between collecting electrodes was used to measure the percent depth doses. GafChromic EBT film measurements were performed both on the phantom surface and maximum dose depth at the same geometry with ion chamber measurements. The surface doses found using GafChromic EBT film were 15%, 20%, 29%and 39%±2% (1SD) for 6MV photons, 6%, 11%, 23% and 32%±2% (1SD) for 18MV photons at 5, 10, 20 and 30cm² field sizes, respectively. GafChromic EBT film provides precise measurements for surface dose in the high energy photons. Agreement between film and plane-parallel chamber measurements was found to be within ±3% for 18MV photon beams. There was 5% overestimate on the surface doses when compared with the plane-parallel chamber measurements for all field sizes in the 6MV photon beams.

Keywords: Surface dose, High energy photons, GafChromic EBT films