MO-D-T-617-08: Skin Dose Measurement with Radiochromic Film

Abstract

Purpose: Due to the build-up properties of megavoltage x-ray beams, skin dose varies significantly within the first few millimeters of the skin depth. The practical measurement depth depends on equipment type and design and the biological effect one is interested in. The skin depth recommended for practical skin dose assessment is at 0.07 mm depth according to the ICRP 26 and the ICRU 39. The goal of our study was to determine the correction procedure in order to obtain an accurate skin dose at the depth of 70 microns, for 6 MV photon beams using different GafChromic film models. Method and Materials: We used new GAFCHROMIC ® film models, HS, XR-T, or EBT which have effective points of measurement at depths slightly higher than 70 microns. Film pieces were exposed to 6 MV photon beams placed at the surface of solid water phantom. In addition to the films, we also used Attix plane parallel chamber and extrapolation chamber in order to cover tissue equivalent depths in the range from 10 microns to 1 mm. Results: Our measurements suggest that within the first millimeter of the skin region, the PDD for 6 MV photon beam and field size of 10 cm × 10 cm increases from 14 % to 40 %. Conclusions: For the three different GafChromic film models, 6 MV beam skin dose corrections are: 12% for EBT, 15% for HS and 16 % for XR-T model GafChromic films.