GAFCHROMIC MD-55 - INVESTIGATED AS A PRECISION DOSIMETER

GafChromic MD-55 is a fairly new, thin film dosimeter that develops a blue color (lambda(max)=676 nm) when irradiated with ionizing radiatio n. The increase in absorbance is roughly proportional to the absorbed dose. In this study, GafChromic MD-55 was irradiated with Co-60 gamma rays. A double irradiation method was used in which a dosimeter is giv en an unknown dose followed by a known, calibration dose. With this me thod, GafChromic MD-55 was used to measure doses in the vicinity of 6 Gy with an uncertainty of less than 1%. It was found that the measured optical density of GafChromic MD-55, as presently fabricated, is affe cted by the polarization of the analyzing light, an important consider ation when using GafChromic MD-55 as a precision dosimeter. GafChromic MD-55 was found to consist of seven layers. The response to polarized light was measured for the whole dosimeter and for the three Mylar fi lms which form part of the dosimeter. (C) 1997 American Association of Physicists in Medicine.