Use of multiple layers of Gafchromic film to increase sensitivity

This note investigates the increase of the sensitivity of radiochromic film by layering the film together. Investigations with up to five layers of ra diochromic film placed together as a single dosimeter have allowed accurate two-dimensional dosimetry at low radiotherapy doses. The sensitivity of th e response of the layered film increases with the number of layers, with th e five-layer dosimeter increasing the change in optical density by 4.3 +/-0 .2 times that for a single layer film at 670 nm readout wavelength. Measure ments in the penumbral region of a 6 MV x-ray beam show that the spatial re solution is slightly reduced with the layered film. The distance across the region from 20 to 80% of the maximum dose at the beam edge (20/80% penumbr a) measured at 1.5 cm depth was measured as 3.1 +/-0.3 and 3.5 +/-0.3 nm fo r one and five layers, respectively. Thus no major reduction in spatial res olution was found by layering the film to five layers but the sensitivity w as increased by 430% at 670 nm readout wavelength.