Spatial resolution of a stacked radiochromic film dosimeter

Purpose: The spatial resolution of stacked radiochromic film dosimeters, wh ich have increased sensitivity from a single layer radiochromic film detect or, has been studied. Methods: A 5-layer film which can easily be constructed provided a 4.3-time s increase in sensitivity over a single layer film at 670 nm readout wavele ngth which meant that doses as low as 0.6 Gy could be measured with an accu racy of +/-4% with the stacked dosimeter. The spatial resolution was tested by comparison of the 80%/20% penumbral widths of a 5x 5cm 6 MV X-ray field . Results: The MD-55-2 film measured the penumbral width as 3.0 = whereas the 5-layer stack dosimeter measured the same penumbra as 3.2 mm. Conclusion: The stack dosimeter can provide useful in vivo information such as the position of a diverging beam edge for treatments around critical st ructures such as eyes during the first fraction of treatment. (C) 2001 Else vier Science Ireland Ltd. All rights reserved.