Spatial resolution of a stacked radiochromic film dosimeter.

PURPOSE: The spatial resolution of stacked radiochromic film dosimeters, which have increased sensitivity from a single layer radiochromic film detector, has been studied. METHODS: A 5-layer film which can easily be constructed provided a 4.3-times increase in sensitivity over a single layer film at 670 nm readout wavelength which meant that doses as low as 0.6 Gy could be measured with an accuracy of +/-4% with the stacked dosimeter. The spatial resolution was tested by comparison of the 80%/20% penumbral widths of a 5 x 5 cm 6 MV X-ray field. RESULTS: The MD-55-2 film measured the penumbral width as 3.0 mm 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 structures such as eyes during the first fraction of treatment.