Metal screen-film detector MTF at megavoltage x-ray energies

The MTF of metal screen film detectors used in radiation treatment verification has been measured at 4 and 8 MV x-ray energies. The results show that lead screens provide better resolution than copper screens, and a single-emulsion film offers considerable advantage over the traditional double-emulsion film. A rear lead screen was found to seriously degrade the resolution properties of a front lead screen single-emulsion film detector. The detector MTF was found to be energy dependent. In general, both the low and the high spatial frequency response decreased with increasing x-ray energy. This, in part, accounts for the noticeable image quality difference between 4 and 8 MV radiographs.