| Successful radiotherapy requires accurate dosimetry for treatment verification. Existing dosimeters such as ion chambers, TLD, and diodes have drawbacks such as relatively long measurement time and poor spatial resolution. These disadvantages become serious problems for dynamic-wedged beams. Thus, the clinical use of a dynamic wedge requires an improved dosimetry method. X-ray film may serve this purpose. However, film is not clinically accepted as a dosimeter for photon beams, because it overresponds to photons with energies below about 400 keV. The purpose of this work is to develop methods which will improve the dose-response of x-ray film in a phantom, so that x-ray film can be used as an in-phantom dosimeter for both static and dynamic-wedged photon beams.;In this study, three methods have been investigated. The first method (i.e. high-Z screen filtration method) is based on placing high-Z foils next to the film, which preferentially remove incident low-energy photons before they reach the film. The second method (i.e. high-Z particulate filtration method) is similar to the first method except it is based on uniformly distributing high-Z particulate in a plastic phantom to remove low-energy photons. For this purpose, a solid phantom containing high-Z particulate was fabricated. The third method (i.e. scintillation method) is based on sandwiching the film by two scintillating screens to enhance the film response to electrons, and therefore minimize the overresponse by low-energy photons.;The results indicate that all three methods generate dose distributions close to those measured by ion chambers for 4, 6, and 18 MV photon beams. However, considering a few facts such as ease of the phantom setup and the accuracy of the results, the second method is the best practical solution. |
