(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To determine the Percentage Depth Dose (PDD) using radiographic film in tissue equivalent materials.
Methods: In this method the linear region of the H-D curve of a radiographic film was used for relative depth dose determination. The films were, placed in between slabs of solid water phantom at the test depths in separate sessions of exposure. The exposures at all test depths were confined to within the linear range of the H-D curve. In the linear portion, the slope is proportional to the dose rate at the point of measurement. PDD was obtained by normalizing the slopes of the H-D curves at test depths, to that at the respective dmax depths. Measurements were performed using EDR2 ready pack films for a field size of 10cm x 10cm with 4, 6 & 15 MV photons and 8, 12 & 15 MeV electrons. Films were developed in a batch and optical densities were measured using X-RITE 331 densitometer.
Results: There is very good agreement in the relative depth dose obtained by the film method and the ionization chamber measurements. However, there is poor agreement in the region below the depth of dmax, because, in the steep gradient of the buildup region, the large size of the ion chamber averages the values over its volume, whereas the film measures at a point. For 4, 6 and 15 MV photon beams deviations were within 2.2%, 3.5%, and 2.9% respectively except at surface for 6 and 15 MV. For 8, 12 and 15 MeV electron beams observed deviations were within 2.5%, 3% and 2.1% respectively.
Conclusion: A novel method using radiographic films was applied, to obtain relative depth dose for photon and electron beams. It offers a unique method to determine depth dose data with a high spatial resolution in fields of steep gradient
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