Film dosimetry: linearisation of dose-response for relative measurements of dose distribution

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Abstract
The authors have demonstrated a practical method to transform the densitometer readings to a quantity (apparent dose) that linearises the dose-response curve for the Kodak XV-2 film for all conditions used (different energies, irradiation geometries and processing). The determination of the constants for the pair film-densitometer has to be done only once, using a set of conditions chosen as reference. The linearisation method proposed permits relative film dosimetry, in the same film, without any calibration. Beam profiles (electrons or photons) obtained in several depths in a single film (parallel geometry), can be used to obtain the isodose chart, for a given field size. Only central axis depth dose data for the particular field is additionally required. Treatment plan systems can usually use these data as input to generate isodose charts.