Radiochromic film calibration based on gradient radiation fields

[S. Pecić]

100 str.

Fizika - Primenjena fizika / Physics - Applied Physics

Ova disertacija istražuje razvoj alternativnog pristupa kalibraciji radiohromatskog filma, fokusirajući se na upotrebu gradijentnih radijacionih polja...

This dissertation explores the development of an alternative approach to radiochromic film calibration, focusing on the use of gradient radiation fields. Compared to uniformly irradiated film, the advantage of the gradient is that one exposure contains a large number of different and previously known dose values, allowing for more efficient calibration. The methodology developed in this work includes experimental and numerical calibration techniques with an emphasis on the application of a physical wedge filter as the basic dose gradient. The dynamic range coefficient is defined, the evaluation of which indicates a significant influence of parameters such as depth and field size, while the influence of beam quality is negligible. The measurement uncertainty of the calibration for the case of the gradient field was examined, where the maximum deviations were defined and the total uncertainty model obtained by uncertainty propagation was presented. Taking into account the importance of the film scanning process, the topics of spatial resolution and the effect of lateral response artifacts were discussed in particular. In order to extend the calibration range, the methodology shows possibilities of extrapolation and combination of multiple gradients. Through the formalism of the described method, the possibilities of optimizing the positioning of the gradients for a more even distribution of calibration points were analyzed, with a demonstration of the optimization of the procedure through a histogram of calibration points. Optimization of the gradient placement enabled convergence for seven exposures in the range [1, 10] Gy and eight exposures in the range [1, 20] Gy. Based on the existing results, an algorithm for the general case of gradient field calibration is presented. The methodology has the potential to be implemented within standard clinical settings, enabling routine film measurement and simplifying quality control procedures. Automation of the protocol opens the possibility of wide application, especially for complex gradient fields characteristic of modern therapeutic sources.

Radiohromatski film, Radijaciona dozimetrija, Medicinska fizika

Radiochromic film, Radiation dosimetry, Medical physics

544.2:539.16(043.3)

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