On correction factors for profile measurements with small solid state detectors and with small ionization chambers

Introduction: Measured profiles, which are crucial to treatment planning system commissioning, are generally affected by averaging effect linked to the size of sensitive volume of detectors used. Such averaging leads to deviation from the true profiles in water even when small field detectors are employed. In order to have access to profile data which are free from the influence of the measuring device, a guidance is required, on when and how much correction is required for a detector in use. Material and methods: Profile correction factors were determined as the ratio between true profiles in water and associated measured profiles, both as a function of off-axis distance. The identical free air profile is used to simulate measurement and to generate ‘measured’ profiles at different depths in water. The MC generated profiles in water without the detector were taken as true profiles. Based on such MC generated profile results, detector specific correction factors were determined. Additionally, such factors were approximated by an analytical function using a fit procedure for the function parameters. Optimized parameters were systematically compiled depending on measuring conditions such as beam size, depths in water for detectors-pinpoint, pinpoint 3D, microSilicon and microDiamond. Results: The method to generate a common dataset of true profiles in water was successful. Also, measured and simulated profiles well agree for all measuring conditions. In addition, correction factors, as well as approximated correction functions were derived. Application of analytical correction functions to measured profiles for given conditions, well reproduced true profiles with the detector being absent. Conclusions: The MC method to derive correction factors for profile measurements is feasible for all detectors used in this study. Such correction factors can be well approximated by a simple analytical function. It is recommended that ionization chamber measured profiles generally need correction while solid state detectors measured profiles fairly approach the true profiles in water.

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Opracowanie rekordu ze środków MNiSW, umowa nr POPUL/SP/0154/2024/02 w ramach programu "Społeczna odpowiedzialność nauki II" - moduł: Popularyzacja nauki (2025).