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RESEARCH PRODUCT

[P149] Beam profile characteristic points designation for off-axis, wedged and FFF beams

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description

Purpose The main aim of this work is the search of characteristic points of a beam profile and application of these points for the TPS commissioning purposes. The comparison between profiles during the commissioning of the treatment planning system is a very important procedure. It is impossible to designate a field size for the off-axis, wedged and FFF beams directly using the definition of the on-axis symmetric field size. This work demonstrates how to compute good indicators of the field size that can be used for commissioning and QA purposes. Methods The proposal is to use profile inflection points as the beam profile characteristic points. The comparison of distances between inflection points and between points of 50% intensity was done using a dedicated software. For the off-axis, wedged and FFF fields comparisons were done to the nominal field sizes. Results Distances between inflection points were smaller than 1 mm compared to nominal field sizes for all kinds of investigated beams. Conclusions With a finite accuracy, inflection points can be used for the off-axis, wedged and FFF field sizes comparison. The main advantage of inflection points for the beam sizes designation is their independence from the method of profile normalization.