Assessing feasibility of a flat ion chamber for surface dose measurement of 6FF and 6FFF X ray photon beams

Abstract

Author(s): Kanakavel Kandasamy, E. James Jebaseelan Samuel

To prevent reddening on the patient's surface during radiotherapy treatment with MV X-ray beams, the surface dose must be low. In this study, we aimed to assess the feasibility of a flat ionization chamber for surface dose measurement. We used a medical linear accelerator capable of producing 6 FF and 6 FFF beams for three collimator sizes. We used Tref and Markus chambers, slab phantoms made of both acrylic and polystyrene from PTW. The thickness of the slabs was 1 mm, 2 mm, 5 mm, and 10 mm. First, the study evaluated basic dosimetric characteristics such as the linearity, reproducibility, and dose rate dependency of the Tref chamber. Next, we measured the surface dose using the Tref chamber and compared it with the Markus chamber. We found that the linearity, reproducibility, and dose rate dependency results were all within 0.5%. In both detectors, for the FF and FFF, SDs revealed a maximum difference of 8%. We observed an average surface dose difference of 10% between both chambers. Compared to Markus Chamber’s results, Tref overestimated the surface dose. The Tref chamber, if associated correction factors are available to account for its overestimation in the buildup region, is to be an alternative solution for surface dose measurement.

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