# Dosimetric impact of calibration coefficients determined using linear accelerator photon and electron beams for ionization chamber in an on-site dosimetry audit

## TL;DR

This study examines how using different calibration beams affects radiation dose measurements in audits, finding minimal impact for photon beams but larger effects for electron beams.

## Contribution

The study quantifies the dosimetric impact of calibration beam quality for ionization chamber coefficients in on-site audits.

## Key findings

- Photon beam measurements showed minimal dosimetric impact when using linac calibration coefficients.
- Electron beam measurements had larger dosimetric differences, with linac-based coefficients providing the most consistent results.
- Cross-calibration coefficients improved agreement for electron beam dosimetry.

## Abstract

This study aimed to clarify the dosimetric impact of calibration beam quality for calibration coefficients of the absorbed dose to water for an ionization chamber in an on-site dosimetry audit. Institution-measured doses of 200 photon and 184 electron beams were compared with the measured dose using one year data before and after the calibration of the ionization chamber used. For photon and electron reference dosimetry, the agreements of the institution-measured dose against two measured doses in this audit were evaluated using the calibration coefficients determined using 60Co (\documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$\end{document}) and linear accelerator (linac) (\documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document}) beams. For electron reference dosimetry, the agreement of two institution-measured doses against the measured dose was evaluated using\documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document}. Institution-measured doses were evaluated using direct- and cross-calibration coefficients. For photon reference dosimetry, the mean differences and standard deviation (SD) of institution-measured dose against the measured dose using \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$\end{document} and \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document} were −0.1% ± 0.4% and −0.3% ± 0.4%, respectively. For electron reference dosimetry, the mean differences and SD of institution-measured dose using the direct-calibration coefficient against the measured dose using \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},{}^{60}\mathrm{Co}}$\end{document} and \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document} were 1.3% ± 0.8% and 0.8% ± 0.8%, respectively. Further, the mean differences and SD of institution-measured dose using the cross-calibration coefficient against the measured dose using \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document} were −0.1% ± 0.6%. For photon beams, the dosimetric impact of introducing calibration coefficients determined using linac beams was small. For electron beams, it was larger, and the measured dose using \documentclass[12pt]{minimal}
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${N}_{D,\mathrm{w},Q}$\end{document} was most consistent with the institution-measured dose, which was evaluated using a cross-calibration coefficient.