Development and evaluation of a water-profile-based calibration method for 2D ionization chamber arrays in medical linear accelerator quality assurance.

Authors

Kihong Pak, Sung-Woo Kim, Byungchul Cho, Jungwon Kwak, Seonghoon Jeong, Kyeongyun Park, Jisoo Kim, Jonghan Park, Si Yeol Song, Seonyeong Noh, Jongin Oh, Seokjin Kang, Chiyoung Jeong

Published in

Journal of applied clinical medical physics. Volume 27. Issue 10. Pages e70830.

Abstract

To develop and evaluate a water-profile-based (WP) calibration method for two-dimensional (2D) ionization chamber arrays used in medical linear accelerator (linac) quality assurance (QA), and to compare its accuracy, efficiency, and cross-energy applicability with the manufacturer-provided wide-field (WF) calibration method.
Beam profiles were measured using an IC Profiler (ICP) and a 3D water scanner on three TrueBeam linacs (TB1-TB3) at five photon energies (4, 6, 10 MV flattened; 6, 10 MV flattening-filter-free [FFF]) with a 20 × 20 cm² field size at a depth of 10 cm. A total of 240 profiles were acquired across eight independent measurement sessions. The WP method derived adjusted calibration factors (ACFs) by directly matching ICP detector responses to water-scanner reference profiles, and was evaluated under three strategies: (i) machine-specific (single linac reference), (ii) machine-integrated (reference pooled across three linacs), and (iii) cross-energy applicability across 20 inter-energy combinations. Performance metrics included per-detector relative differences (mean absolute error [MAE] and standard deviation [SD]) and beam profile characterization (symmetry and flatness). Paired t-tests (n = 30) compared the machine-integrated WP method with the WF method.
The WF method yielded a per-detector MAE of 0.31%, with symmetry and flatness MAEs of 0.49% and 0.44%, respectively. The WP method significantly reduced these uncertainties to 0.15-0.16% (per-detector), 0.21-0.27% (symmetry), and 0.27-0.28% (flatness), with medium-to-large effect sizes (Cohen's d = 0.55-0.99; all p < 0.01). Cross-energy application of WP-derived ACFs yielded a per-detector MAE of 0.25%, higher than that of energy-specific WP calibration but lower than that of the WF method in this dataset. Total calibration time decreased from approximately 75 min (WF) to 10-15 min (WP).
For the tested 20 × 20 cm² field on TrueBeam linacs with a CC13/Blue Phantom2 water-scanner reference, the proposed WP calibration method provided closer agreement with the water-scanner reference and a substantially shorter calibration time than the manufacturerprovided WF method. Machine-integrated calibration is recommended for routine multi-linac implementation, while energy-specific ACFs should be used whenever feasible to maximize accuracy.

PMID:
42798172
Bibliographic data and abstract were imported from PubMed on 26 Sep 2026.

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