Inter-Institutional Comparison of Computed Tomography Dose Index and Half-Value Layer In Helical Kilovoltage Computed Tomography System for Tomotherapy
Abstract
Purpose
To evaluate inter-institutional variability in the computed tomography dose index (CTDI) and aluminum half-value layer (HVL) for ClearRT (Accuray, Inc., Sunnyvale, CA), and to assess the consistency of imaging dose and beam quality across institutions.
Methods
Using the same dosimeter and X-ray analyzer (RaySafe X2, Fluke Biomedical, Cleveland, OH) with a lead slit (RTQM System Co., Ltd., Hiroshima, Japan) and standard CTDI phantoms (16 cm and 32 cm diameter), CTDI and HVL were measured at six independent institutions in Japan. The lead slit was used to restrict the incident X-ray beam to forward-incident X-rays only during HVL measurements. Identical scanning protocols, based on the manufacturer’s acceptance testing procedures, were applied at all sites to minimize procedural variability.
Results
Three scanning protocols (head, thorax, and pelvis) were evaluated. The mean ± standard deviations (SD) values of helical CTDIvol across all participating institutions were 10.15 ± 0.18 mGy, 12.20 ± 0.21 mGy, and 10.71 ± 0.23 mGy, respectively. The corresponding HVL values were 8.63 ± 0.04 mmAl, 6.69 ± 0.05 mmAl, and 7.36 ± 0.08 mmAl. The maximum inter-institutional differences were 0.5 mGy (4.8%) for CTDIvol and 0.26 mmAl (3.6%) for HVL for the same imaging protocol.
Conclusion
Inter-institutional variability in helical CTDIvol and HVL for ClearRT was within the measurement uncertainty of the same dosimeter and X-ray analyzer used in this study and within the tolerance levels recommended by the AAPM TG-198 QA guidelines. These results demonstrate consistent imaging dose and beam quality across institutions. These results demonstrate consistent imaging dose and beam quality across institutions.