Purpose This study aimed to test the sensitivity of a transmission detector for online dose monitoring of intensity-modu- lated radiation therapy (IMRT) for detecting small delivery errors. Furthermore, the correlation of changes in detector output induced by small delivery errors with other metrics commonly employed to quantify the deviations between calculated and delivered dose distributions was investigated. Methods Transmission detector measurements were performed at three institutions. Seven types of errors were induced in nine clinical step-and-shoot (S&S) IMRT plans by modifying the number of monitor units (MU) and introducing small deviations in leaf positions. Signal reproducibility was investigated for short- and long-term stability. Calculated dose distributions were compared in terms of γ passing rates and dose–volume histogram (DVH) metrics (e.g., D ,D ,V ). mean x% x% The correlation between detector signal variations, γ passing rates, and DVH parameters was investigated. Results Both short- and long-term reproducibility was within 1%. Dose variations down to 1 MU (signal 1.1 ± 0.4%) as well as changes in ﬁeld size and positions down to 1 mm (signal 2.6 ± 1.0%) were detected, thus indicating high error-detection sensitivity. A moderate correlation of detector signal was observed with γ passing rates (R = 0.57–0.70),
Strahlentherapie und Onkologie – Springer Journals
Published: Dec 18, 2017
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