High‐speed bioimpedance‐based gating system for radiotherapy: Prototype and proof of principle

Abstract

PurposeTo investigate a novel bioimpedance‐based respiratory gating system (BRGS) designed for external beam radiotherapy and to evaluate its technical characteristics in comparison with existing similar systems.Materials and methodsThe BRGS was tested on three healthy volunteers in free breathing and breath‐hold patterns under laboratory conditions. Its parameters, including the time delay (TD) between the actual impedance change and the gating signal, temperature drift, root mean square (RMS) noise, and signal‐to‐noise ratio (SNR), were measured and analyzed.ResultsThe gate‐on TD and the gate‐off TD were found to be 9.0 ± 2.0 ms [mean ± standard deviation (M ± SD)] and 7.2 ± 1.3 ms, respectively. The temperature drift of the BRGS output signal was 0.02 Ω after 30 min of operation. RMS noise averaged 0.14 ± 0.05 Ω (M ± SD) for all subjects and varied from 0.08 to 0.20 Ω with repeated measurements. A significant difference in SNR (p < 0.001) was observed between subjects, ranging from 4 to 15.ConclusionThe evaluated bioimpedance‐based gating system showed a high performance in real‐time respiratory monitoring and may potentially be used as an external surrogate guidance for respiratory‐gated external beam radiotherapy. Direct comparison with commercially available systems, 4D correlation studies, and expansion of the patient sample are goals for future preclinical studies.