Room: AAPM ePoster Library
Purpose: For patients with left-sided breast cancer, the heart is in close proximity to the treatment field. Dose received during radiotherapy leads to increased risk of cardiovascular complications in later life. The deep inspiration breathhold (DIBH) technique increases separation between heart and target, reducing heart dose. However, efficacy depends on maintenance of a stable breathhold.
The aim of this research is to compare monitoring and visual feedback systems monitoring the chest and abdomen. The hypothesis is that chest surface monitoring will more accurately reflect true chest wall displacement as the monitoring region is closer to and more rigidly linked with the chest wall.
Methods: Breathing traces were obtained from patients following either the chest or abdominal monitoring systems. Deviation of the trace from the gating window centre was compared to the ground truth chest wall displacement relative to the planned position taken from EPID images. To test the hypothesis, an ‘accuracy per breathhold’ metric was defined to be the averaged sum of the absolute differences between the breathing trace deviation and chest wall displacement. In addition, reproducibility and stability were assessed following Cerviño et al. (reproducibility: maximum difference between average amplitudes of DIBHs per fraction; stability: per fraction maximum amplitude difference across a DIBH given by least squares fit).
Results: analysis of 11 patients showed mean accuracy per breathhold (as defined above) was 1.6±1.6mm and 1.6±1.4mm for chest surface and abdominal monitoring respectively. The chest surface monitoring system has superior reproducibility (0.6±0.7mm vs 2.7±0.5mm) and stability (0.1±0.2mm vs 0.2±0.5mm) for the analysed fractions. However, more patients are needed to assess statistical validity.
Conclusion: The mean accuracy of both systems was equivalent, indicating that both chest surface and abdominal monitoring reflect true chest wall motion equally well. Breathholds were more stable and reproducible for patients using the chest surface monitoring system.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by a National Breast Cancer Foundation (Australia) pilot study grant: PS_17_055. Paul Keall is a founder, shareholder and member of the Board of Directors of Opus Medical Pty Ltd, a University of Sydney spin-off company commercializing Breathe Well.