SU-E-J-157: Comparison Between Internal Respiratory Signal and External Respiratory Signal in 4D CT




To investigate the effectiveness of using a Fourier transformbased internal respiratory signal (IRS) to sort four-dimensional (4D) CT images, compared to images sorted using the external respiratory signal from the real-time position management (RPM) system.


80 patients with abdominal or thoracic cancers were retrospectively selected for this study. The IRS were computed using an algorithm previously described by our group. 4D images were then sorted using the end inspiration times calculated from the IRS. We compared the IRS to the RPM signals by assessing their similarities using the normalized cross correlation (NCC), and the end inspiration times identified from the respective signals. The IRS-sorted 4D images were also compared to the RPM-sorted clinical images using a correlation-based metric to compare their image qualities.


In 90% of the data sets, the IRS matched with the RPM signal with NCC >= 0.5. In this cohort of matching signals, the average difference between end inspiration times from the IRS and RPM signal was 0.11 s. In the remaining 10% of the data sets, the IRS did not match the RPM signal in at least one couch position (NCC < 0.5). The average difference between end inspiration times was 0.73 s in the non-matching couch positions. The correlation-based metric indicated poorer matching of neighboring couch positions in the RPM-sorted images. This implied that, when the IRS did not match the RPM signal, the images sorted using the IRS showed fewer artifacts than the clinical images sorted using the RPM signal.


The IRS is in good agreement with the RPM signal in most cases. In some cases, the IRS provides better sorting than the RPM signal, especially when the RPM system fails. The IRS can therefore be a viable complementary tool or even a replacement for the RPM system.