Comparative analysis of respiratory motion tracking using Microsoft Kinect v2 sensor.

Evan Silverstein,Michael Snyder

doi:10.1002/acm2.12318

Abstract

PurposeTo present and evaluate a straightforward implementation of a marker‐less, respiratory motion‐tracking process utilizing Kinect v2 camera as a gating tool during 4DCT or during radiotherapy treatments.MethodsUtilizing the depth sensor on the Kinect as well as author written C# code, respiratory motion of a subject was tracked by recording depth values obtained at user selected points on the subject, with each point representing one pixel on the depth image. As a patient breathes, specific anatomical points on the chest/abdomen will move slightly within the depth image across pixels. By tracking how depth values change for a specific pixel, instead of how the anatomical point moves throughout the image, a respiratory trace can be obtained based on changing depth values of the selected pixel. Tracking these values was implemented via marker‐less setup. Varian's RPM system and the Anzai belt system were used in tandem with the Kinect to compare respiratory traces obtained by each using two different subjects.ResultsAnalysis of the depth information from the Kinect for purposes of phase‐ and amplitude‐based binning correlated well with the RPM and Anzai systems. Interquartile Range (IQR) values were obtained comparing times correlated with specific amplitude and phase percentages against each product. The IQR time spans indicated the Kinect would measure specific percentage values within 0.077 s for Subject 1 and 0.164 s for Subject 2 when compared to values obtained with RPM or Anzai. For 4DCT scans, these times correlate to less than 1 mm of couch movement and would create an offset of 1/2 an acquired slice.ConclusionBy tracking depth values of user selected pixels within the depth image, rather than tracking specific anatomical locations, respiratory motion can be tracked and visualized utilizing the Kinect with results comparable to that of the Varian RPM and Anzai belt.

Highlights

As radiotherapy treatments become increasingly precise, identifying and visualizing tumor movement during treatment becomes exceedingly important
For comparison and accuracy measurements, Respiratory Gating system (RPM) and Anzai were both employed to a subject at the same time with the Kinect mounted above the patient
The point selected by the system to represent the respiratory motion is done so by calculating the largest amplitude between the traces created for all points selected

Summary

Introduction

As radiotherapy treatments become increasingly precise, identifying and visualizing tumor movement during treatment becomes exceedingly important. Tumors located within the thorax and abdomen are significantly affected by motion induced with a patient’s natural respiratory cycle. Accounting for this additional internal motion becomes paramount. One specific way to acquire and process this information is through the use of a 4DCT, by which the respiratory motion of the patient is tracked using a gating device.[1,2] The respiratory motion trace is processed in tandem with the CT acquisition and CT slices are binned to specific portions of the respiratory cycle.[3] This process allows internal motion visualization of the tumor by use of external motion tracking.[4]

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Discussion

Conclusion