Online model checking for monitoring surrogate-based respiratory motion tracking in radiation therapy.
OBJECTIVE
Correlation between internal and external motion is critical for respiratory motion compensation in radiosurgery. Artifacts like coughing, sneezing or yawning or changes in the breathing pattern can lead to misalignment between beam and tumor and need to be detected to interrupt the treatment. We propose online model checking (OMC), a model-based verification approach from the field of formal methods, to verify that the breathing motion is regular and the correlation holds. We demonstrate that OMC may be more suitable for artifact detection than the prediction error.


MATERIALS AND METHODS
We established a sinusoidal model to apply OMC to the verification of respiratory motion. The method was parameterized to detect deviations from typical breathing motion. We analyzed the performance on synthetic data and on clinical episodes showing large correlation error. In comparison, we considered the prediction error of different state-of-the-art methods based on least mean squares (LMS; normalized LMS, nLMS; wavelet-based multiscale autoregression, wLMS), recursive least squares (RLSpred) and support vector regression (SVRpred).


RESULTS
On synthetic data, OMC outperformed wLMS by at least 30 % and SVRpred by at least 141 %, detecting 70 % of transitions. No artifacts were detected by nLMS and RLSpred. On patient data, OMC detected 23-49 % of the episodes correctly, outperforming nLMS, wLMS, RLSpred and SVRpred by up to 544, 491, 408 and 258 %, respectively. On selected episodes, OMC detected up to 94 % of all events.


CONCLUSION
OMC is able to detect changes in breathing as well as artifacts which previously would have gone undetected, outperforming prediction error-based detection. Synthetic data analysis supports the assumption that prediction is very insensitive to specific changes in breathing. We suggest using OMC as an additional safety measure ensuring reliable and fast stopping of irradiation.
['Antoni|Sven-Thomas|ST|', 'Rinast|Jonas|J|', 'Ma|Xintao|X|', 'Schupp|Sibylle|S|', 'Schlaefer|Alexander|A|']
D000465:Algorithms D016477:Artifacts D006801:Humans D008175:Lung Neoplasms D008962:Models, Theoretical D008991:Monitoring, Physiologic D009862:Online Systems D016634:Radiosurgery D011880:Radiotherapy Planning, Computer-Assisted D012119:Respiration D012371:Robotics D012815:Signal Processing, Computer-Assisted
Model checking Radiosurgery Prediction Internal–external correlation Respiration