Room: AAPM ePoster Library
Purpose: To quantify the use of anterior torso skin surface position measurement as a breathing surrogate.
Methods: Patients were scanned 25 times using a free-breathing low-mA fast helical CT protocol with real-time breathing monitored by an abdominal bellows surrogate. The diaphragm position was used to measure breathing-induced motion. The craniocaudal diaphragm positions were correlated against the bellows signal acquired at the corresponding scan times. To estimate the effectiveness of skin surface positions as surrogates, the anterior torso surface position was measured from the CT scans and correlated against the bellows signal in 1 cm2 patches. The correlation coefficients were analyzed over the surface for fourteen studied patients and the surrogate error was defined as the root-mean square correlation residual.
Results: A strong correlation (average patient R = 0.93) was measured between the diaphragm motion and the abdominal bellows signal with an average surrogate error of 9.63%. The correlations between the bellows and patient surface positions varied throughout the torso and from patient to patient. However, a consistently strong correlation was found at the abdomen for each patient, and the average maximum correlation coefficient was 0.95. The average minimum surrogate error was 9.22%. From this high correlation point in the abdomen to the chest, the correlation degraded with patient-dependent patterns.
Conclusion: The abdominal bellows was an accurate surrogate for diaphragm motion. The abdominal patient surface was also shown to be an accurate surrogate, but the accuracy varied across the abdomen sufficiently that care would need to be taken to use the surface as a reliable surrogate. Future studies will use surface imaging to investigate the aggregate effect over the entire chest as well as thoracic and abdominal breathing relationships. This research could yield improvements in capturing as much information as possible to measure and account for patient breathing motion.