AbstractID: 8192 Title: Lung motion tracking with a combined spirometer-laser sensor system
Highly conformal IMRT treatments of non small-cell lung cancer require control of respiratory motion. Beam gating, breath holding and active breath control are some of the techniques used to minimize the motion effect. We have developed a new system to track the tumor motion.
Spirometers provide a direct measurement of the lung volume change and its signal is therefore correlated to tumor motion. However, the drift of such systems prevents them from monitoring breathing for a long period of time.
The measurement of chest wall displacement is drift free, however may not correlate well with tumor motion.
In our approach, we combined the spirometer with a laser distance sensor to take the advantages of both devices. The spirometer is used to monitor the air flow and the laser distance sensor is used to simultaneously monitor the chest wall motion. Both signals are acquired during a few initial breathing cycles to calibrate the laser distance sensor signal to the spirometer signal.
After calibration, the laser distance sensor yields a volume-time relation similar to the spirometer, but without any drift.
Results from healthy volunteers indicate a stable correlation between the two signals during normal breathing cycles. During the initial phase of breathhold, a strong anti-correlation was observed, as the chest wall moved although the air flow was zero. This integrated approach is a powerful monitoring system and provides a sensitive interlock to prevent treatment during any abnormal breathing motion.