Body motion during dynamic couch tracking with healthy volunteers

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Biomechanical Engineering

Background:

• Intrafractional motion during radiotherapy introduces significant uncertainty in tumor targeting.
• Current methods to account for motion include target volume expansion, which can irradiate healthy tissue.
• Couch-tracking offers an alternative by dynamically compensating for intrafractional motion.

Purpose of the Study:

• To quantify the uncertainty in patient body position relative to the couch during static and dynamic couch-tracking conditions.
• To assess the viability of couch-tracking as a precision radiotherapy technique despite potential body motion.

Main Methods:

• Healthy volunteers were positioned supine on a robotic couch.
• Optical markers tracked volunteer torso and couch positions using an optical surface measurement system.
• Body position uncertainty relative to couch position was calculated during static and moving couch conditions.

Main Results:

• Median uncertainty increased with couch motion: 0.8 mm (Superior-Inferior), 0.4 mm (Lateral), 0.4 mm (Anterior-Posterior).
• Couch motion was confirmed to increase body position uncertainty.
• This motion-induced uncertainty was significantly smaller (one order of magnitude) than typical intrafractional tumor motion.

Conclusions:

• Couch-tracking increases body position uncertainty, but this increase is clinically insignificant compared to tumor motion.
• The couch-tracking approach remains a viable option for precision radiotherapy, even in the presence of patient body motion.