Unconscious physiological response of healthy volunteers to dynamic respiration-synchronized couch motion.

Background: Intrafractional motion can be a substantial uncertainty in precision radiotherapy. Conventionally, the target volume is expanded to account for the motion. Couch-tracking is an alternative, where the patient is moved to compensate for the tumor motion. However, the couch motion may influence the patient's stress and respiration behavior decreasing the couch-tracking effectiveness.

Methods: In total, 100 volunteers were positioned supine on a robotic couch, which moved dynamically and respiration synchronized. During the measurement, the skin conductivity, the heartrate, and the gaze location were measured indicating the volunteer's stress. Volunteers rated the subjective motion sickness using a questionnaire. The measurement alternated between static and tracking segments (three cycles), each 1 min long.

Results: The respiration amplitude showed no significant difference between tracking and static segments, but decreased significantly from the first to the last tracking segment (p < 0.0001). The respiration frequency differed significantly between tracking and static segments (p < 0.0001), but not between the first and the last tracking segment. The physiological parameters and the questionnaire showed mild signals of stress and motion sickness.

Conclusion: Generally, people tolerated the couch motions. The interaction between couch motion and the patient's breathing pattern should be considered for a clinical implementation.

Trial Registration: The study was registered at ClinicalTrials.gov (NCT02820532) and the Swiss national clinical trials portal ( SNCTP000001878 ) on June 20, 2016.