Program Information
Quantifying Patient Motion During Deep-Inspiration Breath-Hold Using the ABC System with Simultaneous Surface Photogrammetry
Y Cheung*, A Rahimi , A Sawant , UT Southwestern Medical Center, Dallas, TX
Presentations
SU-F-BRB-3 (Sunday, July 12, 2015) 4:00 PM - 6:00 PM Room: Ballroom B
Purpose:
Active breathing control (ABC) has been used to reduce treatment margin due to respiratory organ motion by enforcing temporary breath-holds. However, in practice, even if the ABC device indicates constant lung volume during breath-hold, the patient may still exhibit minor chest motion. Consequently, therapists are given a false sense of security that the patient is immobilized. This study aims at quantifying such motion during ABC breath-holds by monitoring the patient chest motion using a surface photogrammetry system, VisionRT.
Methods:
A female patient with breast cancer was selected to evaluate chest motion during ABC breath-holds. During the entire course of treatment, the patient’s chest surface was monitored by a surface photogrammetry system, VisionRT. Specifically, a user-defined region-of-interest (ROI) on the chest surface was selected for the system to track at a rate of ~3Hz. The surface motion was estimated by rigid image registration between the current ROI image captured and a reference image. The translational and rotational displacements computed were saved in a log file.
Results:
A total of 20 fractions of radiation treatment were monitored by VisionRT. After removing noisy data, we obtained chest motion of 79 breath-hold sessions. Mean chest motion in AP direction during breath-holds is 1.31mm with 0.62mm standard deviation. Of the 79 sessions, the patient exhibited motion ranging from 0-1 mm (30 sessions), 1-2 mm (37 sessions) , 2-3 mm (11 sessions) and >3 mm (1 session).
Conclusion:
Contrary to popular assumptions, the patient is not completely still during ABC breath-hold sessions. In this particular case studied, the patient exhibited chest motion over 2mm in 14 out of 79 breath-holds. Underestimating treatment margin for radiation therapy with ABC could reduce treatment effectiveness due to geometric miss or overdose of critical organs.
Funding Support, Disclosures, and Conflict of Interest: The senior author receives research funding from NIH, VisionRT, Varian Medical Systems and Elekta
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