Room: AAPM ePoster Library
Purpose: Significant internal organ mismatch was observed between the planned DRR and treatment kV image on several DIBH breast patients. A tried-and-true solution was to add a time delay on the RGSC signal which triggers the kV image acquisition. This study is to systematically investigate the time delay between the external monitoring surrogate and internal organ movement in the DIBH. The result should guide the clinical setup for optimum treatment.
Methods: Varian RGSC and Philips Bellow system were used to monitor test volunteers’ breathing motion on the chest and belly region. The assumption is the internal organ would stop moving if both signals reach a stationary state during DIBH. Those systems were calibrated and synchronized to record the breathing trace of the volunteers. The raw breathing traces were exported out to determine the time delay between those two monitored locations while the volunteers were instructed to do DIBH at different couch pitch level: flat, 2.5° pitch, and 5° pitch. A Matlab script was programmed to extract the data and do analysis.
Results: The volunteer mentioned the different couch pitches significantly affected the breathing pattern: with flat couch, a belly breathing was more likely comparing to a pitched couch location. Preliminary data on one volunteer’s multiple DIBH attempts on the flat couch shown the time delay between the chest and belly movements were ranging from 0.36 sec to -1.2 sec with the mean value of 0.5 sec. More volunteers’ data will be acquired and presented.
Conclusion: The physiological nature of DIBH should be carefully analyzed for radiation therapy. The timing for CT imaging, planar kV imaging, and treatment delivery should be set considering the delay between the physiological movement of internal organ and external surrogate location to avoid mistreatment.