Program Information
Liver Position Consistency Across Breath Holds with ABC Used for SBRT
S Holler1*, E Fields2 , L Padilla1 , T Kim1 , (1) Virginia Commonwealth University, Richmond, VA, (2)Virginia Commonwealth University Health, Richmond, VA
Presentations
MO-L-GePD-JT-2 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Joint Imaging-Therapy ePoster Theater
Purpose: To investigate the validity of the current active breathing coordinator (ABC) system for usewith stereotactic body radiotherapy (SBRT) by evaluating changes in liver position as measured onsimulation CT images and relating them to lung volume variation as measured by the ABC spirometer. Touse the results to inform treatment margins and determine the need for a more clinically reliablesystem.
Methods: Eighteen abdominal CT simulations for SBRT for liver tumors were used in this study. Alleighteen simulations involved three sequential CT scans (Philips Big Bore) done under three separatebreath holds. On each scan, the liver was contoured. Position shift was measured by the treatmentplanning system (Pinnacle v9.8) upon completion of the contours. Shifts in position of superior boundaryof the liver were quantified and examined with respect to the variation in lung volume.
Results: Results were broken down into three groups based on clinical treatment margins andmagnitude shift. A change of position of <6mm was recorded in 48/54 CT scans with an averagemagnitude shift of the diaphragm of 2.3±1.9mm. For changes in position >6mm, the average magnitudechange for the superior boundary of the liver was 7.6±1.5 mm. Two patients exhibited changes >10mm,with an average magnitude shift of 13.5±1.2mm. Additionally, one patient’s scan showed a respiratorymotion artifact (duplication) while the spirometer indicated sustained breath hold.
Conclusion: In four patients, large changes (7.6 mm) in liver position were observed with small changesin lung volume. It is especially concerning that a patient may breathe while the ABC system isregistering a breath hold, which results in sizable shifts in the liver. Due to differences across breathholds and the possibility of unregistered free breathing, a geometric miss could occur, leading tounderdosing of the target and overdosing of normal tissue.
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