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One Institution's Experience with Surface Imaging in Proton Therapy

L Zhao

L Zhao*, H Singh , Y Zheng , ProCure Proton Therapy Center, Oklahoma City, OK


SU-E-J-139 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

X-ray system is commonly used for IGRT in proton therapy, however image acquisition not only increases treatment time but also adds imaging dose. We studied a 3D surface camera system (AlignRT) performance for proton therapy.

System accuracy was evaluated with rigid phantom under two different camera location configurations. For initial clinical applications, post mastectomy chest wall and partial breast treatments were studied. X-ray alignment was used as our ground truth. Our studies included: 1) comparison of daily patient setup shifts between X-ray alignment and SI calculation; 2) interfractional breast surface position variation when aligning to bony landmark on X-ray; 3) absolute positioning using planning CT DICOM data; 4) shifts for multi-isocenter treatment plan; 5) couch isocentric rotation accuracy.

Camera locations affected the system performance. After camera relocation, the accuracy of the system for the rigid phantom was within 1 mm (fixed couch), and 1.5 mm (isocentric rotation). For intrafractional patient positioning, X-ray and AlignRT shifts were highly correlated (r=0.99), with the largest difference (mean ± SD) in the longitudinal direction (2.14 ± 1.02 mm). For interfractional breast surface variation and absolute positioning, there were still larger disagreements between the two modalities due to different focus on anatomical landmarks, and 95% of the data lie within 5mm with some outliers at 7 mm-9 mm. For multi-isocenter shifts, the difference was 1 ± 0.56 mm over an 11 cm shift in longitudinal direction. For couch rotation study, the differences was 1.36 ± 1.0 mm in vertical direction , 3.04 ± 2.11 mm in longitudinal direction, and 2.10 ± 1.66 mm in lateral direction, with all rotation differences < 1.5 degree.

Surface imaging is promising for intrafractional treatment application in proton therapy to reduce X-ray frequency. However the interfractional discrepancy between the X-ray and SI requires future validation.

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