SU‐E‐T‐249: Evaluation of the Surface Rendering Patient Localization System for Proton Therapy Facility

Abstract

Purpose: Proton therapy carries a number of dosimetric and radiobiological advantages for cancer patients and calls for rigorous quality assurance of patient registration. This work is a report of evaluation and use of surface rendering patient positioning system (AlignRTTM) in proton facility. Method and Materials: The AlignRT three‐camera system was installed in a specific non‐symmetric geometry, specific to the proton gantry room. Series of phantom shifts/rotations were done to assess the system performance versus shifts/rotations of the 6D PPS (Patient Positioning System) that accounts for proton gantry sag. 4D phantom (CIRS,inc.) was used to evaluate motion tracking capabilities of AlignRT. Finally, AlignRT installation was used for on‐line monitoring of thorax patients (emphasis on breathing motion). Retrospective analysis of breathing data was performed versus latest weekly 4DCT of these patients. Results: In case of the baseline images taken at specific PPS rotation angles, from which shifts were performed, the proton room‐specific 3‐camera AlignRTTM system shows satisfactory results with shifts/rotations within 0.5mm/0.3degrees maximum difference. The accuracy of SSD determination was within 1 mm. In case of treatment planning system‐generated baseline images and baseline images taken at PPS angle of zero degrees, the system performance depended on PPS rotation angle, the fact whether the AlignRT system had the nominal couch angle input, and the size of the shift. At shifts within +/−3cm from isocentric position, AlignRT system performed with accuracy of 2.0mm/0.3degrees maximum deviations for PPS rotation angles within 30degrees from the “golden standard” surface and for PPS rotations 90+/− 10degrees. At intermediate PPS angles (60+/−10degrees), accuracy shown: within 10mm longitudinal/lateral, sub‐millimeter vertical directions. Reproducibility of phantom position was within 0.5mm/0.3degree. The measured amplitude of the patient breathing motion was within 0.5mm from 4DCT. Conclusion: Installation of surface rendering patient positioning system (AlignRTTM) in proton room‐specific geometry was evaluated and used for patient positioning monitoring.