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Localization Accuracy of a Novel Patient Positioning System with Four X-Ray Tubes and Flat Panel Detectors: A Phantom Study

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S TANABE1*, S Utsunomiya2 , O Umetsu3 , T Sasage3 , H Takatou3 , M Kunii3 , A Amaki3 , G Kawaguchi3 , H Aoyama4 , (1) Niigata University Medical and Dental Hospital, Niigata, Niigata, (2)Graduate School of Health Sciences, Niigata University, Niigata, Niigata(3) Uonuma Kikan Hospital, Minami Uonuma, Niigata, (4) Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Niigata


SU-I-GPD-T-78 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: A novel real-time tracking radiotherapy (RTRT) system, SyncTraX FX4 (SFX4), which consisted of four X-ray tubes and four flat panel detectors (FPDs) combined with a linear accelerator, was installed in our institution. This system enables to perform bony structure-based patient positioning and verification for any regions in addition to RTRT. The purpose of this study was to investigate a localization accuracy of this system compared to cone-beam CT (CBCT).

Methods: The localization accuracy was evaluated using three kinds of phantoms (head, thorax, pelvis). Each phantom was positioned on the couch with a total of 20 intentionally generated initial setup errors with a range of up to ±20 mm and ±1.5 degrees. In order to correct the initial errors through automatic image registration, bony structure-based matchings with CBCT and SFX4 systems were used, respectively. As for SFX4, using two out of four X-ray devices consisted of X-ray tubes and FPDs, one of four predetermined combinations was selected to acquire each data set. The differences in the couch shifts including the rotation calculated by each system were compared.

Results: Median values of shift differences between CBCT and SFX4 systems were 0.28 mm/-0.21 mm/0.10 mm/-0.11°/-0.16°/0.08° (vertical/longitudinal/lateral/rotation/roll/pitch) for head phantom, 0.20 mm/-0.40 mm/0.0 mm/0.0°/-0.10°/0.03° for thorax phantom, and 0.50 mm/-0.35 mm/0.10 mm/0.0°/-0.20°/0.03° for pelvis phantom. The Pearson coefficients of correlation for each shift were at least over 0.95 in all phantoms and directions. Although the significant differences were found in vertical, longitudinal, and rotational directions among three phantoms, median values of translational and rotational shifts differences were within 0.5 mm and 0.2°, respectively.

Conclusion: This work showed the localization accuracy of SFX4 system was highly correlated with that of CBCT system in head, thorax, and pelvis phantoms, implying that this system has a competent performance to be an alternative to CBCT system.

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