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Evaluation of Imaging Dose of a Novel Patient Positioning System with Four X-Ray Tubes and Flat Panel Detectors

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O Umetsu

O Umetsu1*, S TANABE2 , T Sasage1 , S Utsunomiya3 , K Cho1 , H Takatou1 , M Kunii1 , A Amaki1 , G Kawaguchi1 , H Aoyama4 , (1) Uonuma Kikan Hospital, Minami Uonuma City, Niigata, (2) Niigata University Medical and Dental Hospital, Niigata, Niigata, (3) Graduate School of Health Sciences, Niigata University, Niigata, Niigata (4) Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Niigata


TU-C3-GePD-TT-4 (Tuesday, August 1, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Theater

Purpose: A novel real-time tracking radiotherapy (RTRT) system, SyncTraX FX4, which consisted of four X-ray tubes and four ceiling mounted flat panel detectors (FPDs) combined with a linear accelerator, was installed in our institution for the first time in the world. This system enables to perform bony structure-based patient positioning and verification for any tumor sites in addition to RTRT. The purpose of this study was to evaluate imaging dose from the SyncTraX FX4 by comparing to an on-board kV imager.

Methods: Imaging X-ray can be delivered at an angle of 37.7° from two X-ray tubes (#1 and #2) in SAD=235 cm, and of 43.8° from the other two tubes (#3 and #4) in SAD=208 cm, respectively. We measured air kerma at isocenter of double exposure from the tube #3 with a solid-state dosimeter for the several predetermined imaging parameters settings (kV, mA, time). The tube #3 was the one nearest to isocenter and proved to give the maximum imaging dose. Entrance surface doses (ESDs) were calculated from air kerma by considering back scatter factor and inverse square law. We also estimated the total ESDs of AP and lateral images by on-board kV imager in similar manner.

Results: For the on-board kV imager, ESDs were ranged from 1.02 to 4.77 mGy for several predetermined imaging parameter settings: Head, Thorax, Abdomen, Pelvis, and Extremity. The ESDs for the SyncTrax FX4 were ranged from 0.18 to 0.83 mGy which were about 5.6 times smaller than the on-board kV imager at most.

Conclusion: The estimated imaging doses of a novel patient positioning system, SyncTrax FX4 were much lower than on-board kV imager for similar predetermined imaging parameters. The results showed an advantage of the system in IGRT era.

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