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Estimation of Patient-Specific Imaging Dose for Real-Time Tumor-Tracking in Lung During Respiratory-Gated Radiotherapy

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T Shiinoki

T Shiinoki1*, D Kawahara2 , R Onizuka3 , T Suzuki2 , Y Yuasa1,3 , K Fujimoto1,3 , T Uehara3 , H Hanazawa1 , K Shibuya1 , (1) Yamaguchi University, Ube, Yamaguchi, (2) Hiroshima University, Hiroshima, Hiroshima, (3)Yamaguchi University Hospital, Ube, Yamaguchi


SU-H4-GePD-J(A)-3 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: The respiratory gating (RG) system combined the TrueBeam and a new real-time tumor-tracking radiotherapy (RT) system, SyncTraX (Shimadzu Co., Japan) was installed. The SyncTraX consists of two x-ray tubes and color image intensifiers. Using fluoroscopic images, the fiducial marker which was implanted near the tumor was tracked using image processing and used as the internal surrogate for RG. The purpose of this study was to evaluate the patient-specific imaging dose for real-time tumor-tracking in lung during the course of treatment using Monte Carlo.

Methods: Using one x-ray tube, the PDD and OCR were measured in water equivalent phantom for 60-120 kV. A phase space file (PSF) was commissioned for PDD and OCR using BEAMnrc. Absolute dose was measured to acquire the calibration factor for each energy. In clinical cases, 8 patients who underwent RGRT with 6 MV-FFF of the lung were enrolled in this study. Fluoroscopic time and the positions of x-ray tube were calculated using a log file of SyncTraX. The couch angles were acquired using RT-plan. The clinical situation was simulated in DOSXYZnrc using a PSF. The patient-specific dose was calculated using planning CT and to evaluate the dose-volume-metrics for normal organs.

Results: The simulated dose along the beam axis beyond the buildup region agreed with the measured dose within an error of 2%, and the simulated lateral dose agreed within 2%, expect around the penumbra for each energy. For clinical cases, the mean ± S.D. of D2 for the ispilateral lung were 105.9 ± 65.9 mGy. Those for the skin were 135.7 ± 69.7 mGy. For the PTV, imaging dose from the SyncTraX did not affect the prescribed dose.

Conclusion: We evaluated the patient-specific imaging dose for real-time tumor-tracking in lung. Our results showed the imaging dose from the SyncTraX might be clinically negligible during RGRT.

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