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Efficient Verification of X-ray Target Replacement for the C-series High Energy Linear Accelerator

 Jin Dong Cho  ;  Minsoo Chun  ;  Jaeman Son  ;  Hyun Joon An  ;  Jeongmin Yoon  ;  Chang Heon Choi  ;  Jung-in Kim  ;  Jong Min Park  ;  Jin Sung Kim 
 Korean Journal of Medical Physics (의학물리), Vol.29(3) : 92-100, 2018 
Journal Title
 Korean Journal of Medical Physics (의학물리) 
Issue Date
Linear accelerator ; Target degradation ; Target melting ; Beam verification ; IMRT verification
The manufacturer of a linear accelerator (LINAC) has reported that the target melting phenomenon could be caused by a non-recommended output setting and the excessive use of monitor unit (MU) with intensity-modulated radiation therapy (IMRT). Due to these reasons, we observed an unexpected beam interruption during the treatment of a patient in our institution. The target status was inspected and a replacement of the target was determined. After the target replacement, the beam profile was adjusted to the machine commissioning beam data, and the absolute doses-to-water for 6 MV and 10 MV photon beams were calibrated according to American Association of Physicists in Medicine (AAPM) Task Group (TG)-51 protocol. To verify the beam data after target replacement, the beam flatness, symmetry, output factor, and percent depth dose (PDD) were measured and compared with the commissioning data. The difference between the referenced and measured data for flatness and symmetry exhibited a coincidence within 0.3% for both 6 MV and 10 MV, and the difference of the PDD at 10 cm depth (PDD10) was also within 0.3% for both photon energies. Also, patient-specific quality assurances (QAs) were performed with gamma analysis using a 2-D diode and ion chamber array detector for eight patients. The average gamma passing rates for all patients for the relative dose distribution was 99.1%±1.0%, and those for absolute dose distribution was 97.2%±2.7%, which means the gamma analysis results were all clinically acceptable. In this study, we recommend that the beam characteristics, such as beam profile, depth dose, and output factors, should be examined. Further, patient-specific QAs should be performed to verify the changes in the overall beam delivery system when a target replacement is inevitable; although it is more important to check the beam output in a daily routine.
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1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
Yonsei Authors
Kim, Jinsung(김진성) ORCID logo https://orcid.org/0000-0003-1415-6471
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