title: Impact of radiation attenuation by a carbon fiber couch on patient dose verification.
abstract: The aim of this study was to understand the difference between the measured and calculated irradiation attenuations obtained using two algorithms and to identify the influence of couch attenuation on patient dose verification. We performed eight tests of couch attenuation with two photon energies, two longitudinal couch positions, and two rail positions. The couch attenuation was determined using a radiation treatment planning system. The measured and calculated attenuations were compared. We also performed 12 verifications of head-and-neck and rectum cases by using a Delta phantom. The dose deviation (DD), distance to agreement (DTA), and gamma index of pencil-beam convolution (PBC) verifications were nearly the same. The agreement was least consistent for the anisotropic analytical algorithm (AAA) without the couch for the head-and-neck case, in which the DD, DTA, and gamma index were 74.4%, 99.3%, and 89%, respectively; for the rectum case, the corresponding values were 56.2%, 95.1%, and 92.4%. We suggest that dose verification should be performed using the following three metrics simultaneously: DD, DTA, and the gamma index.
authors.affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, ROC.|Medical Physics and Radiation Measurements Laboratory, Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.|3Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan, ROC.
authors.forename: Chun-Yen
authors.initials: CY
authors.lastname: Yu
authors.affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, ROC.
authors.forename: Wen-Tsae
authors.initials: WT
authors.lastname: Chou
authors.affiliation: School of Medical Laboratory Science and Biotechnology, Collage of Medical Science and Technology, Taipei Medical University, Taipei, Taiwan, ROC.
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Liao
authors.affiliation: Health Physics Division, Institute of Nuclear Energy Research, Longtan, Taiwan, ROC.
authors.forename: Jeng-Hung
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, China Medical University Hospital, Taichung, Taiwan, ROC.
authors.forename: Ji-An
authors.initials: JA
authors.lastname: Liang
authors.affiliation: Medical Physics and Radiation Measurements Laboratory, Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.|Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.|Biophotonics and Molecular Imaging Research Center, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Shih-Ming
authors.initials: SM
authors.lastname: Hsu