title: Mechanical quality assurance using light field for linear accelerators with camera calibration.
abstract: Mechanical Quality Assurance (QA) is important to assure spatially precise delivery of external-beam radiation therapy. As an alternative to the conventional-film based method, we have developed a new tool for mechanical QA of LINACs which uses a light field rather than radiation. When light passes through the collimator, a shadow is projected onto a piece of translucent paper and the resulting image is captured by a digital camera via a mirror. With this method, we evaluated the position of the LINAC isocenter and the accuracy of the gantry, collimator, and couch rotation. We also evaluated the accuracy of the digital readouts of the gantry, collimator, and couch rotation. In addition, the treatment couch position indicator was tested. We performed camera calibration as an essential pre-requisite for quantitative measurements of the position of isocenter, the linear motion of the couch, and the rotation angles of the gantry and collimator. Camera calibration reduced the measurement error to submillimeter based on uncertainty in pixel size of the image, while, without calibration, the measurement error of up to 2 mm could occur for an object with a length of 5 cm.
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Kwangwoo
authors.initials: K
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Wonhoon
authors.initials: W
authors.lastname: Choi
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Ki Chang
authors.initials: KC
authors.lastname: Keum
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Ho
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Jeongmin
authors.initials: J
authors.lastname: Yoon
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Chang Geol
authors.initials: CG
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea.
authors.forename: Ik Jae
authors.initials: IJ
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, College of Medicine, Yonsei University, Seoul, Republic of Korea. Electronic address: jjhmd@yuhs.ac.
authors.forename: Jaeho
authors.initials: J
authors.lastname: Cho
mesh_terms: D002138:Calibration; D055595:Mechanical Phenomena; D010315:Particle Accelerators; D011786:Quality Control; D011878:Radiotherapy / Q000295:instrumentation*; D012399:Rotation
keywords: Camera calibration; Lens distortion; Light field; Mechanical isocenter; Quality assurance (QA)