title: Dose verifications by use of liquid ionization chamber of an electronic portal imaging device (EPID).
abstract: In this study, we examined the ability of an L-EPID to verify rectangular and irregular fields and to measure the transmitted exit doses. With respect to the beam profile of rectangular and irregular fields and the doses transmitted through an inhomogeneous phantom, the L-EPID dose obtained from the L-EPID measurement was compared with the conventional dose measured by use of a 0.12-cc ionization chamber and a 3D water phantom. In the comparison of the rectangular and irregular fields, the difference in the off-center ratio (OCR) between the L-EPID dose and the conventional dose was approximately 3% in the steep-dose-gradient region (penumbra regions, >30%/cm) and approximately +/-0.5% in the gentle-dose-gradient region (5%/cm). On the other hand, the dose differences between the L-EPID and the measured doses were less than approximately 2% in the gentle-dose-gradient region. In addition, in the steep-dose-gradient region, the maximum difference was 30%. However, the differences in the distance-to-agreement (DTA) were less than approximately +/-1 mm and were unrelated to the dose gradient. These results suggest that dose verification by L-EPID is very useful in clinical applications.
authors.affiliation: Radiation Oncology, Imaging and Diagnosis, Division of Organ Function and Therapeutics, Molecular and Organ Regulation, Sapporo Medical University Graduate School of Medicine, Sapporo, Japan. tateoka@sapmed.ac.jp
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tateoka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Oouchi
authors.forename: Kensei
authors.initials: K
authors.lastname: Nakata
authors.forename: Masato
authors.initials: M
authors.lastname: Hareyama
mesh_terms: D000465:Algorithms; D004581:Electronics / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D010315:Particle Accelerators / Q000295:instrumentation; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water
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