title: Practical method for determination of air kerma by use of an ionization chamber toward construction of a secondary X-ray field to be used in clinical examination rooms.
abstract: We propose a new practical method for the construction of an accurate secondary X-ray field using medical diagnostic X-ray equipment. For accurate measurement of the air kerma of an X-ray field, it is important to reduce and evaluate the contamination rate of scattered X-rays. To determine the rate quantitatively, we performed the following studies. First, we developed a shield box in which an ionization chamber could be set at an inner of the box to prevent detection of the X-rays scattered from the air. In addition, we made collimator plates which were placed near the X-ray source for estimation of the contamination rate by scattered X-rays from the movable diaphragm which is a component of the X-ray equipment. Then, we measured the exposure dose while changing the collimator plates, which had diameters of 25-90 mm(ϕ). The ideal value of the exposure dose was derived mathematically by extrapolation to 0 mm(ϕ). Tube voltages ranged from 40 to 130 kV. Under these irradiation conditions, we analyzed the contamination rate by the scattered X-rays. We found that the contamination rates were less than 1.7 and 2.3 %, caused by air and the movable diaphragm, respectively. The extrapolated value of the exposure dose has been determined to have an uncertainty of 0.7 %. The ionization chamber used in this study was calibrated with an accuracy of 5 %. Using this kind of ionization chamber, we can construct a secondary X-ray field with an uncertainty of 5 %.
authors.affiliation: School of Health Sciences, Tokushima University, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Itsumi
authors.initials: I
authors.lastname: Maehata
authors.affiliation: Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan. hayashi.hiroaki@tokushima-u.ac.jp.
authors.forename: Hiroaki
authors.identifier: http://orcid.org/0000-0002-8836-5068
authors.initials: H
authors.lastname: Hayashi
authors.affiliation: School of Health Sciences, Tokushima University, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Kimoto
authors.affiliation: Graduate School of Health Sciences, Tokushima University, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Takegami
authors.affiliation: Graduate School of Health Sciences, Tokushima University, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Okino
authors.affiliation: Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kanazawa
authors.affiliation: Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
authors.forename: Masahide
authors.initials: M
authors.lastname: Tominaga
mesh_terms: D004867:Equipment Design; D006801:Humans; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation*; D014965:X-Rays
keywords: Air kerma; Contamination rate; Diagnostic X-ray equipment; Ionization chamber; Scattered X-rays; Secondary X-ray field