title: Characterization of stochastic noise and post-irradiation density growth for reflective-type radiochromic film in therapeutic photon beam dosimetry.
abstract: The aim of this study is to investigate the dosimetric uncertainty of stochastic noise and the post-irradiation density growth for reflective-type radiochromic film to obtain the appropriate dose from the exactly controlled film density. Film pieces were irradiated with 6-MV photon beams ranging from 0 to 400cGy. The pixel values (PVs) of these films were obtained using a flatbed scanner at elapsed times of 1min to 120h between the end of irradiation and the film scan. The means and standard deviations (SDs) of the PVs were calculated. The SDs of the converted dose scale, usd, and the dose increases resulting from the PV increases per ±29min at each elapsed time, utime, were computed. The combined dose uncertainties from these two factors, uc, were then calculated. A sharp increase in the PV occurred within the first 3h after irradiation, and a slight increase continued from 3h to 120h. usdwas independent of post-irradiation elapsed time. Sharp decreases in utimewere obtained within 1h after irradiation, and slight decreases in utimewere observed from 1 to 24h after irradiation. ucfirst decreased 1h after irradiation and remained constant afterward. Assuming that the post-irradiation elapsed times of all of the related measurements are synchronized within ±29min, the elapsed time should be at least 1h in our system. It is important to optimize the scanning protocol for each institution with consideration of the required measurement uncertainty and acceptable latency time.
authors.affiliation: Department of Therapeutic Radiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kamomae
authors.affiliation: Department of Radiological Technology, Graduate School of Health Sciences, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan. Electronic address: oita-m@cc.okayama-u.ac.jp.
authors.forename: Masataka
authors.initials: M
authors.lastname: Oita
authors.affiliation: Faculty of Radiological Technology, School of Health Sciences, Fujita Health University, 1-98, Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Hayashi
authors.affiliation: Department of Radiological Technology, Tokushima University Hospital, 2-50-1 Kuramoto-cho, Tokushima, Tokushima 770-8503, Japan.
authors.forename: Motoharu
authors.initials: M
authors.lastname: Sasaki
authors.affiliation: Department of Radiological Technology, Okayama University Hospital, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Aoyama
authors.affiliation: Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daiko-minami, Higashi-ku, Nagoya 461-8673, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Oguchi
authors.affiliation: Department of Radiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Kawamura
authors.affiliation: Department of Medical Physics, Graduate School of Medicine, Kindai University, 377-2 Ohno-Higashi, Osaka-Sayama, Osaka 589-8511, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Monzen
authors.affiliation: Department of Therapeutic Radiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Itoh
authors.affiliation: Department of Radiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Naganawa
mesh_terms: D055592:Biophysical Phenomena; D005373:Film Dosimetry / Q000379:methods* / Q000706:statistics & numerical data*; D006801:Humans; D017785:Photons / Q000627:therapeutic use*; D011882:Radiotherapy, High-Energy; D013269:Stochastic Processes; D035501:Uncertainty
keywords: Dosimetric uncertainty; Post-irradiation density growth; Radiochromic film; Stochastic noise