title: Dosimetric properties of radiophotoluminescent glass detector in low-energy photon beams.
abstract: OBJECTIVE
  A radiophotoluminescent glass rod dosimeter (RGD) has recently become commercially available. It is being increasingly used for dosimetry in radiotherapy to measure the absorbed dose including scattered low-energy photons on the body surface of a patient and for postal dosimetry audit. In this article, the dosimetric properties of the RGD, including energy dependence of the dose response, reproducibly, variation in data obtained by the RGD for each energy, and angular dependence in low-energy photons, are discussed.
  
  
  METHODS
  An RGD (GD-301, Asahi Techno Glass Corporation, Shizuoka, Japan) was irradiated with monochromatic low-energy photon beams generated by synchrotron radiation at Photon Factory, High Energy Accelerator Research Organization (KEK). The size of GD-301 was 1.5 mm in diameter and 8.5 mm in length and the active dose readout volume being 1 mm diameter and 0.6 mm depth located 0.7 mm from the end of the detector. The energy dependence of the dose response and reproducibility and variation were investigated for RGDs irradiated with a plastic holder and those irradiated without the plastic holder. Response of the RGD was obtained by not only conventional single field irradiation but also bilateral irradiation. Angular dependence of the RGD was measured in the range of 0°-90° for 13, 17, 40, and 80 keV photon beams by conventional single field irradiation.
  
  
  RESULTS
  The dose responses had a peak at around 40 keV. For the energy range of less than 25 keV, all dose response curves steeply decreased in comparison with the ratio of mass energy absorption coefficient of the RGD to that of air. As for the reproducibility and variation in data obtained by the RGD, the coefficient of variance increased with decrease in photon energy. Furthermore, the variation for bilateral irradiation was less than that for single field irradiation. Regarding angular dependence of the RGD, for energies of 13 and 17 keV, the response decreased with increase in the irradiation angle, and the minimum values were 93.5% and 86%, respectively.
  
  
  CONCLUSIONS
  Our results showed the dosimetric properties of the RGD, including the energy dependence of the dose response, reproducibly, variation, and angular dependence in low-energy photons and suggest that the accuracy of the absorbed dose in low-energy photons is affected by the readout method and the distribution of radiophotoluminescence centers in the RGD.
authors.affiliation: Department of Radiation Oncology, Tohoku University, Sendai, Japan. kadoya.n@rad.med.tohoku.ac.jp
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kadoya
authors.forename: Kouhei
authors.initials: K
authors.lastname: Shimomura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kitou
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Shiota
authors.forename: Yukio
authors.initials: Y
authors.lastname: Fujita
authors.forename: Suguru
authors.initials: S
authors.lastname: Dobashi
authors.forename: Ken
authors.initials: K
authors.lastname: Takeda
authors.forename: Keiichi
authors.initials: K
authors.lastname: Jingu
authors.forename: Haruo
authors.initials: H
authors.lastname: Matsushita
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Namito
authors.forename: Syuichi
authors.initials: S
authors.lastname: Ban
authors.forename: Syuji
authors.initials: S
authors.lastname: Koyama
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Tabushi
mesh_terms: D005898:Glass; D049408:Luminescent Agents; D009010:Monte Carlo Method; D017785:Photons; D011874:Radiometry / Q000379:methods*
chemical_list: D049408:Luminescent Agents