title: Rapid two-dimensional dose measurement in brachytherapy using plastic scintillator sheet: linearity, signal-to-noise ratio, and energy response characteristics.
abstract: Because of the large dose gradients encountered near brachytherapy sources, an efficient, accurate, low-atomic number areal detector, which can record dose at many points simultaneously, is highly desirable. We have developed a prototype of such a system using thin plates of plastic scintillator as detectors. A micro-channel plate (MCP) image intensifier was used to amplify the optical scintillation images produced by radioactive 125I and 137Cs sources in water placed 0.5-5.7 cm distance from the detector. A charge-coupled device (CCD) digital camera was used to acquire 2-D light-intensity distributions from the image intensifier output window. For both isotopes, a small area (2 x 3 mm2) PVT detector yields a CCD net count rate that is linear with respect to absorbed dose rate within +/- 3% out to 5.7 cm distance. Acquisition times range from 1.5-400 sec with a reproducibility of 0.5-5.5%. If a large-area (6 x 20 cm2) PVT detector is used, a four-fold increase in count rate and large deviations from linearity are observed, indicating that neighboring pixels contribute light to the signal through diffusion and scattering in PVT and water. A detailed noise analysis demonstrates that the image intensifier reduces acquisition time 10000-fold, reduces noise relative to signal 200-fold, and reduces amplifier gain noise as well.
authors.affiliation: Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: H
authors.initials: H
authors.lastname: Perera
authors.forename: J F
authors.initials: JF
authors.lastname: Williamson
authors.forename: S P
authors.initials: SP
authors.lastname: Monthofer
authors.forename: W R
authors.initials: WR
authors.lastname: Binns
authors.forename: J
authors.initials: J
authors.lastname: Klarmann
authors.forename: G L
authors.initials: GL
authors.lastname: Fuller
authors.forename: J W
authors.initials: JW
authors.lastname: Wong
mesh_terms: D001918:Brachytherapy; D006801:Humans; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D012588:Scintillation Counting / Q000295:instrumentation*