Performance characteristics of a gated fiber-optic-coupled dosimeter in high-energy pulsed photon radiation dosimetry
ABSTRACT Fiber-optic-coupled dosimeters (FOCDs) are a new class of in vivo dosimetry systems that are finding increased clinical applications. Utility of FOCDs has been limited in dosimetric applications due Cerenkov-ray signal contamination. The current study reports on the characterization of a novel FOCD, with a gated detection system for the discrimination and effective elimination of the direct contribution of Cerenkov radiation, for use in the radiotherapeutic realm. System reproducibility, linearity and output dependence on dose rate, energy, field size, and temperature response were characterized for 6, 10, and 15MV photon energies. The system exhibited a linear response to absorbed dose ranging from 1 to 2400cGy and showed little dependence to dose rate variations. Overall system reproducibility was 0.52% with no field-geometry and temperature dependence.
- SourceAvailable from: Claus E Andersen
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- "Since dosimeter probes can be made fairly small (w1 mm outer diameter) and since the probes do not contain electrical wires, online in vivo patient dosimetry during diagnostic and therapeutic radiology has been one potentially important application of this technique (Aznar et al., 2004, 2005; Andersen et al., 2009b). Similar work aimed for general quality-assurance in radiotherapy has also been carried out using fiber-coupled organic plastic scintillators (Fontbonne et al., 2002; Archambault et al., 2010; Lambert et al., 2008; Beierholm et al., 2011) and fiber-coupled inorganic phosphors (Justus et al., 2004; Tanyi et al., 2010; Veronese et al., 2010; Molina et al., 2011; Konnoff et al., 2011). Fiber-coupled luminescence dosimetry based on single crystals of Al 2 O 3 :C has primarily been studied using a combined RL/OSL readout protocol. "
ABSTRACT: Radioluminescence (RL) and optically stimulated luminescence (OSL) from carbon-doped aluminum oxide crystals can be used for medical dosimetry in external beam radiotherapy and remotely afterloaded brachytherapy. The RL/OSL signals are guided from the treatment room to the readout instrumentation using optical fiber cables, and in vivo dosimetry can be carried out in real time while the dosimeter probes are in the patient. The present study proposes a new improved readout protocol based solely on the RL signal from Al2O3:C. The key elements in the protocol are that Al2O3:C is pre-dosed with ∼20 Gy before each measurement session, and that the crystals are not perturbed by optical stimulation. Using 6 and 18 MV linear accelerator photon beams, the new RL protocol was found to have a linear dose-response from 7 mGy to 14 Gy, and dosimetry in this range could therefore be performed using a single calibration factor (∼6 × 106 counts per Gy for a 2 mg crystal). The reproducibility of the RL dosimetry was 0.3% (one relative standard deviation) for doses larger than 0.1 Gy. The apparent RL sensitivity was found to change with accumulated dose ((−0.45 ± 0.03)% per 100 Gy), crystal temperature ((−0.21 ± 0.01)%/ °C), and dose-delivery rate ((−0.22 ± 0.01)% per 100 MU/min). A temporal gating technique was used for separation of RL and stem signals (i.e. Cerenkov light and fluorescence induced in the optical fiber cable during irradiation). The new readout protocol was a substantial improvement compared with the combined RL/OSL protocol, that required relatively long readout times and where the optical stimulation greatly affected the RL sensitivity. The only significant caveat was the apparent change in RL-response with accelerator dose-delivery rate.Radiation Measurements 10/2011; 46(10):1090-1098. DOI:10.1016/j.radmeas.2011.06.063 · 1.14 Impact Factor
Conference Paper: A hysteresis model for magnetic materials using the Giles-Atherton model[Show abstract] [Hide abstract]
ABSTRACT: The problem of determining parameters of the Giles-Atherton model used for defining hysteresis curves of magnetic materials was analyzed. Results obtained by numerical simulation of hysteresis curves of the ferromagnetic, hard magnetic core and anisotropic materials have been given. The hysteresis curve obtained is in good agreement with the curve defined for these materials in the PSpice program packet. The proposed method for parameter determination enables simulation of any magnetic material, which has a characteristic R, Z or F-shaped hysteresis curveAUTOTESTCON '99. IEEE Systems Readiness Technology Conference, 1999. IEEE; 02/1999
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ABSTRACT: We describe the current effort to develop a standardized data set, or suite of digital video sequences, that can be used for test and evaluation of digital video motion detectors (VMDs) for exterior applications. We have drawn from an extensive video database of typical application scenarios to assemble a comprehensive data set. These data, some existing for many years on analog videotape, have been converted to a reproducible digital format and edited to generate test sequences several minutes long for many scenarios. Sequences include non-alarm video, intrusions and nuisance alarm sources, taken with a variety of imaging sensors including monochrome CCD cameras and infrared (thermal) imaging cameras, under a variety of daytime and night-time conditions. We present an analysis of the variables and estimates the complexity of a thorough data set. Some of this video data test has been digitized for CD-ROM storage and playback. We are considering developing a DVD disk for possible use in screening and testing VMDs prior to government testing and deploymentSecurity Technology, 1999. Proceedings. IEEE 33rd Annual 1999 International Carnahan Conference on; 02/1999