Elimination of Cerenkov interference in a fibre-optic-coupled radiation dosemeter

Abstract

An optical fibre point dosemeter based on the gated detection of the luminescence from a Cu(1+)-doped fused quartz detector effectively eliminated errors due to Cerenkov radiation and native fibre fluorescence. The gated optical fibre dosemeter overcomes serious problems faced by scintillation and optically stimulated luminescence approaches to optical fibre point dosimetry. The dosemeter was tested using an external beam radiotherapy machine that provided pulses of 6 MV X rays. Gated detection was used to discriminate the signal collected during the radiation pulses, which included contributions from Cerenkov radiation and native fibre fluorescence, from the signal collected between the radiation pulses, which contained only the long-lived luminescence from the Cu(1+)-doped fused quartz detector. Gated detection of the luminescence provided accurate, real-time dose measurements that were linear with absorbed dose, independent of dose rate and that were accurate for all field sizes studied.

Cerenkov radiation: a multi-functional approach for biological sciences

“…Thus, the liner electron beam might produce a stronger CL. In some external radiotherapy beam dosimetry instruments, such as plastic scintillators, the CL has sometimes been considered as an unwanted background signal [51][52][53][54][55]. However, CL produced by charged particles, and monitoring the CL generated in the medium can potentially be used for dosimetry measurement.…”

Optical Fibers and Optical Fiber Sensors Used in Radiation Monitoring

“…The radioluminescent peaks observed, function of the material investigated, its dopants and the type of the irradiation, are located from UV -185 nm, 250 nm, 285 nm, to visible -420 nm, 450 nm, 696 nm (Toh et al, 2002;Treadaway et al, 1975;Yoshida et al, 2007). The superposition of the two spectra makes the discrimination of the luminescence signal difficult, and so, several methods to improve the S/N in detecting the radioluminescent signal against the Cerenkov radiation were developed: the gated detection of the luminescence (Justus, 2006;Plazas, 2005), different time frames or the different angular distribution of the two signals are used to detect the RIL (Akchurin et al, 2005); the subtraction method by employing a dummy optical fiber to record the Cerenkov radiation separately; an optical filter or a set-up based on a spectrometer (Archambault, 2005;Lee et al, 2007b;Jang et al, 2010a;Jang et al, 2011a). An alternative to the generation of radioluminescence in optical materials is represented by the use of commercially available scintillating optical fibers as those delivered by SaintGobain Crystals and Detectors -France (Saint-Gobain, 2005) -core material: Polystyrene, core refractive index: 1.6, cladding material: acrylic, cladding refractive index: 1.49, NA: 0.58, scintillation efficiency: 2.4%, trapping efficiency: 3.4%, by Kuraray Co. (Japan) or specially designed ones, as Ce doped optical fibers (Chiodini et al, 2009).…”

“…The possible applications of optical fibers and the optical fiber sensors in radiation monitoring and dosimetry refer to: 1. measurement of the absorbed dose in radiotherapy (Andersen et al, 2002;Jang et al, 2009;Justus et al, 2006) and brachytherapy (Suchowerska et al, 2007); 2. spatial dose distribution in the case of linear electron and proton accelerators for medical treatment Jang et al, 2010a;Lee et al, 2007a); 3. evaluation of beam losses (dose rate, total dose, location) in particle accelerators Intermite et al, 2009;Wulf & Körfer, 2009), beam profiling (Wulf & Körfer, 2009), and the operating conditions of an electron storage ring (Bahrdt et al, 2009;Rüdiger et al, 2008); 4. synchrotron radiation beam profile diagnostics (Byrd et al, 2007 ;Chen et al, 1996); 5. neutron or mixed gamma-ray neutron dosimetry (Bartesaghi et al, 2007a;Jang et al, 2010b); 6. the investigation of isotopic composition of cosmic rays (Connell et al, 1990); 7. radiation dosimetry in computed tomography (Jones & Hintenlang, 2008;Moloney, 2008); 8. distributed radiation dosimetry for beta & gamma rays, and neutrons (Naka et al, 2001); 9. beam profile in the case of free electron lasers (Goettmann et al, 2007) or proton beams (Benoit et al, 2007); 10. remote monitoring of ground water or soil for radioactive contamination (Jones et al, 1993); 11. radiation protection and monitoring of nuclear installations (Magne et al, 2008); 12. monitoring of radioactive waste (Nishiura & Izumi, 2001); 13. reconstruction of the charge particle tracks (Adinolfi et al, 1991;Angelini et al, 1989;Atkinson et al, 1988;Mommaert, 1992;Nakajima et al, 2009 ;Yukihara et al, 2006); 14. the use as transfer detectors for dosimetric calibrations …”

“…Prior to exposure to 6 MV X-rays from a linear accelerator, the radiation detection tip was pre-sensitised under soft X-ray radiation in order to stabilize its responsivity (Justus et al, 2006). To remove the background noise, composed of the native fluorescence in the coupling optical fibers (having a decay time of several ns) and the Cerenkov radiation (emitted in the ps range), and to keep for the dose measurement only the scintillation signal from the Cu + -doped fused quartz optical fiber (lasting several hundreds ms) a gated data acquisition is performed by temporarily selecting the signal to be processed.…”

Comparison of the New MOSkin Detector and Fiber Optic Dosimetry System for Radiotherapy

“…Since the amount of Cerenkov produced in the fiber is not directly proportional to the dose delivered to the fiber, the Cerenkov contribution to the signal is considered background noise. 2,3,4) Methods such as background subtraction and optical filtering are used to reduce the majority of this noise 2,3) . MOSFET-based dosimeters utilize a different technology to measure dose, but share many characteristics with fiber optic dosimeters such as small size, water equivalence for MV X-ray, and the ability to measure dose in real-time.…”