An investigation into a novel in-vivo PMMA (polymethyl methacrylate) plastic fiber-optic dosimeter for monitoring low doses of ionizing radiotherapy radiation in real time and for integrating measurements is presented. The fabricated optical fiber tip possessed an embedded structure. A scintillation material, terbium-doped gadolinium oxysulfide (Gd 2 O 2 S:Tb), capable of emitting visible light at around 545 nm which is ideal for transmission through the PMMA when exposed to ionizing radiation was embedded in the PMMA plastic fiber. The dose rate of incident ionizing radiation is measured by analyzing the signal intensity emitted from the scintillation material which propagates through the fiber to a distal MPPC (multi-pixel photon counter). The dosimeter exhibits good repeatability with an excellent linear relationship between the fiber-optic dosimeter output and the absorbed radiation dose with an outstanding isotropic response in its radial angular dependence. "Characterization of a fiber-optic-coupled radioluminescent detector for application in the mammography energy range," Med. Phys. 34(6), 2220-2227 (2007). 7. T. Aoyama, S. Koyama, and C. Kawaura, "An in-phantom dosimetry system using pin silicon photodiode radiation sensors for measuring organ doses in x-ray CT and other diagnostic radiology," Med. Phys. 29(7), 1504-1510 (2002). 8. A. S. Beddar, T. R. Mackie, and F. H. Attix, "Water-equivalent plastic scintillation detectors for high-energy beam dosimetry: I. physical characteristics and theoretical consideration," Phys. Med. Biol. 37(10), 1883-1900 (1992). 9. A. S. Beddar, T. R. Mackie, and F. H. Attix, "Water-equivalent plastic scintillation detectors for high-energy beam dosimetry: II. properties and measurements," Phys. Med. Biol. 37(10), 1901-1913 (1992). 10. M. A. Clift, R. A. Sutton, and D. V. Webb, "Dealing with Cerenkov radiation generated in organic scintillator dosimeters by bremsstrahlung beams," Phys. Med. Biol. 45(5), 1165-1182 (2000). #254911Received 2
A novel real-time optical fibre X-Ray dosimeter for monitoring the radiation pulses delivered from a clinical Linear Accelerator (Linac) is presented. The primary focus of the sensor is to measure low doses of ionising X-ray radiation in real-time (limited to 0.1 ms gate time of the detector). The sensor tip material scintillates upon exposure to X-ray energy and the resultant low level visible light signal is coupled to a PMMA (poly methyl methacrylate) plastic optical fibre, used to guide it towards a distal Avalanche Photodiode based detector. The detector measures the low level scintillating light from the sensor thereby converting the ionizing radiation energy to a measurable signal with a time resolution of 0.1 ms. Results show that the scintillating optical fibre X-ray dosimeter is capable of capturing the individual X-Ray pulses delivered by the Linac during normal operation. Further examination of the results demonstrates that the sensor is capable of measuring dose rate and hence dose with a linearity (R 2 = 0.9995-0.9999) and in a highly repeatable manner for dose rates in the range 100 to 600 Monitor Units/ Min (MU/Min).
Highlights:1. An embedded structure X-Ray optical fiber dosimeter is presented to monitor real time absorbed dose in-vivo.2. We identified five kinds of scintillator materials to select the optimum one for the dosimeter.3. Every scintillator material has their own emission spectra and characteristics when exposed to X-Rays. 4. Gd2O2S:Tb is the optimum choice of material for the X-ray optical fiber dosimeter.Abstract: In-vivo real-time dose rate measurement has attracted much attention in the tumortreatment field because of the demand for precise delivery of radiotherapy. An optical fiber based dosimeter is presented, which is fabricated by embedding scintillator materials inside the fiber core. Five micron-scale powder based scintillator materials have been identified and their characteristics are compared in this investigation. The dosimeters have been fabricated separately but with exactly the same production process. Their emission spectra have been measured.Furthermore, an evaluation of the dosimeter's performance has been made by analyzing the signal intensity emitted from the scintillation material following transmission through a 25m length of plastic optical fiber (POF) to a distal MPPC (multi-pixel photon counter) detector. The excellent linearity of the relationship of the signal intensity and the dose rate has been established and simultaneously measured using an ionization chamber (IC) to ensure efficacy of the results. The dependence of the resulting fluorescence signal on water depth of two materials was also obtained and compared with the IC. The investigation clearly shows that currently Gd2O2S:Tb is the optimum choice of material for the X-ray optical fiber dosimeter.
An inorganic scintillating material plastic optical fiber (POF) dosimeter for measuring ionizing radiation during radiotherapy applications is reported. It is necessary that an ideal dosimeter exhibits many desirable qualities, including water equivalence, energy independence, reproducibility, dose linearity. There has been much recent research concerning inorganic dosimeters. However, little reference has been made to date of the depth-dose characteristics of dosimeter materials. In the case of inorganic scintillating materials, they are predominantly non water-equivalent, with their effective atomic weight (Z) being typically much greater than that of water. This has been a barrier in preventing inorganic scintillating material dosimeter from being used in actual clinical applications. In this paper, we propose a parallel-paired fiber light guide structure to solve this problem. Two different inorganic scintillating materials are embedded separately in the parallel-paired fiber. It is shown that the information of water depth and absorbed dose at the point of measurement can be extracted by utilizing their different depth-dose properties.
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