Polymer Scintillator Detector for Real-time Proton Beam Quality Assurance

Abstract

Purpose/Objective(s)The purpose of this study is to demonstrate the feasibility of implementing a high resolution detector based on scintillating polymer technology to perform dosimetry and quality assurance of passive and scanned proton beams in real time along the central axis plane depth dose.Materials/MethodsPolymer scintillators can be molded or machined to any arbitrary shape, and the composite polymer formulation can be matched to the attenuation coefficient of water. These particular properties make them ideal for producing detectors constructed using water equivalent volumes where spatially distributed scintillating elements can be positioned to record the dose delivered by a proton beam at points of interest. Based on this property, we designed a cylindrical proton beam detector with scintillating disks placed along a cylindrical phantom axis and at multiple positions in the transverse planes. This will determine the dose in real time delivered by a proton beam along the phantom's major axis which is oriented in coincidence with the proton beam propagation. Non-scintillating optical fibers couple the fluorescence light emitted by the active elements to a monolithic photodetector/front end amplifier device, located just outside the phantom volume to avoid damage and perturbation of the beam profile. The monolithic photodetectors have high coupling efficiency with the optical fibers. The electronics time response constant and gain can be tuned to calibrate each sensor sensitivity and integration time.ResultsInitial estimations of the detector output when exposed to a proton beam with a specified energy of 250 MeV indicates that a fluorescence emission of the scintillating elements will be on the order of 6.6x10^15 photons per second, per nA of beam current. With a typical coupling efficiency of 60% between the photodetector and scintillating fiber, our developed monolithic high speed fiber coupled detector will have a sensitivity of 92 mV/nA when an integration time of 100 usec is selected. The signal to noise ratio of the system will be adequate to determine changes in beam dose of 1%, considering that the noise level of the detector is one order of magnitude lower than 1% of the signal. High efficiency coupling of the scintillating polymer disks with the detector can be achieved with scintillating elements of 0.45 mm thickness. This establishes the maximum spatial resolution of the detector along the Bragg peak.ConclusionsWe present the design of a real time dosimeter for proton beam quality assurance to determine the energy and dose of the proton beam along the central axis depth dose plane. The detector is based on scintillating polymers and high speed electronics to achieve real time measurements of both passive and scanning beam treatment delivery systems. Purpose/Objective(s)The purpose of this study is to demonstrate the feasibility of implementing a high resolution detector based on scintillating polymer technology to perform dosimetry and quality assurance of passive and scanned proton beams in real time along the central axis plane depth dose. The purpose of this study is to demonstrate the feasibility of implementing a high resolution detector based on scintillating polymer technology to perform dosimetry and quality assurance of passive and scanned proton beams in real time along the central axis plane depth dose. Materials/MethodsPolymer scintillators can be molded or machined to any arbitrary shape, and the composite polymer formulation can be matched to the attenuation coefficient of water. These particular properties make them ideal for producing detectors constructed using water equivalent volumes where spatially distributed scintillating elements can be positioned to record the dose delivered by a proton beam at points of interest. Based on this property, we designed a cylindrical proton beam detector with scintillating disks placed along a cylindrical phantom axis and at multiple positions in the transverse planes. This will determine the dose in real time delivered by a proton beam along the phantom's major axis which is oriented in coincidence with the proton beam propagation. Non-scintillating optical fibers couple the fluorescence light emitted by the active elements to a monolithic photodetector/front end amplifier device, located just outside the phantom volume to avoid damage and perturbation of the beam profile. The monolithic photodetectors have high coupling efficiency with the optical fibers. The electronics time response constant and gain can be tuned to calibrate each sensor sensitivity and integration time. Polymer scintillators can be molded or machined to any arbitrary shape, and the composite polymer formulation can be matched to the attenuation coefficient of water. These particular properties make them ideal for producing detectors constructed using water equivalent volumes where spatially distributed scintillating elements can be positioned to record the dose delivered by a proton beam at points of interest. Based on this property, we designed a cylindrical proton beam detector with scintillating disks placed along a cylindrical phantom axis and at multiple positions in the transverse planes. This will determine the dose in real time delivered by a proton beam along the phantom's major axis which is oriented in coincidence with the proton beam propagation. Non-scintillating optical fibers couple the fluorescence light emitted by the active elements to a monolithic photodetector/front end amplifier device, located just outside the phantom volume to avoid damage and perturbation of the beam profile. The monolithic photodetectors have high coupling efficiency with the optical fibers. The electronics time response constant and gain can be tuned to calibrate each sensor sensitivity and integration time. ResultsInitial estimations of the detector output when exposed to a proton beam with a specified energy of 250 MeV indicates that a fluorescence emission of the scintillating elements will be on the order of 6.6x10^15 photons per second, per nA of beam current. With a typical coupling efficiency of 60% between the photodetector and scintillating fiber, our developed monolithic high speed fiber coupled detector will have a sensitivity of 92 mV/nA when an integration time of 100 usec is selected. The signal to noise ratio of the system will be adequate to determine changes in beam dose of 1%, considering that the noise level of the detector is one order of magnitude lower than 1% of the signal. High efficiency coupling of the scintillating polymer disks with the detector can be achieved with scintillating elements of 0.45 mm thickness. This establishes the maximum spatial resolution of the detector along the Bragg peak. Initial estimations of the detector output when exposed to a proton beam with a specified energy of 250 MeV indicates that a fluorescence emission of the scintillating elements will be on the order of 6.6x10^15 photons per second, per nA of beam current. With a typical coupling efficiency of 60% between the photodetector and scintillating fiber, our developed monolithic high speed fiber coupled detector will have a sensitivity of 92 mV/nA when an integration time of 100 usec is selected. The signal to noise ratio of the system will be adequate to determine changes in beam dose of 1%, considering that the noise level of the detector is one order of magnitude lower than 1% of the signal. High efficiency coupling of the scintillating polymer disks with the detector can be achieved with scintillating elements of 0.45 mm thickness. This establishes the maximum spatial resolution of the detector along the Bragg peak. ConclusionsWe present the design of a real time dosimeter for proton beam quality assurance to determine the energy and dose of the proton beam along the central axis depth dose plane. The detector is based on scintillating polymers and high speed electronics to achieve real time measurements of both passive and scanning beam treatment delivery systems. We present the design of a real time dosimeter for proton beam quality assurance to determine the energy and dose of the proton beam along the central axis depth dose plane. The detector is based on scintillating polymers and high speed electronics to achieve real time measurements of both passive and scanning beam treatment delivery systems.