Scintillating Fiber Dosimeter Research Articles

Validation of a New Scintillating Fiber Dosimeter for Radiation Dose Quality Control in Computed Tomography.

(1) Background: The IVIscan is a commercially available scintillating fiber detector designed for quality assurance and in vivo dosimetry in computed tomography (CT). In this work, we investigated the performance of the IVIscan scintillator and associated method in a wide range of beam width from three CT manufacturers and compared it to a CT chamber designed for Computed Tomography Dose Index (CTDI) measurements. (2) Methods: We measured weighted CTDI (CTDIw) with each detector in accordance with the requirements of regulatory tests and international recommendations for the minimum, maximum and the most used beam width in clinic and investigated the accuracy of the IVIscan system based on the assessment of the CTDIw deviation from the CT chamber. We also investigated the IVIscan accuracy for the whole range of the CT scans kV. (3) Results: We found excellent agreement between the IVIscan scintillator and the CT chamber for the whole range of beam widths and kV, especially for wide beams used on recent technology of CT scans. (4) Conclusions: These findings highlight that the IVIscan scintillator is a relevant detector for CT radiation dose assessments, and the method associated with calculating the CTDIw saves a significant amount of time and effort when performing tests, especially with regard to new CT technologies.

In vivo surface dosimetry with a scintillating fiber dosimeter in preclinical image-guided radiotherapy.

New preclinical image-guided irradiators and treatment planning systems represent a huge progress in radiobiology. Nevertheless, quality control of preclinical treatments is not as advanced as in clinical radiotherapy and in vivo dosimetry is less developed. In this study, we evaluate the use of a scintillating fiber dosimeter called DosiRat to verify the agreement between the doses planned with SmART-Plan and the measured doses during small animal irradiations. In vivo dosimetry was first evaluated with DosiRat through dose measurements performed at the surface of a 3×9×3cm3 phantom. Measured and planned doses were compared for different irradiation conditions (prescription point, anterior, and posterior beams, 5mm and 10mm irradiation fields). In a second phase, measured and planned doses were compared for rat brain irradiations performed with anterior beams, with DosiRat positioned at the beam entrance. Comparisons were performed for different tube currents (1.3 and 13mA), collimations (5, 10 and 25mm diameter), and planned doses (0.1, 0.5, 2, and 10Gy). In the case of the phantom irradiations, planned and measured doses showed discrepancies smaller than the 5% accuracy of the TPS, except in cases in which the dosimeter was not centered in the irradiation field. The differences were larger for animal irradiations (from -3.3% to 8.8%) because of variations of the beam energy spectrum and the nonequivalence between materials at medium and low energy. This study highlighted the complexity to implement one-dimension in vivo dosimetry in orthovoltage millimetric beams. Nevertheless, DosiRat is well adapted to in vivo dosimetry because of its small volume and its direct reading and allowed in vivo control of planned doses for anterior beams down to 5mm diameter.

Characterization of a plastic scintillating detector for the Small Animal Radiation Research Platform (SARRP).

The purpose of this study was to characterize a small plastic scintillator developed for high resolution, real-time dosimetry of therapy and imaging x-ray beams delivered by an image-guided small animal irradiator. A 1mm diameter, 1mm long polystyrene BCF-60 scintillating fiber dosimeter was characterized with 220kVp therapy and 40, 50, 60, 70, and 80kVp imaging beams on the Small Animal Research Platform (SARRP). Scintillator output, sensitivity (charge per unit dose), linearity, and 0.2-mm resolution beam profile measurements were performed. A validated in-house Monte Carlo (MC) model of the SARRP was used to compute detailed energy spectra at locations of dosimetry, and validated scintillator measurement with MC simulations. Mass energy-absorption coefficients from the National Institute of Standards and Technology (NIST) tables convolved with MC-derived spectra were used in conjunction with Birks ionization quenching factors to correct scintillator output. An air kerma calibration method was employed to correct scintillator output for in-air beam profile measurements with open, 5×5, and 3×3mm2 square field sizes, and compared to MC simulations. Scintillator dose response showed excellent linearity (R2 ≥0.999) for all sensitivity measurements, including output as a function of tube current. Detector sensitivity was 2.41μCGy-1 for the 220kVp therapy beam, and it ranged from 1.21 to 1.32μCGy-1 for the 40-80 imaging beams. Percentage difference in sensitivity between the therapy and imaging beams before sensitivity correction and after using the Birks quenching factors were 52.3% and 10.2%, respectively. Percentage differences between the therapy and imaging beam sensitivities after using the air kerma calibration method for in-air measurements was excellent and below 0.3%. In-air beam profile measurements agreed to MC simulations within a mean difference of 2.4% for the 5×5 and 3×3mm2 field sizes, however, the scintillator showed signs of volume averaging at the penumbra edges. A small plastic scintillator was characterized for therapy and imaging energies of a small animal irradiator, with output corrected for using an in-house MC model of the irradiator. The characterization of the scintillator detector system for small fields presents steps toward implementing real-time measurements for quality assurance and small animal treatment and imaging dose verification.

Implementation and evaluation of respiratory gating in small animal radiotherapy

Major advance was done in preclinical radiotherapy thanks to the development of image guided micro-irradiator. Nevertheless, some applications still can benefit of improvements, such as the irradiation of mobile tumors. This preclinical radiotherapy case presents increased difficulties compared to clinical practice because of the waveform of small animals breathing cycle, its frequency and amplitude. To answer this issue, we developed a specific beam shutter and implemented respiratory gating on the X-RAD 225Cx preclinical irradiator.In the first step of this study, the shutter was accurately characterized. Opening and closing speed of 1.28 and 0.33 mm ms−1 were respectively measured, and a transmission of 0.7% of the beam was measured with the shutter fully closed. Beam-on times were also determined for various gating parameters and highlighted a difference of 57 ms between the beam delivery duration and the gate width. This discrepancy was compensated during the respiratory monitoring adjustment.In a second step, a respiratory protocol was evaluated with two vertical beams of 2.5 and 5 mm diameters, for motion amplitudes ranging from 0.5 to 4 mm. This evaluation demonstrated the effectiveness of our set up to perform motion compensation for amplitude as small as 0.5 mm despite a dose gradient of 1.47 cGy mm−1 observed with the 5 mm irradiation field, due to the shutter opening and closing durations.We also investigated the efficiency of a scintillating fiber dosimeter, adapted to small beams and providing real-time dose rate measurements. This detector showed very good performances to detect motion in small irradiation fields and would be very suitable to monitor the number of delivered gates until the planned delivered dose is achieved.This study presented a new respiratory gating set up and showed that very efficient motion compensation could be achieved in small animal radiotherapy.

Brachytherapy dosimeter with silicon photomultipliers

In-vivo and in-situ measurement of the radiation dose administered during brachytherapy faces several technical challenges, requiring a very compact, tissue-equivalent, linear and highly sensitive dosimeter, particularly in low-dose rate brachytherapy procedures, which use radioactive seeds with low energy and low dose deposition rate. In this work we present a scintillating optical fiber dosimeter composed of a flexible sensitive probe and a dedicated electronic readout system based on silicon photomultiplier photodetection, capable of operating both in pulse and current modes. The performance of the scintillating fiber optic dosimeter was evaluated in low energy regimes, using an X-ray tube operating at voltages of 40–50kV and currents below 1mA, to assess minimum dose response of the scintillating fiber. The dosimeter shows a linear response with dose and is capable of detecting mGy dose variations like an ionization chamber. Besides fulfilling all the requirements for a dosimeter in brachytherapy, the high sensitivity of this device makes it a suitable candidate for application in low-dose rate brachytherapy. According to Peralta and Rego [1], the BCF-10 and BCF-60 scintillating optical fibers used in dosimetry exhibit high variations in their sensitivity for photon beams in the 25–100kVp energy range. Energy linearity for energies below 50keV needs to be further investigated, using monochromatic X-ray photons.

A new scintillating fiber dosimeter for real-time measurement in radiology and radiotherapy

A new scintillating fiber dosimeter for real-time measurement in radiology and radiotherapy

TH-C-17A-08: Monte Carlo Based Design of Efficient Scintillating Fiber Dosimeters

Purpose: To accurately predict Cherenkov radiation generation in scintillating fiber dosimeters. Quantifying Cherenkov radiation provides a method for optimizing fiber dimensions, orientation, optical filters, and photodiode spectral sensitivity to achieve efficient real time imaging dosimeter designs. Methods: We develop in-house Monte Carlo simulation software to model polymer scintillation fibers' fluorescence and Cherenkov emission in megavoltage clinical beams. The model computes emissions using generation probabilities, wavelength sampling, fiber photon capture, and fiber transport efficiency and incorporates the fiber's index of refraction, optical attenuation in the Cherenkov and visible spectrum and fiber dimensions. Detector component selection based on parameters such as silicon photomultiplier efficiency and optical coupling filters separates Cherenkov radiation from the dose-proportional scintillating emissions. The computation uses spectral and geometrical separation of Cherenkov radiation, however other filtering techniques can expand the model. Results: We compute Cherenkov generation per electron and fiber capture and transmission of those photons toward the detector with incident electron beam angle dependence. The model accounts for beam obliquity and nonperpendicular electron fiber impingement, which increases Cherenkov emission and trapping. The rotational angle around square fibers shows trapping efficiency variation from the normally incident minimum to a maximum at 45 degrees rotation. For rotation in the plane formed by the fiber axis and its surface normal, trapping efficiency increases with angle from the normal. The Cherenkov spectrum follows the theoretical curve from 300nm to 800nm, the wavelength range of interest defined by silicon photomultiplier and photodiode spectral efficiency. Conclusion: We are able to compute Cherenkov generation in realistic real time scintillating fiber dosimeter geometries. Design parameters incorporate fiber dimensions, orientations, several types of detector spectral response, optical coupling filters and light transport. We can vary these parameters to design and optimize high efficiency real time dosimeters capable of enhancing external beam patient safety and treatment accuracy. This research was supported in part by a GAANN Fellowship from the Department of Education.

Si-PIN photodiode readout for a scintillating optical fiber dosimeter

Abstract For more than a decade plastic optical fiber based dosimeters have been developed for medical applications. PMT's have been widely used as the readout photodetector but for a number of applications, Si-PIN photodiodes are a good alternative. They are robust, present good stability over time and have enough sensitivity so that an electrometer can be used as a measuring device. This work describes the tests made with the S9195 Si-PIN photodiode from Hamamatsu used as the readout photodetector for a scintillating optical fiber dosimeter using a BCF-60 polystyrene optical fiber.

SU-E-T-147: Scintillating Fiber Array to Determine the Proton Beam Range

Purpose: To develop the scintillating fiber array dosimeter to determine the proton beam range for the purpose of quality assurance of the patient in the proton therapy. Methods: A scintillating fiber dosimeter was composed of a commercial scintillating fiber optically coupled with organic based optical fiber. An array of scintillating fibers was settled inside a water bath. The scintillating light was amplified by photo multiplier tube before being gathered by commercial data acquisition system. Bragg peak and SOBP was measured with scintillating fiber dosimetry. The correction of the signal between the dosimeters and quenching effect of each dosimeter itself were conducted in home-made software. The results were compared with the ion chamber.Results: The signals from each scintillating fiber dosimeter showed randomly distributed along the depth. After calibrating between the dosimeters, the signals showed similar curve to Bragg peak and SOBP. Then correcting the quenching effect made the signal to coincident with the icon chamber results Conclusions: We improved the scintillating fiber optic dosimetry system which is previously developed in scanning type to the array type. The developed dosimetry system can provided more applicable and faster way to determine the proton beam range.

SU‐GG‐T‐347: Determination of Proton Beam Range by Using Scintillating Fiber Optic Dosimetry

Purpose: Scintillating fiber type dosimeter was investigated to determine the proton beam range in a short time for the purpose of quality assurance of the patient in the proton therapy. Degradation of output signal in scintillator has to be overcome for applying the scintillating fiber dosimeter on clinical use. One dimensional dosimeter array was tried to measure the range at a time and required characteristics for this application were evaluated. Methods: The dosimetry system was composed of commercial scintillating fiber optically coupled with organic based optical fiber. Scintillating light was amplified by photo multiplier tube before being gathered by commercial data acquisition system. Bragg peak and SOBP was measured with scintillating fiber dosimetry. One dimensional scintillating fiber array dosimeter was prepared and Bragg peak and SOBP of proton beam were measured and analyzed. Results: The Bragg peak measured by scintillating fiber dosimetry showed degradation of the output signal in high dose region when comparing with the results of the ionization chamber, which is known as quenching effect of scintillator. Quenching effect could corrected by fitting the measured data to quenching equation. However, it didn't show significant degradation of the signal enough to miss the range within sub‐millimeter for the scintillator smaller than the diameter of 0.5 mm. The SOBP curve also showed good agreement with the ionization chamber results after being modified by considering the quenching effect. It can be applied to construct the scintillator array to measure the depth dose distribution at a time. Conclusions: Scintillating fiber optic dosimetry was suitable for measuring depth dose distribution of proton therapy beam and determining its range. Quenching effect of scintillator was dealt with well within our tolerable range by fitting method. One dimensional scintillating fiber array provided more applicable and faster way for applying it to clinical field.

SU‐EE‐A1‐02: In Vivo Dosimetry for HDR Brachytherapy Using a Scintillating Fiber Dosimeter

Purpose: The goal was to develop a scintillating fiber dosimeter and verify its suitability in assessing the dose deposited during brachytherapy HDR treatments. As a first step toward in vivo dosimetry, it has been decided to conduct a full process, from planning to treatment, using a prostate phantom. Method and Materials: The scintillating fiber dosimetry system is composed of a RGB photodiode (MCS3AT) detecting light emitted from a scintillator (BCF‐60) coupled to a plastic optical fiber. Fiber is aligned on the photodiode, and its output is then amplified and acquired through a National Instruments acquisition card. Signal processing, including Cerenkov and fluorescence light subtraction, is done and dose deposited during treatment is obtained through integration. A prostate phantom (CIRS ♯053) has been used to conduct the study. An ultrasound‐guided catheter insertion procedure was performed by a radiation oncologist at our institution. A total of 13 catheters were inserted, one of those being used for the dosimeter. Following a CT scan, the prostate and urethra were contoured and treatment planning was performed according to our prostate clinical protocol on a PLATO workstation (Nucletron BV, Netherlands). The plan was delivered using a microSelectron V2 192Ir afterloader. Results: We measured dose rate as function of time. It varies with distance between the dosimeter and the dwell‐positions. Dose rate integration, once the contamination component is subtracted, determines the total dose deposited during treatment. Measurements were within 2% of the dose predicted by the planning system. Conclusion: Scintillating fiber dosimeter provides an accurate method to assess dose deposited to targets and organs at risk during HDR brachytherapy. Dose rates measured allow QA of treatment delivery for each catheter and total delivered dose. Measurements have been done in a prostate phantom, but there is a potential for a variety of clinical sites.

SU-FF-T-75: Importance of Contamination Signal Removal On HDR Brachytherapy In Vivo Dosimetry When Using a Scintillating Fiber Dosimeter

Purpose: To quantify the importance of removing the contamination signal, composed of Cerenkov and fluorescence light, from the output of an in vivo scintillating fiber dosimeter during Iridium‐192 HDR brachytherapy treatments. Method and Materials: The scintillating fiber dosimetrysystem is composed of a miniature monochrome CCD camera (Apogee Alta U‐4000) detecting light from optical fibers. Two fibers were used for the purpose of this study: one of those had a 3 mm x 1 mm cylindrical scintillator (BCF‐60) coupled to its extremity. Integrating light coming out from both fibers under the same irradiation conditions allows, following proper calibration, to determine the scintillation and the contamination components of the detector signal. This study has been conducted in a solid water phantom. Components of the detector signal have been studied as a function of angular, longitudinal and radial position of the Ir‐192 source with respect to the detecting volume (i.e. scintillator). Results: The contamination component ranged from 4% to 42% of the detector signal, depending on the relative source to scintillator and fiber positions. The highest ratio was obtained when the source was the closest to the scintillator. The lowest was obtained when the source is longitudinally the furthest from the source. The ratio increased from 4% to 10% with the source going from 1cm to 5cm on the radial axis of the scintillator. Angular study reveals that both contamination and scintillation components of the signal varies under 3.4 percents over the complete angles range. Conclusion:Dose determination is proportional to the amount of scintillating light measured. Based on our measurements, the necessity of removing the contamination component of the signal is obvious to obtain an accurate dose calculation. Any scintillating fiber dosimeter for in vivo brachytherapydosimetry should then include an efficient removal technique of the contamination signal.

In vivo dose measurements for high-dose-rate brachytherapy using a new scintillating fiber dosimetry system: A prostate phantom study

Purpose: The goal of this study was to develop a scintillating fiber dosimeter and verify its suitability in assessing the dose deposited during brachytherapy high-dose-rate (HDR) treatments. As a first step toward in vivo dosimetry, it has been decided to conduct a full process, from planning to treatment, using a prostate phantom.

Clinical prototype of a plastic water-equivalent scintillating fiber dosimeter array for QA applicationsa)

A clinical prototype of a scintillating fiber dosimeter array for quality assurance applications is presented. The array consists of a linear array of 29 plastic scintillation detectors embedded in a water-equivalent plastic sheet coupled to optical fibers used to guide optical photons to a charge coupled device (CCD) camera. The CCD is packaged in a light-tight, radiation-shielded housing designed for convenient transport. A custom designed connector is used to ensure reproducible mechanical positioning of the optical fibers relative to the CCD. Profile and depth dose characterization measurements are presented and show that the prototype provides excellent dose measurement reproducibility (+/-0.8%) in-field and good accuracy (+/-1.6% maximum deviation) relative to the dose measured with an IC10 ionization chamber.

WE-E-AUD-06: Clinical Prototype of a Plastic Water-Equivalent Scintillating Fiber Dosimeter Matrix for IMRT QA Applications

Purpose: To develop a clinical prototype of a plastic water-equivalent scintillating fiber dosimeter array for IMRT beam quality assurance (QA) applications. Method and Materials: A clinical prototype of a scintillating fiber dosimeter array has been developed. The system comprises twenty-nine (29) 1 mm diameter and 2 mm long (1,6 mm3) scintillating fiber detectors (BCF-12, Saint-Gobain, inc.) spaced 1 cm apart encapsulated in a Plastic Water (MedTec inc.) phantom. The detectors are coupled to clear non-scintillating transport fibers (BCF-98, Saint-Gobain, inc.) that collect scintillation photons and transport them to a color charge-coupled device (CCD) placed on the treatment table outside of the primary beam. A spectral discrimination technique is used to remove the Cerenkov radiation contaminating the scintillation signal. The CCD is encased in a custom designed, Cerrobend shielded aluminum carrying-case equipped with a custom-made optical fiber connector enabling reproducible removal and insertion of the fibers. Residual radiative noise on the CCD is removed with a post-processing algorithm. All dose points are processed simultaneously. Results: Open field crossplane profiles from 4×4 to 20×20 cm2 and a 10×10 cm2 depth-dose in Plastic Water are compared to ionization chamber (CC13, Wellhofer) measurements in water. The maximum in-field relative difference across all points and measurements is found to be 0.9% for profiles and 1.6 % for the depth dose. The standard deviation on the scintillation detector response is smaller than 1% in-field. The optical fiber connector insertion and removal is repeatable to within the measurement resolution (1%). This will allow for “hot swappable” detector modules. Conclusion: The scintillating fiber dosimeter array prototype is found to be accurate, precise and practical. The current system detector capacity exceeds 3500 measurement points per single irradiation. Such array detectors could find application for IMRT QA and general beam dosimetry monitoring measurements.

Water‐equivalent dosimeter array for small‐field external beam radiotherapy

With the increasing complexity of dose patterns external beam radiotherapy, there is a great need for new types of dosimeters. We studied the first prototype of a new dosimeter array consisting of water-equivalent plastic scintillating fibers for dose measurement in external beam radiotherapy. We found that this array allows precise, rapid dose evaluation of small photon fields. Starting with a dosimeter system constructed with a single scintillating fiber coupled to a clear optical fiber and read using a charge coupled device camera, we looked at the dosimeter's spatial resolution under small radiation fields and angular dependence. Afterward, we analyzed the camera's light collection to determine the maximum array size that could be built. Finally, we developed a prototype made of ten scintillating fiber detectors to study the behavior and precision of this system in simple dosimetric situations. The scintillation detector showed no measurable angular dependence. Comparison of the scintillation detector and a small-volume ion chamber showed agreement except for 1 x 1 and 0.5 x 5.0 cm (2) fields where the output factor measured by the scintillator was higher. The actual field of view of the camera could accept more than 4000 scintillating fiber detectors simultaneously. Evaluation of the dose profile and depth dose curve using a prototype with ten scintillating fiber detectors showed precise, rapid dose evaluation even with placement of more than 75 optical fibers in the field to simulate what would happen in a larger array. We concluded that this scintillating fiber dosimeter array is a valuable tool for dose measurement in external beam radiotherapy. It possesses the qualities necessary to evaluate small and irregular fields with various incident angles such as those encountered in intensity-modulated radiotherapy, radiosurgery, and tomotherapy.

A new scintillating fiber dosimeter using a single optical fiber and a CCD camera

Radiotherapy treatments become more and more accurate, using very small irradiation fields and complex dose depositions. So small dosimeters for real time and in vivo dosimetry, suitable for photons as well as for electrons beams are highly desired. In this context, a scintillating fiber dosimeter (SFD) has been developed by the Laboratoire de Physique Corpusculaire de Caen (LPC Caen), France, in collaboration with one of the French regional center for cancer treatment Centre Regional de lutte contre le cancer F. Baclesse (CRLCC F. Baclesse), Caen, France, and the ELDIM Company, Herouville, France. This plastic dosimeter is water equivalent, and it is suitable for photons as well as for electrons beams without correction. It is a real time dosimeter, with an excellent signal to noise ratio, and a spatial resolution of about a few millimeters. The aim of this study was to reduce the size of the scintillator in order to improve the spatial resolution of this dosimeter. So, a new light collection device has been developed to reduce the length of the scintillator from 1 cm to 1 mm without loss in the signal to noise ratio. The accuracy of this improved prototype has been tested by comparison with standard ionization chambers and the difference between the two devices never exceeded one percent for photon and for electron irradiation beams. A first set of commercial SFD is under completion at ELDIM and it will be soon clinically tested in several French centers for cancer treatment.

130 螺旋軌道X線CTの被曝線量測定 : 検出部の長いシンチレーションファイバ線量計の試作

130 螺旋軌道X線CTの被曝線量測定 : 検出部の長いシンチレーションファイバ線量計の試作

13. シンチレーションファイバ線量計のX線CTへの応用

13. シンチレーションファイバ線量計のX線CTへの応用

97.診断領域X線用シンチレーションファイバ線量計の開発

97.診断領域X線用シンチレーションファイバ線量計の開発