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Sep 17, 2010 · 4 A plastic scintillator (BC-400) and a scintillating fiber (BCF-12), both attached by a plastic-core 4 fiber stem, are modeled.

Also studied is a plastic scintillator (BC-400) attached by an air-core 4 fiber stem with a silica tube coated with silver.

The detectors’ responses are calculated as the detector 4 per 4 phantom dose.
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Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams PMID: Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams Department of Radiation Physics, The University of Texas M.
Anderson Cancer Center, Houston, Texas 77030 a Author to whom correspondence should be addressed.
Electronic mail: ; Telephone: 713 563-2609; Fax: 713 563-2479.
Purpose: By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors PSDs in photon beams.
Methods: Three PSDs were modeled in this study: A plastic scintillator BC-400 and по этому адресу scintillating fiber BCF-12both attached by a plastic-core optical fiber stem, and a plastic scintillator BC-400 attached by an air-core optical fiber stem with a silica tube coated with silver.
For energy dependence, the response of the detectors is calculated as the detector dose per unit water dose.
The perturbation caused by the optical fiber stem connected to the PSD to guide the optical light to a photodetector was studied in simulations using different optical fiber materials.
Results: For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.
The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range.
For the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam.
This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber.
For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles, except in the case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%.
Conclusions: At ±1% level, no beam energy correction is necessary for the response of all three PSDs modeled in this study in the photon energy ranges from 200 keV monoenergetic to 18 MV linac beam.
The PSD would be even closer to water equivalent if there is a silica tube around the sensitive volume.
The angular dependence of the response of the three PSDs in a 6 MV photon beam is not of concern at 2% level.
INTRODUCTION Plastic scintillation detectors PSDs have many advantages for ionizing radiation dosimetry,e.
All these merits make PSDs preferable to other detectors for real-time in vivo dosimetry.
Those with cladding around the scintillating core are called scintillating https://chmall.ru/100/lopatka-mertz-323.html and those without it are called plastic scintillators.
Scintillating fibers are recently developed PSDs.
Their major merits are their small detector volume roughly 1 mm 3which gives them high spatial resolution, and their cladding, which reduces the loss of optical photons.
Plastic scintillators are traditional PSDs.
They can be made into any size and shape and thus cladding is not used.
For in-phantom dose measurements, such as percent-depth dose curves or dose profiles, the placement and orientation of PSDs are usually well controlled, thus the angular or directional dependence of PSDs are not of concern.
For in vivo applications, however, since it is difficult to control and ensure the orientation of the detectors штука, Майка женская Эмо фраза to the radiation source either external beams or brachytherapy sourcesthe angular dependence of PSDs could be an issue and needs to be investigated.
This is especially true considering the presence of an optical fiber coupled to a PSD to guide the optical light to a photodetector.
Angular dependence can be https://chmall.ru/100/akkumulyatornaya-batareya-cs-ipd100sl-dlya-planshetov-apple-ipad.html e.
Axial dependence should not exist for PSDs because of their cylindrical symmetry.
In this work, therefore, we investigated only azimuthal angular dependence.
Only a few studies have been published on the angular dependence of PSD responses and they considered only low-energy photon beams, a diagnostic x-ray source, and a brachytherapy source.
The signal was reduced dramatically when the radiation was incident from the back of the PSD because of the attenuation of the x ray in the optical fiber.
It is expected that the effect would be reduced for in-phantom measurements due to scattering effect.
For the brachytherapy sources, the measurement was performed in a polymethylmethacrylate PMMA phantom with an 192Ir high dose-rate brachytherapy source.
Unfortunately, no data are available for back-incident situations; in particular, when the приведу ссылку fiber stem points directly to the radiation посетить страницу />In this study, we used EGSnrcMonte Carlo codes to investigate the angular dependence of PSD responses in photon beams.
Čerenkov radiation induced in the optical fiber by the incident radiation beam is an important issue with the PSD-based dosimetry.
In this work, we assumed the Čerenkov light was not present or was completely removed.
Next, we studied the angular dependence of PSDs and the perturbation effect of the optical fiber of different materials plastic, glass, or air on detector response.
Computational models of PSDs We modeled three PSDs based on the specifications of the commonly used BC-400 plastic scintillator and BCF-12 scintillating fiber Saint-Gobain Crystals, Nemours, France.
Figure shows schematically the computational models for the two of the three modeled PSDs coupled to an optical fiber 3 Отпариватель Philips GC442/40 long.
The optical fiber modeled was the Eska Premier GH4001 Mitsubishi Rayon Co.
Figure shows the BC-400 plastic scintillator model 1.
The detector material is polyvinyltoluene PVT wrapped with polystyrene.
The core of the optical fiber is PMMA which is нажмите для деталей by a polyethylene jacket.
No cladding is used for this scintillator and so no cladding was modeled for the attached optical fiber.
The thickness of the polystyrene on the tip of the PVT detector was modeled at 1 mm in this study.
Figure shows the BCF-12 scintillating fiber model 2in which the sensitive material is polystyrene doped with fluor.
A PMMA cladding 30 μm thick was modeled for both the scintillating fiber and the optical fiber.
Also modeled was a polyethylene jacket outside of the optical fiber.
The optical fiber core of the scintillating fiber is PMMA.
To see how the optical fiber core material affects, if any, the response of the PSD, we replaced the PMMA core with either silica or glass, SiO 2 or air and calculated the responses of the PSDs.
With a glass-core fiber of diameter of 1 mm, we simulate the Ft-1.
The glass-core fiber was used in scintillator dosimetry because it has high light transmission efficiency.
Air has also been used as a core material for optical fibers to circumvent the generation of Čerenkov light.
Since a simple replacement of PMMA core by air does not correspond to the realistic air-core optical fiber, we also modeled this scintillator with air-core fiber as in Fig.
Computational models of two PSDs for a BC-400, which uses PVT as the sensitive material, and b BCF-12, which uses polystyrene doped with fluor as the sensitive material.
The sensitive region is designated by the shaded area.
All measures are in millimeters.
For BC-400, the polystyrene thickness at the tip of the PVT is either 3 or 1 mm.
Computational model of a BC-400 scintillator, which was used by Naseri et al.
The 4 region is designated by the shaded area.
All measures are in millimeters unless specified.
Energy cutoff and other Monte Carlo parameters As there exists a very подробнее на этой странице structure, e.
The generally used energy cutoff for electron ECUT and energy cutoff for photon PCUT transports in EGSnrc is 521 keV or 10 keV kinetic energy and 10 keV, respectively.
The 10 keV electron kinetic energy corresponds to a continuous slowing down approximation range of electrons in silver of 0.
To increase the spatial resolution, a lower energy cutoff should be used and this would lead to a longer simulation time.
We have compared the calculated dose in the scintillator for different particle energy cutoffs for three orientations of the scintillator at 10 cm depth in a 6 MV photon beam.
The results suggest that for this particular model, the difference in detector doses by using different energy cutoffs is negligible at about 0.
For this reason, we used 521 keV for electron понравилось LVIR LVIR STITCHED CTTN WAISTED JKT наступающим and 10 keV for photon cutoff in this study, which takes roughly only one third of calculation time than when 512 keV and 1 keV are used.
The detector dose was scored in the sensitive region of the scintillators shaded areas in Figs.
The photon splitting variance reduction technique was used with the splitting number varying from 10 to 100 depending on the radiation source quality.
Comparison of dose in the BC-400 scintillator attached by an air-core optical fiber with a silica tube Fig.
The orientation angles are defined as shown in Fig.
The ratio of the dose in the sensitive region of the detector to that in the phantom without the presence of the detector i.
Both monoenergetic and spectrum-based photon beams were used in the calculations.
The energy of the monoenergetic photon beams ranged from 150 keV 4 18 MeV.
All spectrum-based sources were megavoltage beams: The spectrum for the 60Co beam was taken from Mora et al.
The radiation source was modeled as a посетить страницу источник source at a 100 cm source-to-surface distance with a 10×10 cm 2 field size.
For medium-energy photon beams down to 150 keVthe PSD was modeled at a depth of 2 cm in a cubic water phantom with 20 cm sides, which corresponds to conditions of reference dosimetry for medium-energy x rays as specified by AAPM TG-61.
The radiation source was at a 20 cm source-to-surface distance with a 5×5 cm 2 field size.
These arrangements were also chosen Велосипед Big.Nine 100 Серый 22 ростовка improving computational efficiency, as these medium-energy photons attenuate much faster in a phantom than megavoltage photons.
To compare our findings to those from a previous study, we also modeled a PVT scintillator embedded in a polystyrene protective layer but without the attached 3 cm optical fiber.
Since there is no universal way to specify the photon beam quality for energies from 150 keV to 18 MeV, we used the photon energy or nominal energy as the quality specifier for monoenergetic photon beams or spectrum-based beams, respectively, e.
For the 60Co beam, we used the mean energy 1.
The exact specification of beam quality is not relevant here since all high-energy data points are approximately жмите the same horizontal line in the graphs shown later Figs.
For the realistic model of the BC-400 scintillator attached by an air-core optical fiber Fig.
Thus we also studied the variation of the energy dependence on the thickness of the silver layer either with or without the 0.
For the latter case, the silica is replaced by polystyrene in the simulation.
The ordinate is the detector dose per unit phantom dose.
For linac spectrum sources, the photon energy is the nominal energy of the photon beam i.
For the 60Co beam, the mean photon energy 1.
The statistical uncertainty is less than 0.
Solid circles are the results obtained by applying the Burlin cavity theory Ref.
Open squares are the results from a previous Monte Carlo calculation with MCNP code Ref.
The optical fibers are modeled as 3 cm long.
The ordinate is the detector dose per unit phantom dose.
For data points with photon energy greater than 1 MeV, spectrum sources are used, with the nominal energy as the abscissa.
The statistical uncertainty is less than 0.
Calculation of angular dependence We studied the azimuthal angular dependence of the all three PSD models for a 6 MV spectral photon beam and a 300 keV monoenergetic photon beam in a water phantom.
Figure shows how the orientation angle of the PSD is defined relative to the incident radiation beam.
The detector dose is normalized to that for the angle of 90° when the incident beam is perpendicular to the axis of the detector.
For the 300 keV photon beam, since the PSD is modeled at a depth of 2 4, the optical fiber length is set at 1.
We also studied the angular dependence for a bare PVT scintillator, and a PVT scintillator with a polystyrene layer but not the optical fiber, in the 6 MV photon beam.
In addition to the in-phantom simulations, we calculated the free-in-air angular dependence for the polystyrene scintillating fiber with PMMA optical fibers of different lengths.
The radiation source modeled is a monoenergetic photon 4 point source with an energy of 100 keV, a https://chmall.ru/100/linvel-lv-90175-e27.html distance of 40 cm, and a field size of 5×5 cm 2 at the detector.
The space surrounding the detector and that between the source and the detector are modeled as if filled with air.
The calculation results are compared to free-in-air measurements of Hyer et al.
Diagram showing how the azimuthal angle is defined.
The thick arrows with angular degrees indicate the direction of the incident radiation beams.
For example, at 90°, the radiation beam axis is perpendicular to the axis of the scintillator.
Energy dependence Figure shows the energy dependence of the PVT scintillator with a polystyrene protective layer but no optical fiber attached.
This scintillator model is studied here solely for a comparison to a previous study by MCNP code on the same model.
There is no significant difference between using spectrum sources and using monoenergetic beams at megavoltage photon energies.
This finding is reasonable since the curve for energy dependence of monoenergetic beams is вот ссылка flat across photon energies of almost two orders of magnitude.
The results also agree with those obtained using the Burlin cavity theory except at a photon energy of 2 MeV, where the discrepancy по этому адресу about 1%.
This discrepancy is probably due to the limitations of the Burlin cavity theory for some of the assumptions made.
Figure shows the energy dependence of the BC-400 scintillator coupled with the PMMA optical fiber model 1the BCF-12 scintillating fiber coupled with PMMA-core, glass-core, and air-core optical fibers model 2and the BC-400 scintillator coupled with the air-core fiber with a silica tube model 3.
Since there is no difference between using spectrum sources and using monoenergetic photon beams, the data points for both sources are combined on a single curve for each PSD.
Similar to the results for the scintillator without optical fiber shown in Fig.
Below 300 keV the responses drop which is the behavior of the ratio of the mass energy absorption coefficients of water to polystyrene or PVT.
For the PSD of the third model, BC-400 with air-core fiber with silica tube, the detector dose per unit water dose is closer to unity.
This is because the presence of the high-Z atoms Si and Ag around the sensitive volume enhances the energy deposition to the scintillator, thus making the whole response curve ссылка на подробности upward by about 2%.
The flatness of the detector response is Магистральные HGO 100 MP little bit worse than others but the variation is still within 1% in the photon energy range from 300 keV to 18 MV.
For energies lower than 300 keV, the scintillator over-responses due to the presence of silver.
Figure shows the effects of the silver layer thickness on the energy dependence of the PSD for нажмите чтобы узнать больше third model either a without or b with a 0.
This is what we expected since the polystyrene is close to water equivalent.
A silver layer of 1 μm will have a significant effect on the detector: Increasing the response by a couple of percent in megavoltage region and dramatically for photon energies below 300 keV.
A silver layer thickness of 10 μm will make the detector essentially useless because of the very large energy dependence.
For узнать больше здесь silver layer thickness of 0.
Figure also shows the result for a 10 μm aluminum coating, which is almost the same as the result for zero thickness silver layer because the atomic number of aluminum is only one less than silicon and 10 μm is negligible compared to the 0.
The energy dependence of a BC-400 scintillator coupled with an air-core fiber with a silica SiO 2 tube see the model in Fig.
The legend shows in μm the silver layer thickness except the one explicitly specified as aluminum.
Angular dependence Figure shows the angular dependence of the bare PVT scintillator simulated at a 10 Мужские сандалии Dpn 054 depth in a water phantom irradiated by a 6 MV photon beam.
The figure also shows the azimuthal angle between the detector and the incident beam.
The detector dose at any azimuthal angle is normalized to that calculated at 90°.
For the bare scintillator, because of the symmetry, only responses for angles from 90° to 180° are calculated.
The relative response varies at most 0.
When the polystyrene 4 thickness is 1 mm, the angular variation of the response is about the same as that of the bare scintillator.
For a 3 mm polystyrene tip thickness, the angular variation of the response could be as large as 1.
Figure shows the angular dependence of the three PSD models simulated at a 10 cm depth in a water phantom in the 6 MV photon beam.
For simulations in which the detector head points toward the radiation source i.
When the detector head points away from the radiation source i.
Note, however, that these values are for a fiber stem length of 3 cm.
This is mainly an attenuation issue: Air causes less attenuation on the incident photon beam than water, but glass SiO 2 causes more attenuation than water due to its higher density and effective atomic number.
However, for the PMMA-core optical fiber, the effect is at most 2% for all angles for its close to water equivalent.
For the BC-400 scintillator coupled with the air-core fiber with a silica tube model 3the variation of the response for all angles is also within 2%.
This behaves differently from the other PSD with air-core fiber in model 2 because the presence of high-Z atoms Si and Ag in the air-core fiber in model 3 KIM Gold Парфюмированная вода 100 to compensate the effect of air.
The inset shows the definition of the angle читать полностью is the same as in Fig.
In the inset, the fiber stem is drawn in dashed line indicating that it is not modeled but only for identification purpose.
The detector dose at any angle is normalized to that at 90°.
The statistical uncertainty is less than 0.
Angles are defined as shown in Fig.
The detector dose at any angle is normalized to that at 90°.
The length of the optical fibers is modeled as 3 cm.
The statistical uncertainty is less than 0.
Figure shows the angular dependence for all of these PSD models in a water phantom irradiated by a 300 keV monoenergetic photon beam.
The relative response of the detectors deviates significantly from unity only for angles very close to 0°.
For angles greater than 10°, the relative response of all the detectors varies within 2% regardless of the models or the optical fiber core material used.
This https://chmall.ru/100/gorodskie-bryuki-keotica-bdu-multicam-razmer-54.html is true even at 0° for the detectors attached by the PMMA-core optical fiber.
The apparent different behaviors of the angular dependence between Figs.
For example, for the BC-400 PSD with air-core fiber model 3 at 0°, the effects of air and high-Z atoms Si and Ag compensate mutually in the 6 MV beam where Compton effect dominates; they no longer cancel each other in the 300 keV beam where photoelectric effect becomes important.
The angle is defined as shown in Fig.
The detector dose at any angle is normalized to that at 90°.
The length of the optical fibers is modeled as 1.
The relative responses for the scintillating fiber attached to optical fibers with glass and air cores at 0° are 0.
The statistical uncertainty is less than 0.
Figure shows the free-in-air calculations of the angular dependence of the BCF-12 scintillating fiber coupled to a PMMA-core fiber stem 3 or 10 cm long in a 100 keV monoenergetic photon beam.
There is essentially no scatter in this case, so the drop in signal at 0° is very steep compared to that in the phantom case Fig.
The length of the optical fiber stem mainly has an effect at 0° due to attenuation by the fiber.
The calculated angular dependence agrees qualitatively with the measurements as far as the large drop in response near 0° is concerned.
Quantitatively, however, there is still disagreement between the calculations and the experiments since we were not able to model the exact material and geometrical data used in the experiments.
The factors most responsible for the disagreement would be the length and path of the curved fiber exposed to the radiation and the material and shape of the detector holder.
Using a monoenergetic x-ray beam instead of a more realistic spectrum source might also result in some differences.
Another factor to be noted is that the measured data are normalized at 90° where the data point itself has an uncertainty of about 5%.
So, for example, if the response at this angle happens to be overestimated by 5%, then the actual measured curve would be shifted upward by 5%, which would make the agreement better.
The angular dependence of the BCF-12 scintillating fiber coupled with PMMA plastic optical fibers with lengths of 3 and 10 4 irradiated free-in-air by a 100 keV https://chmall.ru/100/eglo-eg-3362-e27-60-vt.html photon beam.
The angle is defined here as shown in Fig.
The detector dose at any angle is normalized to that at 90°.
The statistical uncertainty for the calculation is around 2% 1σ.
The solid symbols represent a measurement by Hyer et al.
CONCLUSIONS In this study, we used Monte Carlo simulations to investigate the response of PSDs to photon beams.
A plastic scintillator BC-400 and a scintillating fiber BCF-12both attached by a plastic-core optical fiber stem, are modeled.
Also studied is a plastic scintillator BC-400 attached by an air-core optical fiber stem with a silica tube coated with silver.
For the energy dependence of the PSDs in photon beams, the calculations show that the PSDs with plastic-core fiber have excellent energy independence within about 0.
The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range and it is even closer to water equivalent due to the presence of silica wall around the scintillator.
About the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam.
This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber.
For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles except in 4 case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%.
For a PSD with a glass-core fiber in either photon beams, the variation of the response is also within 2% for most of the angles except when the fiber stem is pointing to the radiation source.
These results suggest that for most situations where the orientation of the detectors can be controlled, the angular dependence of PSDs is not of concern no matter what kind of material is used for the optical fiber core.
In this extreme condition, the response of PSDs either with plastic-core fiber or with air-core fiber with a silica tube has a maximum deviation of 2%, while a PSD with glass-core fiber would have large deviations in dose reading thus should be avoided.
The authors are very thankful to the associate editor and 4 anonymous referee for their comments which have helped to improve this manuscript a lot.
This research was supported by the National Cancer Institute NCI Grant No.
PIRS-701 National Research Council of Canada, Ottawa, Canada, 2000.
Methods 64, 157—166 1968.
LA-UR-02—5253, edited by Waters L.
PIRS-898 National Research Council of Canada, Ottawa, Canada, 2005.
Articles from Medical Physics are provided here courtesy of American Association of Physicists in Medicine.