Technical note: removing the stem effect when performing Ir-192 HDR brachytherapy in vivo dosimetry using plastic scintillation detectors: a relevant and necessary step.
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ABSTRACT:
SUBMITTER: Therriault-Proulx F
PROVIDER: S-EPMC3188655 | biostudies-other | 2011 Apr
REPOSITORIES: biostudies-other
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Project description:The goal of the present work was to evaluate the accuracy of a plastic scintillation detector (PSD) system to perform in-phantom dosimetry during 192Ir high dose rate (HDR) brachytherapy treatments.A PSD system capable of stem effect removal was built. A red-green-blue photodiode connected to a dual-channel electrometer was used to detect the scintillation light emitted from a green scintillation component and transmitted along a plastic optical fiber. A clinically relevant prostate treatment plan was built using the HDR brachytherapy treatment planning system. An in-house fabricated template was used for accurate positioning of the catheters, and treatment delivery was performed in a water phantom. Eleven catheters were inserted and used for dose delivery from 192Ir radioactive source, while two others were used to mimic dosimetry at the rectum wall and in the urethra using a PSD. The measured dose and dose rate data were compared to the expected values from the planning system. The importance of removing stem effects from in vivo dosimetry using a PSD during 192Ir HDR brachytherapy treatments was assessed. Applications for dwell position error detection and temporal verification of the treatment delivery were also investigated.In-phantom dosimetry measurements of the treatment plan led to a ratio to the expected dose of 1.003 +/- 0.004 with the PSD at different positions in the urethra and 1.043 +/- 0.003 with the PSD inserted in the rectum. Verification for the urethra of dose delivered within each catheter and at specific dwell positions led to average measured to expected ratios of 1.015 +/- 0.019 and 1.014 +/- 0.020, respectively. These values at the rectum wall were 1.059 +/- 0.045 within each catheter and 1.025 +/- 0.028 for specific dwell positions. The ability to detect positioning errors of the source depended of the tolerance on the difference to the expected value. A 5-mm displacement of the source was detected by the PSD system from 78% to 100% of the time depending on the acceptable range value. The implementation of a stem effect removal technique was shown to be necessary, particularly when calculating doses at specific dwell positions, and allowed decreasing the number of false-error detections-the detection of an error when it should not be the case--from 19 to 1 for a 5% threshold out of 43 measurements. The use of the PSD system to perform temporal verification of elapsed time by the source in each catheter--generally on the order of minutes--was shown to be in agreement within a couple of seconds with the treatment planWe showed that the PSD system used in this study, which was capable of stem effect removal, can perform accurate dosimetry during 192Ir HDR brachytherapy treatment in a water phantom. The system presented here shows some clear advantages over previously proposed dosimetry systems for HDR brachytherapy, and it has the potential for various online verifications of treatment delivery quality.
| S-EPMC3104721 | biostudies-other
Project description:The aim of this work was to create a mailable phantom with measurement accuracy suitable for Radiological Physics Center (RPC) audits of high dose-rate (HDR) brachytherapy sources at institutions participating in National Cancer Institute-funded cooperative clinical trials. Optically stimulated luminescence dosimeters (OSLDs) were chosen as the dosimeter to be used with the phantom.The authors designed and built an 8 × 8 × 10 cm(3) prototype phantom that had two slots capable of holding Al2O3:C OSLDs (nanoDots; Landauer, Glenwood, IL) and a single channel capable of accepting all (192)Ir HDR brachytherapy sources in current clinical use in the United States. The authors irradiated the phantom with Nucletron and Varian (192)Ir HDR sources in order to determine correction factors for linearity with dose and the combined effects of irradiation energy and phantom characteristics. The phantom was then sent to eight institutions which volunteered to perform trial remote audits.The linearity correction factor was kL = (-9.43 × 10(-5) × dose) + 1.009, where dose is in cGy, which differed from that determined by the RPC for the same batch of dosimeters using (60)Co irradiation. Separate block correction factors were determined for current versions of both Nucletron and Varian (192)Ir HDR sources and these vendor-specific correction factors differed by almost 2.6%. For the Nucletron source, the correction factor was 1.026 [95% confidence interval (CI) = 1.023-1.028], and for the Varian source, it was 1.000 (95% CI = 0.995-1.005). Variations in lateral source positioning up to 0.8 mm and distal∕proximal source positioning up to 10 mm had minimal effect on dose measurement accuracy. The overall dose measurement uncertainty of the system was estimated to be 2.4% and 2.5% for the Nucletron and Varian sources, respectively (95% CI). This uncertainty was sufficient to establish a ± 5% acceptance criterion for source strength audits under a formal RPC audit program. Trial audits of four Nucletron sources and four Varian sources revealed an average RPC-to-institution dose ratio of 1.000 (standard deviation = 0.011).The authors have created an OSLD-based (192)Ir HDR brachytherapy source remote audit tool which offers sufficient dose measurement accuracy to allow the RPC to establish a remote audit program with a ± 5% acceptance criterion. The feasibility of the system has been demonstrated with eight trial audits to date.
| S-EPMC3820626 | biostudies-other
Project description:BackgroundElectronic brachytherapy (eBT) is considered a safe treatment with good outcomes. However, eBT lacks standardized and independent dose verification, which could impede future use.PurposeTo validate the 3D dose-to-water distribution of an electronic brachytherapy (eBT) source using a small-volume plastic scintillation detector (PSD).MethodsThe relative dose distribution of a Papillon 50 (P50) (Ariane Medical Systems, UK) eBT source was measured in water with a PSD consisting of a cylindrical scintillating BCF-12 fiber (length: 0.5 mm, Ø: 1 mm) coupled to a photodetector via an optical fiber. The measurements were performed with the PSD mounted on a motorized stage in a water phantom (MP3) (PTW, Germany). This allowed the sensitive volume of the PSD to be moved to predetermined positions relative to the P50 applicator, which pointed vertically downward while just breaching the water surface. The percentage depth-dose (PDD) was measured from 0 to 50 mm source-to-detector distance (SDD) in 1-3 mm steps. Dose profiles were measured along two perpendicular axes at five different SDDs with step sizes down to 0.5 mm. Characterization of the PSD consisted of determining the energy correction through Monte Carlo (MC) simulation and by measuring the stability and dose rate linearity using a well-type ionization chamber as a reference. The measured PDD and profiles were validated with corresponding MC simulations.ResultsThe measured and simulated PDD curves agreed within 2% (except at 0 mm and 43 mm depth) after the PSD measurements were corrected for energy dependency. The absorbed dose decreased by a factor of 2 at 7 mm depth and by a factor of 10 at 26 mm depth. The measured dose profiles showed dose gradients at the profile edges of more than 50%/mm at 5 mm depth and 15%/mm at 50 mm depth. The measured profile widths increased 0.66 mm per 1 mm depth, while the simulated profile widths increased 0.74 mm per 1 mm depth. An azimuthal dependency of > 10% was observed in the dose at 10 mm distance from the beam center. The total uncertainty of the measured relative dose is < 2.5% with a positional uncertainty of 0.4 mm. The measurements for a full 3D dose characterization (PDD and profiles) can be carried out within 8 h, the limiting factor being cooling of the P50.ConclusionThe PSD and MP3 water phantoms provided a method to independently verify the relative 3D dose distribution in water of an eBT source.
| S-EPMC9314913 | biostudies-literature
Project description:The goal of this study was to prove the feasibility of using a single-fiber multipoint plastic scintillation detector (mPSD) as an in vivo verification tool during (192)Ir high-dose-rate brachytherapy treatments.A three-point detector was built and inserted inside a catheter-positioning template placed in a water phantom. A hyperspectral approach was implemented to discriminate the different optical signals composing the light output at the exit of the single collection optical fiber. The mPSD was tested with different source-to-detector positions, ranging from 1 to 5 cm radially and over 10.5 cm along the longitudinal axis of the detector, and with various integration times. Several strategies for improving the accuracy of the detector were investigated. The device's accuracy in detecting source position was also tested.Good agreement with the expected doses was obtained for all of the scintillating elements, with average relative differences from the expected values of 3.4 ± 2.1%, 3.0 ± 0.7%, and 4.5 ± 1.0% for scintillating elements from the distal to the proximal. A dose threshold of 3 cGy improved the general accuracy of the detector. An integration time of 3 s offered a good trade-off between precision and temporal resolution. Finally, the mPSD measured the radioactive source positioning uncertainty to be no more than 0.32 ± 0.06 mm. The accuracy and precision of the detector were improved by a dose-weighted function combining the three measurement points and known details about the geometry of the detector construction.The use of a mPSD for high-dose-rate brachytherapy dosimetry is feasible. This detector shows great promise for development of in vivo applications for real-time verification of treatment delivery.
| S-EPMC3663866 | biostudies-other
Project description:The possibility to detect fast neutrons as a distinct signal from that one of ?-rays background is surely of great importance for several topics, spanning from homeland security to radiation monitoring in nuclear physics research plants. Nowadays, Helium-3 based detectors are extremely expensive, while the use of large volume liquid scintillators presents serious concerns related to spillage risks and waste disposal. A very attractive alternative is the use of commercially available solid scintillators, which exploits an aromatic polymer matrix entrapping very high loadings of primary dye, thereby enabling the use of pulse shape analysis (PSA) to discriminate between fast neutrons and ?-rays. In this work, we analyse in detail the optical features of a solid scintillator composed by polymethylphenylsiloxane (PMPS) as base polymer loaded with moderate amounts of 2,5-diphenyloxazole (PPO). Furthermore, fluorescence decay kinetics have been correlated to the observed pulse shape discrimination capabilities of this radiation and thermally resistant scintillator, whose performances have been discussed in terms of conformational features and excimers formation revealed by the optical analyses.
| S-EPMC6591301 | biostudies-literature
Project description:To investigate the response of plastic scintillation detectors (PSDs) in a 6 MV photon beam of various field sizes using Monte Carlo simulations.Three PSDs were simulated: A BC-400 and a BCF-12, each attached to a plastic-core optical fiber, and a BC-400 attached to an air-core optical fiber. PSD response was calculated as the detector dose per unit water dose for field sizes ranging from 10 x 10 down to 0.5 x 0.5 cm2 for both perpendicular and parallel orientations of the detectors to an incident beam. Similar calculations were performed for a CC01 compact chamber. The off-axis dose profiles were calculated in the 0.5 x 0.5 cm2 photon beam and were compared to the dose profile calculated for the CC01 chamber and that calculated in water without any detector. The angular dependence of the PSDs' responses in a small photon beam was studied.In the perpendicular orientation, the response of the BCF-12 PSD varied by only 0.5% as the field size decreased from 10 x 10 to 0.5 x 0.5 cm2, while the response of BC-400 PSD attached to a plastic-core fiber varied by more than 3% at the smallest field size because of its longer sensitive region. In the parallel orientation, the response of both PSDs attached to a plastic-core fiber varied by less than 0.4% for the same range of field sizes. For the PSD attached to an air-core fiber, the response varied, at most, by 2% for both orientations.The responses of all the PSDs investigated in this work can have a variation of only 1%-2% irrespective of field size and orientation of the detector if the length of the sensitive region is not more than 2 mm long and the optical fiber stems are prevented from pointing directly to the incident source.
| S-EPMC3064682 | biostudies-other
Project description:By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors (PSDs) in photon beams.Three PSDs were modeled in this study: A plastic scintillator (BC-400) and a scintillating fiber (BCF-12), both 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. The authors then calculated, with low statistical uncertainty, the energy and angular dependences of the PSDs' responses in a water phantom. 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.For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.5% at photon energies ranging from 300 keV (monoenergetic) to 18 MV (linac beam). 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%.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.
| S-EPMC2951997 | biostudies-other
Project description:PurposeThe implementation of photon-counting detectors is widely expected to be the next breakthrough in X-ray computed tomography (CT) instrumentation. A small number of prototype scanners equipped with direct-conversion detectors based on room-temperature semiconductors, such as CdTe and CdZnTe (CZT), are currently installed at medical centers. Here, we investigate the feasibility of using silicon photomultiplier (SiPM)-based scintillation detectors in photon-counting computed tomography (PCCT) scanners, as a potential alternative to CdTe and CZT detectors.MethodsWe introduce a model that allows us to compute the expected energy resolution as well as the expected pulse shape and associated rate capability of SiPM-based PCCT detectors. The model takes into account SiPM saturation and optical crosstalk, because these phenomena may substantially affect the performance of SiPM-based PCCT detectors with sub-mm pixels. We present model validation experiments using a single-pixel detector consisting of a 0.9 × 0.9 × 1.0 mm3 LuAP:Ce scintillation crystal coupled to a 1 × 1 mm2 SiPM. We subsequently use the validated model to compute the expected performance of the fast scintillators LYSO:Ce, LuAP:Ce, and LaBr3 :Ce, coupled to currently available SiPMs, as well as to a more advanced SiPM prototype with improved dynamic range, for sub-mm pixel sizes.ResultsThe model was found to be in good agreement with the validation experiments, both with respect to energy resolution and pulse shape. It shows how saturation progressively degrades the energy resolution of detectors equipped with currently available SiPMs as the pixel size decreases. Moreover, the expected pulse duration is relatively long (~200 ns) with these SiPMs. However, when LuAP:Ce and LaBr3 :Ce are coupled to the more advanced SiPM prototype, the pulse duration improves to less than 60 ns, which is in the same order of magnitude as pulses from CdTe and CZT detectors. It follows that sufficient rate capability can be achieved with pixel sizes of 400 μm or smaller. Moreover, LaBr3 :Ce detectors can provide an energy resolution of 11.5%-13.5% at 60 keV, comparable to CdTe and CZT detectors.ConclusionsThis work provides first evidence that it may be feasible to develop SiPM-based scintillation detectors for PCCT that can compete with CdTe and CZT detectors in terms of energy resolution and rate capability.
| S-EPMC8596580 | biostudies-literature
Project description:High-resolution arrays of discrete monocrystalline scintillators used for gamma photon coincidence detection in PET are costly and complex to fabricate, and exhibit intrinsically non-uniform sensitivity with respect to emission angle. Nanocomposites and transparent ceramics are two alternative classes of scintillator materials which can be formed into large monolithic structures, and which, when coupled to optical photodetector arrays, may offer a pathway to low cost, high-sensitivity, high-resolution PET. However, due to their high optical attenuation and scattering relative to monocrystalline scintillators, these materials exhibit an inherent trade-off between detection sensitivity and the number of scintillation photons which reach the optical photodetectors. In this work, a method for optimising scintillator thickness to maximise the probability of locating the point of interaction of 511?keV photons in a monolithic scintillator within a specified error bound is proposed and evaluated for five nanocomposite materials (LaBr3:Ce-polystyrene, Gd2O3-polyvinyl toluene, LaF3:Ce-polystyrene, LaF3:Ce-oleic acid and YAG:Ce-polystyrene) and four ceramics (GAGG:Ce, GLuGAG:Ce, GYGAG:Ce and LuAG:Pr). LaF3:Ce-polystyrene and GLuGAG:Ce were the best-performing nanocomposite and ceramic materials, respectively, with maximum sensitivities of 48.8% and 67.8% for 5?mm localisation accuracy with scintillator thicknesses of 42.6?mm and 27.5?mm, respectively.
| S-EPMC6989685 | biostudies-literature
Project description:This work presents a comprehensive commissioning and workflow development process of a real-time, ultrasound (US) image-guided treatment planning system (TPS), a stepper and a US unit. To adequately benchmark the system, commissioning tasks were separated into (1) US imaging, (2) stepper mechanical, and (3) treatment planning aspects. Quality assurance US imaging measurements were performed following the AAPM TG-128 and GEC-ESTRO recommendations and consisted of benchmarking the spatial resolution, accuracy, and low-contrast detectability. Mechanical tests were first used to benchmark the electronic encoders within the stepper and were later expanded to evaluate the needle free length calculation accuracy. Needle reconstruction accuracy was rigorously evaluated at the treatment planning level. The calibration length of each probe was redundantly checked between the calculated and measured needle free length, which was found to be within 1 mm for a variety of scenarios. Needle placement relative to a reference fiducial and coincidence of imaging coordinate origins were verified to within 1 mm in both sagittal and transverse imaging planes. The source strength was also calibrated within the interstitial needle and was found to be 1.14% lower than when measured in a plastic needle. Dose calculations in the TPS and secondary dose calculation software were benchmarked against manual TG-43 calculations. Calculations among the three calculation methods agreed within 1% for all calculated points. Source positioning and dummy coincidence was tested following the recommendations of the TG-40 report. Finally, the development of the clinical workflow, checklists, and planning objectives are discussed and included within this report. The commissioning of real-time, US-guided HDR prostate systems requires careful consideration among several facets including the image quality, dosimetric, and mechanical accuracy. The TPS relies on each of these components to develop and administer a treatment plan, and as such, should be carefully examined.
| S-EPMC8425918 | biostudies-literature