Transmission Detector Research Articles

EP-1711 Discover Prostate SBRT or Validation of motion-tracked SBRT treatments with a transmission detector

EP-1711 Discover Prostate SBRT or Validation of motion-tracked SBRT treatments with a transmission detector

EP-1698 TRAPS upstream transmission detector for tracking mlc positions in VMAT and IMRT radiotherapy fields

EP-1698 TRAPS upstream transmission detector for tracking mlc positions in VMAT and IMRT radiotherapy fields

Design and simulation of a multienergy gamma ray absorptiometry system for multiphase flow metering with accurate void fraction and water-liquid ratio approximation

Abstract Multiphase flow meters are used to measure the water-liquid ratio (WLR) and void fraction in a multiphase fluid stream pipeline. In the present study, a system of multiphase flow measurement has been designed by application of three thallium-doped sodium iodide scintillators and a radioactive source of 133Ba simulated by Monte Carlo N-particle (MCNP) transport code. In order to capture radiations passing across the pipe, two direct detectors have been installed on opposite sides of the radioactive source. Another detector has been placed perpendicular to the transmission beam emitted from the 133Ba source to receive radiations scattered from the fluid flow. Simulation was done by the MCNP code for different volumetric fractions of water, oil, and gas phases for two types of flow regimes, namely, homogeneous and annular; training and validation data have been provided for the artificial neural network (ANN) to develop a computation model for pattern recognition. Depending on applications of the neural system, several structures of ANNs are used in the current paper to model the flow measurement relations, while the detector outputs are considered as the input parameters of the neural networks. The first, second, and third structures benefit from two, three, and five multilayer perceptron neural networks, respectively. Increasing the number of ANNs makes the system more complicated and decreases the available data; however, it increases the accuracy of estimation of WLR and gas void fraction. According to the results, the maximum relative difference was observed in the scattering detector. It was clear that transmission detectors would demonstrate the difference between the flow regimes as well. It is necessary to note that the error calculated by the MCNP simulator is <0.5% for the direct detectors (TR1 and TR2). Due to the difference between the data of the two flow regimes and the errors of data in the simulation codes of the MCNP, it was possible to separate these flow regimes. The effect of changing WLR on the efficiency for a constant void fraction confirms a considerable variance in the results of annular and homogeneous flows occurring in the scattering detector. There is a similar trend for the void fraction; hence, one can easily distinguish changes in efficiency due to the WLR. Analysis of the simulation results revealed that in the proposed structure of the multiphase flow meter and the computation model used for simulation, the two flow regimes are simply distinguishable.

Clinical evaluation of a transmission detector system and comparison with a homogeneous 3D phantom dosimeter

PurposeTo evaluate the performances of the Dolphin system for pre-treatment verification (IBA Dosimetry, Schwarzenbruck, Germany) based on transmission measurements, employing a clinical perspective. Methods and materialsFifty treatment plans were verified by Dolphin and Delta4 detectors (Scandidos, Uppsala, Sweden) during the same session and subsequently by the Delta4 itself. The attenuation factor of the transmission detector (required for on-line dosimetry) was evaluated by comparing Delta4 measurements with and without Dolphin. Gamma evaluation was performed to compare the plan dose with the one delivered in case of Delta4 and Dolphin (gamma analysis within the structures). Dose–volume based parameters for PTV and OARs doses were considered for Compass calculation and Dolphin reconstruction and clinical decisions were made by two expert physicians in order to assess the “pass”, “fail” or “evaluate” grade of the treatment plans. A statistical analysis was performed to investigate the eventual correlation between Delta4 gamma analysis and Dolphin clinical evaluation. ResultsA value of 10.7% ± 0.7% was found for detector attenuation. No patients were classified as “fail” by the two instruments as well as by physicians. No correlation was found between the Delta4gamma metric and physician classification; conversely, a significant correlation was observed for Dolphin between the numbers of points with gamma ≥1 (gamma failure rate, as evaluated by the Dolphin) in the PTV area and clinical decision. ConclusionThe Dolphin system demonstrated to be an accurate detector for pre-treatment purposes and could be used as a clinical decision making tool for plan acceptance.

199. Evaluation of beam’s attenuation using the Delta4 Discover transmission detector in various treatment application

Purpose Delta4 Discover (ScandiDos, Uppsala, Sweden) is a new device developed in order to monitor online complex radiation techniques such as volumetric-modulated arc therapy (VMAT). It can be inserted between the radiation source and the patient so it can potentially impact the beam quality that the patient receives. The aim of this work is to investigate, in terms of beam’s attenuation, the feasibility of using Discover transmission array [1] . Methods 9 VMAT treatment plans, generated using Pinnacle3’s SmartArc algorithm v.9.10 (Philips Fitchburg, USA), for various treatment sites, were delivered using Delta4 Phantom+ (ScandiDos, Uppsala, Sweden). The response, with and without the Discover mounted on the linac was evaluated. All plans were delivered on a Varian TrueBeam STx equipped with HD MLC. For phantom verification, plans were recalculated replacing the patient planning CT scan with a phantom CT scan. Dose distributions of each plan delivered with and without Discover were verified using the Delta4 Phantom + and compared to calculated dose. Results Analyzing dose difference profiles, the Relative Dose Difference, between the measured dose relative to both configurations, showed that the absorption of beam radiation observed was on average about 1%. About Median Dose Deviation between the calculated and measured dose for both configurations we found that the all Median Dose Deviation shift values are ranging from 0.2% to 1.3%. Conclusions The thin transmission detector Delta4 Discover shows good potential for real time quality assurance. The minimal attenuation observed potentially allows for a real time verification and independent monitoring of complex VMAT deliveries during patient treatment.

10 Preliminary evaluation on phantom for the transmission detector Delta4 Discover for the VMAT treatments

Introduction To evaluate the Delta4 Discover behavior during the VMAT treatments deliverance and to determine the error detection thresholds. Methods The transmission detector Discover (Scandidos) is placed at the exit of the beam on Clinac 2100C Varian with Millenium MLC 120 leaves. It is composed of 4040 diodes with a 1 mm diameter, spaced 5 mm perpendicularly to the leaves movement and 2.5 mm in the same direction than the leaves movement and covering a 19.5 cm x 25 cm field size. The attenuation has been measured with 6 and 18MV beams at isocenter (field size 10 cm x 10 cm at a depth of 10 cm). The system repeatability has been evaluated to control 3 VMAT treatment plans. It was also measured by sequentially inserting different errors like leaves position, change of energy, depth, thickness and patient positioning. The errors of leaves position have been inserted for 3 leaves pairs on 4 control points of each beam. The following parameters can be analyzed: -The index gamma of dose distribution (3%-3 mm) -The delivered dose in function of angulation gantry ( Δ = ± 1%) -The angulation collimator ( Δ = ± 1°) -The MLC index gamma: the beam signal integrated every 25 ms measuring the gantry angulation and the end leaves position. Download : Download high-res image (46KB) Download : Download full-size image Results The measured attenuation is 1.6% in 6MV and 0.9% in 18MV. The repeatability results show an average standard deviation of 0.7% and maximum at 1.6% for 3 treatment plans with gamma index calculation. The results systematically decrease of more than 80% in the gamma index score when the energy of treatment plans has been changed. The results bring out a difference from −6% to −8% with gap of leaves position superior at 2 mm on a beam with 12 inserted mistakes: -5 are > 2 mm -5 are between 1 mm and 2 mm -2 are 1 mm The leaves whose positions are not those expected are correctly identified. Conclusions The Discover system is an advantage for pre- and per-treatment control of patients treated with VMAT. The attenuation modeling directly in the TPS is also an advantage for a daily use on the entire treatment. All measured parameters may show discrepancies or predict premature wear of certain components of the collimator.

12. Clinical evaluation of a transmission detector system and comparison with a homogeneous 3D phantom dosimeter

12. Clinical evaluation of a transmission detector system and comparison with a homogeneous 3D phantom dosimeter

Sensitivity of the IQM transmission detector to errors of VMAT plans.

The integral quality monitor (IQM) transmission detector is a wedge-shaped large area ionization chamber that reports a position-weighted dose area product for each control point of an IMRT or VMAT plan. In this study, the accuracy of the signal prediction is verified for the Synergy Agility MLC. Tolerance criteria for VMAT plan verification with the IQM were obtained from the observed sensitivity for the detection of incorrectly delivered plans. The predicted IQM signal was compared to the measured signal recorded for a set of 30 VMAT plans for each beam quality of 6 and 10MV. The system's capability to detect incorrectly delivered plans was tested by measuring altered plans containing small, random deviations. In addition, the observed deviations were related to measurements performed with a second QA phantom. The cumulative IQM signal per arc deviated from the respective calculation on average by -0.48% (6MV) and +0.21% (10MV) with a standard deviation of 1.08% in both cases, suggesting a 2% warning and 3% action threshold as plan acceptance criteria. This choice was confirmed by the optimum threshold of 2.5% obtained via receiver operating characteristic (ROC) analysis. Reproducibility of individual control points in multiply measured plans was low (on average 7% for 1SD) and thus, segment-by-segment comparison was impractical. A suitable criterion to resolve the angular distribution of the plan was identified by binning three to five control points as a running average. While the correlation between IQM signal deviations and gamma passing rates obtained with the ArcCHECK phantom was low for clinical plans, it was apparent for erroneous plans. Binning led to even higher sensitivity to errors. The IQM was able to detect induced errors at least as reliable as the standard phantom and showed the potential to be used in pretreatment plan verification to ensure the correct plan transfer and delivery. However, there is no direct correlation between the IQM signal deviation and DVH metrics, so the IQM should be primarily used to screen for errors. Finer diagnostics should then be carried out using a different phantom.

Transmission detectors are safe and the future for patient-specific QA in radiation therapy.

Transmission detectors are safe and the future for patient-specific QA in radiation therapy.

Brightness measurements of the nano-aperture ion source

A new type of ion source capable of delivering bright and monochromatic beams of various ionic species has been developed. The brightness of this source was measured using an ion focusing column in combination with a knife-edge ion transmission detector. The emission current was varied in the range 200 pA to 20 nA by varying the particle density and the in-chip electric field. Most data were obtained using argon ions, but helium and xenon ions were also produced. The setup was used to experimentally demonstrate a brightness of B≈1105 A/m2 sr V. The measurements match reasonably well with ray-trace simulations.

Transmission measurements and resonance parameter analysis for Mo-98 and Mo-100

Molybdenum can exist in many nuclear reactor components, including fuel, cladding, or as a high yield fission product. As a result, accurate isotopic nuclear data for molybdenum are important for reactor simulation. To this end, high-resolution time-of-flight neutron transmission measurements on highly enriched isotopic metallic samples of Mo-98 and Mo-100 were performed and data were reduced to transmission in the resolved resonance region from 10 eV to 53 keV for Mo-98 and 10 eV to 26.5 keV for Mo-100. Measurements were taken with Li-6 glass transmission detectors at 31 m and 100 m flight paths. The Bayesian R-matrix code SAMMY 8.0 was used to shape-fit the data and to extract resonance parameters from the transmission spectra. The newly fitted resonance parameters were compared with those given in ENDF/B-VII.1. The results represent a refinement of those given in the current evaluation due to the improvement in the experimental resolution in these measurements. The comparison included analysis of level statistics. The resonance parameters for Mo-98 show many differences with the current evaluations. The results of the analysis indicated missing levels in Mo-98 starting at 10 keV, which implies an inability to resolve all resonances at higher energies. The resonance parameters for Mo-100 agree well with the current evaluation. Level statistics analysis indicates there are few missing levels up to 26.5 keV.

Validation of new transmission detector transmission factors for online dosimetry: an experimental study

BackgroundThe demand for dose verification during treatment has risen with the increasing use of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in modern radiation therapy. This study aims to validate the transmission factors of a new transmission detector, the Dolphin online monitoring system (IBA Dosimetry, Schwarzenbruck, Germany), for clinical use.MethodsThe transmission factors of the Dolphin detector were evaluated using 6 MV, 6 flattening filter free (FFF), 10 MV, and 10 FFF clinical beams from a TrueBeam STx linear accelerator system. Two-dimensional (2D) dose distributions were measured through portal dosimetry with and without Dolphin to derive the transmission factors. The measurements were performed using 10 IMRT and 10 VMAT treatment plans. The transmission factors were calculated using a non-negative least squares problem solver for the 2D dose matrix. Normalized plans were generated using the derived transmission factors. Patient-specific quality assurance with normalized plans was performed using portal dosimetry and an ArcCheck detector to verify the transmission factors. The gamma passing rates were calculated for the 2%/2 mm and 1%/1 mm criteria.ResultsThe transmission factors for the 6 MV, 6 FFF, 10 MV, and 10 FFF beams, were 0.878, 0.824, 0.913, and 0.883, respectively. The average dose difference between the original plan without Dolphin and the normalized plan with Dolphin was less than 1.8% for all measurements. The mean passing rates of the gamma evaluation were 98.1 ± 2.1 and 82.9 ± 12.6 for the 2%/2 mm and 1%/1 mm criteria, respectively, for portal dosimetry of the original plan. In the case of the portal dosimetry of the normalized plan, the mean passing rates of the gamma evaluation were 97.2 ± 2.8 and 79.1 ± 14.8 for the 2%/2 mm and 1%/1 mm criteria, respectively.ConclusionsThe Dolphin detector can be used for online dosimetry when valid transmission factors are applied to the clinical plan.

P220] DVH-based stereotactic plan QA using Dolphin detector

Purpose QA experience on stereotactic plans with Dolphin transmission detector and compass DVH analysis program. Methods 12 spine SBRT, 20 lung SBRT and 25 SRS/SRT patients were prepared non-coplanar VMAT field plans in the Monaco 5.11 treatment planning system. Patient QA was measured with the Dolphin transmission detector and evaluated by gamma index analysis in the DVH-based Compass 4.0.27 program. Gamma index values were calculated according to the criteria of 3%-3 mm, 2%-2 mm, 1%-1 mm and 3%-1 mm as dose difference and distance to agreement in QA of stereotactic plans. For a more detailed analysis, average gamma index values were calculated. In addition,1 cm, 2 cm, 3 cm and 4 cm margins were given to the PTV to form the gamma analysis volumes. Results Differences between Monaco TPS and Dolphin in SRS/SRT plans, PTV1: 5.1%, PTVaverage: 8.1% and PTV99: 9.2%. Differences between Compass and Dolphin in SRS/SRT plans, PTV1: 2.9%, PTVaverage: 4.8% and PTV99: 6.5%. Differences between Monaco TPS and Dolphin in lung SBRT plans, PTV1: 3.5%, PTVaverage: 2.2% and PTV99: 2.6%. Differences between Compass and Dolphin in Lung SBRT plans, PTV1: 2.7%, PTVaverage: 2% and PTV99: 2.6%. Differences between Monaco TPS and Dolphin in spine SBRT plans, PTV1: −1.9%, PTVaverage: −5.8% and PTV99: −6.8%. Differences between Compass and Dolphin in spine SBRT plans, PTV1: 3.3%, PTVaverage: −0.47% and PTV99: −1.1%. When average gamma values are examined in the regions formed with 1,2,3,4 cm margins in SRS/SRT/SBRT plans: 3%–3 mm 0.34–0.6, 2%–2 mm 0.51–0.83, 1%–1 mm 0.92–1.15, 3%–1 mm 0.36–0.86. In 2D gamma analysis, SRS/SRT was 96%, lung SBRT was 88% and spine SBRT was 84.1% according to the criteria of %2–2 mm. SRS/SRT was 93%, lung SBRT was 83% and spine SBRT was 72.4% according to the criteria of %3–1 mm. Conclusions DVH-based analysis has a crucial role in validating stereotactic plans. Assessment of QA from differences in PTV and OAR doses is one of the best verification methods.It is more accurate to analyze according to the criteria of 3–1 mm and 2–2 mm because it has high heterogeneity and gradient index in stereotactic plans. We do a more comprehensive analysis with average gamma. The main reason for differences between Monaco and Compass with dolphin measurement is that the plans have high dose gradients and high dose heterogeneity. Especially differences in small volume PTVs have been increasing.

Online measuring density of oil products in annular regime of gas-liquid two phase flows

Gamma-ray densitometry is widely implemented in oil industry because it is an online technique and also has a good precision. If there is single phase flow in oil pipelines, measuring the density is possible just by using one source and one detector. But if in addition to oil, there is gas in oil pipelines and in fact there is a two-phase flow, conventional gamma ray densitometry (one source and one detector) could not be used for determining the density of liquid phase. In this study, a novel method is proposed for online measuring density of liquid phase in annular regime of liquid-gas two-phase flows using dual modality densitometry technique and artificial neural network (ANN). An experimental setup was designed in order to provide the required input data for training and testing the network. Registered counts in both scattering and transmission detectors were used as the inputs of the ANN and density of liquid phase was used as the output of the ANN. Using the proposed methodology, density of liquid phase was predicted with error of less than 0.031 g/cm−3 in annular regime of gas-liquid two phase flows for void fractions in the range of 10–70 percentages.

Scattering intensity distribution dependence on collection angles in annular dark-field STEM-in-SEM images

A scanning electron microscope (SEM) equipped with a zero-dimensional solid-state transmission electron detector and a modular aperture system was used to examine the relationship between annular dark-field image intensity distributions and several imaging parameters. The effects of primary electron energy, transmission detector acceptance angle and span, and beam convergence angle on scattering intensity distributions exhibited by a 10 nm thick amorphous silicon nitride film were examined. Results showed that angular distributions varied significantly with only minor changes in transmission detector acceptance angle span. Distributions collected with narrow apertures and normalized to acceptance angle span exhibited broad, distinct peaks that shifted to greater angles with decreasing primary electron energy, while even modestly wide apertures resulted in large distribution variations. A comparison between scattering distributions (i.e., diffraction patterns) quantified using the modular aperture system and a two-dimensional pixelated detector demonstrated that equivalent information could be obtained with either detector for this sample.

EP-1841: DVH based patient QA in SRS/SRT/SBRT using a new transmission detector

EP-1841: DVH based patient QA in SRS/SRT/SBRT using a new transmission detector

Commissioning and validation of fluence-based 3D VMAT dose reconstruction system using new transmission detector.

In this study, we evaluated the basic performance of the three-dimensional dose verification system COMPASS (IBA Dosimetry). This system is capable of reconstructing 3D dose distributions on the patient anatomy based on the fluence measured using a new transmission detector (Dolphin, IBA Dosimetry) during treatment. The stability of the absolute dose and geometric calibrations of the COMPASS system with the Dolphin detector were investigated for fundamental validation. Furthermore, multileaf collimator (MLC) test patterns and a complicated volumetric modulated arc therapy (VMAT) plan were used to evaluate the accuracy of the reconstructed dose distributions determined by the COMPASS. The results from the COMPASS were compared with those of a Monte Carlo simulation (MC), EDR2 film measurement, and a treatment planning system (TPS). The maximum errors for the absolute dose and geometrical position were -0.28% and 1.0mm for 3months, respectively. The Dolphin detector, which consists of ionization chamber detectors, was firmly mounted on the linear accelerator and was very stable. For the MLC test patterns, the TPS showed a > 5% difference at small fields, while the COMPASS showed good agreement with the MC simulation at small fields. However, the COMPASS produced a large error for complex small fields. For a clinical VMAT plan, COMPASS was more accurate than TPS. COMPASS showed real delivered-dose distributions because it uses the measured fluence, a high-resolution detector, and accurate beam modeling. We confirm here that the accuracy and detectability of the delivered dose of the COMPASS system are sufficient for clinical practice.

Characterization of a quadrant diamond transmission X-ray detector including a precise determination of the mean electron-hole pair creation energy.

Precise monitoring of the incoming photon flux is crucial for many experiments using synchrotron radiation. For photon energies above a few keV, thin semiconductor photodiodes can be operated in transmission for this purpose. Diamond is a particularly attractive material as a result of its low absorption. The responsivity of a state-of-the art diamond quadrant transmission detector has been determined, with relative uncertainties below 1% by direct calibration against an electrical substitution radiometer. From these data and the measured transmittance, the thickness of the involved layers as well as the mean electron-hole pair creation energy were determined, the latter with an unprecedented relative uncertainty of 1%. The linearity and X-ray scattering properties of the device are also described.

Beta-spectrometer with Si-detectors for the study of 144Ce–144Pr decays

Here we present the specifications of a newly developed beta-spectrometer, based on full absorption Si(Li) detector and thin transmission detector, allowing one to perform efficient separation beta-radiation and accompanying X-rays and gamma radiation. Our method is based on registration of coincident events from both detectors. The spectrometer can be used for precision measurements of various beta-spectra, namely for the beta-spectrum shape study of 144Pr, which is considered to be an advantageous anti-neutrino source for sterile neutrino searches.

Novel methodologies for dosimetry audits: Adapting to advanced radiotherapy techniques.

With new radiotherapy techniques, treatment delivery is becoming more complex and accordingly, these treatment techniques require dosimetry audits to test advanced aspects of the delivery to ensure best practice and safe patient treatment.This review of novel methodologies for dosimetry audits for advanced radiotherapy techniques includes recent developments and future techniques to be applied in dosimetry audits. Phantom-based methods (i.e. phantom-detector combinations) including independent audit equipment and local measurement equipment as well as phantom-less methods (i.e. portal dosimetry, transmission detectors and log files) are presented and discussed. Methodologies for both conventional linear accelerator (linacs) and new types of delivery units, i.e. Tomotherapy, stereotactic devices and MR-linacs, are reviewed.Novel dosimetry audit techniques such as portal dosimetry or log file evaluation have the potential to allow parallel auditing (i.e. performing an audit at multiple institutions at the same time), automation of data analysis and evaluation of multiple steps of the radiotherapy treatment chain. These methods could also significantly reduce the time needed for audit and increase the information gained. However, to maximise the potential, further development and harmonisation of dosimetry audit techniques are required before these novel methodologies can be applied.