Computerized Imaging Reference Systems Research Articles

Assessment of ultrasound image quality in a reference phantom using gel and liquid standoff pads

Backgroundand Methods: This paper presents a review of image quality in ultrasound imaging when using gel and liquid standoff pads, compared to imaging without a standoff pad. Imaging metrics assessed are lateral resolution, nearfield target intensity, and contrast to noise ratio of echogenicity targets. Measurements were made with a Canon Aplio i800 ultrasound system on a standardized ultrasound phantom (Computerized Imaging Reference Systems, Inc.), and custom-made agarose phantoms. Two cases are examined: when the ultrasound images are taken with the probe at different heights above the phantom (the normal clinical use-case for standoff pads); and when the ultrasound probe is artificially always placed at the same height above the phantom (allowing for direct image comparison). Results and conclusionThe main differences in the standard clinical use-case were observed in nearfield image intensity, with a mean difference of 22.4 ± 11.1 % between highest and lowest positions. Investigation of probes at the same height above the phantom shows that differences appear to be due primarily due to the height of the probe above the phantom, rather than the pads themselves. Elevational beamwidth was found to be a minimum of 2.2 mm at 25 mm axial depth, and adding a standoff pad can change vessel and cyst visualization due to the elevational beamwidth. This is a useful result to be aware of for clinicians using standoff pads on modern ultrasound systems.

Non-Isocentric Geometry for Next-Generation Tomosynthesis With Super-Resolution.

Our lab at the University of Pennsylvania (UPenn) is investigating novel designs for digital breast tomosynthesis. We built a next-generation tomosynthesis system with a non-isocentric geometry (superior-to-inferior detector motion). This paper examines four metrics of image quality affected by this design. First, aliasing was analyzed in reconstructions prepared with smaller pixelation than the detector. Aliasing was assessed with a theoretical model of r -factor, a metric calculating amplitudes of alias signal relative to input signal in the Fourier transform of the reconstruction of a sinusoidal object. Aliasing was also assessed experimentally with a bar pattern (illustrating spatial variations in aliasing) and 360°-star pattern (illustrating directional anisotropies in aliasing). Second, the point spread function (PSF) was modeled in the direction perpendicular to the detector to assess out-of-plane blurring. Third, power spectra were analyzed in an anthropomorphic phantom developed by UPenn and manufactured by Computerized Imaging Reference Systems (CIRS), Inc. (Norfolk, VA). Finally, calcifications were analyzed in the CIRS Model 020 BR3D Breast Imaging Phantom in terms of signal-to-noise ratio (SNR); i.e., mean calcification signal relative to background-tissue noise. Image quality was generally superior in the non-isocentric geometry: Aliasing artifacts were suppressed in both theoretical and experimental reconstructions prepared with smaller pixelation than the detector. PSF width was also reduced at most positions. Anatomic noise was reduced. Finally, SNR in calcification detection was improved. (A potential trade-off of smaller-pixel reconstructions was reduced SNR; however, SNR was still improved by the detector-motion acquisition.) In conclusion, the non-isocentric geometry improved image quality in several ways.

CT number calibration audit in photon radiation therapy.

Inadequate computed tomography (CT) number calibration curves affect dose calculation accuracy. Although CT number calibration curves registered in treatment planning systems (TPSs) should be consistent with human tissues, it is unclear whether adequate CT number calibration is performed because CT number calibration curves have not been assessed for various types of CT number calibration phantoms and TPSs. The purpose of this study was to investigate CT number calibration curves for mass density (ρ) and relative electron density (ρe ). A CT number calibration audit phantom was sent to 24 Japanese photon therapy institutes from the evaluating institute and scanned using their individual clinical CT scan protocols. The CT images of the audit phantom and institute-specific CT number calibration curves were submitted to the evaluating institute for analyzing the calibration curves registered in the TPSs at the participating institutes. The institute-specific CT number calibration curves were created using commercial phantom (Gammex, Gammex Inc., Middleton, WI, USA) or CIRS phantom (Computerized Imaging Reference Systems, Inc., Norfolk, VA, USA)). At the evaluating institute, theoretical CT number calibration curves were created using a stoichiometric CT number calibration method based on the CT image, and the institute-specific CT number calibration curves were compared with the theoretical calibration curve. Differences in ρ and ρe over the multiple points on the curve (Δρm and Δρe,m , respectively) were calculated for each CT number, categorized for each phantom vendor and TPS, and evaluated for three tissue types: lung, soft tissues, and bones. In particular, the CT-ρ calibration curves for Tomotherapy TPSs (ACCURAY, Sunnyvale, CA, USA) were categorized separately from the Gammex CT-ρ calibration curves because the available tissue-equivalent materials (TEMs) were limited by the manufacturer recommendations. In addition, the differences in ρ and ρe for the specific TEMs (ΔρTEM and Δρe,TEM , respectively) were calculated by subtracting the ρ or ρe of the TEMs from the theoretical CT-ρ or CT-ρe calibration curve. The mean±standard deviation (SD) of Δρm and Δρe,m for the Gammex phantom were -1.1±1.2g/cm3 and -0.2±1.1, -0.3±0.9g/cm3 and 0.8±1.3, and -0.9±1.3g/cm3 and 1.0±1.5 for lung, soft tissues, and bones, respectively. The mean±SD of Δρm and Δρe,m for the CIRS phantom were 0.3±0.8g/cm3 and 0.9±0.9, 0.6±0.6g/cm3 and 1.4±0.8, and 0.2±0.5g/cm3 and 1.6±0.5 for lung, soft tissues, and bones, respectively. The mean±SD of Δρm for Tomotherapy TPSs was 2.1±1.4g/cm3 for soft tissues, which is larger than those for other TPSs. The mean±SD of Δρe,TEM for the Gammex brain phantom (BRN-SR2) was -1.8±0.4, implying that the tissue equivalency of the BRN-SR2 plug was slightly inferior to that of other plugs. Latent deviations between human tissues and TEMs were found by comparing the CT number calibration curves of the various institutes.

Evaluation of 3D Printed Anthropomorphic Head Phantom for Calibration of TLD in Eye Lens Dosimeter

Calibration of Thermo Luminescent Dosimetry (TLD) in eye lens dosimeter requires a standard phantom. The use of anthropomorphic phantoms in calibration needs evaluation. This study aimed to analyze the angular response of the TLD on the fabricated 3D anthropomorphic head phantom and Computerized Imaging Reference Systems (CIRS)- Computed Tomography (CT) dose phantom as a standard phantom irradiated with Cs-137 and to compare the absorbed dose and linear attenuation for both phantoms. Hp(3) analysis, conversion coefficient (hpK(3)), and calibration factor (CF) are also investigated. In this experimental study, the fabricated 3D printed anthropomorphic head phantom was analyzed using polylactic acid (PLA) with the skull and then filled with the artificial brain and cerebrospinal fluid (CSF) as a test phantom. TLD-700H and TLD Reader Harshaw 6600 plus were used to analyze the angular response of Cs-137 radiation and to determine the absorbed dose and linear attenuation coefficient of test and standard phantoms. The effect of the angle of radiation source towards TLD reading at the anthropomorphic head phantom has a similar value to the standard phantom with a calibration factor ranging from 0.82 to 1. The absorbed dose measurement and the linear attenuation coefficient of the anthropomorphic head phantom with the standard phantom have different values of 2.52 and 3.78%, respectively. The fabricated 3D printed anthropomorphic head phantom has good potential as an alternative to standard phantoms for TLD calibration in eye lens dosimeter.

Accuracy and Feasibility of Synthetic CT for Lung Adaptive Radiotherapy: A Phantom Study.

The respiratory variations will lead to inconsistency between the actual delivery dose and the planning dose. How the minor interfractional amplitude changes affect the geometry and dose delivery accuracy remains to be investigated in the context of lung adaptive radiotherapy. Planning 4-dimensional-computed tomography and kV-cone beam computed tomography were scanned based on the Computerized Imaging Reference Systems phantom, which was employed to simulate the minor interfractional amplitude variations. The corresponding synthetic computed tomography for a particular motion pattern can be generated from Velocity program. Then a clinically meaningful synthetic computed tomography was analyzed through the geometrical and dosimetric assessment. The image quality of synthetic computed tomography was improved obviously compared with cone beam computed tomography. Mean absolute error was minimized when no significant interfractional motion occurs and Velocity can be qualified for dealing with the regular breathing motion patterns. The mean percent hounsfield unit difference of the synthetic hounsfield unit values per organ relative to the planning 4-dimensional-computed tomography image was 22.3%. Under the same conditions, the mean percent hounsfield unit difference of the cone beam computed tomography hounsfield unit values per organ, relative to the planning 4-dimensional-computed tomography image was 83.9%. Overall, the accuracy of hounsfield unit in synthetic computed tomography was improved obviously and the variability of the synthetic image correlates with the planning 4-dimensional-computed tomography image variability. Meanwhile, the dose-volume histograms between planning 4-dimensional-computed tomography and synthetic computed tomography almost coincided each other, which indicates that Velocity program can qualify lung adaptive radiotherapy well when there were no interfractional respiratory variations. However, for cases with obvious interfractional amplitude change, the volume covered at least by 100% of the prescription dose was only 59.6% for that synthetic image. The synthetic computed tomography images generated from Velocity were close to the real images in anatomy and dosimetry, which can make clinical lung adaptive radiotherapy possible based on the actual patient anatomy during treatment.

A New Criterion for Shear Wave Elastometric Assessment Using Modulus of Stiffness Difference between Object and Environment.

Using the original technology of building two-dimensional color elastogram, point and two-dimensional shear wave elastography were performed using linear sensors on commercial ultrasound scanners: Aixplorer (SuperSonic Imagine, France), Acuson S2000 (Siemens, Germany), and Verasonics acoustic system (Verasonics Inc., USA) with an open architecture to determine the stiffness values of focal inclusions and compare them with each other with the help of a new comparative elastomeric assessment criterion: modulus of stiffness difference between object and environment. First, the accuracy of the scanners under test was compared on a calibrated Elasticity QA Phantom, model 049 (Computerized Imaging Reference Systems Company, USA) with a known stiffness of various inclusions and thereafter on an uncalibrated BP1901 phantom (Blue Phantom, USA) with unknown stiffness of inclusions. The obtained values were compared to determine the influence of subjective factors on the measurement results. To assess the stiffness of the foci and compare the values with each other taking into account the rigidity of the environment, it is proposed to use a new criterion for the comparative assessment - the modulus of stiffness difference between focus and environment, which quantitatively characterizes the difference between these values. According to this criterion, all three ultrasound scanners have been established to show high and comparable accuracy in determining the stiffness of inclusions within the homogeneous medium in the experiments on phantoms. Two-dimensional shear wave elastography has revealed the effect of the control volume size and the correctness of the color scale setting, especially in the heterogeneous objects, on the results of elastometry. Methodological techniques to reduce the influence of subjective factors have also been proposed. The study has showed the possibility of using the modulus of stiffness difference between object and environment as a new criterion for comparative assessment of objects in shear wave elastometry taking into account stiffness of the environment. To reduce operator-dependence, it is necessary to take into consideration both the way of realizing elastometry (point or two-dimensional color elastography) and a number of other methodological factors.

Technical note: Characterization of novel iterative reconstructed cone beam CT images for dose tracking and adaptive radiotherapy on L-shape linacs.

Cone-beam computed tomography (CBCT) allows for patient setup and positioning, and potentially dose verification or adaptive replanning prior to each treatment delivery. Poor CBCT image quality due to scatter artifacts and patient motion has been a major limiting factor. A new image reconstruction algorithm was recently clinically implemented for improving image quality through iterative reconstruction (iCBCT). This study aims to characterize iCBCT image quality, establish image value (HU)-to-relative electron density (RED) calibration curves for dose calculation, and assess the dosimetric accuracy for different anatomical sites. Both conventional CBCT and iCBCT scans were acquired from a Varian TrueBeam On-Board Imager system. A Catphan 604 phantom was scanned to compare image quality between the traditional Feldkamp-Davis-Kress (FDK) and novel iterative reconstruction techniques. Computerized Imaging Reference Systems (CIRS) electron density phantom was used to construct site-specific HU-RED curves corresponding to various scan settings. The CIRS Dynamic Thorax phantom, Rando pelvis phantom, and BrainLab head phantom were used for assessing dosimetric accuracy calculated on iCBCT images, compared to that on traditional FDK-based CBCT images. All phantoms were scanned on a computed tomography (CT) to obtain baseline HU values for comparison. Test results obtained from Catphan showed statistically significant improvement with iCBCT, compared to FDK CBCT. Average HU differences from the baseline CT values were improved to within ±30HU for iCBCT, compared to FDK CBCT for phantom studies. Dose calculated on iCBCT for both phantoms and patient cases directly using baseline HU-RED calibration from CT showed 0.5%-2.0% accuracy from the baseline dose calculated on CT, which is comparable to doses calculated using site-specific HU-RED calibration curves. iCBCT provides improved image quality, improved HU accuracy compared to CT baseline, and has potential to provide online dose verification as part of the adaptive radiotherapy workflow directly using the baseline HU-RED calibration curve from CT.

Dual-energy CT based mass density and relative stopping power estimation for proton therapy using physics-informed deep learning

Proton therapy requires accurate dose calculation for treatment planning to ensure the conformal doses are precisely delivered to the targets. The conversion of CT numbers to material properties is a significant source of uncertainty for dose calculation. The aim of this study is to develop a physics-informed deep learning (PIDL) framework to derive accurate mass density and relative stopping power maps from dual-energy computed tomography (DECT) images. The PIDL framework allows deep learning (DL) models to be trained with a physics loss function, which includes a physics model to constrain DL models. Five DL models were implemented including a fully connected neural network (FCNN), dual-FCNN (DFCNN), and three variants of residual networks (ResNet): ResNet-v1 (RN-v1), ResNet-v2 (RN-v2), and dual-ResNet-v2 (DRN-v2). An artificial neural network (ANN) and the five DL models trained with and without physics loss were explored to evaluate the PIDL framework. Two empirical DECT models were implemented to compare with the PIDL method. DL training data were from CIRS electron density phantom 062M (Computerized Imaging Reference Systems, Inc., Norfolk, VA). The performance of DL models was tested by CIRS adult male, adult female, and 5-year-old child anthropomorphic phantoms. For density map inference, the physics-informed RN-v2 was 3.3%, 2.9% and 1.9% more accurate than ANN for the adult male, adult female, and child phantoms. The physics-informed DRN-v2 was 0.7%, 0.6%, and 0.8% more accurate than DRN-v2 without physics training for the three phantoms, respectfully. The results indicated that physics-informed training could reduce uncertainty when ANN/DL models without physics training were insufficient to capture data structures or derived significant errors. DL models could also achieve better image noise control compared to the empirical DECT parametric mapping methods. The proposed PIDL framework can potentially improve proton range uncertainty by offering accurate material properties conversion from DECT.

Commissioning and routine quality assurance of the Radixact Synchrony system

The Radixact Synchrony system allows for target motion correction when tracking either fiducials in/around the target or a dense lesion in the lung. As such evaluation testing and quality assurance (QA) tests are required. To allow for QA procedures to be performed with a range of available phantoms evaluation of the dosimetric delivery accuracy was performed for a range of motions, phantoms, and motion platforms. A Computerized Imaging Reference Systems, Incorporated (CIRS) 1D motion platform and Accuray Tomotherapy "Cheese" phantom was utilized to perform absolute dose and GafChromic EBT3 film measurements. A HexaMotion platform and Delta4 phantom were utilized to quantify the effects of 1D and 3D motions. Inter-device comparison was performed with the ArcCHECK and Delta4 phantoms and GafChromic EBT3 film, five patient plans were delivered to each phantom when static and with two different motion types both with and without Synchrony motion correction. A range of QA tests are described. A phantom was designed to allow for daily verification of system functionality. This test allows for the detection of either fiducials or a dense silicone target with a stationary phantom. Monthly testing procedures are described that allow the user to verify the dosimetric improvement when utilizing synchrony delivery motion compensation versus uncorrected motions. These can be performed utilizing a 1D motion stage with an ion-chamber and GafChromic EBT3 film to allow for a 2D dosimetric validation. Alternatively, a 3D motion platform can be utilized where available. Monthly and annual imaging tests are described. Finally, annual test procedures designed to verify the coincidence of the imaging system and treatment isocenter are described. The evaluation of the Synchrony system using a range of QA devices shows consistently high dosimetric accuracy with similar trends in passing criteria found with GafChromic EBT3 film, ArcCHECK, and Delta4 phantoms for density-based respiratory model compensation. These results highlight the large improvements in the dose distribution when motion is accounted for with the Synchrony system as measured with a range of phantoms and motion platforms that the majority of users will have available. The testing methods and QA procedures described provide guidance for new users of the Radixact Synchrony system as they implement their own QA programs for this system, until such time as an AAPM task group report is made available. QA procedures including Kilovolts (kV) imaging quality metrics and imaging dose parameters, dose deposition accuracy, target detection coincidence, and target position detection accuracy are described.

Radiation Oncology Exhibits

Purpose: The Australian Clinical Dosimetry Service (ACDS) has been auditing Australian and New Zealand radiotherapy providers for nearly 10 years building the National Dataset of audit measurements. The audits have uncovered numerous issues with varying significance. This paper will present an update of the ACDS audits including trends within the National Dataset and recent audit findings and will then cover recent audit of more advanced modalities such as SRS, SBRT, VMAT and adaptive radiotherapy. The presentation will conclude with a summary of the COVID-19 impact on the ACDS. The audits demonstrably improve the treatment quality and safety for patients undergoing radiotherapy. Methods and Materials: The ACDS began life in November 2010 and has developed a comprehensive three level auditing service which has expanded beyond Australia's borders. To minimize dosimetric uncertainties the ACDS has been using Computerized Imaging Reference Systems (CIRS)1 plastic water and phantoms across all on-site audits. As phantom complexity increased to meet auditing needs, CIRS was engaged to produce bespoke phantoms for the ACDS. The most recent examples of this are the Stereotactic Radio-Surgery (SRS) head phantom, SBRT, and a thorax customized for stereotactic ablative radiotherapy (SABR) auditing. Results: Audits provide two key outcomes for participating facilities. The first is that independent measurements demonstrate whether the facility's predicted dose is being delivered to the phantom within an acceptable tolerance. For an out-of-tolerance finding the ACDS works with the facility to resolve any discrepancies on the day of audit. Examples include inaccurate data entry in a planning system or inaccurate phantom positioning. Sometimes, however, there may be a systemic issue with calculation algorithms. The National Dataset has enables the ACDS to identify characteristic behavior of certain equipment combinations. As the ACDS perform more audits, the statistical power of the dataset increases and trends can be identified. This is the second key capability which a mature auditor provides to the auditee. Conclusion: The ACDS has development a coherent and successful auditing service which is proactively responding to changing technologies and environment.

Dual-Energy Computed Tomography Proton-Dose Calculation with Scripting and Modified Hounsfield Units.

PurposeTo describe an implementation of dual-energy computed tomography (DECT) for calculation of proton stopping-power ratios (SPRs) in a commercial treatment-planning system. The process for validation and the workflow for safe deployment of DECT is described, using single-energy computed tomography (SECT) as a safety check for DECT dose calculation.Materials and MethodsThe DECT images were acquired at 80 kVp and 140 kVp and were processed with computed tomography scanner software to derive the electron density and effective atomic number images. Reference SPRs of tissue-equivalent plugs from Gammex (Middleton, Wisconsin) and CIRS (Computerized Imaging Reference Systems, Norfolk, Virginia) electron density phantoms were used for validation and comparison of SECT versus DECT calculated through the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, California) application programming interface scripting tool. An in-house software was also used to create DECT SPR computed tomography images for comparison with the script output. In the workflow, using the Eclipse system application programming interface script, clinical plans were optimized with the SECT image set and then forward-calculated with the DECT SPR for the final dose distribution. In a second workflow, the plans were optimized using DECT SPR with reduced range-uncertainty margins.ResultsFor the Gammex phantom, the root mean square error in SPR was 1.08% for DECT versus 2.29% for SECT for 10 tissue-surrogates, excluding the lung. For the CIRS Phantom, the corresponding results were 0.74% and 2.27%. When evaluating the head and neck plan, DECT optimization with 2% range-uncertainty margins achieved a small reduction in organ-at-risk doses compared with that of SECT plans with 3.5% range-uncertainty margins. For the liver case, DECT was used to identify and correct the lipiodol SPR in the SECT plan.ConclusionIt is feasible to use DECT for proton-dose calculation in a commercial treatment planning system in a safe manner. The range margins can be reduced to 2% in some sites, including the head and neck.

Computed tomography simulator conversion curve dependence on scan parameters and phantom dimension

Introduction: Using computed tomography (CT) and treatment planning systems (TPS) in radiotherapy, due to the difference in photon beam energy on CT and linear accelerator, it is necessary to convert Hounsfield units (HU) to relative electron density (RED) values. The aim of this dosimetric study was to determine whether there is a significant effect of potential in the CT tube, field of view size (FOV), and phantom dimensions on the CT conversion curve CT-RED. The second aim is whether there are significant differences between the CT-RED obtained by the Computerized Imaging Reference Systems (CIRS) Thorax 002LFC phantom and the “reference” curve in the TPS, obtained by the CIRS 062M pelvis phantom, at the same CT conditions.Methods: Heterogeneous CIRS 062M and CIRS Thorax 002LFC phantoms were used, which anatomically and dimensionally represent the human pelvis, head, and thorax, with a set of known RED inserts. They were scanned on a CT LightSpeed GE simulator and obtained CT-RED.Results: The high voltage in the CT tube had a significant effect on the HU (t = 10.72, p < 0.001) for RED values >1.1, while FOV as a parameter did not show statistical significance for the 062M pelvis phantom. Comparing the slopes (062M pelvis and head) of the CT-RED for RED ≥ 1.1, the obtained value is t = 1.404 (p = 0.163). In the case of a 062M pelvis and a 002LFC phantom, we have seen a difference in RED values (for the same HU value) of 5 % in the RED region ≥ 1.1 (bone).Conclusion: Patients should be imaged on a CT simulator only at the potential of the CT tube on which the conversion curve was recorded. The influence of the FOV and scanned phantom dimensions is not statistically significant on the appearance of the calibration curve (RED ≥ 1.1).

Synthetic CT in assessment of anatomical and dosimetric variations in radiotherapy - procedure validation

Abstract Introduction: One of many procedures to control the quality of radiotherapy is daily imaging of the patient’s anatomy. The CBCT (Cone Beam Computed Tomography) plays an important role in patient positioning, and dose delivery monitoring. Nowadays, CBCT is a baseline for the calculation of fraction and total dose. Thus, it provides the potential for more comprehensive monitoring of the delivered dose and adaptive radiotherapy. However, due to the poor quality and the presence of numerous artifacts, the replacement of the CBCT image with the corrected one is desired for dose calculation. The aim of the study was to validate a method for generating a synthetic CT image based on deformable image registration. Material and methods: A Head & Torso Freepoint phantom, model 002H9K (Computerized Imaging Reference Systems, Norfolk, USA) with inserts was imaged with CT (Computed Tomography). Then, contouring and treatment plan were created in Eclipse (Varian Medical Systems, Palo Alto, CA, USA) treatment planning system. The phantom was scanned again with the CBCT. The planning CT was registered and deformed to the CBCT, resulting in a synthetic CT in Velocity software (Varian Medical Systems, Palo Alto, CA, USA). The dose distribution was recalculated based on the created CT image. Results: Differences in structure volumes and dose statistics calculated both on CT and synthetic CT were evaluated. Discrepancies between the original and delivered plan from 0.0 to 2.5% were obtained. Dose comparison was performed on the DVH (Dose-Volume Histogram) for all delineated inserts. Conclusions: Our findings suggest the potential utility of deformable registration and synthetic CT for providing dose reconstruction. This study reports on the limitation of the procedure related to the limited length of the CBCT volume and deformable fusion inaccuracies.

Calculation of Radiomic Features to Validate the Textural Realism of Physical Anthropomorphic Phantoms for Digital Mammography.

In this paper, radiomic features are used to validate the textural realism of two anthropomorphic phantoms for digital mammography. One phantom was based off a computational breast model; it was 3D printed by CIRS (Computerized Imaging Reference Systems, Inc., Norfolk, VA) under license from the University of Pennsylvania. We investigate how the textural realism of this phantom compares against a phantom derived from an actual patient's mammogram ("Rachel", Gammex 169, Madison, WI). Images of each phantom were acquired at three kV in 1 kV increments using auto-time technique settings. Acquisitions at each technique setting were repeated twice, resulting in six images per phantom. In the raw ("FOR PROCESSING") images, 341 features were calculated; i.e., gray-level histogram, co-occurrence, run length, fractal dimension, Gabor Wavelet, local binary pattern, Laws, and co-occurrence Laws features. Features were also calculated in a negative screening population. For each feature, the middle 95% of the clinical distribution was used to evaluate the textural realism of each phantom. A feature was considered realistic if all six measurements in the phantom were within the middle 95% of the clinical distribution. Otherwise, a feature was considered unrealistic. More features were actually found to be realistic by this definition in the CIRS phantom (305 out of 341 features or 89.44%) than in the phantom derived from a specific patient's mammogram (261 out of 341 features or 76.54%). We conclude that the texture is realistic overall in both phantoms.

Assessment of the accuracy of truebeam intrafraction motion review (IMR) system for prostate treatment guidance.

Intrafraction motion review (IMR), a real-time 2D, motion management feature of the Varian Truebeam™ incorporates triggered imaging, automatic fiducial marker detection and automatic beam hold. With the increasing adoption of high dose per fraction stereotactic body radiotherapy (SBRT) this system provides a potential means to ensure treatment accuracy. The goal of this study was therefore to investigate and quantify key performance characteristics of IMR for prostate treatment guidance. Phantom experiments were performed with a custom Computerized Imaging Reference Systems, Inc (CIRS) pelvis phantom with implanted gold seeds and the Hexamotion™ 5D motion platform. The system accuracy was assessed statically and under typical prostate motion trajectories. The IMR functionality and marker detectability was tested under different anatomical conditions and with different imaging acquisition modes. Imaging dose for triggered imaging modes was determined using an ionisation chamber based on IPEMB dose calibration protocol for kV energies. For zero displacement, the IMR demonstrated submillimeter agreement with the known position. Similarly, dynamic motion differences between the IMR reported position and 2D trajectory displacement were within 1mm. Static displacement in the anterior direction was reported by IMR as sinusoidal motion on the x-axis (kV angle). The 2D nature of IMR limits the ability to detect motion out of the plane of the kV image detector. Using typical clinical imaging settings, imaging dose determined at the patient surface was 2.58mGy/frame and the corresponding IMR displayed dose was 2.63mGy/frame. The methodology used was able to quantify the accuracy of the IMR system. The IMR was able to accurately and consistently report fiducial positions within the limitations inherent of a 2D system. IMR is fully integrated with the Truebeam system with an easy to use and efficient workflow and is clinically beneficial especially within the context of SBRT.

Computer-aided osteoporosis detection from DXA imaging

Background and objectiveOsteoporosis is a skeletal disease caused by a high rate of bone tissue loss, and it is a major cause of bone fracture. In contemporary society, osteoporosis is more common than cancer and stroke and results in a higher rate of morbidity and mortality in the human population. Osteoporosis can conclusively be diagnosed with dual energy X-ray absorptiometry (DXA). In this study, we propose a computer-aided osteoporosis detection (CAOD) technique that automatically measures bone mineral density (BMD) and generates an osteoporosis report from a DXA scan. MethodsThe CAOD model denoise and segments DXA images using a non-local mean filter, Machine learning pixel label random forest respectively, and locates regions of interest with higher accuracy. Pixel label random forest classifies a pixel either bone or soft tissue; then contours are extracted from binary image to locate regions of interest and calculate BMD from bone and soft tissues pixels. Mean standard deviation and correlation coefficients statistical analysis were used to evaluate the consistency and accuracy of BMD measurements. ResultsDuring a consistency test of BMD measurements using three consecutive scans from Computerized Imaging Reference Systems’ Bona Fide Phantom (CIRS-BFP) for the spine, the CAOD model showed an averaged standard deviation of 0.0029 while the standard deviation from manual measurements on the same data set by three different individuals was recorded as 0.1199. During another correlation study of BMD measurements evaluating real human scan images by the CAOD model versus manual measurement, the model scored a correlation coefficient of R2 = 0.9901 while the CIRS-BFP study scored a correlation coefficient of R2 = 0.9709. ConclusionsThe CAOD model increases the preciseness and accuracy of BMD measurements. This CAOD method will help clinicians, untrained DXA operators, and researchers (medical scientists, doctors, and bone researchers) use the DXA system with reliable accuracy and overcome workload challenges. It will also improve osteoporosis diagnosis from DXA systems and increase system performance and value.

Investigation of Exposure Factors for Various Breast Composition and Thicknesses in Digital Screening Mammography Related to Breast Dose

Objective: To investigate the effect of exposure factors used in digital screening mammography on image quality of different breast compositions. Material and Methods: A digital mammography unit, with tungsten (W) as target, rhodium (Rh) and silver (Ag) as filters, and amorphous selenium detectors, was used to image Computerized Imaging Reference Systems (CIRS) Model 12A phantoms of thickness 4, 5, and 6 cm. Images of each phantom were obtained using target-filter combinations of W/Rh and W/Ag, at 28, 30, and 32 kVp. Images were evaluated by 5 senior technologists with experience in mammography. Image scores were assigned, for each type of feature present in the phantom. Statistical analysis was performed using nonparametric tests to compare sets of image scores at p = 0.05. Results: A small but statistically significant improvement was detected in the visibility of microcalcifications (8.8 ± 0.2; p = 0.031) for the W/Rh combination but this did not show any differences in the visibility of masses or fibers. The entrance skin dose (ESD) and mean glandular dose (MGD) were lower for the W/Ag (ESD = 1.30–3.70; MGD = 0.44–0.93 mGy) combination compared to W/Rh (ESD = 1.66–5.40; MGD = 0.52–1.12 mGy). The Mann-Whitney test revealed that 30-kV exposure with the W/Rh combination showed a significantly better visibility of specks in the 30/70 phantom compared to other exposures. Conclusion: The use of an Rh filter showed a better image quality for all phantoms. 28 and 30 kVp with the W/Rh combination provided a slightly better image quality, and the MGD is less than 1.2 mGy.

Imaging and Dosimetric Study on Direct Flat-Panel Detector-Based Digital Mammography System.

Introduction:Image quality of digital mammography system is generally defined by three primary physical parameters, namely, contrast, resolution, and noise. Quantification of these metrics can be done by measuring objective image quality parameters defined as contrast-to-noise ratio (CNR), modulation transfer function (MTF), and noise power spectra (NPS).Materials and Methods:In the present study, various imaging metrics such as CNR, contrast detail resolution, MTF, and NPS were evaluated for a direct flat-panel detector-based digital mammography system following the European Guidelines. Furthermore, system performance relating to both image quality and doses were evaluated using figure of merit (FOM) in terms of CNR2/mean glandular dose (MGD) under automatic exposure control (AEC) and clinically used OPDOSE operating mode.Results and Conclusion:Under AEC mode, FOM values for the 4.5 cm thick BARC polymethyl methacrylate (PMMA) phantom were found to be 15.02, 15.88, and 19.82 at Mo/Mo, Mo/Rh, and W/Rh target/filter (T/F), respectively. Under OPDOSE mode, FOM values were found to 65.32, 11.80, and 1.14 for the BARC PMMA phantom thickness of 2, 4.5, and 8 cm, respectively. Under OPDOSE mode, the calculated MGD values for three Computerized Imaging Reference Systems slab phantoms having total thickness of 7 cm were observed to be 3.03, 2.32, and 1.75 mGy with glandular/adipose tissue compositions of 70/30, 50/50, and 30/70, respectively, whereas for the 2–8-cm thick BARC PMMA phantom, the calculated MGDs were found to be in the range of 0.57–3.32 mGy. All the calculated MGDs values were found to be lower than the acceptable level of dose limits provided in European Guidelines.

CyberKnife with integrated CT-on-rails: System description and first clinical application for pancreas SBRT.

This article reports on the integration of a sliding-gantry CT-on-rails with a robotic linear accelerator. The system consists of a SOMATOM Definition AS CT scanner (Siemens Healthcare, Forchheim, Germany) and a CyberKnife M6 FIM (Accuray, Inc., Sunnyvale, CA, USA). Additional movement programs were implemented in the robotic treatment table (RoboCouch, Accuray Inc.) to move between CT and treatment position. Acceptance testing was performed on the CT scanner according to AAPM83 guidelines, as well as safety tests for collision avoidance and electromagnetic (EM) compatibility. For the first clinical application of the system, daily dose was evaluated in five pancreas SBRT patients. A second envisioned use is the optimal alignment of the treatment beams to soft-tissue targets without the use of implanted fiducials. To this end, an offset vector feature has been implemented, which shifts the treatment center according to the daily position of the tumor relative to the spine (established by a CT scan). This offset can be applied by either moving the treatment couch (physical couch shift) or by moving the CyberKnife robot (virtual couch shift). An End-to-End (E2E) test was specifically designed to evaluate the accuracy of this feature using the Xsight Lung Tracking Phantom (Computerized Imaging Reference Systems, Inc., Norfolk, VA, USA). The position of the tumor with respect to the spine was varied by moving the insert inside the phantom and a CT scan was made for each position. The treatment plan was subsequently delivered to the phantom employing spine tracking. The test was repeated four times for a physical couch shift and four times for a virtual couch shift. All acceptance, safety and EM compatibility testing was successful. For the first pancreas SBRT patients treated using daily CT imaging, the volume of stomach, duodenum, or small bowel receiving >35 Gy was found to increase or remain constant during treatment; however, the clinical constraint of 5 cc was not violated. For the offset vector E2E test, the reference accuracy (without any tumor shift) was (0.74, -0.61, -0.33) mm in the inferior, left, and anterior direction respectively. The difference in deviation with respect to the reference was (-0.1 ± 0.15, 0.01 ± 0.16, -0.17 ± 0.25) mm, when applying a physical couch shift. With a virtual couch shift, the deviations were (0.02 ± 0.15, 0.06 ± 0.23, -0.4 ± 0.31) mm. The first combination of a CyberKnife treatment unit with a sliding-gantry CT scanner is operational in our department enabling future developments toward image-guided online-adaptive SBRT supported by diagnostic-quality CT imaging.

Evaluation of dose calculation accuracy of various algorithms in lung equivalent inhomogeneity: Comparison of calculated data with Gafchromic film measured results.

To evaluate dose calculation accuracy of various algorithms in lung equivalent inhomogeneity comprising tumor within it and comparison with Gafchromic film data. Gafchromic film measured central axis absorbed dose in lung insert (-700 Hounsfield unit [HU]), in racemosa wood cylindrical inhomogeneity (-725 HU) and at three surfaces of tumor (-20 HU) created in cylindrical inhomogeneity, put in the cavity of computerized imaging reference systems (CIRS) thorax phantom were compared with convolution (CON), superposition (SP), fast SP (FSP), and X-ray voxel Monte Carlo (XVMC) algorithms calculated dose using 6 MV beams of field size 2 cm × 2 cm, 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm, and 8 cm × 8 cm. XVMC was in good agreement with film measured results for all selected field sizes except 3 cm × 3 cm. SP under estimated by 5.7% at the center of the lung insert while deviation up to 6% was found at the cent of wood inhomogeneity in 2 cm × 2 cm. Except CON, increase in dose from proximal to the central surface of the tumor and then dose falloff from central to the distal surface for field size 2 cm × 2 cm to 4 cm × 4 cm was recorded. The change in film measured percentage depth dose from 2 cm × 2 cm to 3 cm × 3 cm field sizes was found -8% however for consecutive field size(s) larger than 3 cm × 3 cm this difference was less. CON and FSP produced overestimated results. Out of four algorithms, XVMC found consistent with measured data. The electronic disequilibrium within and at the interface of inhomogeneity make the accurate dose predictions difficult. These limitations results in deviations from the expected results of the treatments.