bluuebunny/crossref_metadata_2025_split huggingface dataset:
WE‐D‐BRF‐01: FEATURED PRESENTATION – Investigating Particle Track Structures Using Fluorescent Nuclear Track Detectors and Monte Carlo Simulations
Authors: Dowdell S , Greilich S , Zimmerman F , Evans C , Paganetti H , Schuemann J 
Published: July 2014

Purpose:To report on the efforts funded by the AAPM seed funding grant to develop the basis for fluorescent nuclear track detector (FNTD) based radiobiological experiments in combination with dedicated Monte Carlo simulations (MCS) on the nanometer scale.Methods:Two confocal microscopes were utilized in this study. Two FNTD samples were used to find the optimal microscope settings, one FNTD irradiated with 11.1 MeV/u Gold ions and one irradiated with 428.77 MeV/u Carbon ions. The first sample provided a brightly luminescent central track while the latter is used to test the capabilities to observe secondary electrons. MCS were performed using TOPAS beta9 version, layered on top of Geant4.9.6p02. Two sets of simulations were performed, one with the Geant4‐DNA physics list and approximating the FNTDs by water, a second set using the Penelope physics list in a water‐approximated FNTD and a aluminum‐oxide FNTD.Results:Within the first half of the funding period, we have successfully established readout capabilities of FNTDs at our institute. Due to technical limitations, our microscope setup is significantly different from the approach implemented at the DKFZ, Germany. However, we can clearly reconstruct Carbon tracks in 3D with electron track resolution of 200 nm. A second microscope with superior readout capabilities will be tested in the second half of the funding period, we expect an improvement in signal to background ratio with the same the resolution.We have successfully simulated tracks in FNTDs. The more accurate Geant4‐DNA track simulations can be used to reconstruct the track energy from the size and brightness of the observed tracks.Conclusion:We have achieved the goals set in the seed funding proposal: the setup of FNTD readout and simulation capabilities. We will work on improving the readout resolution to validate our MCS track structures down to the nanometer scales.
WE‐D‐BRF‐05: Quantitative Dual‐Energy CT Imaging for Proton Stopping Power Computation
Authors: Han D , Siebers J , Williamson J 
Published: July 2014

Purpose:To extend the two‐parameter separable basis‐vector model (BVM) to estimation of proton stopping power from dual‐energy CT (DECT) imaging.Methods:BVM assumes that the photon cross sections of any unknown material can be represented as a linear combination of the corresponding quantities for two bracketing basis materials. We show that both the electron density (ρe) and mean excitation energy (Iex) can be modeled by BVM, enabling stopping power to be estimated from the Bethe‐Bloch equation. We have implemented an idealized post‐processing dual energy imaging (pDECT) simulation consisting of monogenetic 45 keV and 80 keV scanning beams with polystyrene‐water and water‐CaCl2 solution basis pairs for soft tissues and bony tissues, respectively. The coefficients of 24 standard ICRU tissue compositions were estimated by pDECT. The corresponding ρe, Iex, and stopping power tables were evaluated via BVM and compared to tabulated ICRU 44 reference values.Results:BVM‐based pDECT was found to estimate ρe and Iex with average and maximum errors of 0.5% and 2%, respectively, for the 24 tissues. Proton stopping power values at 175 MeV, show average/maximum errors of 0.8%/1.4%. For adipose, muscle and bone, these errors result range prediction accuracies less than 1%.Conclusion:A new two‐parameter separable DECT model (BVM) for estimating proton stopping power was developed. Compared to competing parametric fit DECT models, BVM has the comparable prediction accuracy without necessitating iterative solution of nonlinear equations or a sample‐dependent empirical relationship between effective atomic number and Iex. Based on the proton BVM, an efficient iterative statistical DECT reconstruction model is under development.
WE‐D‐17A‐02: Evaluation of a Two‐Dimensional Optical Dosimeter On Measuring Lateral Profiles of Proton Pencil Beams
Authors: Hsi W , Lee T , Gao M , Boyer S , Pillainayagam M , Schultz T , Arjomandy B , Park S , Pankuch M , Schreuder A , Mah D 
Published: July 2014

Purpose:To evaluate the accuracy of a two‐dimensional optical dosimeter on measuring lateral profiles for spots and scanned fields of proton pencil beams.Methods:A digital camera with a color image senor was utilized to image proton‐induced scintillations on Gadolinium‐oxysulfide phosphor reflected by a stainless‐steel mirror. Intensities of three colors were summed for each pixel with proper spatial‐resolution calibration. To benchmark this dosimeter, the field size and penumbra for 100mm square fields of singleenergy pencil‐scan protons were measured and compared between this optical dosimeter and an ionization‐chamber profiler. Sigma widths of proton spots in air were measured and compared between this dosimeter and a commercial optical dosimeter. Clinical proton beams with ranges between 80 mm and 300 mm at CDH proton center were used for this benchmark.Results:Pixel resolutions vary 1.5% between two perpendicular axes. For a pencil‐scan field with 302 mm range, measured field sizes and penumbras between two detection systems agreed to 0.5 mm and 0.3 mm, respectively. Sigma widths agree to 0.3 mm between two optical dosimeters for a proton spot with 158 mm range; having widths of 5.76 mm and 5.92 mm for X and Y axes, respectively. Similar agreements were obtained for others beam ranges. This dosimeter was successfully utilizing on mapping the shapes and sizes of proton spots at the technical acceptance of McLaren proton therapy system. Snow‐flake spots seen on images indicated the image sensor having pixels damaged by radiations. Minor variations in intensity between different colors were observed.Conclusions:The accuracy of our dosimeter was in good agreement with other established devices in measuring lateral profiles of pencil‐scan fields and proton spots. A precise docking mechanism for camera was designed to keep aligned optical path while replacing damaged image senor. Causes for minor variations between emitted color lights will be investigated.
WE‐D‐17A‐04: Magnetically Focused Proton Irradiation of Small Volume Targets
Authors: McAuley G , Slater J , Wroe A 
Published: July 2014

Purpose:To explore the advantages of magnetic focusing for small volume proton irradiations and the potential clinical benefits for radiosurgery targets. The primary goal is to create narrow elongated proton beams of elliptical cross section with superior dose delivery characteristics compared to current delivery modalities (eg, collimated beams). In addition, more general beam shapes are also under investigation.Methods:Two prototype magnets consisting of 24 segments of samarium‐cobalt (Sm2Co17) permanent magnetic material adhered into hollow cylinders were manufactured for testing. A single focusing magnet was placed on a positioning track on our Gantry 1 treatment table and 15 mm diameter proton beams with energies and modulation relevant to clinical radiosurgery applications (127 to 186 MeV, and 0 to 30 mm modulation) were delivered to a terminal water tank. Beam dose distributions were measured using a PTW diode detector and Gafchromic EBT2 film. Longitudinal and transverse dose profiles were analyzed and compared to data from Monte Carlo simulations analogous to the experimental setup.Results:The narrow elongated focused beam spots showed high elliptical symmetry indicating high magnet quality. In addition, when compared to unfocused beams, peak‐to‐entrance depth dose ratios were 11 to 14% larger (depending on presence or extent of modulation), and minor axis penumbras were 11 to 20% smaller (again depending on modulation) for focused beams. These results suggest that the use of rare earth magnet assemblies is practical and could improve dose‐sparing of normal tissue and organs at risk while delivering enhanced dose to small proton radiosurgery targets.Conclusion:Quadrapole rare earth magnetic assemblies are a promising and inexpensive method to counteract particle out scatter that tends to degrade the peak to entrance performance of small field proton beams. Knowledge gained from current experiments will inform the design of a prototype treatment nozzle that incorporates similar focusing magnets.This project was sponsored in part by funding from the Department of Defense (DOD# W81XWH‐BAA‐10‐1).
WE‐D‐17A‐06: Optically Stimulated Luminescence Detectors as ‘LET‐Meters’ in Proton Beams
Authors: Granville D , Sahoo N , Sawakuchi GO 
Published: July 2014

Purpose:To demonstrate and evaluate the potential of optically stimulated luminescence (OSL) detectors (OSLDs) for measurements of linear energy transfer (LET) in therapeutic proton beams.Methods:Batches of Al2O2:C OSLDs were irradiated with an absorbed dose of 0.2 Gy in un‐modulated proton beams of varying LET (0.67 keV/μm to 2.58 keV/μm). The OSLDs were read using continuous wave (CW‐OSL) and pulsed (P‐OSL) stimulation modes. We parameterized and calibrated three characteristics of the OSL signals as functions of LET: CW‐OSL curve shape, P‐OSL curve shape and the ratio of the two OSL emission band intensities (ultraviolet/blue ratio). Calibration curves were created for each of these characteristics to describe their behaviors as functions of LET. The true LET values were determined using a validated Monte Carlo model of the proton therapy nozzle used to irradiate the OSLDs. We then irradiated batches of OSLDs with an absorbed dose of 0.2 Gy at various depths in two modulated proton beams (140 MeV, 4 cm wide spread‐out Bragg peak (SOBP) and 250 MeV, 10 cm wide SOBP). The LET values were calculated using the OSL response and the calibration curves. Finally, measured LET values were compared to the true values determined using Monte Carlo simulations.Results:The CW‐OSL curve shape, P‐OSL curve shape and the ultraviolet/blue‐ratio provided proton LET estimates within 12.4%, 5.7% and 30.9% of the true values, respectively.Conclusion:We have demonstrated that LET can be measured within 5.7% using Al2O3:C OSLDs in the therapeutic proton beams used in this investigation. From a single OSLD readout, it is possible to measure both the absorbed dose and LET. This has potential future applications in proton therapy quality assurance, particularly for treatment plans based on optimization of LET distributions.This research was partially supported by the Natural Sciences and Engineering Research Council of Canada.
WE‐D‐18A‐02: Performance Evaluation of Automatic Exposure Control (AEC) Across 12 Clinical CT Systems
Authors: Winslow J , Wilson J , Christianson O , Samei E 
Published: July 2014

Purpose:Automatic exposure control (AEC) is not typically evaluated or monitored in CT quality assurance programs. The purpose of this study was to develop/evaluate a new AEC testing platform for the clinical physics program at our institution, and characterize AEC performance across different CT systems.Methods:The Mercury Phantom comprises three tapered and four uniform regions of polyethylene(16, 23, 30, and 37 cm in diameter); each region includes four inserts: air, Polystyrene, Acrylic, and Teflon. The phantom was imaged using AEC and a fixed tube current technique across 12 clinical CT scanners. Those included five Siemens Somatom Definition Flash, four GE Discovery CT750HD, and three GE Lightspeed VCT systems. A custom MATLAB software package provided MTF, NPS, and detectability indices for each diameter section of the phantom. Detectability indices were used to evaluate the relationship between AEC setting, patient size, and image quality. The magnitude of the power of a best fit exponential curve to the detectability indices and phantom diameter was used as a measure of AEC strength. Results were compared within/across scanner models, and as baseline values for comparison with future system performance testing.Results:For each scanner model, the percent difference in expected image quality and AEC setting was under 3%(+/−2%). The average decrease in detectability between the small and large diameter phantom sections for the Siemens Flash, GE CT750, and GE VCT was 99%(+/−10%), 42%(+/−25%), and 33%(+/−41%), respectively. The value signifying AEC strength was 0.051(+/−13%), 0.019(+/−18%), and 0.018(+/−26%), for the Siemens Flash, GE CT750, and GE VCT models, respectively.Conclusion:This study demonstrated a practical approach to test the AEC performance of clinical CT systems at a large academic medical center. The quantification and evaluation of AEC performance should be included in acceptance testing and in annual physics testing of clinical CT systems.
WE‐D‐18A‐03: BEST IN PHYSICS (IMAGING) – Statistical Model Based Iterative Reconstruction (MBIR) in Clinical CT Systems: Experimental Assessment of Z‐ and Axial Spatial Resolution
Authors: Li Ke , Garrett John , Ge Yongshuai , Chen G.‐H. 
Published: July 2014

Purpose:The purpose of this work was to experimentally assess the unique spatial resolution characteristics of statistical model based iterative reconstruction (MBIR) along both axial and z directions and to examine the impact of spatial resolution on the task‐based diagnostic detection performance.Methods:An anthropomorphic chest phantom was repeatedly scanned 100 times using a clinical CT scanner at four dose levels (25%, 50%, 75%, 100%). Both FBP and MBIR (Veo™) were used for reconstruction. Nine objects with contrasts ranging from 13 to 1710 HU were used to assess spatial resolution. The axial and z resolutions were quantified locally in the image domain by point spread functions (PSF) and slice sensitivity profiles (SSP) respectively. The tradeoff between local image noise and resolution and their joint impact on the channelized Hotelling observer (CHO) detectabilities (d ') was investigated.Results:The axial resolution of MBIR improved monotonically with increasing dose and contrast level (FWHM_PSF=2.0 mm at 13 HU/25% dose and was 0.8 mm 1710 HU/100% dose). In comparison, axial resolution of FBP was independent of dose and contrast (FWHM_PSF=1.2 mm). The z resolution of MBIR demonstrated similar contrast dependence but only negligible dose dependence. The spatial resolution of MBIR and FBP became equivalent at some transitional contrast levels (280 HU for 25% dose and 90 HU for 100% dose), above which MBIR demonstrated superior resolution than FBP (and vice versa). Spatial resolution and noise assessed at the same location demonstrated a strong tradeoff in MBIR, and CHO detectability index d' was improved by MBIR for all contrast and dose levels.Conclusion:MBIR produces images with unique spatial resolution characteristics and introduces new challenges to its clinical use and evaluation. One potential solution, as suggested by this work, is to perform rigorous spatial resolution and noise measurements at different dose levels for each specific task.K. Li, J. Garrett, Y. Ge: Nothing to disclose; G.‐H. Chen: Research funded, General Electric Company Research funded, Siemens AG Research funded, Varian Medical Systems, Research funded, Hologic, Inc.
WE‐D‐18A‐04: How Iterative Reconstruction Algorithms Affect the MTFs of Variable‐Contrast Targets in CT Images
Authors: Dodge C.T. , Rong J. , Dodge C.W. 
Published: July 2014

Purpose:To determine how filtered back‐projection (FBP), adaptive statistical (ASiR), and model based (MBIR) iterative reconstruction algorithms affect the measured modulation transfer functions (MTFs) of variable‐contrast targets over a wide range of clinically applicable dose levels.Methods:The Catphan 600 CTP401 module, surrounded by an oval, fat‐equivalent ring to mimic patient size/shape, was scanned on a GE HD750 CT scanner at 1, 2, 3, 6, 12 and 24 mGy CTDIvol levels with typical patient scan parameters: 120kVp, 0.8s, 40mm beam width, large SFOV, 2.5mm thickness, 0.984 pitch. The images were reconstructed using GE's Standard kernel with FBP; 20%, 40% and 70% ASiR; and MBIR. A task‐based MTF (MTFtask) was computed for six cylindrical targets: 2 low‐contrast (Polystyrene, LDPE), 2 medium‐contrast (Delrin, PMP), and 2 high‐contrast (Teflon, air). MTFtask was used to compare the performance of reconstruction algorithms with decreasing CTDIvol from 24mGy, which is currently used in the clinic.Results:For the air target and 75% dose savings (6 mGy), MBIR MTFtask at 5 lp/cm measured 0.24, compared to 0.20 for 70% ASiR and 0.11 for FBP. Overall, for both high‐contrast targets, MBIR MTFtask improved with increasing CTDIvol and consistently outperformed ASiR and FBP near the system's Nyquist frequency. Conversely, for Polystyrene at 6 mGy, MBIR (0.10) and 70% ASiR (0.07) MTFtask was lower than for FBP (0.18). For medium and low‐contrast targets, FBP remains the best overall algorithm for improved resolution at low CTDIvol (1–6 mGy) levels, whereas MBIR is comparable at higher dose levels (12–24 mGy).Conclusion:MBIR improved the MTF of small, high‐contrast targets compared to FBP and ASiR at doses of 50%–12.5% of those currently used in the clinic. However, for imaging low‐ and mediumcontrast targets, FBP performed the best across all dose levels. For assessing MTF from different reconstruction algorithms, task‐based MTF measurements are necessary.
WE‐D‐18A‐05: Construction of Realistic Liver Phantoms From Patient Images and a Commercial 3D Printer
Authors: Leng S , Vrieze T , Kuhlmann J , Yu L , Matsumoto J , Morris J , McCollough C 
Published: July 2014

Purpose:To assess image quality and radiation dose reduction in abdominal CT imaging, physical phantoms having realistic background textures and lesions are highly desirable. The purpose of this work was to construct a liver phantom with realistic background and lesions using patient CT images and a 3D printer.Methods:Patient CT images containing liver lesions were segmented into liver tissue, contrast‐enhanced vessels, and liver lesions using commercial software (Mimics, Materialise, Belgium). Stereolithography (STL) files of each segmented object were created and imported to a 3D printer (Object350 Connex, Stratasys, MN). After test scans were performed to map the eight available printing materials into CT numbers, printing materials were assigned to each object and a physical liver phantom printed. The printed phantom was scanned on a clinical CT scanner and resulting images were compared with the original patient CT images.Results:The eight available materials used to print the liver phantom had CT number ranging from 62 to 117 HU. In scans of the liver phantom, the liver lesions and veins represented in the STL files were all visible. Although the absolute value of the CT number in the background liver material (approx. 85 HU) was higher than in patients (approx. 40 HU), the difference in CT numbers between lesions and background were representative of the low contrast values needed for optimization tasks. Future work will investigate materials with contrast sufficient to emulate contrast‐enhanced arteries.Conclusion:Realistic liver phantoms can be constructed from patient CT images using a commercial 3D printer. This technique may provide phantoms able to determine the effect of radiation dose reduction and noise reduction techniques on the ability to detect subtle liver lesions in the context of realistic background textures.
WE‐D‐9A‐01: A Novel Mesh‐Based Deformable Surface‐Contour Registration
Authors: Zhong Z , Cai Y , Guo X , Jia X , Chiu T , Kearney V , Liu H , Jiang L , Chen S , Yordy J , Nedzi L , Mao W 
Published: July 2014

Purpose:Initial guess is vital for 3D‐2D deformable image registration (DIR) while dealing with large deformations for adaptive radiation therapy. A fast procedure has been developed to deform body surface to match 2D body contour on projections. This surface‐contour DIR will provide an initial deformation for further complete 3D DIR or image reconstruction.Methods:Both planning CT images and come‐beam CT (CBCT) projections are preprocessed to create 0–1 binary mask. Then the body surface and CBCT projection body contours are extracted by Canny edge detector. A finite element modeling system was developed to automatically generate adaptive meshes based on the image surface. After that, the projections of the CT surface voxels are computed and compared with corresponding 2D projection contours from CBCT scans. As a result, the displacement vector field (DVF) on mesh vertices around the surface was optimized iteratively until the shortest Euclidean distance between the pixels on the projections of the deformed CT surface and the corresponding CBCT projection contour is minimized. With the help of the tetrahedral meshes, we can smoothly diffuse the deformation from the surface into the interior of the volume. Finally, the deformed CT images are obtained by the optimal DVF applied on the original planning CT images.Results:The accuracy of the surface‐contour registration is evaluated by 3D normalized cross correlation increased from 0.9176 to 0.9957 (sphere‐ellipsoid phantom) and from 0.7627 to 0.7919 (H&N cancer patient data). Under the GPU‐based implementation, our surface‐contour‐guided method on H&N cancer patient data takes 8 seconds/iteration, about 7.5 times faster than direct 3D method (60 seconds/iteration), and it needs fewer optimization iterations (30 iterations vs 50 iterations).Conclusion:The proposed surface‐contour DIR method can substantially improve both the accuracy and the speed of reconstructing volumetric images, which is helpful for applying in adaptive radiotherapy.This research is supported by CPRIT individual investigator award RP110329.
WE‐D‐12A‐01: Stereotactic Breast Biopsy
Authors: Pizzutiello R , Patel V 
Published: July 2014

This presentation will begin by comparing the image quality and dose characteristics of Stereotactic Breast Biopsy (SBB) with those of screen‐film and full field digital mammography. Part 2 of the presentation will explore several practical aspects of the ACR SBB Accreditation Program. When SBB was introduced as a commercial product in the 1990' s, x‐ray breast imaging was limited to screen‐film mammography. By the time SBB became common, all SBB systems utilized digital imaging technology. These small field of view SBB image receptors were the first common examples of digital imaging for the breast. The ACR is the only accrediting body that accredits SBB facilities. The ACR SBB QC Manual was published in 1999. Current methods of maintaining a QC program for SBB, current SBB equipment will be discussed. In addition, the process of an ACR Scheduled On‐Site Survey (for facilities that have failed to meet ACR accreditation standards) will be presented.Learning Objectives:

Understand the image quality and dose characteristics of SBB, Screenfilm and full field digital mammography
Understand the current QC requirements for SBB facilities accredited by ACR
Understand the ACR process for Scheduled On‐Site Surveys of facilities that have failed to meet the accreditation standards