bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐C‐BRC‐04: Avoidance of Perfused Lung by Optimization of Functional Mean Dose in Direct Machine Parameter Optimization
Authors: St‐Hilaire J , Lavoie C , Dagnault A , Morin F , Beaulieu L , Tremblay D 
Published: November 2011

Purpose: To implement and evaluate a functional mean dose‐based objective in a well‐established IMRT system, using lung perfusion images and direct machine parameter optimization (DMPO). Methods: Nineteen patients underwent SPECT perfusion imaging prior to treatment. In this retrospective study, plans were generated using Pinnacleˈ DMPO (Philips Healthcare, Andover, MA) with the aim of minimizing either the mean lung dose (MLD) or the lung functional mean dose (FMD). A seven equidistant beam configuration was used in all plans. Two levels of dose were prescribed: 50 Gy to the PTV1 (clinical target volume with margins) and 66 Gy to the PTV2 (gross tumor volume with margins). The MLD or FMD objective was decreased by steps of 1 Gy until dose to target volumes or organs at risk was deemed unacceptable. Plans were compared in terms of dose‐volume and dose‐function parameters. Statistical significance was assessed with a Wilcoxon matched pairs test. Results: While keeping PTV coverage similar (volumes receiving 93% of the prescribed dose were all over 98%), differences in MLD between both types of plans for a given patient ranged from –1.0 to +1.5 Gy (p = 0.2050), while FMD decreased significantly with a range of –2.1 to 0.0 Gy (p = 0.0003). The net improvement (FMD difference − MLD difference) ranged between −2.2 and 0.0 Gy. Dose to other organs at risk were similar and below widely‐ accepted tolerances. Conclusions: The use of SPECT perfusion images in conjunction with DMPO allowed a significant decrease of FMD while keeping dose to other structures at an acceptable level. Functionality‐aware dose redistribution could prove useful for dose escalation to improve tumor control with similar or lower lung complication probabilities. The approach can also be easily ported to arc therapy treatment planning using SmartArc.This work is supported by the Natural Sciences and Engineering Research Council of Canada and by a research agreement with Philips Healthcare.
SU‐C‐214‐01: Design and Evaluation of a Low Megavoltage Imaging Beam from a Prototype Waveguide
Authors: Roberts D , Hansen V , Niven A , Poludniowski G , Seco J , Thompson G , Evans P 
Published: November 2011

Purpose: To design and evaluate an optimised radiotherapy imaging beam, based on a prototype Elekta waveguide, with a novel coupling device (rotovane) allowing for a wide, continuously variable energy range. Methods: A waveguide test piece consisting of a buncher, rotovane and short relativistic section was used to investigate the performance of the novel continuously variable coupling device, and in particular investigate imaging at low megavoltage energies. An optimised imaging system utilising the lowest electron energy of the waveguide (1.4 MeV) was designed using BEAMnrc and implemented experimentally. Characterisation of the imaging beam was conducted experimentally and via Monte Carlo simulations. Cone beam computed tomography images (CBCT) were acquired using a Caesium Iodide imaging panel of humanoid anthropomorphic phantoms and a Catphan phantom. The contrast to noise ratio was assessed for CBCT and compared to kilo‐voltage and megavoltage imaging systems. Results: The optimised imaging beam target assembly consisted of an electron window, 5 mm carbon electron absorber and 2.5 mm of Aluminium filtration. The x‐ray beam had an average photon energy of 220 keV and a half value layer of 5.9 mm of Copper. Images with the same contrast to noise ratio as a 100 kVp CBCT system (XVI, Elekta) were obtained in doses less than 2 cGy; this is 11x higher than XVI but 150x lower than a megavoltage imaging system. Qualitatively, kilo‐voltage equivalent images of head and pelvis phantoms were obtained in doses between 1 and 8 cGy. Conclusions: The prototype waveguide section was capable of producing electron energies from 1.4 to 9 MeV, suitable for imaging and therapy. The waveguide technology has the potential for producing near kilo‐voltage equivalent images in acceptable dose from the therapy beam portal without the need for add‐on x‐ray systems. Additionally such a system could provide for enhanced target tracking during radiotherapy treatment.This work is supported by Elekta Ltd and The Institute of Cancer Research. Work of the ICR radiotherapy physics group is partially supported by Cancer Research UK under programme grant C46/A3970
SU‐C‐214‐06: Noise Power Properties of a Dual‐Detector Cone‐Beam CT System
Authors: Li H , Giles W , Roper J , Bowsher J , Yin F 
Published: November 2011

Purpose: Very little information is available for noise properties using a dual‐detector cone‐beam CT (CBCT) system. Geometric misalignment, cross‐scatter, and inhomogeneous detector response are additional concerns in a dual‐detector system. This study characterizes the noise power spectrum of a dual CBCT system for image‐guided radiation therapy (IGRT). Methods: A bench‐top dual‐detector CBCT system with two orthogonal 40×30cm flat panels has been developed in our laboratory. The noise power spectrum (NPS) was evaluated by scanning two uniform phantoms with diameters of around 26cm and 20cm under different kVs, mAs, and acquisition modes. The three‐dimensional NPS was calculated using 3D Fourier transform for a region of interest of 10×10×10cm3 as the metric to evaluate the noise performance. The structural fluctuations were removed by subtraction between two identical scans. The radial averaging is then calculated every degree in the central slice of the 3D Fourier space to reduce the measurement fluctuation. The profile of the radial averaging is used for comparison between dual/single detectors, at different kVs, mAs, and acquisition modes. Results: The NPS amplitude of the dual CBCT system can be up to 50% lower than that of a single CBCT system in simultaneous acquisition mode. In alternating acquisition mode, the NPS of the dual CBCT system is comparable both in amplitude and shape with a single CBCT system. The cross‐scatter is identified as the major contributing factor for the discrepancy. The cross‐scatter and the amplitude of the discrepancy are correlated with the sizes of the scanned objects under various current and voltage parameters. Conclusions: The Cross scatter reduces the amplitude of NPS. The effect is more dominant for large objects. Quantitative results from this noise power analysis provide guidance for dual CBCT reconstruction, cross‐scatter reduction and acquisition optimization.This work is supported in part by a research grant from Varian Medical Systems.
SU‐C‐211‐05: Improved Target Localization with Integrated X‐Ray/bioluminescent Tomography
Authors: Naser M , Pekar J , Wong J , Patterson M 
Published: November 2011

Purpose: Bioluminescence tomography (BLT) is a promising approach to guide focal irradiation of pre‐palpable tumors in small animals, but is limited in resolution. In this study, we investigate the use of x‐ray and diffuse optical tomography tomography to provide spatial and optical information about the object to improve BLT reconstruction. Methods: In a 3‐step approach, x‐ray CBCT is used first to provide the anatomic spatial information about the object. Secondly, photons of different wavelengths are transmitted through the object for detection by a CCD camera. The optical properties of the anatomic regions are then found by solutions of the diffuse optical tomography problem. In the final step, the anatomic and optical “priors” are employed in BLT reconstruction, where optical filters are used again to extract the multi‐spectral information required to derive the position and power of the internal source. The approach was tested in an experimental setup where a 1.5 mm diameter (dia) optical fiber light source was inserted at 5 different lateral positions in a 12 mm dia optical heterogeneity within a 25 mm dia cylindrical tissue‐mimicking phantom. The reconstructed positions and powers were compared with the known inputs. Results: The average error in locating the source centroid was 0.13 mm, range 0.3 mm to 0 mm. The average error in source power estimations was 9%, range 14% to −1%. The results are an improvement over commercial systems that typically have an average localization uncertainty of 1 mm and error in power estimation of more than 20%. Conclusions: The spatial and spectral prior information provided by x‐ray CT and diffuse optical tomography improves the accuracy of BLT. Integrated x‐ray/BL tomographic capability on board new small animal radiation research systems can contribute significantly to accurate biological targeting in realistic animal models.J Wong has a sponsored research agreement with Xstrahl Ltd on small animal radiation research.
SU‐C‐211‐07: Quantitative Reconstruction of Multiplexed Multi‐Pinhole SPECT with Scatter and Attenuation Correction
Authors: Strydhorst J , Wells R Glenn 
Published: November 2011

Purpose: Small animal microSPECT is an important pre‐clinical imaging modality. However, the quantitative accuracy is limited by photon attenuation in the subject and scatter in the subject and the collimator. In this study we investigate correcting for both scatter and attenuation in the reconstruction of a small animal sized phantom. Methods: A phantom consisting of a cold centre surrounded by a hot shell, surrounded by an outer layer of either water or air, was scanned in a multiplexing multi‐pinhole (MMP) SPECT scanner. Scan parameters were as follows: 9 pinholes/detector, 2.5 mm diameter; 48 projections; helical scan; 3 minutes per projection. Projection data was recorded for two energy windows, one centered at the photopeak (140 keV) and a second window below the photopeak centered at 110 keV. The phantom was also scanned with the built‐in CT scanner (45 keV, cone beam) and reconstructed using filtered backprojection. The SPECT data were reconstructed using an iterative ordered subsets expectation maximization (OSEM) algorithm with no correction, attenuation correction (AC) only, and both scatter (SC) and AC. Attenuation was estimated from the CT and incorporated into the system matrix as part of the reconstruction. Scatter was estimated using the dual energy window method and subtracted from the projections prior to reconstruction. Absolute quantification was derived from a scan of a point source with known activity. Results: With attenuation and scatter correction, the measured activity concentrations in the hot region of the phantom were within 12% of the true value with the external chamber of the phantom both full and empty. Scatter correction in addition to AC improves the accuracy over AC alone in the cold regions. Conclusions: Attenuation correction significantly reduces the subject‐size dependence of the quantitative accuracy in small‐animal MMP SPECT. Scatter correction may provide some additional benefit.Heart and Stroke Foundation of Ontario (NA6374) National Science and Engineering Research Council of Canada (PGS D)
SU‐C‐211‐09: Translational Imaging Applications in Traumatic Brain Injury
Authors: Selwyn R , Tang H 
Published: November 2011

Purpose: To develop a high‐resolution, multimodal and translatable imaging protocol to characterize experimental models of traumatic brain injury (TBI). Small animal imaging modalities include fluorodeoxyglucose (FDG)‐positron emission tomography (PET) with computed tomography (CT) and magnetic resonance imaging (MRI).Methods: Male Sprague‐Dawley rats were exposed to either lateral fluid percussion (LFP) or controlled cortical impact (CCI) TBI with mild or moderate severity. Baseline FDG‐PET and MRI scans were conducted prior to injury and at various times post‐TBI. FDG‐PET/CT images were acquired on a Siemens Inveon Multimodality scanner based on IV injection of 37 – 74 MBq (1 – 2 mCi) of FDG. Diffusion, perfusion, and spectroscopic images along with susceptibility and T1/T2‐weighted images were acquired on a Bruker Biospec 7T/20 cm magnet running Paravision 5.1. Results: For translatable FDG‐PET imaging, a tail vein injection of FDG with 45 minutes of anesthetized uptake and 30 minutes of scanning was optimal. With the brain centered in the field of view, uptakes (ipsilateral and contralateral) were normalized by cerebellar uptake since blood sampling was not conducted. The 2‐hour MRI protocol included fast spin echo (100 um), 3D multi‐echo gradient echo susceptibility (100 um), 4‐shot EPI‐based continuous arterial spin labeling (152 um), 8‐shot EPI‐based with three direction diffusion (100 um), and single voxel PRESS spectroscopy(3 mm) Conclusions: The impact of TBI on military service members is significant with more than 5,500 soldiers diagnosed with TBIs. Early diagnosis and development of an effective treatment for veterans with TBI is a priority for the military. A multimodal and multi‐parameter imaging protocol for experimental TBI that is both translatable and efficient (high throughput) is pivotal for studying neuroprotection, regeneration, and plasticity. An optimized small animal imaging protocol was developed to investigate longitudinal changes in glucose utilization (FDG‐PET/CT), cortical volume, diffuse axonal injury, perfusion, and metabolite concentration (MRI).Funding provided by the Center for Neuroscience and Regenerative Medicine, Uniformed Services University
SU‐C‐301‐04: Development of Iterative Image Reconstruction Algorithm for TBCT System
Authors: Kim J , Xu X , Gersten D , Zhang T 
Published: November 2011

Purpose: Tetrahedron Beam Computed Tomography (TBCT) circumvents some problems of cone beam CT (CBCT) but still shares the same approximate reconstruction artifact with FDK algorithm. Recently, iterative image reconstruction has been widely employed in diagnostic CT scanners in order to suppress noise and reduce imaging dose. In this study we developed an iterative TBCT image reconstruction algorithm which is able to mitigate the cone beam reconstruction artifact as well as reduce image noise. Methods: Simultaneous algebraic reconstruction technique (SART) image reconstruction algorithms were developed based on our TBCT benchtop geometry. The algorithms were tested using both numerical and physical phantoms. The projection matrix was calculated using a distance driven method. Noise levels in reconstructed images were quantified. The approximate image reconstruction artifact at larger cone angle was evaluated. Results: With the same numerical and real scanned projection data, SART algorithm produces similar spatial resolution as the FDK algorithm. The cone artifact was significantly reduced as compared with FDK algorithm. The noise levels were reduced 16–20% by the iterative algorithm at different regions of the images. Conclusions: Iterative reconstruction algorithm further improves the image quality of the TBCT system. TBCT system with SART image reconstruction algorithm potentially may be used as a mobile CT scanner for diagnostics.This work is partially supported by NIH grant 1R21CA130330‐01A1 and DOD Prostate Cancer Research Program W81XWH‐07‐0083.
SU‐C‐301‐05: Comparative Low‐Contrast Performance of Scan Equalization Digital Mammography (SEDM) v.s. Full‐Field Digital Mammography (FFDM): A Simulation Study with Micro‐Calcifications
Authors: Liu X , Lai C , Shaw C , Shen Y , Zhong Y , Yi Y , Ge S , You Z 
Published: November 2011

Purpose: To investigate the effects of exposure equalization on the noise property and visibility of micro‐calcifications using simulated SEDM imaging experiments. Method: An anthropomorphic breast phantom was imaged at various exposure levels using a full‐field digital mammography system. A lead plate with two‐dimensional array of aperture holes was used to measure primary signals which were then subtracted from those obtained without the lead plate to separate scatter components from total image signals. Exposure equalization factors were determined from a standard FFDM image and these factors were then multiplied with images acquired at various exposure levels to simulate SEDM image. Two sets of image were acquired and subtracted from each other to estimate the noise properties for different imaging techniques. Images of simulated micro‐calcifications with different sizes were composed with primary signals and then added with scatter components to form FFDM and simulated SEDM images for visualization studies. Results: SEDM resulted in reduced noise level in dense area while increased noises level in less attenuating area (fatty area or at the board of the breast where the thicknesses are reduced) compared with the standard FFDM method. The visualization of simulated micro‐calcification is seen slightly improved in dense area of the breast phantom due to improved signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR). Conclusion: SEDM technique can improve image SNRs and CNRs in dense area of the breast, hence to improve the visibility of micro‐calcification in breast images.This work was supported in part by grants CA104759, CA124585 and CA13852 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐C‐220‐04: Electrostatic Focal Spot Correction for X‐Ray Tubes Operating in Strong Magnetic Fields
Authors: Lillaney P , Constantin D , Ganguly A , Fahrig R 
Published: November 2011

Purpose: To evaluate the effectiveness of electrostatic mechanisms for controlling the focal spot position in X‐ray tubes operating in the fringe field of an MR bore, and to determine a cathode design to implement the correction mechanism while not compromising normal X‐ray tube operation.Methods: Using a combination of theoretical calculations and high voltage vacuum standoff constraints, a cathode design was derived that is practical for standard X‐ray tube geometry. The crucial part of the design consists of two voltage‐biased deflection electrodes placed adjacent to the cathode. Space charge beam simulations were performed for the design to determine current density changes and beam deflection in the presence of a magnetic field. Phase space information from the beam simulation was input into a Monte Carlo engine to determine the effect of the cathode design on the X‐ray photon energy spectrum.Results: For a 0.07T magnetic field, a 120 kV cathode‐anode potential, a 14.4 mm cathode‐anode separation distance, and a 35 kV electrode potential, the deflection of the X‐ray tube focal spot is within 2 mm of the original position with slight distortions to focal spot shape. However, the curvature of the electron trajectories is altered resulting in a significant velocity component tangential to the anode that is on average 10 times larger than in the control case. The electron velocity changes coupled with slightly lower current density on the anode reduces the total number of photons generated by 7.5% without significantly altering the energy spectrum of the X‐ray photons Conclusions: The beam simulations demonstrate that focal spot deflection can be controlled to within reasonable values. The generated spectrum is not significantly different from that of a standard X‐ray tube, with only a moderate decrease in overall photon fluence. Work is underway to evaluate the cathode design in an experimental setting.Funding Sources: NIHR01 EB007626, Stanford Bio‐X Fellowship, and the Lucas Foundation
SU‐C‐220‐06: Comparison of the Absorption Coefficient and Diffraction Enhanced Imagingˈˈs Apparent Absorption Coefficient of Lung Tissue
Authors: Connor D , Cole E , Zhong Z , Dilmanian F , Wiebe S , Parham C , Pisano E 
Published: November 2011

Purpose: Diffraction enhanced imaging (DEI) generates image contrast in a fundamentally different way than absorption x‐ray imaging—the refraction and extinction of x‐rays yield unique contrast. The purpose of this study was to measure the apparent absorption coefficient of the lung tissue in normal rats and to quantify the difference in contrast between DEIˈs peak image and radiography. Methods: Chest radiographs and DEI peak images (analyzer crystal aligned to the Bragg peak) were acquired of anesthetized and paralyzed Sprague Dawley rats (n=14) at Beamline X15A of the National Synchrotron Light Source at an x‐ray energy of 60 keV. The images were acquired in the anteroposterior (AP) direction. Intensity measurements were used to calculate an approximate apparent absorption coefficient of rat lung tissue. Measurements of the transmitted intensity of both the radiograph and DEI peak images were then used to calculate contrast within the lung. Results: The measured apparent absorption coefficient for the inflated lungs was 0.86 +/− 0.15 cm̂−1. To put this in context, the absorption coefficient of air, water and bone at 60 keV are 0.0002 cm̂−1, 0.21 cm̂−1 and 0.50 cm̂−1, respectively. Thus, the DEI contrast generated by the lung is about two times that generated by the same thickness of bone. DEI showed a significant gain in contrast over radiography (C_DEI/C_Rad) of 1.7 +/− 0.6. Conclusions: DEI generates 70% greater lung contrast than radiography at 60 keV. The large difference in the apparent absorption coefficient of DEI and the absorption coefficient of conventional radiography shows that DEI can be used to either enhance lung contrast for the same radiation dose, or could be used to substantially reduce the required radiation dose for a chest x‐ray while maintaining the same contrast‐to‐noise ratio.Drs. Connor, Parham, Pisano and Zhong are equity holders in NextRay, Inc. Dr. Pisano is on the Board of Directors at NextRay, Inc. Drs. Connor, Parham and Zhong are consultants to NextRay, Inc.
SU‐D‐BRA‐01: The Impact of Continuous Variable Dose Rate (CVDR) on VMAT Plan Quality, Delivery Efficiency and Accuracy
Authors: Cao D , Shepard D 
Published: November 2011

Purpose: Elekta VMAT utilizes a binned variable dose rate (BVDR) whereby the dose rate jumps between a series of discrete levels during the VMAT delivery. The use of discrete dose rate levels may limit the plan quality and delivery efficiency. A continuous variable dose rate (CVDR) delivery technique has now been developed with the goal of solving such limitations. This work studies the impact of CVDR on VMAT plan quality, delivery efficiency and accuracy. Methods: 10 cases covering a variety of treatment sites were selected for this study. Among them, three cases were selected for plan quality comparison. All VMAT plans were created using Pinnacle3 SmartArc® and were delivered on an Elekta Synergy linac equipped with an 80‐leaf conventional MLC. The delivery accuracy was checked using a 2D ion chamber array. Results: Similar dose distributions were observed in both the BVDR and CVDR plans. For the more complex H&N case, however, the CVDR plan had a slightly improved target dose coverage with an average V95 (target volume receives at least 95% prescribed dose) of 99.0% as compared with 98.4% for the BVDR plan. For all three cases, the average V95 for the BVDR and CVDR plans are 96.7% and 97.0%, respectively. The average delivery time per arc was 2.35 minutes for the BVDR plans. This value decreased 25% to 1.75 minutes for the CVDR plans. As to the plan delivery accuracy, the gamma analysis passing rate of the VMAT plan QA delivered using BVDR and CVDR remains essentially the same for each case. Conclusions: The availability of continuous variable dose rate represents a significant advancement in VMAT delivery on Elekta linacs providing a 25% reduction in treatment times while providing similar or slightly improved plan quality.This work was sponsored in part through a grant from Elekta.