bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐71: Susceptibility Weighted Imaging (SWI) Software for Post‐Processing of SWI Data
Authors: Jambawalikar S , Krishnamoorthy S , So J , Dutta A , Li H , Button T , Nickoloff E
Published: June 2012

Purpose: To develop open source software for post processing of susceptibility weighted (SWI) MR images using magnitude and phase data. Methods: SWI data was acquired using Philips MRI 3T scanner with the following parameter: 3D T1 FFE axial with TR=40ms, TE=25ms, FOV=22 cm, acquisition matrix of 440×440 and 40 slices. Both magnitude and phase data was stored for SWI post processing. The SWI homodyne filtering is performed by converting the magnitude and phase image to complex real and imaginary images. The SWI software was implemented in C++ using ITK (Image registration and segmentation toolkit) toolkit. To generate SWI maps the user needs to provide the DICOM data directory, the series number of DICOM SWI series, low pass filter size and the weighting factor of phase mask. This outputted SWI series is saved as DICOM and appended to the patient series and can be viewed in any DICOM compatible viewer. The software also outputs SWI filtered phase maps which can be further used for iron quantification in organs like brain, liver etc. Results: An open source implementation of SWI post‐processing tool using ITK was provided. The SWI processed phase weighted data can be used for qualitative assessment of iron deposits. The filtered phase map outputted can be used for quantitative iron measurements. Conclusions: SWI post processing software is implemented here to provide qualitative SWI maps of iron deposits in brain and other organs. The post processed images can also be useful for MR Venography with minimum intensity projection. This tool would be useful to study disease processes involved with accumulation of iron in different organs.
SU‐E‐I‐72: Modulation of Hypothalamic Connectivity by Food Ingestion
Authors: Huerta C , Li J , Wey H , Duong T
Published: June 2012

Purpose: In this study we utilized resting state fMRI (rsfMRI) to identify and compare hypothalamic connectivity in lean subjects during fasting and satiated state. Methods: rsfMRI were performed on 7 healthy lean subjects (4 male, 3 female, 20–35 yo, BMI = 18–25 kg/m2). Subjects fasted overnight (8 hrs), average blood glucose of 80± 5 mg/dL. None of the subjects were on diet program or recently lost/gain weight. rsfMRI EPI parameters:TR = 3000ms, TE = 30 ms, and spatial resolution of 1.7 × 1.7 mm × 5mm, ST= 65 mins (10‐min pre‐glucose ingestion acquisition, followed by 50 mins of post‐glucose ingestion). During rsfMRI, subjects ingested standard glucola (75 g of glucose dissolved in 296 ml of flavored water) over 4.5 ± 0.75 min via a peroral rubber tube. Preprocessing procedure was implemented using FSL consisting of 1) motion correction 2) spatial smoothing, 3) temporal filtering between 0.01–0.08 Hz. Using the Talairach‐Daemon atlas, ROI in the hypothalamus was selected. The individual timeseries of hypothalamus was used as seed to find neural structures that share similar temporal pattern that hypothalamus. Results: Structures that were engaged only during fasting were (Table 1): Inferior frontal gyrus (BA 47) has been linked to the modulation of hunger. The output from the orbitofrontal cortex to both striatum (lentiform nucleus) and lateral hypothalamus has been reported. The structures that were engaged only during satiated state were: Superior temporal gyrus has been implicated in food inhibition and mid temporal gyrus has been reported to be engaged in satiation. Cerebellum is activated when the brain is monitoring its sensory systems.
SU‐E‐I‐77: X‐Ray Coherent Scatter Diffraction Pattern Modeling in GEANT4
Authors: Kapadia A , Samei E , Harrawood B , Sahbaee P , Chawla A , Tan Z , Brady D
Published: June 2012

Purpose: To model X‐ray coherent scatter diffraction patterns in GEANT4 for simulating experiments involving material detection through diffraction pattern measurement. Although coherent scatter cross‐sections are modeled accurately in GEANT4, diffraction patterns for crystalline materials are not yet included. Here we describe our modeling of crystalline diffraction patterns in GEANT4 for specific materials and the validation of the results against experimentally measured data. Methods: Coherent scatter in GEANT4 is currently based on Hubbell's non‐relativistic form factor tabulations from EPDL97. We modified the form‐factors by introducing an interference function that accounts for the angular dependence between the Rayleigh‐scattered photons and the photon wavelength. The modified form factors were used to replace the inherent form‐factors in GEANT4. The simulation was tested using monochromatic and polychromatic x‐ray beams (separately) incident on objects containing one or more elements with modified form‐factors. The simulation results were compared against the experimentally measured diffraction images of corresponding objects using an in‐house x‐ray diffraction imager for validation. The comparison was made using the following metrics: number of diffraction rings, radial distance, absolute intensity, and relative intensity. Results: Sharp diffraction pattern rings were observed in the monochromatic simulations at locations consistent with the angular dependence of the photon wavelength. In the polychromatic simulations, the diffraction patterns exhibited a radial blur consistent with the energy spread of the polychromatic spectrum. The simulated and experimentally measured patterns showed identical numbers of rings with close agreement in radial distance, absolute and relative intensities (barring statistical fluctuations). No significant change was observed in the execution time of the simulations. Conclusions: This work demonstrates the ability to model coherent scatter diffraction in GEANT4 in an accurate and efficient manner without compromising the accuracy or runtime of the simulation. This work was supported by the Department of Homeland Security under grant DHS (BAA 10‐01 F075), and by the Department of Defense under award W81XWH‐09‐1‐0066.
SU‐E‐I‐79: Correction of Dark Current and Image Lag in Multi‐Source Carbon Nanotube Imaging Systems
Authors: Frederick C , Lalush D , Chang S
Published: June 2012

Purpose: To correct for dark current and detector image lag in multi‐source carbon nanotube (CNT) based imaging systems. Methods: CNTs can be used as a novel electron source for X‐ray generation. Here a small (∼2 kV) gate voltage induces a large electric field at the CNT tip that causes field emission as opposed to thermionic emission. This enables faster switching times and allows miniaturization which aids in the development of stationary multi‐source systems. These systems may encounter two key problems: dark current in non‐active sources and detector lag. In damaged and perhaps end‐of‐life devices, sources may develop significant electron output without gate voltage, interfering with images from non‐active sources. Although the output is small, it is constant, and continuous integration of detectors compared with small X‐ray exposure time magnifies its contribution to the signal. A method based on binary multiplexing is developed to mitigate the dark current contributions possibly extending device lifetime. Having discrete sources, these multi‐source systems have coarser angular sampling than rotating systems. This coarser sampling means that the detector signal changes more in adjacent projections than rotating systems exacerbating the effect of detector lag. Since flat panel detectors have a capacitive behavior, readout only removes some charge from pixels. As a result, a device dependent amount (6.6% in our device) of the signal from the current image contributes to the subsequent image. A fast, stable inverse filter separating detector lag has been developed. Results: Projection data were simulated based on parameters measured from a multi‐source CNT system. Incorporating dark current and image lag phenomena into reconstruction improves contrast to noise ratio. Conclusions: These correction methods can be easily implemented on clinical multi‐source systems to improve image quality and extend the device's usable lifetime. Supported in part by Siemens Medical
SU‐E‐I‐81: Toward in Vivo Magnetic Spectroscopy of Brownian Motion
Authors: Reeves D , Brown S , Fiering S , Weaver J
Published: June 2012

Purpose: Magnetic spectroscopy of Brownian motion (MSB) has been used previously to measure temperature, viscosity, and cellular binding in vitro. The MSB signal ‐ a ratio of the 5th to 3rd harmonic of the response from magnetic nanoparticles to an oscillating field ‐ provides insight into particle microenvironment. These biosensing capabilities would be productive in vivo but until now were prevented by sensitivity limits. Our goal was to design and create a similar apparatus for work in vivo. In vivo spectroscopy is a viable precursor to imaging, and is essential for drug delivery or therapeutic methods like hyperthermia. Methods: Coil geometries were modeled to optimize a uniform Helmholtz drive coil and imaging coil with maximal spatial resolution. The completed apparatus includes balancing and trim coils to zero out unwanted background fields. The coils were characterized and experiments were performed to verify consistency with previous in vitro experiments. Finally, as an in vivo experiment, we took MSB spectra on living mice with five week old melanomas injected with 200ug of 100nm starch coated nanoparticles. Results: The drive coil is capable of sustaining 12.5mT fields up to 1.5kHz with a field variation of 3% throughout the sample volume. The pickup coil is frequency independent and has a vertical and horizontal range of 5mm and 10mm respectively before the MSB signal drops below 50%. The minimum sensitivity is 50–70μg of iron. MSB signal response to viscosity changes shows the same signatures as the in vitro apparatus. The in vivo data showed successful sensing of nanoparticles. We also saw the MSB signal decay with time showing the apparatus can detect changes in particle behavior due to interactions with biology. Conclusions: We achieved in vivo MSB and due to sufficient sensitivity we are motivated to further work in monitoring in vivo cellular uptake and viscosity.
SU‐E‐I‐88: Realistic Pathological Simulations of the NCAT and Zubal Anthropomorphic Models, Based on Clinical PET/CT Data
Authors: Papadimitroulas P , Loudos G , Le Maitre A , Efthimiou N , Visvikis D , Nikiforidis G , Kagadis GC
Published: June 2012

Purpose: In the present study a patient‐specific dataset of realistic PET simulations was created, taking into account the variability of clinical oncology data. Tumor variability was tested in the simulated results. A comparison of the produced simulated data was performed to clinical PET/CT data, for the validation and the evaluation of the procedure. Methods: Clinical PET/CT data of oncology patients were used as the basis of the simulated variability inserting patient‐specific characteristics in the NCAT and the Zubal anthropomorphic phantoms. GATE Monte Carlo toolkit was used for simulating a commercial PET scanner. The standard computational anthropomorphic phantoms were adapted to the CT data (organ shapes), using a fitting algorithm. The activity map was derived from PET images. Patient tumors were segmented and inserted in the phantom, using different activity distributions. Results: The produced simulated data were reconstructed using the STIR opensource software and compared to the original clinical ones. The accuracy of the procedure was tested in four different oncology cases. Each pathological situation was illustrated simulating a) a healthy body, b) insertion of the clinical tumor with homogenous activity, and c) insertion of the clinical tumor with variable activity (voxel‐by‐voxel) based on the clinical PET data. The accuracy of the presented dataset was compared to the original PET/CT data. Partial Volume Correction (PVC) was also applied in the simulated data. Conclusions: In this study patient‐specific characteristics were used in computational anthropomorphic models for simulating realistic pathological patients. Voxel‐by‐voxel activity distribution with PVC within the tumor gives the most accurate results. Radiotherapy applications can utilize the benefits of the accurate realistic imaging simulations, using the anatomicaland biological information of each patient. Further work will incorporate the development of analytical anthropomorphic models with motion and cardiac correction, combined with pathological patients to achieve high accuracy in tumor imaging. This research was supported by the Joint Research and Technology Program between Greece and France; 2009–2011 (protocol ID: 09FR103)
SU‐E‐I‐92: Accuracy Evaluation of Depth Data in Microsoft Kinect
Authors: Kozono K , Aoki M , Ono M , Kamikawa Y , Arimura H , Toyofuku F
Published: June 2012

Purpose: Microsoft Kinect has potential for use in real‐time patient position monitoring in diagnostic radiology and radiotherapy. We evaluated the accuracy of depth image data and the device‐to‐device variation in various conditions simulating clinical applications in a hospital. Methods: Kinect sensor consists of infrared‐ray depth camera and RGB camera. We developed a computer program using OpenNI and OpenCV for measuring quantitative distance data. The program displays depth image obtained from Kinect sensor on the screen, and the cartesian coordinates at an arbitrary point selected by mouse‐clicking can be measured. A rectangular box without luster (300 × 198 × 50 mm3) was used as a measuring object. The object was placed on the floor at various distances ranging from 0 to 400 cm in increments of 10 cm from the sensor, and depth data were measured for 10 points on the planar surface of the box. The measured distance data were calibrated by using the least square method. The device‐to‐device variations were evaluated using five Kinect sensors. Results: There was almost linear relationship between true and measured values. Kinect sensor was unable to measure at a distance of less than 50 cm from the sensor. It was found that distance data calibration was necessary for each sensor. The device‐to‐device variation error for five Kinect sensors was within 0.46% at the distance range from 50 cm to 2 m from the sensor. The maximum deviation of the distance data after calibration was 1.1 mm at a distance from 50 to 150 cm. The overall average error of five Kinect sensors was 0.18 mm at a distance range of 50 to 150 cm. Conclusions: Kinect sensor has distance accuracy of about 1 mm if each device is properly calibrated. This sensor will be useable for positioning of patients in diagnostic radiology and radiotherapy.
SU‐E‐I‐98: PET/CT's Most‐Cited 50 Articles since 2000: A Bibliometric Analysis of Classics
Authors: Sayed G
Published: June 2012

Purpose: Despite its relatively recent introduction to clinical practice, PET/CT has gained wide acceptance both in diagnostic and therapeutic applications. Scientific publication in PET/CT has also experienced significant development since its introduction. Bibliometric analyses allow an understanding of how this publication trend has developed at an aggregated level. Citation analysis is one of the most widely used bibliometric tools of scientometrics. Analysis of classics, defined as an articles with 100 or more citations, is common in the biomedical sciences as it reflects an article's influence in its professional and scientific community. Our objective was to identify the 50 most frequently cited classic articles in PET/CT in the past 10 years. Methods: The 50 most‐cited PET/CT articles were identified by searching ISI's Web of Knowledge and Pubmed databases for all related publications from 2000 through 2010. Articles were evaluated for several characteristics such as author(s), institution, country of origin, publication year, type, and number of citations. An unadjusted categorical analysis was performed to compare all articles published in the search period. Results: The search yielded a cumulative total of 22,554 entries for the publication period, of which 15,943 were original research articles. The 50 most‐cited articles were identified from the latter sum and selected out of 73 classics. The number of citations for the top 50 classics ranged from 114 to 700. PET/CT classics appeared in three general and 12 core journals. The majority of the classics were in oncologic applications of PET/CT (62%). Articles related to diagnostic topics were 6%. The rest were focused on physics and instrumentation 24% and other basic sciences 16%. Conclusions: Despite its relatively short history PET/CT accumulated 73 classic articles in a decade. Such information is of importance to researchers and those who wish to study the scientific development in the field.
SU‐E‐I‐99: An Ultra‐High Resolution Small Field‐Of‐View Solid State X‐Ray Imaging Detector Based on an Electron Multiplying CCD
Authors: Singh V , Loughran B , Jain A , Sharma P , Bednarek D , Rudin S
Published: June 2012

Purpose: To demonstrate the ultra‐high resolution capability of a small field‐of‐view (FOV) solid state x‐ray imaging detector based on an EMCCD sensor. Methods: A micro‐solid state x‐ray image intensifier (micro‐SSXII) was developed to serve as an ultra‐high resolution region‐of‐interest (ROI) imaging detector. It is based on an 8 micron, 1004 by 1002 pixel electron multiplying CCD (EMCCD) optically coupled to a 100 micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm. The modulation transfer function (MTF) of the micro‐SSXII was measured by the slanted edge method. A cast of a rat kidney (made by mixing resin and iodine for contrast) and a mammography line pair test object were imaged at 50 kVp to demonstrate the detector's ultra‐high resolution capability visually. Results: The MTF was determined and was 5% at 20 cycles/mm. This is consistent with the clear visualization of the maximum 20 lp/mm group in the image of the mammography test object. Also, iodine bubbles with diameters as small as 25 microns, which are formed by the non‐uniform mixing of the iodine in the resin cast, can be clearly identified in the rat kidney vessels. Conclusions: The ultra‐high resolution capability (>20 lp/mm) but small FOV (8 mm) of the micro‐SSXII in combination with a low‐energy x‐ray source may have application for investigations of vascular specimen details and other fine structures where optical or other surface imagers would be unsuited for evaluating features below the surface. Contact radiography with this imager combined with a large higher‐load focal spot x‐ray tube may be a promising substitute for magnification radiography which is limited by the use of specialized low output microfocus x‐ray tubes and geometric un‐sharpness for large magnifications. Supported in part by: NIH Grants R01‐EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐100: Feasibility Study of Gamma‐Ray Medical Radiography
Authors: Alyassin A , Maqsoud H , Mashat A , Al‐Mohr A , Abdulwajid S
Published: June 2012

Purpose: The purpose of this research is to study an alternative technique to conventional x‐ray radiography that requires less patient radiation dose, less cost, portable, requires less maintenance, and less power consumption. This research explores the feasibility of using gamma‐ray radiography in medical imaging. Gamma‐ray medical radiography has the potential to provide alternative diagnostic medical information to X‐ray radiography. Methods: Approximately one Ci of Am‐241 radioactive source which emits monoenergetic 59.5 KeV gamma rays was used in this study. Several factors that influence this feasibility were studied. These were the radiation source uniformity, image uniformity, image quality parameters such as contrast, noise, and spatial resolution. In addition, visual assessment of several human phantom gamma‐ray and x‐ray images were conducted. The images were recorded on computed radiography image receptors and displayed on a standard monitor. Results: The radioactive source provided a relatively uniform radiation exposure and uniform images. Image noise was mainly dependent on the exposure time and the source size. Although the contrast depended on the window and level setting, it was also dependent on the exposure time and the source size. Spatial resolution was dependent on the source size and the magnification. The generated gamma‐ray images were of lower quality than the X‐ray images which was mainly due to the low radioactivity used. However, the gamma‐ray images displayed most of the main structures contained in the humanoid phantoms. Conclusions: Thisresearch explored the feasibility of using gamma‐ray radiography in medical imaging and showed that gamma‐ray medical radiography has the potential to provide alternative diagnostic medical information to X‐ray radiography. Finally, this research also paves the way for the usage and production of high radioactive Am‐241 source that will show high quality medical gamma‐ray radiography is feasible.
SU‐E‐I‐101: Initial Implementation and Evaluation of AAPM TG‐150 Draft Image Receptor Non‐Uniformity Testing Recommendations
Authors: Dave J , Gingold E , Yorkston J , Bercha I , Goldman L , Walz‐Flannigan A , Willis C
Published: June 2012

Purpose: To implement in software the procedures described in AAPM Task Group 150's draft recommendations for image receptor performance testing, and to evaluate the effectiveness and practicality of these procedures. Methods: Images of flat fields were acquired using digital x‐ray image receptors at 6 cooperating institutions. Four flat field images obtained with each detector spanned a range of input detector air kerma. Software based on AAPM TG150's draft report processed the test images and generated results. Image receptor response and several measures of non‐uniformity were evaluated. Images were divided into 10 mm square regions, after eliminating 10 mm borders. For each region, signal (mean), noise (standard deviation) and SNR were calculated. Characteristic signal, noise and SNR were calculated based on average values from all regions. Local non‐uniformity for signal (SLN), noise (NLN) and SNR (SNRLN) were expressed as the maximum ratio of the absolute difference between each region's value and its 4 nearest neighbors, to the respective characteristic value. Global non‐uniformity (SGN, NGN, SNRGN) were expressed similarly but differences between maximum and minimum values obtained from the regions were used (without comparison to local neighbors). Results: TG150 tests discriminated between good and poorly performing detectors. Improper detector calibration was detectable, with noise non‐uniformity proving to be a more sensitive measure than signal or SNR non‐uniformity. Detector rotation relative to calibration conditions produced a greater change in signal non‐uniformity than the other measures. Image receptor structured noise was characterized by an increase in noise non‐uniformity with incident air kerma. Conclusions: AAPM TG150's proposed approach to image receptor testing was implemented and evaluated. The approach appears to be an effective and practical one for routine quality assurance testing of digital radiographic image receptors.
SU‐E‐I‐102: Independent Implementation of AAPM TG‐150 Draft Image Receptor Test Recommendations
Authors: Greene T , Nishino T , Willis C
Published: June 2012

Purpose: To determine whether a proposed suite of generic tests for digital radiography (DR) detectors could be reduced to practice. Methods: MATLAB software was developed to analyze images according to descriptions in a document drafted by the TG150 Detector Subgroup. Forprocessing images were acquired directly from the acquisition stations of three DR and one Computed Radiography system. Images included flat‐field exposures at the manufacturer's calibration condition, twice the exposure, ½ the exposure, and a low exposure, plus three images of a lead bar pattern in different orientations, also at the calibration condition. The flat field images were analyzed to determine Detector Response; Gain Correction; Signal, Noise, and Signal‐to‐noise (SNR) Uniformity; SNR Magnitude; and Anomalous Detector Element (del) Identification. The program also allowed visual inspection for evaluation of collimation and non‐uniformity. Bar pattern images were analyzed to evaluate spatial resolution by a variance method. Results: Acquisition revealed a number of pitfalls. Some manufacturers have multiple calibration points. For‐processing images are not directly available from all systems, and PACS may modify them from their original state. The orientation of the flat field with respect to the anodecathode axis may not be defined by the manufacturer. Care must be taken to ensure collimation outside the edges of detectors, or the software must exclude collimator shadows. The matrix size of images differs among manufacturers, so the size of the region of interest (ROI) for analysis varies from the default size of 100×100 dels, as does the number of ROIs. The approach for dealing with edges and ROIs may affect the numerical results. The detector response function may also affect the interpretation of results. Conclusions: The software successfully implements most of the detector tests recommended by TG150. Comparison of these results with those of the parallel effort will validate the draft test definition.
SU‐E‐I‐107: Suitability of Various Radiation Detectors Used in Radiation Therapy for X‐Ray Dosimetry in Computed Tomography
Authors: Liebmann M , Poppe B , von Boetticher H
Published: June 2012

Purpose: Assessment of suitability for X‐ray dosimetry in computed tomography of various ionization chambers, diodes and two‐dimensional detector arrays primarily used in radiation therapy. Methods: An Oldelft X‐ray simulation unit was used to irradiate PTW 60008, 60012 dosimetry diodes, PTW 23332, 31013, 31010, 31006 axial symmetrical ionization chambers, PTW 23343, 34001 plane parallel ionization chambers and PTW Starcheck and 2D‐Array seven29 as well as a prototype Farmer chamber with a copper wall. Peak potential was varied from 50 kV up to 125 kV and beam qualities were quantified through half‐value‐layer measurements. Energy response was investigated free in air as well as in 2 cm depth in a solid water phantom and refers to a manufacturer calibrated PTW 60004 diode for kV‐dosimetry. Results: The thimble ionization chambers PTW 31010, 31013, the uncapsuled diode PTW 60012 and the PTW 2D‐Array seven29 exhibit an energy response deviation in the investigated energy region of approximately 10% or lower thus proving good usability in X‐ray dosimetry if higher spatial resolution is needed or rotational irradiations occur. Conclusions: It could be shown that in radiation therapy routinely used detectors are usable in a much lower energy region. The rotational symmetry is of advantage in computed tomography dosimetry and enables dose profile as well as point dose measurements in a suitable phantom for estimation of organ doses. Additional the PTW 2D‐Array seven29 can give a quick overview of radiation fields in non‐rotating tasks.
SU‐E‐I‐108: Simple Approach to Determine Patient's Entrance Skin Exposure for Radiographic
Authors: Maricle S , Jeutang L , Prasad G
Published: June 2012

Purpose: To evaluate a model which can predict patient's Entrance Skin Exposure (ESE) from height and weight and a single kVp mR/mAs measurement for radiographic. Methods: Patient height, weight and post exposure mAs are obtained to assess ESE based on IAEA model. Patient's thickness is obtained by assuming a cylindrical geometry. The validity of this assumption is tested against actual measurements. Source to Skin Distance (SSD) is computed from patient's thickness and the Source‐Image receptor Distance (SID) used during exposure. Entrance Skin Exposure is calculated as a product of post exposure mAs and a single 80 kVp mR/mAs obtained at a reference distance corrected inversely for SSD. Values of mR/mAs at other kVp's are obtained by quadratic variation of output with kVp. Results: The validity of predicting patient thickness will be presented based on numerous measurements performed on test subjects. Deviation between the ESE values using of single kVp, mR/mAs measurement and the ones obtained by the conventional multiple kVp mR/mAs will be presented as well. Conclusions: This work indicates a simple approach to determine the patient's ESE based on the patient's height and weight for radiographic units, which will be very useful for institutions that do not have a dedicated physicist.
SU‐E‐I‐109: Sensitivity Analysis of an Electronic Portal Imaging Device Monte Carlo Model to Variations in Optical Transport Parameters
Authors: Blake S , Vial P , Holloway L , McNamara A , Greer P , Kuncic Z
Published: June 2012

Purpose: To investigate the sensitivity of a Monte Carlo (MC) model of a standard clinical amorphous silicon (a‐Si) electron portal imaging device (EPID) to variations in optical photon transport parameters. Methods: The Geant4 MC toolkit was used to develop a comprehensive model of an indirect‐detection a‐Si EPID incorporating x‐ray and optical photon transport. The EPID was modeled as a series of uniform layers with properties specified by the manufacturer (PerkinElmer, Santa Clara, CA) of a research EPID at our centre. Optical processes that were modeled include bulk absorption, Rayleigh scattering, and boundary processes (reflection and refraction). Model performance was evaluated by scoring optical photons absorbed by the a‐Si photodiode as a function of radial distance from a point source of x‐rays on an event‐by‐event basis (0.025 mm resolution). Primary x‐ray energies were sampled from a clinical 6 MV photon spectrum. Simulations were performed by varying optical transport parameters and the resulting point spread functions (PSFs) were compared. The optical parameters investigated include: x‐ray transport cutoff thresholds; absorption path length; optical energy spectrum; refractive indices; and the ‘roughness' of boundaries within phosphor screen layers. Results: The transport cutoffs and refractive indices studied were found to minimally affect resulting PSFs. A monoenergetic optical spectrum slightly broadened the PSF in comparison with the use of a polyenergetic spectrum. The absorption path length only significantly altered the PSF when decreased drastically. Variations in the treatment of boundaries noticeably broadened resulting PSFs. Conclusions: Variation in optical transport parameters was found to affect resulting PSF calculations. Current work is focusing on repeating this analysis with a coarser resolution more typical of a commercial a‐Si EPID to observe if these effects continue to alter the EPID PSF. Experimental measurement of the EPID line spread function to validate these results is also underway. Cancer Institute NSW Research Equipment Grants 10/REG/1‐20 and 10/REG/1‐10 Cancer Council NSW Grant, ID RG 11‐06 NHMRC Project Grant, ID569211 The University of Sydney Postgraduate Research Scholarship in Medical Physics SWSCS Radiation Oncology Student Scholarship, 2012
SU‐E‐I‐113: Alignment and Assembly of Small Field of View Pre‐Clinical Images Taken with a Micro‐Solid State X‐Ray Imaging Detector
Authors: Loughran B , Singh V , Bednarek D , Rudin S
Published: June 2012

Purpose: We have developed a Micro‐Solid State X‐ray Imaging Intensifier (μSSXII) detector with an electron multiplying (EM)CCD chip which allows for an ultra‐high pixel resolution of 8 × 8 microns. However, the EMCCD chip area of 1004 × 1002 pixels results in an 8.032 × 8.016 mm imaging area and restricts the ability of the user to orient and properly image larger pre‐clinical objects such as rat‐kidney‐vasculature casts. We propose a method to align and assemble images of such larger structures while preserving the ultra‐high spatial resolution of the μSSXII. Methods: An imaging platform of negligible attenuation was attached to a stepper motor giving the platform free movement in the plane normal to the fluoroscopic x‐ray beam. By alternating the detector's image acquisition and the stepper movement, many adjacent overlapping views of the object are acquired. The user then identifies the two pixel coordinates in adjacent images which represent the same point in space. A custom Matlab computer code uses the pixel coordinates to aggregate and average the input images which results in a larger field of view consisting of many ultra‐high resolution images. Results: The images were able to be successfully combined to form a large image while preserving the ultra‐high resolution of the detector. In experimental tests, multiple portions of a mammography test object were imaged and virtually no spatial resolution degradation was found in the combined image. Additionally, when imaging a resin cast of rat‐kidney‐vasculature, vessels of less than 50 μm could be viewed in the combined image. Conclusions: The setup and method were found to preserve the ultra‐high resolution inherent to the μSSXII while allowing pre‐clinical imaging of objects larger than the detector's field of view. The large field of view was effective in orienting the user towards specific areas of interest in the objects imaged. Supported in part by: NIH Grants R01‐EB008425, R01‐EB002873, and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐114: Clinical Ultrasound Transducer Degradation Effects on the Accuracy of Spectral Doppler Velocity Measurements
Authors: Kruger R , Wolf K , Bloms N , Accola I
Published: June 2012

Purpose: Ultrasound Doppler velocity measurements are routinely used to determine the severity of a stenosis in the carotid, renal or peripheral arteries. The objective of this study is to investigate and demonstrate the relationship between Doppler velocity measurements and transducer degradation conditions encountered in a clinical environment. Methods: Assessing transducer performance was accomplished using the First Call aPerio Test System transducer analyzer (Sonora Medical Systems, Longmont, CO). This system was used to conduct 1,145 semi‐annual transducer assessments at 7 clinical sites from September 2007 to February 2012 as part of a comprehensive quality control program. The results were evaluated to determine the degree of transducer degradation encountered in the clinical environment. A Siemens Acuson S2000 (Siemens AG, Erlangen, Germany) ultrasound system was employed with the 1425A LE Doppler Flow System (Gammex, Middleton, WI) to determine Doppler velocity measurements. A transducer fixation device was fabricated to provide accurate, repeatable velocity measurements. Transducers with the most severe degradation were evaluated by comparing velocity measurements to those without defects. Using several matched transducer pairs, simulated failure modes were tested. The Doppler measured time‐average mean (TAMn) and time‐average maximum (TAMx) velocities were obtained and reported. Results: This investigation found that 4.5% of the transducers surveyed during this 5‐year period of time failed at least one acceptance criteria. Many (346 or 30%) had at least one defect. Typical findings include dead elements, lens delamination, wire cuts, and capacitance shorts. Only the most severe transducer defects and degradation conditions resulted in a noticeable deviation in the velocity measurements. Simulated transducer degradation testing confirmed this finding. Conclusions: The relationship between Doppler velocity measurements and transducer degradation conditions is limited, becoming significant for only the most severe degradation conditions. Based on our experience, this level of transducer degradation is rarely encountered in the clinical environment.
SU‐E‐J‐04: Initial Experience with 4D‐CBCT for Lung Cancer: Physician Verification of Computed Shifts Remains Necessary
Authors: Chapman K , Doyle L , Werner‐Wasik M , Peng C
Published: June 2012

Purpose: Four‐dimensional cone‐beam CT (4D‐CBCT) is a novel imaging technique used to guide treatment setup for patients with pulmonary lesions by providing additional information about tumor motion at the time of treatment. This study aimed to evaluate the efficacy of the 4D‐CBCT capability in ensuring accurate patient setup during SBRT. Methods: Twelve patients with pulmonary lesions were imaged pre‐treatment with Elekta XVI4.5 using the Symmetry protocol resulting in a respiratory correlated 4D‐CBCT. Reconstruction produced 10 phased‐based and one average 3DCT image set. Patient shifts were derived from contour‐based(mask) registration driven by the weighted average of shifts from each phased CT(4D shifts). Physicians reviewed registration and manually adjusted shifts based on visual registration. We exported the average 3DCT to MIM Vista Software 5.1.1 in reference volume coordinates and manually fused to the reference CT. All manual fusions were contour‐based registrations performed by a single observer. No rotations were permitted in manual fusion to mimic clinical procedure. Translational 3D shifts from manual fusion were compared to 4D(automatic registration) shifts and final physician‐corrected shifts. Results: Mean differences between 4D and 3D shifts in lateral, longitudinal, and vertical directions were 1.07mm, 5.92mm, and 1.43mm, respectively. Mean differences between physician‐corrected and 3D shifts were 1.41mm, 4.83mm, and 1.61mm. Differences between 4D shifts and 3D shifts increased with increasing tumor motion. One patient had consistently large longitudinal differences between 4D and 3D shifts (mean=3.0cm). Further review revealed poor 4D registration(via mask and clipbox) on the XVI system which was corrected by physician adjustment prior to treatment. Conclusions: 4D‐CBCT is a valuable imaging tool in patient setup. Physician review of contour‐based registration is imperative in preventing a geometrical miss. Caution must be employed in tumors that exhibit a large degree of motion. Further research is necessary in determining functional limits of the 4D‐CBCT system.
SU‐E‐J‐05: Validation of an Iterative Tomosynthesis Algorithm for Low Dose on Board Cone Beam CT Patient Localization
Authors: Izaguirre EW , Price SG , Yang D , Rangaraj D
Published: June 2012

Purpose: Cone beam CT (CBCT) is a well established technique to localize patients using bone and soft tissue anatomy. Current protocols are limited to one weekly CBCT due to the considerable imaging dose delivered to the patient. The purpose of this project is to develop and validate a low dose CBCT algorithm to reduce dose and imaging time of current 3D imaging localization procedures using a novel iterative tomosynthesis algorithm to allow daily CBCT for patient positioning and target localization. Methods: The algorithm is based on the combination of a tomosynthesis filtered back propagation (TFBP) acquisition geometry algorithm and a maximum likelihood expectation maximization (MLEM) iterative reconstruction. Circular or arc acquisition trajectory, projection number, and angular projection position are optimized according to the anatomical treatment site and region of interest. The TFBP method provides the first 3D image estimate, and the MLEM improves its quality. In this study, we focused on head and neck treatment localization imaging. Results: We studied the performance of our tomosynthesis algorithm imaging resolution on an anthropomorphic head and neck phantom to determine image quality as a function of dose reduction techniques. Reconstructed anatomy shows that a 1/8 dose reduction provides similar image quality and resolution as current CBCT protocols. Seven iterations show an optimal compromise between image quality and reconstruction time. Tomosynthesis images provide digitally reconstructed radiographs with similar resolution and contrast as full CBCT. We verified that the iterative process eliminates phantom images originated by the acquired sparse angular data projections. Conclusions: We developed and validated an iterative algorithm for low dose cone beam CT based on circular or arc tomosynthesis geometries and iterative reconstruction techniques. The algorithm combines the strengths of both techniques to provide a novel low dose method to image patient anatomy for patient positioning and target localization.
SU‐E‐J‐07: Image Guided Radiotherapy for Prostate Cancer: To Shift Or to Re‐Plan?
Authors: Ma C , Shan G , Hu W , Xu Q , Mohamed I , Fan J , Chen L
Published: June 2012

Purpose: Advanced imaging techniques have been developed to facilitate patient setup and target localization for advanced prostate radiotherapy. These techniques work well for translational, interfractional organ motion but may Result in poor target coverage for some cases where the effects of rotational motion and organ deformation are not corrected. This work investigates the feasibility of the use of 3D dose distributions to match the target volume to improve target coverage and critical structure sparing. Methods: Fifteen previously treated prostate patients were selected for this retrospective study. Siemens CT‐on‐rails scans were performed before and after the IMRT treatment weekly. Ninety‐eight post‐treatment CT‐on‐rails scans were used to reconstruct the dose distributions. The isodose distributions and DVH were compared with those of the original plans. Target localization was also performed using the prescription isodose surface from the original plan to match the target volume and a new isocenter shift was applied in the dose reconstruction, which was evaluated against the original plans and the reconstructed dose distributions using the standard contour‐based target‐localization technique. Results: The results show that for contour/anatomy matching, 7.1% of the 98 treatment fractions exhibit poor target coverage (Dmin<65Gy). For the rectum, 27.6% fractions violated our rectal criterion of V65<17% and 26.5% fractions violated the criterion of V40<35%. After the isocenter realignment based on 3D dose/target volume matching, all the fractions delivered >65Gy to the target, and the percentages of fractions that violated the rectal criteria (V65<17% and V40<35%) were reduced to 14.3% and 18.4%, respectively. Conclusions: The current IGRT procedure for isocenter alignment based on contour/anatomy matching is not ideal due to poor soft‐tissue contrast, residual translational/rotational organ motion and organ deformation. Target localization based on 3D dose/target volume matching provides better target dose coverage and critical structure sparing that reduces the need for adaptive re‐planning.
SU‐E‐J‐12: Initial Clinical Experiences in Using 4D‐CBCT as Image Guidance for Lung SBRT
Authors: Peng C , Chapman K , Lu B , Werner‐Wasik M , Yu Y
Published: June 2012

Purpose: The authors started to use Symmetry 4D‐CBCT as image guidance for lung SBRT in August 2011. Here the authors present the initial clinical experiences with this novel image guidance technique. Methods: In total 118 4D‐CBCT scans have been acquired for 17 lung patients among which 15 received SBRT and the other 2 received hypofractionated treatments. 4D‐CBCT scans are acquired with Elekta XVI 4.5 usingSymmetry, a procedure module in XVI that acquires 4D‐CBCT, registers daily images to reference 3D‐CT and generates shifts for patient setup. Results: Typical thoracic 4D‐CBCT scans with Symmetry take 3 minutes with a 200 degree gantry rotation. Symmetry automatically sorts images into 10 phases based on automatic detection of diaphragm position. Then Symmetry generates two independent intensity‐based registrations, one according to a pre‐defined large volume of interest including the tumor, surrounding tissues and bony structures, the other only according to an expanded target volume. The registrations are obtained by registering each phase image to the reference image and averaging across all phases in a time‐weighted manner. Eventually Symmetry provides users the freedom to pick either one of the two registrations, a compromise, or a manual tuning. Compared to regular 3D‐CBCT, 4D‐CBCT enables physicians to visually place the moving target in the center of PTV, greatly reducing the probability of missing target due to respiratory motion, thus enables possible reduction in PTV margin. 4D‐CBCT also provides the ability to repeatedly evaluate the quality of ITV. It is possible that ITV does not fully cover the tumor motion due to a low quality 4D‐CT simulation for a patient with difficulties in regular breathing. Conclusions: 4D‐CBCT is a superior image guidance technique for lung SBRT treatments for its ability to visualize moving target. It provides physicians more confidence in tumor targeting and ability to repeatedly evaluate ITV quality during the treatment course.
SU‐E‐J‐19: How Should CTV to PTV Margin Be Created ‐ Analysis of Set‐Up Uncertainties of Different Body Parts Using Daily Image Guidance
Authors: Zhou G , Xu S , Yang Y , Yang D , Xie C , Yin L , Zhang H , Liu A
Published: June 2012

Purpose: The objective for this study is to systematically evaluate how the CTV to PTV margin should be created to compensate for setup error as afunction of treatment site. Methods: A total of 1757 setup MVCT images were analyzed using the registration between the MVCT and planning KVCT images. Among them, 526 images were from patients with head and neck cancers; 342 were from thoracic site; 447 from upper abdomen and 442 from patients treated at pelvic region. The correction was shifts in 3 directions from setup with skin marks to final treatment position due to volumetric image registration. Registration was based on soft tissue anatomy when tumor was visible in both KVCT and MVCT. Otherwise, bony landmarks were used when tumors could not be identified. Results: The anterior to posterior (A/P) direction requires the smallest correction for all body sites. The percentage of treatment with < 3mm set‐up correction in A/P direction was 82.4%–96.0% for all disease sites. In medial to lateral direction (M/L), that number was 51.5%–74.7%. The largest set‐up correction occurred in the superior to inferior (S/I) direction. As a function of the body site, 68.6% of head and neck patient had <3mm shift in the S/I direction. However, that number dropped to 41.8%ã€ 42.5% and 31.9% for thoracic, upper abdomen and pelvic sites respectively. In addition, 48.0% of pelvic tumor required >5mm shift in the S/I direction. For thoracic and abdominal tumors, there were still 34.9% and 30.7% of the treatments where >5mm shift in the S/I direction was needed. Conclusions: Uniform expansion margins in all directions are often used in radiation oncology practice. Our study showed setup error was directionally dependent. Therefore, non‐uniform margin should be applied. Smaller margin can be used in A/P while larger expansion needs to be given in the S/I direction.