bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐127: Evaluation of Displacement Force, Image Artifact and Heating of the Envoy Medical Esteem System at 1.5 and 3 Tesla
Authors: King D , Gorny K , Cole Y , Glumac D , Felmlee J
Published: November 2011

Purpose: In March 2010, the US Food and Drug Administration (FDA) approved the first fully implantable hearing device, Esteem Implantable Hearing System (Envoy Medical Corporation, St Paul, MN), for use in patients with moderate to severe hearing loss. With the FDA approval, MRI scanning of patients with these devices is expected to become part of routine clinical practice. The purpose of this work was to investigate interactions between the Esteem system and MRI environment, at 1.5T and 3T, and provide the characterization of the device within the framework of standards established by American Society for Testing and Materials (ASTM). Methods: All tests were performed on the clinical 1.5T and 3T MRI Scanners (Signa Excite, GE Healthcare, Milwaukee, WI, running 14.0 M5 software) using the body coil to transmit RF power. The following characteristics were tested: magnetically‐induced displacement force, RF‐ induced heating near the implant, and MR image artifact. The Esteem® hearing implant consists of three main components: the driver, sensor and sound processor (weight 1.4g, 1.3g and 22.3g, respectively). Characteristics of all components were tested individually. Results: The screening test using the handheld magnet did not show any attraction when any of the device components (sound processor, driver and sensor) were tested. Deflection angles for each component were all measured to be less than 45 degrees (12.3 degrees or less at 3T, 5.3 degrees or less at 1.5T) indicating that the deflection force was significantly weaker than the force on the implant due to gravity. No significant RF‐induced heating of the implant was observed during MRI scanning at both field strengths. Artifact analysis conducted showed that appreciable artifacts were present and are a consideration for MR imaging near this implant Conclusions: The device was found to be safe for clinical MRI scanning using 1.5T and 3T MRI systems evaluated.
SU‐E‐I‐136: MR Imaging Techniques with Reduced Metal Artifact for Improved Brachytherapy Device Visualization
Authors: Warner L , Kotys‐Traughber M , Blume U
Published: November 2011

Purpose: Applicators and seeds for brachytherapy composed of metal have very short T2/T2* species, that induce severe susceptibility artifacts in the surrounding tissue with conventional MR imaging turbo spin echo (TSE) methods, making accurate dose planning and treatment assessment difficult. Nevertheless, recent advances may facilitate imaging of these short T2/T2* species and simplify the current workflow. We propose to use these techniques for improved visualization of brachytherapy devices using MRI. Various imaging strategies for metal artifact reduction, such as an ultrashort echo time (UTE), slice encoding for metal artifact correction (SEMAC), view angle tilting (VAT), and multi acquisition variable resonance image combination (MAVRIC) were investigated. Methods: The tandem from an MR‐compatible FSD‐style applicator set (Varian Medical Systems, Palo Alto, CA, USA) was embedded in 20% gelatin. Scanning was performed on an Achieva 3.0T TX system using a 16 element phased array coil (Philips Healthcare, Best, NL). Images were acquired along the plane parallel to the tandem axis. Sequences parameters are summarized in Table 1. Studies were repeated for a gold seed embedded in 20% gelatin and seed dimensions quantified by the profile image full width half maximum along longitudinal and transverse seed axes. Results: The SEMAC sequence imaged the tandem tip exceptionally well, Figure 1. The gold seed was distinctly visible with all sequences, Figure 2, and the SEMAC dimensions were closest to the true dimensions. Conclusions: All investigated sequences outperform conventional TSE imaging. Overall, the SEMAC sequence is timely (6x< MAVRIC) with superior metal artifact reduction, and the UTE sequence is ideally suited for quick survey scans and may be useful for distinguishing seeds. MAVRIC has the greatest SNR, but requires long scan times. Although VAT limits in‐plane metal artifact, it is poorly suited for brachytherapy planning. Therefore, the use of a SEMAC sequence is beneficial in brachytherapy planning.

I have the following conflict of interest to disclose with regard to the subject matter of this presentation: Company Name: Philips Healthcare, Type of Relationship: Employer
SU‐E‐I‐148: New Way for Calculating the Average Glandular Dose in the Mammography
Authors: Penchev P , Schopphoven S , Smirnov A , Bock K , Fiebich M
Published: November 2011

Purpose: According to the national regulations the absorbed dose to the breast tissue must be calculated and protocolled. Correct and individual calculation would allow right assessment of the additional risk and the comparison of the different mammography units. The current procedure for calculating the average glandular dose (AGD) relays on the right multiplication of three different tabulated conversion factors and implies measurement of the HVL. Method and Materials: To calculate the conversion factor, which relays the incident air kerma to the absorbed dose in the sensitiver glandular tissue, we used the Monte Carlo simulations software EGSnrc. In it no electrons were transported and the photons were followed down to 1 keV. The photons cross section data was taken from XCOM. The breast was simulated as a D‐shaped mathematical model. It consists of 5 mm outer region made of 100% adiposal tissue. The inner region was made of five different mixtures of adiposal and glandular tissue. Six different breast thicknesses from 2 cm to 6 cm were investigated. Five different anode/filter combinations (Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag) and for each three different energies were used. Results: Conversion factors were calculated for each anode/filter combination, x‐ray tube potential, breast thickness and breast composition. Through the means of regression analysis for each anode/filter combination a general function was proposed. It has as an input the potential, breast thickness and glandularity and returns one conversion factor, which is to be multiplied with the incident air kerma to calculate the AGD. The error due to this method is less than 1%. Conclusions: An individual calculation of the AGD is possible. For each patient we consider only one conversion factor and not a combination of three. We do not need tabulated values. This method represents an easy and straightforward way of calculating the AGD.
SU‐E‐I‐151: Performance Evaluation of a New Commercially Available Portable Pixelated Gamma Camera for 99mTc‐Scintimammography
Authors: Kappadath S Cheenu , Siman W
Published: November 2011

Purpose: To characterize the imaging performance of a pixelated gamma camera (Ergo, Digirad) for 99mTc‐scintimammography. Methods: The 31×40cm̂2 Ergo detector consists of 6mm thick 3.31×3.24mm̂2 CsI(Tl) crystals coupled to silicon photodiodes. The sensitivity and resolution was measured according to NEMA NU 1‐2007. Scintimammography performance was evaluated as hot tumor detection capabilities. We acquired images of different 99mTc‐spheres (inner diameters 3.95, 4.95, 6.23, 7.86, 9.89, 12.43mm) suspended in a 6.6cm thick 500mL 99mTc‐water bath. Images were acquired at tumor depths of 1.7 and 3.7mm with different sphere‐to‐background ratios (SBR: 5.0, 8.0, 10.1, 12.5, 18.8) for 10min acquisition using low‐energy collimation (LEHR). Acquisitions for 10, 5, 2.5, 1.25min were performed at SBR=5 where the 99mTc‐activity concentration (uCi/mL) in spheres/background was 34/6.8. The sphere‐CNR was estimated as: Sphere‐CNR = (SphereCounts_Max ‐ BackgroundCounts_Mean)/ BackgroundNoise. BackgroundNoise was the average standard deviation of 10 different 9‐pixel ROIs distributed across the image. BackgroundNoise was modeled as a power‐law function of BackgroundCounts_Mean and used to predict the sphere‐CNR at different activity levels and acquisition times. A preliminary visual assessment of sphere visibility was used to establish the threshold‐CNR for detection. Results: The sensitivity and resolution at 10cm using LEHR was measured to be 128cpm/uCi and 7.5mm. BackgroundNoise was found to vary as BackgroundCounts_Mean̂−0.67 suggesting a Poisson noise dominated imaging system. Threshold‐CNR of ∼8 corresponded to visible spheres. For SBR=5, depth=3.7cm, acquisition=10min, the measured sphere‐CNR for diameters 6.23, 7.86, 9.89, 12.43mm were 12.1, 15.9, 22.8, 33, respectively; that decreased to <3, 6.6, 10.1, 14.6 for acquisition=2.5min. The CNR predicted by the power‐law model for BackgroundNoise was in good agreement (differences of 9‐26%) with measured sphere‐CNR at lower acquisition times. Conclusions: The Ergo system is suitable for 99mTc‐ scintimammography with predictable performance at different imaging conditions. Small tumors (<1cm) could be visualized at a range of SBR under tested conditions.
SU‐E‐I‐155: Esophageal Squamous Cell Carcinoma: Relationship Between 18F‐FDG PET‐CT Maximum Standardized Uptake Value, Metabolic Tumour Volume and TNM Classification
Authors: Zhu W , Sun X , Xing L , Yue J , Qu W , Yu J
Published: November 2011

Purpose: The prognosis for patients with esophageal squamous cell cancer depends on the complex interplay of TNM classifications as well as nonanatomic factors, including histopathologic cell type, histologic grade and cancer location. Few reports have discussed the relationships of both MTV and SUV max measured by PET/CT and stage in esophageal cancer, especially which classified by the last edition staging system. We aimed to evaluate the relationships between primary tumour maximum standardized uptake value, metabolic tumour volume and 7th edition American Joint Committee on Cancer (AJCC) classification in esophageal squmous cell carcinoma (ESCC) patients. Methods: Fluorine‐18 fluorodeoxyglucose positron emission tomography‐computed tomograhy (18F‐FDG PET/CT) scans of 41 consecutive newly diagnosed ESCC patients were retrospectively reviewed. Maximum standard uptake value (SUV max) and metabolic tumour volume (MTV) were recorded. Two‐tailed spearmanˈs correlation was used to analyse the relationships between the metabolic parameters and AJCC stageing system. Results: Positive correlations were observed between SUVmax, MTV and N stage stage (P=0.002, R=0.477; P<0.001, R=0.563) in additon to AJCC stage (P=0.002, R=0.460; P<0.001, R=0.539). Both metabolic parameters were independent variables that significantly affected N stage and AJCC stage by the multiple analysis (P<0.001, adjusted R2=0.348; P=0.002, adjusted R2=0.238), and only SUVmax was independent variables that sinificantly affected T stage (P=0.003, R=0.459; P=0.004, adjusted R2=0.464). Conclusions: The metabolic parameters derived from 18F‐FDG PET/CT were positively correlated with T, N and AJCC stage in primary ESCC. Our findings may suggest a complementary role of these parameters to last 7th edition AJCC staging in prognostication of ESCC patients.
SU‐E‐I‐161: Quantifying the Viscoelastic Properties of Human Hepatic Malignancies Using Dynamic Compression Testing
Authors: DeWall R , Bharat S , Varghese T , Hanson M , Kliewer M
Published: November 2011

Purpose: Manual palpation is often used to qualitatively assess the presence of diseases because of known correlations between tissue stiffness and pathological state. Ultrasound elastographic techniques provide an objective form of palpation and include strain imaging, acoustic radiation force imaging (ARFI), and transient elastography. However, tissue compression can affect tissue stiffness estimates. In this study, we dynamically compress several different hepatic malignancies through a range of compressional loads to determine the effect of strain hardening on modulus estimates and modulus contrast.Methods: Fourteen hepatic tissue samples with various pathologies were obtained from the UW Pathology lab from patients undergoing surgical resection. Among them were hepatocellular carcinomas (HCCs; n=2), colon metastases (METs; n=7), rectal METs (n=1), gastrointestinal (GIST) METs (n=1), neuroendocrine METs (n=1), and cirrhosis (n=2). Samples were dynamically tested using an Enduratec ELF 3220 (Bose Corp., Minnetonka, MN) from 1 to 6% precompression at 1, 10, 20, and 30 Hz.Results: The storage modulus, a measure of the elastic energy stored each compression cycle, was quantified for pathological and normal tissue. The average storage modulus for normal tissue tested at 1% compression and 1 Hz was 3.3 kPa. The storage moduli for pathological tissue were 3.5, 23.1, 30.9, 4.3, 3.9, and 13.7 kPa for HCCs, colon METs, rectal METs, GIST METs, neuroendcrine METs, and cirrhosis, respectively Conclusions: These results show the effects of strain hardening on normal and pathological human liver tissue. Some cancers were significantly stiffer than the surrounding background, indicating that elastographic techniques may be useful in delineating the pathology. Some cancers, such as HCCs, were approximately the same stiffness as the surrounding background. Strain hardening observed with some cancers suggests that compression may increase contrast between the cancer and the surrounding tissue.

This work is supported by NIH grants R01 CA112192‐04, R01 CA112192‐ S103, and T32 CA09206‐31.
SU‐E‐I‐162: Quantitative Analysis of Human Soft Tissue Using Grating‐Based X‐ Ray Phase Contrast
Authors: Herzen J , Willner M , Hahn D , Schleede S , Bech M , Noël P , Sztrókay A , Bamberg F , Zanette I , Weitkamp T , Pfeiffer F
Published: November 2011

Purpose: In the last decade, grating‐based x‐ray phase‐contrast imaging was developed as a novel and very promising imaging modality. It is demonstrated to not only significantly increase the soft tissue contrast compared to conventional absorption‐ based imaging, but also to provide quantitative information about the tissue. In this work we report on the results of our study to determine quantitative CT numbers in phase contrast (corresponding to Hounsfield Units (HU) in absorption CT) for various healthy and cancerous human soft tissue, and to correlate these numbers to the HUs in absorption contrast. Methods: The study concentrates on two types of human soft tissue, breast and liver tissue, as the imaging of theses tissue types is already a great demand on the conventional absorption CT. The specimens are fixated in formalin and analyzed tomographically with grating‐based imaging at a synchrotron radiation source. This benchmarking study used monochromatic synchrotron radiation to ensure a high accuracy of the measured values. Results: Our study shows that the grating‐based imaging modality significantly enhances the soft‐tissue contrast and allows clearly distinguishing between healthy and cancerous tissue. From the gray values the CT numbers can be calculated directly by averaging over different regions and geometrical corrections, as the values are measured relative to those of water. Conclusions: With this work we demonstrate the potential of grating‐based phase‐contrast imaging to determine quantitative, tissue specific values for human soft tissue. We strongly believe that these results will enhance the quality of the tumor detection in both, human breast and liver, as the tissue‐specific values can directly be used for numerical simulations and optimization of the setup, as well as for phase‐contrast imaging dedicated phantoms design.
SU‐E‐I‐165: Initial Imaging Results with Manganese‐52 PET Tracer
Authors: Topping GJ , Schaffer P , Sossi V
Published: November 2011

Purpose: Initial imaging results with the novel positron emission tomography (PET) tracer Mn‐52 in phantoms are reported. This project aims to develop and characterize Mn‐52 as a PET tracer, and to compare results with manganese‐enhanced magnetic resonance imaging (MEMRI). Methods: Mn‐52 was produced by irradiating natural chromium foil (0.5 mm nominal thickness) with protons (12.5 MeV, 2 μA, 60 min). After 10 hours decay, foil was dissolved in aqueous HCl and placed in phantoms for imaging in a Focus 120 microPET scanner. Energy spectra were acquired by varying the scanner photon energy acceptance window. PET images were acquired with and without surrounding non‐radioactive water, with multiple energy windows. A sample of the dissolved foil solution was measured in a gamma‐spectrometer to measure the produced activity. Results: Irradiation produced approximately 6.1 MBq Mn‐52, with 27 kBq Mn‐54. microPET energy spectra feature significantly higher singles count rates at energies above and below the 511 keV positron annihilation peak (compared with F‐18 or Ge‐68) which are attributed to cascade photons from Mn‐52 decay. Phantoms appear clearly in Mn‐52 PET images, with background structure in images attributed to cascade coincidences, amplified by attenuation correction. Background is reduced or eliminated with tighter energy windows (450–600 keV) than are used for standard F‐18 imaging at our centre (350–750 keV). Scanner dead time correction was below 4% with 3.2 MBq Mn‐52 at the centre of the scanner field of view. Conclusions: Mn‐52 is a potentially valuable PET tracer, with some challenges to achieving good quantification. Future work will include testing cascade coincidence correction methods, additional phantom imaging for resolution and image quality, and in vivo imaging studies to characterize and compare with MEMRI.
SU‐E‐I‐170: Improvement of Quantification for Tumors with Non‐Uniform Activity Distributions: SPECT Simulation Study
Authors: Shcherbinin S , Celler A
Published: November 2011

Purpose: We examined the ability of a template‐based method for partial volume effect correction (PVEC) to improve activity distributions inside tumors. Methods: We simulated oncology SPECT scans with an 80mL cylindrical object representing the tumor. This object was divided into two parts filled with different activities. In total, three cases with different activity ratios in those parts were considered and, correspondingly, the spill‐ in and spill‐out between (i) tumor/background and (ii) parts of the tumor were modeled. We assumed that a structural imaging modality could be used to visualize the boundaries of our tumor‐like object, but not the internal boundary between the parts of the object. From simulated SPECT acquisitions, we first reconstructed images by method M1 with corrections for attenuation, scatter, and resolution loss, portraying the most advanced reconstruction currently available in clinics. Secondly, we applied our PVEC technique M2, which iteratively updates activity both inside and outside the delineated tumor. This method takes into account that not only is the tumor affected by spill‐out, but also the surrounding background is affected by spill‐in. Results: Our PVEC effectively corrected for the partial volume effect by accurately modeling spill‐in and spill‐out through known “external” boundaries of the tumor‐like object. In three considered cases, method M1 underestimated total activities in tumors by 5–21%. After applying PVEC, these errors ranged from 8% to 12%. Additionally, method M2 improved the activity distribution. The relative error of the voxelized tumor activity distribution was 21–26% for method M1 and 11–17% for method M2. However, as the borderline between tumor parts was unavailable, accurate restoration of activity in this zone could not be performed. This limitation becomes more pronounced as the ratio of activities in these two parts increases. Conclusions: Template‐based PVECs can considerably improve not only the total activity, but also vozelized activity distributions in tumors.
SU‐E‐I‐173: Factor Analysis with Prior Information Using Projected Gradient Method — Application to 11C‐DTBZ Dynamic PET Dataset for Early Detection of Parkinsonˈs Disease
Authors: Lee D , McEwan A , Robinson D , Jans H , Martin W , Wieler M , Riauka T
Published: November 2011

Purpose: To apply factor analysis technique to a sequence of 11C‐DTBZ dynamic PET images to healthy and diseased subjects in order to extract factor curves (or time activity curves) and associated factor images and develop a metric to detect extent of Parkinsonˈs disease. Methods: Philips Gemini (C) PET/CT scanner (with 4mm isotropic voxels) is used to collect a dynamic dataset consisting of a time sequence of 16 frames (with unequal temporal spacing) of the brain from healthy and diseased subjects. Several image preprocessing techniques (e.g. noise reduction using singular value decomposition, voxel‐averaging) are used on these dynamic datasets prior to implementing factor analysis using projected gradient method in the framework of non‐negative matrix factorization to extract physiologically meaningful structures. A priori information (region‐of‐interest based time activity curves) is used to warm start the optimization process in order to reduce the number of possible solutions. Results: The factor analysis technique separates each dynamic dataset into two time‐dynamic factors — one factor represents the striatum (directly related to the disease) while the other factor represents the non‐striatum tissues. The factor curves and images related to the former show clear difference in the tracer uptake among the healthy and diseased subjects. Our metric, which relies on such difference, indicates that the tracer uptake in striatum tissue for the healthy subject is roughly four times higher than that of the diseased subject. Conclusions: This study suggests that the technique can decompose large dynamic datasets into parts‐based images (or volumes) that represent the underlying physiological structures, and has the potential to significantly aid in the review process for evaluating dynamic datasets by clinicians. The technique is not limited to dynamic PET images and can be applied to any sequence of dynamic images.
SU‐E‐I‐178: Spatial Analysis of PET Images Using 3D Moment Invariants (3DMI)
Authors: Gonzalez M , Sossi V , McKeown M , Dinelle K , Vafai N
Published: November 2011

Purpose: We propose to characterize the spatial distribution of PET‐derived voxel statistics within anatomically‐defined Regions Of Interest (ROIs) as a means to characterize disease‐related changes. Methods: We used 3D moment invariants (3DMIs) to characterize the spatial distribution of PET data ([11C]Raclopride, [11C]Tetrabenazine and [18F]Fluorodopa) recorded from subjects with Parkinsonˈs Disease (PD) and healthy controls. 3DMIs are mathematical spatial descriptors designed to be invariant to scaling, translation and rotation. In fMRI studies, assessing the spatial characteristics of voxel‐based statistics has recently been shown to utilized be a powerful and sensitive method to characterize brain activation. Crucially, this allows characterization of the spatial characteristics of activation without the need to warp brain images to a common brain template. Analogously, we propose characterizing the spatial distribution of PET‐derived voxel statistics within anatomically‐defined ROIs using 3DMIs. The 3DMIs used here were a combination of terms describing spatial variance, skewness and kurtosis. Subjects also underwent MRI scans so that the T1‐weighted MRI data could be used to anatomically delineate basal ganglia ROIs to act as binary masks on the PET data. Results: 3DMIs were found to accurately describe the “3D texture” of PET images despite changes in the size and orientation of these regions across subjects. In addition, we were able to find differences in the 3DMIs of PD patients distinct from those of healthy volunteers. These changes suggest that disease‐related variations in the spatial distribution measured using PET can be quantitatively described with the proposed method Conclusions: This method shows great promise to extract additional information from PET data with a wealth of potential applications to disease diagnosis, staging, treatment assessment and more. The quantification of the observed disease‐related changes for PD subjects is currently under way.
SU‐E‐I‐181: Calibration of the Relation between Signal‐To‐Background Ratio and Threshold SUV Maximum on a Gemini TF PET‐CT
Authors: Vicedo A , Granero D , Garcia‐Hernandez T , Rosello J , Brualla L , Pamos J , Sanchez R , Ferrer‐Rebolleda J
Published: November 2011

Purpose: The use of PET‐CT to delineate target volumes in radiotherapy planning is extending nowadays. Volume determination from functional imaging is not a forward step, nevertheless many methods have been proposed for automatic tumour determination. The aim of this study is to determine the threshold of SUV maximum which best fits the CT volume taking into account the signal‐background ratio (SBR). This method has been previously established, but depends on camera properties and reconstruction algorithm which justifies the new calibration when a camera is acquired. Methods: Our institution is equipped with a high‐performance, time of flight (TOF) Gemini TF PET‐CT from Philips. A NEMA torso phantom filled with six spheres ranging from 0,5 ml to 26,5 ml was used to generate the relation between the threshold SUV maximum and the SBR. Signal‐to‐background ratios from 1.5 to 11 were used. Images were reconstructed using the TOF information with a 3D OSEM algorithm. Results: The relation between the threshold SUV and the SBR for the different lesions fits an inverse first order function (y = 0.37 + 0.47 * (1/SBR)) with a r= 0.95 for the larger lesions. To validate these results the phantom was filled to get a SBR of 3 and 6, and lesions were delimited applying the threshold determined in the above expression (52% for a SBR of 3 and 44% for a SBR of 6), an overestimation for the larger lesions was found. For the smaller lesions, the change in the threshold is very dependent on the lesion size for a given SBR, making necessary to know the size of the lesion in advance. Conclusions: The relation between the SBR ratio and the threshold of the SUV maximum has been calibrated For larger lesions a useful threshold has been found for each SBR which agrees with previous studies.
SU‐E‐J‐57: Clinical Protocol for DTS‐Based APBI Setup: Optimal Data Acquisition, Reconstruction and Registration Parameters Using Varian DTS Software
Authors: Ng SK , Lyatskaya Y , Hesser J , Jeung A , Mostafavi H , Bellon J , Wong J , Zygmanski P
Published: November 2011

Purpose: Digital tomosynthesis (DTS) was evaluated as an alternative to CBCT for minimizing possibility of collisions and reducing imaging dose. While feasibility of DTS was demonstrated for APBI patient setup, clinical implementation has not been optimized for this technique. This work characterizes data acquisition/registration parameters and establishes clinical protocol for accurate setup using: Varian OBI system for data acquisition; and non‐clinical Varian DTS software for DTS reconstruction/registration for APBI patient setup. Methods: Backprojection‐and‐deblurring algorithms were used for DTS volume reconstructions. DTS volume registrations were done manually and automatically (cross‐correlation). Subsequent triangulation on two short DTS arcs was done to improve registration accuracy. Software performance was evaluated on a breast phantom and nine breast cancer patients, under an IRB‐approved protocol. Parameters investigated include arc lengths, arc orientations, number of arcs, reconstruction slice spacing and other limiting factors relevant to clinical practice. Shifts determined from the registration of DTS volumes were compared to the shifts based on registration between planning CT and CBCT. The difference between these shifts was used to evaluate the software performance and accuracy. The findings were quantified and optimal parameters for clinical use of DTS technique were determined. Results: At least two arcs were necessary for accurate setup evaluation. Registration accuracy of 2 mm was achieved when reconstruction arc length was > 5 deg for clips with HU>1000; larger arc length (> 8 deg) was required for low HU clips. Optimal arc separation was found to be > 20 deg. Optimal arc length was determined to be 8–10 deg. No dependence on DTS slice spacing was found. Time required for DTS reconstruction was 10s– 45 s and it was less than 20s for registration. Conclusions: Optimal data acquisition/registration parameters were determined for DTS imaging utilized for APBI patient setup, and performance of the software was objectively quantified.

This study is supported by grant from Varian Medical Systems Inc. and Kayes grant
SU‐E‐J‐59: GPU‐Based Interactive Multi‐Volume Visualization in Radiotherapy Treatment Planning
Authors: Zhuge Y , Xie H , Ning H , Cheng J , Arora B , Han‐Oh Y , Miller R
Published: November 2011

Purpose: To develop a GPU‐based interactive multi‐volume visualization program in radiotherapy treatment planning (RTP) which is able to show the spatial relationships between patient anatomical data and radiation dose distribution. Methods: The radiation dose matrix is extracted from commercial RTP systems such as the Eclipse from Varian Oncology Systems (Palo Alto, CA, USA) and the Hi‐Art from the TomoTherapy Incorporated (Madison, WI, USA), and is then co‐registered with the CT volume such that all three volumes of CT data, dose distribution, and segmented radiotherapy structures share the same geometry, resolution, and position, and show no rotation against each other. A GPU‐based multi‐volume ray casting technique is developed by using NVIDIAˈs CUDA framework for simultaneously volume renderings of patient anatomy data and radiation dose distribution. The program is executed on an NVIDIA Tesla C1060 computing processor. Each ray emitted from view point is independently processed by a thread on GPU. The ray transverses both volumes and the visual contributions are mixed for every sample points. Results: The program has been tested on brain tumor patient data and lung tumor patient data. High quality volume rendering of patient anatomy and dose distribution has been generated interactively. The performance of 8 FPS has been achieved for patient data size of 512×512×188, and view window size of 512×512. Conclusions: A multi‐volume visualization program in RTP has been developed on GPU. The program offers visualization through interactive volume rendering of patient anatomical data and radiation dose distribution. The program can be used to improve the understanding of the spatial relationships between patient anatomical data and radiation dose distribution.
SU‐E‐J‐63: Discrete‐Event Simulation Modelling to Improve Radiation Therapy Planning Process
Authors: Oddiraju S , Mutic S
Published: November 2011

Purpose: Inadequate scheduling of RT treatment planning can result in underutilization of resources or, more importantly, in creation of bottlenecks and potentially hazardous situations. In this study we evaluate a method for design of robust and efficient RT planning processes through the use of discrete event simulation (DES) and a novel system for collection of real life planning statistics. Methods: DES is used to model systems which evolve over time by representation of state variables which change instantaneously at separate points in time. As such, DES is very well suited for modeling of RT operations. In this study, we use commercial DES software (ARENA, Rockwell Automation, Inc.). The software allows detail representation of clinical RT workflows and it also enables inclusion of typical RT resources and constraints. The RT planning model requires data describing the patient arrival process, typical task times, percentage of rework and the resource availability. To facilitate collection of real life data, we designed an electronic white board system which automatically captures relevant clinical statistics. The system requires minimal input by staff and the majority of data is collected through routine clinical activities. This design facilitates high compliance and accuracy of collected data. Results: The whiteboard system enabled efficient collection and analysis of real life clinical performance data. The Arena model was able to identify failures and delays in planning process and their propagation through the system. The model allowed estimation of the failure probabilities at different stages in the planning process and their impact on the overall system. In addition, the model facilitated investigation of the effects of workflow alteration and patient load on the system performance, and identification of optimal system design schemes. Conclusions: The proposed method can be used for improvement of safety, quality, and efficiency of RT operations.
SU‐E‐J‐65: Order of Magnitude Reduction of Radiation Exposure in Fluoroscopically Guided Interventional Procedures
Authors: Rowlands JA , Robert N
Published: November 2011

Purpose: The role of fluoroscopic imaging is important and expanding for diagnostic and image guided therapy application. However, fluoroscopic imaging requires significant amounts of radiation leading to increased risk of cancer induction as well as non‐stochastic effects such as radiation burns. Our purpose is to reduce the exposure and dose to the patient by an order of magnitude by the simultaneous application of previously established methods in a manner which alleviates the shortcomings of each. Method and Materials:Pulsed fluoroscopy can reduce dose and exposure rate by replacing a 30 frame per second sequence by a 15 or 7.5 frames per second rate, but the unnatural jumpy nature of the reduced update rate disturbs the natural eye/brain comprehension of the image sequence. Region of interest fluoroscopy is where the central region of the image has full exposure and the peripheral image, there to provide context only, has been reduced in dose. It has been shown in several studies to reduce exposure rate and dose to the patient by an interesting but not compelling amount of ∼2 times. The scientific reason for this unimpressive result is the very poor DQE(0) of flat panel imagers at low exposure rates. Results: A newly designed collimator which permits the exposure of only the region of interest to be inserted or removed between images at the 30 frame/second rate used in real time imaging has permitted a new approach to ROI imaging where the peripheral image can be obtained at very low frame rates and hence low total exposure while the central region can be obtained at full frame rate and normal exposure rates. Conclusions: A practical technical solution to reduction of exposure and dose during fluoroscopic procedures has been identified and tested.

IKON Inc. have agreed to provide prototype ROI collimators for use in this work at no cost to the authors.
SU‐E‐J‐66: Improvement in SRS Commission and Patient‐Specific Quality Assurance
Authors: Ding M , Heard D , Ma C
Published: November 2011

Purpose: A linac‐based SRS system with a stereotactic mask was implemented. This work aims at selecting a proper detector for small‐field beam commissions, setting up a specially designed phantom for patient‐specific plan QA, and validating the dosimetric accuracy of SRS plans based on the Varian MLC‐120 and BrainLAB cones.Methods: Four different detectors — diode, micro ion chamber, IBA chamber, and Farmer chamber, were evaluated for small field commissioning. PDD, profile, and output measurements of fields from 5×5mm to 150× 150mm were compared and discussed. A micro‐chamber was selected based on its good spatial resolution (0.016cc sensitive volume) and higher stability and sensitivity (3 and 1.5 times greater, respectively, than a diode). To reduce measurement uncertainties, both PDD and profile scans were iterated (more iterations were used for smaller fields) and summed up using commercial software. The shift of reference‐field readings was within 0.3% during the output measurements. A Lucy phantom was set up in the SRS frame and CT scanned. Treatment plans were mapped to the CT image and measured with a calibrated micro‐chamber. The implemented SRS system was validated by comparing the planned and measured doses for targets with different volumes and shapes.Results: For a typical SRS target (1.26cc), the dose differences were 0.71% for a dynamic arc/MLC plan and 0.75% for an arc plan using a 20mm cone. For a small and spherical target (0.50cc), the differences were 2.13% for a dynamic arc/MLC plan and 0.17% for an arc plan using a 15mm cone. For a very small and irregular target (0.35cc), the differences were 2.60% for a dynamic arc/MLC plan and 4.72% for an arc plan using a 10mm cone Conclusions: Considering its dosimetric accuracy for different targets and the availability of a safety‐interlock, MLC based SRS treatment is highly recommended.
SU‐E‐J‐72: In Vivo Quality Assurance of Head and Neck Cancer IMRT Treatments Using TomoTherapyˈˈs Exit Detector Data
Authors: Goddu S , Rodriguez V , Gay H , Yang D , Ramirez J Garcia , Yaddanapudi S , Mutic S , Thorstad W
Published: November 2011

Purpose: The primary objective of this study was to explore the feasibility of utilizing the exit‐detector‐data (EDD) for in vivo quality assurance of head and neck (H&N) cancer patient treatments. Methods: Using TomoTherapyˈs Delivery‐Verification (DVS) software we retrospectively evaluated treatments (53 fractions) of ten H&N cancer patients for dose delivery deviations. MV‐CT scans covering the entire length of treatment volumes and respective EDD files were used for DVS reconstruction and subsequent dose computation on a GPU platform. Differences between planned and reconstructed sinograms were analyzed to evaluate the leaf‐opening time (LOT) differences. Reconstructed dose distributions of fractionated‐deliveries were scaled, convolved to estimate composite dose distributions, and compared against planned dose distributions. The dose summation was strictly based on rigid registrations of the fractionated doses and it did not account for soft‐tissue/dose deformations. Computed DVHs were strictly based on the plannned contours and they did not include anatomical changes, if any. Results: Typical average LOT differences were −3msec‐eq with a standard‐deviation of 8msec‐eq, indicating the integrity of delivered treatments. Although, significant differences were noted for individual reconstructed fraction‐doses, the differences in cumulative reconstructed dose‐distributions were found to be small. Cumulative reconstructed plans show that the minimal dose (D99%) to the PTV was decreased by 1.6±1.4Gy. Average mean doses of the left and right parotids decreased by 1.0±0.6Gy and 0.8±0.7Gy, respectively. The mean dose and volume receiving >60Gy for the upper‐esophagus decreased by 0.7±1.0Gy and 0.6±2.3%, respectively. Overall all the reconstructed doses are lower than the original plans by ∼1.0% and this is consistent with our antropomorphic phantom measurements. Conclusions: The results of study suggest that EDDs are useful for DVS reconstruction and subsequent dose computation and can be a great tool for in vivo quality assurance of clinical H&N cancer treatments. Further studies are needed to account for deformation effects.
SU‐E‐J‐73: Preventing Errors in Radiotherapy: A Real‐Time System Using in Vivo EPID Dosimetry
Authors: Yang Y , Jacques R , McNutt T , Ford E
Published: November 2011

Purpose: In vivo dosimetry using an electronic portal imaging device (EPID) may provide a uniquely effective means for preventing errors and may allow for real‐time beam interlocks. We present graphical processor (GPU)‐based fast EPID dose computation and simulate the sensitivity for detecting errors caused by patient mispositioning. Methods: We implemented an enhanced superposition convolution algorithm to compute the EPID dose. The patient was simulated using a digital cylinder phantom (15cm length and 15cm diameter) with air and bone structure built in. Setup parameters are: SAD 100cm, 12×12‐cm2 open field, 1.5×1.5×1.5‐mm3 dose grid, 6‐MV photon and isocenter at the center of cylinder. 2D dose images were obtained at 1.6‐cm depth of a water slab positioned 60‐cm below the isocenter to simulate the EPID readout. To examine errors caused by mispositioning, we shifted the phantom left‐and‐right and up‐and‐down and compared dose profiles to those with no shifts. Gamma value of each pixel was calculated as an index to identify dose mismatch. Dose failure was determined as gamma > 1 using 3‐mm distance‐to‐agreement and 3% dose difference criteria. Results: Dose failures occur mainly in air‐tissue and bone‐tissue interfaces and in regions with rapid thickness change. Gamma is sensitive to the left‐and‐right shift, with a 3‐mm shift causing dose failure in ∼10% pixels; but is much less sensitive to the up‐and‐down shift, with dose failure detected only after a shift of several centimeters. Analysis with patient CT data sets is underway and will be presented. Conclusions: In vivo EPID dosimetry enabled by GPU‐based dose computation offers the potential for real‐time beam interlocks. Future directions include simulation of other error scenarios, optimization of dose computation, improved EPID modeling and comparison with measured EPID profiles.
SU‐E‐J‐77: Tract Based White Matter Abnormalities in Alzheimer Disease with Diffusion Image
Authors: Juh R , Suh T , Kim S
Published: November 2011

Purpose: White matter (WM) damage has been reported in Alzheimerˈs Disease (AD) and Mild Cognitive Impairment (MCI) in diffusion tensor imaging (DTI) studies. DTI provides microstructural information about WM integrity and coherence by measuring fractional anisotropy (FA) values. The aim of this study was to investigate WM abnormalities in AD based on voxel‐wise comparison with controls and to explore their relationship with cortical atrophy and WM integrity detected by voxel based analysis. Methods: Sixty individuals (20 controls, 20 MCI and 20 AD) with age‐matched underwent DTI and volumetric MRI. Voxel‐based tract based spatial‐statistics was used to obtain whole‐brain maps of WM bundles for FA and mean diffusivity(MD). Voxel‐based morphometry was conducted to detect regions of gray matter (GM) atrophy in the AD, MCI group relative to the control group. FA maps were processed to make voxel‐wise comparison of anisotropy in whole brain between each the two groups. The relationship between locations of abnormalities in the WM and GM were examined Results: Significant reductions in FA were found in the WM of both medial temporal lobes, bilateral superior longitudinal fasciculus, bilateral internal capsules, as well as the WM of left middle temporal gyrus and right superior parietal lobule, the body and genu of the corpus callosum, cingulum, and the uncinate, superior longitudical fasciculus in patients with AD. Although the decrease in FA was consistent with cortical volumetric reduction in both temporal lobes, the widespread involvement of superior longitudinal fasciculus and uncinate fasciculus was dominant in these WM findings. Conclusions: Voxel‐wise comparison of whole‐brain anisotropy revealed widely distributed disintegration of WM in AD. The WM shows a different pattern of degeneration from GM and may be an independent factor in the progress of AD. These results suggest that DTI analysis of WM structural integrity can serve as potential biomarkers of AD progression.
SU‐E‐J‐78: Initial Experience with MR Simulation in Radiation Therapy Using An Open‐Platform MR Scanner: Considerations for Routine Clinical Use
Authors: Nurushev T , Kim J , Hearshen D , Pantelic M , Kotys‐Traughber M , Elshaikh M , Walker E , Chetty I , Movsas B
Published: November 2011

Purpose: To evaluate the considerations associated with use of magnetic resonance imaging (MRI) as a simulation tool in radiation therapy. Methods: A 1.0 Tesla(1T) Open‐platform MRI scanner (Panorama, Philips Healthcare) was used to acquire whole pelvis T1, T2 and 3D bTFE images on 3 prostate cancer patients to define extra capsular involvement. For the MRI setup, a flat table top insert (Civco) and our standard immobilization devices, were used to reproduce patient positioning during treatment. MR images were used in conjunction with CT simulation datasets to define anatomical structures and validate typical treatment planning clinical flow with the goal of using MRI as a stand‐alone modality. Contouring was done on T2 images and validated against T1 and 3D bTFE datasets. Dose calculation on MRI was performed by assigning bulk densities to structures based on average CT intensities (HUs) and compared with CT calculations using heterogeneity correction. Atlas‐based contouring has been investigated to improve on organ‐specific HU representation. Results: Significant differences in organ contours were noted between MRI and CT. For the 3 patients, with MR, reduction in prostate and penile bulb volumes was on average, 25% (max. 36%) and 22% (max. 31%), respectively. Seminal vesicle volumes varied on average by 71% (max. of 202%). MR was found to be especially useful in defining boundaries of the prostate and penile bulb; the latter structure was indiscernible on CT. MRI‐based calculations with assigned bulk densities agreed within 1% of CT‐based planning calculations with heterogeneity correction for all cases. Conclusions: This study confirms the feasibility of using MRI as a sole imaging modality for treatment planning simulation and dose calculations. Significant volume reduction in the PTV based on the MRI images may be beneficial for dose escalation studies, and improved structure delineation affords possible additional dose sparing to surrounding critical organs.
SU‐E‐J‐82: MRI‐Guided Lung Tumor Tracking
Authors: Cerviño L , Du J , Jiang S
Published: November 2011

Purpose: To track lung tumor in cine MR images. Methods: 5 healthy volunteers underwent sessions of a single sagittal‐slice cine‐MRI with image acquisition frequency of 4Hz. A slice with a visible vascular structure (target) was imaged, and the field of view was adjusted so that the diaphragm was visible in all the slices. Volunteers were asked to breathe under 4 different breathing patterns, each one of 5‐minute duration: free breathing; normal inspiration followed by elongated expiration; irregular breathing; and inhale through the nose and impeded exhale through the mouth. Targetˈs location was manually identified in all the frames. Two tracking algorithms were implemented and evaluated: a template matching (TM) algorithm in combination with surrogate tracking using the diaphragm (surrogate was used when the maximum correlation between the template and the image in the search window was less than specified); and an artificial neural network (ANN) model based on the principal components of a region of interest that encompasses the target motion. Mean tracking error e and error at 95% confidence level e95 were evaluated for each model. Results: The ANN model led to e=1.5mm and e95=4.2mm, while TM led to e=0.6mm and e95=1.1mm. A series with out‐of‐plane motion was considered separately to evaluate the benefit of using surrogate tracking in combination with TM. For this series, the mean error was 7.2mm using only TM and 1.7mm then the surrogate was used in combination with TM (due to out‐of‐plane motion, the ground truth in this has an inherent error component). Conclusions: As opposed to tracking with other imaging modalities, ANN does not perform well in MR‐guided tracking. TM, however, leads to highly accurate tracking results. Preliminary results suggest that out‐of‐plane motion could be addressed by surrogate tracking using the diaphragm, which is easily identified in the images.

This work was supported by Varian Medical Systems, Inc.