bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐A‐BRA‐02: Incorporating PET/CT Images into 3D Ultrasound‐Guided Biopsy of the Prostate
Authors: Fei B , Schuster D , Master V , Nieh P
Published: June 2012

Purpose: Prostate cancer is the second leading cause of cancer mortality in American men. Systematic transrectal ultrasound (TRUS)‐guided prostate biopsy is considered as the standard method for prostate cancer detection. The current biopsy technique has a significant sampling error and can miss up to 30% of cancers. As a Result, a patient may be informed of a negative biopsy Result but may in fact be harboring an occult early‐stage cancer because the current ultrasound imaging technology has difficulty to differentiate carcinoma from benign prostate tissue and because the current TRUS‐guided biopsy is blind and random. We are developing methods to combine PET/CT with three‐dimensional (3D) ultrasound images for targeted biopsy of the prostate with the aim of improving cancer detection rate. Methods: The 3D ultrasound‐guided biopsy system consists of a 3D mechanical localization system and software workstation for image segmentation, registration, and biopsy planning. For PET imaging, we use a new molecular imaging tracer called anti‐1‐amino‐3‐18F‐fluorocyclobutane‐1‐carboxylic acid ([F18]FACBC) that has shown promising results for detecting and localizing prostate cancer in our human clinical trials. In order to plan biopsy, we developed a 3D, automatic segmentation method for the prostate ultrasound images. In order to incorporate PET/CT images into ultrasound‐guided biopsy, we developed image registration methods to fuse TRUS and PET/CT images. Results: The segmentation method was tested in ten patients with a DICE overlap ratio of 92.4% ±1.1%. The registration method has been tested in phantoms. The biopsy system was tested in prostate phantoms. Three‐dimensional ultrasound images were acquired from four human patients. We are integrating the system for PET/CT directed, 3D ultrasound‐guided, targeted biopsy in human patients. Conclusions: A PET/CT image‐directed, 3D ultrasound‐guided biopsy system has been developed for the prostate. This research is supported in part by NIH grant R01CA156775 (PI: Fei), Georgia Cancer Coalition Distinguished Clinicians and Scientists Award (PI: Fei), and the Emory Molecular and Translational Imaging Center (NIH P50CA128301).
TU‐A‐BRA‐03: Obtaining Elemental Tissue Composition of Proton Therapy Patients Using Positron Emission Tomography: A Pilot Study
Authors: Cho J , Ibbott G , Gillin M , Gonzalez‐Lepera C , Mawlawi O
Published: June 2012

Purpose: Determination of patient tissue elemental composition is vital to improve proton dose, range calculation and verification; however, currently no method of obtaining elemental composition currently exists. Our aim was to investigate the feasibility of obtaining tissue elemental composition after proton therapy by measuring several positron‐emitting radioisotopes. Methods: Six 2‐mm thick samples each containing carbon[C], oxygen[O], carbon/oxygen composite[C+O], carbon/nitrogen composite[C+N], O+N, or C+O+N were irradiated parallel using a monoenergetic proton beam with a median energy of 50‐MeV delivering 2.5 Gy. Irradiated samples were moved to a gamma counter and 511 ‐keV annihilation photons were counted for 60 min. Next, three 12‐cm long phantoms each composed of C, O, or C+O were irradiated simultaneously first using a monoenergetic proton beam and then using a 6‐cm SOBP proton beam of a range of 10‐cm with ∼2 Gy. After each irradiation, phantoms were PET scanned for 30‐min in dynamic mode. Distinct radioisotope fractions from irradiated C‐only and O‐only phantoms/samples were used to calculate the relative fraction of C and O in composite phantom/samples. In addition, two patients were PET scanned after proton treatments of the head region. Three ROIs ‐ bone &fat, eye, soft‐tissue were analyzed. Time‐activity signals from all measurements were separated into the constituting radioisotopes' decay curves (O15, N13, C11, etc). The methods above were compared with Monte Carlo and analytical methods using published proton nuclear cross‐section data. Results: The fractions of each element in the C+O and C+O+N samples were estimated with errors of 8 and 15% respectively. The composition of O+C phantom was estimated within 5% error. Elemental compositions of three ROIs were compared with ICRU elemental compositions and showed consistent C/O ratios with uncertainties of 20 to 30%. Conclusions: Elemental compositions of phantoms, samples and patients were estimated with relatively small errors. PET imaging may potentially be used to improve proton treatment planning and verification. Part of the data presented here are kindly provided by Massachusetts General Hospital
TU‐A‐BRA‐09: Phase‐Matched Digital Tomosynthesis (DTS) Imaging for Simultaneous Target Verification during Volumetric Modulated Arc Therapy (VMAT) Treatment
Authors: Zhang Y , Ren L , Vergalasova I , Cai J , Yin F
Published: June 2012

Purpose: To develop a phase‐matched DTS technique to allow tomographic verification of moving targets simultaneous to VMAT delivery. Methods: This study proposes to verify moving targets by comparing phase ‐matched reference DTS (Ref ‐DTS) generated from simulation 4DCT to corresponding on ‐board DTS (OBI ‐DTS) acquired during VMAT delivery. The 4D Digital Extended Cardiac Torso (XCAT) Phantom was used for demonstration. A normal patient breathing pattern was input into the XCAT phantom to generate on ‐board CBCT projections, simulation 4DCT, average intensity projection (AIP) of the 4DCT and free ‐breathing CT (FBCT).These simulation CT sets (FBCT, AIP and 4DCT) were used to project digitally reconstructed radiographs (DRRs): DRR ‐FBCT and DRR ‐AIP (both with no respiratory phase information), and DRR ‐4DCT matched to phases of onboard projections. These DRR sets were further used to reconstruct three Ref ‐DTS sets: Ref ‐DTS ‐FBCT, Ref ‐DTS ‐AIP, and phase ‐matched Ref ‐DTS ‐4DCT. Each Ref ‐DTS set was compared with OBI ‐DTS (generated from on ‐board projections) to identify relative differences between both. To quantitatively assess the feasibility of comparing each Ref ‐DTS set with OBI ‐DTS for target verification, the simulation CT sets were shifted by a given amount to simulate target motion/setup variation, and the resulting Ref ‐DTS sets were registered to OBI ‐DTS automatically. The accuracy of target verification was evaluated by the discrepancies between simulated and registered shifts. Results: For a 1mm discrepancy criterion between simulated and registered shifts, the success rates between OBI‐DTS /Ref‐DTS‐FBCT, OBI‐DTS /Ref‐DTS‐AIP, and OBI‐DTS /Ref‐DTS‐4DCT registrations are 14.3%, 28.6%, and 100% for 2mm shifts, 0%, 14.3%, 100% for 5mm shifts, and 42.9%, 28.6%, 100% for 10mm shifts, respectively. Conclusions: The simulation study indicated that the phase‐matched Ref‐DTS‐4DCT technique considerably improved the target verification accuracy than that provided by non‐phase‐information Ref‐DTS‐FBCT or Ref‐DTS‐AIP. Therefore, it has the potential to validate VMAT treatment of moving targets. (Research partially supported by grant from Varian Medical Systems) Research partially supported by grant from Varian Medical Systems.
TU‐A‐213CD‐02: Contrast‐To‐Noise Ratio (CNR) Enhancement and Lag Correction in Cone Beam CT (CBCT) Using a Synchronized‐MOving‐Grid (SMOG) System
Authors: Ren L , Jin J , Yin F
Published: June 2012

Purpose: To develop a synchronized moving grid (SMOG) system to enhance the contrast‐to‐noise ratio (CNR) and correct image lag in cone‐beam CT (CBCT). Methods: The SMOG system uses a rapidly oscillating, synchronized moving grid attached to the kV source. Multiple exposures are taken at each gantry angle with the grid offset by a distance equal to the grid interspace width after each exposure, before the gantry moves to the next position during a scan. In each projection image, patient image data are acquired within the grid interspace area and scatter is measured under the area blocked by the grid for post‐scan scatter correction. The grid provides direct scatter reduction by blocking part of the beam, which enhances CNR in the reconstructed CBCT images. Image lag was also estimated from the blocked area and used for lag correction in the image area since both areas have similar radiation history during SMOG acquisition. Experimental studies were performed to evaluate the CNR enhancement for different numbers of exposures (1, 2, and 4) taken at each gantry angle using an enlarged CATphan. Simulation studies were performed to evaluate the lag correction using a lag model. Results: Experimental results showed that SMOG enhanced the CNR by 16% and 13% when increasing exposure number from 1 to 2 and from 2 to 4, respectively. This enhancement was more dramatic for large phantoms. The gain in CNR by increasing the exposure number gradually diminished as the exposure number became large. The CNR values from 4‐exposure SMOG were similar to those from the quasi‐fan beam scan. Simulation results showed that image lag was reduced from 19% to 0.6% using 4‐exposure SMOG. Conclusions: SMOG has the advantages of substantially enhancing the CNR and correcting image lag while removing the scatter artifacts in CBCT with similar scanning time and imaging dose as conventional CBCT.
TU‐G‐217BCD‐04: Automated Organ Dose Calculation for Thousands of Computed Tomography Scans
Authors: Lee C , Lamart S , Miglioretti D , Johnson E , Kruger R , Flynn M , Weinmann S , Smith‐Bindman R
Published: June 2012

Purpose: To develop and demonstrate an automated computational method used to provide organ and effective dose assessments of computed tomography (CT) examinations, using a pre‐calculated organ dose database. Methods: A five dimensional organ dose matrix, D (33 organs, 6 age groups, 2 genders, 3 tube potentials, scan positions with 1 cm z‐resolution), was calculated using a Monte Carlo transport method which couples a reference CT scanner model (Siemens Sensation 16) with a series of pediatric and adult hybrid computational phantoms. CT scans with a given scan range were approximated as the sum of doses from multiple axial slices included in the scan range of interest. Patient‐specific doses were calculated using the organ and effective doses normalized to CTDIvol of the reference scanner and patient/scan‐specific parameters: body part scanned, CTDIvol, age, gender, scan length, kVp, and mAs. The parameters were obtained from a manually‐ and electronically‐extracted DICOM dataset of 3,982 CT exams randomly selected from five health care systems participating in the NCI‐funded Cancer Research Network (CRN). Illustrative dose analysis and comparison of dose for a subset of scans were performed. Results: Based on an evaluation of 3,983 CT examinations the following values were provided: effective dose, CTDIvol, dose length product (DLP) and the absorbed doses for 33 organs. Illustrative analysis for brain dose in head scans revealed a large dose variation in the age less than 30‐year scans (COV=0.445) compared to the age above 30‐year (COV=0.104). We observed that brain dose is strongly correlated with scan length compared to other scan parameters. Conclusion: The automated organ and effective dose calculation method developed in this study reduces the time needed to calculate doses on a large number of patients. We have successfully utilized this program for a variety of CT‐related studies including retrospective epidemiological study and CT dose trend analysis studies.
TU‐G‐217A‐03: Validation of Diffusion Spectrum Imaging (DSI)‐Derived Crossing Fiber Angles Using a Novel Phantom and Post‐Processing
Authors: Juneja V , Zhou Y , Narayana P
Published: June 2012

Purpose: The purpose of this study was to build diffusion phantoms and employ post‐processing techniques for validating the diffusion spectrum imaging (DSI)‐derived fiber orientation distribution function (ODF) in the crossing regions. Methods: To establish a ground truth, we constructed a phantom with a fixed crossing fiber configuration of 45° and another with 3 crossing fibers at 60°. Phantom construction involved hollow plastic capillaries which were filled with water and wrapped around a plastic plate to form a number of interleaved parallel layers resulting in fibers crossing at the desired angle. We also implemented a technique to de‐convolve the response function of an individual peak from the overall ODF. The technique involves representing a DSI derived ODF with its spherical harmonic coefficients and performing the de‐convolution using the Funk‐ Hecke theorem. Unlike the methodology in which deconvolution is applied to the spherical q‐ball signal by Descoteaux et. al, (2009), our method applies it directly on the ODF derived from DSI.DSI data was acquired on the phantom on a Philips 3.0 T Intera scanner (with SENSE Flex M coil) using spin‐echo echo‐planar imaging (EPI) sequence with b‐value of 6000 and 515 sampling points. Results: Our deconvolution methodology greatly improves the angular resolution of the otherwise un‐resolvable peaks in the ODF. Quantification of a crossing region with 10±10 pixels in the 45° and 60° phantoms resulted in a successful detection with mean ± sd of 44.6°±1.6° and 59.4°±6.8° respectively, while simultaneously sharpening the ODFs in regions containing single fibers. Conclusions: We developed a diffusion phantom with 3 crossing fibers for the first time. Our proposed methodologies significantly improved the angular accuracy of the crossing fibers and are applicable to ODFs obtained from other high angular resolution diffusion imaging such as Q ball imaging.
TU‐G‐217A‐05: Improved Look‐Locker Acquisition Scheme and Curve Fitting Procedure
Authors: Hui C , Narayana P
Published: June 2012

Purpose: To improve the quality of 3D Look‐Locker (LL) T1 mapping by optimizing the k‐space segmentation in MRI. In addition, a multi‐step curve fitting procedure is developed to reduce the effect of curve fitting error on the T1 estimation. Methods: Traditional 3D LL acquisition generally utilizes centric encoding scheme that is limited to single phase encoding direction. To minimize reconstruction artifacts, we optimized the k‐space segmentation by implementing the elliptical segmentation scheme along both phase encoding directions. We also developed a multi‐step curve fitting procedure to compute the T1 values. First, four‐parameter curve fit (flip angle, inversion angle, equilibrium magnetization and T1) is performed to obtain the angle maps. Then, the acquired angle maps are smoothed based on the chi‐square weighting of the fit. These smoothed angle maps are treated as the actual angle maps and a two‐parameter (equilibrium magnetization and T1) fit is used to create the final T1 map. Simulation and phantom study were performed to assess the performance of the proposed LL modification and the multi‐step fitting algorithm. Results: Reconstruction artifacts are reduced using the elliptical segmentation scheme relative to the traditional encoding method. In addition, the subsequent T1 computation using the elliptical encoding data along with the chi‐square weighted angle maps is shown to yield more precise T1 values and was more immune to fitting errors. Conclusions: An elliptical centric k‐ space segmentation scheme is implemented on a 3D LL sequence to reduce reconstruction artifacts. A multi‐step curve fitting procedure that uses chi‐ square weighting is used to reduce the effect of false angles obtained from spurious signal. These methods were shown to improve the precision and accuracy of 3D LL T1 estimation.
TU‐G‐217A‐08: Camer‐Rao Lower Bound Analysis of 1H Magnetic Resonance Spectroscopic Imaging for Breast With Singular Value Decomposition Method and Linear Combination Method
Authors: Feng W , Xuan Y , Chu A , Hu J
Published: June 2012

Purpose: To study the Singular Value Decomposition (SVD) and Linear Combination (LC) quantification with Camer‐Rao Lower Bound (CRLB) analysis. Methods: In‐house Singular Value Decomposition (SVD) and LC program was developed with Matlab version 7.6 (Mathworks.com). Hankel SVD method (singular value decomposition of the acquired FID signal arranged in a Hankel matrix) is used to compute the signal poles and amplitude, and from them the signal frequencies and damping factors. In LC method, poles are generated from SVD analysis of averaged 10 FID, the amplitudes of the signal components were estimated by the least square method for individual FID signal. The estimated FID signals are constructed from the quantification parameters, residue error spectrum was calculated by FFT of the difference of original FID and estimated FID. In order to study the CR lower bound, known simulated spectrum without noise was analyzed with SVD and LC method. Then introduce random noise, quantification residue was analyzed, and estimated parameters with CRLB were compared with results without noise. Results: CRLB estimation is verified with the standard deviation calculation, CRLB is larger than and comparable to standard deviation. For small signal as low as 1.5% of maximum, SVD can detect at SNR 10, LC can handle SNR 5. For SNR 5, SVD can reliably detect signal like 12.5% of maximum. Typical patient data from breast tumor data was analyzed with SVD and LC methods too, results are reliable and consistent. Conclusions: CRLB estimation is verified with the standard deviation calculation. Both SVD and LC method can be used for human MRSI, the SVD method is sensitive to noise, since it has no prior knowledge to reduce noise; if noise is larger than signal, fake peak can be introduced. LC method combined with SVD generated poles can be exploited in MRSI with best results.
WE‐A‐BRB‐05: Methods to Optimize COMS Plaque Loading for Improved Dose Homogeneity and Conformity
Authors: Gagne NL , Cutright D , Rivard MJ
Published: June 2012

Purpose: To investigate the dosimetric optimization methods of varied intra‐plaque seed strength and radionuclide choice for COMS eye plaque brachytherapy. Methods: The COMS plaque Silastic insert arranges seeds about concentric circles (rings) of different radii. Thus, each plaque dose distribution may be considered as the superposition of its constituent rings. The MCNP5 radiation transport code was used to simulate a 16mm COMS plaque populated with 103Pd, 125I, and 131Cs sources. Each constituent source ring was then activated to determine its contribution to the total dose distribution while accounting for the dosimetric influences of inter‐seed attenuation and scatter. Tumor dose distributions were generated from >106 permutations of ring weightings and radionuclides for a given apical prescription dose. These dose distributions were analyzed for target dose uniformity and conformity, and compared to that of a uniformly‐loaded 125I plaque. Results: Using 131Cs seeds in only the plaque‘s outer ring yielded the most homogeneous dose distribution (+16% vs. 125I). The proximal sclera dose was 42% lower, yet center of the eye and opposite retina doses were 16% and 30% higher, respectively. Combinations with 103Pd in the plaque inner ring weighted to deliver >98% of the prescription dose yielded the most conformal dose distributions (>24% vs. 12 5I). Though doses to the eye center and opposite retina were >32% and >55% lower, respectively, the proximal sclera dose was >26% higher. Various combinations using only 103Pd with the outer ring contributing >50% of the prescription dose produced dose distributions both more homogeneous and more conformal than 125I. Proximal sclera, eye center, and opposite retina doses were typically 8‐12%, 11‐14%, and 38–40% lower, respectively, than using 125I. Conclusions: Intra‐plaque radionuclide and seed strength variations produced more homogeneous and conformal dose distributions than uniformly‐loaded COMS plaques. This optimization approach is generalizable to all plaque sizes and tumor dimensions.
WE‐A‐BRB‐10: Validation of the AAPM/ESTRO TG‐192 Protocol for Robotic Implantation of Brachytherapy Seeds: Spatial Positioning Assessment
Authors: Podder T , Beaulieu L , Caldwell B , Cormack R , Crass J , Dicker A , Fenster A , Fichtinger G , Meltsner M , Moerland M , Nath R , Rivard M , Salcudean T , Song D , Thomadsen B , Yu Y
Published: June 2012

Purpose: To date, 13 robotic brachytherapy systems have been developed incorporating a variety of imaging, control, and delivery techniques. The joint AAPM/ESTRO TG‐192 report presents a new protocol for the validation of brachytherapy robotic systems and a review of the various brachytherapy systems. This study examines spatial positioning accuracy of implanted seeds. Methods: A recommendation is that a uniform test protocol should be followed for evaluating performance of any robotic systems that would be used for brachytherapy, especially for radioactive source implantation. Parameters needed to be evaluated are needle tip positioning accuracy, needle tip positioning repeatability, positioning accuracy of the delivered sources, robot‐to‐imager calibration accuracy, and qualitative assessment of tissue damage if needle rotation is used. To accomplish these goals, a phantom (polyvinylchloride) mimicking soft tissue is recommended. For the validation study, phantoms were prepared at Thomas Jefferson University and then sent to participating institutes to ensure phantom consistency and quality. A treatment plan was developed with needle and seed coordinates. Participating institutes would deposit 100 dummy seeds in the phantom using their robotic system. Five seeds would be deposited along each needle at inter‐seed spacing of 10mm; needles would be arranged in a specified order in a 10mm×10mm grid. Upon completion of seed deposition, the phantoms would be imaged using CT and fluoroscopy and/or digital photography. An example test run and observed accuracies are presented. Results: Observations so far from two robotic brachytherapy systems indicate that the protocol is feasible and easy to implement. Robotic systems following this protocol can deposit seeds within 1mm (3D) of the intended location. Conclusions: The TG‐192 protocol will be useful for commissioning any robotic brachytherapy seed‐implantation system. Use of this standardized method will allow quantitative comparisons of seed deposition positioning accuracies obtained from any robotic brachytherapy system.
WE‐A‐BRA‐02: First Commercial Hybrid MRI‐IMRT System
Authors: Mutic S
Published: June 2012

The first commercially available MRI‐guided IMRT (MRIGRT) system (ViewRay, Cleveland, OH) has been installed at Washington University in St. Louis. This novel medical instrument combines magnetic resonance imaging and intensity modulated radiation therapy at a single isocenter for simultaneous use during therapy along with automated tissue tracking and beam control based on images of soft tissue acquired in real time rates of 2–4 FPS simultaneous to the delivery. The purpose of this presentation is to describe and evaluate the technical aspects of the instrument as well as its adaptive and image guided radiotherapy workflows. The ViewRay system consists of a 0.35‐T double‐doughnut MRI coupled with a gantry that houses three radiotherapy heads containing 15,000‐Ci Co‐60 sources (120° apart). IMRT delivery is enabled by 3 doubly‐focused MLCs that serve as the only collimators for each head, allowing a maximum field size of 27 cm2 at the 105‐cm isocenter. MRI imaging is used prior to and during delivery for patient setup evaluation, adaptive radiotherapy, and tissue tracking and beam control based on real time 2–4 FPS imaging (2 FPS in 3 parallel planes or 4 FPS in a single plane). The fast MR imaging coupled with fast autocontouring, image fusion that can transfer tissue densities (via contours through bulk density or from fused CT imaging), and dose calculation facilitate real time dose delivery evaluation, on couch reoptimization, and replanning when necessary. The instrument's multiframe per second MR imaging enables motion correlated delivery based on the actual target volumes rather than on surrogates. Following treatment, the image, contours, and control system data produce a record of the delivery that is automatically recorded and registered to the orginal plan for evaluation. All imaging and adaptive features are controlled by clinician directives at the planning stage and can be set as required, optional, or prohibited. The design and capabilities of the system create several novel concepts and promising capabilities in RT delivery from imaging and treatment to workflow and QA/QC. This presentation discusses the initial assessment of these features and their implementation and the early clinical experience with the system including validation of its capabilities.

Learning Objectives:

1. To describe technical design and capabilites of ViewRay system

2. To describe adaptive and image guided RT workflow with this system

3. To present initial validation assessment of the system
WE‐A‐218‐04: Tube Current Modulation and Patient Size Adjustment for CT Dosimetry Software ImPACT in Thoracic CT Exams
Authors: Khatonabadi M , Zhang D , Cagnon C , DeMarco J , McNitt‐Gray M
Published: June 2012

Purpose: The purpose of this study was to improve dose calculations performed using ImPACT by taking into account tube current modulation and patient size. Methods: Monte Carlo based methods were used to estimate lung and breast dose to 20 female models of various sizes by performing detailed simulated thoracic CT scans, including the effects of TCM. The z‐axis modulation functions extracted from patients' images were used to determine organ‐specific tube current values (average tube current of images containing the organ). To account for TCM, these were used as the mA values entered into ImPACT spreadsheet. Calculated organ doses using global mA (average mA over the entire scan) and local mA (organ‐specific average mA) were compared to simulated organ doses. For both methods percent differences from simulated organ doses were calculated. For the organ‐specific average mA a linear trend with respect to patient size was observed. This suggests a possible size correction using the ratio of MIRD's perimeter at the level of the nipples and each patient's perimeter. Using percent difference versus perimeter plot, a perimeter was calculated at which percent difference was zero and used to adjust for patient size by multiplying it with the TCM‐adjusted results. Results: After adjusting organ doses for tube current modulation the Root Mean Square Error (RMSE) decreased from 4.9 to 2.7 and from 4.0 to 3.4 mGy for breasts and lungs, respectively. Furthermore RMSE decreased to 1.0 and 0.02 mGy, respectively, after adjusting for patient size. Conclusion: ImPACT has been used to estimate dose from CT, but this software is only capable of estimating dose from fixed tube current scans. However, most clinical protocols make use of TCM. We have shown that results from ImPACT can be adjusted for TCM and for patient size utilizing organ‐specific average mA and an adjustment for patient size.
WE‐A‐218‐09: A Comprehensive CT Organ Dose Database for Weight‐Specific Adult and Pediatric Patients
Authors: Ding A , Gao Y , Caracappa P , Long D , Bolch W , Xu X
Published: June 2012

Purpose: To describe the joint effort to develop a comprehensive CT organ dose database for weight‐specific adult and pediatric patients. Methods: Two validated CT scanner models (GE LightSpeed Pro 16 and Siemens SOMATOM sensation 16) operated at different tube voltages (80–140kVp) and beam collimations (1.25 mm, 5 mm, 10 mm and 20 mm) with both the head and body bowtie filters were adopted to calculate the organ dose. Detailed X‐ray sources and bowtie filter geometry were modeled using the MCNPX v2.6 code. The x‐ray source moved along a single axial trajectory to allow for the calculations of organ doses from a single CT slice. This simulation process was repeated to cover from the top of the head to the feet for one phantom. This approach was applied to a set of voxel phantoms covering 50th percentile of adults and children at different ages (1‐, 5‐, 10‐, and 15‐year‐old), a pregnant female at three gestational stages, and obese patients of different body weights. Results: A detailed database of slice‐by‐ slice organ doses was established for a total of 27 phantoms at RPI and the University of Florida. All the related organ doses are incorporated into a standardized database compiled using Microsoft SQL server 2008. The CT organ doses calculated in this study for a GE and Siemens scanner can be used to estimate dose from other scanners using organ‐specific adjustment factors or CTDIvol normalization factor to account for the different organ doses from different scanner types. Conclusions: This set of new and comprehensive organ dose database is expected to improve both the accuracy and usability in CT dose reporting and tracking in the future. Combined with the additional knowledge that can be extracted from the DICOM file the software package can be a helpful tool in the management of CT dose. This project was supported by the National Institute of Biomedical Imaging and Bioengineering (R42EB010404).
WE‐A‐218‐11: Investigation of Image Extrapolation Methods to Improve Accuracy of CT Dose Calculations Based on Patient CT Images
Authors: Liang Q , DeWerd L
Published: June 2012

Purpose: The radiation dose received by patients from computed tomography (CT) scans has become a major public concern. A promising approach for individual CT dose determination is to use Monte Carlo (MC) simulations to calculate the dose to a patient based on their CT images. To accurately calculate the organ dose in the prescribed scan region, a whole body image is needed to properly simulate scatter effects. However, whole body images are not typically acquired for clinical exams. To address this issue, image extrapolation beyond the scan region was used, and its impact on dose calculation accuracy was investigated. Methods: An EGSnrc‐based MC tool, GMctdospp, was used to perform dose calculations. Dose distributions within the scan region, based on images with and without the region beyond the scan region (scatter region), were calculated. A mathematical cylindrical water phantom and a Rando phantom were used to demonstrate the effects of the scatter. For the Rando phantom, whole body and chest DICOM images were used to perform dose calculations. The doses calculated for these two sets of images were compared. Linear, polynomial, and nearest neighbor extrapolations of the slices on the edge were performed to determine the size of extrapolation region needed to provide enough scatter. The calculated dose based on chest images with extrapolated images were compared against the calculated dose based on the whole body images. Results: Without the image extrapolation, an average of 10% dose underestimation was found on the edge of scan region for the water cylinder and up to 30% dose underestimation for the Rando phantom. With image extrapolation, the dose underestimation was negligible for these two cases. Conclusions: Extrapolation of the images on the edge of scan region provides an effective way to improve the accuracy of determining patient‐specific CT dose based on the CT images.
WE‐C‐211‐01: International Radiation Safety Standards and Systems
Authors: Rehani M
Published: June 2012

International organizations play an important role in establishing roles, responsibilities and needs of medical physicists, be it for radiation protection or functional needs. The international Standards of safety (Basic Safety Standards‐BSS) steered by the IAEA and the European BSS provide requirements that may be mandatory directly or indirectly. In addition, International Commission on Radiological Protection (ICRP) provides principles of radiation protection. Both the IAEA and the EC have provided requirements for medical physicist to be in place, previously dominantly for radiotherapy and more recently for diagnostic radiology, nuclear medicine and other practices that utilize ionizing radiations. There are a number of new requirements in both BSS that are likely to be released in 2012–2013 but drafts are available. Besides requirements, international organizations provide means to meet requirements. These are training material and actions directed at both human resource development and development and enrichment of skills, capacity building through provision of equipment, publications and guidelines to promote rational and safer practice. A large number of IAEA and EC projects provide assistance towards the goals of organizations and there are many publications of IAEA, EC and ICRP that medical physicists should be aware of. Recent statement of the ICRP on tissue reaction lowering threshold and dose limit for lens of the eye and circulatory disease is of interest. EC has developed guideline on medical physics expert. The talk will review activities of IAEA, EC, and ICRP with focus on medical physicists and the impact in less resourced countries.

Learning Objectives:

1. To understand the system that has influence on countries outside US pertaining to activities of interest to medical physicists

2. To become familiar with actions pertaining to medical physics experts and requirements on radiation protection

3. To become familiar with new information from ICRP on thresholds and dose limits for tissue reaction

4. To understand the potential role you can play in international activities
WE‐C‐213AB‐03: Preparing for Part II of the ABR Radiotherapy Physics Exam
Authors: Flynn R
Published: June 2012

Attendees are taught an efficient organizational framework for Part II exam preparation that maximizes high‐yield active learning study activities and minimizes low‐yield study activities. This method is then combined with a productive group‐based study technique. The format and scope of the Part II ABR exam in radiotherapy physics is described, and the eligibility requirements are reviewed. High‐yield and low‐yield study activities are defined and examples are discussed in detail. A problem‐based strategy for limiting the scope of study material is described. A method for studying in groups by distributing delegable tasks among multiple group members and ensuring their completion is described.

Learning Objectives:

1. Understand the scope of material covered on Part II of the ABR radiotherapy physics exam and which references to study for the exam.

2. Be able to design and execute an efficient study plan that enables an active learning approach.

3. Learn to use group study techniques to enhance efficiency.
WE‐C‐BRA‐07: Assessment of Heterogeneous Treatment Response in Patients with Multiple Solid Tumors
Authors: Scully P , Vanderhoek M , Perlman S , Liu G , Jeraj R
Published: June 2012

Purpose: Imaging biomarkers of treatment response have been defined for individual tumors, but when multiple tumors are present the evaluation is not straightforward. This study investigates the intra‐patient heterogeneity of tumor response in patients with multiple metastatic lesions. Methods: Twelve patients with two or more metastatic solid tumors of various histology were treated with molecular targeted therapy. Each patient received [18F]FLT PET/CT scans pre‐, mid‐, and post‐treatment, and tumors were manually segmented on each scan. SUVmean, SUVmax, SUVpeak, SUVtotal, and PET‐defined volume were calculated for each tumor. Response was defined as the percent change relative to baseline for a single tumor, and heterogeneity was quantified as the range of response across all tumors within a single patient. This was calculated for both mid/pre and post/pre response, yielding 120 total measurements of response heterogeneity. Results: For all response measures, substantial intra‐patient heterogeneity in tumor response was observed. The average inter‐tumor range of response was highest for volume and SUVtotal (45%) and lowest for SUVmean (25%). Heterogeneity greater than 40% was observed in 35% of cases (42/120), and in 10% of cases (12/120) heterogeneity greater than 75% was observed. Interestingly, in 18% of cases (21/120), tumors exhibited opposite trends in response, with one increasing and one decreasing at least 20% relative to baseline. Volume and SUVtotal are most sensitive to ROI definition, which represents the largest source of uncertainty for response calculation in this study. Conclusions: Heterogeneous treatment response was observed in patients with multiple tumors, in some cases resulting in ambiguous trends. Accordingly, assessment of a single lesion is insufficient to fully characterize such patients' response to therapy. Future research will investigate how to apply imaging biomarkers of treatment response for this population, as this study suggests either new methods for interpretation or entirely new metrics are required.
WE‐C‐BRA‐10: Ultrasound Nakagami Imaging for Noninvasive Evaluation of Vaginal Fibrosis Following Radiotherapy for Gynecologic Malignancies
Authors: Liu T , Yang X , Bruner D , Tridandapani S , Chen H , Henry S , Rossi P
Published: June 2012

Purpose: Radiation therapy is an important treatment modality for most gynecologic (GYN) malignancies. However, radiation‐induced vaginal fibrosis is a debilitating side‐effect, affecting 80% of women post pelvic or vaginal radiotherapy. Vaginal fibrosis leads to pain, sexual dysfunction, and poor quality of life. This study's purpose is to develop an ultrasonic tissue characterization technique based on Nakagami parameter imaging to evaluate vaginal fibrosis. Methods: We investigated the Nakagami imaging concept in a pilot study of 10 patients. All patients were previously diagnosed with endometrial cancer. Four patients who received surgery alone served as the control group. Six patients received surgery plus radiotherapy, and the follow‐up time ranged from 12 to 38 months after radiotherapy. Each participant underwent one transvaginal ultrasound study with a 7.5 MHz biplane probe. Three transverse images of the anterior vaginal wall were acquired in a 2 cm step‐wise progression from the apex (vaginal cuff) to the introitus (vagina opening). Vaginal wall thickness, Nakagami probability density function (PDF), and Nakagami parameter were calculated to evaluate radiation‐induced vaginal injury. Results: Significant differences in vaginal wall thickness and Nakagami PDF were observed between the post‐irradiation and non‐irradiated vaginal walls. The average vaginal wall thicknesses were 1.99±0.54 mm for the control group and 4.81±1.55 mm for the post‐irradiation group (p<0.01). The average Nakagami PDF values were 2.05±0.13E‐3 for the control and 3.54±0.40E‐3 for the post‐irradiation group (p<0.001). The average Nakagami parameter values were 0.92±0.31 for the control group and 1.31±0.12 for the post‐ irradiation group (p=0.15). Vaginal fibrosis appears to be associated with a thickened vaginal wall and increased Nakagami parameter. Conclusions: In this study, we demonstrate the feasibility of using Nakagami imaging to evaluate vaginal fibrosis. Quantitative ultrasound provides a noninvasive, objective means of assessing radiation‐induced vaginal injury. This imaging method may be useful as we try to address vaginal toxicities and sexual dysfunction in women after radiotherapy for GYN malignancies.
WE‐C‐213CD‐01: Decision Support for Radiation Therapy
Authors: Yin F
Published: June 2012

Informatics in radiation therapy is less understood. Decision support for, or knowledge‐guided, radiation therapy, is a major component of informatics, where the data is mined, modeled and turned into computable knowledge. It is critically important for radiation therapy as it employs highly complex procedures, such as IMRT and IGRT, where radiation related normal tissue/organ damages and clinical outcomes require delicate balance. Decision support can be provided in passive, active, and cooperative modes. The passive mode focuses on improved presentation of available data and knowledge to minimize cognitive burden in decision making. The active mode applies machine learning algorithms, such as support vector machines, to generate decision suggestions based on existing knowledge. The cooperative mode allows users to interact with the decision support system to iteratively reach an optimal decision. Decision support for the execution of Clinical Practice Guidelines (CPG) is another important area in which significant improvement can be achieved by helping physicians following best clinical practices specified in the guidelines. In radiation therapy, significant data, algorithms, knowledge, and guidelines have been developed in the past two decades. Various modes of decision support systems have been proposed in recent years that incorporate different data, optimization algorithms, knowledge representations, and machine learning algorithms. In this session, we will first review concepts and systems of clinical decision support in general; followed by specific applications of decision support in radiation therapy. The basic principles of making decisions when the outcomes of any available actions are uncertain are discussed. Methods for applying these principles in medical environments are described. We will conclude our discussion with a number of state‐of‐the‐art techniques for decision support in radiation treatment planning and quality assurance.

Learning Objectives:

1. To discuss the need for decision support in health care and specifically in radiation therapy

2. To review major concepts and approaches in clinical decision support systems

3. To describe example systems for decision support in radiation therapy

4. To present a number of new techniques for decision support in intensity modulated radiation treatment planning
WE‐G‐211‐02: Origins and Development of Magnetic Resonance Imaging
Authors: Clarke G
Published: June 2012

The method of magnetic resonance imaging (MRI) was an extension of nuclear magnetic resonance (NMR) spectroscopy that was enabled by computational systems capable of performing the Fast Fourier Transform. Initially, a diverse group of methods were proposed for producing images with NMR, with the multi‐slice spin‐warp spin echo MRI method winning out as the first clinically useful approach. Immediately radiologists were impressed in the soft tissue contrast seen in MR images and the great flexibility with which image contrast could be manipulated. Over the years, advances in both hardware and the implementation of new pulse sequences of increasing complexity led to the increasing utility of MRI. The great success of MRI research contributed to the awarding of both the Nobel Prize in Chemistry for Richard Ernst in 1991 and the Nobel Prize in Physiology or Medicine for Lauterbur and Mansfield in 2003. The evolution of the modality produced increasing speed of acquisition, finer spatial resolution and an expanding range of clinical applications. Technological advances included improvements in gradient coils, superconducting magnets, phased array radiofrequency coils, and partially parallel image reconstruction algorithms. The wide range of applications developed include MR angiography, BOLD contrast functional MRI, and diffusion‐weighted MRI. This section of the symposium will conclude with a look a current developments and where they are likely to take the field into the future.
WE‐G‐211‐03: Development of Ultrasound Imaging Equipment
Authors: Zagzebski J
Published: June 2012

One of the earliest man‐made ultrasound images of the human body was produced by Dussik in 1941, when he attempted to image the brain using a through transmission technique. These early images were later judged to be artifacts related to sound wave transmission through skull bone. Pulse‐echo examination of the body started in the late 1940's following developments of sonar, radar, and ultrasound flaw detectors. Ludwig and colleagues measured speeds of sound in tissues, publishing the value 1540 m/s for many tissue paths, a figure still used today. Among the pioneering pulse‐ echo imaging teams in the USA were Wild and Reid who developed real time imaging of the breast in the early 1950's, and Howry and Bliss, who were able to generate detailed anatomical pictures of the neck by employing water bath scanners. Many other groups, including from Japan, Australia, and Europe were pursuing both A‐scope and B‐scope applications of ultrasound around this time. Notable achievements include work by Ian Donald in the UK, who in 1955 described a contact scanner and published B‐scope images depicting a variety of anatomical regions. The systems of Donald and of Wild are said to have inspired engineers from Howry's water bath team in Colorado to develop their own contact scanner, and in 1963 a new company, Physionics produced the first commercial, single element transducer “articulated arm” scanner. It provided bi‐stable B‐mode images on a storage oscilloscope, marking the beginning of widespread acceptance of this modality. Gradual instrument improvements include analog then digital scan converters for gray scale in the 70's, and both auxiliary and stand alone mechanical scanning real time probes. Phased array technology also emerged for cardiac imaging, as did linear arrays for obstetrics and abdominal imaging. Perhaps the most revolutionary instrument ever was produced in the early 1980's, the Acuson 128, introducing high image quality linear and phased array beamformed images for radiology applications and helping to conclude the brief era of manual scanners. As beamformers became digital devices in the 1990's, unprecedented image quality, diagnostic features, two dimensional arrays, and even system miniaturization evolved, bringing ultrasound imaging to its present state. The ultrasound field is still characterized by novel instruments emerging from the laboratories of clever scientists, addressing diagnostic and therapeutic needs not provided by present day technology.

Learning Objectives:

1. Describe features of the first commercially available ultrasound scanners.

2. Identify the relationship between technological developments in radar and emergence of ultrasound as a modality

3. Explain the significance of a high large channel count in beamforming

4. Contrast echo acquisition and processing in a modern scanner with first generation devices.
WE‐G‐BRB‐05: On the Importance of Fluorescence Within the Stem Effect of Scintillation Detectors
Authors: Therriault‐Proulx F , Beaulieu L , Archambault L , Beddar S
Published: June 2012

Purpose: To quantify the nature and composition of the light produced in optical fibers under different irradiation conditions and evaluate its impact on dosimetry. Methods: Irradiation of a bare PMMA optical fiber (Mitsubishi ESKA Premier) was performed using a superficial therapy unit, an Ir‐192 HDR brachytherapy source, a Co‐60 external‐beam unit as well as photon and electron beams from a linear accelerator. Spectra of the radiation‐induced visible light in the fiber were acquired and signals were compared as a function of depth and irradiation type. Irradiation of a 75 kVp beam from the superficial therapy unit was used to isolate the fluorescence spectrum. Isolation of the Cerenkov spectrum component was obtained from irradiation of a 15 MeV electron beam at a 45 degree angle. Relative composition in fluorescence and Cerenkov of the stem effect light has been determined for all irradiations. Results: The total stem effect spectra can be represented by a linear superposition of the fluorescence and Cerenkov spectra. The fluorescence contribution was shown to strongly differ between the superficial therapy unit (99%±1%), the Ir‐192 HDR source (25%±3%) and higher energy irradiations (3%±2%). Variations within each energy regime (kV, HDR brachytherapy and MV) were small at 3% or lower. These were observed for irradiations at angle or when the fiber was near the surface. This study suggests it is better to calibrate the stem effect of a scintillation detector using the same irradiation modality. Conclusions: Stem effect light was shown to be composed of fluorescence and Cerenkov light in different proportions depending on the geometry of the experimental setup, nature of the irradiation, and irradiation energy. Calibrating detectors separately for fluorescence and Cerenkov may lead to better performance of the stem effect removal technique.