bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐B‐ValB‐01: Optimizing MR Imaging Procedures: The Physicist as a Consultant
Authors: Lemen L 
Published: July 2006

Every MR system has its strengths and weaknesses, often varying tremendously both within and between the various system designs. Added to that, each site will have its own priorities and styles of use of their system. For an MR physicist to best assist in optimizing imaging procedures, it is extremely important for that individual to be both well‐versed in basic MR physics, and to be able to recognize (and understand) the impacts and trade‐offs of the technology in a large variety of imaging situations. The physicist should be able to determine and evaluate problems in patient images as well as phantom tests.For this presentation, the basic relationships between MR imaging parameters will be reviewed with an emphasis on their implementation in common clinical protocols. Examples of how they are adapted for specialized procedures will then be given to demonstrate trade‐offs between contrast requirements; imaging speed; spatial resolution; geometrical accuracy, and patient safety issues. How specific field strength and gradient configurations affect these options will also be examined. Differences in RF coil properties will be discussed from the perspective of optimizing applications for a facility.Educational Objectives:1. Understand the primary tissue contrast characteristics of the standard clinical sequences; methods of selective elimination of tissue signals; and the role of exogenous agents to alter contrast.2. Know how to consider the interactions between SNR, spatial resolution and imaging speed and how their combined effects determine image quality for a variety of clinical situations.3. Understand circumstances under which patient physiology and system configuration may require modification of image acquisition parameters to achieve optimal image quality.
TH‐C‐330A‐04: Novel Learning‐Based Approach to Optimal EPID Image Deblurring and Enhancement
Authors: Roessler P , Maltz J , Somphone O , Blanz E , Gangadharan B , Ghelmansarai F , Morin O , Pouliot J , Bani‐Hashemi A 
Published: July 2006

Purpose: Finite focal spot size in X‐ray imaging equipment has a blurring effect on acquired images. For practical reasons, it is neither possible nor desirable to reduce the spot size of medical linacs below a certain diameter. This affects task performance in IGRT, where the blurring of the edges of structures reduces positioning accuracy. Since the focal spot size and shape of linacs vary, the filter must be customized to a particular linac. We have developed an algorithm that learns to deblur portal images by comparing actual images to their Monte Carlo (MC) generated ideal counterparts. Method and Materials: A training object containing sharp edges of all orientations is imaged to capture the blurring and noise characteristics of the system. MC simulations in which a point source irradiates a digital version of the training object are used to generate ideal images. These are used as training data to optimize the convolution kernel that effects deblurring. Owing to the nature of the training data, the kernel will deblur the image as well as enhance edges. We assume since the object is 1m from the source, blurring is uniform for all transverse object planes. Results: Large samples of phantom and patient images were used to evaluate filter performance. A marked improvement in image quality is apparent. Evaluation of spatial resolution (MTF) and contrast‐to‐noise ratio (CNR) reveals a dramatic improvement in MTF but reduction in CNR. However, since the CNR remains above 70 at doses of 1MU, the increase in noise will not effect IGRT task performance. Conclusion: This work indicates the utility of this novel image enhancement technique in clinical images. In particular, visibility of small objects in images, such as prostate seeds, is remarkably enhanced.Conflict of Interest: Sponsored by Siemens.
TH‐C‐330A‐06: Effects of KVp Setting and Radiation Dose On Calcification Visibility in Cone Beam CT
Authors: Lai C , Shaw C , Meng Y , Chen L , Altunbas M , Tu S , Liu X 
Published: July 2006

Purpose: To investigate how the kVp setting and radiation dose affects the detection of microcalcifications in cone beam CT (CBCT). Materials and Methods: Calcium carbonate grains, ranging from 200–212 to 355–425 micron, were used to simulate microcalcifications. The simulated microcalcifications from the same size were arranged to form a 5×5 microcalcification cluster. Each cluster was embedded between two slices of a stacked lunch meat and positioned at the center of each slice of the lunch meat. The lunch meat was then imaged with an experimental CBCT system, which employs a 30 × 40 cm2 a‐Si/CsI based flat panel detector with a pixel size of 194 microns. 300 projection images over 360 degrees were acquired in the non‐binning mode at two kVp setting (60 and 80 kVp) and various doses (4.2, 6, 12, 18, and 24 mGy). The projection images were reconstructed with the Feldkamp algorithm. After that, 767×767×9 volume data were extracted from the CBCT reconstructed images for each MC size group and each dose level as well as each kVp. The images were sequentially displayed on a review workstation with a 1600×1200 CRT monitor and reviewed by six readers independently. The order of the images was randomized for each reader. The readers were asked to count the number of visible microcalcifications. The ratios of the visible microcalcifications were averaged over all readers. Student t‐test was used to compute the p values. Result: For 80 kVp, the images acquired with 4.2 mGy performed similarly to those acquired with 6 mGy (p > 0.05) for each MC size. Additionally, the images acquired with 18 mGy performed similarly to those with 24 mGy (p > 0.05) for most MC sizes.This work was supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI.
TH‐C‐224A‐02: QA for Linac KV Imaging Systems
Authors: Bissonnette J‐P , Moseley D , Purdie T , White E , Jaffray D 
Published: July 2006

The recent commercialization of linac‐mounted kilovoltage imaging systems (i.e., kV systems) has allowed high‐precision verification and correction of patient position immediately prior to the delivery of radiation therapy using fluoroscopic, radiographic, or cone‐beam tomographic modes. This novel technology challenges the radiotherapy community to redefine their patient positioning practice. One can now correct patient position using image information displaying not only bony anatomy and airways, like portal imaging, but also markers and soft tissue structures within the patient, including the target to be irradiated. On‐line kilovoltage imaging further allows, using daily imaging sessions, on‐line correction of patient translations and rotations, and the comparison for successive daily volumetric images permits to track changes of anatomy through the course of therapy. Introducing kV systems within busy radiation therapy clinics requires thoughtful testing and quality assurance protocols (QA) of the device, and judicious modification of existing radiation therapy processes and protocols.The individual components making up kV systems are well‐established technologies, and the quality assurance for each component follows accepted standards. However, the specific features of the integrated systems require particular attention. First, the kilovoltage beam may not share a common central axis with the megavoltage treatment beam; therefore, the relation of the kilovoltage imaging matrix to the megavoltage treatment beam must be monitored to ensure adequate localization, scaling, and geometric accuracy. Second, cone‐beam tomography differs from conventional or helical CT imaging, and thus encounters specific image quality issues. A well‐planned QA program integrates closely the kV system procedures with linac procedures described in accepted QA standards such as the AAPM task group 40 report.This lecture will present a brief review of commercial systems, but will focus on a suitable QA program, with special emphasis on issues germane to the system and the clinical processes relying on its use. Examples of clinical use in a number of sites will also be presented.Educational Objectives:1. Understand the technical issues related to kV systems.2. Understand the impact of kV systems on clinical processes.3. Present a comprehensive commissioning protocol and QA program for kV systems.This work is supported, in part, by a research grant from Elekta Oncology Systems.
TH‐C‐224C‐02: MicroRT/microRTP: A Conformal Small Animal Planning and Irradiation System
Authors: Stojadinovic S , Hope A , Vicic M , Mutic S , Deasy J , Cui J , Khullar D , Parikh P , Esthappan J , Grigsby P , Low D 
Published: July 2006

Purpose: We have developed a novel small animal radiation therapy device (microRT), which integrates multi‐modality imaging, radiation treatment planning, and conformal radiation therapy. In this study, we evaluated the accuracy of the treatment planning and positioning systems of the microRT device. Method and Materials: The microRT system utilizes a clinical 192Ir HDR source collimated via machined tungsten inserts to deliver photon beams at a source to target distances of 1–8cm at four angles (0, 90, 180, and 270). Beams were modeled using Monte Carlo and a parameterized analytic dose engine was created. Radiochromic film (5mm steps) in a solid water phantom was used to evaluate actual delivered doses in multiple planes. Treatment plans using these beams were created by a custom treatment planning system (microRTP) based on imported fiducial‐registered imaging (CT, MR, PET) of animals immobilized in the treatment position. A three‐axis computer‐controlled stage supports and positions animals in the beams according to the microRTP plan. Validation of the positioning system was performed using a phantom and images of phantom and collimator via a kV C‐arm. Results: The analytic dose model agreed with the Monte‐Carlo predicted dose within 5% and 10% outside and inside the 1 mm deep build‐up regions, respectively. Film dosimetry agreed with the analytic model within 10% and also demonstrated an effective field diameter of 8mm at 17mm from the source. The 192Ir line source geometry caused a radial anisotropy of up to 12% at 17 mm depth from the source. The positioning accuracy of the animal support hardware was sub‐millimeter. Conclusions: The microRT system provides conformal radiation therapy based on pre‐treatment imaging and planning for small animal models of cancer and tissue injury.This work supported in part by NIH R21 CA108677 and by a grant from Varian, Inc.
TH‐C‐224C‐08: Estimating Differences in Volumetric Bone Growth by Treatment Method
Authors: Hua C , Krasin M , Shukla H , Merchant T 
Published: July 2006

Purpose: To estimate potential differences in volumetric bone growth in children with sarcoma treated with intensity‐modulated (IMRT) and conformal (CRT) radiation therapy using an empiric dose‐effect model.Methods: Volumetric bone growth was estimated 4 years after radiation therapy for 36 pelvic bones (ischio‐pubis and ilium) from 11 patients using a random coefficient model for flat bone growth that incorporated patients age, pre‐RT bone volume, integral bone dose >35Gy, and time after completion of RT. Dosimetry representing the actual CRT/IMRT plan, a non‐treated comparable IMRT/CRT plan and an idealized plan delivering dose only to the PTV, with no dose delivered to tissue outside the PTV, were entered into the model and the resultant volumes compared relative to modeled normal bone growth (integral dose of zero). The prescribed dose to the PTV ranged from 36–55.8 Gy and the median values for the PTV and studied bone volumes were 774 ml (147–1964 ml) and 76 ml (14–215 ml), respectively. Results: Relative to normal bone growth, patients were predicted to maintain 93%, 87% and 84% (p=0.06) of their expected growth with idealized, IMRT and CRT approaches, respectively. Older patients, age ⩾10 years were predicted to maintain a mean growth of 98% compared to normal regardless of method. Those age < 10 years maintained 87% (idealized), 76% (IMRT) and 70% (CRT) of expected growth (p=0.015). On post hoc testing (Tukey) CRT and IMRT both differed significantly from idealized but not from one another. Conclusions: Linear dose‐effect models facilitate comparison of treatment methods and potentially interventions. For older patients, treatment methods do not significantly impact growth for specific flat bones; however, for younger patients, treatment methods may significantly impact flat bone growth especially as we move towards idealized dose distributions potentially feasible with particle therapy.
TH‐C‐VaIA‐02: In's and Out's of Non‐Equilibrium Dosimetry
Authors: Seuntjens J 
Published: July 2006

Typical procedures for clinical dosimetry are well established for measurements in charged particle equilibrium situations. These situations only form a subset of the measurement challenges of a clinical physicist. Dose measurements in regions of charged particle disequilibrium require special considerations before the measurement can be assumed accurate. These disequilibrium conditions occur in association with measurements performed for standard clinical treatment techniques as well as for special treatment techniques. In the symposium we identified four major areas that complicate accurate clinical dosimetry: (1) the photon build‐up region, (2) narrow photon beams, (3) measurements in heterogeneous phantoms and (4) modulated fields and dynamic measurements.In the present lecture we describe the principles of accurate dose measurements in general in equilibrium and non‐equilibrium situations. Principles of detector response, energy dependence and characteristics of practical detectors are described with emphasis on the understanding of detector behaviour in non‐equilibrium conditions. By way of introduction, practical examples will be provided of non‐equilibrium measurements in the build‐up region, narrow beams, heterogeneous phantoms and IMRT beams. The lecture will provide general guidelines about detector suitability for commercially available devices for the discussed areas of application. Finally, uncertainties of the procedures in a clinical context will be discussed.Educational Objectives:1. To understand the fundamental complications of non‐equilibrium measurements.2. To understand the impact of detector properties on measurement accuracy in non‐equilibrium situations.3. To place measurement uncertainties in non‐equilibrium conditions in a clinical perspective.
TH‐C‐VaIA‐04: Accurate Dosimetry in Photon Build‐Up Region
Authors: Abdel‐Rahman W , Devic S , Seuntjens J , Podgorsak E 
Published: July 2006

Accurate measurements in the dose build‐up region for high energy photon beams are not easily obtained. While dosimetry in situations where electronic equilibrium exists is well understood, there is in general no consensus on the most accurate method for measuring doses in the build‐up region. In the past, data acquired with an extrapolation chamber were regarded as the benchmark by which the data from other more commonly used dosimeters are evaluated. As extrapolation chambers are clinically impractical devices there is a need to study the behaviour of commercially available and clinically suitable detector systems for accurate dosimetry in the build‐up region.This lecture will provide an overview on the characteristics of the dose build‐up region measurements for photon beams, the suitability of several clinical dosimeters for build‐up dose measurement and limitations in measurement accuracy.Educational Objectives:1. Understanding the reasons why doe measurements in the build‐up region are challenging.2. Grasp issues of the suitability of several dosimeters for measurements in the dose build‐up region.3. Discussion of ongoing research on dosimetry in the dose build‐up region.4. Discussion of the associated uncertainties and their clinical relevance.
TH‐D‐330A‐01: Annual Gamma Camera QC: Techniques And Phantoms To Simplify The Implementation Of The NEMA NU‐1 Procedures For Tests Recommended By The ACR
Authors: Hamacher K , Goldsmith S 
Published: July 2006

The objective of this work is to present techniques to perform the NEMA tests that are suggested by the ACR for annual gamma camera QC. Since the recommendation contains nine tests, the goal is to devise simple and efficient procedures to reduce the required time without compromising the quality. Also included is a comparison of test equipment conforming to NEMA specifications to equipment made in‐house.The time to complete the annual QC is markedly reduced by the availability of specifically designed phantoms. They provide a reliable means to compare the cameras and to establish a performance baseline. For two tests, Multi Window Spatial Registration and SPECT Resolution with scatter, the NEMA prescribed equipment is compared with readily available devices. The comparison of the commercial MWSP device and the one produced in‐house showed that the average maximum difference of the center of mass for the three Ga‐67 peaks measured at various points across the crystal face is 0.35 mm vs. 0.33 mm for the commercial and the in‐house device, respectively. For the SPECT resolution using three capillary tubes filled with Tc‐99m, a NEMA phantom is compared to a modified Jaszczak phantom. The FWHM is 4.78 pxl vs. 4.79 pxl (radial) and 4.144 pxl vs. 4.167 pxl (azimuthal) for NEMA and Jaszczak phantom, respectively.Further topics include sensitivity, count rate performance, comparison of fit methods, and monitor/printer QC.
TH‐D‐330D‐01: BIROW — Biomedical Imaging Research Opportunities Workshop: Intersociety Project to Accelerate Biomedical Imaging Discovery and Application
Authors: Fullerton G , Bourland J , Pelizzari C , Ling C , Jaffray D , Eckelman W , Patt B , Hendee W , Mulvaney J , Mackie T , Fenster A , Nagy P , McNitt‐Gray M , Chan H 
Published: July 2006

The Biomedical Imaging Research Opportunities Workshops (BIROW) held over the past 4 years examined the leading edge of research opportunities in biomedical imaging, to recommend strategies to advance imaging research and thereby improve imaging applications in preventive medicine, medical diagnosis and treatment. Funded through grants from the National Institute of Biomedical Imaging and Bioengineering (NIBIB) and the Whitaker Foundation, and held each spring in Bethesda MD, the BIROW workshops were sponsored by 5 organizations: the American Association of Physicists in Medicine, Radiological Society of North America, Biomedical Engineering Society, Academy for Radiology Research, and the American Institute of Medical and Biological Engineers.This session introduces the purpose and accomplishments of BIROW and plans for its future, followed by discussions by several leading researchers on topics of substantial current interest in biomedical imaging research: Image‐Guided Therapy (Drs. Bourland, Pelizzari, Ling and Jaffray); Small Animal Imaging Systems (Drs. Fullerton, Eckelman and Patt); Medical Imaging Technology: From Concept to Clinic (Drs. Hendee, Mulvaney, Mackie and Fenster); and Informatics and Computerized Image Analysis (Drs. Nagy, McNitt‐Gray and Chan). Participants in this session will gain insight into the types of research challenges and opportunities present in BIROW workshops through the presentation of these examples.1:30 – 1:50Introduction Session: Purpose of BIROW1:50 – 3:20Image‐Guided TherapySmall Animal Imaging Systems4:00 – 5:30Medical Imaging Technology: From Concept to Clinic Informatics and Computerized Image Analysis.
TH‐D‐ValB‐07: Development of a Novel High Quantum Efficiency Flat Panel Detector for Megavoltage Cone Beam CT/DT: Construction and Evaluation of a Prototype Single‐Row Detector
Authors: Pang G , Mei X , Rowlands J A 
Published: July 2006

Purpose: Most electronic portal imaging devices (EPIDs) developed so far have low x‐ray absorption, i.e., low quantum efficiency (QE) of 2–4% for megavoltage x rays. A significant increase of QE is desirable for applications such as megavoltage cone‐beam CT (MV‐CBCT) and digital tomosynthesis (MV‐CBDT). Our overall goal is to develop a new generation of area detectors for MV‐CBCT/DT, with a QE an order of magnitude higher than that of current EPIDs and yet an equivalent spatial resolution. To this end, a novel direct‐conversion design of such a high QE detector was introduced recently [Pang and Rowlands, Med. Phys. 31, 3004 (2004)]. The purpose of this work is to construct and evaluate a prototype single‐row detector. Method and Materials: A prototype single‐row detector was constructed based on the novel design. It consists of a single custom‐made printed circuit board (with microsize cavities, charge collection electrodes and microstrip spacers) sandwiched between two identical tungsten plates. The detector array has 128 pixels each with dimensions of 0.45mm (width)×0.6mm (length)×22mm (height). The detector array was placed inside a sealed vessel filled with Xe gas (ionization medium) and then connected to a data acquisition board (XDAS, Electron Tubes Ltd.) for readout. Some fundamental imaging properties including QE, noise power spectrum (NPS) and detective quantum efficiency (DQE) were measured with a 6MV beam. Results: Phantom images were obtained using a dose as low as one Linac pulse. The QE of the prototype is ∼ 66% at 6MV. The DQE at zero frequency is more than an order of magnitude higher than that of current EPIDs. Conclusion: This work demonstrated the feasibility of our novel design for a high QE MV detector. Construction and evaluation of a prototype flat‐panel area detector is in progress.Conflict of Interest: Supported by the DOD Prostate Cancer Research Program (DAMD17‐04‐1‐0276).
TH‐D‐224C‐02: The State of Radiotherapy Physics Through The Eyes of a Quality Auditor
Authors: Followill D , Molineu A , Alvarez P , Ibbott G 
Published: July 2006

Purpose: To assess the radiotherapy programs of institutions participating in NCI sponsored clinical trials and assist them to implement remedial actions. Materials and Methods: The Radiological Physics Center (RPC) has developed an extensive Quality Assurance (QA) program over the past 38 years. This program includes on‐site dosimetry reviews where measurements on therapy machines are made, records are reviewed and personnel are interviewed. The program's remote audit tools include mailed dosimeters (TLD) to verify output calibration, comparison of dosimetry data with RPC “standard” data, evaluation of benchmarkd and patient calculations to verify the treatment planning algorithms, review of institution's QA procedures and records, and use of anthropomorphic phantoms to verify tumor dose delivery. The RPC assists institutions in finding the origins of discrepancies, and in resolving them. Results: The percent of institutions receiving dosimetry recommendations has been level at 70% for the past 5 years. The most frequent recommendations were for maintenance of an appropriate QA program, beam calibration, depth dose and wedge factors. Since TG‐51 was published, the number of reference calibrations meeting the RPC's ±3% criterion has decreased. The TLD program shows that only ∼3% of the beams are outside our ±5%/±5mm criteria, but these discrepancies are distributed over nearly 15% of the institutions. There continues to be a 33% percent first time failure rate for the IMRT H&N anthropomorphic phantom. The other anthropomorphic phantoms, i.e. pelvic IMRT, lung stereotactic and liver stereotactic, have higher pass rates. Conclusion: Numerous dosimetry errors continue to exist and the RPC's QA program plays an important role in identifying and helping institutions resolve these errors to improve not only the quality of clinical trial patients' treatments, but also all patients treated at the participating institution.This work was supported by PHS grants CA10953 and CA081647 awarded by NCI.