bluuebunny/crossref_metadata_2025_split huggingface dataset:
MO‐D‐L100F‐04: Imaging With Distributed Source Arrays
Authors: Pelc N 
Published: July 2007

While the vast majority of x‐ray imaging procedures use a single x‐ray source, a growing number require measurement of x‐ray transmission from different locations. These exams are generally performed by moving a single x‐ray source to many positions. Examples include computed tomography (CT) and tomosynthesis. At the same time, several technologies are now becoming more available that enable to construction of source arrays, i.e., a large number of sources that can be turned on in sequence. The purpose of this presentation is to explore the capabilities and benefits of imaging with these source arrays.In CT, small deflections of the x‐ray focal spot (on the order of a millimeter) have been used to improve data sampling. Multiple sources or much larger deflections (on the order of centimeters) in the axial direction can be quite useful for increasing the thickness of the imaging slab in a single scan while reducing cone beam artifacts. Distributing sources in the circumferential direction can dramatically reduce the mechanical rotation needed to obtain a complete data set and therefore can shorten the scan time. The recently introduced dual source CT system is the most recent incarnation in this direction. The limiting case is CT scanning with no mechanical rotation, as in electron beam CT. An array of sources separated in the circumferential direction can also be used to reduce the size of the detector array. This can lead to a reduction in detected x‐ray scatter and perhaps in the adoption of more advanced detector technologies. It also provides a reasonable method for optimization of the incident intensity distribution, thereby potentially reducing the dose to the patient while also tailoring the distribution of quantum noise across the image.In tomosynthesis, as in CT, measurements from different directions are used to produce tomographic information, albeit with imperfect spatial separation due to data insufficiency. Nonetheless, tomosynthesis can be powerful in many settings where obtaining complete CT data is difficult, and is gaining popularity. Data acquisition with mechanical motion of a single source is limiting both in the needed imaging time and in the number of projections that can be obtained. A small number of projections makes the blurring function (the “crosstalk” from one location to another from imperfect spatial separation) very discrete and potentially distracting to the viewer. Source arrays can be used to produce tomosynthesis images with very short imaging time and smooth blurring functions, both of which are preferred.Thus, there are significant benefits from the use of distributed sources. The author anticipates that these source arrays will become more widely adopted.Research sponsored by GE Healthcare.Educational Objectives:1. become familiar with the types of source arrays and their capabilities.2. understand the benefits of source arrays in computed tomography.3. understand the benefits of source arrays in tomosynthesis.
MO‐D‐AUD‐04: A Comparison of Heterogeneity Correction Algorithms Within a Lung PTV
Authors: Alvarez P , Molineu A , Hernandez N , Followill D , Ibbott G 
Published: July 2007

Purpose: To compare the measured dose distribution with the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center's anthropomorphic thorax phantom includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was sent to 25 institutions, each of which was instructed to design and deliver a stereotactic treatment plan. The plan was intended to deliver 20Gy (homogeneous calculation) to ⩾ 95% of the PTV and limit the lung dose at point 2 cm from the PTV edge to 11.7 Gy. The institutions were asked to recalculate the dose distribution with the heterogeneity correction using the monitor units determined from the homogeneous calculated plan. TLD and radiochromic films were used as dosimeters within the target region. Results: A total of 17 institutions met the phantom irradiation criteria: +/− 5% for DTLD/DInst, and +/−5mm DTA on all sides of the PTV, based on the heterogeneous calculated plan. For these irradiations, the delivered doses over the central 80% of the PTV were compared to the planned doses along 3 orthogonal profiles through the PTV. An average of 85% of the points in the profiles from the cases calculated with the superposition/convolution algorithm were within 5% of the calculation, while only 69% of the points from the plans using pencil beam and Clarkson were within the 5% of the plan. Conclusions: The superposition/convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms because it more accurately accounted for the lack of lateral scatter.Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.
MO‐D‐M100J‐01: Dose Painting With Intensity Modulated Proton Therapy and Intensity Modulated X‐Ray Therapy: A Comparison
Authors: Flynn R , Barbee D , Bowen S , McCall K , Bentzen S , Mackie T , Jeraj R 
Published: July 2007

Purpose: To compare intensity modulated proton therapy (IMPT) versus intensity modulated x‐ray therapy (IMXT) for the delivery of nonuniform dose prescriptions based on hypoxia‐imaging, so‐called dose painting. Materials and Methods: IMXT delivered with helical tomotherapy (HT) was compared to IMPT delivered with spot scanning (SS) and distal gradient tracking (DGT). The novel DGT method places beam spots where dose prescription gradients occur along the pencil beam axis. Fundamental dosimetric properties of each modality were assessed by creating optimized plans for 144 variations of a cylindrical phantom with six boost regions embedded inside a base tumor region. Clinical cases with biologically conformal dose prescriptions based on PET with the ‐ATSM hypoxia imaging radiopharmaceutical were planned. The effects on the nonuniform dose distribution of delivering IMPT on a 180° arc versus equi‐spaced beams spread over 360° were investigated. Results: Phantom studies showed that nonuniform dose plan quality for tomotherapy, SS, and DGT, was similar, but DGT plans were most sensitive to phantom size and boost region proximity. IMPT reduced normal tissue integral dose by a mean factor of around two relative to IMXT. Clinical dose deviations from the prescription were comparable for all modalities, but arc IMPT deliveries markedly reduced normal tissue dose and improved critical structure sparing without compromising the dose distribution in the tumor. Conclusions: In the target volume, IMXT and IMPT deliver comparable nonuniform dose distributions. IMPT offers improved integral normal tissue dose and sparing of critical structures over IMXT, as was the case for uniform dose deliveries. DGT reduces required beam spots by a factor of about three relative to SS. IMPT dose painting will require similar management of intrafractional patient motion as for IMXT, with the additional consideration of proton spot placement uncertainty.TR Mackie has a conflict of interest due to financial interest in TomoTherapy, Inc.
MO‐D‐BRA‐01: Hypofractionated RT: Biological Basis and Clinical Application in the Prostate and Lung
Authors: Bentzen SM 
Published: July 2007

Hypo‐fractionation, the delivery of radiation therapy with a dose per fraction >2.0 Gy, was introduced in curative radiotherapy in many centers all over the World in the period from WWII to the mid‐1970's, mainly for health economics reasons. Clinical studies published in the late 70's and early 80's showed that these schedules were often associated with excessive late toxicity compared to standard fractionation schedules, and hypo‐fractionation was abandoned in most centers. In hindsight, this negative experience largely resulted from the over‐estimation of tolerance doses in hypo‐fractionated schedules arising from the Ellis NSD formula. Logically, this historical clinical experience does not exclude that hypo‐fractionation can be acceptable or even advantageous under certain defined circumstances.The current status of the linear‐quadratic bio‐effect model in clinical practice is reviewed. Two clinical settings, where hypo‐fractionation is considered, are presented and discussed: (1) definitive radiotherapy for nonsmall cell lung cancer (NSCLC); (2) definitive radiotherapy for prostate cancer.For both NSCLC and prostate cancer the current interest in the development and clinical testing of safe hypo‐fractionation regimens springs partly from the improved physical dose distribution achievable with 3D conformal radiotherapy or IMRT. This provides a window of opportunity for escalating dose per fraction. But there is also a biological rationale for hypo‐fractionation in these two tumor types — and a slightly different one in the two cases! For NSCLC there is strong evidence that shortening the overall treatment time creates a favorable efficacy:toxicity ratio with respect to late toxicity: hypo‐fractionation is a convenient way of delivering accelerated radiotherapy. In other words, we are trading in time for dose per fraction. For prostate cancer, there are no good reasons to believe that there is a strong time factor. However, there is increasingly convincing evidence that the α/β ratio for this tumor type is low, perhaps even lower than for the dose‐limiting rectal side‐effects. This alone creates a case for exploring hypo‐fractionation in this disease.Hypo‐fractionation schedules are being tested in controlled clinical trials in several tumor types at the moment. These schedules should not be introduced in the clinic without appropriate evidence that they are safe and effective. However, based on our improved knowledge of clinical radiobiology, it appears that hypo‐fractionation schedules may yield a beneficial therapeutic ratio and/or a superior cost‐effectiveness in some clinical indications.Learning objectives:After this session the participants should be able to:1. Recognize the limitations of the traditional linear‐quadratic model.2. Summarize the changes in biological understanding of dose fractionation that have occurred over the last 10–15 years.3. Explain the rationale behind the current interest in hypo‐fractionation in NSCLC and prostate cancer.
MO‐D‐L100E‐01: Ultrasound QC Workshop
Authors: Larson S , Pfeiffer D 
Published: July 2007

Quality control (QC) testing of ultrasound scanners is important to verify the proper and consistent operation of these devices in diagnostic imaging. The increasing popularity of the American College of Radiology's ultrasound accreditation program and the upcoming Task Group 128 report, Development of QC Test Procedures for Endorectal Ultrasound Imaging, emphasize the importance of establishing a strong ultrasound quality assurance (QA) program. The American College of Radiology's ultrasound accreditation program requires a QA program be established for all ultrasound scanners, but the nature of this QA program is left largely to the discretion of the medical physicist or physician in charge. This year's workshop has been streamlined to provide information on and hands‐on experience with the types of tests recommended for a comprehensive ultrasound QA/QC program. Two brief presentations on QC testing of general‐purpose ultrasound and of endorectal ultrasound equipment particularly for prostate brachytherapy will be followed by 90 minutes of hands‐on demonstrations with experienced instructors. Various tools and phantoms for QC testing of ultrasound scanners and transducers will be available for demonstration.Educational Objectives:1. To learn the basics of ultrasound QC testing with a goal toward establishing a comprehensive QA program.2. To gain experience with various test tools for ultrasound QC.
MO‐E‐L100J‐06: Slot Scan Imaging with a High Frame Rate Flat Panel Detector‐Measurement and Correction for In‐Slot Scatter
Authors: Altunbas M , Shaw C , Liu X , Lai C , Chen L , Han T , Wang T 
Published: July 2007

Purpose: To report on the use of a new scatter measurement technique to characterize the scatter rejection properties and to further correct for the in‐slot scatter in slot scan imaging with a high frame rate flat panel detector. Method and Materials: A new slot scan imaging technique was developed with a high frame rate (7.5 fps) flat panel detector. 300 images were acquired as an x‐ray fan beam, defined by a slot collimator placed in front of the tube, was scanned across an anthropomorphic chest phantom. Time‐intensity curves were formed from the image sequence for all pixels. They were integrated over the fan beam passing frames to form the scatter rejected image signals and over all frames to form the open field image signals. By assuming the primary component to be constant during the fan beam exposure, the scatter components were extracted from the time‐intensity curves to estimate the in‐slot scatter using an iterative background estimation algorithm. The results were used to measure the scatter signals and to correct for in‐slot scatter. Results: Slot scan images of an anthropomorphic chest phantom were acquired and formed for various projected fan beam widths. 2D maps of scatter‐to‐primary ratios and contrast‐to‐noise ratio (CNR) improvement factors were generated and plotted for the slot‐scan images and compared with those for the full field, non‐grided images . In the lungs, CNR was improved by 30 to 50%, and in the mediastinum, CNR was improved by 60 to 150%. Conclusion: We have described and demonstrated the use of a new scatter measurement technique to estimate and correct for the in‐slot scatter on a pixel‐by‐pixel basis in slot scan imaging with a high frame rate flat panel detector.This work was supported in part by research grants EB00117 from the NIH‐NIBIB and CA51248 and CA104759 from the NIH‐NCI.
MO‐E‐L100F‐02: Vibro‐Acoustography: Speckle Free Ultrasonic Imaging
Authors: Greenleaf J , Fatemi M 
Published: July 2007

In this paper, we describe the principles of an imaging technique that produces a map of the mechanical response of an object to a force applied at each point. The method uses ultrasound radiation force to remotely exert a localized oscillating stress field at a desired frequency within (or on the surface of) an object. Harmonic radiation force is produced by mixing two ultrasound beams of different frequencies at their focal point. The resulting radiation force occurs at the difference and the sum of the two frequencies. In response to this force, a part of the object vibrates. The size of this part and the motion pattern depend on object viscoelastic and reflection characteristics. The acoustic field resulting from object vibration at the difference frequency, which we refer to as “acoustic emissions,” is detected by a sensitive hydrophone and used to form the image of the object that represents magnitude or phase or frequency content of the signal at each point over a raster scanned region. This method benefits from the high spatial definition of ultrasound radiation force and high motion‐detection sensitivity offered by the hydrophone. The images have no speckle and are of high contrast. We call this technique ultrasound‐stimulated vibroacoustography (USVA). The method has been applied to imaging lesions in breast, detection of calcification in vessels, detection of brachytherapy seeds in prostate, and modal vibration of vessels.Educational Objectives:1. Understand radiation pressure.2. Understand vibro‐acoustography.3. Understand possible applications of vibro‐acoustography in Medical Imaging.
MO‐E‐M100F‐02: Marker‐Less Intra‐Fraction Position Verification of Lung Tumors with An EPID in Cine Mode
Authors: Ionascu D , Park S , Killoran J , Allen A , Berbeco R 
Published: July 2007

Purpose: Patient positioning represents one of the most challenging problems in radiation therapy, especially for some thoracic and abdominal target locations that are under the influence of respiratory motion. To monitor the target during treatment, we have developed an algorithm using a conventional EPID in cine mode and a prior 4DCT scan. A study based on patient data is presented to demonstrate the feasibility of the method. Materials and Methods: Based on the 4DCT recorded prior to treatment, a digitally reconstructed fluoroscopic (DRF) series is produced for each of the treatment fields. During the treatment, a cine EPID acquisition is performed for each field as it is delivered. Post‐treatment, we produce an image mask for the individual EPID and DRF images based on the MLC leaf positions. The masks are spatially registered and the required changes are induced so that the two images have consistent field shape and size. Following the image processing, the two image series are passed through a correlation algorithm that identifies the closest DRF image for each EPID image. This enables us to associate a 4DCT predetermined breathing phase to the EPID series of images, hence allowing us to recover the tumor position during the treatment relative to the planned position. Results: Depending on the number of acquired EPID images per treatment field (depending on the prescribed treatment dose per field) we were able to recover between 70% (4 images per field) and 91% (6 images) of the 4DCT prerecorded tumor motion.Conclusion: Based on a prior 4DCT and a cine EPID image sequence taken during the treatment, we have developed a computational algorithm that enabled us to quantify the differences between the tumor motion within the 4DCT that was used to plan the dose distribution on and the actual tumor motion during the treatment.
MO‐E‐BRA‐01: IGRT and Treatment Planning: Geometric Uncertainties and Individualized Patient Treatment
Authors: Balter J , Ten Haken R , Lam K 
Published: July 2007

Widespread use of precision conformal and intensity modulated treatment techniques puts extreme emphasis on targeting. While the cloud of uncertainty associated with defining and localizing targeted tissue has been realized for quite some time, standards for working with this uncertainty are hardly widespread. When looking at the range of variations in target position across a population, it becomes clear that there is quite a range for any given body site, with some patients exhibiting very small variations, and others at extremes far beyond the population mean. The ability to characterize individual patients early on in treatment permits modification of the population assumptions used in planning, providing potential benefit to a subset of patients. Making plans robust to expected variations, especially at the start of treatment, may further aid in this individualization process. One critical tool in these endeavors is the ability to estimate potential dosimetric consequences of various levels of uncertainty, as opposed to the use of geometric margins as approximations.The educational objectives of this talk are:1. Gain an understanding of the range of geometric uncertainties in a population.2. Look at various methods of assessing individual variations and their impact.3. Compare geometric and dosimetric means of assessing the impact of variations.4. Introduce the topic of robust planning.
TU‐A‐L100E‐01: ACR MR Accreditation: Changes and the Expanding Role of the Medical Physicist
Authors: Jackson E 
Published: July 2007

The American College of Radiology MRI Accreditation Program has been active since 1996. As of November 2006, almost 4400 facilities and over 5900 individual MR units had been accredited since the initiation of the program. Until recently, there have been few changes to the accreditation requirements since the program was initiated. However, the ACR recently expanded the original Whole Body MRI Accreditation Program to include 3T systems and very recently announced a Cardiac MRI Accreditation Module. Additional modules, such as a Breast MRI Accreditation Module, are under development. In addition, the MRI Quality Control Manual, first printed in 2001 and revised, with minor changes, in 2004, is currently under revision.This continuing education course will review the current status and requirements of the ACR Whole Body MRI Accreditation Program, the requirements for and issues related to 3T system accreditation, and the recently released Cardiac MRI Accreditation Module. In addition, this course will focus on the expanding roles of medical physicists outside of the conventional ACR MR Accreditation Program involvement.Educational Objectives:1. Review of the current ACR Whole Body MRI Accreditation Program requirements and current program statistics.2. Review the recent modifications of the ACR MRI Accreditation Program, including the 3T scanner requirements as well as the requirements of the new Cardiac MRI Accreditation Module.3. Review the status of other MR initiatives that have been announced by the ACR.4. Outline the expanding role of the medical physicist in MR quality assurance and accreditation.
TU‐A‐L100F‐01: Quality Assurance Procedures for Digital Radiography
Authors: Willis C 
Published: July 2007

Diagnostic medical physicists have traditionally played a key role in the radiology department's Quality Assurance (QA) program. Procedures for QA of digital radiography (DR) systems are less well‐established than those designed for conventional screen‐film radiography. Some methods that were appropriate for conventional systems do not yield accurate results for digital systems. Methods that rely on images on film cannot be performed in a facility devoid of chemical processing. Methods that do not consider effects of all stages of the digital imaging chain from acquisition to display are likely to provide erroneous results. Digital systems often do not provide data in a convenient form for assessing performance. Nevertheless, medical physicists are responsible for designing and directing efforts to assure the safety and efficacy of DR.Development of standards for performance verification of digital radiographic systems has been outpaced by commercialization of the technology. Practitioners, operators, vendors, and medical physicists are uncertain as to how to configure, calibrate, and verify systems for the best diagnostic quality images at the lowest practical radiation exposure to the patient. Several manufacturers have fielded commercial systems for performance verification, but long term data indicating trends and action limits is rare. Sources of definitive information on practical clinical methods are also scarce in the scientific literature. This has led to the current situation where clinical imaging operations are routinely conducted using systems that are not optimized.The good news is that methods in common practice for conventional radiography can be applied with modification to digital radiography. Some of these methods are described in recent literature. The AAPM has recognized the dilemma and has initiated an effort to provide practical guidance to clinical physicists, i.e. Task Group 150.This lecture will discuss some components of a QA program for DR, including adaptation of conventional QA processes. The lecture will discuss methods of evaluating system performance and provide examples of potential interferences. The lecture will review commercial devices for performance evaluation and their limitations. Finally, some ongoing standardization efforts will be described.Educational Objectives:1. Review components of a QA program and show how they apply to DR.2. Understand how some conventional tests should be modified for a digital radiographic system integrated into an electronic image management system.3. Identify key references and standards that can be useful in QA of DR.