bluuebunny/crossref_metadata_2025_split huggingface dataset:
MO‐B‐T‐6E‐01: Fundamental Issues in IMRT Treatment Planning
Authors: Xia P 
Published: June 2005

Inverse planning in intensity‐modulated radiotherapy (IMRT) drastically changes our thinking process in treatment planning because of using computer optimization. Unlike conventional forward planning, which highly depends on the geometric relationship between the tumor and the surrounding normal tissues, inverse planning critically depends on the specification of dose constraints to the target tumor and sensitive structures. For a particular inverse planning system, one has to have a good understanding of the inverse planning system and a good intuition about the relationship between the dose constraints and the resulting dose distributions. This review course session will focus on fundamental issues in IMRT treatment planning. We will try to answer the following questions: What are the basic components of commercial IMRT treatment planning systems, and how do they work? What is typical behavior of an IMRTP system? How can the user systematically search for a proper dose constraint for a specific disease site? How does the planner know when to quit trying to improve the plan? Lastly, to what extent and how can the typical problems with generated plans be ameliorated? Issues specific to head and neck and prostate IMRT treatment planning will be discussed.Educational Objectives:1. To understand the basic components of commercial IMRT treatment planning systems;2. To obtain a good intuition about the relationship between the dose constraints and the resulting dose distributions;3. To understand methods for developing class solutions for specific disease sites to streamline the planning process;4. To understand special clinical issues related to IMRT treatment planning.Research is supported by Siemens and Prowess.
TU‐A‐I‐611‐01: Effect of Scan Parameters in Cardiac Imaging with MDCT
Authors: Mahesh M 
Published: June 2005

Cardiac imaging has become a reality with the introduction of multiple‐row detector computed tomography (MDCT) technology. Rapid evolutions in multiple row detectors ranging from 4 to 64 rows have led to the progression towards isotropic resolution imaging. This has become possible with improved technical factors such as sub‐millimeter spatial resolution in z‐direction (< 1mm), shorter scan time (< 400 ms), high temporal resolution (< 250 ms) and fast reconstruction of multiple data sets at various intervals in the cardiac cycle yielding larger 3D image data sets. Recently CT imaging, especially cardiac imaging is not confined only to conventional imaging areas such as Radiology but is also performed outside the conventional imaging areas such as Cardiology. In such cases, medical physicists often become the conduit between imaging and non‐imaging areas in assisting the clinicians to understand key features of MDCT. Therefore, it is critical for the medical physicists to become familiar with the various scan parameters and how they influence the overall image quality, so that he or she can provide valuable contributions towards developing appropriate scan protocols, developing strategies for radiation dose reductions and many other aspects. CT image quality in general is influenced by a variety of scan parameters such as kVp, mAs, pitch, image noise, slice thickness, reconstruction algorithms etc. With cardiac CT imaging in mind, the presentation will discuss the effect of various scan parameters and how it affects the radiation dose and image quality.Educational Objectives:1. To become familiar with the advantages and disadvantages of various MDCT data acquisition modes.2. To describe the effects of scan parameters on image quality and patient radiation dose.3. To become familiar with spatial, temporal resolution and other key requirements in cardiac imaging.4. To illustrate the image quality requirements in select clinical imaging sequences.
TU‐A‐T‐6E‐01: Patient QA
Authors: Ramsey C , Mahan S 
Published: June 2005

The number of patients treated with Intensity Modulated Radiation Therapy (IMRT) has grown dramatically over the past five years. Recent clinical studies have shown that IMRT has the potential to improve outcomes for multiple disease sites and pathologies. However, the clinical successful or failure of each individual institution's IMRT program is dependant on the correct delivery of the 3D dose distributions calculated by the planning system (Planned Dose) to the correct location in the patient (Delivered Dose). There are many sources for errors that can arise during IMRT planning and delivery, but it is ultimately the responsibility of the Medical Physicist to ensure that the Planned Dose “agrees” with the Delivered Dose. Unlike conventional and 3D conformal radiotherapy, IMRT plans must be verified for each individual patient because of the many sources of potential error. The difference between Planned Dose and Delivered Dose (i.e. Error) in IMRT can originate from at least three different sources: 1.) The Treatment Planning Model, 2.) Treatment Delivery Mechanics, and 3.) Time‐Dependant Target/Tissue Positioning. The only method for determining the cumulative effect of all these potential sources of error is to measure the entire delivery sequence on the linear accelerator for each patient. Patient‐Specific IMRT quality assurance (QA) measurements can be classified into three levels. Level I measurements are taken using film, diode arrays, electronic imaging devices, etc. The measurement device(s) are typically placed at depth in water‐equivalent material. Level II measurements are taken with a phantom that moves to simulate intra‐fraction motion (such as respiration motion). These measurements are typically made with film, diodes, and/or ionization chambers. Level III measurements are performed using daily CT imaging acquired on the delivery system (CT‐on‐Rails, Cone‐Beam CT, Megavoltage CT, etc…). Electronic detector data acquired during treatment delivery is then combined with the daily CT images to reconstruct the doses delivered to the patient. This presentation will discuss commercially available dose measurement tools, phantoms, and techniques for performing Level I and II patient‐specific IMRT quality assurance. The current status of research and development in Level III IMRT quality assurance will also be discussed. Issues associate each technique will be discussed and clarified with practical examples. Recommendations will be presented for acceptable tolerances and testing frequencies.Educational Objectives:1. To understand the issues surrounding patient‐specific IMRT quality assurance2. To understand the difference between patient‐specific QA techniques3. To identify potential sources of errors in IMRT quality assurance4. To understand the impact of target localization and patient positioning on IMRT
TU‐C‐T‐6C‐03: Simplifying IMRT Plans Through Efficient Segmentation
Authors: Siochi R 
Published: June 2005

Purpose: To analyze the various methods for creating efficient leaf sequences for an IMRT plan, subject to MLC constraints. Method and Materials: An IMRT treatment plan can be simplified at several stages. Careful beam placement can lead to simpler intensity maps. The choice of the dose optimization engine, as well as the spatial and intensity resolution can also affect map complexity. To further reduce the total number of segments and monitor units, an optimal leaf sequence must be used. This reduction is accomplished by a combination of segment extractions and sweeps. The algorithms involve the determination of MLC shape and MUs. Some algorithms use predefined MUs according to a sequence (e.g. Power of two, Half‐Maximum, Triangular numbers), while others optimize the MU selection by evaluating the complexity of the difference between the intensity map and the segment being considered. The selection of the MLC shape can also be achieved through a predetermined geometric process (e.g. largest area, largest area with maximum intensity, leftmost segment, graph theory) or by minimizing the complexity of the difference map. In this step, the machine constraints and the desire to reduce the tongue and groove effect are considered, as they can dramatically increase the number of segments and MUs. Once the leaf sequences have been generated, an examination of the plan may reveal degradation in the DVHs, and appropriate leaf‐sequence modifications can help restore the plan quality. Results: Plans with beams that have minimal critical structure involvement and modulate with more leaves yield less segments and MUs. Optimizers that use gradient methods rather than simulated annealing tend to reduce modulation scaling factors by a factor of 2 to 3. A map resolution of 10 to 15 intensity levels and a leaf spacing of 6 mm produce a reasonably efficient plan without sacrificing its quality, provided that the leaf sequence is optimized by minimizing the difference map complexity. The collision constraint increases the number of segments and MUs by about 20%, and various levels of tongue and groove correction provide an additional increase of about 20 to 30%. Post processing can remove low weight segments, and leaf positions can be adjusted to eliminate hot and cold spots. Conclusion: In order to simplify an IMRT plan, one must take advantage of all the options that affect the leaf sequencing process, including beam placement, map resolution, segmentation algorithm choice and post‐processing.Educational Objectives:1. To understand the importance of beam selection and set‐up prior to plan optimization.2. To know the impact of map resolution set‐up on complexity and the achievement of clinical goals.3. To know the limitations and strengths of the various algorithms for leaf sequencing and how to choose the appropriate one.4. To become familiar with the post‐processing of leaf sequences.
TU‐D‐I‐609‐04: Effect of Reader Variability On Improvements in Breast Cancer Detection Rates
Authors: Jiang Y , Miglioretti D , Metz C , Schmidt R 
Published: June 2005

Previous investigations have demonstrated variability among radiologists in the interpretation of screening mammograms. This presentation will discuss the extent of this variability and its effect on clinical trials that compare the conventional screening‐film mammography and new technologies such as full‐field digital mammography (FFDM) and computer‐aided detection (CADe). We will present data on breast cancer detection rates at the conventional screen‐film mammography of over 500 practicing community radiologists in the US. By postulating a large improvement in the cancer detection rate that would be achieved with a hypothetical new technology, we predicted the cancer detection rate that would be observed in a hypothetical clinical trial comparing the new technology and the conventional screen‐film mammography. Despite a large postulated improvement in the cancer detection rate, it is difficult for clinical trials to demonstrate this improvement. Variability among radiologists in the observed cancer detection rates is an important cause for this difficulty. Clinical trials need to include large samples of radiologists in addition to large samples of patients to achieve sufficient statistical power to detect an improvement in the breast cancer detection rate in screening mammography. FFDM and CADe clinical trials, many of which appear to lack statistical power, will be discussed.Educational Objectives:1. To understand the sources and extent of variability in radiologists' breast cancer detection rates in screening mammography.2. To understand the impact of reader variability on clinical trials that compare imaging technologies in screening mammography.3. To understand the need to sample a large number of radiologists in addition to sampling a large number of patients to demonstrate an improvement in breast cancer detection rate in screening mammography.4. Financial Disclosure: C Metz and R Schmidt are shareholders of R2 Technology, Inc.
WE‐A‐I‐617‐01: PET/CT Attenuation Correction and Image Fusion
Authors: Carney J 
Published: June 2005

PET/CT scanners provide intrinsically co‐registered CT and PET images in a single scan session, which can then be viewed together as a fused image showing both anatomy and function. This in particular allows for excellent localization of features in the PET image. Furthermore, with the CT scan performed prior to the PET scan, routine attenuation correction of the acquired PET data is possible. The use of CT images for this purpose in PET/CT scanners has the advantages of shorter scan times and effectively noiseless transmission images as compared to the transmission scans that are used in standalone PET cameras. This does however require the non‐trivial step of transforming the CT images to 511 keV attenuation images that are reprojected to obtain the desired attenuation correction factors. This lecture will describe the use of CT images for attenuation correction in PET/CT scanners and address the advantages and challenges of this procedure and the use of fused images in the clinical environment. Improved attenuation correction procedures to take account of different kVp settings in the CT protocol, as well as the particular challenges in emerging applications such as cardiac PET/CT will be addressed.Educational Objectives:1. Review the principles of attenuation correction in PET and the implementation of this procedure using CT images in PET/CT imaging.2. Understand the particular challenges of CT‐based attenuation correction, including the choice of respiration protocols and other problems of patient motion, the use of CT contrast agent, and the presence of foreign objects in the body.3. Review the advantages of image fusion in PET/CT, and the clinical challenges of registering the CT and PET imaging modalities that remain, such as respiration.
WE‐B‐I‐617‐01: Optimizing MRI Protocols — Clinical Practice and Compromises
Authors: Clarke G 
Published: June 2005

Modern MRI systems are extremely flexible so that optimal usage requires a solid understanding of the physics of the basic processes involved. In the end, determination of the “best” protocol to address a clinical problem requires careful consideration of trade‐offs between image contrast, signal‐to‐ noise ratio (SNR), spatial resolution, temporal resolution and patient safety. The major factors in considering MR image contrast are the relaxation times: T1 & T2, magnetization transfer mechanisms, physiological motion and the radio frequency (rf) pulsing scheme. The most important issues for SNR are field strength, rf coil properties, voxel size, and receiver bandwidth. Factors pertinent to spatial resolution include magnetic field homogeneity, gradient strength, matrix size, slice thickness and field of view. Imaging speed is determined by gradient slew rate, signal digitization rate, number of slices, parallel imaging mode & signal‐to‐ noise ratio. Patient safety issues are related to patient size, field strength, rf pulsing method and gradient slew rate. In this presentation the basic relationships amongst all of these parameters in MRI will be reviewed and their interactions discussed. For instance, the long TR values required for strongly T2‐weighted images is an example of how contrast requirements can limit imaging speed. High‐speed T2‐ weighted images can be obtained using Fast Spin Echo strategies, but only by compromising spatial resolution and the number of slices while increasing rf heating. Specialized clinical imaging protocols that push the envelope in several of these general areas will also be examined. The use of three‐dimensional MR angiography to maximize contrast while preserving good SNR at high imaging speeds will be explored. The conditions under which certain signals from particular types of tissues, such as adipose or cerebrospinal fluid, can be entirely eliminated will be surveyed. Roles for the use of exogenous agents to alter tissue contrast shall also be reviewed. Trade‐offs required to image the heart's motion in real time will be appraised. The implications of rf heating, as measured by the specific absorption rate, will also be considered. At the end of this presentation the attendee shall:1. understand the primary types of image contrast used in clinical MRI and the relationships between pulse timing parameters and relaxation times of tissue on the acquired MRI signal.2. know how to consider the interactions between SNR, spatial resolution and imaging speed and their relative weighting in defining image quality for a variety of clinical situations.3. be conversant with circumstances under which patient physiology and magnet field strength may require modification of image acquisition parameters to achieve optimal image quality.
WE‐C‐P‐618‐01: Radiological Awareness Training for First Responders and Health Care Providers
Authors: Adair J 
Published: June 2005

The Washington State Department of Health's Division of Environmental Health has been actively involved in providing radiological training for a broad spectrum of first responders and health care providers since 2003, through its Office of Radiation Protection (ORP). Much of the training is given by ORP staff, which also coordinates training given by outside experts. The topics include response to weapons of mass destruction (U.S. Department of Justice) and radiation emergency medical care (U.S. Department of Energy). Attendees include local public health, doctors and nurses, the Federal Emergency Management Agency, the U.S. Navy, emergency medical technicians, firefighters, hazmat responders, and law enforcement. Classes are customized for each profession, are unique and interactive, and include real radioactive materials at a mock incident scene to incorporate a sense of believability. The Department of Health's goal is to educate Washington's first responders and health care providers about the health risks from incidents involving radioactivity, both to the victims and to themselves.Educational Objective:1. To review the current NRC Part 35 training and experience requirements.
WE‐D‐T‐6C‐03: Development of Image Software Tools for Radiation Therapy Assessment
Authors: Cao Y 
Published: June 2005

There has been extensive recent interest in the potential power of emerging imaging tools for early prediction of therapy effectiveness, both related to tumor control and normal tissue damage. These prognostic indicators are the results of combining improved imaging hardware, specialized scanning protocols, and advanced image processing and analysis paradigms. In order to study and eventually use these tools routinely in the radiotherapy process, serious consideration needs to be given to the software environment necessary for proper data collection and analysis ties to individual patients' treatments. Imaging for therapy assessment (IAT) presents a multidimensional information environment, requiring data from different imaging modalities and acquisition methods, as well as handling temporal data series, combined over short (breathing, dynamic contrast) and long (temporal changes over weeks of treatment) time periods. The information needed for relating these data sets for analysis (non‐rigid transformations, proper labeling of studies to measurement states) exceeds the capacities of existing DICOM standards. The extraction of analyzed information and relation to regional (radiation) dose should be multidimensional, and not restricted to voxel‐specific regions. Examples of imaging studies underway for therapy assessment will be presented. Software requirements will be demonstrated through an example system currently in use to support clinical trials at the University of Michigan. This system was designed around the unique needs of IAT, and is able to combine information from multiple sources (e.g., MRI, MRS, CT, PET, radiation dose) and time periods in an intuitive interface. This system has been used for studies of blood flow and volume, regional venous perfusion, vascular permeability, water diffusion, metabolite, and local contrast enhancement for high dose radiotherapy trials in the brain, lung, and liver to date.Educational Objectives:1. Understanding the unique needs related to imaging for assessment of radiation therapy.2. Understanding the required tools beyond those found in a typical treatment planning system3. Understanding a common ground needed for combining efforts of imaging physicists, radiation physicists, physicians and statisticians.4. Understanding opportunities for novel paradigm and algorithm development
Aristides Leão’s discovery of cortical spreading depression
Authors: Somjen G. G. 
Published: June 2005

This essay looks at the historical significance of three APS classic papers that are freely available online:Leão AAP. Spreading depression of activity in the cerebral cortex. J Neurophysiol 7: 359–390, 1944 ( http://jn.physiology.org/cgi/reprint/7/6/359 ).Leão AAP. Pial circulation and spreading depression of activity in the cerebral cortex. J Neurophysiol 7: 391–396, 1944 ( http://jn.physiology.org/cgi/reprint/7/6/391 ).Leão AAP. Further observations on the spreading depression of activity in the cerebral cortex. J Neurophysiol 10: 409–414, 1947 ( http://jn.physiology.org/cgi/reprint/10/6/409 ).
Development of Forest Structure and Leaf Area in Secondary Forests Regenerating on Abandoned Pastures in Central Amazônia
Authors: Feldpausch Ted R. , Riha Susan J. , Fernandes Erick C. M. , Wandelli Elisa V. 
Published: June 2005

AbstractThe area of secondary forest (SF) regenerating from pastures is increasing in the Amazon basin; however, the return of forest and canopy structure following abandonment is not well understood. This study examined the development of leaf area index (LAI), canopy cover, aboveground biomass, stem density, diameter at breast height (DBH), and basal area (BA) by growth form and diameter class for 10 SFs regenerating from abandoned pastures. Biomass accrual was tree dominated, constituting ≥94% of the total measured biomass in all forests abandoned ≥4 to 6 yr. Vine biomass increased with forest age, but its relative contribution to total biomass decreased with time. The forests were dominated by the tree Vismia spp. (&gt;50%). Tree stem density peaked after 6 to 8 yr (10 320 stems per hectare) before declining by 42% in the 12- to 14-yr-old SFs. Small-diameter tree stems in the 1–5-cm size class composed &gt;58% of the total stems for all forests. After 12 to 14 yr, there was no significant leaf area below 150-cm height. Leaf area return (LAI = 3.2 after 12 to 14 yr) relative to biomass was slower than literature-reported recovery following slash-and-burn, where LAI can reach primary forest levels (LAI = 4–6) in 5 yr. After 12 to 14 yr, the colonizing vegetation returned some components of forest structure to values reported for primary forest. Basal area and LAI were 50%–60%, canopy cover and stem density were nearly 100%, and the rapid tree-dominated biomass accrual was 25%–50% of values reported for primary forest. Biomass accumulation may reach an asymptote earlier than expected because of even-aged, monospecific, untiered stand structure. The very slow leaf area accumulation relative to biomass and to reported values for recovery following slash-and-burn indicates a different canopy development pathway that warrants further investigation of causes (e.g., nutrient limitations, competition) and effects on processes such as evapotranspiration and soil water uptake, which would influence long-term recovery rates and have regional implications.