bluuebunny/crossref_metadata_2025 huggingface dataset:
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‐M100F‐03: A Projection Point Tracking Method for Gated 4DRT Validation
Authors: Siochi R
Published: July 2007

Purpose: To test the use of projection point tracking as an alternative to strain gauges for respiratory phase determination. Method and Materials: Projection point tracking uses 2D projection images acquired for the localization MV cone‐beam CT. A point, e.g. the top of the diaphragm under the ipsilateral lung, can be identified in each projection. In views where the top point of a surface is on a plateau, it is difficult to determine such points. By identifying the tracking point in two projections, near full exhale, separated by about 90 degrees, the location of the point in the patient can be calculated and subsequently projected onto every view, providing guide points. The tracking points on full exhale views are the guide points. Since tracking points have minimal motion between adjacent views, the tracking point on a view can be inferred from the one on the previous view and the view's guide point. A plot of the tracking point's coordinates versus view angle provides the projection track. For constant gantry rotation speeds, the projection track provides a plot of the respiratory phase. Results: An examination of projection tracks for a trained patient revealed 1) good agreement with strain gauge measurements, 2) inter‐fraction variation of tumor range of motion, and 3) inter‐fraction reproducibility of phase cycle. Two of the fractions were 180 degrees out of phase, raising the possibility of combining “near‐full‐exhale” projections to reconstruct a “full‐exhale” MV CT. With enough projection sets, it may be possible to reconstruct a 4D MV CT. The projection tracks could be used to select the appropriate views for each phase. Conclusion: Compared to strain gauges that only provide phase, projection point tracking is a more powerful method of characterizing respiration, since the amplitude of motion is also determined.
MO‐E‐BRB‐01: ASTRO's 2007 Core Physics Curriculum for Radiation Oncology Residents
Authors: Klein E , Gerbi B , Price R , Balter J , Paliwal B , Hughes L , Huang E
Published: July 2007

Purpose: In 2004, ASTRO published a curriculum for physics education. The document described a 54‐hour course. In 2006, the committee reconvened to update the curriculum. Method and Materials: The committee is composed of physicists and physicians from various residency program teaching institutions. Simultaneously, members have associations with the AAPM, ASTRO, ARRO, ABR, and the ACR. Representatives from the latter two organizations are key to provide feedback between the examining organizations and ASTRO. The subjects are based on ACGME requirements (particles, hyperthermia), while the majority of the subjects and appropriated hours/subject was developed by consensus. Results: The new curriculum is 55 hours containing new subjects, redistribution of subjects with updates, and reorganization of core topics. For each subject learning objectives are provided and for each lecture hour, a detailed outline of material to be covered. Some changes include: a decrease in basic radiological physics; addition of informatics as a subject, increase in IMRT; and migration of some brachytherapy hours to radiopharmaceuticals. The new curriculum was by the ASTRO board in late 2006. It is hoped physicists will adopt the curriculum for structuring their didactic teaching program, and simultaneously the ABR for its written exam. The ACR uses the ASTRO curriculum for their training exam topics. In addition to the curriculum, the committee added suggested references, a glossary, and a condensed version of lectures for a PGY2 resident physics orientation. Conclusion: To ensure continued commitment to a current and relevant curriculum the subject matter will be updated again in two years' time.
MO‐E‐BRB‐03: Simulation and Training Tools for Image‐Guided Radiation Therapy
Authors: Robison B , Seibert R , Ramsey C
Published: July 2007

Purpose: The goal of this study was to develop tools for the training of radiation therapists, radiation oncologists, medical physicists, and medical dosimetrists in the clinical usage of CT‐based Image‐Guided Radiation Therapy. The training application was developed in MATLAB, and will be compiled for free distribution when completed. The first version of the application will include CT‐based IGRT imaging data. Method and Materials: When the IGRT Training and Simulation application is launched, the user will be prompted to 1.) Select one of the case studies for image review, or 2.) Review Random Images. The simulator will then load the reference CT images and the IGRT CT images into the simulator from an IGRT database of example images. When loaded, the images will not be co‐registered with each other. The user will have the option to 1.) Perform an automatic image registration, or 2.) Manually register the images. Approximately one third of the stored image registrations will contain known positional errors that were purposely inserted by the investigators. In addition to developing skills with image‐registration, the IGRT simulator also contains tutorials and training datasets that address other clinical scenarios. Results: Images have been acquired from IGRT treatments that contain common errors and/or anatomical changes that occur during the course of therapy. These images will be used in the IGRT Training and Simulation application to aid in the identification of errors, such as a new tumor being developed in a lung patient, substantial tumor regression, or rectal and bladder filling in prostate patients. Conclusion: An IGRT simulator is currently being developed for the training of radiation therapists, radiation oncologists, medical physicists and medical dosimetrists. Results from the initial release of the application will be presented at the meeting.
MO‐E‐AUD‐02: A Novel Infrared Camera System for Mechanical QA of Radiation Treatment Accelerators
Authors: Kadam D , Levitsky G , Hacker F , Chin L , Lyatskaya Y
Published: July 2007

Purpose: To develop a fast and accurate procedure for mechanical QA of linear accelerators that can be used during installation and routine mechanical QA. Method and Materials: A system was developed which consists of an IR‐camera and an IR‐marker attached to the gantry, treatment table or collimator. Software was written to process signals from the IR‐camera for the duration of gantry rotation and reconstruct the trace of the marker in three orthogonal planes. A circular fit of the trace in the plane of gantry rotation provides 3D coordinates of mechanical isocenter for gantry rotation. A linear fit of this trace in orthogonal planes provides information on gantry sag and rotational hysteresis. A similar procedure was developed for table mechanical QA. Orthogonality of the planes of table and gantry rotation is determined by the angle between linear fits for the gantry and table traces. Results: Mechanical QA tests were performed in two different treatment rooms equipped with IR‐camera systems. The accuracy of mechanical alignment of the axis of rotation of the gantry and couch was demonstrated to be within 1mm of the nominal isocenter defined by the room lasers. In each treatment room, the tests were repeated three times and reproducibility of the tests was better than 1mm. The tests revealed both the known effect of gantry sag and also rotational hysteresis. Orthogonality of the planes of gantry and table rotation was also determined. Conclusions: An IR‐based procedure for mechanical QA of radiation treatment accelerators was developed and tested. This procedure accurately detects the location of mechanical isocenter and provides additional information such as the extent of gantry sag and rotational hysteresis. The system provides quantitative 3D displacement of mechanical isocenter that can be effectively used in the initial installation of accelerators as well as in an ongoing quality assurance program.
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.
TU‐A‐M100J‐01: Quality Assurance and Acceptance Testing of Gamma Camera and SPECT Systems
Authors: Halama J
Published: July 2007

The general purpose gamma camera and those configured for SPECT are the bread‐and‐butter imaging instruments in nuclear medicine, and remains the principle component in systems specifically designed for cardiac SPECT. Routine maintenance, calibration, and quality control of these imaging systems is crucial for providing the nuclear physician or radiologist images of high quality without artifact, the bane of nuclear medicine imaging. Acceptance testing, for the most part, provides baseline measurements that are used as reference data for future comparisons.

Performance measurements and quality assurance testing of gamma camera and SPECT have been quite variable. The vendors are very specific about calibration procedures that are done one site, but the quality assurance testing by the customer are left up to the individual laboratories that vary to a large part based on the expertise of the staff. Federal and state radiation safety regulatory agencies purposely do not include any gamma camera quality assurance testing in their regulations. There are now two nuclear medicine accreditation programs, one by the American College of Radiology (ACR) and the other by the Intersocietal Commission for Accreditation of Nuclear Medicine Laboratories (ICANL), that have sought to standardize nuclear medicine imaging and quality assurance procedures performed. Also specified are the qualifications of the personnel who perform and interpret the imaging results.

This lecture will provide an overview of the gamma camera and SPECT calibrations, performance measurements, and quality assurance tests, whether they are for acceptance testing or routine quality control. NEMA, ACR and ICANL accreditation program documents, and AAPM Task Group reports will be used as a backdrop for the presentation. A discussion of common image artifacts and how to avoid and correct them will also be included.

Educational Objectives:

1. Learn the basic gamma camera and SPECT performance measurements and quality assurance test procedures.

2. Become familiar with the test procedures and the frequency of testing prescribed by the ACR and ICANL accreditation programs.

3. Be able to identify common gamma camera and SPECT image artifacts and how to correct them.
TU‐A‐BRA‐01: EPID, MVCT
Authors: Pouliot J
Published: July 2007

The Mega‐Voltage Cone‐Beam CT (MVCBCT) system provides a 3D image of the patient anatomy in the actual treatment position that can be tightly aligned to the planning CT, allowing daily verification and correction of the patient position moments before the dose delivery. Integrated onto a linear accelerator, the system consists of a new a‐Si flat panel adapted for MV imaging and a workflow application allowing the automatic acquisition of projection images at low dose rate, CBCT image reconstruction, CT to CBCT image registration and couch position adjustment. MVCBCT provides accurate electron density and allows studies of dosimetrical impact of setup error, anatomical changes or in presence of implanted metallic objects.

This lecture will provide an overview of the physics characteristics of MV and MV CBCT imaging, acquisition and reconstruction, image registration, alignment precision and quality assurance procedures. A description of the workflow and a survey of the clinical applications, indications and protocols will be presented. Finally, current challenges and future developments will be addressed.

Educational objectives

1. Understand the basics of MV Cone‐Beam CT imaging.

2. Understand the possibilities of daily 3D Imaging for patient alignment and other applications.

3. Understand the clinical roles of Image‐Guided (IGRT) and Dose‐ Guided (DGRT) Radiation Therapy.

This work was supported by Siemens Oncology Care Systems.
TU‐SAMS‐L100J‐02: Determination of Dose From CT Examinations: Estimating Organ Dose Using Monte Carlo‐Based Methods
Authors: McNitt‐Gray M
Published: July 2007

Radiation dose from computed tomography has been an important issue for medical physicists for some time. This issue has increased in significance in the past several years due to advances in multidetector CT, which have resulted in increased utilization in areas such as pediatric CT, cardiac CT and even screening applications. Some of the key issues currently facing the medical physics community are assessing dose to patients from these various exams. One of the key building blocks to these assessments is the estimation of organ dose.

The purpose of this presentation is to describe an approach to estimating organ doses to patients using Monte Carlo‐based simulation methods. In this approach, both the scanner and patient are modeled in some detail and a CT exam may be simulated.

The detailed modeled of the CT scanner is created by including information such as the source spectra and filtration, its geometry, beam collimation and the path that the source travels around the patient (such as the path during a helical CT exam). The development, testing and validation of these models will be discussed.

Patient models generally fall into two categories. The first consists of geometric descriptions of organs (based on cones, cylinders, etc.) such as the MIRD phantom. The second consists of voxelized descriptions of patient anatomy that are created based on actual patient scans. In these, radiosensitive organs are identified in the image data to create a voxelized model of the patient geometry. For both types of models, there are challenges to create models representing patients of different sizes, ages and genders.

Once both the scanner and patient are modeled, then different scan protocols can be simulated using a Monte Carlo based software package (such as MCNP or EGS). This involves selecting a scanner model, a patient model and then selecting a set of technical parameters, such as one would do for an actual scan — including body region being examined, etc. The Monte Carlo software then simulates the specified scan and tallies absorbed dose in each voxel or geometric unit of the patient model, which then allows the calculation of either mean organ dose or the distribution of dose within an organ.

In this presentation, the results of this approach in several applications will be described, including: (a) dose to the fetus in pregnant women of early, middle and late gestational ages, (b) comparing dose to glandular breast tissue from thoracic CT scans both with and without tube current modulation.

Educational Objectives:

1. Understand the Monte Carlo simulation based approach to estimating radiation dose to radiosensitive organs from CT scans.

2. Understand the current limitations of the Monte Carlo based approach.

3. Describe the results of some current applications of this approach to estimating fetal dose as well as breast dose reduction from tube current modulation.
TU‐SAMS‐AUD‐01: QA for Linacs and MLC Used for IMRT
Authors: Xia P
Published: July 2007

Intensity‐modulated radiotherapy (IMRT) has become a part of our routine treatment for external beam radiotherapy. Most quality assurance procedures set for linear accelerators and multi‐leaf collimators (MLC) have been designed for conventional external beam radiotherapy. With IMRT, radiation portals are often irregular, small, off‐center, and abutting in the middle of the target volumes, which require specific IMRT QA for the linear accelerators and MLCs. Some of the QA issues are related to the specific IMRT delivery method, and the specific treatment planning system. This course will discuss: (1) the characteristics of three major MLC collimators and the specific QA related to the unique MLC design; (2) additional QA for linear accelerators pertinent to the small MU and small field sizes used in IMRT; (3) tools often used to perform these QA tasks; (4) specific QA issues for different IMRT delivery methods, step and shoot vs sliding window.

Educational Objectives:

1. Understand the characteristics of three major MLC systems.

2. Understand different IMRT delivery methods and their specific QA issues.

3. Understand effect of QA on the IMRT delivery accuracy.
TU‐B‐L100E‐01: Medical Response Planning for Nuclear/Radiological Emergencies: Roles of the Medical Physicist
Authors: Ansari A
Published: July 2007

Medical health physicists working in a clinical setting have a number of key roles in preparing for and responding to a nuclear or radiological emergency, such as a terrorist attack involving a radiological dispersal device or an improvised nuclear device. Their first responsibility, of course, is to assist hospital administrators and facility managers in developing radiological emergency response plans for their facilities and train staff prior to an emergency. During a hospital's response to a nuclear or radiological emergency, medical health physicists may be asked to (1) evaluate the level of radiological contamination in or on incoming victims; (2) help the medical staff evaluate and understand the significance of the levels of radioactivity with which they are dealing; (3) orient responding medical staff with principles of dealing with radioactive contaminants; (4) provide guidance to staff on decontamination of patients and facilities; and (5) assist local public health authorities in monitoring people who are not injured but who have been or are concerned that they may have been exposed to radioactive materials or radiation as a result of the incident. Medical health physicists may also be called upon to communicate with staff, patients, and the media on radiological issues related to the event. The Centers for Disease Control and Prevention (CDC) is developing guidance in the areas of radiological population monitoring, handling contaminated fatalities, and using hospital equipment for emergency monitoring. CDC is also developing training and information materials that may be useful to medical health physicists who are called upon to assist in developing facility response plans or respond to a nuclear or radiological incident.

Educational Objectives:

1. Understand how the medical community will be involved in respond to a nuclear or radiological emergency.

2. Understand key roles that medical health physicists can play in preparing for and responding to such emergencies.

3. Learn what resources are available to assist medical health physicists and how these resources can be used.
TU‐B‐L100F‐01: Managing Patient Dose and Personnel Protection in Fluoroscopic Procedures
Authors: Balter S
Published: July 2007

Fluoroscopically guided interventional procedures continue to grow both in numbers and in complexity. When individual procedures are clinically justified, their performance should be optimized to minimize the overall (radiogenic and non radiogenic) risks to both patients and staff. Medical physicists' contributions to this objective are in proportion to their knowledge and understanding of the interventional environment.

This lecture will start with an overview of staff radiation safety. It will then emphasize patient radiation management, including the outline of an appropriate clinical program. It will conclude with a brief discussion on QA topics pertinent to interventional fluoroscopy.

Educational Objectives:

1. Understand the range of risks and benefits associated with interventional fluoroscopy.

2. Establish appropriate staff and patient radiation management programs.

3. Improve the routine physics QA process for interventional fluoroscopes.
TU‐B‐M100J‐01: Optimizing Mammography Image Quality and Dose: X‐Ray Spectrum and Exposure Parameter Selection
Authors: Williams M , Raghunathan P , Seibert JA , Kwan A , Lo J , Samei E , Ranger N , Fajardo L , McGruder A , Maxwell S , Maidment A , Yaffe M , Bloomquist A , Mawdsley G
Published: July 2007

Optimization of exposure parameters (target, filter, and kVp) in digital mammography necessitates maximization of the image signal‐to‐noise ratio (SNR), while simultaneously minimizing patient dose. The goal of this talk is to compare, for each of the major commercially available full field mammography (FFDM) systems, the impact of the selection of technique factors on image SNR and radiation dose for a range of breast thickness and tissue types. The comparison will be based on the results of a multi‐center phantom study. The five commercial FFDM systems tested, the Senographe 2000D from GE Healthcare, the Mammomat Novation from Siemens, and the Selenia from Hologic, the Fischer Senoscan, and Fuji's 5000MA used with a Lorad M‐IV mammography unit, are located at five different university test sites. Performance was assessed using all available x‐ray target and filter combinations and nine different phantom types (three compressed thicknesses, and three tissue composition types). Each phantom type was also imaged using the automatic exposure control (AEC) of each system to identify the exposure parameters used under automated image acquisition. The figure of merit (FOM) used to compare technique factors is the ratio of the square of the image SNR to the mean glandular dose (MGD). The results show that, for a given target/filter combination, in general FOM is a slowly changing function of kVp, with stronger dependence on the choice of target/filter combination. In all cases the FOM was a decreasing function of kVp at the top of the available range of kVp settings, indicating that higher tube voltages would produce no further performance improvement. For a given phantom type, the exposure parameter set resulting in the highest FOM value was system‐specific, depending on both the set of available target/filter combinations, and on the receptor type. Noise performance differed noticeably among the FFDM systems and played an important role in determining relative FOM values. In most cases, the AECs of the FFDM systems successfully identified exposure parameters resulting in FOM values near the maximum ones, however there were several examples where AEC performance could be improved.

Educational Objectives:

1. become familiar with the effect of changing kVp, target material, and filtration on the mean glandular dose for a variety of breast.

2. become familiar with the effect of changing kVp, target material, and filtration on image signal and noise for specific commercial FFDM systems.

3. learn how the exposure technique factors selected for a variety of breast types by the AECs of current FFDM systems compare with the technique factors resulting in optimal FOM values.
TU‐B‐BRA‐01: CE: Functional/Molecular Imaging: PET for Planning/assessment
Authors: Bourland J , Jeraj R
Published: July 2007

Purpose: Positron Emission Tomography (PET) images show physiological and biological information through the in vivo distribution of radioactive, positron‐emitting agents. PET imaging shows focal and distributed regions of cancer and its metastases. Initial PET uses in oncology include diagnosis and staging, which are important for determining treatment decisions. Current PET uses now include target definition for radiation planning followed by PET‐based assessment of treatment. Hybrid PET‐CT devices are beginning to be used as radiation treatment simulators. Method and Materials: F‐18‐labled Fluoro‐deoxyglucose (F‐18 FDG) is the most commonly used PET imaging agent. FDG shows regions of active glucose metabolism, such as local cancer, metastases, non‐cancer inflammation, and normal glucose use. Non‐FDG PET agents can be more specific in cell targeting (binding), and can image different aspects of tumor biology, like hypoxia (FMISO, CuATSM) and cell proliferation (FLT) Results: PET imaging has coarse spatial resolution compared to CT and MR. PET's clinical use is valued because of its great sensitivity for cancer detection. Voxel intensity and image fidelity depend on equipment design, patient size, anatomic site, and imaging study parameters. PET‐CT units enable CT‐based attenuation corrections and inclusion of CT information in a registered PET‐CT dataset. The Standardized Uptake Value (SUV) is a normalized intensity measure for quantitative indication of disease, and can be used to identify disease or possibly for target delineation, with certain limitations. While FDG remains the most promising agent for tumor detection, other, biologically more specific agents (e.g., FMISO, CuATSM for hypoxia imaging or FLT for cell proliferation imaging) might be more appropriate for target delineation and treatment assessment. Conclusion: This course reviews PET‐CT hybrid scanning devices, uses of FDG and non‐FDG PET for oncology imaging, and quantitative aspects for PET‐based radiation target definition and treatment assessment. Example images demonstrate the potential contributions and limitations of FDG and non‐ FDG PET oncology imaging. This review course is intended for both imaging and radiation oncology physicists.

Educational Objectives

1. Describe FDG PET imaging and oncologic indications.

2. Review the uses and limitations of PET images in radiation treatment.

3. Describe the SUV and other threshold parameters for target delineation.

4. Review non‐FDG PET imaging of tumor biology.

5. Discuss quantitative aspects of PET imaging for treatment assessment.

Conflict of Interest: (JDB) Research sponsored in part by Varian Medical Systems.
TU‐B‐BRB‐02: Monte Carlo — II: Application of Monte Carlo to Clinical IMRT Treatment Planning
Authors: Siebers J
Published: July 2007

The goal of this course is to familiarize participants with the clinical use of Monte Carlo (MC) dose calculation algorithms in IMRT photon‐beam treatment planning. Particular focus will be applied to the actual and potential clinical impact of MC dose calculation algorithms on patient treatments. Following a brief description of the integration of MC algorithms with commercial planning systems, MC dose re‐calculation results will be compared with plans computed using the conventional commercial treatment planning system algorithms. Specific patient examples where MC computed doses differ significantly from those computed with standard treatment planning system algorithms will be presented, with the causes of the dose discrepancies identified. With this background, the roles that MC has played in actual clinical practice will be described: as a QA tool to validate treatment planning system algorithms, as a QA tool to validate individual IMRT plans, and as a treatment planning tool to improve conformity between optimized and delivered IMRT plans. Strategies to minimize MC dose calculation time during IMRT optimization will be described.

Educational Objectives:

1. To instruct clinical physicists regarding roles of Monte Carlo dose calculations for clinical IMRT patient treatment planning.

2. To describe the role of Monte Carlo in IMRT treatment planning system and patient specific quality assurance.

3. To describe clinical cases where Monte Carlo dose calculation either resulted —or would have resulted— in a change in the clinical treatment.

4. To describe the applications of and impact of Monte Carlo dose calculations for IMRT optimization.

5. This work was sponsored in part by Philips Medical Systems and Varian Medical Systems.
TU‐C‐L100J‐02: A Fiber‐Optic Coupled Point Dosimetry System for the Characterization of Multi‐Detector CT
Authors: Hintenlang D , Moloney W , Jones A
Published: July 2007

Purpose: Advances in CT acquisition techniques, primarily multidetector CT (MDCT) and cone beam CT (CBCT), make it highly desirable to develop measurement techniques that provide a more physically meaningful measurement of dose than the traditional CT dose index (CTDI). This study presents data based on a point dosimetry system utilizing fiber‐optic‐coupled (FOC) radioluminescent dosimeters to measure fundamental parameters associated with CT dosimetry. This point detector approach provides remote, real‐time dose measurements and allows direct recording of single‐scan dose profiles that contain the essential information required to determine dosimetric quantities for MDCT. Method and Materials: FOC dosimeters based on sensitive elements of either a copper‐doped quartz or coupled scintillation phosphor are characterized for their performance across the CT energy range based on energy dependence, dose linearity, and angular response. A custom Labview program provides a user‐friendly interface to control the system. Measurements were made using traditional CTDI as well as FOC dosimeter measurements for a variety of MDCT acquisition protocols. Results: Measurements along the central axis of a CTDI phantom provide a direct evaluation of the single scan dose profile. FOC peripheral point measurements detect intensity variation with tube rotation, a dependence on scanner pitch, and permit the correlation of scan parameters and dose profiles. While CTDI remains an accurate prediction of MSAD for axial CT, it is empirically demonstrated to fail for multiple scan dose profiles when pitch is not equal to one. The development of a small dosimeter that can directly measure the helical dose profile provides a useful characterization of MDCT scanning performance and an accurate prediction of MSAD. Conclusion: FOC dosimeters demonstrate high sensitivity, reproducibility, excellent dose linearity, and combined with their small physical size permit accurate point‐dose measurements. These properties provide a useful tool for the characterization of the dosimetry quantities fundamental to MDCT.
TU‐C‐L100J‐03: Radiation Dose Reduction in Interventional Cardiology Using a Fixed Circular Collimator Attached to Cardiovascular Angiography System with Flat Panel Detector
Authors: Fukuda A , Yamaguchi I
Published: July 2007

Purpose: Fixed Circular Collimator employed in cardiovascular angiography system with flat panel detector was developed to reduce radiation dose to both patient and cardiologist in coronary intervention. This study was designed to assess the radiation dose reduction using this new collimator. Method and Materials: This new collimator makes the radiation field circular and has tapered aluminum to reduce radiation dose at peripheral field.

1. Entrance air kerma with backscatter (patient) and personnel dose equivalent (Hp) to cardiologist (scattered radiation dose) were measured to verify the radiation dose reduction using fixed circular collimator under a fixed geometric arrangement. The PMMA phantom was employed to simulate the patient thickness varying from 1.0 cm to 35.0 cm in increments of 1.0 cm. Upon completion of the data acquisition, entrance air kerma and Hp to cardiologist were plotted against the phantom thickness.

2. Entrance skin regions (patient) were imaged to verify the overlap region reduction under ten routine angulations (RAO30, RAO10‐CAU30, RAO30‐CAU30, RAO30‐CRA30, LAO10‐CRA30, LAO20‐CRA30, LAO30‐CRA30, LAO45‐CRA30, LAO45, and LAO45‐CAU30). All tabletop position for every angulations were set up to image the heart center of chest phantom, subsequently, chest phantom was replaced by computed radiography and irradiated 1 sec. Results: Entrance air kerma and Hp to cardiologist were reduced by 8.0 % and 47.6 %, respectively. On the other hand, the overlapping region of skin was also reduced considerably. Conclusions: Due to the use of fixed circular collimator, entrance air kerma, the overlap region of exposed skin and Hp to cardiologist were decreased concurrently. It was considered that the use of fixed circular collimator makes the lower density of backscatter and region of interest optimize. Therefore, rectangular images should be reconsidered for safer coronary intervention. Although this study doesn't include image quality evaluation, cardiologists adopt this new collimator in clinical study currently.
TU‐C‐L100J‐04: Absorbed Dose Estimates Obtained Via PET Imaging for I‐124 Intact Antibody in Nude Mice
Authors: Williams L , Horling M , Bading J , Strand S , Colcher D , Wong J , Raubitschek A , Ljungberg M , Larsson E
Published: July 2007

Purpose: To estimate tumor targeting and radiation dose in mice receiving I‐124‐labeled anti‐CEA (Carcinoembryonic Antigen) intact monoclonal antibody. Use of I‐124 as a PET emitter is complicated by high‐energy photons (603 keV and 723 keV at 63% and 10% respectively) emitted along with the positrons (23%). Method and Materials: Intact monoclonal antibody cT84.66 was labeled with I‐124 and injected via tail vein into nude mice bearing LS174T human colon tumors (0.04 to 0.19 g). PET imaging was performed using the Siemens MicroPET RF scanner at seven time points out to 8 days post‐injection. Standard energy window of 350–750 keV was employed. Average voxel values from organ volumes of interest were used to determine relative magnitudes of activity in tumor, liver, heart (blood) and whole body. Absolute activities were calculated by normalizing these PET data to dissection results at the last time point. Bi‐exponential functions were fitted to resultant activity vs time curves and integrated to establish Ã values and residence times. Organ‐to‐organ S factors were determined by Monte Carlo analysis of I‐124 in a 20g digital mouse phantom. Organ dose was then estimated as the matrix product of SÃ. Results: Tumors were visualized within one day of injection. Average residence times for blood, tumor, liver and whole body were 45, 6.5, 7.0 and 86 hours respectively. Mean dose for the tumors was 3.3 Gy/MBq; associated liver and whole body average values were only 0.60 and 0.31 Gy/MBq respectively. Conclusions: Small colon tumors can be PET‐imaged in nude mice receiving the I‐124 anti‐CEA antibody cT84.66. By normalizing voxel results to those obtained at sacrifice, quantitative I‐124 uptakes can be measured and used to generate residence times. Ratios of tumor/liver and tumor/whole body dose were approximately 5 and 10 respectively.
TU‐C‐L100J‐07: US Population Dose From Medical Exposures: Analysis of Recent Trends
Authors: Frey G , Huda W
Published: July 2007

Background. NCRP Report 93 estimates that diagnostic x‐rays contributed an average effective dose of 0.39 mSv in 1980, and accounted for 11% of the total US population dose from all sources of man made and background radiation. The last 25 years has seen a dramatic increase of medical imaging, particularly CT, but corresponding data on US population doses are virtually non‐existent. Purpose. To estimate the average effective doses to the US population from diagnostic radiology. Method. We obtained data on the number of CT scans performed in the US in 2005 from M Bhargavan and JH Sunshine, PhD. Average effective doses for CT examinations were obtained from the 2000 UNSCEAR report. Assuming that CT accouts for about 70% of all medical exposures, as reported by Mettler et al we computed the average dose to the current US population of 300 million. Results. The average effective dose per CT examination is reported to be 8.8 mSv. The average dose from diagnostic radiology in the US in 2005, where 60 million exams were reported to be performed in 2005, would be approximately 2.5 mSv. This value is comparable to values reported in the literature, including 1.8 mSv for Belgium (1999), 2.0 mSv for Germany (1997) and 2.0 mSv for Luxembourg (2002). In the US, average natural background is 1 mSv from cosmic/terrestial/internal sources, and 2 mSv from Radon exposure. Medical exposures are becoming the dominant sources of population radiation exposure in industrialized countries. Conclusion. Population doses from medical imaging in the US may appear to have increased a factor of six or so in the last generation.