bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐E‐224A‐01: The Best of Both Worlds: Taking Advantage of Brachytherapy and External Beam Radiotherapy
Authors: Yamada Y
Published: July 2006

Introduction. Brachytherapy and external beam radiation represent opposite ends of the inverse square dose fall off spectrum. Brachytherapy is well suited for the delivery of conformal localized high dose radiation. While external beam radiation is well suited for conformal local and regional treatment, it is able to treat larger volumes in comparison to brachytherapy. This paradigm fits well with the natural history of many malignancies to provide maximal tumor control probability while minimizing normal tissue complications.

Methods and Materials. Two examples of combining brachytherapy and external beam radiation which illustrate the brachytherapy/external beam radiation therapy paradigm will be presented: The combination of high dose rate (HDR) brachytherapy and intensity modulated radiation (IMRT) for the definitive management of localized prostate cancer, and the use of a Yttrium 90 dural plaque in conjunction with image guided IMRT for vertebral body chordomas with significant epidural disease.

Results: HDR prostate brachytherapy and IMRT provides a very high level of disease control with only minor toxicity for patients with localized prostate cancer. This is likely due to careful treatment planning to minimize dose to critical structures such as the rectum and urethra while delivering a very high biologic effective dose to tumor bearing tissue. Similarly, Yttrium 90 dural plaques are able to deliver a very high dose of radiation to the dural surface, while underlying spinal cord will receive less than 5% of the prescribed dose. This will allow for a extremely high dose of radiation to be given to the planning target volume and increase the tumor control probability. Conclusions: Both brachytherapy and IMRT have inherent physical advantages that can be utilized to improve the therapeutic ratio of radiation therapy. Particularly in the management of tumors where a dose‐control relationship exits situated near dose sensitive structures, this paradigm is especially important.
WE‐E‐224A‐02: The Role of External Beam in Brachytherapy
Authors: Zaider M , Happersett L , Cohen G , Chui C , Yorke E , Zelefsky M
Published: July 2006

Combination of permanent low dose‐rate interstitial implantation (LDR‐BRT) and external beam radiotherapy (EBRT) has been used in the treatment of clinically localized prostate cancer. Patients treated with this regimen initially receive an I‐125 implant prescribed to 110 Gy followed, two months later, by 50.4 Gy in 28 fractions using intensity modulated external beam radiotherapy. While a high radiation dose is delivered to the prostate in this setting, the actual biologic dose equivalence compared to monotherapy is not commonly invoked. I shall describe methodology for obtaining the fused dosimetry of this combined treatment and assigning a dose equivalence which in turn can be used to develop desired normal tissue and target constraints for biologic‐based treatment planning. Furthermore, I shall argue that LDR‐EBRT treatments, when properly designed, may confer significant advantages in terms of: a) escalating the dose without normal tissue penalties, b) avoid the question of organ motion, and c) decrease significantly the size of the PTV.
TH‐A‐330A‐01: Optimizing Mammography Image Quality and Dose
Authors: Berns E
Published: July 2006

Digital mammography is quickly becoming the technology of choice for breast imaging with several FDA‐approved systems already available and more on the way. Digital detectors in mammography have different characteristics than the traditional screen‐film systems and care should be taken when implementing these systems into a clinical environment. This lecture is going to discuss the practical issues for the medical physicist who wants to learn how to optimize dose and image quality in mammography primarily focusing on full‐field digital mammography systems (FFDM). The lecture will be broken into several parts. The first will review currently available FFDM equipment including an overview of automatic exposure modes, quality control pertaining to image quality and dose, and system technique selection. The second part will discuss techniques for measuring dose and image quality in FFDM. The third part will discuss factors affecting image quality and dose and ways to optimize FFDM systems in a clinical environment.
TH‐A‐330D‐01: PET ‐ Radiation Safety and Shielding Requirements
Authors: Anderson J
Published: July 2006

PET/CT imaging is a relatively new imaging modality that has become standard‐of‐care for the diagnosis and staging of many medical conditions. This has led to the widespread construction of new PET/CT installations. The design of such facilities, involving aspects of both nuclear medicine and radiology practice, presents some novel problems to the medical physicist. The recently issued report of AAPM Task Group 108, “PET and PET/CT Shielding Requirements,” addresses these difficulties and provides the designer with basic information needed for this work. The information from the report as well as the workflow in PET/CT facilities, the nature of the studies that are performed, the way in which to estimate patient workloads, and the computational approaches to radiation shielding design for high‐energy photon emitters will be discussed. Specific examples for the design of PET/CT shielding will be given.

Educational Objectives:

1. To discuss the recently released report of AAPM Task Group 108 on PET and PET/CT Shielding Requirements and provide some specific examples of the methods described in that report.

2. To provide an overall understanding of the workflow, exam procedures, patient workloads, and radiation safety practices at PET and PET/CT imaging facilities.

3. To review the approaches and necessary data for calculating shielding requirements for PET isotopes.
TH‐A‐ValB‐01: ACR CT Accreditation
Authors: Pfeiffer D
Published: July 2006

The American College of Radiology accreditation program for computed tomography, introduced in 2002, is quickly gaining in popularity. It has established minimum standards for dose and image quality. Since the inception of the program, the scanners themselves have continued to evolve in complexity and capability. Medical physicists are required by the program to perform an annual survey of each scanner and are increasingly called upon to provide assistance with dose/image quality analyses. Thus, the involvement of medical physicists in CT is necessarily increasing.

To provide optimal support for facilities in the accreditation program, it is necessary that physicists be fully aware of the requirements of the program. To that end, the essentials of the program will be briefly reviewed, including personnel requirements. The quality control component of the program will be discussed, with special attention given to the annual medical physics survey. Technologist testing requirements will also be discussed.

The medical physicist can have a positive impact on the phantom images submitted as part of the accreditation process, so the site scanning instructions will be reviewed in detail, with comments made regarding common pitfalls.

With the national awareness of radiation doses in CT, this area is perhaps where the physicist can have the largest impact clinically. In this lecture, the ACR accreditation program dosimetry requirements will be presented, including a discussion of common pitfalls and corrective measures.

The education objectives of this program are to become familiar with:

1. the general requirements for the ACR CT accreditation program

2. the role and responsibilities of the medical physicist

3. the image quality and dose measurements required by the program

4. how to calculate CTDIw, CTDIvol, Dose Length Product and Effective Dose.
TH‐A‐224C‐02: Daily Localization ‐4: US, Calypso and AlignRT
Authors: Balter J
Published: July 2006

Two technologies have been recently applied to commercial product development for localization and monitoring of treatment. Electromagnetic tracking, quite mature in aerospace and surgical guidance, has evolved to development of implantable markers. Video‐based surface mapping systems have been applied to a product that rapidly extracts the anterior surface of a patient as an aid to localization and motion measurement.

These new systems show dramatic promise as aids to initial setup. Precision on the order of 1–2 mm has been described for both technologies. These systems act as surrogates for tumor localization inferring that either a) the patient's skin or b) implanted fiducial locations can be correlated to tumor position. For the prostate, implanted fiducials have shown acceptable accuracy when properly placed. For surface imaging, targets near/at the surface (e.g. breast cancer) should work very well. For other body sites, investigations are ongoing.

In addition to rapid setup, the monitoring capability of these systems presents a paradigm that has been extremely limited to date in treatment rooms. The ability to more directly infer target position to aid in gating and tracking, especially without the use of additional ionizing radiation to the patient, may have dramatic impact on targeting accuracy.

This lecture will overview these technologies, and will discuss core measurements to establish accuracy and compatibility in the radiotherapy environment. Procedures for use will be outlined, as well as potential limitations of these systems.

Educational Objectives:

1. Understand the operating principles of electromagnetic and surface localization.

2. Overview systems using these technologies.

3. Understand critical issues for commissioning of such systems.
TH‐A‐230A‐01: Heterogeneity Corrections in the IMRT Era
Authors: Papanikolaou N
Published: July 2006

Intensity modulated radiation therapy (IMRT) has revolutionized the treatment planning process. We are now able to produce treatment plans for complex target shapes that have remarkable dose conformity while respecting the tolerance doses to critical structures. Although the emphasis has been given in the implementation of faster, more efficient, and more comprehensive optimization algorithms to solve the inverse problem, little has been done in the dose calculation aspect of the planning process. The convolution/superposition algorithm is the most popular photon dose engine used in treatment planning, while the Monte Carlo algorithm although available, remains a futuristic option.

In this presentation we will discuss the algorithms that have historically been used for treatment planning with photon beams with emphasis on the convolution and Monte Carlo based methodologies and their application in IMRT planning. Clinical examples will also be presented to demonstrate the use and outcome of dose calculations in homogeneous and heterogeneous media.

Educational Objectives:

1. Review of dose calculation algorithms for photon beams.

2. Demonstrate the effect of dose algorithm selection in IMRT planning.
TH‐B‐330A‐01: Shielding Design Workshop: CT
Authors: Martin M
Published: July 2006

The application of the structural shielding design techniques and goals as outlined in NCRP Report 147: Structural Shielding Design for Medical X‐ray Imaging Facilities (2004) will be the basis for this practical course. The wide variety of facilities installing CT imaging equipment requires the medical physicist to consider an array of radiation protection concerns for the installation of these units. To meet the challenge of maintaining construction costs to a minimum while providing adequate radiation shielding protection requires the physicist to utilize all available materials to reduce radiation exposure to surrounding personnel and the public. Estimating future workloads as well as considering current workloads for uses of CT scanners as the ability to perform many more scans more quickly can present challenges. Practical examples of implementing multi‐slice scanners with a variety of imaging purposes into facilities with a wide variety of existing shielding materials will be explored in this course.

Educational Objectives:

1. Understand the methods of structural shielding design to use for sing and multi‐scan CT scanners.

2. Understand the radiation exposure limits for surrounding areas occupied by the public and occupational personnel.

3. Understand methods to predict applicable workloads for various types of facilities and CT scanners.
TH‐B‐224A‐01: QA for Linacs and MLC Used for IMRT
Authors: Xia P
Published: July 2006

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 review 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.
TH‐B‐224C‐01: Permanent Prostate Brachytherapy Using Plastic Palladium‐103 Seeds
Authors: Chen Q , Blair H
Published: July 2006

Purpose: A new model of palladium‐103 (Pd‐103) seeds with plastic encapsulation (OptiSeed103 Model 1032P, International Brachytherapy, Norcross, Georgia) is commercially available. The abstract reports the investigation of using the plastic Pd‐103 seeds in prostate brachytherapy. Method and Materials: The RTOG criteria were adopted in patient selection. A real‐time transrectal‐ultrasound (TRUS) guided transperineal implant technique was employed. A Foley catheter was used to localize the urethra. The seed placement followed a modified uniform loading protocol. At the completion of an implant, TRUS images were recorded. Post CT dosimetry was accomplished in the patient's 30‐day follow‐up visit and a seed migration survey was also performed. Results: Three prostate cancer patients underwent the Pd‐103 seed implantation. 386 loose seeds with total activity of 656.1 U were implanted. The patients tolerated the procedure. No abnormal symptoms have been reported in the first half‐year follow‐up, except the detection of 3 migrated seeds to the lungs in a patient. The seed appearances in the pelvic radiographs and CT images were similar to that of the metallic seeds. A significant seed enhancement was observed in the post‐implant TRUS images. Phantom studies showed similar results. A post plan for each patient was generated on the post‐implant TRUS images where 97% of the seeds were identified with confidence. The patterns of the seed distribution in the TRUS and CT images were similar although the GTVs were different due to implant edema. Conclusion: Regarding the dosimetry and implant process, there are no differences between the plastic and metallic seeds. A superior property of the plastic seeds is its appearance in TRUS images. The seed distribution can be immediately displayed in the TRUS images at the completion of an implant. Cold spots can be identified in real time and additional seeds may be added so as to improve the implant quality.
TH‐B‐224C‐02: Performance Evaluation and Optimization of a Novel Brachytherapy Robot
Authors: Meltsner M , Ferrier N , Thomadsen B
Published: July 2006

Purpose: To evaluate and optimize the performance of a prototype robotic manipulator designed for prostate seed implantations in a gel phantom. Methods and Materials: The prototype design is a custom‐built six degree‐of‐ freedom robot engineered for highly accurate prostate seed implantations. The robot allows for a fully automatic insertion or a manually assisted implantation using the device as a guide. The accuracy was determined using a gel phantom with a holed‐template placed at 10 cm depth. Insertion speed and rotation were varied, and the distance from the target hole was measured. The effect on the gel due to needle rotation was observed for increased damage. The experiment included both manual and automatic insertions using 30 cm, 17‐gauge, beveled‐tip prostate brachytherapy needles. Results: The optimal techniques were automatic insertions with a rotation speed of 10 rev/s or 1 rev/s. This provided a “hit” of the target 67% of the insertions with maximum displacement in the “non‐hit” insertions of 2.1 mm. The least accurate technique utilized a non‐rotated needle, which deflects towards its beveled‐tip as inserted. The total displacement from the target with this technique reached distances of greater than 8 mm for a 10 cm depth insertion with an average of 6.9 ± 0.8 mm. Conclusion: Preliminary results yielded an optimization of insertion parameters which increased the accuracy from near 1 cm to sub‐millimeter displacements. The robot was determined to have a high accuracy in tip placement within the gel. Rotation of the needle can dramatically increase the accuracy of the tip's final position. Rotating the needle at 1 rev/s yielded an accurate implant with minimal increase in gel damage. The robot used in conjunction with an optimized needle insertion technique benefits the patient with increased accuracy, leading to a more successful outcome and reduced complications.
TH‐B‐224C‐03: Robotically Assisted Needle Placement for Prostate Brachytherapy
Authors: Kennedy C , Iordachita I , Burdette C , Kronreif G , Ptacek W , Kazanzides P , Song D , Fichtinger G
Published: July 2006

Purpose: To present preliminary results for a robotically‐assisted prostate brachytherapy treatment system. Method and Materials: A 4 degree‐of‐freedom (DOF) robotic device was developed to replace the ultrasound template in a commercially available prostate brachytherapy treatment system (Interplant, Computerized Medical Systems, St. Louis, MO). The robot mounts to the existing template mounting points on the ultrasound stepper, and is capable of positioning the needles at arbitrary positions and orientations. The robot is spatially co‐registered to the Interplant treatment planning software through a calibration procedure. We performed a seed‐implantation experiment on a prostate training phantom in which the needles were positioned by the robot. The needles were preloaded with one seed, then inserted manually by the operator under transrectal ultrasound (TRUS) guidance. In this experiment, ten seeds were implanted, and their implanted positions were reconstructed using data from a post‐implant CT of the phantom and the Interplant post‐implant analysis software (iPAS). Results: Using the results from the iPAS software, we measured both the relative error of each seed (with respect to the other seeds), and the absolute error of each seed with respect to the treatment plan. The relative root‐mean‐ square (RMS) transverse error was 0.8 mm (worst case 2.1 mm, 70% under 0.7mm), and the relative RMS sagittal error was 2.5 mm (worst case 4mm, 60% under 2.5 mm). The absolute transverse RMS error was 2.4 mm (worst case 4.3 mm, 50% under 2.4 mm), and the absolute sagittal RMS error was 2.5 mm (worst case 4.5 mm, 80% under 2.5 mm). However, the absolute transverse errors were characterized by an offset in each direction, most likely resulting from errors in the measurement of the robot position relative to the phantom. Conclusion: Our system for robotically‐assisted prostate brachytherapy shows potential for improved needle placement, repeatability, and accuracy.
TH‐B‐224C‐04: Feasibility of Calibrating Elongated Brachytherapy Sources Using a Well Type Ionization Chamber
Authors: Meigooni A , Awan S , Dou K
Published: July 2006

Purpose: TG‐43 recommended parameters of a brachytherapy source require calibration of the source using the WAFAC system by the NIST. However, the presently available NIST standard system is limited for calibration of sources with active lengths ⩽1 cm. A new procedure has been introduced for calibration of elongated brachytherapy sources (i.e. active lengths > 1 cm) as an interim solution to the calibration standards by the NIST. This procedure is based on commercially available well type ionization chambers. Materials and Methods: The variation of the source calibrator response as a function of the source position along the longitudinal axis of the chamber was measured to determine the relative correction factor (RCF). Then the NIST calibrated source was used to calibrate the response of the source calibrator. A train of the 1 cm source segments were used to create elongated sources with different active‐lengths ranging from 1 cm to 7 cm. The measured air kerma strength were compared with the total source strengths calculated as the sum of the individual 1 cm source segments utilized to compose the source. Results: The results of these investigation have indicated that the response of the Capintec CRC was nearly constant (within 0.5 %) for distances ranging from 4.9 cm to 14.9 cm from the bottom of the chamber. With this information and a calibration factor of 4.881 Reading/U, air kerma strengths of RadioCoil™ Pd‐103 sources with active length of 1 to 7 cm were measured. The results of these measurements were found to be within ± 0.4% of the values calculated by addition of the 1cm source segments used in creating the sources. Conclusion: A well type chamber with the calibration for the 1 cm long RadioCoil™ 103Pd source segment can be utilized for calibrating of an elongated source with different active lengths sources.
TH‐C‐330D‐01: Introduction and Overview
Authors: Sprawls P
Published: July 2006

Medical physics education, especially for radiologists and medical physicists, is faced with several significant challenges because of a variety of conditions including the rapid changes in diagnostic and therapy technology and methods that must be addressed, prevailing attitudes on physics education within the clinical practice, and the need for qualified faculty and educational resources.

Effective and efficient medical physics education for the future will result from a general re‐engineering and adopting revised models of the educational process to clearly define the needs and desired outcomes of educational activities and then develop a variety of methods and resources that will use state‐of‐the‐art technology to enhance the performance of both the learners and learning facilitators/teachers.

This symposium provides a forum for exploring several current activities and initiatives that are significant to the future of medical physics education.
TH‐C‐330D‐03: Web‐Based Education: Current and Future Resources and Applications
Authors: Frey G
Published: July 2006

The course will present a review of web based educational materials for medical physicists. This material can be divided into a number of broad categories. These include: 1) Materials that are available to the physicist that can be used as part of a program for teaching radiology residents, radiation oncology residents, medical physics students and technologists; 2) Materials that can assist the physicists in self‐directed professional development and maintenance of certification; 3) Materials that are designed for use by students and physicists in developing areas; and 4) Materials that are designed to help physicists locate and use materials in the other categories.

This lecture will review materials in the various categories to assist medical physicists with locating and using appropriate materials.

Educational Objectives:

1. The participant will become aware of educational materials that are available on the web.

2. The participant will be able to locate appropriate materials for web based SDED.

3. The participant will be aware of the many different professional areas in which web based materials exist.
TH‐C‐330A‐02: Does Image Quality Impact Mammographic Accuracy?
Authors: Saunders RS , Samei E
Published: July 2006

Purpose: To assess the impact of resolution and noise on observer performance in detecting and classifying breast masses and microcalcifications in x‐ray mammography. Method and Materials: Simulated breast masses and microcalcifications were inserted into normal digital mammograms. A routine modified the images to simulate the effects of reduced dose. Images were viewed on three medical‐grade displays: an LCD, a CRT with normal resolution, and a CRT with degraded resolution. Five experienced breast imaging radiologists scored the lesions in the image set using a custom graphic user interface based on a categorical rating paradigm. The data were analyzed to find overall accuracy and accuracy for four specific diagnostic tasks (detection of benign masses, malignant masses, and microcalcifications, and discrimination between benign and malignant masses). Results: When using different displays but keeping noise constant at full dose, radiologists had similar overall accuracy (LCD: 0.83 ± 0.01, CRTNormal: 0.82 ± 0.01, CRTDegraded: 0.84 ± 0.01). The radiologists also had similar accuracy for each of the four clinical tasks on the three displays. Overall, no statistically significant difference in clinical accuracy was observed between the three displays (p > 0.05). When varying dose levels while only using the LCD display, the radiologist performance dropped somewhat (full dose: 0.83 ± 0.01, half dose: 0.77 ± 0.02, quarter dose: 0.61 ± 0.02). Noise had the greatest impact on the detection of microcalcifications and discrimination between benign and malignant masses. Conclusions: This work suggests that the choice of medical display has a small impact on clinical accuracy in digital mammography. The small drops in clinical performance with increased noise suggests that dose may be somewhat decreased with limited impact on clinical utility. The categorical rating paradigm should be considered for future investigations as it allows for greater image throughput while closely modeling the clinical paradigm.
TH‐C‐330A‐03: Does Display Bit‐Depth Influence Observer Performance?
Authors: Krupinski E , Roehrig H , Fan J
Published: July 2006

Purpose: The display a radiologist reads images from represents a crucial link in the information chain. There has been much debate recently on what bit‐depth is necessary for optimal reading. Greater bit depth permits more gray levels to be displayed initially, possibly obviating the need for the observer to window/level the image during viewing. This project compared an 8‐bit with 11‐bit LCD display in terms of observer performance. Method and Materials: Two Totoku LCD displays (3 Mpixel, grayscale) were used that were identical in every way except for the bit‐depth. One was 8‐bit and the other 11‐bit. Max luminance was set to 500 cd/m2 and min luminance was set to 0.6 cd/m2. The displays were DICOM calibrated and room lights were set to the average display luminance with an image displayed. A set of 100 DR chest images, half with nodules and half without, were shown to 6 radiologists in a counter‐balanced Receiver Operating Characteristic study. They reported whether a nodule was absent or present and rated heir confidence. Results: Performance (ROC Az values) was essentially equivalent for the two bit‐depth displays. There were no significant differences in viewing time or how often the readers used the window/level functions. Conclusion: For chest images with nodules it appears that having greater than 8‐bit depth does not significantly enhance observer performance. It is not clear whether the results would be the same with different types of images or lesions. Conflict of Interest: Totoku provided the displays, software and funds to reimburse the radiologist observers.
TH‐C‐330A‐05: Analysis of the Point Spread Function of Isocentric Digital Tomosynthesis (DTS)
Authors: Blessing M , Godfrey D , Lohr F , Yin F
Published: July 2006

Purpose: This project presents an analysis of the point spread function (PSF) of isocentric digital tomosynthesis (DTS). DTS is a limited angle 3‐ dimensional reconstruction from cone beam projections, with high resolution for excellent imaging of both bony anatomy and soft tissue. Its major application is on‐board imaging. The scans can be acquired during a single breath hold, thus eliminating respiratory motion artifacts without gating techniques. Method and Materials: The geometry of a linear accelerator (Clinac 21EX from Varian) equipped with a kV on‐board imager and CBCT capability was used. We simulated projection data sets of a single point source (PS) for different total scan angles from 26° to 58°. The PS was located along the horizontal axis through the isocenter from the kV x‐ray source to the detector (z‐axis). DTS reconstructions were generated from the simulated projections, using a standard Feldkamp technique. The full width at half maximum (FWHM) of the resulting PSF was computed along the z‐direction in stacks of DTS slices. Results: The PSF shows a bow‐tie shape in the z‐direction. The spread of the blurring function increases for larger scan angles. Furthermore, the FWHM decreases as both distance from the detector and the scan angle increase. FWHM values ranged from ∼2.5mm to ∼5mm near the kV source, and from ∼5mm to ∼11mm near the detector, as the scan angle was varied. For a typical 44∼ scan, the FWHM varied from ∼3mm when the PS was moved 20cm towards the source away from the isocenter, to ∼6mm when was moved 24cm towards the detector. Conclusion: The blurring effect of isocentric DTS is dependent on the total scan angle and the point of interest. These characteristics will provide guidance to imaging techniques using DTS for clinical applications.

This project is partially supported by Varian Medical System.
TH‐C‐330A‐07: Noise and Nodule Detectability in Simulated Cone Beam CT Imaging
Authors: Tu S , Shaw C , Lai C , Chen L , Liu X , Meng Y , Altunbas M , Wang T
Published: July 2006

Purpose: To evaluate and quantify the impact of various types of noise (quantum noise, photon scatter, flat panel detector blurring, and system noise) on the nodule detectability in simulated cone beam CT (CBCT) images by conducting the eight‐alternative forced choice (8‐AFC) observer performance experiment. Method and Materials: We used Radon transform formalism to mathematically model a 3D chest phantom with spherical nodules of various sizes. Quantum noise, photon scatter, detector blurring, and system noise were then simulated and added to the projection images individually. The projection images were reconstructed by using the Feldkamp algorithm and the final images were then used for the observer performance study. Other impact factors for the image quality (e.g., contrast variation, x‐ray dose, nodule size, number of projection images, cone beam angle etc.) were also incorporated into the reading study. Detection curves were then determined statistically from the 8‐AFC experimental data by using a maximum‐likelihood method. Nodule detectability was then quantified directly from the reading performance participated by 6 observers in the 8‐AFC tests. Results: Our preliminary data indicated that at the high x‐ray dose level, photon scatter had the highest impact on the simulated CBCT images; while at the low dose level, system noise had the biggest impact. At all tested dose levels, detector blurring had the lowest impact on the detectability. In consistent with the previous theoretical study, the nodule detectability can be improved by increasing the number of projection images. Conclusion: Our work indicated that using photon scatter correction techniques and reducing the system noise had the biggest potential to improve the CBCT image quality. We are currently investigating the impact of various scatter reduction algorithms and reconstruction methods on the CBCT image quality.

Supported in part by a research grant EB00117 by the National Institute of Biomedical Imaging and Bioengineering.
TH‐C‐330A‐09: Cascaded Systems Analysis of Noise Reduction Algorithms for Dual‐Energy Imaging
Authors: Richard S , Siewerdsen J
Published: July 2006

Purpose: While dual‐energy (DE) imaging provides increased nodule conspicuity in soft‐tissue images and greater calcification visualization in bone‐only images, DE image decomposition amplifies noise present in the projection data. This paper extends task‐based cascaded systems analysis (CSA) to include a variety of DE noise reduction algorithms, offering a general analytical approach to optimizing DE imaging performance. Method and Materials: Two noise reduction algorithms [simple‐smoothing of the high‐energy image (SSH) and anti‐correlated noise reduction (ACNR)] were incorporated into CSA models for DE imaging to describe the DE modulation transfer function (MTFDE), noise‐power spectrum (NPSDE), and noise equivalent quanta (NEQDE). The MTFDE and NPSDE were measured using standard edge‐spread function and flood‐field techniques adapted to DE imaging (with noise‐reduction processing) and compared to theoretical results. The MTFDE and NPSDE were combined to yield the NEQDE and integrated with a spatial‐frequency‐dependent task function to provide a detectability index for evaluation of imaging performance using standard, SSH, and ACNR image decompositions. Results: The MTFDE and NPSDE calculated using CSA agreed well with measurements. Detectability index provided an objective performance metric for identifying superior noise reduction algorithms under conditions of varying kVp, dose, and imaging task. For example, the DE detectability index for a delta‐function detection task in the soft‐tissue image was by far greatest for the ACNR algorithm, whereas SSH performed best for the bone‐only image. A gaussian detection task, on the other hand, indicated superior performance for the ACNR algorithm for both soft‐tissue and bone‐only images. Conclusions: Extension of CSA to include the influence of DE noise‐reduction algorithms such as SSH and ACNR offers a powerful guide to system optimization. The general, analytical approach provides an objective means of selecting superior noise‐reduction algorithms and “tuning” the parameters therein in a manner that weighs spatial resolution and noise in relation to the imaging task.
TH‐C‐ValB‐01: Prostate Contouring Uncertainty in Mega‐Voltage Computed Tomography (MVCT) Images Acquired with a Helical Tomotherapy Unit During Image‐Guided Radiation Therapy (IGRT)
Authors: Song W , Chiu B , Bauman G , Lock M , Rodrigues G , Ash R , Lewis C , Fenster A , Battista J , Van Dyk J
Published: July 2006

Purpose: To evaluate the image guidance capabilities of helical tomotherapy‐based MVCT, this work compares the inter‐ and intra‐observer contouring uncertainty in KVCT used for radiotherapy planning with MVCT acquired with a tomotherapy unit. Methods and Materials: Five prostate cancer patients who underwent tomotherapy treatment (with daily MVCT) at our institution were selected. One planning KVCT and one randomly selected MVCT from each patient were used. Slice spacings for KVCT and MVCT were 3 mm and 6 mm, respectively. Retrograde urethrography was performed on the KVCT studies only. For inter‐observer study, seven observers contoured the prostate on the 10 CT studies. For intra‐observer study, the same seven observers repeat‐contoured one patient's KVCT and MVCT studies. Quantitative analysis of contour variations was performed using volumes and radial distances. F‐test was performed to detect statistically significant differences between KVCT and MVCT. Results: The inter‐ and intra‐observer contouring variability was larger in MVCT than KVCT. The largest variability was mainly found in the prostate apex and base regions. Up to 1 cm (SD) was found in MVCT. In the prostate apex region, interestingly, large but similar variability between KVCT and MVCT was observed. This suggest that the use of urethrography during KVCT simulation was not very helpful. For F‐test, generally, the regions with significant differences were patient‐dependent and uniformly distributed in all directions. In terms of prostate volume, observers consistenly contoured larger prostate in MVCT (by 10 %). This reflects the poorer soft‐tissue contrast in MVCT than KVCT since observers tend to over‐estimate or over‐draw target volumes under less visible conditions. Conclusions: Based on our data, the application of MVCT for estimating daily organ motion and deformation during image‐guided radiotherapy (IGRT) is somewhat discouraging. Optimization of slice thickness and dose utilization may result in better imaging performance for prostate delineation and adaptive tomotherapy.
TH‐C‐ValB‐05: Rapid Low‐Dose 3D Image‐Guided Treatment Verification of Sites Prone to Respiratory Motion Using Breath‐Hold On‐Board Digital Tomosynthesis (DTS)
Authors: Godfrey D , Yin F , Wang Z , Yoo S , Oldham M , Willett C
Published: July 2006

Purpose: This study examines the potential use of on‐board digital tomosynthesis (DTS) for image‐guided treatment verification of sites prone to respiratory motion. DTS is a fast, low‐dose method for reconstructing 3‐ D images from 2‐D projection data, acquired with a limited scan angle. In the treatment room, a 45° DTS scan can be acquired in less than 10 seconds, making rapid breath‐hold DTS a simple method for acquiring 3‐D treatment verification images, devoid of respiratory motion. Method and Materials: On‐board DTS images of ten human liver, pancreas, and lung subjects were reconstructed from kV CBCT projection data, acquired on a Varian 21EX Clinac equipped with an on‐board imager (OBI), either during a breath‐hold or while subjects were freely breathing. Corresponding reference DTS (RDTS) images were reconstructed from breath‐hold planning CT data. Soft‐tissue visibility was compared between breath‐hold DTS and free‐breathing DTS and CBCT, to assess the potential efficacy of the breath‐hold DTS strategy for 4‐D image‐guided treatment verification. Results: Breath‐hold DTS markedly improved the rendering of soft‐tissue abdominal and thoracic anatomy, compared with free‐breathing DTS or CBCT. Organ structures were clearly defined, and even low‐contrast target malignancies were often visible in breath‐hold DTS reconstructions. Free‐breathing DTS and CBCT reconstructions, on the other hand, often exhibited artificially enlarged target volumes and poor visibility of soft‐tissue anatomy, due to motion averaging effects. Conclusion: Rapid breath‐hold DTS enhances the visibility of bony and soft‐tissue anatomy in sites prone to respiratory motion, facilitating daily localization of soft‐tissue targets. Breath‐hold DTS localization is superior to free‐breathing on‐board CBCT for thoracic and abdominal image‐guidance. Conflict of Interest: This research was supported in part by a grant from Varian Medical Systems.
TH‐C‐ValB‐08: Motion Induced Dosimetric Impacts in Breast 3D Radiation Treatment — a 4D CT Based Study
Authors: Yue N , Li X , Beriwal S , Heron D , Sontag M , Huq M
Published: July 2006

Purpose: In radiotherapy treatments of breast patients, respirations may introduce uncertainties in target and heart locations. This study is to investigate the dosimetric impacts of these uncertainties in breast radiation treatments. Method and Materials: A 4D CT scan and a conventional helical CT scan set were acquired on each of 7 left breast patients and 5 right breast patients. Using the helical CT scan, a conventional 3D conformal plan, consisting of two tangential beams, was generated per physician's evaluation and decision. The 4D CT scan set was divided into 10 phases over the respiratory cycle. On each phase, treatment target and heart were contoured. Dose distributions were generated using the same beams as in the conventional plan. Software was developed to compute the cumulative dose distribution (4D doses) from all the phases. This 4D CT image based cumulative dose distribution would be closer to that in reality with motions taken into account. Various dosimetric parameters were obtained for treatment target and heart from the conventional plan and from the 4D cumulative dose distributions and compared to deduce the motion induced dosimetric impacts in breast radiation treatments. Studies were performed for both whole and partial breast treatments. Results: For whole breast treatment, the motion induced changes in D95, Dmax, and Dmin of PTV were 0.88% ± 20%, −0.28 ± 0.65%, and −10.17% ± 47%, respectively. For left breast, the motion induced Dmax change in heart was 22% ± 48%. For partial breast treatments, the motion induced changes in V90 and Dmin of CTV were 1.6% ± 2.7% and 3% ± 4%, respectively. Conclusions: Breathing motion may cause cold spots in the whole breast treatment, and may compromise treatment quality for some patients. It may also increase heart maximum dose. However, for the partial breast treatment, the motion impact may be insignificant with properly selected margin size.

Supported in part by Varian Medical Systems.
TH‐C‐230A‐01: A Monte Carlo Investigation of the Temperature‐Pressure Correction Factor for Kilovoltage X‐Rays
Authors: La Russa D , Rogers D
Published: July 2006

Purpose: To investigate the validity of the standard temperature‐pressure correction factor (PTP) for kilovoltage x‐rays incident on various ionization chambers using Monte Carlo simulations of radiation transport. Method and Materials: The EGSnrc Monte Carlo computer code was used to calculate the response due to 20 kV, 40 kV and 60 kV beams as a function of chamber air density for thimble and spherical ionization chambers. The chambers studied had both graphite and C‐552 plastic walls to investigate the effect of the wall material in addition to the dimensions of the cavity. In principle, the PTP‐corrected response is independent of air density. Thus, a breakdown of the PTP correction factor is identified by any variation in the calculated response as the air density is varied. The air density associated with the reference temperature and pressure conditions in North America (22 °C, 101.325 kPa) is 1.205 kg/m3. Results: At an air density of 1.0 kg/m3, typical of Denver Colorado, the normalized PTP‐corrected response of a graphite‐walled thimble chamber due to the 20 kV and 40 kV spectra is as much as 1.7% and 1.2% below the expected response, respectively. For a graphite spherical chamber at the same air density, the calculated response is 3.8% below unity for 40 kV and 60 kV beam qualities. Calculated responses of chambers with C‐552 plastic walls are all within 0.5% of the expected response at air densities as low as 0.84 kg/m3. Comparisons of calculated air kerma calibration coefficients at different air densities indicate that the breakdown of the PTP correction factor should be easily detected experimentally. Conclusion: Variations in the PTP‐corrected response indicate that for low‐energy x‐rays the PTP correction factor inadequately accounts for the dependence of ion chamber response on the temperature and pressure. Additional correction factors are therefore necessary under these circumstances.
TH‐C‐230A‐02: A Carbon Nanotube Based Low LET Multi‐Microbeam Array Singel Cell Iradiation System
Authors: Chang S , Zhang J , Bordelon D , Schreiber E , Cox A , Zhou O
Published: July 2006

Purpose: Our long‐term objective is to develop innovative carbon nanotube (CNT) based multi‐pixel microbeam array system for single cell irradiation at small temporal scales and under direct microscope observation. The electron microbeam has an adjustable energy (20–60 keV) and dose rate. The microbeam l array can simultaneously irradiate a large number of individually selected cells in vitro, instead of sequentially irradiating cells one at a time using a single radiation source. From its 2,500 or more individually controllable microbeam pixels, the device offers flexibility in irradiation pattern that can be spatially discrete or uniform and temporally continuous or pulsed. Together with new advances in biosensors and cellular imaging, the proposed device can play an important role in understanding critical signaling events for both short and long term radiation effects occurring in cellular level immediately after irradiation. Method and Materials: The CNT single cell irradiation systems utilizes the unique field emission property of CNT, a quantum process that electrons escape from the metal surface under an external field. Each microbeam is generated by an individually controllable CNT pixel. The microbeam size is controlled by the Si3Ni4 electron/vacuum window and the dose rate is controlled by the external field. Results: We have fabricated the CNT field emission electron pixels, Si3Ni4 electron/vacuum windows, and a prototype single pixel CNT microbeam device. We have performed Monte Carlo (MC) simulation on the microbeam dosimetry and the effect of the Si3Ni4 window on the electron microbeam. Initial dosimetry measurement of the CNT microbeam irradiation using GARCHROMIC film and compared with the MC result. The prototype CNT system delivered a microbeam size of 20 micron and dose rate of ∼5Gy/sec. Conclusion: Our preliminary data demonstrated that the CNT‐based low LET microbeam system is feasible to deliver large dose rate and single cell (10–20 micron) microbeam irradiation.
TH‐C‐230A‐04: Characterizing a Monochromatic X‐Ray Beam From a 1.3 GeV Synchrotron for Auger Electron Radiotherapy and Dosimetry Studies
Authors: Dugas J , Oves S , Sajo E , Hogstrom K
Published: July 2006

Purpose: Auger electron radiotherapy and dosimetry methods are being studied in preparation for future small animal irradiations using monochromatic x‐ray beams and IUdR. Aims of the present study are: (1) establish methods for characterizing the LSU CAMD synchrotron monochromatic x‐ray beam and (2) validate MCNP dose calculations in polymethylmethacrylate (PMMA). Method and Materials: The synchrotron's tunable (6–40 keV), monochromatic beam was set to 15 keV and collimated to ≈2.5‐mm wide. Beam energy was determined from photons Compton scattered by a 56 mg⋅cm−2 aluminum target, whose energy was measured using a thin window 1‐mm thick × 2.54‐cm diameter NaI(Tl) scintillation detector. Beam cross section and divergence were measured using radiochromic film digitized with an Epson 1680 scanner. Depth‐dose measurements within a PMMA phantom were made using a 0.23 cm3 air‐ionization chamber. Ionization was converted to dose in air and PMMA at each depth and a percent depth‐dose curve generated. Results of MCNP5 Monte Carlo dose calculations simulating measured conditions were compared with measured data. Results: Measurements indicated the nominal 15 keV beam had energy of 15.5 keV, horizontal width of 3.1 cm, Gaussian distribution vertically with FWHM = 0.1 cm, and beam divergence <0.004 horizontally and vertically. A dose rate of 69 cGy⋅s−1, measured at 0.58‐cm depth in PMMA with 92 mA beam current, corresponds to 3.4×1011 photons⋅cm−2⋅s−1. Measured percent depth‐dose curve agreed with MCNP5 simulated curve, yielding a PMMA mass attenuation coefficient of 1.1 cm2 g−1, approximately equal to the NIST value. Conclusion: The LSU CAMD 15‐keV monochromatic beam has been characterized demonstrating utility of the measurement methods for future studies at energies suitable for iodine k‐edge capture (>33.2 keV). MCNP5 Monte Carlo calculations have been shown to predict depth dose in PMMA validating its use and showing its potential for future treatment planning dose calculations in small animals.