bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐E‐204C‐01: Basic Concepts in Multicriteria Optimization and Their Application in Radiation Therapy
Authors: Bortfeld T
Published: August 2010

The challenge in radiation therapy planning for IMRT (but also for other modalities) is to optimally cover the tumor target volume and to maximally spare the surrounding organs at risk. This is an optimization problem with multiple conflicting objectives. Yet, until recently, all commercial IMRT optimization systems have used a single objective. Multiple objective (”multicriteria”) optimization systems have been developed in research environments, but they have only recently found their way into the clinic and into commercial systems.

There are several ways to handle multiple objectives in multicriteria optimization. One of them, prioritized optimization, is to work on the objectives one by one, starting with the most important objective and then working towards the less important ones. Another one, which will be the focus of this presentation, is to calculate a multitude of plans on the “Pareto frontier”. A Pareto optimal plan is one in which one cannot improve one objective without making at least one other objective worse. If there are only two objectives, the Pareto frontier is the classical tradeoff curve. When there are more objectives, it is a higher dimensional surface.

We will describe methods to calculate Pareto‐optimal plans, and how the Pareto frontier can be sampled with relatively few points (i.e., Pareto optimal plans) using a “sandwiching” technique. Surprisingly, relatively few Pareto plans (20–50) suffice to obtain a good approximation of the Pareto frontier, even in high‐dimensional cases with up to 10 objectives (target volume and 9 critical structures). One reason for this is that different objectives are not fully independent.

Finding the most suitable treatment plan for a patient then means to interactively “navigate” on the Pareto frontier. Navigating in an up to 10‐dimensional space seems like a daunting task. Yet, in practice it is quite doable, especially with a user‐interface that allows to “clamp” objectives, and to exploit correlations between objectives. The Pareto navigation approach can in fact drastically reduce the IMRT planning time, especially for complex cases, and can at the same time yield more suitable treatment plans. Using several examples we will show that Pareto optimality is indeed an important concept for understanding the unavoidable tradeoffs in treatment planning. It is also a requirement for meaningful comparisons between different treatment modalities. Other types of objectives such as plan complexity and delivery time can be incorporated.

Learning Objectives:

1. To be able to define the meaning of Pareto optimal

2. Name the pros and cons of prioritized optimization vs. navigating the Pareto frontier

Research supported in part by RaySearch Laboratories
TU‐E‐204C‐02: VMAT and the Tradeoff between Treatment Time and Dose Conformality
Authors: Yu C
Published: August 2010

Intensity modulated arc therapy (IMAT) was proposed in 1995 by Yu as an alternative to Tomotherapy. Due to the lack of an efficient planning algorithm, wide clinical adoption of IMAT as a major form of radiation treatment delivery did not happen until a 2007 when multiple new planning methods were developed and commercial interests in IMAT were intensified due to competition. Specifically, a commercial product, RapidArc, based on the Volumetric Modulated Art Therapy (VMAT) developed by Otto, was developed and marketed by Varian in 2007. VMAT is a single arc form of IMAT that delivers apertures of varying weightings with a single arc rotation. The intense commercial promotion and fast clinical adoption caused much confusion and controversy. There is a lack of a general understanding of how such arc treatments are planned, and what delivery limitations and compromises are made. It is therefore the purpose of this presentation to provide a summary of this technology and some guidelines on its clinical implementation. A historical review of all the works leading to the wide clinical adoption will be provided. Different planning methods will be described by a companion presentation in the same session. Issues related to clinical implementations, including commissioning and quality assurance will also be described. We will also hope to provide some perspectives on its further development in the context of increased clinical use of image guidance. Because there has been vast experience in IMRT using multiple intensity modulated fields, comparisons between IMAT and IMRT will also be made in the review to illustrate its advantages and limitation in the areas of planning, delivery and quality assurance. The research is partially supported by Varian Medical Systems, Inc., and by NIH grant RO1 CA117997.
TU‐E‐204C‐03: How to Make Clinical Decisions in the Multicriteria Framework
Authors: Phillips M
Published: August 2010

Multiattribute decision making begins with the premise that the solution to the problem at hand involves multiple goals, some of which are mutually antagonistic, and not all of which can be achieved in a single solution. Choosing a multiobjective optimization algorithm should be done in conjunction with the selection of a decision making approach. A vital component of the decision making method is to be explicit about the criteria, how they are to be evaluated and how they relate to the value structure of the decision maker.

Much of the theory of multiattribute decision theory stems from economic theory. In particular, Pareto optimality was first formulated as the condition in which it is impossible to make one person better off without making someone else worse off. Another economic concept, utility, is used to quantify values on a relative scale. In problems not related to economics, it is usually the case that the criteria used to make a decision are difficult to formulate in terms than can be mathematically optimized. For example, in radiation therapy, surrogates for patient outcomes must be formulated in terms of physical dose deposition.

Mathematical optimization algorithms can take several forms. Prior methods require the user to input some preferences before the optimization can proceed. Such methods can produce a single “optimal” solution. Interactive methods rely on feedback between the decision maker and the optimization algorithm. These methods can be the most efficient at searching but require considerable commitment from the decision maker. Posterior optimization methods produce a set of solutions that hopefully spans the trade‐offs of interest. The mathematical optimization is followed by a decision making process that selects one of them.

Learning objectives:

1. To appreciate the relationship between Pareto optimality and decision making.

2. To understand the current state of decision making and how it relates to other approaches.

3. To understand how multiattribute decision making approaches in radiation therapy relate to methods used in other fields such as operations research.

4. To become acquainted with the basics of decision theory such as utility theory.
TU‐E‐204C‐04: New Directions and Clinical Applications of Multicriteria Optimization
Authors: Craft D
Published: August 2010

We report on the first clinical comparisons (10 patients: 5 brain, 5 pancreas) of IMRT planning with a Pareto surface based multi‐criteria optimization (MCO) system versus a traditional IMRT inverse planning system. For the MCO system, we use the MCO‐IMRT planning module provided by RaySearch Laboratories, and for the traditional planning system we use XiO from CMS. For each patient (5 brain cases, 5 pancreatic cases), the patient is planned and treated with XiO plan as is normally done in our clinic. The planning process was logged however to record treatment planner timing data. The planners were not given any special instructions regarding beam angle selection or optimization formulation, in an attempt to accurately capture the process as done day‐to‐day in our clinic. In parallel, the patients were planned in the MCO system using a template based recipe. Specifically, all patients were planned with 7 equi‐spaced beams (starting from an anterior/posterior beam) and using a pre‐defined set of dosimetric optimization objective functions and constraints (we will discuss these templates as well as provide general guidelines for setting up MCO problems). Once the MCO database was computed (an MCO database is a set of Pareto optimal plans that allows the user to navigate through treatment plan possibility space and select the most desirable tradeoff), the physician navigated to the desired plan. The MCO process was also logged.

MCO planning is shown to be far faster than traditional planning, and the reason for this is that the tradeoff decisions are much simpler in the Pareto surface navigation approach. Planning time totaled approximately 15 minutes in the MCO compared with about 2–3 hours for the standard treatment planning. MCO dose distributions were almost always preferred over XiO dose distributions, and otherwise they were considered neither better nor worse. This study provides strong support of the MCO‐based approach for IMRT treatment planning, both in terms of plan quality and treatment planning efficiency.

Given the above positive results, we speculate that MCO‐based treatment planning will become much more popular over the coming years, and will find its way into proton planning and advanced photon techniques such as VMAT. We will review some future topics including comparing modalities (or beam configurations) with multiple Pareto surfaces, robust MCO for IMPT, and VMAT MCO.

Learning Objectives:

1. Understand the workflow and formulation differences between standard IMRT treatment planning and Pareto‐surface based planning.

2. Understand how MCO might be used in tomorrow's clinics, and what work needs to be done to make this a reality.
WE‐A‐204B‐02: Monitoring Tumor and Normal Tissue Response in Radiotherapy: Application of Quantitative Ultrasonic Imaging
Authors: Liu T
Published: August 2010

Radiation therapy, either alone or in combination with surgery and chemotherapy, is a powerful tool in cancer treatment. An estimated half of all newly diagnosed cancer patients receive radiotherapy for tumor control. With recent advances in technology, great focus has been placed on optimizing radiation treatment techniques to reduce normal‐tissue effects. We have investigated noninvasive quantitative ultrasound to assess tumor as well as normal‐tissue response in cancer radiotherapy. Ultrasound is safe, noninvasive, cost‐effective and widely‐accessible making it well‐suited for clinical implementation. Our ultrasound technique combines conventional B‐mode ultrasound with ultrasonic tissue characterization (UTC), which can measure changes in tissue microstructures, to objectively assess radiation‐induced changes to the targeted cancerous regions and the surrounding normal tissues. In a breast‐cancer radiotherapy study, we demonstrated its capability in measuring radiation‐induced acute and late toxicity in the skin and subcutaneous tissues. In this presentation, we report its applications in breast, prostate, as well as head and neck cancer radiotherapy. Such information is important for evaluating the therapeutic ratio. Physicians will gain a better understanding of individual patient's radiation response and therefore, be able to design personalized treatment regimens. We acknowledge the support of NIH CA 114313, Columbia University Women at Risk, and Susan G Komen for the Cure.
WE‐A‐201C‐01: Current US QC Recommendations and Techniques
Authors: Boote E
Published: August 2010

Ultrasound is a widely dispersed imaging modality in the current health‐care environment, encompassing various specialties such as radiology, cardiology, ob/gyn, vascular surgery, and emergency medicine. Reasons for this widespread use include: a) relatively low‐cost, b) small, portable machines and c) the non‐invasiveness of the procedure and general perception of minimal risk. All three reasons present challenges to the medical physicist tasked with implementing a quality control program. Nevertheless, the rationale for establishing a standard‐of‐care is important enough to overcome these perceptions. The ongoing and rapid evolution of US technology brings more complexity to these instruments; thus, quality control tests for US can provide benchmarks of performance that are increasingly important to government and private entities that reimburse for health care services.

This course will review the steps necessary to start an ultrasound quality control program, including a review of the appropriate tests and test objects (phantoms) that a part of such a program. The course will address the more critical aspects of ultrasound system performance that affect image quality. In addition, each test will be described in light of standards established by organizations with an interest in ultrasound quality control. In many cases, these organizations operate some accreditation program for ultrasound imaging facilities. These programs will be reviewed with respect to requirements for a medical physicists contribution to the success of an accreditation application.

Learning Objectives:

1. Understand the beginning steps to implement a Quality Control program for ultrasound equipment

2. Know which tests are appropriate to assessing clinical image quality.

3. Know selection of test objects appropriate for these tests.

4. Knowing how to establish objective criteria and,

5. a basic introduction to accreditation bodies and standards for ultrasound QC.
MO‐B‐201C‐01: CT Dose Reporting
Authors: Flynn M , McNitt‐Gray M , Morin R
Published: August 2010

The high radiation dose for certain CT examinations has been a subject of recent reports. Concern is amplified when patients have a large number of repeated examinations. This course will describe recent efforts to report the CT dose from patient examinations and will discuss how effective dose can be estimated from dose reports.

Learning Objectives:

1. Understand the DICOM dose structured report and the IHE Radiation Exposure Monitoring profile.

2. Learn the status of the ACR project to develop a CT dose registry.

3. Understand how CTDIvol and DLP are determined for a clinical CT scanner.

4. Learn how to estimate organ doses and effective dose from reports of CTDIvol and DLP.

5. Understand current limitation on effective dose estimates with respect to patient size and sex.
WE‐B‐202‐01: IAEA Study of Cataract in Staff Working in Catheterization Laboratories
Authors: Rehani M
Published: August 2010

Staff working in catheterization laboratories, predominantly interventional cardiologists and nurses, are potentially exposed to relatively high levels of ionizing radiation and may be at risk of developing cataracts after several years of work if radiation protection rules are not followed. A number of studies in other radiation exposed populations, including astronauts, atomic bomb survivors, X‐ray technologists and those exposed after the Chernobyl nuclear accident, have indicated an increased risk of radiation associated lenticular changes after low‐dose exposures, raising concerns regarding interventional cardiology professionals. Recent studies indicate that the threshold for cataract development is lower than was previously estimated and that radiation cataractogenesis may in fact be more accurately described by a linear, no‐threshold model and may thus need to be classified as stochastic effect. The higher workload that is typical now in many cath labs, a lack of training in radiation protection and non‐availability or non‐use of radiation protection devices can result in doses to the eye lens that are high enough to cause lens injuries.

International Atomic Energy Agency (IAEA) had launched a project to test the eyes of interventional cardiologists and support staff. The prospective testing was associated with a retrospective dose assessment for the lens of the eye. The eye testing exercises have been done in 20008–2009 at Bogota, Columbia; Montevideo, Uruguay; Kuala Lumpur, Malaysia; Varna and Sofia in Bulgaria.

The talk will review the basic information about radiation catactogenesis and results of recent studies that indicate the need for change. It will present the summary of results of yet to be published studies on interventional cardiologists and nurses that do indicate increased prevalence of dots that represent lens injuries which may lead to cataract after many years.

Learning Objectives:

1. To understand the basic information about radiation cataractogenesis

2. To understand the studies that have been conducted in the last 15 years that show that cataract is seen at doses lower than the currently believed threshold

3. To become aware about the likely changes in current recommendation that may be brought up by international bodies such as ICRP.
WE‐C‐204B‐01: Target Definition of Lung Tumors Combining Patient Specific Pharmacokinetics and Lung Nodule Motion with SUV Distributions in PET‐CT Scans
Authors: Li S , Liu Z , Chan P , Micaily B , Miyamoto C
Published: August 2010

Purpose: FDG metabolism and the standardized uptake value (SUV) in PET‐CT scans vary significantly among patients. Such information is lost in defining target based solely on SUV threshold. The aim of this research is to combine patient‐specific pharmacokinetics and a nodule motion model in target delineation of lung tumor with PET imaging. Method and Materials: Regions of interest (ROIs) for thirty patients were carefully delineated in PET‐co‐scanned CT (petCT). Patient‐specific FDG distributions in any ROIs were determined in co‐registered PET. The voxel values in PET (petVal) were converted to the SUV. Each volume element in the tumor was assumed to travel along a 3D eclipse trajectory with anisotropic axes determined by its location in the lungs. The lung background levels were then adjusted to a preset baseline of 0.6 and tumor SUV were proportionally corrected as they share the same blood feeding stream. In the petCT and simulation CT (simCT), GTVs were defined according to the ground‐glass opacity and overlapping of the SUV‐enhanced region. The 40% source‐background ratio (SBR), threshold of 0.3+0.6 (P3P6) or SUV=2.5 (2P5) were used for automatic contouring of the GTVs. GTV difference from petCT scans to simCT scans measured the tumor growth from the PET diagnosis to the treatment simulation. Results: Squamous cell lung cancer has much higher SUV than that of other tumors. On average, GTVs from SBR and P3P6 methods are consistent with GTVs from petCT. The tumors grow by ∼20% from PET scans to CT simulation. GTVs from 2P5 method are 40% lower which may be improved with more accurate motion and metabolism modeling. Conclusion: The study reveals that combination of nodule motion and patient‐specific pharmacokinetics in PET significantly increases the accuracy in definition of GTV. This is our first step towards correlation of the apparent SUV to the tumor‐vital activity.
WE‐C‐204B‐05: Real‐Time Volumetric Image Reconstruction and 3D Tumor Localization Based on a Single X‐Ray Projection Image during Lung Cancer Radiotherapy
Authors: Li R , Jia X , Lewis J , Gu X , Folkerts M , Men C , Jiang S
Published: August 2010

Purpose: To develop an algorithm for real‐time volumetric image reconstruction and 3D tumor localization based on a single x‐ray projection image in a non‐invasive, accurate, and efficient way for lung cancer radiotherapy. Method and Materials: Given a 4DCT or 4DCBCT as the training data, we perform deformable image registration between a reference phase and all the other phases. The deformation vector fields (DVF) are parameterized efficiently by principal component analysis (PCA). Then we optimize the DVF applied to the reference image by adapting the PCA coefficients such that the DRR of the deformed image matches the acquired x‐ray projection. The inherent regularization of PCA model allows us to reconstruct the volumetric image and localize the tumor in 3D space with a single projection. A realistic and dynamic mathematical phantom was used to validate the algorithm. Results: We generated a dynamic phantom consisting of 60 phases with a 50% increase in breathing amplitude compared with training data. We simulated cone beam projections at all angles with spacing of 1° resulting in 360 projections. The average relative 3D image reconstruction error is 7.5% ± 2.4%. The average 3D tumor localization error is 0.9 mm ± 0.5 mm. We implemented our algorithm on an NVIDIA C1060 GPU. The computation time for each projection is achieved in less than 0.6 seconds (between 0.32 and 0.55 seconds depending on the extent of deformation). Conclusion: We have shown the feasibility of reconstructing volumetric image and localizing tumor in 3D in near real‐time using a single x‐ray image. Further speedup may be achieved by better parameter initialization (e.g., using the previous frame in fluoroscopy) and GPU code optimization. Validation on patient data is under way. Clinical application can potentially lead to accurate 3D tumor tracking from a single imager.
WE‐C‐204B‐08: Sensitivity of 4D‐CT Pulmonary Ventilation Imaging to Deformable Image Registration Algorithms and Metrics
Authors: Yamamoto T , Kabus S , Klinder T , Lorenz C , von Berg J , Keall P
Published: August 2010

Purpose: A novel pulmonary ventilation imaging technique based on 4D‐CT has advantages over existing techniques (e.g., SPECT). 4D‐CT ventilation imaging consists of deformable image registration (DIR) and displacement vector analysis for computing the ventilation metric. However, there are various DIR algorithms and metrics that yield different ventilation images. The purpose of this study was to quantify the sensitivity of 4D‐CT ventilation imaging to DIR algorithms and metrics. Method and Materials: 4D‐CT ventilation images were created for 9 patients in an IRB‐approved study using different combinations of two DIR algorithms: surface‐based registration (DIRsur) and volume‐based registration (DIRvol), and two metrics: Hounsfield unit (HU)‐change (VHU) and Jacobian determinant of deformation (VJac), i.e., four different ventilation images for each patient. The analysis compared voxel‐based correlations between different ventilation images, and coefficients of variation (CV) as a measure of heterogeneity. The relative and absolute lung volume changes were also compared, i.e., calculated vs. measured (ground truth). Results: Different DIR algorithms and metrics yielded spatially variant 4D‐CT ventilation images. The voxel‐based correlations between different ventilation images were inconsistent and ranged from weak (Patient 3, VJacsur vs. VHUvol, r = 0.084) to strong (Patient 7, VHUsur vs. VHUvol, r = 0.819) correlations, VHU resulted in significantly higher CVs (e.g., 3.17 ± 1.64 for VHUsur) than VJac (0.71 ± 0.27 for VJacsur) (p = 0.001). There were high correlations between the calculated and measured lung volume changes for all of four ventilation images (r range, 0.965–0.993, p <0.001). Conclusion: This study has demonstrated that the regional distribution and heterogeneity of 4D‐CT ventilation are sensitive to DIR algorithms and/or metrics, while the global accuracy is not sensitive. Careful validation studies are needed prior to its clinical application. Conflict of Interest: SK, CL and JB are employees of Philips Research Europe.
WE‐D‐BRB‐03: Automated Self‐Test Provides Routine QA for a Narrow‐Field, Low‐Energy X‐Ray, Ophthalmic SRS System
Authors: Firpo M , Herron M , Hernandez C , Chell E
Published: August 2010

Purpose: A narrow‐field, low energy, stereotactic radiosurgery (SRS) device (the “IRay”) designed specifically for the treatment of wet age‐related macular degeneration is being evaluated in a European clinical trial. Because of precise targeting requirements for ophthalmological SRS, a new QA method has been designed to automate the evaluation of system alignment, targeting, and kerma consistency. This poster describes that method. Method and Materials: The IRay delivers up to 24 Gy in three lOOkVp, 4mm‐diameter beams that converge on the retina with a source‐axis distance of 150mm. The beams are delivered inferiorly in a fashion that avoids the patients lens and optic nerve, requiring submillimeter targeting precision. The eye is stabilized with a suction‐enabled lens assembly (the “I‐Guide”) that has retroreflective fiducials used by the imaging system for targeting and eye motion assessment. A self‐test fixture has been designed that incorporates similar fiducials for automatic alignment, a scintillant strip for direct imaging of the X‐ray beam, and an ion chamber for kerma measurements. Results and Discussion Using the retroreflective fiducials, the IRay is able to repeatably and accurately target the fixture. This is critical not only for targeting assessment, but also for accurate kerma measurements which are difficult in a narrow field with a finite‐sized detector. Once targeted, software automatically evaluates and enforces several critical parameters including X‐ray to targeting laser coaxiality (< 100 microns), robotic motion, imaging system alignment (better than 100 microns), X‐ray targeting (within 300 microns), and air kerma consistency (within 3%). Other system tests are performed, including lighting, communication, and dose‐timer checks. Conclusion: Performing comprehensive QA on a narrow‐field, low‐energy SRS unit requiring submillimeter precision is non‐trivial. An automated method of evaluating alignment, targeting, and kerma consistency allows regular (even daily) assessment to provide confidence that all systems are performing within specification. Research sponsored by Oraya Therapeutics.
WE‐D‐BRB‐06: A Novel Phantom for Electron Density Calibration of Linac Cone Beam CT Options
Authors: Cossmann P
Published: August 2010

Purpose: For image‐guided radiotherapy (IGRT) linear accelerators offer also Cone‐Beam‐CT (CBCT) functionality. In order to use such a system for dosimetric planning an electron density calibration, known as hounsfield unit (HU) calibration, is compulsory. Studies on available phantoms for CT performance checks/QA have shown that these are not sufficient for an adequate HU calibration. Therefore we designed a new dedicated phantom and carried out a planning study to determine the usability of such calibrated CBCT data in comparison with diagnostic CT data. Method and Materials: Available linac CBCT options acquire in a single rotation a volumetric CT data set with a scan length of typically 15–23 cm and up to 45 cm field‐of‐view (FOV). In order to 3D‐calibrate the system with regard to HU a special phantom has been designed to include the whole imager area. Removable inserts allow flexible positioning of the probes in x‐z as well as z‐direction. We compared 20 plan setups (10 in the pelvic and 10 in the thoracic region). Results: Within the field of view the HU variation is up to 5%. Towards the imager edges hounsfield units show small deviations relative to the imager center (max. 8%). Relative dose distributions in CBCT‐based plans show minor differences to plans calculated using a diagnostic CT image dataset (p=0.002) and absolute dosage deviations are within 1% (p=0.001). Conclusion: The newly designed phantom allows real 3D‐calibration of linac CBCT. These CBCT data can be used for treatment planning as relative doses distributions and absolute doses are almost equivalent to diagnostic CT data. It is made of water equivalent material and consists of probes with tissue equivalent materials. Probes can be positioned in the phantom in a flexible manner to measure spatial HU dependence. The phantom has additional scatter material to simulate a real patients' situation.
WE‐D‐BRB‐09: Quality Assurance (QA) for Deformable Registration: Measures for Evaluating Displacement Fields in Clinical Settings
Authors: Schreibmann E , Pantalone P , Waller A , Fox T
Published: August 2010

Purpose: Deformable registration is an essential tool in adaptive radiotherapy, as it accounts for anatomical changes during treatment. In recent years, research has focused on proposing different deformable registration algorithms and inter‐comparing their results in academic settings. We contend that finding an efficient method for quality assurance of deformable registration in clinical settings is crucial for a global acceptance of adaptive radiotherapy. This study proposes measures derived from computational fluid dynamics as a simple and efficient tool to quantify a displacement field. Method: Our aim was to develop quantitative metrics of registration quality designed for routine use that are algorithm‐independent, labor‐efficient, and accurately identify errors in a given displacement field. The quality assurance (QA) framework identifies unrealistic anatomical motion through vortexes in the displacement field as detected using the CURL operator and presented as a vortex map overlaid on the original anatomy for a quick identification of problematic regions. Regions of compression/expansion are identified through the determinant of the Jacobian matrix. The warp energy measure is proposed as a global measure of displacement field smoothness. Results: The new evaluation approach was tested on numerous inter and intra patient cases using both single and multi‐modality registration algorithms. The CURL operator quantitatively detected errors in the displacement field and identified problematic regions that were invisible to classical voxel‐based evaluation methods. Warping emerges above 1 indicated unrealistic displacement fields. Conclusions: The proposed QA framework for deformable image registration provides increased usability and accuracy in detecting unrealistic warping over classical registration assessment methods. It is computationally efficient and provides a valuable platform for the clinical acceptance of adaptive therapy in the future.
WE‐D‐204B‐01: Variable Planning Margin Approach to Account for Locoregional Variations of Setup Uncertainties
Authors: Yang J , Garden A , Zhang Y , Zhang L , Dong L
Published: August 2010

Purpose: To implement variable treatment planning margins to account for regional variations of setup uncertainties in Head‐and‐Neck cancer radiotherapy. Method and Materials: Five bony landmarks (C2, mandible, C5, caudal C7, jugular notch) were identified from previous studies. At each point on the CTV, a variable margin was calculated as the weighted average of margins at the landmark points, with the weight determined by a Gaussian falloff function of the distance between the current location and landmark point. Ten CT images of a Head‐and‐Neck cancer patient were used to test this variable margin strategy, in comparison with the standard global margin expansion method. We examined the overlapping of CTV and PTV in these 10 actual setup positions to evaluate the effectiveness of the design strategy. Results: For the variable margin approach using a margin of 2.5mm at the reference landmark C2, an averaged 99.20% of CTV is enclosed within the PTV, while a constant 2.5mm margin expansion results to 97.88% coverage. With reference margin reduced to 2.0mm, the variable margin approach has an averaged coverage of 97.84%, similar to that of constant 2.5mm margin expansion; however, it has a smaller PTV volume than the constant 2.5mm margin design. Paired t‐test on samples from 10 treatment fractions shows no significant difference on CTV coverage between variable 2.0mm margin and constant 2.5 margin approaches (p=0.054), but the non‐overlapped PTV portion is significantly smaller for the variable 2.0mm margin approach than the constant 2.5mm margin approach (p<0.0001). Our result also shows a better CTV coverage when using the variable margin approach in the lower neck area where a larger setup error normally occurs. Conclusion: We implemented a variable margin approach to account for regional variations of setup errors for Head‐and‐Neck cancer radiotherapy, and demonstrated its superiority over the global constant margin expansion approach.
WE‐D‐204B‐04: Distribution of Lung Tissue Motion during Free Breathing
Authors: White B , Wuenschel S , Zhao T , Lamb J , El Naqa I , Low D
Published: August 2010

Purpose: To characterize and quantify free breathing lung tissue motion diction. Method and Materials: 50 patient data sets were acquired using a 4DCT protocol consisting of 25 ciné scans at abutting couch positions on a 16 slice scanner. The tidal volume of each scan was measured by simultaneously acquiring spirometry and an abdominal pneumatic bellows. Because of the natural variation in breathing patterns, we elected to develop the concept of a representative breath. The representative breath was defined by first dividing the breathing traces into individual breaths, from exhalation to exhalation. A linear breathing drift model was assumed and the drift removed for each breath. Breaths that exceeded one standard deviation in period and amplitude were removed from the analysis. A representative breath was defined as the average time from peak inhalation to a normalized tidal volume. Airflow was determined using a sliding polynomial fit to the representative breath profile. The trajectories were computed using an existing 5D lung tissue trajectory model: X = Xo+αngr+βf where α and β were previously determined. In order to characterize the motion patterns, the elongation of the trajectories were examined throughout the subject's lungs. Elongation was defined here by generating a bounding box with one side parallel to the α vector and the box lying in the plane defined by the α and β vectors. Results: The representative breath process provided an excellent method for defining an average breath that had continuous tidal volume and airflow characteristics when the breath was continuously repeated. The elongation varied smoothly throughout the lungs. Left lung elongation was 0.10±0.05 and right lung elongation was 0.09±0.04 in a central coronal lung slice. Conclusion: As expected, motion elongations were relatively small indicating for many tumor sites, hysteresis motion could be ignored. This work supported in part by NIHR01CA116712 and NIHR01CA96679.
WE‐D‐201C‐02: MRI‐Guided Transurethral Diagnosis and Treatment of Localized Prostate Cancer
Authors: Chopra R
Published: August 2010

Minimally‐invasive, image‐guided treatments for localized prostate cancer that provide local control with a low side‐effect profile would have a major impact in improving disease management. Accurate localization of disease with imaging coupled with technologies capable of precise treatment could enable evolution of prostate cancer treatment from a whole gland to a more targeted approach. MRI‐guided transurethral ultrasound therapy is such a technology in which high‐intensity ultrasound energy is delivered to the prostate from a device inserted into the urethra. The goal of the treatment is to generate a prescribed spatial pattern of thermal coagulation in the gland. The treatment is performed in a closed‐bore MR imager to obtain quantitative temperature maps during ultrasound heating of the prostate. This temperature information is used by the treatment delivery system to adapt the exposure conditions dynamically during treatment to compensate for changes in blood flow, tissue absorption and thermal conduction. Previous numerical, phantom, and canine studies have demonstrated that this approach offers a high degree of spatial treatment accuracy (±1–2 mm). Recent clinical evaluation of the technology has confirmed the feasibility of performing this treatment in humans. The desire to deliver more targeted treatments in the prostate for reduced morbidity requires accurate localization of disease, ideally with medical imaging. A unique opportunity that exists in transurethral ultrasound therapy is to generate shear waves in the adjacent prostate gland through vibration of the device. These shear waves can be imaged with MRI and quantitative stiffness maps can be calculated for localization of disease, or evaluation of the pattern of thermal coagulation in the gland. Initial experiments have been performed in phantoms and canines to explore the feasibility of this concept. This presentation will introduce the concept of transurethral ultrasound therapy and will review the results obtained with this technology. In addition the potential to combine this therapy with diagnostic approaches such as MR elastography will be discussed.

Learning Objectives:

1. Describe the role of high‐intensity ultrasound therapy for prostate cancer treatment.

2. Describe the technology for transurethral ultrasound therapy

3. Explain the potential role of prostate MR elastography for prostate imaging/diagnosis using transurethral devices

4. Describe the potential of quantitative MR temperature feedback in achieving closed‐loop heating in vivo, and challenges in its implementation
WE‐D‐201B‐01: Wide Area Detector CT in Cardiovascular Imaging
Authors: Rybicki F
Published: August 2010

Wide area detector CT gives new applications for cardiovascular imaging, based on the ability to perform axial imaging over a craniocaudal field of view that extends up to 16 centimeters. This lecture will review the principles of the technology and focus on current and future clinical applications. Imaging of the cardiac and vascular systems, with related organ perfusion data will be presented. Radiation doses from these applications will be discussed.

Learning Objectives:

1. Develop an understanding of wide area detector CT clinical applications.

2. Highlight examples of current cardiovascular CT protocols.

3. Discuss radiation dose in wide area detector CT.
WE‐D‐201B‐03: Recent Advances in PET Quantitation of Myocardial Blood Flow
Authors: El Fakhri G
Published: August 2010

Absolute myocardial blood flow (MBF) quantitation with dynamic PET has great potential in the assessment of the extent and severity of ischemia in patients without known coronary artery disease (CAD) but is not, to date, part of clinical care.

This lecture will provide an overview of what can be achieved today in terms of accuracy and reproducibility with several PET flow tracers. It will also present recent methodological developments in terms of automated quantitation of MBF using factor and compartment analyses of dynamic PET data that have the potential to bring MBF quantitation to the clinical setting. Finally novel promising tracers will be presented as they can further make MBF quantitation a clinical reality.

Learning Objectives:

1. Understand the fundamentals of myocardial blood flow quantitation

2. Understand the challenges to accurate and reproducible MBF quantitation with PET

3. Understand recent developments and opportunities in MBF quantitation methods using dynamic PET
WE‐E‐BRB‐01: Safety in Radiation Therapy
Authors: Mutic S , Siochi R , Furhang E , Rangaraj D , Fraass B
Published: August 2010

The use of paperless, filmless, and automated computer‐controlled processes in treatment planning and delivery of radiation therapy treatments has drastically increased over the past decade. Treatment plans and delivery records are increasingly available in electronic form and in many situations this is the only way to access these records. However, the processes used to 1) evaluate quality and integrity of treatment plans, 2) validate the data transfer between treatment planning systems and treatment machines, and 3) review treatment records have all remained predominantly manual. Often, the current methods are still based on processes which were developed for paper based and manual radiation therapy delivery. Therefore, there is an opportunity to augment these processes with techniques and software tools that can improve the safety and quality of radiation therapy delivery by more thorough, consistent, and standardized evaluation of treatment planning and delivery data. This is especially important as the amount of data that needs to be reviewed and verified is ever‐increasing. Software tools for plan review and audits of treatment delivery records can increase the number of parameters that are verified and the audit frequency as well as perform checks that are impossible or simply impractical to perform manually. This symposium will present opportunities for automation of QA and QC processes and describe custom solutions which have been developed at various institutions. While most of these solutions are not commercially available, the goal of the symposium is to demonstrate the potential benefits of these techniques, especially after incorporation into commercial systems which are widely employed.

Learning Objectives:

1. To discuss the need for systems thinking and automation in radiation therapy quality management

2. To demonstrate automatic QA/QC solutions which have been clinically implemented

3. To discuss potential benefits and pitfalls of automation in radiation therapy processes
WE‐E‐204B‐03: Feasibility of Bench‐Top Polychromatic Cone‐Beam X‐Ray Fluorescence Computed Tomography (XFCT) for In‐Phantom Detection of Gold Nanoparticles
Authors: Jones BL , Cho SH
Published: August 2010

Purpose: To examine the feasibility of quantifying concentration and spatial distribution of gold nanoparticles (GNPs) present within a small animal‐sized object by applying an x‐ray fluorescence computed tomography (XFCT) technique with a bench‐top, polychromatic, cone‐beam x‐ray source. Method and Materials: The Monte Carlo code MCNP5 was used to simulate the acquisition of gold fluorescence photons under a polychromatic cone‐beam XFCT scenario. Three 1 cm‐diameter columns containing saline solution with GNPs (≤ 2% gold by weight) were inserted into a 5 cm‐diameter cylindrical PMMA phantom. The phantom was irradiated by a 110 kVp x‐ray source, and the resulting gold fluorescence and Compton‐scattered photons were collected by a series of 11 energy‐sensitive tallies. A maximized‐likelihood iterative reconstruction algorithm was implemented to reconstruct the image of GNP distribution. The effects of attenuation of both the primary beam through the phantom and the gold fluorescence photons en route to the detector were corrected during the image reconstruction. The attenuation map of the phantom was known a priori, although it could have been easily measured with a transmission scan. Results: An accurate image of the GNP‐containing phantom was successfully reconstructed, with both spatial distribution and relative concentration of GNPs well defined. The pixel intensity of regions containing GNPs was linearly proportional to gold concentration, which would allow XFCT technique to quantify the GNP concentration and spatial distribution of an unknown sample. Conclusion: This study shows the feasibility of performing XFCT imaging using a bench‐top, polychromatic, cone‐beam x‐ray source. The current approach would make XFCT imaging accessible to applications where a synchrotron‐based XFCT imaging may be inapplicable, such as in vivo measurements of GNP biodistribution.
WE‐E‐204B‐06: Imaging Characterization of Nanoparticles in Micro CT System
Authors: Tu S , Zheng W , Li M , Yang C
Published: August 2010

Purpose: In recent years, various nanoparticles have been identified as excellent contrast agent in x‐ray imaging for small animal experiments. To better evaluate and quantify their potential imaging roles, we used a commercially available micro CT system with different imaging settings to study their imaging properties. Method and materials: Micro CT system used in this work is a commercial imaging scanner and a CCD camera is installed as the x‐ray photon detector. Gold (AuNP) and superparamagnetic iron oxide (SPIO) nanoparticles were fabricated and prepared in test tubes with various concentrations. The average size of AuNPs and SPIOs were determined from transmission electron microscopy to be 1.5 and 50 nm. AuNP samples were prepared in five test tubes with concentrations of 4, 8, 12, 16, and 20 mg/mL. SPIO samples were also in test tubes with concentrations of 2, 4, 6, 8, and 10 mg/mL. For comparison purpose, we also prepared iodinated contrast medium in test tubes with various concentrations. Notice that iodinated contrast medium has been widely used in current clinical x‐ray imaging applications for years. Results: For the concentration of 20 mg/cc at the imaging setting of 30, 40, 50, 60, 70, and 80 keV, linear attenuation coefficients for AuNPs are 0.06329, 0.04282, 0.03362, 0.02798, 0.02292, and 0.01951 cm−1; SPIOs are 0.03506, 0.02504, 0.01995, 0.01664, 0.01432, and 0.01294 cm−1; and iodinated contrast medium samples are 0.03352, 0.02468, 0.02110, 0.01830, 0.01591, and 0.01432 cm−1. Other quantities including CT numbers and scatter‐to‐primary ratios were also quantified for nanoparticle samples. Experiments were repeated three times and estimated errors were less than 1.0%. Conclusion: From our micro CT imaging measurement, nanoparticles show promising indication as an excellent contrast agent in x‐ray imaging. However, we need to further investigate their related biological consequences such as cell toxicity before nanoparticles can officially enter clinical applications.
WE‐E‐204B‐07: A Cold Cathode X‐Ray Source Based on TiO2 Nanotube Field Emission
Authors: Klopfer M.J. , Alivov Y.I. , Molloi S.Y.
Published: August 2010

Purpose: To assess the viability of titanium dioxide (TiO2) nanotube arrays in field emission based x ray sources. Methods and Materials: Aligned TiO2 nanotube (NT) arrays with diameter and height in the range 30–100 nm and 1–10 μm, respectively, were grown by electrochemical oxidation from titanium (Ti) sheets in a glycerol+HF electrolyte. Anodization voltage was varied in the range 13–40 V to control TiO2 NT parameters. As‐grown amorphous TiO2 NTs were annealed at 500° C in air for 1 hour. Field emission properties were tested in a dynamic vacuum of 5×10−7 Torr and the current was measured as a function of applied electric field. The test setup utilizes a copper mesh grid spaced 400μm from a grounded NT array with a mesh density of 70%. A 2 mm diameter copper anode is spaced 10 mm from the grid and held at 60 kV potential for the production of X‐rays, which pass through the stainless steel vacuum chamber via a borosilicate glass window. Radiographs of phantoms were produced using a charge integrating flat panel detector. Results: From current‐voltage characterization a clear Fowler‐Nordheim (F‐N) relationship relating applied NT array electric field and the resulting primary anode current and corresponding X‐ray flux is observed. Initial results show that with an applied electric field of 4.5 V/μm, a stable 1.5 mA/cm2 field effect current density is generated with 80 nm diameter NTs, providing sufficient flux for radiography. This configuration produces a minimum measured horizontal resolution of 3.1 line pairs (lp)/mm. Conclusions: The results show that aligned TiO2 NTs can be used as a field effect emission cold cathode to produce x ray emission.