bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐AUD B‐01: An Analytical Approach to Account for Shielding, Anatomical Heterogeneities and Patient Dimensions for 192Ir High Dose Rate Brachytherapy Applications
Authors: Poon E , Verhaegen F
Published: July 2008

Purpose: Based on a separate primary and scatter dose calculation technique and pre‐computed Monte Carlo (MC) data, we have developed an analytical approach to account for shielding, anatomical heterogeneities and patient dimensions for high dose rate (HDR) brachytherapy. Method and Materials: Using the PTRAN_CT MC code, primary and scatter dose kernels of an HDR source in water were generated. Separate 3D kernels for rectal treatment with a tungsten‐shielded applicator were also created. Photon attenuation and scatter in tissue heterogeneities were corrected for via ray tracing. To quantify the reduced backscatter close to the skin, MC simulations were performed with an isotropic point source placed at various distances from the center of a 30 cm diameter water sphere. Scatter correction factors were derived, which vary as a function of distances between (1) the source and the surface, (2) the point of interest and the source, and (3) the point of interest and the surface. We applied this analytical method for three clinical cases and compared the results with PTRAN_CT calculations. Results: Our technique accurately accounted for the effects of tungsten shielding and anatomical heterogeneities for a rectal patient plan. The reduced backscatter close to the skin was also calculated correctly for a base of tongue and a breast case. Around bony structures several centimeters away from the active dwell positions, there was a minor discrepancy due to softening of the spectrum. Differences in the lung due to reduced scattering in this low density region were also observed. Conclusion: Making use of pre‐computed 3D scatter dose data, our analytical technique is capable of calculating dose around metal shielding and the patient skin with high accuracy. Its validity and limitations have been studied for HDR applications. Conflict of Interest: Research sponsored by Nucletron BV.
MO‐D‐AUD B‐03: An Enabling Technology for Creating Sculpted Brachytherapy Dose Patterns with the Xoft Axxent™ System
Authors: Axelrod S , Pettibone D
Published: July 2008

Purpose: Study a potential means of partially attenuating X‐rays from the Xoft Axxent™ system over controlled spatial areas, while minimizing changes to depth‐dose characteristics. This would be the basis of an enabling technology to sculpt brachytherapy dose patterns to, for example, spare critical structures such as skin in breast brachytherapy treatments. Method and Materials: Measurements of output were made from the Xoft 50 kVp source attenuated by thin (0.001″) dot‐shaped layers of silver, with diameters of several mm. Measurements were made with azimuthal scans around the source at distances from 2 to 7 cm. The dots were attached to the source cooling catheter, approximately 2.6 mm from the source center. Attenuation calculations and Monte Carlo studies of the effect were performed using EGSnrc. Results: Partially attenuating dots of silver create shadows in measured dose that agree with attenuation calculations in proportion, and in the critical behavior of how the attenuation varies with distance. Monte Carlo studies were consistent with measured results. Materials other than silver (or elements nearby in atomic number) will harden the beam, and so the attenuation will lessen with distance. Silver has much less of a hardening effect, because the K absorption edge reduces the higher energy portion of the spectrum at a rate similar to the losses in the lower energy region. Conclusion: It is possible to create predictable, directed shadows in dose around the Xoft 50 kVp x‐ray source using practical thicknesses of silver foils. The shadows have soft edges owing to penumbral effects when the dots are placed on the cooling catheter, within a few mm of the source. Such shadows could be used in future applications to spare healthy tissue during brachytherapy. In a simulated breast treatment plan, using a simple model of the attenuation, isodose lines were shifted by several mm.
MO‐E‐332‐06: Monte Carlo‐Based EPID Dose Kernels Accounting for Variations in Field Size Response
Authors: Wang S , Gordon JJ , Greer P , Li W , Siebers J
Published: July 2008

Purpose: To create a series of EPID Monte Carlo dose computation kernels which accounts for observed machine‐to‐machine variations in EPID response. Method and Materials: Field size response of aS500 and aS1000 imagers are measured for several Varian Cl21‐series machines that were dosimetrically matched in a water phantom. Deviations in imager response are attributed to differences in back‐scattering materials beneath the imaging panels. Mono‐energetic convolution kernels with various backscatter thicknesses are simultaneously created by sub‐dividing a thick back‐scattering slab into multiple sub‐slabs and using the EGSnrc LATCH bit to score sub‐slab kernel contributions. Energy‐binned particle fluence incident upon the detector convolved with the imager‐specific kernels are used to compute the EPID image. Imager‐specific kernels are determined by matching computed and measured EPID field‐size response, using the number of sub‐slabs as a free parameter. Final kernels are used for Monte Carlo‐based pre‐treatment and in‐treatment EPID dose computations. Results: The EPID imagers on dosimetrically matched accelerators are found to differ. Most, but not all of the deviations appear to be correlated with the imager mounting arm type. The imager‐specific kernels matched the field‐size response for each imager within 1%, and resulted in dosimetric agreement between measured and computed images for pre‐treatment dosimetric verification of IMRT fields. Conclusion: Dosimetric differences between portal imagers on matched accelerators can be accounted for by using computation kernels with differing amounts of back‐scattering materials. Kernels for multiple different back‐scattering thickness can be efficiently calculated. Resultant imager‐specific kernels may be useful for efficient pre‐treatment and in‐treatment Monte Carlo‐based EPID dose computations. Conflict of Interest: This work was funded in part by Varian Medical Systems.
MO‐E‐342‐03: Radionuclide Therapy and Dosimetry in Nuclear Medicine
Authors: Sgouros G
Published: July 2008

Advances in our understanding of the molecular biology of cancer and other diseases have identified molecules and signaling pathways that we can now visualize, in vivo, for diagnosis, staging, and to identify optimal therapy and monitor patient response to therapy. These advances have also helped identify targets for targeted radionuclide therapy, making it possible to target radiation at the cellular and molecular level. Planning for this treatment approach is similar, in principle, to external beam radiotherapy treatment planning, but substantially different in practice. Dosimetry for systemic or locoregional administration of a therapeutic radiopharmaceutical requires an understanding of its biodistribution and pharmacokinetics, this must be coupled with a methodology for translating total number of radionuclide disintegration in a particular anatomical volume to the absorbed dose to the volume. Advances in imaging and computing technology over the past 20 to 30 years have fostered corresponding advances in the implementation of the basic radionuclide dosimetry scheme outlined above. Dosimetry in nuclear medicine is evolving from a standard anatomical model‐based calculation that provides mean absorbed dose over a target organ volume to a calculation that provides the spatial distribution of absorbed dose over the individual patient target and organ geometry and that also incorporates radiobiological modeling as a step towards assessing the biological consequences of the dose distribution. The evolution of nuclear medicine dosimetry as well as recently approved and emerging radionuclide‐based therapeutics will be reviewed.
TU‐A‐351‐01: Small Animal Magnetic Resonance Imaging: Current Trends, Challenges and Perspectives for Pathological Imaging
Authors: Quarles C
Published: July 2008

The utilization of magnetic resonance imaging (MRI) in the study of animal models of human pathology began more than 30 years ago. The continual advancement of imaging technology along with the increasing demand for tools to non‐invasively and serially assess disease progression and/or regression in small animals has driven this field forward since its inception. Standard clinical MRI scans primarily focus on disease detection and are based on anatomical and morphological abnormalities, whereas small animal MRI studies center on the serial characterization of the morphological, functional and molecular properties of diseased tissue. Small animal MRI studies often employ novel contrast mechanisms and exogenous chemical reagents, higher magnetic field strengths, higher spatial resolution and multi‐modality imaging but are complicated by issues such as low signal‐to‐noise ratios, enhanced sensitivity to respiratory and susceptibility artifacts, anesthesia‐induced alterations of disease physiology and demanding data processing requirements.

This lecture will provide an overview of the role of small animal MRI in studying human disease, the technical and experimental challenges of such studies and how it could be used in the future to impact clinical treatment planning.

Educational Objectives:

1. Understand the role small animal MRI plays in understanding human disease and its impact on the development and validation of novel therapeutic strategies.

2. Understand the issues and challenges related to a small animal MRI experiment including design, data acquisition and processing.

3. Understand the future directions and potential advancements currently being pursued in small animal MRI.
TU‐A‐352‐01: Fluoroscopic Dose Measurement and Management
Authors: Balter S
Published: July 2008

Radiation usage during fluoroscopically guided interventions can be high enough to warrant careful dosimetry and patient management. Basic compliance with the usual set of local regulatory requirements may not be sufficient for patient safety. Many of these rules date back to an era in which fluoroscopy was used for simple diagnostic procedures. The X‐ray tubes of this earlier era often overloaded and shut down before dangerous doses were delivered. Neither of these suppositions are currently valid. For example, modern systems meeting all regulatory dose restrictions are capable of delivering table top air kerma rates exceeding 200 mGy/min for normal mode fluoroscopy and 1,500 mGy/min for cinefluorography.

Clinical dosimetry during each complex intervention is facilitated by dosimetric instrumentation built into the fluoroscopic system. The FDA now requires such instrumentation in all new fluoroscopes. The Society of Interventional Radiology has published a standard of practice recommending dosimetry for all interventional procedures. The DICOM‐DOSE project, a joint initiative of DICOM and the IEC will shortly provide tools for automated dose reporting. The Joint Commission has included fluoroscopic procedures with skin doses exceeding 15 Gy in its list of sentinel events; with the implicit challenge to facilities that they can prove the absence of such occurrences.

This course reviews technical elements needed in a program of patient fluoroscopic radiation safety. Key concepts include: ICRU diagnostic dosimetric quantities and their fluoroscopic extensions FDA and IEC compliance measurements.

Construction dosimetric features, and performance of modern fluoroscopes Extended QA protocols for compliance measurements, system characterization and clinical dosimetry. Dose recording and reporting, including DICOM‐DOSE. The Joint Commission fluoroscopy sentinel event.

Educational Objectives:

1. Understand dosimetric concepts relating to interventional fluoroscopy.

2. Characterize the dosimetric features and performance of a modern fluoroscope.

3. Be able to set up a clinical dose recording and reporting policy that will meet clinical and JC requirements.
TU‐B‐351‐01: Optimizing CT Examination Protocols with Respect to Image Quality and Radiation Dose
Authors: Kofler J , Cody D
Published: July 2008

CT technology continues to develop at a rapid pace, offering imaging options and features that can dramatically improve image quality. Multichannel systems are now standard and the number of channels and image acquisition options continues to increase, allowing greater coverage per rotation, shorter scan times, and thinner images. Isotropic volumetric data acquisition permits retrospective reconstructions of many different image thicknesses and reformats can be created through multiple planes. These and many other advances have escalated and expanded the utility of CT imaging as a core diagnostic tool.

However, coupled with the improved CT technology is the increased complexity of operating the scanners and the elevated potential of increasing the radiation dose. CT operators must choose from multiple options, many of which are interdependent, for the control of the multitude of available features. The impact of each of these options on image quality and radiation dose can range from subtle to substantial, and may not necessarily be obvious to the operator.

This lecture will focus on the clinical implications of CT scan parameters and provide guidance on achieving an optimal compromise between image quality and radiation dose when constructing CT scan protocols.

Educational Objectives:

1. Understand the influence of primary CT scan parameters on image quality and radiation dose.

2. Learn how to use imaging task‐specific priorities with consideration for radiation dose when determining scanner settings.
TU‐B‐352‐01: Quantification of 3‐D PET/CT Imaging
Authors: Saffer JR , Scheuermann JS , Karp JS , Perkins A
Published: July 2008

In oncology, imaging studies play an increasingly important role in assessing patients' response to treatment. Serial CT scans of a patient are evaluated for changes in the number and size of tumors, while serial PET scans are assessed for changes in the metabolic activity of the lesions. The advent of combined CT and PET systems streamlines the fusion of these anatomic and functional images. However there are many confounding effects that complicate quantification in 3D PET/CT imaging.

This lecture will review these sources of variability in the data, grouped into three broad categories: patient‐related factors (e.g. dose uptake time before imaging, blood glucose level, body habitus); instrument‐related factors (spatial and energy resolution, sensitivity, data acquisition mode (2D or 3D), attenuation and scatter correction method, image reconstruction algorithm, respiratory and cardiac motion‐correction method); and operator‐related factors such as acquisition and reconstruction protocols, instrument and image quality control, instrument calibrations, and method of image analysis. The impact of these variables on quantification will be discussed, with particular emphasis on how to minimize those that are controllable.

The presentation will conclude with a review of current efforts by government agencies, professional organizations, academic institutions, and sponsors of multicenter trials to grapple with the additional complexities that arise from combining data from multiple patients at multiple sites. Research partially supported by the American College of Radiology Imaging Network (ACRIN).

Educational Objectives:

1. Understand the scope of the problems inherent in using PET/CT imaging to detect changes in patient response to treatment.

2. Understand the factors that affect the variability and accuracy of PET/CT quantification.

3. Understand the importance of minimizing variability in order to enhance the ability to identify non‐responders to treatment over ever‐shorter time intervals.

4. Understand the efforts currently underway to standardize acquisition and processing protocols and to monitor equipment performance through credentialing and periodic quality control checks.
TU‐C‐350‐01: Review of Task Group Reports for Their Impacts On Clinical Practice
Authors: Chan M
Published: July 2008

This review task was initiated under the direction of the Clinical Practice Committee of the Professional Council of the AAPM. Some of the Task Group (TG) reports published by the AAPM present a wide range of comprehensive performance tests or QA processes for a particular radiological modality or procedure. Limited by available resources and given the range of clinical uses, full‐time clinical physicists of many medium and small centers often find it difficult to determine the minimum subset of a complete TG report to follow to ensure consistent high quality of patient care and procedure maintenance. Furthermore, state regulators have, in some instances, unfortunately adopted entire sections of TG reports as regulatory requirements despite the clarification in all TG reports that such use would be inappropriate. Therefore, Minimum Practice Recommendations (MPR) should be established and be charged by the new Practice Guideline Subcommittee. The MPRs are intended to provide the AAPM members with a set of requirements for a basic standard of medical physics practice that AAPM would consider necessary in all sizes of clinical practice sites. These MPRs are not designed to replace extensive clinical practice guidelines, TG reports or review articles, but rather to describe minimum common standards. The establishment of MPRs is an important expression of AAPM's mission to disseminate knowledge, in order to maintain a high common standard in medical physics practice. The Subcommittee is charged with reviewing TG reports prior to publication, and determining which reports would benefit from an accompanying Implementation Guideline.

Educational Objectives:

1. Understand the benefits of reviewing TG reports by the Professional Council.

2. Understand the concept of Minimum Practice Recommendation (MPR).

3. Understand the guidelines and issues related to the establishment of MPR.
TU‐C‐AUD A‐01: Experience with IGRT Research, Development, and Clinical Implementation
Authors: Sharpe M
Published: July 2008

At one point or another, almost everyone has recognized a problem and generated ideas they believe would improve clinical practice. In essence, this is what drives the desire to generate technical and clinical research, and translate findings into clinical practice. Some ideas become “practice changing” when the problem is important enough; the ideas compelling; and the right combination of skills, resources, and motivation are brought to bear. Geometric uncertainties in radiation therapy delivery represent an important problem and a fertile area of investigation that captures imaginations in clinical practice, academic research, and industry. This presentation will relate some experiences of participating in the development of image‐guided radiation therapy (IGRT) solutions.

Educational Objectives:

1. To demonstrate the importance of a team approach in making research ideas into clinical practice.

2. To illustrate some essential lessons learned from IGRT research and development.

3. To review some common institutional practices used to assess patient safety and the protection of ideas.
TU‐C‐AUD A‐03: Integrating Research Into the Clinic: Experiences From Implementing Monte Carlo, IMRT, and …
Authors: Siebers J
Published: July 2008

Clinical implementation of in‐house developed research‐based treatment planning software poses challenges for both the code developer and clinical user. This presentation will examine several important aspects of the implementation and integration processes, using in‐house IMRT and Monte Carlo dose calculation programs as examples. For the developer, challenges include the creation of fail‐safe strategies to ensure patient safety; procedures for upgrades, including updates to address clinically urgent issues; and separation of clinically implemented code from research‐based code which is under continual development. Jointly, the developer and clinical user are challenged to create commissioning and quality assurance procedures which not only meet AAPM TG guidelines, but which also test pre‐identified failure modes that are specific to the software implementation. They are further challenged to develop per‐patient quality assurance methods to ensure patient plan quality. A useful strategy in this regard is to utilize a vendor‐supplied FDA approved product for cross‐comparison of the deliverable treatment plan. Finally, the implementation and integration processes should include procedures for dealing with non‐compliant cases, including identifying error sources and implementing remedies. Examples of how these challenges were addressed in our clinic will be presented.

Educational Objectives:

1. To appreciate the challenges inherent in safe clinical implementation of in‐house developed software.

2. To understand strategies for overcoming the challenges of clinical implementation of in‐house developed software.

3. To understand the role of QA in safe clinical implementation of research.

The research discussed is supported in part by NCI Grant P01 CA116602, by Philips Medical Systems, and by Varian Medical Systems.
TU‐C‐AUD B‐01: Using the Air/water Interface to Improve the Accuracy of Entrance Dosimetry
Authors: Ververs J , Kawrakow I , Siebers J
Published: July 2008

Purpose: To improve ionization chamber localization accuracy for depth‐dose measurements used for TPS dose calculation algorithm commissioning and periodic linear accelerator QA. Method and Materials: Ionization chamber depth‐dose scans are set to include points above the water surface, which produces inflections in the depth‐dose curves. Monte Carlo simulations are performed with the EGSnrc Cavity usercode, which simulates the detailed ionization chamber and phantom geometries, and with DOSXYZnrc, which excludes the chamber geometry. The inflection point location in the Cavity simulation with respect to the chamber center quantifies the chamber's absolute location. The difference between the Cavity and DOSXYZnrc depth‐dose results quantifies the ion chamber's effective point of measurement (EPOM) variation as a function of depth. Measurements and simulations are performed for 6 and 18 MV photon beams for multiple field sizes. Measurement results are aligned to the surface position by matching the computed inflection points. Results: The dose inflection point due to the air‐water interface is clearly identifiable in both measurements and calculations. A Cavity simulation at 6 MV with a 10×10 cm2 field finds that the inflection point occurs when the central electrode is ∼1 mm beneath the water surface. After applying the recommended EPOM shift to Cavity simulation results, the distance‐to‐agreement between the Cavity computed “surface” dose and the DOSXYZnrc dose was >2 mm. By 1.0 cm depth, the distance‐to‐agreement is negligible. 18 MV simulations yielded discrepancies in the in‐air dose, presumably due to differences in contaminant electrons. Conclusion: The proposed method of conducting depth‐dose measurements is trivial to implement and provides a way to automatically account for, and correct, shifts and/or offsets in initial chamber positioning. This allows for improved matching, not only of measured and calculated data, but also of measured data such as that acquired in periodic QA testing.
TU‐C‐AUD B‐09: Comparison of Two Photon Dosimetry Protocols: AAPM TG‐51 & IPSM 1990
Authors: Castrillón S Vargas , Cutanda F
Published: July 2008

Purpose: A comparison of two dosimetry codes of practice for photon therapy beams was performed. These codes of practice are: AAPM TG‐51 and IPSM 1990. Both protocols are based on standards of absorbed dose to water. This comparison was carried out for five beam qualities with nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV. Method and Materials: The photon beams were generated by two Elekta Synergy and two Elekta Precise linear accelerators. A PTW MP3 plotting tank was used for relative and absolute measurements. A PTW 31002 thimble chamber was utilized for relative measurements. A NE 2571 Farmer graphite chamber was chosen for absolute dose measurements. A Keithley Therapy 35040 electrometer was used for absolute measurements and a PTW Tandem for relative ones. All measurements are traceable to National Physical Laboratory (UK) dose standards. Absolute dose was measured at 5 cm deep and 7 cm deep (for 18 MV) according to IPSM 1990 and at 10 cm deep for AAPM TG‐51. All correction factors (polarity and recombination) were computed using measurements performed at the recommended depths and following each protocol. Results: Values for all correction and calibration factors were obtained by measurement or computation. ND,w calibration factors provided by NPL for each quality were used for IPSM 1990; in the case of AAPM TG‐51, its method using ND,w for Co‐60 and tabulated kq factors was applied. AAPM TG‐51 and IPSM 1990 absolute dose results lie within 0.6%, which falls within uncertainty limits. Conclusion: A comprehensive absolute dose study was performed according to two protocols: beam quality indexes, correction factors and dose measurements. A complete uncertainty analysis was carried out for all experimental results, according to ISO GUM standards of practice. Results show that absorbed dose to water according to both protocols agrees within uncertainty.
TU‐C‐351‐07: Prospective Displacement and Velocity Based Cine 4D CT
Authors: Langner U , Keall P
Published: July 2008

Purpose: Existing 4D CT scans show artifacts in a large percentage of cases. Additional dose is also given to ensure redundancy in data to minimize artifacts. To solve this a Prospective Displacement and Velocity based (PDV CT) cine method for acquisition of 4D CT images was developed. It is compared against retrospective methods for efficiency, dose, and accuracy. Effects of different model parameters are also illustrated. Method and Materials: With the PDV CT method, image acquisition is only performed if both displacement and velocity of the respiratory signal are within predetermined tolerances. Respiratory signals from a Varian Real Time Position Management (RPM) system for 24 patients (103 sessions) under free breathing conditions were used. To surmount system latency and enhance efficiency, a linear adaptive prediction algorithm was used. The root‐mean‐square of differences between displacements and velocities of the respiratory signal corresponding to subsequent images, were calculated in order to evaluate the accuracy of each method. Results: A reduction in patient dose during image acquisition between 22 – 50% was achieved depending on the parameters chosen. The mean root‐mean‐square difference show PDV CT produces similar results than retrospective displacement sorting in general, although differences ∼20% smaller was achieved for some parameters. Velocity RMS differences improved between 30% – 45% when compared to retrospective phase sorting. The efficiency in acquisition time compared to retrospective phase sorting varied from ∼10% for displacement and velocity tolerances of 1mm and 4mm/s, respectively, to 80% – 93% for 4mm and 4mm/s. Conclusion: The reduced variation in the displacement and velocity of the respiratory signal indicates that the PDV CT method described here, could be a valuable tool for reducing artifacts in 4D CT images, and more importantly, substantial dose reduction to the patient, although the price may be acquisition time. Conflict‐of‐Interest: Research supported by 1P01CA116602.
TU‐D‐352‐04: Novel Decision Aid for IMRT Treatment Plans Generated Using Multiobjective Optimization
Authors: Smith W , Doctor J , Meyer J , Kalet I , Phillips M
Published: July 2008

Purpose: To develop the decision making component of a multiobjective IMRT optimization procedure for prostate cancer that incorporates disparate sources of information used in clinical decision making, the uncertain outcomes inherent in radiation therapy and the preferences of the patient. Method and Materials: Currently, many IMRT plans are developed for each patient without indication of which plan provides the optimal balance between tumor control and complication probability. Coupled with the typical number of objectives, plan selection is difficult. We chose a Bayesian Network (BN) coupled with a Markov Model (MM) and utility theory to calculate Quality Adjusted Life Expectancy (QALE) for IMRT treatment of prostate cancer. The BN was constructed with the advice of experts; conditional probabilities were obtained from research and clinical trial publications and expert opinion. Local, regional, and distant control were included as were complications to bladder and rectum. The MM relied on transition probabilities derived from the BN, published clinical trials and life expectancy tables. Utilities were obtained from the literature. Plan ranking was based on QALE or any of the components, e.g. local control or complications. Results: Probabilities of local and distant control as a function of disease state matched published values well, as did life expectancies. Sensitivity analyses highlighted the critical nodes in the network. Analysis of outcomes versus probability of lymph node involvement provided a basis for decisions regarding pelvic irradiation. A BN is well‐suited to handle rigorously conditional probabilities and the disparate nature of clinical variables. QALE provides a method for ranking plans based on clinically relevant criteria that incorporates the probabilistic nature of the outcome. Conclusion: A decision aid was constructed using a Bayesian Network coupled to a Markov Model. This resulted in the ability to rank competing plans based either on QALE or specific outcomes.
TU‐D‐352‐08: Innovative Instrumentation for Resonant Cancer Theranostics
Authors: Silver E , Pradhan A , Yu Y
Published: July 2008

Purpose: Most current diagnostic and therapeutic X‐ray techniques use nonspecific, broadband continuum radiation. By taking advantage of resonant absorption complexes in heavy‐element‐tagged nanoparticles or contrast agents delivered to disease sites, we can use tunable, narrow energy bands for both therapy and diagnosis (theranostics) that is extremely efficient and minimizes radiation exposure to neighboring tissue. Method and Materials: We use an electron beam ion trap (EBIT) as the source of tunable, monochromatic X‐rays for imaging and therapy and a cryogenic x‐ray microcalorimeter to form spectroscopically resolved images. The high resolving power (E/ΔE > 2000) and low background of the microcalorimeter are essential for verifying the resonant absorption signatures predicted by our relativistic R‐matrix calculations. The microcalorimeter is used to tune the X‐ray emission from the EBIT plasma to the band of resonant absorption lines in the tagged nanoparticles. The unprecedented signal to noise of the microcalorimeter means that it can identify line emission with less than 20 counts per energy resolution element, making the eventual dose necessary for diagnostic imaging potentially very low. Results: We describe the EBIT and the microcalorimeter with emphasis on the X‐ray energy range required by cancer theranostics. Preliminary studies with the microcalorimeter demonstrate that it can image atomic fingerprints of heavy‐element uptake such as gold nanoparticles that can be embedded in malignant tissue. Conclusion: We discuss two key component technologies for atomic level theranostics : The electron beam ion trap is a smart x‐ray source capable of generating monoenergetic resonant X‐rays that maximally interact with the matching high‐Z contrast agent or nanoparticles; the spectroscopic microcalorimeter is a “zero‐background” detector by design and can discriminate resonant signatures with 10 times better resolution than any other X‐ray spectrometer, thus providing very high sensitivity for detailed mapping of elemental distributions such as gold nanoparticles and platinum‐based chemotherapeutic compounds.
TU‐D‐350‐01: Ethical Versus Legal Issues In the Practice of Medical Physics
Authors: Bagne F
Published: July 2008

The practice of Medical Physics requires adherence to both ethical conduct and legal rules when dealing with issues arising in one's professional life. The purpose of this lecture is to discuss and distinguish the fine line between what is considered ethical as opposed to legal. Examples of ethical conduct and legal actions are provided and the ramification of the lack of distinction between the two is discussed. Emphasis is placed on the ethical and legal responsibilities of the medical physicists in delivering health care.
TU‐D‐AUD A‐01: Informatics Needs in Radiation Oncology Research: Challenges and Potential Solutions
Authors: Deasy J
Published: July 2008

Radiation oncology research faces an explosion of data collection, analysis, and management issues. Clinical trials research requires interfacing multiple vendor systems, storage of large‐scale, multi‐type data in systems that provide convenient, and secure access for analyses, quality assurance/improvement, and monitoring. HIPPA concerns are making multi‐institutional datasharing and clinical trial cooperation more challenging. Relevant datatypes now span the spectrum of multiple types of imaging, traditional radiotherapy data objects, image‐guidance data, physician‐reported, or patient‐reported outcomes, and new biological datasets and tissue/fluid samples along with their various bioprofiles and ‘‐omics.’ Effective management schemes must preserve the context, storyline, and linkage amongst related data. Effective utilization and learning based on all the available data will require new informatics tools and a more open approach to realizing the extent of the challenge and how ineffctively it has been addressed to date. In this presentation I will discuss these challenges that vendors, physicians, physicists, and informaticists face in helping to build out effective tools to support radiation oncology research in the next ten years. I will particularly focus on the emerging informatics needs of clinical trial groups (such as RTOG), as well as academic research centers, who want to fully utilize and learn from modern image‐guided, adaptive, biologically‐stratified, treatment paradigms. We will discuss approaches to problems associated with collecting outcomes data, utilizing complex datasets within the clinical workflow, and effectively learning from clinical, imaging, and biological data.
TU‐D‐AUD B‐03: MVCT‐Guided Partial‐Breast Irradiation in Prone Position: Daily Setup Uncertainty and Dose Verification
Authors: Kainz K , White J , Li X
Published: July 2008

Purpose: We analyzed the daily setup uncertainty and dose verification for partial‐breast irradiation (PBI) in prone position using helical tomotherapy. Method and Materials: According to an in‐house protocol, early‐stage breast cancer patients received PBI treatments in the prone position on the TomoTherapy Hi‐Art system using megavoltage‐CT guidance (TomoTherapy, Inc., Madison, WI). For planning, kilovoltage‐CT scans were obtained with the involved breast suspended downward. Treatment plans were generated based on criteria from the NSABP B‐39/RTOG 0413 protocol; the PTV_eval was to receive 3.85 Gy per fraction over 10 fractions administered twice daily. Before each fraction, an MVCT scan was acquired and compared with the planning kVCT images to refine the patient position. Along each shift direction, a margin to estimate the setup uncertainty for treatments without MVCT guidance was calculated from the average and standard deviation among the daily shifts. The dose actually delivered in each fraction was reconstructed based on the daily MVCT, accounting for the daily shifts. Among all fractions, the average and standard deviation for specific DVH points were compiled for comparison with the plan DVH. Results: Among the MVCT‐guided shift data, the random setup uncertainty in general exceeds the systematic difference from the plan. The overall margin was as large as 24.5 mm among the cases analyzed. From the MVCT‐based recalculations, the reconstructed doses differed little from the planned doses for each breast, each lung, thyroid, and heart. Average reconstructed doses for PTV_eval were slightly lower than the planned dose, attributable to increased breast thickness for some fractions. Yet, at least 90% of PTV_eval received over 90% of the prescribed dose. Conclusion: The estimated margin to account for setup uncertainty motivates improvements for PBI positioning. With MVCT guidance for prone‐positioned PBI, the deviation of the delivered target and organ‐at‐risk doses from the planned dose is minimal.
TU‐D‐AUD B‐05: Quantifying the Dosimetric Trade‐Offs When Treating Targets with Concavities Using IMRT
Authors: Reese A , Das S , Marks L
Published: July 2008

Purpose: To quantitatively assess the relationship between intensity‐modulated radiotherapy (IMRT)‐driven sparing of dose to normal tissues located “within” concave targets with (1) heterogeneity in dose delivered to the target and (2) redistribution of dose to normal tissue beyond the concavity. Method and Materials: Idealized volumes resembling mesothelioma and prostate cancer were considered, both with concave targets containing normal tissue. Multiple IMRT plans were generated with progressive dose restriction to the normal tissue within the concavity. We quantified the impact of such sparing on the heterogeneity of dose within the target tissue itself, and the dose received by normal tissues beyond the concavity. Results: As the dose to the normal tissue within the concavity is reduced, the heterogeneity in dose delivered to the target increases in an exponential fashion. Further, there is a rapid increase in redistributed dose to other normal tissue regions, particularly to the other normal tissues immediately adjacent to the outside edges of the concavity (i.e. adjacent to the “free margin” of the target). Conclusion: For targets with concavities, there are dosimetric consequences associated with reducing dose to normal tissue located within these concavities. There appears to be a trade‐off between the heterogeneity in dose delivered to the target, the mean dose to the concavity, and the redistributed dose to other normal tissues. Understanding the interaction between these dosimetric factors can aid the planner in assessing the feasibility of a desired dose distribution.
TU‐D‐AUD C‐05: Development of a Novel Absorbed Dose to Water Calorimeter‐Based Standard for HDR Ir‐192 Brachytherapy
Authors: Sarfehnia A , Seuntjens J
Published: July 2008

Purpose: To study parameters affecting the design of a new standard for absorbed dose to water for high dose rate iridium‐192 brachytherapy sources based on 4 °C stagnant water calorimetry. Method and Materials: The absorbed dose rate of a Nucleotron microSelectron‐HDR brachytherapy source was measured for sources with nominal air kerma strength Sk,air 21000 and 38000 U at several source‐detector separations dsrc‐det ranging between 25–30 mm. The irradiation time was adjusted to ensure a minimum dose of 1 Gy delivered to the measurement point. The heat‐loss correction was calculated using COMSOL MULTIPHYSICS™ and is defined as the ratio of the temperature in the calorimeter under ideal conditions to realistic conditions. Results: The heat‐loss corrected dose rate measurements had a standard deviation of 1.5%, while the agreement between our measurements and the calculated dose rate results obtained using the TG‐43 formalism was within 6.5%. The effects of convection were calculated to be negligible as the glass vessel serves as a convective barrier significantly decoupling the water velocity in the interior and exterior of the vessel (differences in velocity reaching one to two orders of magnitude). It was found that small uncertainties on dsrc‐det significantly affects the shape of the drift curve, while varying the exact value of SK,air, irradiation time, and differences in initial source temperature at the time of insertion into calorimeter have minimal effects. Differences between the shape of experimental and calculated drift curves can be used to optimize the calculation parameters. Conclusion: Feasibility of water calorimetry for absolute dosimetry for HDR brachytherapy sources has been shown both numerically and experimentally. We believe absolute absorbed dose rate measurements with uncertainties significantly better than 5% are possible. Revisions to experimental designs are underway to improve the robustness of setup and improve the repeatability and uncertainty on measurements.
TU‐D‐332‐04: Modulating Mn2+ Efflux with SEA0400, Using Cardiac Manganese‐Enhanced MRI (MEMRI) T1‐Mapping in a Murine Model
Authors: Waghorn B , Yang Y , Klein B , Baba A , Matsuda T , Yanasak N , Hu T
Published: July 2008

Purpose: is an important regulator of contractile function in the heart. Efflux mechanisms of the intracellular concentration are regulated by the exchanger (NCX) and plasma membrane ‐ATPase (PMCA). During myocardial ischemic‐reperfusion intracellular overloads via the reverse mode of the NCX, exacerbating myocardial injuries. Protocols that selectively inhibit this exchanger have shown potential therapeutic effects. Cardiac manganese‐enhanced MRI (MEMRI) can be implemented to quantify concentration in vivo, where has be sugested as a surrogate marker for . This study introduces a potential technique to study cardiac efflux by inhibiting the NCX using SEA0400. Method and Materials: Male C57Bl/6 mice (6–13 weeks) were separated into two groups to study the rate of efflux; a control group and a group treated with SEA0400. Both groups were infused with a single dose of 190±2 nmoles/g BW . The SEA0400 group were injected with 50 mg/kg SEA0400 one hour post‐ infusion. Images were acquired on a horizontal 7.0 T Bruker BioSpec MRI spectrometer equipped with a micro imaging gradient. T1‐maps were acquired pre‐ infusion and at various time points post‐ infusion using an ECG‐gated, flow‐compensated Look‐Locker MRI pulse sequence. The change in relaxivity, ΔR1, in the left ventricular free wall (LV Wall), was calculated at different time points post‐infusion. Results: In the LV Wall 50% of the signal enhancement is attenuated within ∼3–4 hours post‐ infusion. SEA0400 demonstrates the effectiveness of reducing the rate of efflux. At a SEA0400 dose of 50 mg/kg the efflux half‐life was approximately two times longer than the control group. Conclusion: This T1‐mapping technique can be used to quantify efflux rates from the myocardium. By using a NCX inhibiting agent this technique can potentially be employed to interrogate individual efflux mechanisms and rates in vivo.
TU‐D‐332‐07: Endogenous MRI Biomarker to Track Neurological Disorder
Authors: Alyassin A
Published: July 2008

Purpose: The existing literature strongly supports the hypothesis that low T2 values are correlated with the presence of brain iron. Mineralized iron particles associated with tissue ferritin provide an endogenous contrast mechanism leading to decrease T2 in specific brain regions. The effect is enhanced when imaging at higher field strength. This has suggested the use of iron‐dependent MR contrast for the study and monitoring of neurological diseases related to iron dysmetabolism. Method and Materials: Twelve subjects (5 AD & 7 normal) were imaged on 3 Tesla scanner with a dual spin echo sequence, (TR = 4000, TE= 30, 80, NEX=1, 20 cm FOV, 256×128 matrix, 55 coronal slices each 1.5 mm thick, scan time of 11 minutes). The apparent T2 values were calculated using the dual echo images. The T2 values within the brain were delineated using especially developed brain mask. Based on a low T2 window (T2 = 10–47 msec), voxels were delineated and hypothesized to contain high concentration (HC) iron. In addition, five regions of interests (ROI) were drawn manually on the HC iron region and another five nearby regions were drawn on what we call medium concentration iron region. The T2 mean and standard deviations of the T2 window and of the ROI were calculated. Results: The preliminary analysis of global brain iron indicated the T2 values for specific brain regions were shorter for AD subjects than for normal volunteers. In addition, the regional brain analysis indicated that the spin echo sequence is effective in capturing the drop in the apparent T2 values. Conclusion: Our results suggested that the apparent T2 values calculated from high field MR images are correlated with the presence of Alzheimer disease. Our study indicates that high field imaging may become an effective means of monitoring the progression of several important neurodegenerative diseases.
TU‐D‐342‐04: Dedicated Breast CT Imaging of the Breast
Authors: Boone J
Published: July 2008

Dedicated breast computed tomography (CT) systems were designed and fabricated in our laboratory, and patient scanning commenced in November 2004. The breast CT scanner was designed utilizing several off‐the‐shelf components, including the x‐ray system, the flat‐panel detector, and a position encoder/bearing/motor system. These components were integrated into a custom designed scanner frame and gantry. The breast CT scanners were designed for 33 second acquisition, utilizing 500 projection images acquired over 360° around the breast. The breast CT scanner uses 80 kVp and mAs levels adjusted to the size of the woman's breast. The radiation levels are adjusted such that the mean glandular dose is equal to that of two‐view mammography for each woman. The acquisition protocols requires patient breath hold during the 17 second scan. As of May 2008, 150 patients have been scanned, including healthy volunteers (phase 1) and BIRADS 4 and 5 patients who were suspicious for having breast cancer (phase 2). Of the patients imaged, >20 were imaged with and without contrast agent injection. While our clinical evaluation of breast CT technology is still under way, initial evaluation indicates that high‐quality tomographic images of the breast can be achieved at dose levels comparable to two view mammography. The ultimate utility of breast CT may include breast cancer screening, or for diagnostic studies as part of a comprehensive diagnostic breast examination. The breast CT platform also appears ideal for robotically controlled biopsy and other interventional procedures.
TU‐EE‐A1‐03: Multileaf Collimator Performance and Quality Assurance For Volume Modulated Arc Therapy
Authors: Ramsey C , Usynin A , Chase D
Published: July 2008

Purpose: The purpose of this study was to determine the effects of Multi Leaf Collimator (MLC) leaf velocity on leaf positional accuracy during modulated arc delivery. Method and Materials: MLC performance was measured for intensity modulated arcs delivered on a Varian21EX equipped with a 120‐leaf dynamic MLC. The performance of the MLC was tested using arc‐based delivery sequences developed by the investigators for routine MLC leaf velocity testing. MLC performance was also tested using actual VMAT delivery sequences created with a commercially available inverse planning system. Errors in the MLC leaf positions were measured using the MLC controller, which recorded positions of each leaf every 50 milliseconds. To characterize the performance of MLC leaves we introduce the notion of MLC leaf performance curve, which is defined to be a dependency between the MLC leaf velocity and the expected leaf position error. Results: At leaf velocities below 2 cm/sec, the MLC leaves were within 2‐mm of the planned position during 98% of the test sequences. The performance of the MLC leaves did not significantly vary with the MLC moving into or out of the carriage. However, there was a significant difference in the performance between the 5‐mm and 1‐cm MLC leaves. Large leaf velocities translate into large magnitudes of MLC leaf positional errors. The typical shape of the leaf performance curve is linear. Summary: The maximum allowable leaf speed for VMAT treatment delivery will depend on the leaf sequencing. If the intensity is modulated with small MLC leaf separations, then the leaf velocity will need to be limited to 1 cm/sec. Leaf position errors of greater than 1‐mm can have a detrimental impact on the delivered dose distributions for small leaf pair separations. Analyzing the leaf performance curves estimated for each leaf one can easily reveal poorly performing MLC leaves.