bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐FF‐T‐58: Dosimetric Study of a New Surface Applicator for the Xoft Axxent System
Authors: Axelrod S , Kelley L , Walawalkar A , Yao S , Rusch T 
Published: April 2010

Purpose: To determine the dosimetric properties of a new surface applicator designed for the Xoft 50 kVp x‐ray system Method and Materials: A 35mm conical stainless steel applicator with Al flattening filter interfaces to the Xoft 50 kVp x‐ray source to provide therapeutic radiation to surfaces such as skin. Measurements of the dose profile at the surface and at depths to 20 mm were performed using a PTW ionization chamber in a water phantom. The chamber was controlled by a stepper motor and linear stage, and data was read into a controlling computer. In addition, film data was taken both parallel and perpendicular to the surface. Results: Nominal dose profiles and depth dose characteristics were determined from an average of ten sources. Dose profiles across at least 80% of the applicator width were flat to within ± 10% for all sources, and to within 5% on average. Depth dose characteristics are very similar to those published for HDR based surface applicators, with the percent depth dose at 5 and 10 mm at 58% and 36%. Such data can be used for treatment planning purposes. The variation seen among sources determines an error band representative of what will be experienced in clinical use. Conclusion: The FDA approved surface applicator delivers a dose profile that is flat to within ± 10% over a span of 80% of the defined width of the device. It can be used for treatment of skin lesions in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for use intra‐operatively, since the system can be used in an operating room.Conflict of Interest: Research supported by Xoft, Inc.
SU‐FF‐T‐83: An Image‐Guided Adaptive Treatment Planning Optimization for IMRT
Authors: Lee E , Cha K 
Published: April 2010

We present an adaptive IMRT treatment planning approach that is guided by 3D/4D images and that allows exploration of a wide range of beam angles for optimal treatment design. Computational advances to improve solution times are highlight, and robustness of the method and quality of the resulting plans are compared.We focus on column generation of adaptable and clinically acceptable plans. Binary (0/1)variables are used to capture “on”/“off” for each beam. Guided by the tumor image, these candidate beams are generated dynamically throughout the solution process. The treatment model includes explicit clinical constraints, including constraints based on upper/lower/mean dose, approximate organs‐at‐risks dose‐volume relationships, and PTV homogeneity and coverage. During the solution process, at most k active beams are allowed in the branch‐and‐price framework(where k is input by clinicians and is patient/tumor‐specific).Compared to clinical plans, for prostate cases, PTV homogeneity improves by 8–11%, whereas mean‐dose to rectum and bladder reduce uniformly by over 50%. For head‐and‐neck cases, left‐parotid mean dose reduces uniformly by over 50%. In particular, all critical structures receive significantly less dose, as the adaptive approach focuses the radiation onto the tumor volume. The adaptive plans provide over 95% PTV coverage, as requested by the clinicians.The adaptive branch‐and‐price approach proves efficient to simultaneously optimize the beam orientations over the entire space of gantry angles and the fluence map. Two significant advances were made: 1) We efficiently and rapidly solved previously intractable large‐scale treatment instances with important clinical constraints to optimality. 2)We designed a rapid column‐generation approach where candidate beams are chosen adaptively and dynamically, and where the set of active beams are set to clinically acceptable values. These properties allow for generation of plans that are practical for actual delivery and guided in real‐time by tumor images. Clinical experiments showed that our approach produces superior plans.
SU‐FF‐T‐141: Initial Clinical Experience with Elekta VMAT
Authors: Shepard D , Cao D , Rao M , Chen F , Afghan M , Ye J , Wong T , Mehta V 
Published: April 2010

Purpose: Elekta recently introduced a new delivery control system called PreciseBeam® VMAT that provides dynamic delivery capabilities including volumetric modulated arc therapy (VMAT). VMAT is a rotational approach to the delivery of IMRT that can be delivered on a conventional linear accelerator. In this study, we report on our initial clinical experience with Elekta VMAT. Method and Materials: The PreciseBeam® VMAT control system has been installed on an Elekta Synergy and an Elekta Precise linear accelerator in our clinic. We have tested the delivery system in conjunction with three inverse planning solutions: (1) an in‐house arc sequencing algorithm that translates optimized fluence maps into deliverable VMAT plans, (2) the Ergo++ planning system that utilizes anatomy based inverse planning, and (3) the SmartArc planning module in the Pinnacle3 treatment planning system. The optimized treatment plans have been verified using phantom irradiations with the IBA MatriXX 2D ion chamber array embedded in a MULTcube phantom. Results: Using our arc‐sequencing algorithm for VMAT planning, we treated our first Elekta VMAT patient under an institutional review board (IRB) protocol in July 2008. In January 2009, we treated our first Elekta VMAT case planned using Ergo++. Our initial focus was on more simple concave targets. More recently, we have opened up VMAT for all clinical sites. Conclusion: Elekta's Precise Beam® VMAT control system can safely and efficiently delivery highly complex VMAT treatment plans. For simple targets such as prostate, pancreatic, and lung cases, single arc VMAT plans are sufficient and be typically delivered in less than 3 minutes. For more complex cases such as head‐and‐neck, the use of multiple arcs provides a dosimetric benefit and plans typically take between 4 and 6 minutes to deliver.Research sponsored in part through a grant from Elekta.
SU‐FF‐T‐340: A New Parameterisation of Small Photon Fields in Off‐Axis Regions for the 160MLC
Authors: Poppe B , Riediger J , Suft G , Ruehmann A , Willborn K , Harder D 
Published: April 2010

Purpose: Due to the improved over travel capacities of the SIEMENS MLC160, the application of small fields for stereotactic treatments as well as the possibility of applying intensity modulated irradiation fields within the whole 40 cm × 40 cm usable field size is now possible for the first time. In this work we analyzed dose profiles of small off‐axis fields generated with the SIEMENS MLC160. Method and Materials: Measurements have been performed for 6 MeV nominal photon energy at a linear accelerator equipped with a 160MLC (Artiste, SIEMENS, Kemnath, Germany). Dose profiles are measured with a diode PTW‐60012 (PTW‐Freiburg, Germany) in water. Results: Larger deviations from symmetrical dose distributions have been found for fields which are generated at the maximum diagonal off‐axis positions. Two different methods for an analytical description of the dose distribution generated by these fields are presented, based on the convolution of a rectangular linear‐function with a kernel. A sum of two Gaussian distributions as well as a Lorentz‐type function are used as such kernels. While the Gaussian method leads to known field parameterization parameters, the Lorentz type kernel offers a larger data reduction and a full analytical description of the profile. Conclusion: Both methods offer the possibility of analyzing the underlying fluence profiles. Characteristic parameters of the kernel functions are serving to represent the dose drop off at the field edges. While for the Gaussian method the slope can be expressed in terms of a regular wedge‐angle, a linear fluence profile can be applied for the Lorentz method. With this approach an analytical representation of the dose profile is possible which may act as further input for treatment planning systems or data reduction.Conflict of Interest: The work was performed in cooperation with SIEMENS Health Care (Kemnath, Germany).
SU‐FF‐T‐362: Dosimetric Evaluation of the OneDose MOSFET for Measuring Kilovoltage Imaging Dose From Image‐Guided Radiotherapy
Authors: Ding G , Coffey C 
Published: April 2010

Purpose: There is a growing interest to determine and to manage the additional image dose to radiotherapy patients. An easy‐to‐use in vivo dosimeter would be very useful for kilovoltage (kV) x‐rays used in IGRT. This study aims to provide the dosimetric characteristics of the commercially available OneDose™ for measuring dose from kV x‐rays with energy ranging from 60 to 125 kVp used in IGRT procedures with respect to reproducibility and energy correction factors. Method and Materials: The OneDoseTM system consists of a small MOSFET dosimeter with overall physical dimensions of 6 mm wide, 33 mm long, and < 1 mm thick and a portable handheld battery‐powered reader. The dosimeter is wireless with adhesive backing to stick to patient's skin. This single‐use dosimeter was pre‐calibrated by the manufacturer using Co‐60 beams. The energy response for kV x‐rays produced by a Varian OBI system was determined by using an ionization chamber in which the air‐kerma calibration factors were obtained from an Accredited Dosimetry Calibration Laboratory (ADCL). Results: The dosimeters have reproducible readings with a deviation of 1–4% for imaging dose of only a few cGy. The energy correction factors were found to be 0.27 – 0.32 for kV x‐rays from the OBI system ranging from 60 to 125 kVp including beams from cone‐beam CT. Conclusion: OneDose™ dosimeter has a similar reproducibility when used for measuring dose from kV photon beams as that when used for measuring dose from MV photon beams. A correction factor that is energy dependent must be applied because of the over‐responds to x‐rays in the diagnostic energy range. The ease‐to‐use allows the OneDose™ dosimeter to be suitable for in vivo dosimetry of measuring doses resulting from imaging guidance.Conflict of Interest: Research sponsored by Sicel Technologies, Inc. Morrisville NC.
SU‐FF‐T‐407: Full Monte Carlo Computation of K Correction Factors Calculated in Tomotherapy Static and Helical Deliveries for Future Ion Chamber Reference Dosimetry Protocols of Non Standard Beams
Authors: Sterpin E , Mackie T , Lu W , Olivera G , Vynckier S 
Published: April 2010

Purpose: Calculate correction factors for ion chamber dosimetry using Monte Carlo (MC) simulations for future IAEA/AAPM protocols adapted to Tomotherapy treatments. Material and methods: The formalism in Alfonso et al (Med. Phys. 35 2008) introduced two corrections factors: defined for a “machine‐specific‐reference” field fMSR (10×5 cm2 field, source‐surface distance of 85 cm) and for a “plan‐class‐specific‐reference” field, fPCSR, closer to actual clinical treatments. Here, fPCSR was a helical sequence delivering a centered cylindrical homogeneous dose over 10 cm in a homogeneous cylindrical phantom. The k factors were calculated using MC with accurate simulation of static and helical deliveries (using TomoPen, based on PENELOPE) and detailed modeling of the geometry of the ion chambers Exradin A1SL, PTW‐30013, Wellhöfer IC‐70 and NE‐2571. Calculations in the phantoms were performed by the “cavity” EGS++ user code, for static beams, and PENELOPE for both helical and static beams. Correction factors were calculated from the formulas
urn:x-wiley:00942405:media:mp1889:mp1889-math-0003 and
urn:x-wiley:00942405:media:mp1889:mp1889-math-0004 where Dm is the dose at the reference point in medium m (water or Solid Water™) and a is the dose averaged over the air cavity. Results: For the A1SL chamber, equaled 0.997±0.001 (3σ), which is consistent with the values previously reported using existing protocols. was estimated at 0.995±0.002 for the procedure chosen. The work is in progress for the ion chambers listed above and other Tomotherapy “PCSR” settings, like a typical bilateral head and neck treatment delivery planned on a phantom. Conclusions: A powerful MC method is proposed here to compute accurate correction factors for Tomotherapy treatments. The data obtained may be of primary importance during the final definition of a new dosimetry protocol, adapted to nonstandard treatments like Tomotherapy and may also improve global treatment accuracy, especially for helical deliveries.Research partially sponsored by Tomotherapy Incorporated
WE‐D‐210A‐03: Systems and Probes for Ultrasound Molecular Imaging
Authors: Ferrara K , Hu X , Zhang H , Stephens D , Kruse D 
Published: April 2010

Specialized ultrasound systems and targeted microbubbles optimized for vascular molecular imaging continue to advance. The development of methods for sensitive and selective imaging of adherent, targeted contrast agents requires improvements in both the physical systems and probes. We have developed transducers and signal processing techniques to maximize transducer bandwidth and integrated the components with a clinical ultrasound scanner. The transducer integrates low and high‐frequency arrays; the center‐row high‐frequency array is surrounded on each side with confocally‐focused low‐frequency arrays. By transmitting from the low‐frequency (1.6 MHz) arrays and receiving through the high‐frequency (7 MHz) array, harmonic microbubble echoes can be detected and distinguished from the surrounding tissue. Further, by combining echoes over a pulse train, a targeted agent to free agent signal ratio of 15∼22 dB can be obtained without waiting for agent clearance. Further, we report on radiolabeling methods to fully assess microbubble biodistribution with and without molecular targeting or insonation. We find that microbubbles are rapidly accumulated within the liver and spleen, although a small (but significant) mass of the microbubble shell accumulates as a result of local insonation.We acknowledge the support of NIH CA 103828 and CA 112356.
WE‐E‐BRD‐03: Re‐Evaluation of the Product of W/e and the Graphite to Air Stopping Power Ratio for Co‐60 Air Kerma Standards
Authors: Thomson RM , Rogers D 
Published: April 2010

Purpose: To reanalyze experiments which determine , the product of (W / e)air, the average energy deposited per coulomb of charge released in dry air, and , the Spencer‐Attix mass collision stopping‐power ratio for graphite to air, and to calculate an average value for this product for the BIPM air kerma standard: . This value could be adopted for use with air kerma primary standards, along with corrections to account for variations due to cavity size. Methods and Materials: The experiments measured by various methods, often involving calorimeters and ionization chambers. Correction factors, e.g., to account for gaps about a calorimeter core or perturbations due to a cavity's presence, are calculated as needed for each experiment using the EGSnrc user‐codes CAVRZnrc, DOSRZnrc, and CAVITY. Stopping power ratios are evaluated using SPRRZnrc for different choices of graphite density (bulk 1.70 g/cm3 or grain 2.265 g/cm3) for the density effect correction and average excitation energy for graphite (I=78 or 87 eV). For each experiment, the corrected value of is multiplied by , the quotient of the stopping power ratios for the BIPM chamber and the experiment in question. A least squares technique is used to compute an average value of . Results: The correction factors generally decrease the value of for each experiment, often outside the range of one standard deviation quoted with each experimental result. The ratio varies by less than 0.1% for different choices of density correction and I‐value and hence the product is also relatively insensitive to these choices.Conclusion: The preliminary analysis suggests that the accepted value of , 33.97 J/C ±0.15%, is 0.6% too high. This would have implications for primary air kerma standards worldwide and for the value of (W / e)air which is used in low energy x‐ray standards.
WE‐E‐210A‐02: Emerging X‐Ray Fluoroscopic Guidance Technologies for Challenging Cardiovascular Interventions
Authors: Speidel M 
Published: April 2010

X‐ray fluoroscopy remains the primary guidance modality for cardiac interventions due to its appealing combination of real‐time imaging, high spatial resolution, simplicity of use, and compatibility with conventional catheter devices. However fluoroscopy has well‐recognized limitations. The lack of depth resolution and poor soft tissue contrast in an x‐ray projection make it difficult to precisely position devices with respect to target cardiac structures. Ionizing radiation dose is an ongoing concern, particularly for interventions with long imaging times such as catheter‐based electrical mapping and ablation of atrial fibrillation.Technologies which reduce dose and add three‐dimensional context to the live fluoroscopic image offer a route towards overcoming these limitations. Scanning‐beam digital x‐ray (SBDX) is an inverse geometry fluoroscopic system that provides both dose reduction and real‐time tomosynthesis, a feature that can be exploited for image‐based 3D tracking of catheter electrodes. The operating principles of SBDX will be reviewed and recent investigations of 3D catheter tracking based on multiplanar tomosynthesis will be presented. Fusion of live fluoroscopy with roadmaps derived from pre‐acquired 3D image data (e.g. CT, MRI) can allow the interventionist to visualize structures lacking x‐ray contrast, or to perform novel therapies targeted to the physiologic status of cardiac tissue. A fluoroscopic fusion system for recanalization of chronically occluded arteries and for targeted stem cell therapy will be discussed.This lecture will provide an overview of the demands and constraints of fluoroscopically‐guided cardiovascular interventions, dose reduction and 3D catheter tracking capabilities enabled by the SBDX system, and clinical application of fluoroscopy fused with 3D roadmaps.This research was supported in part by NovaRay Medical, Inc. and NIH/NHLBI.Learning Objectives:1. Review the demands and constraints of fluoroscopically‐guided interventions2. Understand the principles of SBDX dose reduction and 3D catheter tracking3. Discuss x‐ray fluoroscopy combined with 3D imaging for cardiovascular interventions
TH‐A‐211A‐01: Digital Tomosynthesis for Target Localization
Authors: Yin F , Wu Q , Godfrey D , Ren L , Yoo S , Maurer J , Yan H 
Published: April 2010

Any deviation between treated and planned volumes for 3‐D conformal therapy, such as IMRT, may cause an adverse clinical outcome. It is therefore critical to minimize all potential deviations using an on‐board (or real‐time) imaging procedure immediately prior to radiation delivery. At present, conventional 2‐D radiographic imaging and state‐of‐the‐art 3‐D cone‐beam CT (CBCT) are typically employed for treatment verification. However, 2‐D radiographic verification is mainly based on bony structures and/or implanted fiducials, and is sub‐optimal for soft‐tissue targets. While on‐board CBCT can provide 3‐D soft tissue information, it has three potential limitations: 1) The acquisition time is limited to a minimum of 60 seconds (≈15 breathing cycles) for on‐board CBCT, making single breath‐hold imaging impractical for organs which exhibit respiratory motion; 2) 360° mechanical clearance for CBCT acquisition may limit the use of CBCT for large patients, those with tumors at peripheral locations (e.g. breast), or those with substantial immobilization or support devices; 3) A high radiation dose (2–9 cGy) is delivered to the imaged volume with current imaging techniques, which is undesirable for daily imaging and may be a particular problem for those who are at high risk of developing second malignancies. To overcome these limitations, innovative digital tomosynthesis (DTS) imaging technologies are being developed for 3‐D and 4‐D target localization.Although DTS technology has been used for digital chest and mammography, its use in target localization is new. DTS only requires limited gantry rotation (e.g., a scan angle of 40° or less) to reconstruct 3‐D anatomic information. Thus, imaging time and dose are substantially reduced compared to CBCT, making breath‐hold DTS a simple solution for daily imaging of moving organs. 4‐D DTS can also be generated much faster than 4‐D CBCT, which is desirable for on‐board 4‐D tomographic imaging. Further, the reduced mechanical clearance needed for DTS makes it more widely applicable than CBCT. At present, limited information has been published regarding the fundamentals of DTS for target localization, and/or preliminary clinical DTS localization results. The purpose of this presentation is to provide updated information about these topics, including the following objectives:1. To understand the technical challenges and clinical potentials of using DTS technologies for target localization in radiation therapy2. To understand the latest developments in DTS reconstruction and registration methods3. To understand the clinical feasibility and efficacy of kV DTS compared to kV CBCT4. To learn about the latest developments in MV DTS and brachytherapy DTS applicationsWork is partially supported by grants from NIH, Varian Medical Systems, and GE Health Care.
TH‐B‐303A‐01: Diffusion Imaging: What It Can Tell Us About Cancer
Authors: Yanasak N 
Published: April 2010

The use of the self‐diffusion characteristics of water to generate image contrast for magnetic resonance imaging (MRI) can provide a wealth of information about tissue microstructure. Diffusion imaging has demonstrated sensitivity to pathology in structured tissues (e.g., white matter, cardiac muscle fiber, kidney), where the structure may be altered. Additionally, the relative volume of water between intra‐ and extra‐cellular compartments, as well as the permeability of tissue membranes dividing the compartments, may be affected by certain diseases. Cancer, in particular, affects water diffusivity in a number of ways. In tumor regions where a high density of cells exists, the diffusion of extra‐cellular water can be more restricted than healthy tissue. In regions where the tumor has become necrotic or cystic, diffusion is less restricted. Tissue structure may not be affected equally in all directions. Invasiveness of cancer into neural fibers in the brain, or their preservation and displacement around a tumor, will exhibit differences in diffusion magnitude as well as direction of restriction. Finally, therapeutic intervention (radiation therapy or chemotherapy) of cancer can be monitored using diffusion techniques, where increases in diffusion within a tumor may suggest the efficacy of treatment.This presentation will provide a survey of different diffusion MRI techniques, focusing in particular on when they may be helpful in the diagnosis and treatment of cancer.Learning Objectives:1. To describe how biological changes in tissue correlate with diffusive behavior of water.2. To provide a simple picture of cancer and the different ways in which it can alter cellular diffusion characteristics.3. To give an overview of the different diffusion imaging techniques in MRI: How do they work? What information do they provide? Under what contexts are they important in the diagnosis of cancer?