bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐C‐ValB‐08: Motion Induced Dosimetric Impacts in Breast 3D Radiation Treatment — a 4D CT Based Study
Authors: Yue N , Li X , Beriwal S , Heron D , Sontag M , Huq M 
Published: July 2006

Purpose: In radiotherapy treatments of breast patients, respirations may introduce uncertainties in target and heart locations. This study is to investigate the dosimetric impacts of these uncertainties in breast radiation treatments. Method and Materials: A 4D CT scan and a conventional helical CT scan set were acquired on each of 7 left breast patients and 5 right breast patients. Using the helical CT scan, a conventional 3D conformal plan, consisting of two tangential beams, was generated per physician's evaluation and decision. The 4D CT scan set was divided into 10 phases over the respiratory cycle. On each phase, treatment target and heart were contoured. Dose distributions were generated using the same beams as in the conventional plan. Software was developed to compute the cumulative dose distribution (4D doses) from all the phases. This 4D CT image based cumulative dose distribution would be closer to that in reality with motions taken into account. Various dosimetric parameters were obtained for treatment target and heart from the conventional plan and from the 4D cumulative dose distributions and compared to deduce the motion induced dosimetric impacts in breast radiation treatments. Studies were performed for both whole and partial breast treatments. Results: For whole breast treatment, the motion induced changes in D95, Dmax, and Dmin of PTV were 0.88% ± 20%, −0.28 ± 0.65%, and −10.17% ± 47%, respectively. For left breast, the motion induced Dmax change in heart was 22% ± 48%. For partial breast treatments, the motion induced changes in V90 and Dmin of CTV were 1.6% ± 2.7% and 3% ± 4%, respectively. Conclusions: Breathing motion may cause cold spots in the whole breast treatment, and may compromise treatment quality for some patients. It may also increase heart maximum dose. However, for the partial breast treatment, the motion impact may be insignificant with properly selected margin size.Supported in part by Varian Medical Systems.
TH‐C‐230A‐06: High‐Energy Proton Acceleration Driven by Ultra‐Intense Ultra‐Clean Laser Pulses
Authors: Maksimchuk A , Bulanov S , Chvykov V , Brantov A , Bychenkov V , Kalintchenko G , Matsuoka T , Rousseau P , Reed S , Yanovsky V , Litzenberg D 
Published: July 2006

Purpose: To improve the contrast ratio of the multi‐terawatt Chirped‐Pulse Amplification (CPA) Ti:Sapphire laser to 1011 to allow Coulomb explosion regime of ion acceleration in the interaction of ultra‐short high‐intensity laser pulses with ultra‐thin (< 1 micron) foils. Method and Materials: The cross‐polarized wave generation (XPW) technique in BaF2 crystals was implemented. This technique improves contrast by rejecting the low‐intensity amplified spontaneous emission (ASE) preceding the main laser pulse. Particle‐in‐cell (PIC) simulations were conducted under the anticipated experimental conditions: 225 TW in a 6.75 J, 30 fs laser pulse with no prepulse, focused to a spot size of 2.4 microns (FWHM) on thin foils of varying thickness. Results: Implementation of the crosspolarized wave generation technique resulted in a contrast improvement of three orders of magnitude to approximately 1011. The performed PIC simulations show that for a 0.2 μm thick hydrogen foil, protons with energy of about 200 MeV can be generated. In the case of the two‐layer aluminum‐hydrogen foil the maximum energy of accelerated protons is about 150 MeV, but the proton spectrum has a flatter distribution, which may be more advantageous for therapy applications. Conclusion: We demonstrated that pulse cleaning based on cross‐polarized wave generation (XPW) using two BaF2 crystals yields a 1011 contrast ratio for a 50 TW laser system. Such contrast may be sufficient for a preplasma‐free interaction of sub‐Petawatt laser pulses with a sub‐micron thickness foils at intensity of ∼1022 W/cm2. Modeling of this interaction with PIC simulations demonstrated proton energies that are of interest for the radiation therapy.This study was supported by the National Science Foundation through the Frontiers in Optical and Coherent Ultrafast Science Center at the University of Michigan and the National Institute of Health.
TH‐C‐230A‐08: A Prototype Rotational Immobilization System for a Proposed Static‐Gantry MicroRT Device with Tomographic Capabilities
Authors: Hope A , Stojadinovic S , Deasy J , Hubenschmidt J , Grigsby P , Low D 
Published: July 2006

Purpose: Proposed small animal irradiation devices are typically isocentric gantry systems. Multi‐axis gantry systems require significant resources to develop and maintain. A static gantry system could provide the functionality of a multi‐axis gantry via subject rotation if subject motion could be minimized. In this study, we evaluated internal organ motion of mice within a prototype immobilization device during rotation. Method and Materials: Mice were anesthetized and immobilized in a prototype device designed to rigidly support animal positioning during rotation along the cranio‐caudal axis. The head and tail of the mouse were allowed to extend beyond the immobilization device as an internal control. Validation of internal and external immobilization was assessed using computed tomography imaging at multiple rotation angles. CT images were co‐registered (translated/rotated) using our research treatment planning system (CERR) into a common reference frame. Internal organ motion was assessed qualitatively by examination of internal anatomy in overlaid multiplane CT images. Quantitative evaluation of organ motion was assessed by delineating organ structures in CERR and comparing relative organ volumes and centers of mass. Results: CT imaging demonstrated minimal exterior contour changes (<1mm) in the immobilized regions during rotation. Un‐immobilized regions demonstrated the expected gravitational positional changes. Internal organs demonstrated sub‐millimeter changes in organ centers of mass (heart and lung) and small (<5 mm3) changes in volume during rotation. These variations were similar to the differences when the same CT was re‐contoured multiple times by the same operator and likely represent intra‐observer contouring variations. Conclusion: A microRT device with a stationary irradiator, collimator, tomographic imaging system, and rotating subject would reduce the overall cost and complexity of the unit. This study demonstrates rotational immobilization of small animals is feasible.This work supported in part by NIH R21 CA108677 and by a grant Varian, Inc.
TH‐C‐VaIA‐03: Accurate Dosimetry in Narrow Stereotactic Photon Fields
Authors: Gibbons J 
Published: July 2006

Dosimetric measurements for stereotactic radiosurgery or radiotherapy fields typically include determination of relative output factors, tissue maximum ratios and off‐axis beam profiles. Accurate measurements of each of these quantities are made more difficult when the measured field sizes are either comparable to the detector size, or less than the distance required for lateral electronic equilibrium. These difficulties are present when measuring either single, static‐field cone or micro‐MLC linac‐based delivery systems, or simultaneous multiple‐field Gamma Knife delivery systems.Several detector characteristics should be considered when choosing a measurement system. The detector size in the radial direction will determine the extent of the beam profile integrated in the reading. Typically solid‐state detectors or film (radiographic or radiochromic) have been used to reduce this volume‐averaging effect. Several other detection systems have also been used, including pin‐point ionization chambers, thermoluminescence dosimetry, and diamond and scintillation detectors. Techniques exist to correct for finite detector volume, including the extrapolation of measured results to zero‐volume, and deconvolution of measured data with the detector response function.The detector energy response also should be considered due to the variation in the number of low energy scattered photons with field size and depth. Additionally, for field sizes below lateral electronic equilibrium, variations in the stopping power ratios affect the conversion of ionization to dose, particularly for higher‐energy measurements. Both of these effects increase with beam energy and depth.This lecture will provide an overview of the measurement techniques used to determine dosimetric quantities for stereotactic fields. Recommendations for measurement systems will be made, and limitations to each system will be discussed. Estimations of error will be provided, both for individual measurements and in the overall planned dose. When available, comparisons will be made with results predicted by theoretical Monte Carlo calculations.Educational Objectives:1. Understand the basic principles and practical aspects of clinical dosimetry for stereotactic radiosurgery.2. Understand the limitations and applicability of various detector types and sizes for small field measurements.3. Understand current techniques available to correct data measurements in small fields.
TH‐C‐VaIA‐05: Accurate Dose Measurements in Heterogeneous Phantoms
Authors: Huq M 
Published: July 2006

The human body consists of tissue types that have radiological properties that are different from water. These include, for example, lung, bone, and oral cavities. Presence of such tissue types and cavities in the treatment fields of high‐energy photon beams creates potential dosimetric problems. For inhomogeneities with density less than that of water electronic disequilibrium situations can be severe. Lateral electronic disequilibrium is present for small field sizes (i.e., 5 cm × 5 cm) and high energy beams (i.e., 15 MV) in a low density inhomogeneity such as lung. Perturbations at air‐tissue interfaces are complex to measure or calculate due to lack of electron equilibrium. The trend of data published in the literature show that for low density media i) dose generally increases beyond the depth of dose maximum; ii) build‐up and build‐down regions exist within tissue near the low density media‐tissue interfaces; the severity of these effects increase with increasing energy and decreasing field size; iii) the penumbra increases with energy in the region of low density region. For high density media the dose is found to decrease beyond the depth of dose maximum.The dosimetric effects of these heterogeneous tissues become even more complicated for IMRT beams. This is because i) small radiation beams are inherently difficult to measure; ii) standard ion chambers have dimensions that are large compared to the beam and do not have the spatial resolutions that are needed to resolve the narrow central region of uniform dose and the sharp dose gradient regions of the penumbra and iii) the chambers may have a dose rate dependence.The dosimetric impact of the presence of heterogeneous tissues in megavoltage photon beams have been addressed with varying degrees of success by various investigators i) experimentally by the use of specially designed ionization chambers, film, TLD and other dosimeters in specially constructed phantoms, ii) theoretically by the development of various dose calculation algorithms and iii) by the use of Monte Carlo simulation.Educational Objectives:Develop an appreciation of1. the challenges involved in accurate dose measurements in heterogeneous phantoms2. the clinical implementation of the results of such measurements, various dose calculation algorithms and/or Monte Carlo simulations to various disease sites that involve the presence of various types of heterogeneous tissues.
TH‐C‐VaIA‐06: Accurate Dosimetry Measurements for IMRT and 4D Delivery
Authors: Ma C 
Published: July 2006

The use of conformal radiotherapy, especially with the IMRT technique, is a major departure from the way radiotherapy is currently delivered. Although the use of multileaf collimator (MLC) provides the possibility of achieving better dose distributions conformed to tumor targets, it also increases the treatment complexity. The sequences of leaf movement and their associated effects on the dose delivered to the patient may vary significantly depending on the accelerator and the MLC design. Accurate measurement of IMRT dose distributions in a clinical setting is not an easy task since many factors may affect the measurement results. In this presentation we will review various factors affecting IMRT dose distributions including the variation of the accelerator head scatter component in the MLC‐collimated beam, the amount of photon leakage through the leaves, and the scatter from the leaf ends, the “tongue and groove” effect, and the effect of back‐scattered photons from the moving jaws and MLC leaves on the monitor chamber signal. We will describe the use of different detectors commonly used for absolute and relative dose determination with both static and dynamic beam delivery. We will discuss the effects of electron disequilibrium, detector perturbation and patient heterogeneous anatomy on the measurement accuracy.Below are the educational objectives of this presentation:1. Review dosimeters for absolute and relative IMRT dose measurements.2. Discuss the process for dose determination under electron disequilibrium conditions.3. Describe the use of Monte Carlo simulations to derive detector correction factors.4. Discuss major factors affecting IMRT dose measurement accuracy.
TH‐D‐VaIB‐01: Correction of Couch Artifacts in KV Cone‐Beam CT From An On‐Board Imaging System
Authors: Ali I , Lovelock D , Kriminski S , Chang J , Amols H , Ali I 
Published: July 2006

Purpose: To evaluate artifacts caused by treatment couch attenuation on 3D image reconstruction for a new kV on‐board‐imager (OBI) and cone beam CT (CBCT) system and to develop an algorithm that filters couch effects from two‐dimensional radiographic projections prior to inputting to the 3D reconstruction algorithm. Material and methods: A standard quality assurance phantom was scanned in air and on couch top using both full and half fan cone‐beam scanning modes with and without bowtie filter combination. A spatial domain filter algorithm was developed to remove couch attenuation from each radiographic projection. This filter is based on a pixel‐by‐pixel subtraction technique of radiographic projections of cone‐beam scans of the couch from the corresponding radiographic projections of scans with phantom on top of the couch. The net couch‐filtered radiographic projections were used to reconstruct CT images. Results: CT numbers for scans of the phantom on couch top are less uniform than for scans of the phantom in air. The couch artifacts vary the linearity of the CT numbers by 5–15%, depending on the density of the material. Noise of the scans with phantom on couch top (3.5%) is higher than that with phantom in air (1.5%). The increased noise hinders the ability of the CBCT system to resolve low‐contrast regions when the couch is present. Pre‐reconstruction processing of the couch suppresses noise (< 1.5%) improves uniformity by a factor of 2 and removes ring and streak artifacts in the couch‐filtered reconstructed CBCT images. Conclusion: The treatment couch produces streaking artifacts, enhances noise, and causes drifting of CT numbers in the reconstructed OBI CBCT images. The developed couch pre‐processing algorithm suppresses noise, improves CT number uniformity by a factor of 2 and removes ring and streak artifacts in the couch‐filtered reconstructed CBCT images.Conflict of Interest: Supported by NCI Grant P01‐CA59017.
TH‐D‐ValB‐05: Evaluation of Image Quality in Megavoltage Digital Tomosynthesis
Authors: Descovich M , Morin O , Aubry J , Aubin M , Chen H , Chen J , Bani‐Hashemi A , Geffen M , Kelly K , Pang G , Pouliot J 
Published: July 2006

Purpose: We report on the characteristics of Megavoltage Cone Beam Digital Tomosynthesis (MVCB DTS) and its potential clinical application for imaging of pulmonary lesions. Method and Materials: MVCB CT refers to the reconstruction of a 3D image from a set of 2D projections, acquired using a medical linear accelerator equipped with an electronic portal imaging device (EPID). A typical MVCB CT scan is acquired over a 200 degrees arc. In the case of MVCB DTS, the angular range is limited to reduce the acquisition time. This limited angular range affects the image quality of the reconstructed tomograms. To study the image quality as a function of the angular range, phantom measurements were performed and data from a head and neck patient were analyzed. The image quality was analyzed in terms of effective slice thickness, shape distortion and contrast sensitivity. MVCB DTS of the lung was performed on patients, with localized and diffuse lesions. Results: The image quality and the capability to distinguish overlaid structures decreases with decreasing angular range: a 20 degrees arc DTS results in a slice thickness of 2.7cm (vs. 1mm), a ratio of the vertical to lateral diameter of a sphere of 0.15, and a reduced contrast sensitivity. The acquisition is faster than MVCB CT. It takes 5–10 seconds for arcs of 20–40 degrees, compared to 45 seconds for a 200 degrees arc. In lung images, the faster acquisition results in a reduced blur due to the respiratory motion. Conclusion: This study indicates some potential advantages of DTS for imaging lung patients in the treatment position. Compared with EPID, DTS provides 3D information and better soft tissue contrast. Compared with CBCT, DTS allows shorter acquisition times, compatible with breath holding.Conflict of Interest: Research sponsored by Siemens OCS.
TH‐D‐230A‐01: Economics Refresher Course: How Medical Physics Services Are Reimbursed
Authors: Hevezi J , White G 
Published: July 2006

Medical physics services in medicine are reimbursed through the Current Procedural Terminology (CPT) Codes published by the American Medical Association in an annual publication. Although CPT codes for medical physics services appear explicitly in the radiation oncology series of CPT codes (77XXX), diagnostic radiological physicists may use several of these codes to cover patient specific work they may be called on to perform. This refresher course will trace the advent of the Centers for Medicare and Medicaid Services (CMS) relative value system for reimbursement for medical services and explain in detail how the complex system operates for current and new technology codes. Payments differ in various settings such as hospital, free‐standing center and ambulatory surgical center and these differences will be traced for each site of service.Additionally, private health insurance carrier are not required to follow the precepts of the CPT formalism and these reimbursement entities will be described in their methodology of reimbursement for these services. Finally, ancillary publications that impinge on these reimbursement rules (eg. Correct Coding Initiative, CCI) will be referenced. Coding compliance guides such as those published by ASTRO and ACR will form the basis for this economics refresher course.
TH‐D‐224A‐01: QA for Tomotherapy
Authors: Tome W , Jaradat H , Westerly D , Fenwick J , Orton N , Mackie T , Paliwal B 
Published: July 2006

Purpose: To describe the commissioning and quality assurance for helical tomotherapy machines. Method and Materials: Helical tomotherapy is a volumetric image guided, fully dynamic, IMRT delivery system. It was been developed at the University of Wisconsin and is now commercially manufactured as the ‘Hi‐Art’. At the core of this fully dynamic IMRT Delivery system lies a short gantry‐mounted linac that is used both for treatment and per‐treatment MVCT imaging. Aside from the primary collimator and the jaws, which set the width of the beam, it is also collimated by a binary multileaf collimator generating a fan beam of intensity‐modulated radiation. Modulation varies with gantry angle. Hence, the Hi‐Art allows for the acquisition of a helical pre‐treatment MVCT scan that is used for online image guidance and allows for precise interfraction positioning of the patient while in the actual treatment position just prior to the start of treatment. Due to its unique design the Hi‐Art system, allows highly conformal dose‐distributions to be delivered to patients in a helical fashion. Patients are treated lying on a couch that is translated through the bore of the machine as the gantry rotates, therefore the Hi‐Art is the therapy equivalent of helical CT. Since this approach to therapy is fully dynamic it requires synchrony of gantry rotation, couch translation, linac pulsing and the opening and closing of the leaves of the binary multileaf collimator used for beam modulation. Results: Over the course of the clinical implementation of the HiArt we have developed a quality assurance (QA) system that covers machine specific QA. The machine specific QA system is similar to that recommended for conventional linear accelerator QA by AAPM Task Group 40; however since the Hi‐Art design and operation differs from that of conventional medical linear accelerators, the tomotherapy QA system contains also novel components, such as QA checks for synchrony of gantry rotation, couch translation, linac pulsing and the opening and closing of the leaves of the binary multileaf collimator. Conclusion: In the first part of the presentation the design and dosimetric characteristics of Hi‐Art machines are summarized and the QA system is described along with experimental details of its implementation, while in the second part the pre‐treatment patient‐specific delivery QA for helical tomotherapy is discussed.Learning Objectives:1. The audience will understand the rationale for the proposed machine specific QA for Tomotherapy machines and how to carry out the various tests in a systematic and controlled fashion.2. The rationale for the proposed patient specific pre‐treatment QA and how to carry it out in a systematic and controlled fashion will be understood.
TH‐D‐224A‐02: Physics Aspects of Clinical Trials: From the Basics to IMRT and IGRT
Authors: Moran J , Olch A 
Published: July 2006

Medical physicists play an important role in the success of clinical trials involving radiation therapy. An understanding of how these clinical trials work is necessary and expected of the physicist involved with these treatments. AAPM Report #86, Quality Assurance for Clinical Trials: A Primer for Physicists, provides background information to physicists participating in clinical trials and will be reviewed.The second part of the presentation introduces a new initiative within the AAPM that will affect how clinical trials are conducted. The goal of AAPM Task Group 113 is to provide guidance to physicists and others involved in clinical trials on methods to improve the consistency and quality of data generated for trials involving external beam radiotherapy. This presentation will discuss factors that impact data quality for the entire treatment planning and delivery process with an emphasis on advanced technologies such as IMRT and IGRT. The scope of Task Group 113 includes image acquisition for volume definition, treatment planning systems, patient localization, treatment guidance and delivery, and credentialing for clinical trials.Educational Objectives:1. To review the primer on QA for Clinical Trials.2. To describe the goals of TG#113 Physics Practice Standards for Clinical Trials.3. To highlight factors that directly impact clinical trials that involve IMRT and IGRT.