bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐FF‐A3‐04: Reliable and Accurate Definition of GTV and ITV Using PET/CT in Radiotherapy Planning for Non Small Cell Lung Cancer (NSCLC)
Authors: Li S , Liu Z , Chan P , Micaily B , Miyamoto C
Published: April 2010

Purpose: To have reliable and accurate definition of GTV and ITV using PET/CT images in radiotherapy planning for NSCLC lesions considering patient‐specific pharmacokinetics and location‐dependent nodule motion Method and Materials: Significant variability (>300%) in GTV and ITV delineation was observed in utilization of available methods in “Use of PET and PET/CT for Radiation Therapy Planning: IAEA expert report 2006–2007”. To deal with background and scanning time variations, the MIRD Report ♯19 model was fitted with patient‐specific tracer distributions to the brain, lung, heart, liver, kidneys, bladder, and whole body. FDG uptake by the gross tumor was assumed uniform but had location‐dependent motion with 3D eclipse trajectories that were derived from comparison of fast‐CT and PET images. A point‐spread function with a range of 1‐mm in tissue and 3‐mm in the lung was finally convoluted with the calculated FDG distribution to include the positron transportation effect. Results: Application of the proposed method on patients with NSCLC had shown that GTV/ITV defined in PET could be directly correlated with the GTV defined from the fast‐CT scans if the location‐dependent motion were included. The anisotropic blurred edges and non‐uniform distribution of the FDG in the lesion were mostly created by the elongated eclipse movements of the nodule elements that stayed longer in these voxels located at the ends of inhalation and exhalation. The maximum SUV to the lesion varied significantly with the pharmacokinetics, lesion size, and amplitude of the nodule motion. Thus, automatic delineation of ITV/GTV from PET has to take those into account. Conclusion: The comprehensive relationship between GTV and its appearance (ITV) in PET images for NSCLC would ensure accurate and reliable delineation of the target in treatment planning that is particularly useful in stereotactic radiotherapy using 3 to 8 treatment sessions.
MO‐FF‐A4‐04: Evaluation of Fluoroscopically Aided Respiratory Gating
Authors: Santoro J , Mageras G , Yorke E , Amols H , Goodman K , Mostafavi H , Sloutsky A
Published: April 2010

Purpose: A key issue in gated radiotherapy with external respiration monitors is the accuracy in predicting internal target position. We examine the positioning accuracy and residual motion of internal structures within the respiration gate at treatment, using in‐room fluoroscopy and research software for image analysis. Method and Materials: We retrospectively analyze data from patients receiving gated radiotherapy (Varian Real‐time Position Management) in abdominal disease sites and having implanted radiopaque markers near tumor. A physician‐specified gate and within‐gate motion extent of implanted markers are determined from a respiration‐correlated CT (RCCT) at simulation. A short kV fluoroscopy session (∼20s, 10fps) is recorded weekly at treatment to evaluate marker position and excursion within the gate. Commercial research software automatically tracks a marker in the images using a cross‐correlation function, calculates its displacement from a user‐specified intended position (end expiration) at the session start, and plots the internal signal vs time alongside the external signal from the respiratory monitor. Analysis compares the within‐gate displacement from the fluoroscopy sessions to that determined at simulation. Results: Data from two patients (8 fluoroscopic sessions) have thus far been analyzed. The percent of within‐gate time that the displacement at simulation was exceeded during treatment ranged from 10% to 50%. For patient 1, the mean in‐gate displacement of the marker in the fluoroscopy sessions ranged from 3.1mm to 11.6mm, compared to 6mm at simulation. For patient 2, the range was 3.0mm to 5.8mm, compared to 4mm at simulation. Results from five patients will be presented. Conclusion: Residual internal motion in external‐monitor gated treatment of abdominal sites may often exceed the prediction from RCCT at simulation. The preliminary findings suggest intra‐fraction imaging is important to verifying gating accuracy.
MO‐FF‐A4‐06: A DICOM‐RT PACS for Peer Review, Quality Assurance and Clinical Outcome Studies in Proton Therapy
Authors: Yeung D , Frouhar V , Palta J
Published: April 2010

Purpose: To implement a web‐based DICOM‐RT PACS for peer review, quality assurance and clinical outcome studies in proton therapy. Method and Materials: We have designed and deployed a web‐based clinical data submission and retrieval system to implement a successful peer review and clinical QA paradigm for proton therapy treatment plans. Our proprietary local DICOM server automates the communication between the TPS and our web‐based secure client application. The TPS outputs the clinical treatment plan as DICOM‐RT objects, which are then uploaded to the central server via a secure web‐based link. The data sets are automatically anonymized based on one‐to‐one mapping that is known only to the submitter of a patient plan. It is often necessary to supplement this data set with additional information in order to appraise the plan reviewers of clinical rationale used in the plan evaluation and selection. The information that is not part of the DICOM ion‐plan includes; proximal and distal margins used to account for range uncertainty, smearing and smoothing margins for compensator design, distal blocking to spare OAR, etc. The submitter may generate screen captured views of a plan and add comments, instructions, and provide planning criteria by adding multi‐media data. This information is converted to DICOM objects and is submitted to the server as a part of a plan. The reviewers can use our web‐based client application to retrieve part or all of the submitted data set and use their own TPS for more comprehensive plan evaluation. Results and Conclusion: The treatment plans for several prostate patients have been successfully submitted to and retrieved from the prototype system at UFPTI. In all cases, the restored plans maintained the integrity of all clinical information as submitted. We found that the supplemental information uploaded with each plan was extremely important and useful for the plan reviewers.
TU‐SAM‐BRB‐01: Model Based Dose Calculation Algorithms in External Radiation Therapy
Authors: Knoos T
Published: April 2010

Accurate photon dose calculation models are today mainly based on dose calculation algorithms in which the dose distribution is predicted from first principles, i.e. model based algorithms. Basically a convolution is performed between the energy released in each voxel and a dose spread kernel. Due to limitations in computer speed and incomplete physics approximations have been introduced. They are to a first level the pencil beam convolution models and secondly the collapsed cone convolution models. This lecture will present these models and discuss the pros and cons for them and when possible also discuss the individual implementations in commercial treatment planning systems.

The models covered are pencil beam models which today still are the basis for most dose calculations in 3DCRT and IMRT optimisations. Secondly, the new pencil beam implementation including modelling of changes in electron transport especially in the lateral direction will be discussed. Finally the highly accurate collapsed cone models will be covered which produce results of the same quality as Monte Carlo simulations. The latter approach is not the topic of this first part of the lecture, however, it will be used to benchmark results from model based algorithms and to highlight limitations of these.

Learning Objectives:

1. To provide an educational review of the physics and techniques behind model based algorithms e.g. convolution/superpositioning models.

2. To review the methods used to improve the simulation efficiency i.e. pencil beam and collapsed cone convolutions.

3. To briefly review the vendor codes currently used for clinical treatment planning.

4. To briefly review the potential clinical implications of accurate calculated dose distributions.
TU‐SAM‐304A‐01: ACR MRI Accreditation Program Update
Authors: Reeve D
Published: April 2010

In October 2008 the American College of Radiology (ACR) expanded the MRI accreditation program to six modules (body, head, MR angiography (MRA), spine, muskuloskeletal and cardiac). The new program enables accreditation of dedicated MR systems, such as those used only for neuro or cardiac imaging, as well as accreditation of special‐purpose MR scanners, such as orthopedic systems. The program introduces a second, smaller ACR phantom, to be used for accreditation and quality control of these small bore orthopedic MR systems.

ACR MRI accreditation is now available for a wide range of MRI system configurations and clinical uses. The expansion of the program presents a challenge to the medical physicist, who needs to be aware of which ACR phantom and coil to use for phantom image acquisition, as well as how to address specific image quality issues.

Learning Objectives:

1. Present the requirements of the new six‐module ACR MRI accreditation program.

2. Discuss the medical physicist/MRI scientist qualifications and CME requirements.

3. Describe small and large phantom image acquisition and analysis.

4. Discuss considerations for low field, 3T, dedicated and special purpose MRI systems in the accreditation and phantom image evaluation process.
TU‐A‐211A‐01: Margins in Radiation Therapy
Authors: Low D , Litzenberg D
Published: April 2010

Conformal radiation therapy has historically used margins to account for geometrical uncertainties in the position of a target volume. The margins, in their simplest form, are simply expansions to the diameter of a treatment beam, to ensure that dosimetric planning criteria are met in the presence of inter‐ and intra‐fraction setup variations. Historically, the size of the margin in a given treatment site was difficult to determine due to the available technology and the time and effort required to obtaining accurate data. Consequently, margins were estimated to accommodate a population of patients. As new technologies have emerged, target volume position errors have become easier to measure, their accuracy has increased, and the measurements can be made much more frequently. As the quantity and quality of data has increased for patient populations, and even for individual patients, the conceptual basis of employing margins has evolved. Strategies for ensuring dosimetric coverage may now be individualized to a specific patient's geometric uncertainty characteristics with customized margins, or they may incorporate geometric correction based on predefined action levels. Other strategies may incorporate continuous monitoring to gate or modify the beam. And finally, other strategies seek to eliminate margins by including the estimated geometrical uncertainty into the development of the dose distribution.

Learning Objectives:

1. To provide an educational review of the technologies and methods of measuring target volume positioning errors.

2. To review methods of determining population margins from measured data.

3. To review corrective and intervention strategies for patients with individualized margins.

4. To review planning strategies which seek to eliminate margins.
TU‐C‐BRD‐05: Carbon Nanotube Field Emission Based Imaging and Irradiation Technology Development for Basic Cancer Research
Authors: Chang S , Zhou O
Published: April 2010

Caron nanotube (CNT) field emission is an emerging nanotechnology enabling the development of novel x‐ray imaging and radiation delivery systems for basic cancer research and clinical application. In this presentation a brief overview of the CNT nanotechnology and its recent development in the application of micro‐CT imaging, micro‐RT, cellular and tissue level microbeam irradiation will be presented.

The CNT field emission technology based systems have clear potential advantages over conventional imaging and irradiation systems based on thermionic emission. Micro‐RT and micro‐CT systems that are based on thermionic emission technology commonly rely on a single radiation source and the imaging and irradiation depend on source rotation and thus can lead to poor temporal resolution for small animal research. The CNT field emission based systems employ individually addressable multipixel cathode array radiation sources and thus are capable of high temporal resolution, static (no rotation) imaging and electronically shaping a small radiation field and its intensity map. In clinical application, a CNT field emission based imaging and irradiation system can also improve treatment/imaging efficiency and improve patient throughput.

Learning Objectives:

1. Understand basic principle of carbon nanotube field emission technology and its potential in imaging and irradiation technology development for cancer research and clinical application

2. Understand current status of the CNT field emission based imaging and irradiation technology development

3. Understand the basic achievements and challenges in the technology development.

The research projects are supported grants from NIH R21 CA118351, U54‐CA119343‐01, R21CA128510, NC Biotechnology Center MRG‐1111, R33EB004204, and Xintek

Conflict of interest: Zhou is the Chairman of Xintek, Inc. and a board member of XinRay Systems, LLC
TU‐C‐BRB‐01: Junior Investigator Winner: Outcome Prediction of Cervical Cancer: Kinetic Model of Tumor Regression During Radiation Therapy
Authors: Huang Z , Mayr N , Yuh W , Lo S , Montebello J , Lu L , Li K , Zhang H , Gupta N , Wang J
Published: April 2010

Purpose: A kinetic model on describing tumor response to radiation therapy (RT) was developed to analyze the tumor regression data and predict the RT outcome for cervical cancer. Methods and Materials: Eighty patients of cervical cancer (stages IB2‐IVA) completed four sequential magnetic resonance imaging (MRI) scans before, during and after RT. The median follow‐up time is 5.5 years (range 0.2–9.4 years). A kinetic model incorporating three major effects: radiation cell killing, dead‐cell resolving, and tumor repopulation, was developed to fit the volumetric regression data measured by serial MRI scans. The derived radiobiological parameters were correlated with long‐term clinical outcome.

Results: The tumor regression kinetics was significantly different for the two outcome groups: local control vs. local failure. The tumor regression rate and model parameters correlated significantly with the treatment outcome (p<0.001), with a median 2‐Gy surviving fraction (S2) of 0.65 and a median half‐time of dead‐cell resolving (T1/2) of 7.9 days for locally controlled tumors, vs. S2=0.70 and T1/2=18 days for locally recurrent tumors. The 6‐year local tumor control rate was 87% vs. 54% for patients with S2<0.70 vs. ⩾0.70 (p=0.001), and 95% vs. 57% for patients with T1/2 <22 days vs. ⩾22 days (p<0.001), respectively. Similarly the 6‐year disease‐free survival was 73% vs. 41% for the patients with S2<0.70 vs. ⩾0.70 (p=0.025), and 87% vs. 52% for patients with T1/2<22 days vs. ⩾22 days (p=0.002), respectively. Conclusion: The kinetic model well fits the temporal change of 3D tumor volume measured by serial MRI. Our data demonstrated that the locally recurrent tumors were not only radioresistant, but also had slow dead‐cell resolving probably due to the poor tumor microcirculation. This approach shows promise for volume‐based tumor response modeling and potential to refine outcome prediction.
TU‐C‐BRB‐05: Proton Relative Biological Effectiveness (RBE) Determined Using Monte Carlo DNA Damage Simulations
Authors: Stewart RD
Published: April 2010

Purpose Determine tissue‐specific proton relative biological effectiveness (RBE) as a function of fraction size, dose‐rate and position within the spread out Bragg peak (SOBP). Methods A general formula derived from the linear‐quadratic (LQ) model is developed to determine a dose‐weighted RBE for mixed radiation fields, including position‐dependent mixtures of protons in the SOBP. Biologically motivated formulas with just two biological parameters (q and q/k) are used to link trends in a and a/b to double strand break (DSB) induction. DSB induction for protons is determined using the Monte Carlo Damage Simulation (MCDS). Because q and q/k are independent or a weak function of radiation quality, cell‐ and tissue‐specific estimates of a and a/b for a reference radiation (e.g., x‐rays or 6 MV photons) can be used to determine cell and tissue‐specific radiosensitivity parameters for protons. Results For constant fraction size, proton RBE increases as a/b decreases. The approach predicts that the RBE for cell survival is always greater than or equal to the RBE for DSB induction. For very low energy protons (0.1 MeV), the proton RBE ranges from 3.2 for DSB induction to 12.3 for cell survival (a/b = 1.5 Gy). Near the proximal edge of the SOBP, the predicted RBE is close to unity. In the center of the SOBP, the dose‐weighted RBE ranges from about 1.13 (a/b = 10 Gy) to 1.15 (a/b = 1.5 Gy). The estimated RBE 5 mm from the Bragg peak ranges from 1.5 (a/b = 10 Gy) to 1.9 (a/b = 1.5 Gy). Conclusion The biologically motivated approach provides a convenient and useful formalism to help incorporate tissue‐, fraction‐size and position‐dependent RBE information into proton therapy treatment planning.
TU‐C‐304A‐02: The Impact of the New ICRP‐103 Recommendations On the Assessment of Effective Doses From CT Procedures
Authors: Caracappa PF , Gu J , Zhang J , Xu X
Published: April 2010

Purpose: To apply a pair of adult phantoms representing ICRP‐89 50th‐percentile adult males and females to the study of impact of the new ICRP‐103 recommendations on the assessment of Effective Dose from CT procedures. Method and Materials: a pair of mesh‐based computational phantoms, RPI Adult Male (RPI‐AM) and RPI Adult Female (RPI‐AF) that were recently developed to represent the ICRP‐89 50th‐percentile adult males and adult females. This pair of phantoms has the detailed bone structures, including the spongiosa which contains the red bone marrow. The detailed RBM distribution was adjusted according to ICRP Publication 70. The CT scanner model used in this study is an MDCT scanner which includes the source geometry and movement, the source energy spectrum, the bow‐tie filter as well and the beam shape. CT scan protocols including whole body scan were carefully modeled in this study, and tube potential of 120 kVp were considered. All simulations were performed using the Monte Carlo code, MCNPX 2.5.0. The three‐correction factor method was used to calculate the RBM dose. Effective Dose results were calculated following the algorithm from ICRP 103. Results: A new set of organ absorbed dose results has been presented using this pair of new developed reference adult phantoms from CT procedures, as well as the effective dose results. Also the new results of red bone marrow dose have been provided. The recently published ICRP 103 updated the radio‐sensitive organ list; also it improved the algorithm of effective dose calculations. Conclusion: Advanced red bone marrow dose calculation method has been used in this study due to the detailed bone structures of this pair of RPI‐AM and RPI‐AF phantoms. This new set of effective dose dataset based on the new ICRP‐103 recommendations could be used to provide latest information for clinical diagnostic dosimetry area.
TU‐C‐304A‐10: Effects of KVp On Dose‐Normalized Contrast‐To‐Noise Ratio Relevant to Pediatric CT
Authors: Feng W , MacDougall R , Schultz C , Drake D , Bakalyar D
Published: April 2010

Purpose: The purpose of this research was to systematically explore the change in contrast‐noise ratio (CNR) for a variety of substances as a function of kV in CT examinations for small body habitus under the condition of constant dose. Method and Materials: The head module of a Gammex RMI 461A Head/Body phantom (constructed from solid water) was suspended from the end of the table of a Philips Brilliance 6‐slice CT scanner. An ion chamber introduced into the center of the phantom was used to adjust the mAs at kVp values of 90, 120 and 140 so that the exposure at the center was the same at all kVp values. Fifteen materials were tested at the center of the phantom for each of the kVp values with the CT number mean and standard deviation (SD) measured for each of the resulting 45 scans. A control area in the solid water was also tested for each scan using an identical ROI. Related tests were performed on all samples at once using other scanners.

Results: For all 45 scans, the SD was independent of kVp demonstrating that the noise was a function of dose only and not kV. For high density materials, lowering the kV improved the CNR in a predictable way. For materials with CT numbers not far from water, however, in some cases the CNR became worse with decreasing kVp while in others, the CNR improved. Conclusion: While lowering the kVp vs. lowering the mAs in small body habitus may result in an improved CNR, it should not be assumed that this is always the case. Dose reduction strategies for particular situations may benefit more by reducing the beam intensity and keeping the kV high.
TU‐C‐210A‐02: Recent Advances in Breast Tomosynthesis
Authors: Zhao W , Hu Y , Zhao B
Published: April 2010

This presentation in the symposium is focused on the recent advances in digital breast tomosynthesis (DBT). DBT is a three‐dimensional (3D) x‐ray breast imaging technique. Several projection images of the breast are obtained from different angles, and image reconstruction is used to generate cross‐sectional slices (with 1 mm thickness) that are parallel to the detector. Several DBT prototype systems have been developed by different manufacturers through modification of screening full‐field digital mammography (FFDM) systems. The x‐ray tube gantry typically rotates around the compressed breast with a limited angular range (15 to 60 degrees) and acquires a limited number of images (11 to 49). In this presentation, an overview of the following aspects of DBT will be provided: 1. Different approaches to system implementation of DBT, and their advantages and limitations; 2. Comparison of different image reconstruction methods, including filtered back projection (FBP) and iterative reconstruction; 3. Special considerations for DBT compared to conventional projection mammography: scattered radiation, x‐ray spectrum and detector performance; 4. Methods for the evaluation and optimization of DBT image quality; 5. Clinical results of breast cancer detection using DBT and its comparison with projection mammography; 6. Combination of DBT with other 3D imaging methods for multi‐modality breast imaging applications.
TU‐E‐304A‐01: Hybrid Patient‐Dependent Phantoms Covering Statistical Distributions of Body Morphometry in the U.S. Adult Population: Development and Validation
Authors: Johnson P , Juneja B , Lee C , Bolch W
Published: April 2010

Purpose: To investigate the usefulness of patient‐dependent phantoms for medical patient dosimetry. Method and Materials: In order to create patient‐dependent phantoms built around the anthropometric distributions of a US adult population, a methodology was developed for modifying hybrid reference phantoms based on target anthropometric parameters as determined from the NHANES III database. This database compiled by the U.S. Center for Health Statistics includes roughly 15,000 adult patients and a variety of primary and secondary anthropometric measurements. Primary parameters including standing height and total body mass were parameterized according to 10th, 25th, 50th, 75th, and 90th percentile values. The database was then culled according to these targets, and secondary parameters including waist, arm, thigh, and buttock circumference were selected based upon the average value within each sub‐grouping. The UF hybrid adult male (UFHADM) and adult female (UFHADF) were used as anchor phantoms for this study and remodeled non‐uniformly according to the target parameters. Fifty patient‐dependent phantoms were created and evaluated based on appearance and internal organ mass. Results: Aesthetically, the phantoms appeared correct and displayed characteristics of a diverse population including variability in shape and size. Organ masses displayed several general trends including a gradual increase with both standing height and weight. Organ mass was also validated by comparing with a series of segmented CAP scans and with a French‐based autopsy study. Conclusions: This work highlights the unique advantages of hybrid phantoms for the construction of diverse anthropomorphic models. These phantoms are of particular importance for medical patient dosimetry where there is a need for computational models that balance the practicality of reference models with the specificity and anatomical accuracy of patient‐specific models. As such, the UFHADM and UFHADF patient‐dependent series may be used for a wide variety of medical applications where body size may have a large influence on dose.
TU‐E‐304A‐02: Characterizing Metal Oxide Semiconductor Field Effect Transistor MOSFET) Radiation Detectors In a Scatter Medium Using CT Radiation Beam Delivery System
Authors: Bercha Ishtiaq H , Maghsoodpour A , Keyes G , Kaufman R
Published: April 2010

Purpose: To study MOSFET radiation response characteristics for CT organ dosimetry applications in a scatter medium (phantom), using multi slice CT as radiation source. Method & Materials: We used five Thomsen‐Nielsen MOSFETs with reader and wireless communication system to a laptop computer, GE Light Speed VCT‐64 scanner, Radcal 9095 dosimeter with 0.6 cc ionization chamber and kVp sensor, 10 cm Acrylic phantom with Acrylic rods. Each MOSFET was placed separately at isocenter, inside the acrylic phantom for characterization. An exposure of approximately 1000 mR (1006.6 mR to 1011.8 mR) was delivered to each MOSFET. Exposures were determined using 0.6 cc ionization chamber placed inside the phantom, at isocenter with CT tube in rotate mode as well as parked at various angles. MOSFET energy dependence, linearity of response and sensitivity with CT X‐ray tube in rotate mode were studied. Angular dependency of MOSFETS response was studied with tube parked at various angles in 45 degree increments. Results: MOSFET response (in mV, averaged for 5 MOSFETS) changed by 14% when kilovoltage varied from 80 through 140 kVp. Linearity of response was very good for all the energies selected. Sensitivity was obtained in the range of 25.6 mV/R to 28.8 mV/R for all the MOSFETs studied. The averaged maximum variation of all MOSFETs as a function of tube angle was about 5% and no statistically significant angular dependence was observed. Conclusion: Calibrating MOSFETs inside scatter media with CT X‐ray tube in rotate mode is recommended for MOSFET use in organ dosimetry applications with multislice CT scanners.
TU‐E‐304A‐04: Methods of Assessing the Dose to the Red Bone Marrow for Diagnostic and Therapeutic Procedures
Authors: Caracappa PF , Gu J , Xu X
Published: April 2010

Purpose: To demonstrate a more accurate method of assessing whole body red bone marrow dose in clinical applications. Method and Materials: Assessment of methods of red bone marrow (RBM) dose calculations is performed using a model constructed from the CT data of the Visible Human Project (VHP) and the EGS4 Monte Carlo code. Calculation of local marrow dose is achieved using the CT Number Method, which describes the fraction of marrow in a given CT voxel. Calculation of whole‐body average RBM dose is performed using two methods: one that assumes an homogeneous mixture of red and yellow bone marrow (HM Method), and one that uses a cellularity‐factor weighted marrow mixture in each bone (CW Method). Distribution of RBM mass in the skeleton calculated using both methods are compared to the color photograph data of the VHP used to construct the VIP‐Man anatomical model. Red bone marrow doses are calculated for broad beam exposures over a large energy range, and for several clinical applications including various CT scan protocols and electron whole‐body irradiation treatments. Results: The average difference in red bone marrow mass in each bone segment compared to the quantity present in VIP‐Man is 45% smaller when calculated with the CW method than the HM method. For clinical CT protocols, the RBM dose shows significant differences, up to 33% for head scans and 25% for abdominal scans. For the electron whole‐body irradiation (WBI) treatments, the RBM dose differs by 39%. Conclusion: Two common methods for calculating whole body average red bone marrow dose have been compared to the observed distribution standard available in the Visible Human Project data. Significant differences in dose are observed between the two methods, suggesting the importance of using appropriate cellularity factors in calculating red bone marrow dose.
TU‐E‐304A‐07: Fast Kerma‐Based Patient Dose Calculations in Diagnostic Radiology Using EGSnrc
Authors: Wulff J , Schmidt R , Fiebich M , Zink K , Heverhagen JT
Published: April 2010

Purpose: Current studies aim at individual, Monte Carlo (MC) based estimation of dose to patients undergoing computed tomography (CT) examinations. The EGSnrc MC code is known to simulate radiation transport accurately and was extended for efficient calculations in x‐ray diagnostic procedures. Method and Materials: Based on the EGSnrc/egspp class‐library the user‐code CTDOSPP was developed, allowing for the rotation of sources in a step&shoot or spiral mode with arbitrary pitch along a CT‐based, voxelized patient geometry. Formfilter geometries are accounted for by weighting primary photons depending on their attenuation in the filter. Photon‐splitting and track‐length estimators (TLE) were implemented for calculation of kerma, usually adequate in energy range of diagnostic x‐rays. The TLE uses precalculated energy‐absorption coefficients and track‐lengths of photons within a voxel. CTDOSPP results were compared to kerma‐distributions in homogeneous phantoms of the standard DOSXYZnrc code for static kV‐fields. Efficiency of the implemented TLE for a complete CT‐simulation was calculated in realistic thorax geometries at various dose‐grid resolutions. Results: Calculated distributions agreed within statistical uncertainty of <1% for kerma‐calculations. DOSXYZnrc was about a factor 2 slower than CTDOSPP, both using photon‐splitting, presumably due to the improved implementation of geometry related functions in egspp. For patient geometries the kerma‐calculations employing the TLE were up to 170 times more efficient than full dose calculations without any variance reduction and including secondary electron transport. Compared to the splitting‐technique, the TLE was up to 14 times more efficient in calculating kerma, depending on the chosen resolution of the dose‐grid. For a complete thorax scan, dose to the lungs could be calculated within a sub‐percent statistical uncertainty in less than a minute on a standard desktop PC. Conclusion: CTDOSPP simulates typical CT‐ and other kV x‐ray procedures and resulting kerma‐distributions efficiently, thus allowing for individual dose estimation in diagnostic radiology in the future.
TU‐E‐210A‐04: Dual Energy CT Image Reconstruction Algorithms and Performance
Authors: O'Sullivan JA
Published: April 2010

Dual energy X‐ray computed tomography (CT) is becoming more important, in part due to the availability of multi‐row scanners that collect data using two source energy spectra. An X‐ray source emits a spectrum of energies for each setting of the source. The energy dependence of Beer's Law leads to the relationship between the overall attenuation function and the mean measured data; the statistics of the data given the mean data determine a more accurate model. In many approaches, linear approximations to these inherently nonlinear phenomena are used to derive algorithms.

The data can be used to form two attenuation images that can be interpreted as coefficients corresponding to component attenuation spectra; given additional constraints such as nonnegative attenuation and a sum of fractional contributions equal to one, a third attenuation image can be recovered. Component attenuation spectra may correspond to physical processes (photoelectric and Compton effects), to known materials (for example, fat and bone), or to spectra that nearly span the set of spectra (for example, computed using a singular value decomposition).

Three classes of dual‐energy algorithms are discussed: prereconstruction, postreconstruction, and statistical iterative reconstruction (SIR), the latter recovering multiple images simultaneously using all data. The tradeoffs in performance of these algorithms are discussed. Analytical techniques for bounding achievable performance based on data models may be used in system analysis and design. Performance in actual systems may vary somewhat from the analytical predictions, due to inevitable differences between the model used for computing reconstructions and the clinical devices. This discrepancy in actual and predicted performance can be quantified in many situations. The approaches described extend in a straightforward fashion to data acquisitions using three or more energy bands.

Learning Objectives:

1. Understand the assumptions underlying dual‐energy image reconstructions.

2. Understand the centrality of the nonlinear data model in dual‐energy CT.

3. Understand the different methods that may be used to compute the image reconstructions.

4. Understand the role of image performance prediction and limitations of performance prediction.
WE‐SAM‐BRB‐01: Image Processing in Radiation Therapy: A Play in Three Acts
Authors: Kessler M , Siewerdsen J , Sonke JJ
Published: April 2010

Acquisition, processing and analysis of medical image data are now fundamental parts of patient management in radiation therapy. Image data are used to aid diagnosis and staging, to guide treatment planning and delivery and to help monitor the patient during and after therapy. Most radiotherapy departments have dedicated CT scanners, some with 4D capabilities. Many departments also have or are contemplating dedicated MR and PET/CT scanners. More imaging devices are also appearing in the treatment room, with in‐room, on‐board and integrated imaging devices becoming commonplace. The availability of hybrid MR scanner/treatment units is not far off.

Naturally, each imaging modality provides both benefits and challenges towards supporting and improving the radiotherapy process. In order to leverage the information in the various imaging studies, effective processing tools are needed to extract useful information and to combine and present it in a way that promotes a clear and efficient workflow. There are several classes of these tools including image enhancement, visualization, segmentation, registration and quantification. These tools may be used individually or in combination at many points in the radiotherapy process with the overall goal to create a more complete and accurate model of the patient so that an effective course of therapy can be devised and carried out.

This course provides an overview of the different imaging modalities and procedures used in radiotherapy and highlights the benefits and challenges of each. A detailed description of the various image processing tools used to extract, combine and analyze the information from different imaging studies is also presented. Finally, the effective use of these tools at each step of the radiotherapy process is described and elucidated using numerous clinical examples.

Learning Objectives:

1. Act 1 Understand the benefits and challenges of the various imaging modalities used in radiation therapy.

2. Act 2 Understand the mechanics of the different classes of image processing tools using in radiotherapy.

3. Act 3 Understand how image processing tools are used to support and improve the radiotherapy process.
WE‐SAM‐304A‐01: PET/CT Technology Update, Quality Assurance and Applications
Authors: Mawlawi O
Published: April 2010

In the past few years, positron emission tomography/computed tomography (PET/CT) imaging has increasingly been used for the diagnosis, staging, and restaging of malignant diseases. The success of this emerging modality has primarily been due to its ability to combine the advantages of both PET and CT imaging while minimizing their separate weaknesses. One of the main advantages of PET/CT imaging is its ability to generate functional images depicting the biodistribution of radioactive compounds that are correlated with anatomical landmarks thereby increasing the physicians' confidence in image interpretation and improving patient management.

The aim of this lecture is to provide an overview of the basic physics principles of PET/CT imaging as well as the advantages and drawbacks of using CT for attenuation correction of PET data. In addition, the lecture will cover the latest in design specifics of commercially available PET/CT scanners from different manufacturers as well as review PET/CT quality control and assurance techniques.

Learning Objectives:

1. To learn the basic physics principles of PET/CT imaging

2. To understand the advantages and drawbacks of using CT for attenuation correction of PET images.

3. Become familiar with design specifics of commercially available PET/CT scanners.

4. Learn quality control and assurance techniques for PET/CT imaging
WE‐A‐BRD‐01: Locating and Targeting Moving Tumors with Radiation Beams
Authors: Keall P , Cho B , Dieterich S , Poulsen P , Ruan D , Sawant A , Suh Y
Published: April 2010

The current climate of rapid technological evolution is reflected in newer and better methods to modulate and direct radiation beams for cancer therapy. This Continuing Education lecture focuses on one aspect of this evolution, locating and targeting moving tumors. The two processes — locating and targeting tumors— are somewhat independent and in principle different implementations of these processes can be interchanged. Advanced localization and targeting methods have an impact on treatment planning, and also present new challenges for quality assurance (QA), that of verifying real‐time delivery. Some methods to locate and target moving tumors with radiation beams are currently FDA approved for clinical use — and this availability and implementation will increase with time. Extensions of current capabilities will be the integration of higher order dimensionality into the estimate of the patient pose and real‐time reoptimization and adaption of delivery to the dynamically changing anatomy of cancer patients.

Learning Objectives:

1. To describe the technology available to determine real‐time target position

2. To review the systems for real‐time target‐beam alignment

3. To discuss the practical considerations of real‐time target tracking systems

Research sponsored by Accuray, Calypso, Cyberheart, GE, NIH/NCI, Philips and Varian.
WE‐A‐210A‐01: Fluoroscopic Imaging Equipment: Guidelines for Detector Input Dose Settings and Image Optimization
Authors: Rauch P
Published: April 2010

Modern fluoroscopy imaging equipment is designed to simultaneously monitor x‐ray generator parameters, detector exposure rate, contrast‐to‐noise ratio, and x‐ray tube loading. Under programmed control, fluoroscopy systems automatically make adjustments to the parameters controlling x‐ray production, beam filtration, detector signal output, digital image processing, and image presentation. Any means intended to reduce patient dose should be implemented in a way that preserves image quality.

For the clinical medical physicist, optimization of fluoroscopic equipment performance begins with an understanding of the variable system parameters, and the identification of the trigger points for changes in these parameters. Secondly, an understanding of how system parameters affect each other, affect image quality, and affect patient dose can lead to better choices in how the system should be set up for specific applications.

A necessary requirement is an understanding of what detector input dose one should expect with an image intensifier fluoroscopy system, and how the detector dose should change when a flat panel detector is utilized. It is also necessary to understand how operational settings on the equipment can obviate superior detector performance as determined by detector type and metrics. This presentation will use imaging examples from installed systems to explore these issues. Also, a clear, concise guideline for determining the appropriate fluoroscopy detector input dose rate for both image intensifier and flat panel detectors will be presented.

Learning Objectives:

1. Provide an understanding of modern fluoroscopic imaging system component design and functionality

2. Determine the appropriate fluoroscopy detector input dose rate for image intensifier and flat panel detectors

3. Describe specific ways in which equipment settings can enhance or detract from optimum performance.
WE‐C‐BRB‐01: In Vivo Measurement of Proton Stopping Power Ratios in Patients Using Dual Energy Computed Tomography
Authors: Yang M , Virshup G , Clayton J , Zhu X , Mohan R , Dong L
Published: April 2010

Purpose: To introduce a new method based on dual‐energy CT (DECT) for determining patient‐specific proton stopping power ratios (SPRs) required for accurate computation of proton dose distributions. Accurate determination of SPRs requires atomic number information, which cannot be deduced from conventional CT scans. Method and Materials: We have developed a two‐parameter model to extract electron density ratios (EDRs) and effective atomic number (EANs) from two CT scans acquired at different energies. Based on an empirical relationship we discovered between the known SPRs and EANs of human biological tissues of standard density and elemental compositions published in ICRU 44 and ICRP 23, we can estimate the SPR of any human biological tissue from its EDR and EAN values obtained from DECT scans. To validate this approach and compare it to existing practice, we introduced variations to the density and compositions of standard biological tissues to simulate unknown biological tissues. SPRs thus estimated using the DECT method are compared with their theoretical SPRs calculated using the Bethe‐Bloch equation and a clinical procedure introduced by Schneider et al. at Paul Scherrer Institute (the PSI method). Results: The accuracy of SPRs of standard human biological tissues estimated using the DECT method are substantially improved compared to those estimated using the PSI method: the maximum absolute (MAX) error and the root‐mean‐square (RMS) error are reduced from 3.19% and 0.89% to 1.10% and 0.29%, respectively. The DECT method is even more effective in SPR calculation when small perturbations were introduced in the standard tissue density and compositions: the MAX and RMS errors were reduced from 8.70% and 3.31% to 1.65% and 0.53%, respectively. Conclusion: The DECT approach is an effective method for accurate determination of voxel‐by‐voxel effective atomic numbers and SPRs of biological tissues.

Conflict of Interest: Research sponsored, in part, by Varian Medical Systems, Inc.
WE‐C‐BRB‐02: A Support Vector Machine (SVM) Classifier Identifies From Prone CT Simulation the Optimal Set Up for Breast Radiotherapy
Authors: Zhao X , Chang J , Wong E , Wang Y , Lymberis S , Formenti S
Published: April 2010

Purpose: To determine optimal (prone vs. supine) treatment positions for breast radiotherapy by classifying geometric features extracted from prone CT scans. Method and Materials: CT scans from patients enrolled in NYU 05‐181 Protocol were studied to discern predicting factors for optimizing treatment positions for breast radiotherapy. Each of the 400 patients accrued for this protocol underwent CT simulation and planning in both supine and prone positions. The treatment set up was chosen based on maximum sparing of heart and lung. Since the results demonstrated that most patients were best treated prone, we studied whether a support vector machine (SVM) classifier could successfully predict optimal position based on a single prone CT scan and limit a second supine CT only to the minority of women best treated supine. To build this classifier, prone CT scans of NYU 05‐181 were de‐identified and exported in DICOM RT format. Three‐dimensional shape and distance features were computed from organs at risk and the planning target volume in the CT scans. We used a k‐fold cross validation procedure to test the performance of the SVM classifier. Results: Images of 36 patients (23 prone‐treated and 13 supine‐treated) were used. Preliminary results indicate that breast volume, heart and lung involvement in the treatment field are significant predicting factors. A weighting of 1:5 (prone‐treated: supine‐treated) was used when determining the soft margin hyper plane of the SVM classifier. The purpose is to increase the specificity [true‐supine/ (true‐supine+false‐prone)] of the classifier since patients classified as prone will not receive a validation supine CT scan. A sensitivity [true‐prone/(true‐prone+false‐supine)] of 87% and a specificity of 92% was achieved using 11 geometric features and the SVM classifier. Conclusion: Preliminary data support the use of a feature‐based classification to predict the optimal treatment position from prone CT scans.
WE‐C‐BRB‐07: Evaluating 4D Interplay Effects for Proton Scanning Beams in Lung Cancers
Authors: Li Y , Zhang X , Li X , Pan X , Mohan R
Published: April 2010

Purpose: The Intensity Modulated Proton Therapy, delivered with spot scanning, provides greater control over dose distributions than passive scattering proton therapy. However, interplay of spot scanning with respiratory organ motion may result in interplay effects in dose distributions. Such effects may cause some parts of the tumor to be under dosed and other parts to be overdosed. 4D dose averaged over 4DCT sets is the de facto standard to evaluate respiratory motion effects. Interplay effects may render this metric insufficient. The purposes of this work are to develop a dynamic 4D dose calculation algorithm incorporating interplay effects and evaluate the dosimetric consequences of such effect for lung IMPT plans. Methods: The complete flow of the scanning spot delivery process was simulated by coupling the information on proton cycles (acceleration, spills and pulses, switching of spots, etc.), beams, and energies, and respiratory cycles. At beginning of spot delivery of each beam or each fraction, the simulation started with a random respiratory phase. The dose contributed by each pulse was calculated on its corresponding phase in the 4DCTs and final dose was mapped to the reference CT phase using deformable image registration. Dose distributions and the biological effects were compared among simulations with different numbers of fractions and pulses per spot. Results: The prescription dose coverage for PTV was 95%, 94.2 %, 93.9%, 91%, and 84% for the designed dose, 4D static dose, 4D dynamic doses delivered in 30, 6 and 1 fractions respectively. Tumor control probability (TCP) was 76% for 4D and 30‐fraction dose, compared to 72% for single fraction. Conclusion: The dose distributions converge to 4D dose only when the number of fractions or pulses per spot is large enough. A dynamic 4D simulation is necessary for evaluating the impact of organ motions in scanning beam proton plans.