bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐213A‐01: ACR Accreditation
Authors: MacFarlane Carolyn R
Published: April 2010

The American College of Radiology's (ACR) Nuclear Medicine and PET Accreditation Programs evaluate qualifications of personnel, equipment, image quality, and quality control measures. It is believed that these are primary factors that impact the quality of patient imaging. The ACR accreditation allows facilities to critique and improve their practices as part of their preparation for the accreditation evaluation process. The goals of the ACR Nuclear Medicine and PET Accreditation Programs are improvement in the quality of imaging, provision of educational information by raising awareness of imaging issues, and the recognition of imaging facilities which meet program objectives. This presentation will outline the program requirements, highlighting some of the common pitfalls that may cause deficiencies in both the clinical and phantom submissions.

This presentation will provide participants with:

1. General information describing the ACR Accreditation Programs

2. Information about the Diagnostic Modality Accreditation Programs

3. Specific information about the ACR Nuclear Medicine and PET Accreditation Program, to include the application process, clinical images submission and quality control requirements.
MO‐EE‐A2‐01: Nuclear Model Evaluation of Uncertainties in Therapeutic Absorbed Dose and Secondary Neutron Production in Proton Radiotherapy Using MCNPX
Authors: Harvey M , Taddei P , Mirkovic D , Newhauser W
Published: April 2010

Purpose: To evaluate differences in nuclear physics models of MCNPX for uncertainties in 1) the dosimetric characteristics of the therapeutic dose for SOBP and cross‐field profiles and 2) stray neutron fields produced in a proton therapy unit using the default Bertini model option as the baseline. Methods and Materials: The general purpose Monte Carlo N‐Particle eXtended (MCNPX) code was used to calculate the therapeutic absorbed dose and spectral neutron fluence with three nuclear model options: the Bertini Model, the Cascade Exciton Model (CEM), and the Liège Intra‐Nuclear Cascade Model (INCL4). Each model is included as a physics option in MCNPX. For initial beam energy of 160 MeV, dose calculations were carried out in a water phantom positioned 24 cm downstream of the nozzle exit while in‐air calculations of the neutron spectral fluence were tallied in spheres positioned at isocenter, 100 cm downstream of isocenter and at lateral distances of ± 100 cm off‐axis. Calculations of secondary neutrons produced external to the nozzle housing were evaluated among the models for several parameters including the ambient neutron dose equivalent per therapeutic absorbed dose. Results: Our results indicate that calculations of the therapeutic absorbed dose were in close agreement (⩽1% difference) for all nuclear model options. On the other hand, the differences in the neutron spectral fluence calculations typically varied by a factor of 2 or more among the models. Conclusions: We found that all three inelastic nuclear interaction models provided excellent agreement in the therapeutic dose distributions. However, we observed substantial differences in the neutron spectral fluence calculations that suggest further investigation may be desirable for estimating the out of field radiation exposure uncertainties among the models.
MO‐EE‐A2‐02: Monte Carlo Simulation and Development of a Multileaf Collimator for Proton Therapy
Authors: Ainsley C , Scheuermann R , Avery S , Dolney D , Maughan R , McDonough J
Published: April 2010

Purpose: To develop a multileaf collimator (MLC) for proton therapy. Method and Materials: We constructed a model of the IBA proton beam delivery nozzle at our facility with the Geant4 (v9.1) toolkit and, in partnership with Varian Medical Systems, employed it to optimize the shielding design for a multileaf collimator system. Simulation studies were carried out with the highest‐energy, maximally‐modulated spread‐out‐Bragg‐peak settings and for the largest possible field size in both double scattering and uniform scanning modes. This led us iteratively to a solution that maintained proton and neutron leakage doses at an acceptable level. Results: Our final design comprised 50 leaf pairs made from a tungsten‐based alloy. Each leaf is roughly 9 cm high and 11 cm long—enabling 1.5 cm of overtravel—and projects to approximately 0.5 cm at isocenter; one half‐height 450 μm side‐step and two one‐third‐height 300 μm end‐steps are built in. Maximum achievable field sizes are 16×16 cm2 and 18×25 cm2 respectively in double scattering and uniform scanning modes. Conclusion: A MLC system has been designed for use in double scattered and uniform scanned proton therapy without significantly changing the standard IBA nozzle design or the mechanical and electronic systems currently used by Varian photon MLCs. Our simulations predict that the system will provide shielding at least as good as that provided by a conventional brass aperture. A prototype has been manufactured and is presently being installed on the nozzle in one of our gantry rooms. We expect to make measurements of leakage, penumbra and activation in the coming weeks and to validate our Monte Carlo simulations. Disclaimer: This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐04‐2‐0022. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.
MO‐EE‐A3‐04: Motion Management for a Novel Ophthalmic Stereotactic Radiosurgical Device
Authors: Chell E , Arnoldussen M
Published: April 2010

Purpose: Teletherapy of an unconstrained eye poses risks because of the likelihood of substantial eye motion. A new 100kVp tabletop stereotactic radiosurgical unit has recently been developed to deliver highly‐collimated beams of x‐rays to the retina. Here we evaluate the efficacy of a hardware and software motion‐management solution designed for that system. Method and Materials: To minimize the effects of motion during therapy, an eye fixation device (the “I‐Guide”) was developed. It consists of a contact‐lens, a central post, and a fixed, horizontal stabilizer bar. The contact lens is held to the eye with suction and attached to the central post. The post is mounted to stabilizer bar via a ball‐joint. The I‐Guide steadies the eye and incorporates reflective fiducials that are used by an imaging system to monitor the position and gaze‐angle of the eye. During treatment, software continuously evaluates the deviation of the eye from nominal position. When necessary, the beam is automatically gated off by an algorithm that incorporates time as well as displacement, allowing brief excursions while still maintaining effective targeting. Results: The motion‐management system was evaluated in a clinical trial of 40 patients. With the I‐Guide in place, rapid eye motion was damped considerably. Because of the time component, the gating algorithm permitted brief, random excursions while stopping the beam when excess drift was apparent. With a 3‐second x‐ray source ramp‐up, this flexibility was important for efficient treatment flow. Although patients' heads were immobilized, head mobility was found to be the dominant source of motion. However, the automatic gating‐off of the beam followed by repositioning kept the average motion error under 0.4mm in all cases. Conclusion: The combination of I‐Guide fixation, fiducial tracking, and automated beam gating enables precise targeting and dose conformality for ophthalmic radiotherapy.

Research sponsored by Oraya Therapeutics
MO‐E‐213A‐03: The Cancer Biomedical Informatics Grid — A Tremendous Resource for Research and Clinical Care
Authors: Siegel E
Published: April 2010

The cancer Biomedical Imaging Workspace is a part of the National Cancer Institute's caBIG initiative which is an effort to utilize grid computing and well defined standards to create a semantic web for exchange of research and clinical information including proteomic, genomic, laboratory, clinical, and imaging data. The Imaging Workspace consists of experts from the diagnostic imaging and radiology oncology communities across the United States with a wide variety of different areas of expertise. The purpose of the workspace is to identify and address challenges in the exchange and cross‐correlation of images and related information including image visualization and processing and analysis algorithms for research and secondarily clinical applications. The current major projects of the workspace include an effort to create a standard for annotation and image markup (AIM), a set of tools to facilitate the creation of applications that utilize the DICOM working group 23 standard (application hosting), middleware to create software bridges between DICOM and grid computing protocols and an algorithm validation toolkit which represents a resource for validation of a wide variety of imaging algorithms. The NCI has also created a free and open source DICOM image archive designed as a research repository for clinical trials that can also be used for a variety of other purposes. The Vasari Project represents a project which integrates the imaging workspace tools and is designed to allow correlation of MRI studies in patients with brain tumors with genomic and clinical data in a demonstration project of the potential role of diagnostic imaging in personalized or stratified medicine.

Learning Objectives

1. Understand the goals and objectives of the NCI's caBIG imaging workspace

2. Be able to list the major projects of the imaging workspace

3. Describe how the Vasari project will integrate the workspace projects in an initiative to allow cross correlation of image data with associated genomic, laboratory, and clinical data
MO‐FF‐A3‐01: Advantages of Multi‐Shot, Variable‐Density Spiral, Diffusion‐Weighted MR Imaging for Radiation Treatment Planning
Authors: Paulson E , Prah D , Ahunbay E , Li X
Published: April 2010

Purpose: The prerequisite for intensity‐modulated radiation therapy (IMRT) is accurate target and critical structure definition. Diffusion‐weighted MRI provides information that may improve target delineation and, therefore, radiation treatment outcome. However, geometric distortion artifacts have hampered the use of diffusion‐weighted MRI in radiation treatment planning. We demonstrate here a multi‐shot (i.e. interleaved), variable‐density spiral method that not only diminishes geometric distortion artifacts, but also permits acquisition of higher resolution diffusion‐weighted images for use in radiation treatment planning. Method and Materials: A custom, multi‐shot, spin‐echo, variable‐density spiral sequence with bipolar diffusion gradients was implemented on a 3.0T GE scanner. High‐resolution, multi‐shot, diffusion‐weighted images were acquired on three healthy volunteers (FOV: 240mm2, matrix: 2562, interleaves: 32, TE: 50 msec, TR: 3000 msec, scan time: 3.2 minutes). To demonstrate the inherent self‐navigating capabilities of variable‐density spiral, diffusion‐weighted images were reconstructed without and with self‐navigated phase correction. For comparison to the current state‐of‐the‐art method, diffusion‐weighted images were also collected using a clinical, single‐shot, spin‐echo echo‐planar imaging (EPI) sequence with ramp sampling, partial k‐space, and parallel imaging (FOV: 240mm2, matrix: 1282, TE: 64.7 msec, SENSE, R=2, scan time: ∼1 minute). Results: The inherent self‐navigating capability of variable‐density spiral was effective at diminishing motion‐induced phase errors, encoded by the diffusion gradients, that varied from shot‐to‐shot. The multi‐shot diffusion‐weighted images exhibited good signal‐to‐noise ratio despite the 47% reduction in voxel volume compared to the diffusion‐weighted EPI images. Off‐resonance effects resulted in geometric distortions in ventral and rostral brain regions on diffusion‐weighted images collected with EPI, but did not compromise the geometric integrity of diffusion‐weighted images acquired with multi‐shot spiral. Conclusions: Multi‐shot, variable‐density spiral permits acquisition of high‐resolution, diffusion‐weighted images that do not suffer from geometric distortions that have previously prohibited their use in radiation treatment planning.
MO‐FF‐A4‐02: Effects of Added X‐Ray Beam Cu Filtration On Image Quality and Patient Dose in Digital Radiography
Authors: Christodoulou E , Goodsitt M , Bailey B , Young R
Published: April 2010

Purpose: To quantify effects of added x‐ray beam Cu filtration on image quality, skin entrance exposure, and effective dose in digital radiography. Method and Materials: A GE Definium 8000 DR unit, in AEC mode, was used with a 20 cm thick acrylic phantom to simulate an average adult abdomen. 0.0, 0.1, and 0.2‐mm of Cu filtration were added to the x‐ray beam. We used 75, 80, 85, 90, 95, 100, and 110kV. Image quality was compared using a contrast‐detail phantom (CDRAD). For each beam quality, we exposed the CDRAD phantom on top, below, and between two 10‐cm sections of the acrylic phantom, and at four different orientations relative to anode‐cathode axis. The results were averaged. Image processing parameters were the ones used clinically for an AP Abdomen exam. The images were analyzed using the CDRAD Analyzer software. Skin‐entrance exposures, based on AEC resultant mAs read‐out, were measured without backscatter, and effective doses for an average size adult phantom were calculated using the PCXMC software. Results: At 75–80kV addition of Cu filtration reduced image quality slightly (∼1–5%), skin‐entrance exposure by 38–52%, and effective dose by 12–21% relative to no additional Cu filtration. At 90–110kV image quality varied little (∼0–4%) with added Cu filtration, skin entrance exposure was reduced by 28–47%, and effective dose was reduced by up to 17%. Only at 85 kV image quality was reduced significantly (∼13–15%) with added Cu filtration. Skin‐entrance exposure was reduced by 35–48%, and effective dose was reduced by 8–17%. Conclusion: Although already a relatively low dose modality, DR may benefit from the use of additional x‐ray beam Cu filtration since, for most x‐ray beam qualities, image quality appears to change little, while patient doses are reduced more appreciably compared to using beams with no additional Cu filtration.
TU‐B‐210A‐01: Quality Assurance Testing of Gamma Camera and SPECT Systems
Authors: White S
Published: April 2010

Routine quality control, calibration and performance testing of gamma cameras are necessary in order to consistently acquire good quality images without artifacts. This lecture will briefly cover the basics of gamma camera image formation and performance characteristics. The lecture will primarily focus on quality assurance tests for gamma cameras, both routine quality control and annual physics surveys. Some of the performance tests proscribed by NEMA are difficult to perform in the field so the physicist needs to know which tests are critical and practical ways to perform them in the field.

It is becoming increasingly common for providers of nuclear medicine imaging services to seek accreditation, either from the American College of Radiology (ACR) or the Intersocietal Commission for Accreditation of Nuclear Medicine Laboratories (ICANL). The ACR defines a set of performance tests for the annual physics survey and these will be discussed as well as the tests required for submission for accreditation.

Common problems and image artifacts will be discussed as well as how to correct these problems. Calibration procedures such as center of rotation and uniformity calibration will be discussed.

Learning Objectives:

1. Learn the basics of gamma camera and SPECT performance measurements and quality assurance test procedures.

2. Become familiar with the annual physics survey performance tests defined by the ACR accreditation program.

3. Be able to identify and correct common problems and image artifacts in gamma camera and SPECT imaging.
TU‐C‐BRD‐04: Development and Application of a Pre‐Clinical Stereotactic Irradiator
Authors: Solberg T , Pidikiti R , Song K , Speiser M , Stojadinovic S , Saha D , Seliounine S
Published: April 2010

With the advent of advanced image‐guidance technologies, stereotactic body radiation therapy (SBRT), the application of an ablative dose of radiation given in one or few fractions and delivered with high accuracy, has emerged as a promising modality in the treatment of cancer. Despite this success, there is remains room in optimizing delivery and understanding response. In this regard, pre‐clinical studies can be very beneficial in systematically evaluating response and predicting and validating clinical protocols. We describe the development and application of a small animal irradiator, which provides high accuracy in target localization and radiation delivery in a manner that mimics clinical SBRT delivery. The essential characteristics of the irradiator include: a high dose rate (⩾ 10 Gy/min), allowing high dose delivery in a clinically‐relevant time frame; precise target localization (⩽ 1 mm) to optimize irradiation to a tumor with respect to normal tissue sparing; and small radiation fields (1 to 10 mm) needed to implement the technology in small animals. The irradiator is based on a commercial X‐ray device (XRAD 320, Precision X‐ray, Inc.). The system can be operated at low energies (20–30 kVp) for high contrast imaging (essential for precise localization), and at high energies (⩾ 250 kVp) for therapeutic delivery. Radiation beam parameters, including energy specification (characterized by the half‐value layer — HVL), depth dose characteristics, and off‐axis profiles, have been determined through direct measurement. We describe the application of the device in a number of subcutaneous tumor, orthotopic tumor, and normal tissue models developed at our institution. Finally, the development of a next‐generation irradiator is also discussed.
TU‐C‐BRD‐06: Preclinical Image Guided Microirradiators: Concepts, Design and Implementation
Authors: Izaguirre EW , Kassebaum BL , Birch J , Su I , Mutic S , Parikh P , Grigsby P , Low D
Published: April 2010

We will introduce small animal image guided microirradiators by reviewing the concepts and requirements for high resolution and high conformality irradiation of tumors implanted in small animal limbs (xenograft tumor models), animal organs and spontaneous tumor models. We will present two preclinical microirradiators developed by our group, a brachytherapy based microirradiator and an orthovoltage x‐ray source based microirradiator. The brachytherapy irradiator has been constructed around a commercial high‐dose rate (HDR) remote afterloader source in a teletherapy geometry. The system consists of a set of exchangeable tungsten collimators (from 2.5 to 5.5 mm diameter) mounted on an aluminum cylindrical support. An HDR catheter is then used to transport the source to the pre‐determined dwell position that centers the source at the collimator hole. With this microirradiator, the anatomical image is obtained using an external clinical CT operated at maximum resolution and coregistration is achieved using fiducial markers.

The x‐ray orthovoltage microirradiator has an onboard cone beam microCT subsystem for submillimeter low dose anatomical imaging. The microCT and the ontrovoltage x‐ray source are aligned using a common rotation axis in a tandem configuration. An axial motorized animal bed transfers the animal from the microCT subsystem to the microirradiation subsystem. The microCT subsystem was constructed using an 80 kVp micro‐focus x‐ray source with a 75 × 75 um2 focal spot and a flat panel amorphous silicon detector with 1024 × 1024 pixels. The orthovoltage irradiator subsystem was constructed using a 320 kVp x‐ray source with dual focus spots (0.4 × 0.4 mm2 at 800W and 1 × 1 mm2 at 1800 W). The orthovoltage beam is collimated using orthogonal jaws and exchangeable apertures. The treatment beam can be aimed at different latitudinal and longitudinal angles in steps of 2 arcmin. and translated at 100 μm steps (x, y and z). The beam cross sections can be modulated with submillimeter precision using steps of 50 μm. The system is designed to deliver a maximum dose rate of 40 Gy/ min.

These irradiators are operated under a common small animal irradiation facility that accepts campus wide preclinical projects. We will conclude our presentation by presenting examples of ongoing radiobiological projects that will allow us to illustrate the performance and operation of both irradiators.
TU‐C‐BRD‐07: Translational Research with Small Animal IGRT
Authors: Hope A , Lindsay P , Hill R , Jaffray D
Published: April 2010

Radiation therapy is a critical component in the management of cancer. However, our understanding of radiotherapy must continue to grow with improvements in conformality (e.g., IMRT) and as more targeted agents become available. Maximizing the therapeutic ratio will require a thorough understanding of biology of tumors and normal tissues. Small animal models of tumor response and normal tissue toxicity can provide unique insights into these issues, but have inherent limitations and challenges which must be overcome. As small animal image‐guided radiation therapy (IGRT) becomes feasible, one of the most important issues becomes “What questions do we want to ask?”. Pure radiotherapy questions such as dose, volume, and time/fractionation can be explored in appropriate small animal tumor models while monitoring normal tissue effects. When combined with the ever‐increasing number of targeted agents, small animal IGRT becomes a powerful pre‐clinical tool that may allow optimal selection of agents and improve the timing and sequencing of concurrent therapies. After strong models of tumor control and normal tissue response are established, exploration of response biomarkers including novel imaging modalities becomes feasible. The wide‐spread availability of small animal multi‐modality imaging including CT, MR, optical, and US combined with novel contrast agents makes this an especially rich area of exploration. Some examples of previous small animal radiotherapy experiments with a brain tumor model and ongoing exploration of normal tissues effects in lung will be reviewed and potential future studies attempting to link pre‐clinical and clinical data will be outlined.

Learning Objectives:

At the end of this lecture, the audience will be able to:

1. Describe some of the challenges of small animal models.

2. Discuss the range of biologic experiments which may be feasible.
TU‐C‐BRB‐06: Modeling Tumor‐Volume Variation During Fractionated Radiotherapy for Non‐Small Cell Lung Cancer
Authors: Chvetsov A , Dong L , Tucker S , Palta J , Mendenhall N
Published: April 2010

Purpose: To validate the four‐level population tumor model using tumor volumetric changes obtained using on‐board imaging techniques during fractionated radiotherapy for non‐small‐cell lung cancer. Method and Materials: The four‐level population tumor model is based on separation of tumor cell population into four subpopulations: 1) oxygenated viable cells, 2) oxygenated lethally damaged cells, 3) hypoxic viable cells, and 4) hypoxic lethally damaged cells. The oxygenated lethally damaged cells are removed from tumor using an exponential decay model. The hypoxic lethally damaged cells stay in tumor for unlimited time; therefore, their removal is governed by reoxygenation process. The model utilizes the following six radiobiological parameters: alpha, beta, potential doubling time Tpot, half‐life T1/2 of lethally damaged cells, initial hypoxic fraction R and reoxygenation rate A. To test the model, we use the clinical data on volumetric tumor changes during fractionated radiotherapy for non‐small‐cell lung cancer obtained using Tomotherapy and Cone‐Beam CT at different institutions. Results: Our preliminary data indicate that adenocarcinoma and squamous cell carcinoma demonstrate different rate of tumor volume variation after irradiation; therefore only cases have been selected where adenocarcinoma o squamous cell carcinoma diagnosis was available. Another problem of accurate tumor‐volume simulation for lung tumors is a significant hypoxic tumor fraction according to the experimental data obtained using fluoromisonidazole PET imaging. The hypoxic tumor fraction can be between 1.3% and 94.7.9% with a median value of 47.6%. Our model with average values of radiobiological parameters describes majority of lung squamous carcinoma cases. However, significant discrepancies have been observed between the model and clinical data for lung adenocarcinoma. Conclusions: The proposed radiobiological model with average values of parameters can be used for simulation of tumor‐volume for lung squamous cell carcinoma with acceptable accuracy. However, this approach does not describe the tumor volume variation for significant fraction of lung adenocarcinoma cases.
TU‐C‐BRB‐08: Validating Normal Tissue Complication Probability Models: A Study of Generalizability and Datapooling for Predictive Radiation Pneumonitis Modeling
Authors: Huang E , Bradley J , El Naqa I , Trovo M , Deasy J
Published: April 2010

Purpose: NTCP models usually do not undergo needed tests of external validation or generalizability for eventual clinical use. Here we test and generalize an NTCP model for predicting radiation pneumonitis (RP) using data‐pooling with institutional data and a multi‐institutional dataset (RTOG 93‐11 data). As accurate dosimetry is unavailable for the RTOG dataset, non‐heterogeneity corrected dose distributions were used throughout. Methods and Materials: Data consisted of 313 patients who received definitive conformal radiotherapy for non‐small‐cell lung cancer (209 from WUSTL, 104 from the RTOG 93‐11 trial). For each individual subset patient groups, heart and lung dosimetric variables (abstracted from corresponding treatment planning archives), existing clinical factors, and tumor/high‐dose positional parameters are included in multivariate logistic regression modeling to obtain the most predictive multi‐variable NTCP model. Cross‐validation and bootstrapping methods were used confirm internal model validity, model stability, and optimal model size. The derived best model for each dataset was tested against the other dataset. Finally, modeling over the combined multi‐instructional dataset (RTOG 93‐11 trial and WUSTL datasets) was conducted and the resulting model was tested against each individual subset of data. Results: Models derived on the separate datasets performed poorly on the other dataset. However, the best model derived on the full dataset included D10_heart, D10_lung, and center‐of‐GTV‐mass‐superior‐inferior. which performed well over each individual subset. Conclusion: These results demonstrate the unique role that full 3‐D data‐pooling can play: models can be derived that work across a wide spectrum of patient datasets, but the actual target populations should be included in the analysis.

Supported by NIH grant R01 CA85181.
TU‐C‐BRC‐02: Infrastructure to Integrate Imaging in Clinical Trials
Authors: Sullivan D
Published: April 2010

Imaging biomarkers are increasingly used as primary or secondary endpoints in therapeutic trials. There are many academic units, professional organizations, industry groups and federal agencies addressing one or more components or issues associated with imaging biomarkers, and communication and coordination of efforts has been minimal. The RSNA has organized an Imaging Biomarkers Roundtable to establish ongoing communication among these organizations, and to develop a roadmap of activities and goals.

Validation of imaging methods as biomarkers is complicated by the variability within and between patients, by the human observer component, by the variability across imaging devices from different manufacturers, and by the need to standardize methods across institutions and centers. To understand the errors and reduce them where possible, the Quantitative Imaging Biomarkers Alliance (QIBA) has been formed. These and other efforts are active and productive. Accomplishments and future plans will be discussed.

Learning Objectives:

1. Understand efforts to integrate imaging biomarkers in clinical trials.

2. Understand efforts to improve the accuracy and precision of imaging biomarkers.
TU‐C‐303A‐06: Quiet Respiration Breathing Motion Model Parameters for Free‐Breathing Patients
Authors: Zhao T , Lu W , Bradley J , Parikh P , Hubenschmidt J , Low D
Published: April 2010

Purpose: To determine the quiet respiration breathing motion model parameters for lung cancer and non‐lung cancer patients. Method and Materials: 49 free‐breathing patient 4DCT image data sets (25 scans, ciné mode) were collected with simultaneous quantitative spirometry. A cross‐correlation registration technique was employed to track the lung tissue motion between scans. The registration results were fed back to a lung‐motion model: , where x is the position of a piece of tissue located at reference position x0. α is a parameter which characterizes the motion due to local air filling (motion as a function of tidal volume) and β is the parameter that accounts for the motion due to the imbalance of dynamical stress distributions during inspiration and exhalation which cause lung motion hysteresis (motion as a function of airflow). The parameters α and β together provide a quantitative characterization of breathing motion that inherently includes the complex hysteresis interplay. The α and β distributions were examined for each patient to determine overall general patterns and intra‐patient pattern variations. Results: For 44 patients, the greatest value of |α| was observed in the inferior and posterior lungs. In three patients, |α| reached its maximum in the anterior lung, while for two patients; |α| was greatest in the lateral lung. The hysteresis motion β had greater variability, but for the majority of patients, |β| was largest in the lateral lungs. Conclusion: This is the first report of the 3‐dimensional breathing motion model parameter for a large cohort of patients. The overall α and β maps varied smoothly as expected. The majority of patients exhibited consistent α maps, and the β maps showed greater intra‐patient variability. The motion parameter intra‐patient variability will inform our need for custom radiation therapy motion models.

This work supported in part by NIHR01CA096679 and NIHR01CA116712
TU‐C‐303A‐09: Can Lung Dose‐Volume Criteria Derived From 3D Era Be Safely Used for 4D Planning?
Authors: Hu B , Kainz K , Rooney J , Li X
Published: April 2010

Purpose: Total lung volume (TLV) varies during respiration. The TLV dose‐volume criteria currently used for treatment planning of lung irradiation are derived based on 3DCT. We investigate the variations of TLV and lung dose during respiration and determine if the current TLV dose‐volume criteria can be safely used for planning respiratory‐correlated treatment. Methods and Materials: The data of 4DCT and 3DCT acquired with free breathing during the same session for nine patients were analyzed. Each 4DCT set consisted of 10 phases. TLVs delineated using an automatic tool on 3DCT, 4DCT individual phases, and the average intensity projection (Ave‐IP) were compared. For each patient, a representative plan designed based on the 3DCT was applied to each phase of the 4DCT and the Ave‐IP CT. The dose volume parameters of V20 (volume receiving 20 Gy), V10, V5, and mean lung dose (MLD) from the above 12 plans for each case were compared. Results: TVL varied by 20% during respiration as compared with the TLV from 3DCT or Ave‐IP. On average, the TLV at 30% (mid‐exhalation) or 70% (mid‐inhalation) phases agreed within 2% with the TLV from 3DCTs for the nine cases studied. The average TLV from the Ave‐IP CTs was consistent within 2% with the average TLV of 20% or 80% phase. For all cases studied, the average MLD, V20, and V10 varied by 2% while the average V5 varied by 3% during respiration. The maximum variation for these dose‐volume parameters was 7%. Conclusion: TLVs for 20%‐ or 30%‐ phase, Ave‐IP, and 3DCT are comparable, and the 20%–30% phase CT may be used as the base CT for non‐gated ITV‐based treatment planning. For treatment planning of a gated delivery at maximum exhalation or inhalation, a margin of 3% should be considered when using the current lung dose‐volume criteria.
TU‐C‐304A‐06: Reducing Dose to a Small Organ by Varying the Tube Start Angle in a Helical CT Scan
Authors: Zhang D , DeMarco J , Cagnon C , Angel E , Turner A , Zankl M , McNitt‐Gray M
Published: April 2010

Purpose: Previous work demonstrated that there are significant dose variations on the peripheral, or surface of either a CTDI 32cm phantom or an anthropomorphic phantom when helical CT scanning is performed. The purpose of this work is to investigate the effectiveness of exploiting these variations to reduce dose to targeted radiosensitive organs solely by varying the tube start angle in CT scans. Method and Materials: Radiation dose to several radiosensitive organs (including breasts, thyroid, uterus, gonads, lens of eyes) from a MDCT CT scanner were estimated using Monte Carlo simulation methods on GSF Baby phantom. Whole body scans were simulated using 120kVp, 300mAs, 28.8 mm nominal collimation, pitch 1.5 under a wide range of start angles (0 to 340 degrees in 20 degree increments). The relationship between tube start angle and organ dose was examined for each organ and the potential dose reduction was calculated. Results: The organ dose shows obvious variation depending on the tube start angle. For small peripheral organs, (e.g. the lens of eyes), the minimum dose can be 35% lower than the maximum dose, depending on tube start angle. For pitch 1.5 scans, the dose is usually lowest when the tube start angle is such that the x‐ray tube is posterior to the patient when it passes the longitudinal location of the organ. Conclusion: Helical MDCT scanning results in “cold spots” and “hot spots” that are created both at surface and even in‐depth locations within patients. If organs have a relatively small longitudinal extent, their dose may be reduced by selecting the tube start angle such that the location of these “cold spots” may be manipulated by appropriately selecting the tube start angle. This dose reduction should not have any implications for image quality as there is no change in mAs or total mAs.
TU‐C‐304A‐09: Radiation Dose Reduction for Pediatric CT
Authors: Massoumzadeh P , Don S , Whiting B
Published: April 2010

Purpose: The purpose of this study was to evaluate potential radiation dose reduction for pediatric CT. Materials and Methods: A dose‐reduction simulation tool, which adds synthetic noise to raw projection measurements and reconstructs images at a simulated lower dose (Massoumzadeh, et al. Med. Phys. Vol. 36, pp. 174–189, 2009), was used to simulate low‐dose CT images. Simulated low‐dose CT images are created from full‐dose CT images of normal and pathological slices (lung nodules and abdominal visceral lesions). The amount of added noise was task dependent, with 10 sets of simulated low dose ranged from 1% to 85% of original dose. Sixteen pediatric cases were selected, including eight normal, three patients with pulmonary nodules, two patients with abdominal visceral organ lesions, and three patients with appendicitis without perforation. All studies performed on a 16‐row scanner, with the effects of tube current modulation and bow tie filters included. Following a short training session, 19 volunteer radiologists, from various clinical centers in the world who were attending the International Pediatric Radiology conference in Montreal in 2006, used a 5‐point scale to rate a sequence of simulated, low‐to‐high exposure images for the presence or absence of lesions. They were total of 176 images with viewing sessions limited to 45 minutes. Diagnostic agreement between full‐dose and reduced‐dose images was assessed with a weighted Kappa statistic. Result: For detection of pulmonary nodules, a decrease in the average intra‐observer agreement (kappa= 0.90) was found at 80% dose reduction, while for the detection of abdominal lesions or appendicitis a 50% reduction was observed. Conclusion: There is potential for dose reduction in CT studies, which is task dependent and greater for pulmonary nodule than for abdominal visceral lesions and appendicitis. The noise simulation methodology is a powerful tool to help understand the relationship among dose, noise, and observer agreement.
TU‐E‐BRC‐05: First MR Images Obtained During Megavoltage Photon Irradiation From An Integrated Linac‐MR System
Authors: Fallone B , Murray B , Rathee S , Stanescu T , Steciw S , Vidakovic S , Blosser E , Tymofichuk D
Published: April 2010

Purpose: To prove whether our hybrid linac‐MR design can sufficiently decrease mutual magnetic and radio frequency (RF) interferences to produce a MR image during linac‐irradiation that has similar geometric accuracy and image contrast to an MR image obtained without linac‐irradiation. Method and Materials: A hybrid prototype has been built consisting of a 6 MV linac mounted on the open end of a bi‐planar 0.2 T permanent‐magnet MR system. Both the linac waveguide and the MR system are mounted onto a single gantry that would rotate around a subject. The permanent magnet poles (82×82 cm2) are rigidly held apart to give 27.9cm pole‐to‐pole opening with flat gradients (40 mT/m max) running under a TMX NRC console (Canada). The linac components are comprised of salvaged magnetron‐based Varian 6 MV 600C decommissioned system. The distance from linac target to MR isocentre is 80 cm. Magnetic and RF shielding calculations were performed by finite element analysis and confirmed with appropriate measurements. Faraday cage shielding, typical of all MR installations, was also provided. The testing phantom was an acrylic rectangular cube, 15.95 × 15.95 × 25.4 mm with holes of diameters 2.52 mm, 3.45 mm and 4.78 mm drilled parallel to the length (25.4 mm) of rectangular cube. The cube was immersed in a 10 mM solution of within a plastic container 22.5 mm inner diameter. The container with the cube insert were placed inside an inductively tuned solenoid RF coil with an integrated pin‐diode transmit/receive switch. Results: Images (128×128) were obtained in about 38 secs using raw gradient echo sequences. Compared to no‐radiation, MR images during linac‐radiation had no geometric distortion but slightly reduced SNR. Conclusion: Our linac‐MR design produces MR images obtained during or without linac irradiation that are sufficiently similar to implement real‐time MR‐guided radiotherapy.
TU‐E‐BRC‐06: On the Synchronization of 3D Surface Cameras with Fluoroscopic Imaging
Authors: Glide‐Hurst C , Yan D
Published: April 2010

Purpose: To investigate the feasibility of using three‐dimensional surface imaging cameras as an external surrogate of target motion through a temporal synchronization with kV imaging. Method and Materials: A gate controller, connected between kV fluoroscopy and AlignRT (Vision RT Ltd, London) computers, was triggered with kV beam‐on and reflected in AlignRT output data. First, phantom experiments were performed using a programmable respiratory motion platform (sinusoidal curves, 12–18 BPM). The platform included a chest‐wall component (A‐P amplitude = 1 cm) tracked with the surface camera, while the object translated superior‐inferior was fluoroscopically tracked (300 frames, frequency ∼5.5 fps). Accuracy of tracking the chest‐wall platform was assessed. Increasing the complexity of experiments, tumor displacement curves from three patients were simulated. Our approach was further validated by imaging a free‐breathing lung cancer patient over 11 fractions with simultaneous AlignRT and kV (300 frames/session, ∼55 seconds). Results: For simple sinusoidal curves, measured amplitude (peak‐to‐peak) was 1.005 ± 0.003, 1.013 ± 0.003 cm, 1.003 ± 0.005 cm for 12, 15, and 18 BPM, respectively, demonstrating excellent agreement with the expected chest platform amplitude of 1.0 cm. Period measurements were within 0.2% of expected for the surface cameras, and within 0.9 % of expected for fluoroscopy. Using simulated patient data and the motion platform, the latency between the surface tracking system and fluoroscopy was determined by performing linear regression between the peak time from AlignRT and fluoroscopy. For the three patient cases studied, latency was found to be 0.65 ± 0.03 seconds. Moderate agreement was observed between the diaphragm, tumor, and abdomen tracked for the patient studied. Conclusion: The utility of surface imaging cameras for tracking while synchronized with fluoroscopy has been demonstrated. Additional patient studies are warranted for further validation, which may facilitate gated radiation therapy treatments using surface imaging cameras as the external surrogate.
TU‐E‐BRC‐07: A New Reconstruction Algorithm for Improved Cone‐Beam CT Image Quality
Authors: Li T , Li X , Yang Y , Heron D , Huq M
Published: April 2010

Purposes: Scatter and noise are well‐known factors that degrade the cone‐beam CT (CBCT) image quality. In addition to these factors, the fundamental reconstruction process adopted by most commercial systems is also imperfect. The reconstructions are mostly based on the Feldkamp formula. Such algorithm gives the accurate solution for the central slice but approximations for the remaining slices. The error increases when the slices are further away from the center due to “incompleteness” of the projection data. To combat this problem, we developed in this work a new reconstruction algorithm, which improved the CBCT image quality significantly. Methods and Materials: The reconstruction algorithm integrated the Feldkamp formula into an iterative optimization process. For validation, a three‐dimensional (3D) digital thoracic phantom was constructed based on a patient CT image and used to simulate CBCT projections. Noise and scatter were excluded from the simulation in order to isolate the basic theoretical issues in reconstruction. The projections were reconstructed with the Feldkamp algorithm, Simultaneous Algebraic Reconstruction Technique (SART), and our proposed “FDK‐ART” algorithm, respectively. The images were then systematically evaluated. Results: Artifacts became apparent for outer slices when Feldkamp algorithm was used. These artifacts were significantly reduced with the proposed algorithm. Although Feldkamp gives an accurate solution for the central slice, the root mean square error was shown to be reduced greatly by the proposed algorithm. By visual and profile comparison, it was found that the image resolution using our new method was clearly superior to that obtained with traditional Feldkamp algorithm or SART algorithm. The algorithm converged within 5 iterations for all sample cases tested. Conclusions: A new reconstruction algorithm has been developed for CBCT imaging. The new algorithm not only reduced the errors for outer slices, but also significantly improved the image resolution and the overall quantitative accuracy for every slice.
TU‐E‐213A‐02: Implementing New Technologies for Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy
Authors: Solberg T
Published: April 2010

Stereotactic radiosurgery has become the standard of care in the treatment of many cranial neoplasms. This success has stimulated significant interest in the application of such an approach for the treatment of extracranial tumors. The development of image guidance techniques has rapidly facilitated adoption of Stereotactic Body Radiation therapy (SBRT) in a number of anatomical sites. Both SRS and SRT pose a number of practical challenges in acceptance testing, commissioning and clinical implementation. These include: uncertainties in small field measurement and dose calculation, appropriate use of phantoms for verifying image fusion and assuring end‐to‐end localization accuracy, implementing effective immobilization techniques, understanding and adapting for intrafraction motion, planning and delivery for fixed beam and rotational irradiation, and maintaining appropriate QA procedures. In this presentation we will review these challenges with respect to linac‐based SRS and SBRT.
WE‐B‐211A‐02: Development of Therapy Response Models Based Upon Functional MRI
Authors: Cao Y
Published: April 2010

The potential clinical value of in vivo functional and physiological MR imaging for assessment of therapeutic response has been explored in recent years. Such imaging may provide early prediction for treatment outcomes including local tumor control as well as normal tissue complications with greater predictive power compared to conventional clinical assessment methods and related anatomic imaging. The advantage of early assessment is to allow for re‐optimizing individual patients' treatment plans, including decisions of total dose, modifying risks of critical normal tissue, and optimizing use of concomitant therapies. A response model, e.g., predicting tumor or normal tissue response to doses based upon functional imaging biomarkers, can aid in clinical decision‐making. The volumetric data presented in both image‐derived metrics as well as local dose appear to provide a significant wealth of information. Care must be taken, however, to understand the limits of input data from which the model is developed.

This lecture will provide an overview on how to use functional imaging to develop a response model for individualized therapy. The limitations of these techniques will also be discussed.

Learning Objectives:

1. Understand functional imaging as a biomarker for therapy response;

2. Understand influence of imaging parameters and image quality on quantitative metrics and uncertainty in the response model.

3. Understand clinical applications and limitations.
WE‐B‐BRC‐01: Dosimetry Metrology for IMRT
Authors: Stern R , Moran J
Published: April 2010

This session will present dosimetry tools and techniques for intensity modulated radiation therapy based on the AAPM Task Group 120 report. First, advantages and disadvantages of different detectors including ion chambers and 2D dosimetry systems will be discussed in the context of IMRT distributions. Second, considerations with respect to phantoms will be discussed. Next, the application of different dosimetric analysis tools will be presented. The final topic is the next generation of detectors for QA such as polymer gels.

The educational objectives of this session are to provide information to:

1. Determine the best detector for a given measurement scenario

2. Assess the impact of phantom selection on the measurement

3. Understand the benefits and limitations of different analysis tools for evaluating calculations and measurements of IMRT fields

4. Learn about new dosimetry systems for IMRT measurements