bluuebunny/crossref_metadata_2025_split huggingface dataset:
TU‐A‐BRB‐11: 4D Optimization for Respiratory Phase‐Dependent IMRT Treatment Planning
Authors: Suh Y , Keall P 
Published: November 2011

Purpose: To develop 4D optimization for respiratory phase‐dependent IMRT treatment planning with dynamic MLC motion tracking, including MLC leaf motion constraints, which takes respiration‐induced anatomic motion into account and is robust to the variations of fractional time spent in respiratory phases within a 4D CT planning scan. Method and Materials: A tool for 4D treatment‐planning optimization that integrates a commercially available treatment‐planning system and a general‐purpose optimization system was developed and applied to the 4D CT planning scans of two lung cancer patients. The optimization variables were MLC leaf positions as a function of monitor units and respiratory phase. The objective function was the deformable dose‐summed 4D treatment plan score. MLC leaf motion was constrained by the maximum leaf velocity between control points in terms of monitor units and between phases and between leaves for tumor motion parallel and perpendicular to the leaf travel direction, respectively, in terms of phases. Without loss of generality, due to the computational burden, 4D optimization was performed with two phases, end inhale and exhale. For comparison and a starting point for the 4D optimization, 3D optimization was performed on each of the phases. Results: 4D treatment plan score improved during 4D optimization by 34% for Patient 1 and 50% for Patient 2, indicating 4D optimization generated a better 4D plan than the sum of individually optimized phase plans. The DVHs for each phase remained similar, indicating robustness of the 4D plan to respiratory variations expected during treatment delivery. Conclusions: 4D optimization for respiratory phase‐dependent treatment planning with dynamic MLC motion tracking improved the 4D plan score by 42% on average compared with 3D optimization. 4D treatment plans generated changed from phase to phase to account for anatomic motion, but showed similar dose distributions in each phase.Research supported by NIH/NCI R01‐93626 and Philips Healthcare.
TU‐C‐211‐05: A New Solid State X‐Ray Image Intensifier (SSXII) with a 1×2 Modular Array and an Acquisition, Correction, and Display System
Authors: Huang Y , Qu B , Panse A , Wang W , Bednarek D , Titus A , Cartwright A , Rudin S 
Published: November 2011

Purpose: To provide an extended field‐of‐view (FOV) with higher resolution images, a new SSXII imager with a two‐detector modular array was built. An acquisition, correction, and display system tiles two image modules in real‐time with geometric and brightness matching at the boundary. Methods: Two fiber‐optic tapers (FOTs) were fitted together with minimum dead‐space and embedded in liquid Sylgard 184 silicone elastomer which is allowed to cure and solidify; this 1×2 FOT array was fitted into an optical “head‐box.” The EMCCD sensors were fixed to the small‐ends of the two FOTs while a single CsI x‐ray phosphor plate was fastened onto the large‐ends. The optical head‐box was then combined with custom‐built electronics boards that control the driving clocks and sample the output. The digitized frames were transmitted to a PC through a CameraLink port accommodating a rate of 30 fps for both modules simultaneously. Customized software enabled acquisition, correction (dealing with the rotational and translational misalignments between the sensors), and display of the x‐ray images in real‐time. Other functions including acquisition control, save options, temporal filters, flat‐field correction, and mode selection for fluoroscopy, roadmapping, digital angiography (DA) and digital subtraction angiography (DSA), were also implemented. Results: The processed high‐resolution image was aligned properly along the boundary. The match up error was less than 1 pixel although there was a coupling loss of just under 7% due to chamfers at the edges of the FOTs; remachining the FOTs in future versions will reduce this loss. The two aligned images from each module exhibited balanced brightness between the sensors and flat‐field correction to eliminate fixed patterns introduced by the FOTs. Conclusions: The custom‐built SSXII detector and its acquisition, correction, and display system provides higher spatial resolution and nearly seamless images for the array in real‐time. Larger arrays are planned for future SSXII implementations.Support: NIH Grants R01‐EB008425, R01‐EB002873
TU‐C‐211‐06: Practical Operational Considerations for Clinical Usage of the Micro‐ Angio Fluoroscope (MAF) in Neuro‐Vascular Interventions
Authors: Ionita C , Wang W , Jain A , Siddiqui A , Levy E , Hopkins N , Bednarek D , Rudin S 
Published: November 2011

Purpose: To demonstrate a C‐arm mounted, high‐resolution, microangiographic‐fluoroscope (MAF) during neuro‐vascular clinical interventions (NVCI) with increased x‐ray tube output while still using the small focal spot. Method and Materials: The MAF consisting of a 300 &#956;m CsI input phosphor coupled to a micro‐channel‐plate light image‐ intensifier, in turn coupled to a CCD sensor through a minifying fiber‐optic taper was mounted on a clinical C‐arm. To take advantage of the MAFˈs high resolution, the small focal spot must be used. In general NVCIs require x‐ray tubes to use near maximum available mAs during fluoroscopy and angiography even with a larger focal spot. To tackle the problem we implemented a variable temporal filter (TF) and modified imaging protocols to enable use of the small focal spot. For DSA we increased the frame rate to 15 fps with the maximum mAs available and implemented a 3‐frame TF. For short but critical fluoroscopy durations where high resolution was essential for guiding a NVCI such as stent deployment, we used the small focal spot with a low exposure angiography protocol at (2– 4)X fluoroscopy settings which we refer to as High Definition (HD) mode. Results: The variable temporal filtering was used successfully during fluoroscopy to compensate for mAs limitations. Depending on patient motion we used TF weights between 3 and 7. Temporally‐filtered, high‐speed angiograms allowed visualization of fine vasculature details better than the standard imager. HD mode was used during stent deployments allowing visualization of detailed stent structure which normally is not visible using standard x‐ray imagers. Conclusions: X‐ray output limitations during NVCI were overcome by a combination TF and x‐ray protocol modification to meet the MAF high‐resolution requirements. The imaging improvements were significant with patients benefiting from more accurate treatments or in one case the elimination of an additional costly procedure.NIH Grants R01‐EB008425, R01‐EB002873.
TU‐C‐220‐04: Photoacoustic Scanning Tomography (PHAST) with Coded Optical Excitation: Theory and Experiment
Authors: Telenkov S , Mandelis A 
Published: November 2011

Photoacoustic (PA) imaging of biological tissues is emerging as a novel diagnostic modality that relies on noninvasive detection of tissue optical contrast, which may be related to specific diseases. Generation of acoustic waves in response to intensity‐modulated laser irradiation of targeted tissues constitutes the basic principle of photoacoustic imaging. A number of clinically important applications are concerned with the maximum imaging depth and image contrast that can be achieved using the PA method. In the present talk, various modes of laser‐induced acoustic wave generation are reviewed with particular attention given to coded optical excitation and frequency‐domain signal processing methods. Advantages of specific forms of optical modulation with emphasis on the signal‐to‐noise ratio, imaging contrast, and maximum imaging depth will be analyzed theoretically and compared with experimental data. The dual‐mode (time and frequency domain) photoacoustic scanner utilizing a multi‐element transducer array will be presented with results obtained using tissue‐simulating phantoms and an ex‐vivo animal model.Learning objectives:1. Understand the principles of photoacoustic imaging with coded optical excitation of tissue chromophores.2. Learn about instrumentation, signal processing and image formation using the PA response to custom optical modulation waveforms.3. Understand issues related to PA system design and potential clinical applications.
TU‐E‐BRB‐05: Streamlining Monte Carlo Dose Calculations for Routing Clinical Use in Proton Therapy
Authors: Schümann J , Perl J , Shin J , Faddegon B , Paganetti H 
Published: November 2011

Purpose: To design and validate a tool for routine verifications of clinical treatment plans using Monte Carlo (MC) simulations.Methods: We focus on the clinical implementation for patient dose calculations using TOPAS (TOol for PArticle Simulation), a user‐friendly interface to the Geant4 MC toolkit. Gantry and patient positioning follow guidelines of the IEC and phase‐space output is compliant with the IAEA format. Different parameterization schemes for voxel navigation have been tested to improve computing speed. Patient geometry and alignment are controlled by text files. CT slice input is currently supported for DICOM and XiO data files. Delivered doses, particle fluxes, energy deposits and many other properties can be scored. This new tool is now available for routine proton treatment planning at MGH. In many instances MC studies are preferred over pencil‐beam algorithms. Results: We present results from a cohort of MGH patients. A reduction in CPU time of up to 30% in patient dose calculations has been achieved with a specialized voxel navigation for CT volumes with 30 million voxels. Clinically required accuracy has been reached and verified in a water phantom with uncertainties of +1/−1.5mm in range, 3mm in modulation width and 2% for the flatness of spread‐out Bragg‐peaks with a variance comparable to measurements. For patient dose calculations, up to 8% of the voxels in patients were found to have larger than 2% and 2mm difference when comparing MC and a pencil‐beam algorithm. Conclusions: Monte Carlo simulations are still an exception in treatment planning, requiring detailed work by medical physicists who are also MC software experts. TOPAS supports an easy‐to‐use interface to set up nozzle and patient simulations without programming knowledge. This study demonstrates routine patient simulations with the MC method and supports the value and feasibility of using MC simulation as a standard in proton treatment planning.The project described was supported by Award Number R01CA140735 (“PBeam: A Fast and Easy to Use Monte Carlo System for Proton Therapy”) from the National Cancer Institute.
TU‐E‐BRC‐02: A Novel Framework of Treating Moving Tumors Using Min‐IP Based PTV and Variable Respiratory‐Synchronized Dose Rates
Authors: Sheng K , Yang W , Read P , Larner J 
Published: November 2011

Purpose: To improve the robustness and duty cycle of treating a moving tumor, the minimum intensity projection (min‐IP) is used as the basis of planning target volume (PTV). Variable dose rates synchronized to the respiratory signal are adapted to overcome the dose heterogeneity resulted from the non‐uniform probability density function (PDF). Methods: 4DCT of a lung cancer patient with gross tumor volume of 43 cm3 is used to compute both maximum intensity projection (MIP) and min‐IP. Two RapidArc plans were generated based on MIP and min‐IP based PTVs. The tumor dose is the prescription dose in the case of MIP plan. For the min‐IP based plan, 3 PDFs, including a linear, a sinusoidal and an actual patient PDF were included in computing the tumor dose. In order to achieve prescription, which is 60 Gy to 95% of the tumor, the dose of the min‐IP plan is first renormalized. In the second method, variable dose rate synchronized to the respiratory signal is assumed. The dose rate is inversely proportional to the dwell time or PDF.Results: Compared with the plan based on MIP, significantly less lung volume is treated by the primary beam with the min‐IP plan, resulting in 62% lower mean lung dose without renormalization. However, with uniform renormalization, the change in mean lung dose is −33%, −8% and 3% respectively for the 3 different PDFs. More significant gains at 28.3% and 25.2% for the sinusoidal and actual patient PDFs in the mean lung dose were observed when variable dose rates were used. Conclusions: Instead of chasing the tumor using a moving aperture, we tested a novel approach to instead let the tumor pass through a smaller static aperture. Variable dose rates synchronized to the respiratory signal substantially improved lung sparing without compromising tumor dose.NIH 1R21CA144063
TU‐E‐BRC‐05: “Step and Shoot MRI:” a Simple Acquisition Method to Reduce Gradient Nonlinearity‐Induced Geometric Distortions for Radiation Treatment Planning
Authors: Paulson ES , Prost RW , Li XA 
Published: November 2011

Purpose: Magnetic Resonance Imaging (MRI) offers great promise in improving target delineation during radiation treatment planning. However, it is well known that MR images may be hampered by geometric distortion. One potentially large source of geometric distortion arises from gradient nonlinearities, which can result in anatomical compression along the superior‐inferior direction, anatomical dilation in the anterior‐posterior and right‐left directions, and aliasing (arising from spins at different spatial locations being mapped to the same frequency). The purpose of this study was to determine the effectiveness of moving table acquisitions in diminishing gradient nonlinearity‐induced geometric distortion. Methods: A custom 20×30×50 cm grid phantom was imaged on a Siemens 3T Verio scanner. Conventional 3D FLASH images were collected in the sagittal plane and reconstructed without and with vendor‐provided 2D and 3D distortion correction. The prescribed volume was then broken into four segments and, immediately prior to acquisition of each segment, the scanner table was moved such that the center of each segment aligned with the scanner isocenter. Following acquisition, images from each segment were combined into a single series. Results: Gradient nonlinearities produced geometric distortion in all three dimensions. The magnitude of the distortion exceeded 2 cm at the periphery of the field of view in the uncorrected images. Although the vendor‐provided 3D correction algorithm was effective at reducing distortion, residual distortion at the periphery of the field of view remained. The images acquired using the proposed step and shoot approach exhibited minimal distortion along the entire length of the field of view. Conclusions: The proposed step and shoot MRI approach is a simple and effective method to diminish gradient nonlinearity‐induced geometric distortion. By breaking up the imaging volume into smaller segments, images in each segment can be acquired in the region of highest gradient linearity.Research supported by Siemens Healthcare and the MCW Cancer Center Fotsch Foundation.
TU‐E‐BRC‐09: An Automated Scoring Method for Motion Artifacts in Cine Four‐Dimensional Computed Tomography Images
Authors: Cui G , Jew B , Hong J , Loo B , Maxim P 
Published: November 2011

Purpose: The aim of this work is to develop an automated method to objectively score the severity of image artifacts in four‐dimensional (4D) computed tomography (CT). Methods: We developed a metric based on the difference of the two‐dimensional normalized correlation coefficients (NCC) between the edge slices at couch transitions and the NCC between edge slices and their neighbors within their respective couch positions. We applied our method to the 4D‐CT images of ten patients that were initially retrospectively sorted using the breathing trace with miscalculated phase values, and then re‐sorted using the same breathing trace with recalculated phase values after manually correcting the peaks of inhalation. The metric was calculated for both sets of 4D‐CT images and a score was determined to assess the severity of the image artifacts in both sets. The accuracy of our method to identify the 4D‐CT image set with fewer or lesser artifacts was validated by two human observers who evaluated three coronal and two sagittal cross‐sections from the same locations in both image sets. The two sets were displayed side by side and each observer independently scrolled through ten respiratory phases of both sets simultaneously (blinded to the selection method of each set), and marked the image set that appeared to have fewer or lesser artifacts. Results: Our method determined that the 4D‐CT sets using the breathing trace with recalculated phase values after manually correcting the peaks of inhalation to result in images with fewer or lesser artifacts. This is in good agreement with the findings of both observers. The observers agreed forty times and disagreed one time among total fifty selections. Conclusions: In this study we have demonstrated proof of principle that our method is able to replicate the findings of two human observers in determining 4D‐CT images with fewer or lesser artifacts.The authors greatly acknowledge the support from Mr. and Mrs. T. Archer Morgan Fellowship in Radiation Oncology at Stanford University.
TU‐G‐214‐03: Functional Imaging for Radiotherapy Guidance and Treatment Monitoring
Authors: Das S 
Published: November 2011

Functional imaging in radiotherapy has great promise to guide radiation delivery as well as to monitor response to treatment. Normal tissues as well as tumor tissues may be imaged with functional imaging. This talk will discuss positron emission tomography (PET), single photon emission tomography (SPECT) and Magnetic Resonance Imaging (MRI) in the context of radiation therapy for thoracic and head‐and‐neck cancers. PET for hypoxia imaging presents an especially appealing way to guide dose painting, wherein doses to hypoxic regions may be increased with the aim of achieving local control. This talk will describe PET hypoxia imaging with F18‐FMISO and, importantly, a novel approach that uses kinetic analysis with serial Cu62‐ATSM/PTSM imaging to map the distribution of oxygen availability. Radiotherapy planning incorporating PET hypoxia imaging for tumor local control will be discussed, as well as normal tissue dose avoidance using SPECT perfusion imaging to reduce dose to functionally active healthy tissue. Other than radiotherapy guidance, functional imaging may also be used to monitor response to chemoradiotherapy. Functional images taken during the initial treatment period, if predictive of overall treatment response, allows modification of the treatment plan to improve efficacy. Specifically, this talk will discuss F18‐FDG PET, dynamic contrast enhanced (DCE) MRI and diffusion MRI to monitor treatment related changes. The intrinsic temporal variability of tumor glucose metabolism versus treatment‐induced changes from chemoradiation will be demonstrated. For reliable utilization of FDG PET imaging in early treatment response assessment, intrinsic variability must be less than treatment‐induced changes. The leakiness of both tumor and normal tissue blood vessels, as measured with the transfer coefficient obtained from DCE‐ MRI, may also be used as a measure of early treatment response. Decreased transfer coefficient values in the tumor may be positively interpreted as corresponding to normalization of vasculature. Conversely, increasing transfer coefficient values in normal tissues likely indicate undesirable damage to vasculature. Increase in the tumor apparent diffusion coefficient (diffusion MRI) signals an expansion in the extracellular space, possibly identifying responders. In summary, this talk will discuss functional imaging in the context of guiding radiotherapy planning as well as treatment monitoring.Learning objectives:1. Familiarization with the utilization of selected PET, SPECT and MRI techniques in radiotherapy.2. Functional imaging to guide radiotherapy planning.3. Treatment response monitoring with functional imaging.
TU‐G‐220‐01: Quantitative Elasticity Imaging with Acoustic Radiation Force Induced Shear Waves
Authors: Nightingale K , Palmeri M , Rouze N , Rosenzweig S , Wang M , Trahey G 
Published: November 2011

Purpose: Shear waves can be generated in soft tissues using impulsive acoustic radiation force (ARFI), and the resulting shear wave speeds (SWS) can be related to the shear moduli (G) by SWS = sqrt(G/rho). Time‐of‐flight (TOF) algorithms can be used to track shear wave positions through time to estimate SWS. The spatial resolution of these methods is inherently limited by the size of the regression kernel, and, improved spatial resolution comes at the cost of increased variance in the SWS estimate. Here existing methods are reviewed, and a novel SWS reconstruction method that employs a spatial homogeneity constraint (SHC method) to obtain improved spatial resolution in ARFI‐based SWS images is presented. Methods: The SHC SWS reconstruction method performs an iterative maximum a posteriori estimation that weights each TOF SWS estimate in the image based upon its similarity to surrounding pixels. Next, ARFI images of relative tissue stiffness are used to identify homogeneous regions for which TOF based SWS estimates are expected to be accurate and precise in matched datasets. These regions are then used to derive a nonlinear mapping between the quantitative SWS estimates, and the the higher spatial resolution ARFI image. Both FEM simulations and experiments were performed to compare the SHC and TOF methods. Results: The spatial resolution of SWS estimates was directly related to the reconstruction kernel size in TOF methods, and the precision increased with increasing kernel size. The spatial resolution of the combined SHC images was comparable to that in the ARFI images, and was significantly better than that in the TOF SWS images. Conclusions: ARF‐induced TOF based SWS estimation methods provide quantitative stiffness information with spatial resolution that is dictated by the ARF shear wavelength, and the reconstruction kernel size. Improved accuracy and precision is obtained with larger reconstruction kernels in homogeneous media. The SHC reconstruction method provides improved contrast over qualitative ARFI images, and improved spatial resolution over TOF based quantitative SWS images.Learning objectives:1. Define acoustic radiation force phenomenon2. Describe its use for elasticity imaging3. Explain tissue response4. Describe wave arrival time and shear wave speed estimation methods5. Provide examples of clinical use