bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐A‐19A‐12: A GPU‐Accelerated and Monte Carlo‐Based Intensity Modulated Proton Therapy Optimization System
Authors: Ma J , Wan Chan Tseung H , Beltran C 
Published: July 2014

Purpose:To develop a clinically applicable intensity modulated proton therapy (IMPT) optimization system that utilizes more accurate Monte Carlo (MC) dose calculation, rather than analytical dose calculation.Methods:A very fast in‐house graphics processing unit (GPU) based MC dose calculation engine was employed to generate the dose influence map for each proton spot. With the MC generated influence map, a modified gradient based optimization method was used to achieve the desired dose volume histograms (DVH). The intrinsic CT image resolution was adopted for voxelization in simulation and optimization to preserve the spatial resolution. The optimizations were computed on a multi‐GPU framework to mitigate the memory limitation issues for the large dose influence maps thatResult from maintaining the intrinsic CT resolution and large number of proton spots. The dose effects were studied particularly in cases with heterogeneous materials in comparison with the commercial treatment planning system (TPS). Results:For a relatively large and complex three‐field bi‐lateral head and neck case (i.e. >100K spots with a target volume of ∼1000 cc and multiple surrounding critical structures), the optimization together with the initial MC dose influence map calculation can be done in a clinically viable time frame (i.e. less than 15 minutes) on a GPU cluster consisting of 24 Nvidia GeForce GTX Titan cards. The DVHs of the MC TPS plan compare favorably with those of a commercial treatment planning system.Conclusion:A GPU accelerated and MC‐based IMPT optimization system was developed. The dose calculation and plan optimization can be performed in less than 15 minutes on a hardware system costing less than 45,000 dollars. The fast calculation and optimization makes the system easily expandable to robust and multi‐criteria optimization.This work was funded in part by a grant from Varian Medical Systems, Inc.
TH‐A‐BRF‐05: MRI of Individual Lymph Nodes to Guide Regional Breast Radiotherapy
Authors: van Heijst T , van Asselen B , Lagendijk J , van den Bongard D , Philippens M 
Published: July 2014

Purpose:In regional radiotherapy (RT) for breast‐cancer patients, direct visualization of individual lymph nodes (LNs) may reduce target volumes and Result in lower toxicity (i.e. reduced radiation pneumonitis, arm edema, arm morbidity), relative to standard CT‐based delineations. To this end, newly designed magnetic resonance imaging (MRI) sequences were optimized and assessed qualitatively and quantitatively.Methods:In ten healthy female volunteers, a scanning protocol was developed and optimized. Coronal images were acquired in supine RT position positioned on a wedge board on a 1.5 T Ingenia (Philips) wide‐bore MRI. In four volunteers the optimized MRI protocol was applied, including a 3‐dimensional (3D) T1‐weighted (T1w) fast‐field‐echo (FFE). T2w sequences, including 3D FFE, 3D and 2D fast spin echo (FSE), and diffusion‐weighted single‐shot echo‐planar imaging (DWI) were also performed. Several fatsuppression techniques were used. Qualitative evaluation parameters included LN contrast, motion susceptibility, visibility of anatomical structures, and fat suppression. The number of visible axillary and supraclavicular LNs was also determined.Results:T1 FFE, insensitive to motion, lacked contrast of LNs, which often blended in with soft tissue and blood. T2 FFE showed high contrast, but some LNs were obscured due to motion. Both 2D and 3D FSE were motion‐insensitive having high contrast, although some blood remained visible. 2D FSE showed more anatomical details, while in 3D FSE, some blurring occurred. DWI showed high LN contrast, but suffered from geometric distortions and low resolution. Fat suppression by mDixon was the most reliable in regions with magnetic‐field inhomogeneities. The FSE sequences showed the highest sensitivity for LN detection.Conclusion:MRI of regional LNs was achieved in volunteers. The FSE techniques were robust and the most sensitive. Our optimized MRI sequences can facilitate direct delineation of individual LNs. This can Result in smaller target volumes and reduced toxicity in regional RT compared to standard CT planning.
TH‐A‐BRF‐10: Quantification of Subject‐Specific Susceptibility‐Related Geometric Distortion in Clinical Liver MRI for Radiation Therapy
Authors: Zhu T , Matakos A , Feng M , Lawrence T , Cao Y 
Published: July 2014

Purpose:Subject‐specific susceptibility‐induced B0 inhomogeneity affects the geometric accuracy of MRI images, with potential impact on the accuracy of treatment planning and image guidance. This study quantifies individual distortions for patients with intrahepatic tumors.Methods:Liver MRI scans of 13 patients who were enrolled in an IRB approved study were acquired on a 3T scanner (Skyra, Siemens). Clinical contrast‐enhanced images were acquired by a 3D Volume Interpolated Breath‐Hold Examination (VIBE) sequence with TE/TR =1.65/4.3ms, voxel size = 2.5×2.5×3mm (axial sets) or 3.5×3.5×5mm (coronal sets), and frequency‐encoding (FE) bandwidth of 440Hz/pixel. B0 inhomogeneity was evaluated by acquisition of dual gradient echoes (GRE) with TE1/TE2/TR =4.92/7.38/106ms, a voxel size of 3.5×3.5×3.75mm, a FE bandwidth of 290Hz/pixel and breath‐hold. The phase difference maps from the two echoes were unwrapped using a quantitative MRI analysis software package (FSL, FMRIB, Oxford, UK). The resulting calculated B0 inhomogeneity maps (ΔB0 in Hz) were converted to voxel distortion maps in the FE direction (ΔX in mm) corresponding to the VIBE images.Results:Maximum susceptibility‐induced distortions were observed in the liver dome near the diaphragm. Using results from coronal VIBE images in this study as examples, we observed clusters of voxels displaced close to or greater than ΔX=3.5mm (440 Hz in ΔB0) in the VIBE images of the liver in 3 patients, and greater than 2 mm but less than 3.5 mm in 12 patients. On average, approximately 14% of imaged liver voxels had distortions ΔX>±1mm (ΔB0>±125Hz) and 1% of the voxels had ΔX>±2mm (ΔB0>±250Hz).Conclusion:Although advanced MRI techniques, like VIBE, permit faster acquisitions allowing for breath‐held examinations with limited motion‐induced artifacts, this study suggests that localized distortions due to subject‐specific susceptibility variations can occur and require additional advanced corrections based on measuring patient‐specific B0 inhomogeneity maps.The authors would like to acknowledge funding support from NIH R01EB016079 and NIH/NCI RO1 CA132834.
TH‐A‐18C‐07: Noise Suppression in Material Decomposition for Dual‐Energy CT
Authors: Dong X , Petrongolo M , Wang T , Zhu L 
Published: July 2014

Purpose:A general problem of dual‐energy CT (DECT) is that the decomposition is sensitive to noise in the two sets of dual‐energy projection data, resulting in severely degraded qualities of decomposed images. We have previously proposed an iterative denoising method for DECT. Using a linear decomposition function, the method does not gain the full benefits of DECT on beam‐hardening correction. In this work, we expand the framework of our iterative method to include non‐linear decomposition models for noise suppression in DECT.Methods:We first obtain decomposed projections, which are free of beam‐hardening artifacts, using a lookup table pre‐measured on a calibration phantom. First‐pass material images with high noise are reconstructed from the decomposed projections using standard filter‐backprojection reconstruction. Noise on the decomposed images is then suppressed by an iterative method, which is formulated in the form of least‐square estimation with smoothness regularization. Based on the design principles of a best linear unbiased estimator, we include the inverse of the estimated variance‐covariance matrix of the decomposed images as the penalty weight in the least‐square term. Analytical formulae are derived to compute the variance‐covariance matrix from the measured decomposition lookup table.Results:We have evaluated the proposed method via phantom studies. Using non‐linear decomposition, our method effectively suppresses the streaking artifacts of beam‐hardening and obtains more uniform images than our previous approach based on a linear model. The proposed method reduces the average noise standard deviation of two basis materials by one order of magnitude without sacrificing the spatial resolution.Conclusion:We propose a general framework of iterative denoising for material decomposition of DECT. Preliminary phantom studies have shown the proposed method improves the image uniformity and reduces noise level without resolution loss. In the future, we will perform more phantom studies to further validate the performance of the purposed method.This work is supported by a Varian MRA grant.
TH‐A‐18C‐11: An Investigation of KV CBCT Image Quality and Dose Reduction for Volume‐Of‐Interest Imaging Using Dynamic Collimation
Authors: Parsons D , Robar J 
Published: July 2014

Purpose:The focus of this work was to investigate the improvements in image quality and dose reduction for volume‐of‐interest (VOI) kV‐CBCT using dynamic collimation.Methods:A prototype iris aperture was used to track a VOI during a CBCT acquisition. The current aperture design is capable of one‐dimensional translation as a function of gantry angle and dynamic adjustment of the iris radius. The aperture occupies the location of the bow‐tie filter on a Varian OBI system. CBCT and planar image quality was investigated as a function of aperture radius, while maintaining the same dose to the VOI, for a 20 cm diameter cylindrical water phantom with a 9 mm diameter bone insert centered on isocenter. Corresponding scatter‐to‐primary ratios (SPR) were determined at the detector plane with Monte Carlo simulation using EGSnrc. Dose distributions for various anatomical sites were modeled using a dynamic BEAMnrc library and DOSXYZnrc. The resulting VOI dose distributions were compared to full‐field distributions.Results:SPR was reduced by a factor of 8.4 when decreasing iris diameter from 21.2 cm to 2.4 cm (at isocenter). Similarly, this change in iris diameter corresponds to a factor increase of approximately 1.4 and 1.5 in image contrast for CBCT and planar images, respectively, and similarly a factor decrease in image noise of approximately 1.7 and 1.5. This results in a measured gain in contrast‐to‐noise ratio of a factor of approximately 2.3 for both CBCT and planar images. Depending upon the anatomical site, dose was reduced to 10%–70% of the full field value along the central axis plane and down to 2% along the axial planes, while maintaining the same dose to the VOI compared to full‐field techniques.Conclusion:The presented VOI technique offers improved image quality for image‐guided radiotherapy while sparing the surrounding volume of unnecessary dose compared to full‐field techniques.
TH‐A‐9A‐04: Incorporating Liver Functionality in Radiation Therapy Treatment Planning
Authors: Wu V , Epelman M , Feng M , Cao Y , Wang H , Romeijn E , Matuszak M 
Published: July 2014

Purpose:Liver SBRT patients have both variable pretreatment liver function (e.g., due to degree of cirrhosis and/or prior treatments) and sensitivity to radiation, leading to high variability in potential liver toxicity with similar doses. This work aims to explicitly incorporate liver perfusion into treatment planning to redistribute dose to preserve well‐functioning areas without compromising target coverage.Methods:Voxel‐based liver perfusion, a measure of functionality, was computed from dynamic contrast‐enhanced MRI. Two optimization models with different cost functions subject to the same dose constraints (e.g., minimum target EUD and maximum critical structure EUDs) were compared. The cost functions minimized were EUD (standard model) and functionality‐weighted EUD (functional model) to the liver. The resulting treatment plans delivering the same target EUD were compared with respect to their DVHs, their dose wash difference, the average dose delivered to voxels of a particular perfusion level, and change in number of high‐/low‐functioning voxels receiving a particular dose. Two‐dimensional synthetic and three‐dimensional clinical examples were studied.Results:The DVHs of all structures of plans from each model were comparable. In contrast, in plans obtained with the functional model, the average dose delivered to high‐/low‐functioning voxels was lower/higher than in plans obtained with its standard counterpart. The number of high‐/low‐functioning voxels receiving high/low dose was lower in the plans that considered perfusion in the cost function than in the plans that did not. Redistribution of dose can be observed in the dose wash differences.Conclusion:Liver perfusion can be used during treatment planning potentially to minimize the risk of toxicity during liver SBRT, resulting in better global liver function. The functional model redistributes dose in the standard model from higher to lower functioning voxels, while achieving the same target EUD and satisfying dose limits to critical structures.This project is funded by MCubed and grant R01‐CA132834.
TH‐C‐18A‐12: Evaluation of the Impact of Body Size and Tube Output Limits in the Optimization of Fast Scanning with High‐Pitch Dual Source CT
Authors: Ramirez Giraldo J , Mileto A. , Hurwitz L. , Marin D. 
Published: July 2014

Purpose:To evaluate the impact of body size and tube power limits in the optimization of fast scanning with high‐pitch dual source CT (DSCT).Methods:A previously validated MERCURY phantom, made of polyethylene, with circular cross‐section of diameters 16, 23, 30 and 37cm, and connected through tapered sections, was scanned using a second generation DSCT system. The DSCT operates with two independently controlled x‐ray tube generators offering up to 200 kW power reserve (100 kW per tube). The entire lenght of the phantom (42cm) was scanned with two protocols using: A)Standard single‐source CT (SSCT) protocol with pitch of 0.8, and B) DSCT protocol with high‐pitch values ranging from 1.6 to 3.2 (0.2 steps). All scans used 120 kVp with 150 quality reference mAs using automatic exposure control. Scanner radiation output (CTDIvol) and effective mAs values were extracted retrospectively from DICOM files for each slice. Image noise was recorded. All variables were assessed relative to phantom diameter.Results:With standard‐pitch SSCT, the scanner radiation output (and tube‐current) were progressively adapted with increasing size, from 6 mGy (120 mAs) up to 15 mGy (270 mAs) from the thinnest (16cm) to the thickest diameter (37 cm), respectively. By comparison, using high‐pitch (3.2), the scanner output was bounded at about 8 mGy (140 mAs), independent of phantom diameter. Although relative to standard‐pitch, the high‐pitch led to lower radiation output for the same scan, the image noise was higher, particularly for larger diameters. To match the radiation output adaptation of standard‐pitch, a high‐pitch mode of 1.6 was needed, with the advantage of scanning twice as fast.Conclusion:To maximize the benefits of fast scanning with high‐pitch DSCT, the body size and tube power limits of the system need to be considered such that a good balance between speed of acquisition and image quality are warranted.JCRG is an employee of Siemens Medical Solutions USA Inc.
TH‐C‐12A‐03: Development of Expanded Field Irradiation Technique with Gimbaled X‐Ray Head
Authors: Ono T , Miyabe Y , Yamada M , Sawada A , Kaneko S , Monzen H , Mizowaki T , Kokubo M , Hiraoka M 
Published: July 2014

Purpose:The Vero4DRT has a maximum field size of 150×150 mm2. The purposes of this study were to develop an expanded field irradiation technique using a unique gimbaled x‐ray head of Vero4DRT and to evaluate its dosimetric characteristic.Methods:The expanded field irradiation consisted of four separate fields with 2.39 degree gimbal rotation around orthogonal two axes. The central beam axis for each field shifted 40 mm from the isocenter for longitudinal and lateral directions, and thus, the field size was expanded up to 230×230 mm2. Adjacent region were created at the isocenter (center‐adjacent expanded‐field) and 20 mm from isocenter (offadjacent expanded‐field). To create flat dose distribution in the combined piecewise‐fields, the overlapping and gaps regions on the isocenter plane were adjusted with the gimbal rotating and the MLC. To evaluate dosimetric characteristic of the expanded‐field, films inserted in water‐equivalent phantoms at 50, 100 and 150 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expandedfield irradiation technique was applied to IMRT. A head and neck IMRT field, which was planned for the conventional linac (Varian Clinac iX), was reproduced with the expanded‐field of the Vero4DRT. The simulated dose distribution for the expanded IMRT field was compared to the measured dose distribution.Results:The field size, penumbra, flatness and symmetry of center‐ and off‐ adjacent expanded‐fields were 230.2–232.1 mm, 7.8–10.7 mm, 2.3–6.5% and –0.5–0.4% at 100 mm depth. The 82.1% area of the expanded IMRT dose distribution was within 5% difference between measurement and simulation, which was analyzed upper 50% dose area, and the 3%/3 mm gamma pass rate was 98.4%.Conclusions:The expandedfield technique was developed using the gimbaled x‐ray head. To extend applied targets, such as whole breast irradiations or head and neck IMRT, the expanded‐field technique would be effective.
TH‐C‐12A‐08: New Compact 10 MV S‐Band Linear Accelerator: 3D Finite‐Element Design and Monte Carlo Dose Simulations
Authors: Baillie D , St. Aubin J , Fallone B , Steciw S 
Published: July 2014

Purpose:To design a new compact S‐band linac waveguide capable of producing a 10 MV x‐ray beam, while maintaining the length (27.5 cm) of current 6 MV waveguides. This will allow higher x‐ray energies to be used in our linac‐MRI systems with the same footprint.Methods:Finite element software COMSOL Multiphysics was used to design an accelerator cavity matching one published in an experiment breakdown study, to ensure that our modeled cavities do not exceed the threshold electric fields published. This cavity was used as the basis for designing an accelerator waveguide, where each cavity of the full waveguide was tuned to resonate at 2.997 GHz by adjusting the cavity diameter. The RF field solution within the waveguide was calculated, and together with an electron‐gun phase space generated using Opera3D/SCALA, were input into electron tracking software PARMELA to compute the electron phase space striking the x‐ray target. This target phase space was then used in BEAM Monte Carlo simulations to generate percent depth doses curves for this new linac, which were then used to re‐optimize the waveguide geometry.Results:The shunt impedance, Q‐factor, and peak‐to‐mean electric field ratio were matched to those published for the breakdown study to within 0.1% error. After tuning the full waveguide, the peak surface fields are calculated to be 207 MV/m, 13% below the breakdown threshold, and a d‐max depth of 2.42 cm, a D10/20 value of 1.59, compared to 2.45 cm and 1.59, respectively, for the simulated Varian 10 MV linac and brehmsstrahlung production efficiency 20% lower than a simulated Varian 10 MV linac.Conclusion:This work demonstrates the design of a functional 27.5 cm waveguide producing 10 MV photons with characteristics similar to a Varian 10 MV linac.
TH‐C‐12A‐12: Veritas: An Open Source Tool to Facilitate User Interaction with TrueBeam Developer Mode
Authors: Mishra P , Lewis J , Etmektzoglou T , Svatos M 
Published: July 2014

Purpose:To address the challenges of creating delivery trajectories and imaging sequences with TrueBeam Developer Mode, a new open‐source graphical XML builder, Veritas, has been developed, tested and made freely available. Veritas eliminates most of the need to understand the underlying schema and write XML scripts, by providing a graphical menu for each control point specifying the state of 30 mechanical/dose axes. All capabilities of Developer Mode are accessible in Veritas.Methods:Veritas was designed using QT Designer, a ‘what‐you‐is‐what‐you‐get’ (WYSIWIG) tool for building graphical user interfaces (GUI). Different components of the GUI are integrated using QT's signals and slots mechanism. Functionalities are added using PySide, an open source, cross platform Python binding for the QT framework. The XML code generated is immediately visible, making it an interactive learning tool. A user starts from an anonymized DICOM file or XML example and introduces delivery modifications, or begins their experiment from scratch, then uses the GUI to modify control points as desired. The software automatically generates XML plans following the appropriate schema.Results:Veritas was tested by generating and delivering two XML plans at Brigham and Women's Hospital. The first example was created to irradiate the letter ‘B’ with a narrow MV beam using dynamic couch movements. The second was created to acquire 4D CBCT projections for four minutes. The delivery of the letter ‘B’ was observed using a 2D array of ionization chambers. Both deliveries were generated quickly in Veritas by non‐expert Developer Mode users.Conclusion:We introduced a new open source tool Veritas for generating XML plans (delivery trajectories and imaging sequences). Veritas makes Developer Mode more accessible by reducing the learning curve for quick translation of research ideas into XML plans. Veritas is an open source initiative, creating the possibility for future developments and collaboration with other researchers.I am an employee of Varian Medical Systems.
TH‐E‐BRE‐10: Independent Verification of Monitor Units for Volumetric Modulated Arc Therapy (VMAT)
Authors: Chen X , Bush K , Ding A , Xing L 
Published: July 2014

Purpose:A challenging problem in VMAT is how to independently validate the monitor units (MUs) of the treatment plan for a patient generated by the treatment planning system (TPS). In this work we establish a novel framework for independent MU verification of VMAT.Methods:The proposed MU verification technique is based on the relationship between the absorbed dose and the weighed sequence of station points. In VMAT, the dose at a point can be expressed as a sum of contributions from all the station points (or control points). To proceed, we first obtain the matrix elements which characterize the dosimetric contribution of the involved station points by computing the doses at a series of voxels, typically on the prescription surface of the VMAT treatment plan, with unit MU setting for all the station points. This dose matrix is calculated using an in‐house Monte Carlo (MC) software. The MUs of the station points are then derived by minimizing the least‐squares difference between doses computed by the TPS and that of the MC for the selected set of voxels. The technique is applied to sixteen clinical cases with a variety of energies, disease sites and TPS dose calculation algorithms.Results:For cases without tissue density inhomogeneity, the independently computed MUs agree with that of TPS to within 2.7% for all the station points. For lung cases, the MC‐calculated MUs differ significantly from that of the treatment plan computed using AAA. However, the discrepancies are reduced to within 3% when the TPS dose calculation algorithm is switched to a transport equation‐based technique (AcurosTM).Conclusion:An independent MU calculation method is developed, for the first time, for patient specific VMAT treatment plan QA.