bluuebunny/crossref_metadata_2025 huggingface dataset:
Shared-Memory Parallelization for Two-Way Coupled Euler–Lagrange Modeling of Cavitating Bubbly Flows
Authors: Ma Jingsen , Hsiao Chao-Tsung , Chahine Georges L.
Published: June 2015

Cavitating and bubbly flows are encountered in many engineering problems involving propellers, pumps, valves, ultrasonic biomedical applications, etc. In this contribution, an openmp parallelized Euler–Lagrange model of two-phase flow problems and cavitation is presented. The two-phase medium is treated as a continuum and solved on an Eulerian grid, while the discrete bubbles are tracked in a Lagrangian fashion with their dynamics computed. The intimate coupling between the two description levels is realized through the local void fraction, which is computed from the instantaneous bubble volumes and locations, and provides the continuum properties. Since, in practice, any such flows will involve large numbers of bubbles, schemes for significant speedup are needed to reduce computation times. We present here a shared-memory parallelization scheme combining domain decomposition for the continuum domain and number decomposition for the bubbles; both selected to realize maximum speedup and good load balance. The Eulerian computational domain is subdivided based on geometry into several subdomains, while for the Lagrangian computations, the bubbles are subdivided based on their indices into several subsets. The number of fluid subdomains and bubble subsets matches with the number of central processing unit (CPU) cores available in a shared-memory system. Computation of the continuum solution and the bubble dynamics proceeds sequentially. During each computation time step, all selected openmp threads are first used to evolve the fluid solution, with each handling one subdomain. Upon completion, the openmp threads selected for the Lagrangian solution are then used to execute the bubble computations. All data exchanges are executed through the shared memory. Extra steps are taken to localize the memory access pattern to minimize nonlocal data fetch latency, since severe performance penalty may occur on a nonuniform memory architecture (NUMA) multiprocessing system where thread access to nonlocal memory is much slower than to local memory. This parallelization scheme is illustrated on a typical nonuniform bubbly flow problem, cloud bubble dynamics near a rigid wall driven by an imposed pressure function (Ma et al., 2013, “Euler–Lagrange Simulations of Bubble Cloud Dynamics Near a Wall,” International Mechanical Engineering Congress and Exposition, San Diego, CA, Nov. 15–21, Paper No. IMECE2013-65191 and Ma et al., 2015, “Euler–Lagrange Simulations of Bubble Cloud Dynamics Near a Wall,” ASME J. Fluids Eng., 137(4), p. 041301).
Experimental and Numerical Investigation of a Single-Phase Square Natural Circulation Loop
Authors: Saha Ritabrata , Sen Swarnendu , Mookherjee Saikat , Ghosh Koushik , Mukhopadhyay Achintya , Sanyal Dipankar
Published: June 2015

Experimental and numerical analyses are carried out for a natural circulation loop (NCL) under low and moderate heater power. The effect of ambient temperature variation on the loop thermal behavior has been taken into account in present study. The effect of liquid inertia has a role in the initial transience, as revealed by the numerical and experimental observations. The steady-state results from the present analyses are validated with the reported dimensionless results for NCL. The experimental steady-state results are in fair agreement with the developed lumped numerical models. At moderate power, the numerical and experimental results indicate periodic oscillations.
Simulations and Experiments for the Detection of Flow-Assisted Corrosion in Pipes
Authors: Sathish Kumar K. , Balasubramaniam Krishnan
Published: June 2015

Flow-accelerated corrosion (FAC) is a phenomenon which causes wall thinning of pipes, fittings, vessels, and other components in the metal based piping systems that carry water or water-steam mixture in power plants and refineries. Currently used nondestructive techniques, such as radiographic testing (RT), ultrasonic testing (UT), and pulsed eddy current (PEC) testing in order to determine the remaining wall thickness, are time consuming and not economical. Hence, in this work, the use of the fundamental torsional mode ultrasonic guided wave to detect FAC was investigated using the finite element method (FEM) simulations and that were validated with experiments. The torsional wave was generated by the magnetostriction principle using surface mounted strips made of magnetostrictive Hyperco (FeCo) material that provided the source for the surface tractions required to generate the ultrasonic guided wave. The transient electric field was provided through a solenoid coil wound over the strips and permanent magnets were employed to provide the bias magnetic field. From this work, it was observed that the pulse-echo method is not suitable for the FAC detection because of the insignificant reflections from FAC defect region that could not be effectively detected. The through-transmission method was found to be more suitable for the FAC detection because the amplitude of transmitted signal decreased with increase in radial depth of FAC in both the simulation and experiment.
Impact Welding of Aluminum Alloys 6061 and 5052 by Vaporizing Foil
Actuators: Heat-Affected Zone Size and Peel Strength
Authors: Hansen Steven R. , Vivek Anupam , Daehn Glenn S.
Published: June 2015

Joining aluminum alloy sheets is increasingly important in manufacturing. Traditional welding techniques create a heat-affected zone (HAZ) around the joint; however, solid-state joining methods such as impact welding produce joints without significant heat. Here, electrically vaporized foil actuators (VFA) provided the high-pressure pulses needed for impact welding. 0.96 mm thick AA6061-T6 and 0.76 mm thick AA5052 were joined in lap and spotlike configurations, at a variety of impact velocities. The welds failed in coach-peel outside the joint interface. The 5052 hardened within 100 μm of the interface. The 6061-T6 may have softened slightly within 50 μm of the interface.
Removal Mechanism and Defect Characterization for Glass-Side Laser Scribing of CdTe/CdS Multilayer in Solar Cells
Authors: Wang Hongliang , Lawrence Yao Y. , Chen Hongqiang
Published: June 2015

Laser scribing is an important manufacturing process used to reduce photocurrent and resistance losses and increase solar cell efficiency through the formation of serial interconnections in large-area solar cells. High-quality scribing is crucial since the main impediment to large-scale adoption of solar power is its high-production cost (price-per-watt) compared to competing energy sources such as wind and fossil fuels. In recent years, the use of glass-side laser scribing processes has led to increased scribe quality and solar cell efficiencies; however, defects introduced during the process such as thermal effect, microcracks, film delamination, and removal uncleanliness keep the modules from reaching their theoretical efficiencies. Moreover, limited numerical work has been performed in predicting thin-film laser removal processes. In this study, a nanosecond (ns) laser with a wavelength at 532 nm is employed for pattern 2 (P2) scribing on CdTe (cadmium telluride) based thin-film solar cells. The film removal mechanism and defects caused by laser-induced micro-explosion process are studied. The relationship between those defects, removal geometry, laser fluences, and scribing speeds are also investigated. Thermal and mechanical numerical models are developed to analyze the laser-induced spatiotemporal temperature and pressure responsible for film removal. The simulation can well-predict the film removal geometries, transparent conducting oxide (TCO) layer thermal damage, generation of microcracks, film delamination, and residual materials. The characterization of removal qualities will enable the process optimization and design required to enhance solar module efficiency.
Straight Bevel Gear Generation Using the Dual Interlocking Circular Cutter Cutting Method on a Computer Numerical Control Bevel Gear-Cutting Machine
Authors: Shih Yi-Pei , Hsieh Hsin-Yen
Published: June 2015

The dual interlocking circular cutter (DICC) cutting method, used to produce straight bevel gears (SBGs), employs two interlocked cutters to generate tooth surfaces with a combination of profile and lengthwise crowning. The gear pairs produced have the advantage of low assembly sensibility. However, the cutting method can only be carried out on a dedicated machine with complicated mechanisms, which are not only difficult to setup but also reduce stiffness and accuracy. Gleason recently applied this cutting method on the modern CNC bevel gear-cutting machine to increase productivity and accuracy in manufacturing SBGs; however, they revealed no details of this application because of commercial considerations. The main goal of this work, therefore, is to establish a mathematical model of an SBG produced by the DICC method on a virtual machine. The work gear is cut by an imaginary generating gear that enables derivation of the SBG tooth surface. Ease-off and tooth contact analysis (TCA) are applied to confirm the correctness of the proposed model. A cutting method is also proposed that can be transformed from a specific traditional machine to a modern CNC bevel gear-cutting machine. Conversion from the virtual machine enables derivation of the five-axis nonlinear machine coordinates and subsequent programming of the NC data. Finally, the correctness of NC data for machining is confirmed using the vericut nc verification software.
Toward Automatic Tolerancing of Mechanical Assemblies: First-Order GD&T Schema Development and Tolerance Allocation
Authors: Haghighi Payam , Mohan Prashant , Kalish Nathan , Vemulapalli Prabath , Shah Jami J. , Davidson Joseph K.
Published: June 2015

Geometric and dimensional tolerances must be determined not only to ensure proper achievement of design function but also for manufacturability and assemblability of mechanical assemblies. We are investigating the degree to which it is possible to automate tolerance assignment on mechanical assemblies received only as STEP AP 203 (nominal) geometry files. In a previous paper, we reported on the preprocessing steps required: assembly feature recognition, pattern recognition, and extraction of both constraints and directions of control (DoC) for assembly. In this paper, we discuss first-order tolerance schema development, based purely on assemblability conditions. This includes selecting features to be toleranced, tolerance types, datums, and datum reference frames (DRFs), and tolerance value allocation. The approach described here is a combination of geometric analysis and heuristics. The assumption is that this initial geometric dimensioning and tolerancing (GD&T) specification will be sent to a stack analysis module and iterated upon until satisfactory results, such as desired acceptance rates, are reached. The paper also touches upon issues related to second-order schema development, one that takes intended design function into account.
Numerical Methodology to Evaluate the Effects of Bone Density and Cement Augmentation on Fixation Stiffness of Bone-Anchoring Devices
Authors: Chevalier Yan
Published: June 2015

Bone quality is one of the reported factors influencing the success of bone anchors in arthroscopic repairs of torn rotator cuffs at the shoulder. This work was aimed at developing refined numerical methods to investigate how bone quality can influence the fixation stiffness of bone anchors. To do that bone biopsies were scanned at 26-μm resolution with a high-resolution microcomputer tomography (micro-CT) scanner and their images were processed for virtual implantation of a typical design of bone anchor. These were converted to microfinite element (μFE) and homogenized classical FE models, and analyses were performed to simulate pulling on the bone anchor with and without cement augmentation. Quantification of structural stiffness for each implanted specimen was then computed, as well as stress distributions within the bone structures, and related to the bone volume fraction of the specimens. Results show that the classical method is excellently correlated to structural predictions of the more refined μFE method, despite the qualitative differences in local stresses in the bone surrounding the implant. Predictions from additional loading cases suggest that structural fixation stiffness in various directions is related to apparent bone density of the surrounding bone. Augmentation of anchoring with bone cement stiffens the fixation and alters these relations. This work showed the usability of homogenized FE (hFE) in the evaluation of bone anchor fixation and will be used to develop new methodologies for virtual investigations leading to optimized repairs of rotator cuff and glenoid Bankart lesions.
Microcalcification detectability using a bench‐top prototype photon‐counting breast CT based on a Si strip detector
Authors: Cho Hyo‐Min , Ding Huanjun , Barber William C. , Iwanczyk Jan S. , Molloi Sabee
Published: June 2015

Purpose:

To investigate the feasibility of detecting breast microcalcification (μCa) with a dedicated breast computed tomography (CT) system based on energy‐resolved photon‐counting silicon (Si) strip detectors.

Methods:

The proposed photon‐counting breast CT system and a bench‐top prototype photon‐counting breast CT system were simulated using a simulation package written in matlab to determine the smallest detectable μCa. A 14 cm diameter cylindrical phantom made of breast tissue with 20% glandularity was used to simulate an average‐sized breast. Five different size groups of calcium carbonate grains, from 100 to 180 μm in diameter, were simulated inside of the cylindrical phantom. The images were acquired with a mean glandular dose (MGD) in the range of 0.7–8 mGy. A total of 400 images was used to perform a reader study. Another simulation study was performed using a 1.6 cm diameter cylindrical phantom to validate the experimental results from a bench‐top prototype breast CT system. In the experimental study, a bench‐top prototype CT system was constructed using a tungsten anode x‐ray source and a single line 256‐pixels Si strip photon‐counting detector with a pixel pitch of 100 μm. Calcium carbonate grains, with diameter in the range of 105–215 μm, were embedded in a cylindrical plastic resin phantom to simulate μCas. The physical phantoms were imaged at 65 kVp with an entrance exposure in the range of 0.6–8 mGy. A total of 500 images was used to perform another reader study. The images were displayed in random order to three blinded observers, who were asked to give a 4‐point confidence rating on each image regarding the presence of μCa. The μCa detectability for each image was evaluated by using the average area under the receiver operating characteristic curve (AUC) across the readers.

Results:

The simulation results using a 14 cm diameter breast phantom showed that the proposed photon‐counting breast CT system can achieve high detection accuracy with an average AUC greater than 0.89 ± 0.07 for μCas larger than 120 μm in diameter at a MGD of 3 mGy. The experimental results using a 1.6 cm diameter breast phantom showed that the prototype system can achieve an average AUC greater than 0.98 ± 0.01 for μCas larger than 140 μm in diameter using an entrance exposure of 1.2 mGy.

Conclusions:

The proposed photon‐counting breast CT system based on a Si strip detector can potentially offer superior image quality to detect μCa with a lower dose level than a standard two‐view mammography.
SU‐C‐213‐01: 3D Printed Patient Specific Phantom Composed of Bone and Soft Tissue Substitute Plastics for Radiation Therapy
Authors: Ehler E , Sterling D , Higgins P
Published: June 2015

Purpose:

3D printed phantoms constructed of multiple tissue approximating materials could be useful in both clinical and research aspects of radiotherapy. This work describes a 3D printed phantom constructed with tissue substitute plastics for both bone and soft tissue; air cavities were included as well.

Methods:

3D models of an anonymized nasopharynx patient were generated for air cavities, soft tissues, and bone, which were segmented by Hounsfield Unit (HU) thresholds. HU thresholds were chosen to define air‐to‐soft tissue boundaries of 0.65 g/cc and soft tissue‐to‐bone boundaries of 1.18 g/cc based on clinical HU to density tables. After evaluation of several composite plastics, a bone tissue substitute was identified as an acceptable material for typical radiotherapy x‐ray energies, composed of iron and PLA plastic. PET plastic was determined to be an acceptable soft tissue substitute. 3D printing was performed on a consumer grade dual extrusion fused deposition model 3D printer.

Results:

MVCT scans of the 3D printed heterogeneous phantom were acquired. Rigid image registration of the patient and the 3D printed phantom scans was performed. The average physical density of the soft tissue and bone regions was 1.02 ± 0.08 g/cc and 1.39 ± 0.14 g/cc, respectively, for the patient kVCT scan. In the 3D printed phantom MVCT scan, the average density of the soft tissue and bone was 1.01 ± 0.09 g/cc and 1.44 ± 0.12 g/cc, respectively.

Conclusion:

A patient specific phantom, constructed of heterogeneous tissue substitute materials was constructed by 3D printing. MVCT of the 3D printed phantom showed realistic tissue densities were recreated by the 3D printing materials.

Funding provided by intra‐department grant by University of Minnesota Department of Radiation Oncology
SU‐C‐213‐03: Custom 3D Printed Boluses for Radiation Therapy
Authors: Zhao B , Yang M , Yan Y , Rahimi A , Chopra R , Jiang S
Published: June 2015

Purpose:

To develop a clinical workflow and to commission the process of creating custom 3d printed boluses for radiation therapy.

Methods:

We designed a workflow to create custom boluses using a commercial 3D printer. Contours of several patients were deformably mapped to phantoms where the test bolus contours were designed. Treatment plans were created on the phantoms following our institutional planning guideline. The DICOM file of the bolus contours were then converted to stereoLithography (stl) file for the 3d printer. The boluses were printed on a commercial 3D printer using polylactic acid (PLA) material. Custom printing parameters were optimized in order to meet the requirement of bolus composition. The workflow was tested on multiple anatomical sites such as skull, nose and chest wall. The size of boluses varies from 6×9cm2 to 12×25cm2. To commission the process, basic CT and dose properties of the printing materials were measured in photon and electron beams and compared against water and soft superflab bolus. Phantoms were then scanned to confirm the placement of custom boluses. Finally dose distributions with rescanned CTs were compared with those computer‐generated boluses.

Results:

The relative electron density(1.08±0.006) of the printed boluses resemble those of liquid tap water(1.04±0.004). The dosimetric properties resemble those of liquid tap water(1.04±0.004). The dosimetric properties were measured at dmax with an ion chamber in electron and photon open beams. Compared with solid water and soft bolus, the output difference was within 1% for the 3D printer material. The printed boluses fit well to the phantom surfaces on CT scans. The dose distribution and DVH based on the printed boluses match well with those based on TPS generated boluses.

Conclusion:

3d printing provides a cost effective and convenient solution for patient‐specific boluses in radiation therapy.
SU‐C‐213‐04: Application of Depth Sensing and 3D‐Printing Technique for Total Body Irradiation (TBI) Patient Measurement and Treatment Planning
Authors: Lee M , Han B , Jenkins C , Xing L , Suh T
Published: June 2015

Purpose:

To develop and validate an innovative method of using depth sensing cameras and 3D printing techniques for Total Body Irradiation (TBI) treatment planning and compensator fabrication.

Methods:

A tablet with motion tracking cameras and integrated depth sensing was used to scan a RANDOTM phantom arranged in a TBI treatment booth to detect and store the 3D surface in a point cloud (PC) format. The accuracy of the detected surface was evaluated by comparison to extracted measurements from CT scan images. The thickness, source to surface distance and off‐axis distance of the phantom at different body section was measured for TBI treatment planning. A 2D map containing a detailed compensator design was calculated to achieve uniform dose distribution throughout the phantom. The compensator was fabricated using a 3D printer, silicone molding and tungsten powder. In vivo dosimetry measurements were performed using optically stimulated luminescent detectors (OSLDs).

Results:

The whole scan of the anthropomorphic phantom took approximately 30 seconds. The mean error for thickness measurements at each section of phantom compare to CT was 0.44 ± 0.268 cm. These errors resulted in approximately 2% dose error calculation and 0.4 mm tungsten thickness deviation for the compensator design. The accuracy of 3D compensator printing was within 0.2 mm. In vivo measurements for an end‐to‐end test showed the overall dose difference was within 3%.

Conclusion:

Motion cameras and depth sensing techniques proved to be an accurate and efficient tool for TBI patient measurement and treatment planning. 3D printing technique improved the efficiency and accuracy of the compensator production and ensured a more accurate treatment delivery.
SU‐C‐304‐02: Robust and Efficient Process for Acceptance Testing of Varian TrueBeam Linacs Using An Electronic Portal Imaging Device (EPID)
Authors: Yaddanapudi S , Cai B , Harry T , Sun B , Li H , Noel C , Goddu S , Pawlicki T , Mutic S
Published: June 2015

Purpose:

The purpose of this project was to develop a process that utilizes the onboard kV and MV electronic portal imaging devices (EPIDs) to perform rapid acceptance testing (AT) of linacs in order to improve efficiency and standardize AT equipment and processes.

Methods:

In this study a Varian TrueBeam linac equipped with an amorphous silicon based EPID (aSi1000) was used. The conventional set of AT tests and tolerances was used as a baseline guide, and a novel methodology was developed to perform as many tests as possible using EPID exclusively. The developer mode on Varian TrueBeam linac was used to automate the process. In the current AT process there are about 45 tests that call for customer demos. Many of the geometric tests such as jaw alignment and MLC positioning are performed with highly manual methods, such as using graph paper. The goal of the new methodology was to achieve quantitative testing while reducing variability in data acquisition, analysis and interpretation of the results. The developed process was validated on two machines at two different institutions.

Results:

At least 25 of the 45 (56%) tests which required customer demo can be streamlined and performed using EPIDs. More than half of the AT tests can be fully automated using the developer mode, while others still require some user interaction. Overall, the preliminary data shows that EPID‐based linac AT can be performed in less than a day, compared to 2–3 days using conventional methods.

Conclusions:

Our preliminary results show that performance of onboard imagers is quite suitable for both geometric and dosimetric testing of TrueBeam systems. A standardized AT process can tremendously improve efficiency, and minimize the variability related to third party quality assurance (QA) equipment and the available onsite expertise.

Research funding provided by Varian Medical Systems. Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.
SU‐C‐BRD‐03: Closing the Loop On Virtual IMRT QA
Authors: Valdes G , Scheuermann R , Y H C. , Olszanski A , Bellerive M , Solberg T
Published: June 2015

Purpose:

To develop an algorithm that predicts a priori IMRT QA passing rates.

Methods:

416 IMRT plans from all treatment sites were planned in Eclipse version 11 and delivered using a dynamic sliding window technique on Clinac iX or TrueBeam linacs (Varian Medical Systems, Palo Alto, CA). The 3%/3mm and 2%/2mm local distance to agreement (DTA) were recorded during clinical operations using a commercial 2D diode array (MapCHECK 2, Sun Nuclear, Melbourne, FL). Each plan was characterized by 37 metrics that describe different failure modes between the calculated and measured dose. Machine‐learning algorithms (MLAs) were trained to learn the relation between the plan characteristics and each passing rate. Minimization of the cross validated error, together with maximum a posteriori estimation (MAP), were used to choose the model parameters.

Results:

3%/3mm local DTA can be predicted with an error smaller than 3% for 98% of the plans. For the remaining 2% of plans, the residual error was within 5%. For 2%/2mm local DTA passing rates, 96% percent of the plans were successfully predicted with an error smaller than 5%. All high‐risk plans that failed the 2%/2mm local criteria were correctly identified by the algorithm. The most important metric to describe the passing rates was determined to be the MU per Gray (modulation factor).

Conclusions:

Logs files and independent dose calculations have been suggested as possible substitutes for measurement based IMRT QA. However, none of these methods answer the fundamental question of whether a plan can be delivered with a clinically acceptable error given the limitations of the linacs and the treatment planning system. Predicting the IMRT QA passing rates a priori closes that loop. For additional robustness, virtual IMRT QA can be combined with Linac QA and log file analysis to confirm appropriate delivery.
SU‐C‐BRD‐04: Comparison of Shallow Fluence to Deep Point Dose Measurements for Spine VMAT SBRT Patient‐Specific QA
Authors: Cheung J , Held M , Morin O , Weethee B , Chuang C , Perez‐Andujar A , Sudhyadhom A
Published: June 2015

Purpose:

To investigate the sensitivity of traditional gamma‐index‐based fluence measurements for patient‐specific measurements in VMAT delivered spine SBRT.

Methods:

The ten most recent cases for spine SBRT were selected. All cases were planned with Eclipse RapidArc for a TrueBeam STx. The delivery was verified using a point dose measurement with a Pinpoint 3D micro‐ion chamber in a Standard Imaging Stereotactic Dose Verification Phantom. Two points were selected for each case, one within the target in a low dose‐gradient region and one in the spinal cord. Measurements were localized using on‐board CBCT. Cumulative and separate arc measurements were acquired with the ArcCheck and assessed using the SNC patient software with a 3%/3mm and 2%/2mm gamma analysis with global normalization and a 10% dose threshold. Correlations between data were determined using the Pearson Product‐Moment Correlation.

Results:

For our cohort of patients, the measured doses were higher than calculated ranging from 2.2%–9.7% for the target and 1.0%–8.2% for the spinal cord. There was strong correlation between 3%/3mm and 2%/2mm passing rates (r=0.91). Moderate correlation was found between target and cord dose with a weak fit (r=0.67, R‐Square=0.45). The cumulative ArcCheck measurements showed poor correlation with the measured point doses for both the target and cord (r=0.20, r=0.35). If the arcs are assessed separately with an acceptance criteria applied to the minimum passing rate between all arcs, a moderate negative correlation was found for the target and cord (r=−0.48, r= −0.71). The case with the highest dose difference (9.7%) received a passing rate of 97.2% for the cumulative arcs and 87.8% for the minimum with separate arcs.

Conclusion:

Our data suggest that traditional passing criteria using ArcCheck with cumulative measurements do not correlate well with dose errors. Separate arc analysis shows better correlation but may still miss large dose errors. Point dose verifications are recommended.
SU‐C‐BRD‐06: Sensitivity Study of An Automated System to Acquire and Analyze EPID Exit Dose Images
Authors: Olch A , Zhuang A
Published: June 2015

Purpose:

The dosimetric consequences of errors in patient setup or beam delivery and anatomical changes are not readily known. A new product, PerFRACTION (Sun Nuclear Corporation), is designed to detect these errors by comparing the EPID exit dose image from each field of each fraction to those from baseline fraction images. This work investigates the sensitivity of PerFRACTION to detect the deviation of induced errors in a variety of realistic scenarios.

Methods:

Eight plans were created mimicking potential delivery or setup errors. The plans consisted of a nominal field and the field with an induced error. These were used to irradiate the EPID simulating multiple fractions with and without the error. Integrated EPID images were acquired in clinical mode and saved in ARIA. PerFRACTION automatically pulls the images into its database and performs the user defined comparison. In some cases, images were manually pushed to PerFRACTION. We varied the distance‐to‐agreement or dose tolerance until PerFRACTION showed failing pixels in the affected region and recorded the values. We induced errors of 1mm and greater in jaw, MLC, and couch position, 2 degree collimation rotation (patient yaw), and 0.5% to 1.5% in machine output. Both static and arc fields with the rails in or out were also acquired and compared.

Results:

PerFRACTION detected position errors of the jaws, MLC, and couch with an accuracy of better than 0.5 mm, and 0.2 degrees for collimator and gantry error. PerFRACTION detected a machine output error within 0.2% and detected the change in rail position.

Conclusion:

A new automated system for monitoring daily treatments for machine or patient variations from the first fraction using integrated EPID images was found to be sensitive enough to detect small positional, angular, and dosimetric errors within 0.5mm, 0.2 degrees, and 0.2%, respectively.

Sun Nuclear Corporation has provided a software license for the product described.
SU‐C‐BRB‐03: Novel Technique to Implement GRID Therapy in a Commercial Treatment Planning System
Authors: Park H , Mohiuddin M , Yaldo D , Tom B , Worlikar N
Published: June 2015

Purpose:

Due to the difficulty of creating an accurate multi‐aperture block in treatment planning systems (TPS), spatially fractionated radiation therapy (GRID Therapy) is limited to clinical setups using simple monitor unit calculations. In this work, we present a novel approach to accurately model a grid block in a TPS and evaluate its dosimetric accuracy.

Methods:

An acrylic GRID block was fashioned such that the hole size and spacing were the same dimensions of the brass GRID block (dotDecimal) at isocenter. Holes were non‐divergent and drilled 1 cm deep. CT scans (RT Lightspeed, GE Healthcare) of the block were acquired using axial slices with a thickness of 0.625 mm. These were imported into Eclipse (version 11, Varian Medical Systems) and holes were auto‐contoured into structures. The GRID block was created in Eclipse by forming apertures around the hole structures using a simple three step process. Treatment plans were created in a water‐equivalent phantom using 6 and 10 MV beams, delivered with a linear accelerator (Clinac iX, Varian Medical Systems) and measured using a water tank, film and a diode array.

Results:

Comparisons of percent depth dose curves and profiles at depths of maximum dose, 5cm, and 10cm for field sizes ranging from 5 cm2 to 25 cm2 using water and film were within 3% of their respective positions in Eclipse. GRID plans utilizing various jaw sizes and MLC blocking measured with film and a diode array showed pass rates with an average of 97% using Gamma analysis at 3%/ 3 mm and no lower than 93%.

Conclusion:

We have developed a simple yet accurate method of incorporating a GRID block into a commercially available TPS and demonstrated that the TPS accurately reflects the dose delivered. This will allow for real‐time planning using patient scans and encourage new methods for GRID therapy.

Support provided by dotDecimal, Sanford, FL
SU‐C‐BRB‐04: Characteristics and Performance Evaluation of the First Commercial MLC for a Robotic Delivery System
Authors: Fuerweger C , Prins P , Coskan H , Heijmen B
Published: June 2015

Purpose:

To assess characteristics and performance of the “Incise™” MLC (41 leaf pairs, 2.5mm width, FFF linac) mounted on the robotic SRS/SBRT platform “CyberKnife M6™” in a pre‐clinical 5 months (11/2014–03/2015) test period.

Methods:

Beam properties were measured with unshielded diodes and EBT3 film. The CyberKnife workspace for MLC was analyzed by transforming robot node coordinates (cranial / body paths) into Euler geometry. Bayouth tests for leaf / bank position accuracy were performed in standard (A/P) and clinically relevant non‐standard positions, before and after exercising the MLC for 10+ minutes. Total system and delivery accuracy were assessed in End‐to‐End tests and dosimetric verification of exemplary plans. Stability over time was evaluated in Picket‐Fence‐and adapted Winston‐Lutz‐tests (AQA) for different collimator angles.

Results:

Penumbrae (80–20%, with 100%=2*dose at inflection point; SAD 80cm; 10cm depth) parallel / perpendicular to leaf motion were 2.87/2.64mm for the smallest (0×76×0.75cm2) and 5.34/4.94mm for the largest (9.76×9.75cm2) square field. MLC circular field penumbrae exceeded fixed cones by 10–20% (e.g. 60mm: 4.0 vs. 3.6mm; 20mm: 3.6 vs. 2.9mm). Interleaf leakage was <0.5%. Clinically accessible workspace with MLC covered (non‐coplanar) gantry angles of [‐113°;+112°] (cranial) and [‐108°;+102°] (body), and collimator angles of [‐100°;+107°] (cranial) and [‐91°;+100°] (body). Average leaf position offsets were ≤0.2mm in 14 standard A/P Bayouth tests and ≤0.6mm in 8 non‐standard direction tests. Pre‐test MLC exercise increased jaggedness (range ±0.3mm vs. ±0.5mm) and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.39±0.06mm in 6 End‐to‐End tests. Picket‐Fence and AQA showed no adverse trends during the test period.

Conclusion:

The Incise™ MLC for CyberKnife M6™ displayed high accuracy and mechanical stability over the test period. The specific CyberKnife geometry and performance after exercise demand dedicated QA measures.

This work is in part funded by a research grant from Accuray Inc, Sunnyvale, USA. Erasmus MC Cancer Institute also has research collaborations with Elekta AB, Stockholm, Sweden. C Fuerweger has previously received speaker honoraria from Accuray Inc, Sunnyvale, USA.
SU‐C‐BRB‐05: Investigation of Conformal Arc Therapy Utilizing Newly Designed Cobalt 60 Machine
Authors: Eldib A , Chibani O , Jin L , Li J , Veltchev I , Price R , Mora G , Ma C
Published: June 2015

Purpose:

A new modernized design for cobalt 60 (Co‐60) machines is being developed with a ring type gantry. In this study we investigate the beneficial outcome of the new design for conformal arc therapy for various clinical sites. The new modality was evaluated based on isodose distributions and dose volume histograms as compared to 6MV photon beams from conventional linear accelerators.

Methods:

Computed tomographic images of seven different SBRT patients were selected from our patient database. All of these cases were previously planned on the Eclipse treatment planning system. New plans for these patients were generated with a modified conformal arc technique using both 6MV and Co‐60 beams. The conformal arc was created by the delivery of treatment fields conformal to the target cross‐section at every 5 or 10 degrees. The field shape was modified or turned off when it initially passed through a critical structure. Monte Carlo codes, MCBEAM and MCPLAN, were used for the machine head simulation and phantom/patient dose calculation, respectively. In the new Co‐60 machine design, the source‐to‐isocenter distance was 60cm and the treatment head included the Co‐60 source, primary collimator, jaws and MLC.

Results:

For all cases investigated, conformal arc plans utilizing Co‐60 beams achieved similar conformity (mean conformity index=1.19) comparing to 6MV photon beams. Isodose distributions were tailored similarly around the PTV; both Co‐60 and 6MV plans met our clinical acceptance criteria for the target coverage, and the maximum and minimum target doses. The DVH for the Co‐60 plans showed slightly lower doses to the critical structures although the differences were small in most cases.

Conclusion:

There were no significant dosimetric differences between 6MV and Co‐60 plans. Our results confirmed that this new Co‐60 design could be a cost‐effective machine for advanced radiotherapy due to its low cost, low maintenance and high up time.
SU‐C‐BRA‐01: 18F‐NaF PET/CT‐Directed Dose Escalation in Stereotactic Body Radiotherapy for Spine Oligometastases From Prostate Cancer
Authors: Wu L , Zhang W , Kwee S , Li M , Peng X , Xie L , Lin Z , Wang H , Kuang Y
Published: June 2015

Purpose:

To investigate the technical feasibility of SBRT dose painting using 18F‐NaF positron emission tomography (PET) scans guidance in patients with spine oligometastases from prostate cancer.

Methods:

As a proof of concept, six patients with 14 spine oligometastatic lesions from prostate cancer who had 18F‐NaF PET/CT scan prior to treatment were retrospectively included. GTVreg was delineated according to the regular tumor boundary shown on PET and/or CT images; and GTVMATV was contoured based on a net metabolically active tumor volume (MATV) defined by 60% of the SUVmax values on 18F‐NaF PET images. The PTVs (PTVreg and PTVMATV) were defined as respective GTVs (plus involved entire vertebral body for PTVreg) with a 3‐mm isotropic expansion margin. Three 1‐fraction SBRT plans using VMAT technique along with 10 MV FFF beams (Plan24Gy, Plan24–27Gy, and Plan24–30Gy) were generated for each patient. All plans included a dose of 24 Gy prescribed to PTVreg. The Plan24–27Gy and Plan24–30Gy also included a simultaneous boost dose of 27 Gy or 30 Gy prescribed to the PTVMATV, respectively. The feasibility of 18F‐NaF PET‐guided SBRT dose escalation was evaluated by its ability to achieve the prescription dose objectives while adhering to organ‐at‐risk (OAR) dose constraints. The normal tissue complication probabilities (NTCP) calculated by radiological models were also compared between the plans.

Results:

In all 33 SBRT plans generated, the planning objectives and dose constraints were met without exception. Plan24–27Gy and Plan24–30Gy had a significantly higher dose in PTVMATV than Plan24Gy (p < 0.05), respectively, while maintaining a similar OAR sparing profile and NTCP values.

Conclusion:

Using VMAT with FFF beams to incorporate a simultaneous 18F‐NaF PET‐guided radiation boost dose up to 30 Gy into a SBRT plan is technically feasible. The relationship between local control and normal tissue toxicity in SBRT dose painting should be validated in clinical trials.
SU‐C‐BRA‐07: Virtual Bronchoscopy‐Guided IMRT Planning for Mapping and Avoiding Radiation Injury to the Airway Tree in Lung SAbR
Authors: Sawant A , Modiri A , Bland R , Yan Y , Ahn C , Timmerman R
Published: June 2015

Purpose:

Post‐treatment radiation injury to central and peripheral airways is a potentially important, yet under‐investigated determinant of toxicity in lung stereotactic ablative radiotherapy (SAbR). We integrate virtual bronchoscopy technology into the radiotherapy planning process to spatially map and quantify the radiosensitivity of bronchial segments, and propose novel IMRT planning that limits airway dose through non‐isotropic intermediate‐ and low‐dose spillage.

Methods:

Pre‐ and ∼8.5 months post‐SAbR diagnostic‐quality CT scans were retrospectively collected from six NSCLC patients (50–60Gy in 3–5 fractions). From each scan, ∼5 branching levels of the bronchial tree were segmented using LungPoint, a virtual bronchoscopic navigation system. The pre‐SAbR CT and the segmented bronchial tree were imported into the Eclipse treatment planning system and deformably registered to the planning CT. The five‐fraction equivalent dose from the clinically‐delivered plan was calculated for each segment using the Universal Survival Curve model. The pre‐ and post‐SAbR CTs were used to evaluate radiation‐induced segmental collapse. Two of six patients exhibited significant segmental collapse with associated atelectasis and fibrosis, and were re‐planned using IMRT.

Results:

Multivariate stepwise logistic regression over six patients (81 segments) showed that D0.01cc (minimum point dose within the 0.01cc receiving highest dose) was a significant independent factor associated with collapse (odds‐ratio=1.17, p=0.010). The D0.01cc threshold for collapse was 57Gy, above which, collapse rate was 45%. In the two patients exhibiting segmental collapse, 22 out of 32 segments showed D0.01cc >57Gy. IMRT re‐planning reduced D0.01cc below 57Gy in 15 of the 22 segments (68%) while simultaneously achieving the original clinical plan objectives for PTV coverage and OAR‐sparing.

Conclusion:

Our results indicate that the administration of lung SAbR can Result in significant injury to bronchial segments, potentially impairing post‐SAbR lung function. To our knowledge, this is the first investigation of functional avoidance based on mapping and minimizing dose to individual bronchial segments.

The presenting author receives research funding from Varian Medical Systems, Elekta, and VisionRT.
SU‐C‐303‐01: Activation‐Induced Cytidine Deaminase Confers Cancer Resistance to Radiation Therapy
Authors: Yi S , La Count S , Liu J , Bai X , Lu L
Published: June 2015

Purpose:

To study the role of activation‐induced cytidine deaminase (AID) in malignant cell resistance to radiation therapy.

Methods:

We first developed several small devices that could be used to adopt radiation beams from clinical high dose rate brachy therapy (HDR) or linac‐based megavoltage machines to perform pre‐clinical cell and mouse experiments. Then we used these devices to deliver radiation to AID‐positive and AID‐silenced cancer cells or tumors formed by these cells in mice. Cells and mice bearing tumors received the same dose under the same experimental conditions. For cells, we observed the apoptosis and the cell survival rate over time. For mice bearing tumors, we measured and recorded the tumor sizes every other day for 4 weeks.

Results:

For cell experiments, we found that the AID‐positive cells underwent much less apoptosis compared with AID‐silenced cells upon radiation. And for mouse experiments, we found that AID‐positive tumors grew significantly faster than the AID‐silenced tumors despite of receiving the same doses of radiation.

Conclusion:

Our study suggests that AID may confer cancer resistance to radiation therapy, and AID may be a significant biomarker predicting cancer resistance to radiation therapy for certain cancer types
SU‐C‐303‐03: Dosimetric Model of the Beagle Needed for Pre‐Clinical Testing of Radiopharmaceuticals
Authors: Shang M , Sands M , Bolch W
Published: June 2015

Purpose:

Large animal models, most popularly beagles, have been crucial surrogates to humans in determining radiation safety levels of radiopharmaceuticals. This study aims to develop a detailed beagle phantom to accurately approximate organ absorbed doses for therapy nuclear medicine preclinical studies.

Methods:

A 3D NURBS model was created subordinate to a whole body CT of an adult beagle. Bones were harvested and CT imaged to offer macroscopic skeletal detail. Samples of trabecular spongiosa were cored and imaged to offer microscopic skeletal detail for bone trabeculae and marrow volume fractions.

Results:

Organ masses in the model are typical of an adult beagle. Trends in volume fractions for skeletal dosimetry are fundamentally similar to those found in existing models of other canine species.

Conclusion:

This work warrants its use in further investigations of radiation transport calculation for electron and photon dosimetry. This model accurately represents the anatomy of a beagle, and can be directly translated into a useable geometry for a voxel‐based Monte Carlo radiation transport program such as MCNP6.

Work supported by a grant from the Hyundai Hope on Wheels Foundation for Pediatric Cancer Research.
SU‐C‐303‐04: Evaluation of On‐ and Off‐Line Bioluminescence Tomography System for Focal Irradiation Guidance
Authors: Zhang B , Wang K , Iordachita I , Reyes J , Tran P , Wong J
Published: June 2015

Purpose:

We have developed offline and on‐board bioluminescence tomography(BLT) systems for the small animal radiation research platform(SARRP) for radiation guidance of soft tissue targets. We investigated the effectiveness of offline BLT guidance.

Methods:

CBCT is equipped on both the offline BLT system and SARRP that are 10 ft. apart. To evaluate the setup error during animal transport between the two systems, we implanted a luminescence source in the abdomen of anesthetized mice. Five mice were studied. After CBCT was acquired on both systems, source centers and correlation coefficients were calculated. CBCT was also used to generate object mesh for BLT reconstruction. To assess target localization, we compared the localization of the luminescence source based on (1)on‐board SARRP BLT and CBCT, (2)offline BLT and CBCT, and (3)offline BLT and SARRP CBCT. The 3rd comparison examines if an offline BLT system can be used to guide radiation when there is minimal target contrast in CBCT.

Results:

Our CBCT results show the offset of the light source center can be maintained within 0.2 mm during animal transport. The center of mass(CoM) of the light source reconstructed by the offline BLT has an offset of 1.0 ± 0.4 mm from the ‘true’ CoM as derived from the SARRP CBCT. The results compare well with the offset of 1.0 ± 0.2 mm using on‐line BLT.

Conclusion:

With CBCT information provided by the SARRP and effective animal immobilization during transport, these findings support the use of offline BLT in close vicinity for accurate soft tissue target localization for irradiation. However, the disadvantage of the off‐line system is reduced efficiency as care is required to maintain stable animal transport. We envisage a dual use system where the on‐board arrangement allows convenient access to CBCT and avoids disturbance of animal setup. The off‐line capability would support standalone longitudinal imaging studies.

The work is supported by NIH R01CA158100 and Xstrahl Ltd. Drs. John Wong and Iulian Iordachita receive royalty payment from a licensing agreement between Xstrahl Ltd and Johns Hopkins University. John Wong also has a consultant agreement with Xstrahl Ltd.