bluuebunny/crossref_metadata_2025 huggingface dataset:
Chip Level Refrigeration of Portable Electronic Equipment Using Thermoelectric Devices
Authors: Solbrekken Gary L. , Yazawa Kazuaki , Bar-Cohen Avram
Published: July 2013

It is well established that the power dissipation for electronic components is increasing. At the same time, high performance portable equipment with volume, weight, and power limitations are gaining widespread acceptance in the marketplace. The combination of the above conditions requires thermal solutions that are high performance and yet small, light, and power efficient. This paper explores the possibility of using thermoelectric (TE) refrigeration as an integrated solution for portable electronic equipment accounting for heat sink and interface material thermal resistances. The current study shows that TE refrigeration can indeed have a benefit over using just a heat sink. Performance maps illustrating where TE refrigeration offers an advantage over an air-cooled heat sink are created for a parametric range of CPU heat flows, heat sink thermal resistances, and TE material properties. During the course of the study, it was found that setting the TE operating current based on minimizing the CPU temperature (Tj), as opposed to maximizing the amount of heat pumping, significantly reduces Tj. For the baseline case studied, a reduction of 20–30°C was demonstrated over a range of CPU heat dissipation. The parametric studies also illustrate that management of the heat sink thermal resistance appears to be more critical than the CPU/TE interfacial thermal resistance. However, setting the TE current based on a minimum Tj as opposed to maximum heat pumping reduces the system sensitivity to the heat sink thermal resistance.
A Review of the Economics of Embedded Passives
Authors: Sandborn Peter A.
Published: July 2013

This paper provides an overview of the economic issues and cost models associated with the conversion of discrete passives to embedded passives in printed circuit boards. Three attributes of economic analysis are included herein: fabrication and manufacturing cost analyses, embedded resistor trim and rework economics, and non-manufacturing life cycle costs that are impacted by the conversion of discrete passives to embedded passives. In addition, a complete set of references to existing work on the economics of embedded passives is provided.
Air Cooled Compact Heat Exchanger Design for Avionics Thermal Management Using Published Test Data
Authors: Hall George , Marthinuss James
Published: July 2013

This paper will discuss air-cooled compact heat exchanger design using published data. Kays & London’s “Compact Heat Exchangers” [1] contains measured heat transfer and pressure drop data on a variety of circular and rectangular passages including circular tubes, tube banks, straight fins, louvered fins, strip or lanced offset fins, wavy fins and pin fins. While “Compact Heat Exchangers” is the benchmark for air cooled heat exchanger test data it makes no attempt to summarize the results or steer the thermal designer to an optimized design based on the different factors or combination of heat transfer, pressure drop, size, weight, or even cost. Using this reduced data and the analytical solutions provided highly efficient compact heat exchangers could be designed. This paper will guide a thermal engineer toward this optimized design without having to run trade studies on every possible heat exchanger design configuration. Typical applications of published fin data in the aerospace and military electronics include electronics cold plates, card rack walls and air-to-air heat exchangers using fan driven and ECS driven air. Airborne electronics often require extremely dense packaging techniques to fit all the required functions into the available volume. While leaving little room for cooling hardware this also drives power densities up to levels (20 W/sq-cm) that require highly efficient heat transfer techniques. Several design issues are discussed including pressure drop, heat transfer, compactness, axial conduction, flow distribution and passage irregularities (bosses). Comparisons between fin performance are made and conclusions are drawn about the applicability of each type of fin to avionics thermal management.
The Effect of Ducting on the Performance of a Vertical Axis Tidal Turbine
Authors: Alidadi Mahmoud , Nabavi Yasser , Calisal Sander
Published: July 2013

The effect of ducting on the performance of a vertical axis tidal turbine is studied. The calculation of the output power is done using a commercial code and a discrete vortex method. The results show that duct can highly boost the performance of the turbine in comparison to a turbine running in an open free stream. Increasing the output power along with providing a structure for mooring of the turbine introduces ducting as one of the best ways to make a reliable and efficient tidal turbine.
Fatigue Fracture Behavior of Steel Pipes With a Pre-Crack
Authors: Lim Jae-Kyoo , Bian Lichun
Published: July 2013

The behaviour of fatigue crack propagation of mild steel pipes, each consisting of an inclined semi-elliptical crack, subjected to axial loading was investigated both experimentally and theoretically. The inclined angle of the crack with respect to the axis of loading varied between 0° and 90°. In the present investigation, the gowth of the fatigue crack was monitored using the AC potential drop technique. The Von Mises yield criterion was applied to define the core region, instead of assuming a core region with a constant distance r from the crack lip. The two commonly employed fracture criteria, i.e., the maximum tensile stress and the minimum strain energy density criteria, were modified by adopting Von Mises elasto-plastic boundary. The results obtained using the innproved fracture criteria are, in most cases, in better agreement with test results as compared with those obtained using the commonly employed fracture criteria.
French RPV Assessment — Contribution of Expertises in Mechanical Analyses
Authors: Bezdikian G. , Rouillon Y. , Bourgoin J.
Published: July 2013

The process used by the French utility, concerning the Reactor Pressure Vessel assessment, applied on 54 PWR NPPs (3-loop and 4-loop Reactors), involves the verification of the integrity of the component by mechanical studies, in the most severe conditions of loading in relation with RTndt (Reference Nil Ductility Transition Temperature), and considering major parameters. This approach, is based on mechanical safety studies, to demonstrate the absence of risk of failure by brittle fracture. For these mechanical studies two major input data are necessary: 1 - the fluence distribution and the values during the lifetime in operation for each NPPs, 2 - the thermal-hydraulic evaluation and temperature distribution values in the downcomer. The main results must show significant margins against initiation of the brittle fracture. The flaws considered in this approach are shallow flaws beneath the cladding (subclad flaws) or in the first layer of cladding. The major tasks and expertises engaged by EDF are: • more precise assessment of the fluence and neutronic calculations, • better knowledge of the vessel material properties, including the effect of radiation, • the NDE inspection program based on the inspection of the vessel wall, with a special NDE tool to inspect the area in subcladding zone, • the evaluation of vessel integrity, the mechanical analysis of margins in major loading conditions. The principal actions conducted during recent years are: • the fuel management optimisation (low-leakage core design) and the new development to evaluate the fluence, • the data gathered from radiation specimen capsules, removed from the vessels (3 loop reactor), within the framework of the radiation surveillance program, and • the thermal-hydraulic-mechanical calculations based on finite element thermal-hydraulic computations and three dimensional elastic-plastic mechanical analyses.
Constraint Based Assessment of Postulated Nozzle Corner Cracks
Authors: Siegele Dieter , Varfolomeyev Igor , Nagel Gerhard
Published: July 2013

Brittle failure for reactor pressure vessels (RPV) under loss of coolant accidents (LOCA) considering strip and plume cooling show the nozzle corner as leading region in load level (e.g. Siegele et al., 1999). For such transients postulated nozzle corner cracks are also leading in crack driving force compared to the fracture toughness of the material. On the other hand, the crack tip constraint and consequently the failure probability is reduced by yielding caused by high thermal stresses and in addition by the crack size being small relative to the bulk of the flange material. Under these conditions, the flaw assessment in the nozzle corner using fracture toughness data obtained on standard specimens with high constraint level is over-conservative. In this situation it is suitable to introduce the loss of crack tip constraint into the brittle failure analysis of the nozzle corner. This investigation focuses on the assessment of surface cracks in the nozzle corner of an RPV. Using the finite element method temperature and stress calculations are carried out for a postulated LOCA event. For crack postulates in the nozzle corner of various size and geometry in the nozzle corner, crack driving parameters (such as the J-integral and the stress intensity factor) are determined as functions of the crack tip temperature. To account for the crack tip constraint, the T-stress is then evaluated and used along with the master curve approach as suggested by Wallin (2001). Significant loss of constraint is found for the nozzle corner resulting in a large shift of the fracture toughness curve to lower temperatures, thus excluding initiation of the crack postulates.
Load History Effect on Plastic Collapse in a Single-Edge Notched SUS316 Subjected to a Combined Tension and Bending
Authors: Izawa Satoru , Matsubara Masaaki , Nezu Kikuo , Sakamoto Kenji
Published: July 2013

This paper is evaluates the effects of load history on the plastic collapse load of stainless steel members with a single-edge notch. It considers, both the tension force due to an internal pressure and the bending moment caused by an earthquake, considered as load cases for a structure. Experimental equipment was specially developed to cope with the indeterminate problems in fracture mechanics. In this experiment, the stress state of a plastic collapse point was assessed using a membrane stress and axial displacement chart as well as a bending stress and deflection angle chart, which is well known as the ligament method. As a result, we successfully developed a new method for assessing plastic collapse under a complex load. We found that a different load history affects the formation of the plastic region and the collapse point position. The effects of load history on the plastic collapse load were not very big.
Predicting Mixed Mode Crack Initiation Angles in Anisotropic Materials Using the Shape of the Crack Tip Core Region
Authors: Khan Shafique M. A. , Khraisheh Marwan K.
Published: July 2013

Accurate simulation of crack propagation paths in engineering materials is what designers and engineers are always looking for. An important element of any simulation package is to define a criterion for crack initiation angles. Many criteria have been proposed to predict crack initiation angles under mixed mode loading. Most of them assume either a constant radius or a Mises type variable radius for the core region at the crack tip. In a recent study, we presented a detailed analysis of the core region and showed strong dependence of mixed mode crack initiation angles on the shape of the core region. In addition, we proposed a criterion based on the shape of the crack tip core region for isotropic materials. Since most engineering materials are anisotropic, it is necessary to modify the criterion developed for isotropic materials. In this study, we investigate the shape of the core region at the crack tip in mixed mode loading for anisotropic materials under different loading conditions. We employ isotropic linear elastic stress field along with Hill’s anisotropic yield criterion at the crack tip and examine the effect of anisotropy on the shape of the core region and its relation to crack initiation angles.
The Behaviour of a Process Zone at the Root of a Deep Sharp Flaw
Authors: Smith E.
Published: July 2013

Many fracture problems involving flaws and cracks can be quantified by using the process zone representation of non-linear behaviour at the root of a flaw or crack. A common way of analysing such situations is to couple a knowledge of the stress distribution along the prospective process zone plane with the weight function approach. In an earlier paper, the author showed that with regard to the behaviour of a process zone at the root of a blunt flaw, i.e. blunter than a semi-circle, one can for practical purposes, use the stress distribution ahead of the actual flaw surface, and input this information into a process zone analysis for a zone emanating from the planar surface of a semi-infinite solid, this being a far simpler procedure. The present paper proceeds to the opposite extreme and considers the behaviour of a process zone at the root of a deep sharp flaw. It is shown that the behaviour can be described, to a very good degree of accuracy, by inputting the stress distribution ahead of the actual flaw root into an analysis of a process zone at the root of a semi-infinite crack in an infinite solid.
Alternative RTNDT for Linde 80 Weld Materials
Authors: Yoon K. K. , Hall J. B.
Published: July 2013

The ASME Boiler and Pressure Vessel Code provides fracture toughness curves of ferritic pressure vessel steels that are indexed by a reference temperature for nil ductility transition (RTNDT). The ASME Code also prescribes how to determine RTNDT. The B&W Owners Group has reactor pressure vessels that were fabricated by Babcock & Wilcox using Linde 80 flux. These vessels have welds called Linde 80 welds. The RTNDT values of the Linde 80 welds are of great interest to the B&W Owners Group. These RTNDT values are used in compliance of the NRC regulations regarding the PTS screening criteria and plant pressure-temperature limits for operation of nuclear power plants. A generic RTNDT value for the Linde 80 welds as a group was established by the NRC, using an average of more than 70 RTNDT values. Emergence of the Master Curve method enabled the industry to revisit the validity issue surrounding RTNDT determination methods. T0 indicates that the dropweight test based TNDT is a better index than Charpy transition temperature based index, at least for the RTNDT of unirradiated Linde 80 welds. An alternative generic RTNDT is presented in this paper using the T0 data obtained by fracture toughness tests in the brittle-to-ductile transition temperature range, in accordance with the ASTM E1921 standard.
Simultaneous Solution Algorithms for Gas-Solid Flows: An Efficient Parallel Line Solver
Authors: De Wilde Juray , Baudrez Edward , Heynderickx Geraldine J. , Vierendeels Jan , Constales Denis , Marin Guy B.
Published: July 2013

A pointwise simultaneous solution algorithm based on dual time stepping was developed by De Wilde et al. (2002). With increasing grid aspect ratios, the efficiency of the point method quickly drops. Most realistic flow cases, however, require high grid aspect ratio grids, with the highest grid spacing in the streamwise direction. In this direction, the stiffness is efficiently removed by applying preconditioning (Weiss and Smith, 1995). In the direction perpendicular to the stream wise direction, stiffness remains because of the viscous and the acoustic terms. To resolve this problem, a line method is presented. All nodes in a plane perpendicular to the stream wise direction, a so-called line, are solved simultaneously. This allows a fully implicit treatment of the fluxes in the line, removing the stiffness in the line wise directions. Calculations with different grid aspect ratios are presented to investigate the convergence behavior of the line method. The line method presented is particularly suited for parallelization. At each pseudo-time step, the lines (typically hundreds) can be solved independently of each other. The Message Passing Interface (MPI) standard (Snir et al., 1996) is used. The communication between the processors can be easily reduced by solving a block of lines per processor. The communication is then limited to information regarding only the outer lines of the block. In common practice, the number of lines is much higher than the number of processors available. In this region of the lines/processor space, the reduction of the calculation time is linear with the number of processors that is used.
Troubleshooting Furnace Operations Using Computational Fluid Dynamics (CFD)
Authors: Mehrotra Vibhor , Diwakar Philip , Vallavanatt Rimon
Published: July 2013

Industrial application of Computational Fluid Dynamics (CFD) requires the solution of complex fluid-flow problems in conjunction with equipment design, process and product development and optimization. For the successful solution of these problems, a high degree of coordination between industrial CFD engineers, software developers, consultants and academic scientists is necessary. In a refinery, CFD may be applied to a variety of problems. In particular, combustion, flames, flares and chemical reaction are of interest because of the physics and the complex nature of the process. Two applications are presented in this paper to demonstrate the use of CFD modeling for improving furnace operations. The first concerns improvements in reboiler operation by changing burner arrangement. A three-burner arrangement has resulted in tube burnout in the past. CFD modeling suggested a four-burner arrangement is better. The recommendation was accepted and implemented by the refinery in 2002. Feedback from the refinery suggests a much cooler furnace operation is observed in the field. The second application concerns predicting Coker furnace operation of as yet uninstalled heater. The Coker radiant section is modeled with 4 burners. Predicting the impact of burner-burner interaction on the radiant heat flux helps in determining the time period for decoke. Several mitigation steps are suggested to increase the run length between decoking intervals. Further recommendation to create a balanced heat flux profile is provided.
3-D Numerical Simulation on Reheater Fouling in a Utility Boiler
Authors: Pang Liping , Sun Baomin
Published: July 2013

A numerical simulation investigation into the furnace and horizontal chimney process in a utility boiler is presented. The work is based on the commercial software FLUENT 6.1. Flow, chemistry, energy, conservation and radiation models are combined with the FLUNENT solver to simulate the process inside the furnace. Radiation and convection models are considered in the horizontal heater. The reheater is processed as a limited thickness heater and the convective heat transfer is considered in this numerical simulation. The temperature and velocity fields are calculated to unveil the process inside and outside the furnace. The result shows that the fouling in reheater is formed because of the temperature and velocity field in the flue gas passage. A limited test is done to validate the numerical simulation.
Numerical Investigations of Arched Vortex Characteristics Generated at T-Junction Piping Systems
Authors: Muramatsu Toshiharu
Published: July 2013

Thermohydraulic analyses for a fundamental water experiment simulating thermal striping phenomena at T-junction piping systems were carried out using a quasi-direct numerical simulation code DINUS-3, which is represented by instantaneous Navier-Stokes equations and deals with a modified third-order upwind scheme for convection terms. Calculated results were compared with experimental results on the flow patterns in the downstream region of the systems, the arched vortex structures under a deflecting jet condition, the generation frequency of the arched vortex, etc. in the various conditions; i.e., diameter ratio α, flow velocity ratio β and Reynolds number Re. From the comparisons, it was confirmed that (1) the DINUS-3 code is applicable to the flow pattern classifications in the downstream region of the T-junction piping systems, (2) the arched vortex characteristics with lower frequency components and their generation possibilities can be estimated numerically by the DINUS-3 code, and (3) special attentions should be paid to the arched vortex generations with lower frequency components of fluid temperature fluctuations in the design of T-junction systems from the viewpoints of the avoidances for the thermal striping.
SU‐A‐141‐01: AAPM Medical Physics Student Meeting: Pathways to a Career in Medical Physics
Authors: Starkschall G , Smith W
Published: July 2013

In the current climate of Medical Physics employment, establishing an entry‐level position may be a daunting task for all individuals seeking to enter the profession. Whether enrolled in a CAMPEP‐accredited graduate program or transitioning from a related field of study, the pathways into Medical Physics have become narrow and competitive. The purpose of this meeting is to summarize available post‐graduate training opportunities en route to ABR certification. Our distinguished speakers will also be happy to answer general questions and address the major concerns of all students and trainees in attendance.
SU‐C‐105‐01: Interferometry for Detection of Temperature Rise in a Water Phantom
Authors: Tosh R
Published: July 2013

Purpose: Imaging of absorbed dose fields directly in a water phantom has been done using ultrasonic phase‐sensitive detection. The question arises as to whether similar or better sensitivity could be obtained via phase‐sensitive detection of optical probe radiation traversing a water phantom. The present study was undertaken to compare the relative thermal sensitivity of optical and ultrasonic probes of water heated by a source capable of elevating the water temperature over a range (∼100 mK) that typifies heating in a radiotherapy beam. Methods: To obtain a direct comparison of the optical and ultrasonic approaches, a dual interferometer was constructed in which both types of probe radiations could sample the same thermal field simultaneously. For the ultrasonic measurements, two 5 MHz contact transducers were placed on opposite sides of a rectangular water phantom (10 ltr), and the phase change along the ultrasonic flight path was measured using an rf lock‐in amplifier. For the optical measurements, a Michelson interferometer was constructed using a HeNe laser as light source, and it was configured so that one of the two arms passed through the water phantom adjacent to the path followed by the ultrasound radiation. A string of power resistors placed in the water, configured to lie parallel to both ultrasonic and laser beam paths, provided heat, and a calibrated thermistor probe provided temperature reference. Results: Both ultrasonic (above) and optical (below) results were found to track temperature changes registered by the thermistor probe, and, moreover, gave results that agreed very well with theory. Preliminary findings indicate that the optical system was ∼25x more sensitive than the ultrasonic system. Conclusion: The preliminary findings suggest that optical interferometry may outperform both ultrasound and thermistor detectors for resolving radiation‐induced changes in water temperature. Testing in radiotherapy beams is planned for the near future.
SU‐C‐105‐04: Measurement of Absorbed Dose Due to Secondary Radiation Produced by Passively Scattered and Uniformly Scanned Proton Beams
Authors: Diffenderfer E , McDonough J , Maughan R
Published: July 2013

Purpose: Using the dual ionization chamber (IC) method we compare the neutron and combined gamma + proton (γ+p) components of absorbed dose in water due to secondary radiation produced by passively scattered and uniformly scanned proton beams collimated by a tungsten MLC. Methods: We adapt the dual IC method of mixed field dosimetry for use in measuring the components of absorbed dose due to secondary radiation produced by proton beams. Measurements are performed in water 5 cm beyond the distal edge and 15 cm lateral to the beam isocenter for passively scattered/uniformly scanned proton beams. Beams with ranges of 15 cm or 25 cm and modulation 10 cm (R15M10 and R25M10) are employed, collimated to 10 × 10 cm field size at isocenter with the MLC. Results: Measured neutron dose per primary proton dose ranges from 0.2–0.4 mGy/Gy for R15M10 and 0.3–0.8 mGy/Gy for R25M10 beams. The secondary γ+p dose is 0.3–0.7 mGy/Gy for R15M10 and 0.5–2.0 mGy/Gy for R25M10. Doses are reported here as physical dose without application of a radiation quality factor. Conclusion: The largest difference in secondary radiation dose for the two modalities is seen at 5 cm beyond the distal edge for R15M10, with increases of 40–50% for neutron dose and 20% for γ+p for scattered over scanned beams. For the R25M10 beam the difference is smaller, about 10% higher neutron and γ+p doses for scattered over scanned beams. Outside the beam at 15 cm lateral to isocenter, the γ+p dose dominates the neutron dose and smaller differences are observed between the two beam delivery modalities. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.
SU‐C‐105‐05: Reference Dosimetry of High‐Energy Electron Beams with a Farmer‐Type Ionization Chamber
Authors: Muir B , Rogers D
Published: July 2013

Purpose: To investigate gradient effects and provide Monte Carlo calculated beam quality conversion factors to characterize the Farmer‐type NE2571 ion chamber for high‐energy reference dosimetry of clinical electron beams. Methods: The EGSnrc code system is used to calculate the absorbed dose to water and to the gas in a fully modeled NE2571 chamber as a function of depth in a water phantom. Electron beams incident on the surface of the phantom are modeled using realistic BEAMnrc accelerator simulations and electron beam spectra. Beam quality conversion factors are determined using calculated doses to water and to air in the chamber in high‐energy electron beams and in a cobalt‐60 reference field. Calculated water‐to‐air stopping power ratios are employed for investigation of the overall ion chamber perturbation factor. Results: An upstream shift of 0.3–0.4 multiplied by the chamber radius, r_cav, both minimizes the variation of the overall ion chamber perturbation factor with depth and reduces the difference between the beam quality specifier (R5 0) calculated using ion chamber simulations and that obtained with simulations of dose‐to‐water in the phantom. Beam quality conversion factors are obtained at the reference depth and gradient effects are optimized using a shift of 0.2r_cav. The photon‐electron conversion factor, k_ecal, amounts to 0.906 when gradient effects are minimized using the shift established here and 0.903 if no shift of the data is used. Systematic uncertainties in beam quality conversion factors are investigated and amount to between 0.4 to 1.1% depending on assumptions used. Conclusion: The calculations obtained in this work characterize the use of an NE2571 ion chamber for reference dosimetry of high‐energy electron beams. These results will be useful as the AAPM continues to review their reference dosimetry protocols.
SU‐C‐105‐07: A New Criterion for Detector Usability in Nonstandard Beam Dosimetry
Authors: Kamio Y , Bouchard H
Published: July 2013

Purpose: To accurately convert the detector signal to absorbed dose to water in nonstandard beams, beam quality correction factors (kQ) are required. To avoid calculating such factors, we define a criterion based on the hypothesis that, for a given detector, kQ is unity within a given tolerance. This allows establishing detector‐specific critical regions to limit the field sizes usable experimentally without the need for evaluating kQ. Methods: A theoretical relation between the relative deviation of kQ from unity and a function that depends on dose response kernels is derived. Kernels are computed using the Monte Carlo user code egs_chamber for water and for three different ionization chambers (Exradin A12, A14 and A1SL), simulating 6 MV photon pencil beams at several lateral positions. Critical regions around the centroid of the chambers that guarantee kQ to remain within +/−0.005 from unity are obtained. For field sizes equal to the critical regions, kQ factors are calculated to validate the theoretical approach. Results: To limit kQ within +/−0.005 from unity, field sizes were determined to be 2.6× 5.2 cm2 for the A12, 3.8 × 3.8 cm2 for the A14 and 2.5 × 2.9 cm2 for the A1SL chamber. The corresponding kQ were found to be 1.0019 +/− 0.0026 for the A12, 1.0001 +/− 0.0047 for the A14 and 1.0011 +/− 0.0024 for the A1SL. These results are found within the expected deviation and fully support the validity of the new criterion. Conclusion: In this study, the limitation of the field size to a detector‐specific critical region allows small beam measurements to be done without the need for evaluating kQ factors. While this work will be extended to other types of detectors, the methodology will serve as a basis to study IMRT beams in the scope of new dosimetry protocols.
SU‐C‐137‐06: What Was the Impact Of European Medical Exposure Directive On Regulation On Clinical Practice Associated with Accidental Exposures, Reporting and Risk Analyses in Radiotherapy?
Authors: Malicki J , Jarvinen H , Godet J , Skrobala A , Valero M , Jahnen A , Przybylska K , Maingon P , Krengli M , Bly R
Published: July 2013

Purpose: The objective of the study was to perform an EU‐wide study on the implementation of the MED requirements aimed at the reduction of the probability and the magnitude of accidents in radiotherapy. Methods: The two‐step questionnaire was carried out using internet‐based facility (Lime survey, www.limesurvey.org) and was sent out to establish the overall status and the legal and practical arrangements in EU Member States. Results: The General questionnaire was sent to 38 countries, from which 21 have replied. 10 more countries have provided some data, but have not finished the questionnaire. The second questionnaire covered more details of the available risk analysis systems, results of such analyses, as well as incident classification, reporting and registration systems. The second questionnaire was completed by respective number of countries: detailed questionnaire ‐ 10, description of local proactive risk assessment/ and retrospective risk analysis ‐ 13, radiotherapy event report ‐ 5, incident reporting systems‐20. More than half of the countries already implemented the legal basis for risk analysis and classification of events, recording and reporting. However, the lack of this basis in many countries and the lack of practical implementation in most of the countries highlight the need for further European guidelines. The factor that influences the current situation in Europe is its diversity, variety of legal systems and different radiotherapy care organizations. Conclusion: Fifteen years that passed since the introduction of EU Directive made it clear that next step on European level has to be made. The requirement for legal framework for risk analysis, classification of events, recording and reporting systems has not been addressed in some EU countries, and thus, the practical implementation of the systems in many countries is still incomplete.
SU‐C‐108‐01: Comparison of Fast Rotational IMRT with a 2d Binary Multileaf Collimator (2D‐BMLC) with Helical Tomotherapy (HT)
Authors: Altenstein G , Nill S , Sterzing F , Oelfke U
Published: July 2013

Purpose: We developed a treatment planning system(TPS) for fast rotational IMRT treatments with a 2D‐bMLC. For the dosimetric evaluation of the achievable dose distributions 2D‐bMLC plans were optimized for two patients and compared to HT plans. Methods: Within the TPS a treatment machine with a FFF 7MV linac source and a 2D‐bMLC was modeled. The total fraction dose is delivered in one gantry rotation within the time TF. 2D‐bMLC plans were generated for TF of 40s(P40), 25s(P25) and 15s(P15). The maximum dose rate was either 2000MU/min(P40, P25) or 4000MU/min(P15). The considered clinical indications were carcinomas of the oral cavity (patient A) and the nasopharyngs(B). For both patients 57.6Gy in 32 fractions were prescribed to the PTV, 70.4Gy to the boost regions. Dose constraints for OARs were the same as for the clinically accepted HT plans (TF=410s and 650s). An additional tool was developed to recompute the 2D‐bMLC plans with a Monte‐Carlo(Geant4.9.5) method, including a realistic model of the collimator absorber and gantry dynamic. Results: Concerning dose to the OARs the 2D‐bMLC plans are in good agreement with the HT plans. Target conformity was increased and the mean dose to healthy tissue was decreased by >10%(A) and >20%(B) respectively. For patient A, 95%‐coverage of the boost regions was the same as for the HT plan. Coverage of PTV was 95%(P40), 94%(P25) and 93%(P15) compared to 97%(HT). Patient B had larger target volumes. Compared to HT the coverage was decreased by ∼4% for the boosts and ∼3% for the PTV. Target dose inhomogeneity(TDI) was increased(diff.<5%). Concerning these parameters, best results were obtained with P40. Conclusion: Clinically acceptable 2D‐bMLC plans were optimized for both patients. For patient A, dosimetric parameters are comparable to the HT plan. For patient B, some minor degradation has to be accepted for the significant reduction in treatment time. This work was partially supported by Siemens Corporate Research.
SU‐C‐108‐03: Investigation of MLC Leaf Tolerance and Dose Accuracy in VMAT Delivery
Authors: Song Y , Zhang Q , Mueller B , Obcemea C , Mychalczak B
Published: July 2013

Purpose: VMAT employs a multi‐parameter modulation methodology. It tends to perform less reliably than the one‐dimensional IMRT. Therefore, setting a suitable leaf positioning tolerance on the machine is crucial. In this study, we investigated the relationship between the leaf tolerance and the dose delivery accuracy for VMAT SBRT lung plans. The goal was to determine the optimal leaf tolerance for daily VMAT SBRT treatments. Methods: The study was performed on a VMAT‐enabled Trilogy LINAC. To minimize the systematic bias in leaf and gantry speeds, all the VMAT SBRT plans had a prescription dose of 1800 cGy × 3. Prior to each plan delivery, the leaf positioning tolerance was reset to a new value in Machine Hardware Configuration in Treatment Administration. Upon completion of the plan delivery, the Dynalog Files and, more importantly, the Treatment Log File, i.e., the Dlog File, were saved and exported for post‐processing. For our initial investigation, we tested leaf tolerance values of 1, 2, 3, 4, 5, and 6 mm, respectively. Results: We found that when the leaf tolerance was set to a tighter value, such as 1, 2, and 3 mm, a good delivery accuracy was preserved without any MLC interlock occurrences. However, when the leaf tolerance was increased to be greater than a threshold value, such as 3 mm in this case, the delivery accuracy deteriorated almost linearly beyond that point. We also found that except for the leaf tolerance = 1 mm, the gantry angle accuracy virtually remained unchanged as the leaf tolerance was increased, indicating a decoupling between the leaf tolerance and the gantry angle uncertainty. Conclusion: We recommend that for VMAT SBRT lung plans with a prescription dose of 1800 cGy × 3, the optimal leaf tolerance should be set to 3 mm.
SU‐C‐108‐05: A Novel Technique to Evaluate 4D Dose Delivery to a Moving Tumor
Authors: Aliotta E , Read P , Benedict S , Larner J , Wijesooriya K
Published: July 2013

Purpose: Delivering highly modulated radiation beams accurately to a moving tumor is a difficult task; it is crucial to have tools to evaluate the efficacy of treatment delivery in such cases. We are reporting a novel technique to evaluate 4D dose delivery to moving tumors. We are also presenting an evaluation of RapidArc treatment delivery using this method. 4D position dependant dose is crucial because the peripheral regions of the tumor may not get adequate dose due to moving out of the MLC aperture. In our procedure we accomplish the position dependant dose evaluation by creating the effects of tumor motion as follows: instead of moving the tumor, we simulate to move the active MLCs in the direction opposite to tumor motion by the corresponding motion amplitude calculated at the time of delivery. Methods: Ten RapidArc plans were created, delivered at a Varian Trilogy unit and corresponding log files were recorded. A simulation, written in MATLAB, reads in the dynalog files, and calculates average time per each control point delivery with respect to beam initiation. A sinusoidal respiratory motion signal with a given maximum amplitude and period was implemented to obtain the motion amplitude at the time of delivery of each control point. A modified DICOM file was created where the active MLCs were moved to simulate the effects of tumor motion. This DICOM plan was reimported to Eclipse treatment planning system, and 4D dose was recalculated. To verify the accuracy of our simulation, a sample plan with 2.5cm motion amplitude was compared with delivery. Results: Simulation agrees well with the dose measurement (3% /3mm gamma acceptance of 98%). GTV under‐dosing is observed for large motion amplitudes, and small tumor volumes. Conclusion: A novel technique is developed to obtain delivered 4D dose distributions for moving tumors using machine log files.
SU‐C‐500‐01: Quantifying the Impact of Intra‐Prostatic Calcifications and Seed Orientation in Low‐Dose Rate Prostate Brachytherapy Using Monte‐Carlo Dose Calculations
Authors: Fekete C‐A Collins , Plamondon M , Martin A , Vigneault E , Beaulieu L
Published: July 2013

Purpose: To quantify the impact intra‐prostatic calcifications and seed orientation in prostate brachytherapy using Monte‐Carlo (MC) dose calculations. Methods: MC simulations were made with ALGEBRA (based on Geant4 C/C++ toolkit v4.9.6.p01) to simulate dose deposition in 1mm3 voxelized geometries using post‐planning exported DICOMRT files. Materials are assigned from the physicians contours, based on TG186 recommendations, and electron density from CT number. SelectSeed and OncoSeed6711 seeds are modeled and place in the CT geometries. 3D dose maps, isodoses, DVHs and dosimetric indices for each structure are calculated. Orientation study: Orientations are obtained using automated seed detection from five fluoroscopic projections. Five dose algorithms are compared: TG43 1D(1), TG43 2D (parallel to the CT scans (2)/ with orientations (3)) and MC (parallel (4) /with orientations (5)). Calcifications study: Breast calcification definition is used to define the prostate calcification. 6 different scenarios were tested: water‐based MC with (1) and without (2) seeds fully modeled, 2) water‐based prostate MC with densities from the CT and calcification areas with (3) and without seeds (4) and full heterogeneities with (5) and without seeds (6). Results: Orientation study: Calculations on 296 clinical geometries indicate no significant difference between parallel and oriented seeds for prostate and urethra but an average difference of 3% (min‐max = X‐Y%) for rectum and bladder between TG43 and MC. Calcification study: 42 patients (out of 296) with observable calcifications were analyzed. We measure, large differences relative to TG43, up to −27(−28)% for D90 (V100) when all materials are defined and seeds modeled, and up to −25(−22)% when only the calcified areas are considered. Conclusion: Large patient cohorts have been analyzed to extract the (previously neglected) effect of seed orientations and calcification. Significant discrepancies relative to TG‐43 have been outline. Correlation to toxicities and survival will be studied in a forthcoming study. NSERC ‐ Natural Sciences and Engineering Research Council of Canada
SU‐C‐500‐02: Comparison of a Commercial Electronic Brachytherapy Source and Ir‐192/Co‐60 HDR Source for Endometrial and Cervical Cancers
Authors: Mobit P , Nguyen A , Yang C
Published: July 2013

Purpose: To evaluate the dosimetric differences between Iridium‐192, Co‐60 based HDR plans and plans generated by electronic brachytherapy source (EBS) for cervical and endometrial cancers. Material/Methods: Our institution uses volume based planning for each tandem and ovoid (T&O) or vaginal cylinder insertion and treatment. We attempt to characterize the differences between the three sources (Ir‐192, Co‐60 and EBS). For vaginal cylinder cases, patients receive 6 Gy x3 prescribed to a depth 5 mm. For T&O cases, the prescription is 8Gy x3 to point A. Organs at risk (OARs) contoured were rectum, bladder, sigmoid & small bowel. Our planning protocol requires adjustment of source dwell times and positions to keep doses to the OARs below 70% of the prescription dose. For vaginal cylinder, dose coverage is optimized to a line drawn 5mm from the vaginal cylinder surface. This is a retrospective study of previously planned Ir‐192 treated patients. Results: There is no difference between the Co‐60 and Ir‐192 plans but plans generated using the EBS offer better sparing of OARs as evaluated using the dose to highest 2cc of the organ at risk but the differences are not statistically significant. However, there are significant differences in the DVH between EBS and the other two sources. There was a reduction of up to 50% between EBS and other two sources using v15%, v25%, v50% v75% (% of volume getting 15, 50, 75 percent of the prescription dose). Conclusion: All three sources are suitable for HDR Brachytherapy but the use of EBS can reduce the organ at risk dose while achieving similar dose coverage. Even though D2cc is the recommended dose volume point for HDR plans evaluation, V15%, V25%, V50% and V75% are also useful indicator of the plan quality as they characterize the lower dose region of the DVH curves more adequately
SU‐C‐500‐03: GGEMS‐Brachy: Fully GPU Geant4‐Based Efficient Monte Carlo Simulation for Brachytherapy Applications
Authors: Lemarechal Y , Bert J , Boussion N , Pradier O , Visvikis D
Published: July 2013

Purpose: In brachytherapy, dosimetric plans are routinely calculated with the TG43 formalism which considers the patient as a simple water box. However, an accurate modeling of the physical processes considering patient heterogeneity using Monte Carlo (MC) methods is currently too time‐consuming and computationally demanding to be routinely used. As solution we implemented an accurate and fast MC simulation on graphics processing unit (GPU) for brachytherapy (HDR and LDR) applications. Methods: Based on Geant4 a MC simulation framework was developed on GPU. This framework was extended to include a hybrid GPU navigator, allowing navigation within a voxelized phantom derived from CT imaging including an analytical based structure for accurately modeling the 125I seeds (Source Tech Medical STM1251). In addition, dose scoring based on TLE including uncertainty calculations was incorporated. The implemented full GPU based modeling was compared with a classical CPU MC simulation based on GATE/GEANT4, as well as previously proposed GPU approaches based on the use of phasespace files for the seeds and their positioning based on simple replacement of voxels within the CT volumes. Results: Energy distribution from the seed and dose mapping including uncertainty were compared showing a high agreement (differences <1%). Preliminary results have shown that the GPU implementation is faster by at least two orders of magnitude compared to the GATE mono‐CPU version. A comparison between dosimetric plans based on TG43 and a full MC simulation using the GPU code for LDR prostate brachytherapy led to 40%–100% differences depending on the level of tissue heterogeneity. Conclusion: We propose a full GPU MC simulation based on Geant4, with a hybrid navigator dedicated for brachytherapy applications. Our evaluation shows large dose differences compared to the simplistic TG43 formalism in LDR and very fast execution times compatible with clinical practice.
SU‐C‐500‐06: Development of a Hybrid Stochastic‐Deterministic Method for Dose Calculation in Radiotherapy
Authors: Hayward R , Rahnema F
Published: July 2013

Purpose: To develop a hybrid stochastic‐deterministic method, COMET‐PE, for dose calculation in external beam photon radiotherapy. Methods: To calculate dose, COMET‐PE solves the coupled Boltzmann Transport Equations for photons and electrons. The method uses a deterministic iteration to compose response functions that are pre‐computed using Monte Carlo. Thus, COMET‐PE takes advantage of Monte Carlo physics without incurring the computational costs typically required for statistical convergence. Dose distributions are calculated for a heterogeneous benchmark problem using both COMET‐PE and DOSXYZnrc (Monte Carlo) methods. The benchmark consists of a CT‐based lung phantom, composed of air, lung, soft tissue, and bone, irradiated by a 2 cm × 2 cm photon field. The 6 MV source spectrum comes from Monte Carlo simulation of a Varian Clinac 2100. The COMET‐PE solution is computed at resolution of 1 mm (27,648,000 voxels) before being reduced to a resolution of 5 mm (221,184 voxels) for compatibility with the DOSXYZnrc reference solution. Results: The agreement between dose distributions calculated with COMET‐PE and Monte Carlo is excellent. Of voxels receiving greater than 10% of the maximum dose, 98.73% pass the 2% (point‐wise relative difference) or 2 mm (distance‐to‐agreement) criterion and 99.38% pass the 3% / 3 mm criterion. Localized discrepancies are observed at the beam corners; these are caused by the difficulty of using a continuous representation for the discontinuous primary fluence. Most of the failures, however, occur where the beam exits the phantom and where Monte Carlo uncertainties are the highest. The COMET‐PE calculation is over 10 times faster than the Monte Carlo reference solution. Conclusion: The COMET‐PE method calculates dose with accuracy comparable to Monte Carlo while using only a fraction of the time and providing a solution with orders of magnitude more detail.