bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optimal Control of Planar Musculoskeletal Arm Model With Minimum Muscles Stress Criterion
Authors: Sharifi Mojtaba , Salarieh Hassan , Behzadipour Saeed
Published: August 2016

In this paper, the optimal performance of a planar humanlike musculoskeletal arm is investigated during reaching movements employing an optimal control policy. The initial and final states (position and velocity) are the only known data of the response trajectory. Two biomechanical objective functions are taken into account to be minimized as the central nervous system (CNS) strategy: (1) a quadratic function of muscle stresses (or forces), (2) total time of movement plus a quadratic function of muscle stresses. A two-degress of freedom (DOF) nonlinear musculoskeletal arm model (for planar movements) with six muscle actuators and four state variables is used in order to evaluate the proposed optimal policy, while the constraints of the arm motion and muscle forces are considered mathematically. The nonlinear differential equations of this optimal control problem with the first objective function are solved using the method of variation of extremals (VE). For the second objective function, a modified version of the VE method is employed. Accordingly, the optimal total time of the motion is predicted via the second objective function in addition to the optimal trajectory and forces that are also predicted using the first objective function. The influence of the motion time duration on the optimal trajectory is shown and discussed. Finally, the obtained optimal trajectories are compared to the experimental trajectories of the human arm movements.
Table-Based Volumetric Error Compensation of Large Five-Axis Machine Tools
Authors: Creamer Jennifer , Sammons Patrick M. , Bristow Douglas A. , Landers Robert G. , Freeman Philip L. , Easley Samuel J.
Published: August 2016

This paper presents a geometric error compensation method for large five-axis machine tools. Compared to smaller machine tools, the longer axis travels and bigger structures of a large machine tool make them more susceptible to complicated, position-dependent geometric errors. The compensation method presented in this paper uses tool tip measurements recorded throughout the axis space to construct an explicit model of a machine tool's geometric errors from which a corresponding set of compensation tables are constructed. The measurements are taken using a laser tracker, permitting rapid error data gathering at most locations in the axis space. Two position-dependent geometric error models are considered in this paper. The first model utilizes a six degree-of-freedom kinematic error description at each axis. The second model is motivated by the structure of table compensation solutions and describes geometric errors as small perturbations to the axis commands. The parameters of both models are identified from the measurement data using a maximum likelihood estimator. Compensation tables are generated by projecting the error model onto the compensation space created by the compensation tables available in the machine tool controller. The first model provides a more intuitive accounting of simple geometric errors than the second; however, it also increases the complexity of projecting the errors onto compensation tables. Experimental results on a commercial five-axis machine tool are presented and analyzed. Despite significant differences in the machine tool error descriptions, both methods produce similar results, within the repeatability of the machine tool. Reasons for this result are discussed. Analysis of the models and compensation tables reveals significant complicated, and unexpected kinematic behavior in the experimental machine tool. A particular strength of the proposed methodology is the simultaneous generation of a complete set of compensation tables that accurately captures complicated kinematic errors independent of whether they arise from expected and unexpected sources.
Transient Simulations of the Fluid–Structure Interaction Response of a Partially Confined Pipe Under Axial Flows in Opposite Directions
Authors: Kontzialis Konstantinos , Moditis Kyriakos , Païdoussis Michael P.
Published: August 2016

This paper presents a numerical study of the dynamic response and stability of a partially confined cantilever pipe under simultaneous internal and external axial flows in opposite directions. The onset of flow-induced vibrations is predicted by the developed numerical model, and moreover, limit-cycle motion occurs as the flow speed becomes larger than a critical value. The numerical results are in good agreement with existing experimental results. The simulation gives control over many physical parameters and provides a better insight into the dynamics of the pipe. A parametric study regarding the stability of the system for varying confinement length is performed. The current results show that there is an increase in the susceptibility of the system to instability as the extent of confinement is increased.
Piping Fragility Evaluation: Interaction With High-Rise Building Performance
Authors: Ju Bu Seog , Gupta Abhinav , Ryu Yong Hee
Published: August 2016

Many recent studies have emphasized the need for improving seismic performance of nonstructural systems in critical facilities in order to reduce the damage as well as to maintain continued operation of the facility after an earthquake. This paper is focused on evaluating system-level seismic fragility of the piping in a representative high-rise building. Piping fragilities are evaluated by incorporating the nonlinear finite-element model of a threaded Tee-joint that is validated using experimental results. The emphasis in this study is on evaluating the effects of building performance on the piping fragility. The differences in piping fragility due to the nonlinearities in building are evaluated by comparing the fragility curves for linear frame and nonlinear fiber models. It is observed that as nonlinearity in the building increases with increasing value of peak ground acceleration, the floor accelerations exhibit a reduction due to degradation/softening. Consequently, the probabilities of failure increase at a slower rate relative to that in a linear frame. It is also observed that a piping located at higher floor does not necessarily exhibits high fragilities, i.e., the fundamental building mode is not always the governing mode. Higher order building modes with frequencies closest to critical piping modes of interest contribute more significantly to the piping fragility. Within a particular building mode of interest, a good indicator of the amplification at different floor levels can be obtained by the product of mode shape ordinate and modal participation factor. Piping fragilities are likely to be higher at floor levels at which this product has a higher value.
Unique Design of Pressure Vessel With Tooth-Locked Quick-Actuating Closures Based on Finite Element Model Analysis
Authors: Su Wenxian , Geng Wanyi , Widera G. E. O.
Published: August 2016

A novel method is developed for the design of pressure vessels with tooth-locked quick-actuating closures by considering the contact between the teeth and utilizing the surface-to-surface contact model with contact element and coulomb friction. Elastic and elastic–plastic analyses via the finite element method were employed. It is shown that these pressure vessels can meet the requirements of strength and fatigue.
Dynamic Characteristics of Spiral-Grooved Opposed-Hemisphere Gas Bearings
Authors: Yang Guangwei , Du Jianjun , Ge Weiping , Liu Tun , Yang Xiaowei
Published: August 2016

The traditional eight-coefficient bearing model only considers the translational motion of the bearings and neglects the tilting motion and coupling effects between them. In this paper, the dynamic characteristics of the spiral-grooved opposed-hemisphere gas bearing considering five degrees-of-freedom are studied, and 50 dynamic coefficients including the translational, tilting, and coupling components are completely calculated. The Reynolds equations and their perturbed equations are solved by the finite element method to obtain the dynamic stiffness and damping coefficients. The effects of the tilting motion on the dynamic coefficients and response are analyzed, respectively. The results show that the coupling coefficients between the translational and tilting motions, which have been neglected in most previous studies, are significant at large eccentricity ratio. But these coupling coefficients have little effect on the dynamic response. On the other hand, the influences of the tilting motion on the synchronous response and natural frequency are remarkable and will decrease the stability of the rotor bearing system.
The Geometric Role of Precisely Engineered Imperfections on the Critical Buckling Load of Spherical Elastic Shells
Authors: Lee Anna , López Jiménez Francisco , Marthelot Joel , Hutchinson John W. , Reis Pedro M.
Published: August 2016

We study the effect of a dimplelike geometric imperfection on the critical buckling load of spherical elastic shells under pressure loading. This investigation combines precision experiments, finite element modeling, and numerical solutions of a reduced shell theory, all of which are found to be in excellent quantitative agreement. In the experiments, the geometry and magnitude of the defect can be designed and precisely fabricated through a customizable rapid prototyping technique. Our primary focus is on predictively describing the imperfection sensitivity of the shell to provide a quantitative relation between its knockdown factor and the amplitude of the defect. In addition, we find that the buckling pressure becomes independent of the amplitude of the defect beyond a critical value. The level and onset of this plateau are quantified systematically and found to be affected by a single geometric parameter that depends on both the radius-to-thickness ratio of the shell and the angular width of the defect. To the best of our knowledge, this is the first time that experimental results on the knockdown factors of imperfect spherical shells have been accurately predicted, through both finite element modeling and shell theory solutions.
Fractional Differential Equations With Dependence on the Caputo–Katugampola Derivative
Authors: Almeida Ricardo , Malinowska Agnieszka B. , Odzijewicz Tatiana
Published: August 2016

In this paper, we present a new type of fractional operator, the Caputo–Katugampola derivative. The Caputo and the Caputo–Hadamard fractional derivatives are special cases of this new operator. An existence and uniqueness theorem for a fractional Cauchy-type problem, with dependence on the Caputo–Katugampola derivative, is proved. A decomposition formula for the Caputo–Katugampola derivative is obtained. This formula allows us to provide a simple numerical procedure to solve the fractional differential equation (FDE).
A Large-Eddy Simulation–Linear-Eddy Model Study of Preferential Diffusion Processes in a Partially Premixed Swirling Combustor With Synthesis Gases
Authors: Li Shaoshuai , Zheng Yunzhe , Mira Daniel , Li Suhui , Zhu Min , Jiang Xi
Published: August 2016

A lean partially premixed swirling combustor operated with synthesis gases is studied using large-eddy simulation (LES). The linear-eddy model (LEM) is employed to close the unresolved scalar fluxes with the nonunity Lewis number assumption. Several terms resulting from the LES filtering operation are not modeled but directly resolved considering their unique length and time scales, such as molecular diffusion, scalar mixing, and chemical reactions. First, the validation results on a well-established jet flame indicate a good level of correlation with the experimental data and allow a further analysis of syngas combustion on a practical combustor. Second, the effects of preferential diffusion on the characteristics of flow and combustion dynamics on a lean partially premixed swirling combustor are investigated. The obtained results are expected to provide useful information for the design and operation of gas turbine combustion systems using syngas fuels.
Large-Eddy Simulation of Soot Formation in a Model Gas Turbine Combustor
Authors: Koo Heeseok , Hassanaly Malik , Raman Venkat , Mueller Michael E. , Peter Geigle Klaus
Published: August 2016

The computational modeling of soot in aircraft engines is a formidable challenge, not only due to the multiscale interactions with the turbulent combustion process but the equally complex physical and chemical processes that drive the conversion of gas-phase fuel molecules into solid-phase particles. In particular, soot formation is highly sensitive to the gas-phase composition and temporal fluctuations in a turbulent background flow. In this work, a large-eddy simulation (LES) framework is used to study the soot formation in a model aircraft combustor with swirl-based fuel and air injection. Two different configurations are simulated: one with and one without secondary oxidation jets. Specific attention is paid to the LES numerical implementation such that the discrete solver minimizes the dissipation of kinetic energy. Simulation of the model combustor shows that the LES approach captures the two recirculation zones necessary for flame stabilization very accurately. Further, the model reasonably predicts the temperature profiles inside the combustor. The model also captures variation in soot volume fraction with global equivalence ratio. The structure of the soot field suggests that when secondary oxidation jets are present, the inner recirculation region becomes fuel lean, and soot generation is completely suppressed. Further, the soot field is highly intermittent suggesting that a very restrictive set of gas-phase conditions promotes soot generation.
Sci‐Thur AM: YIS – 09: Treatment Time Optimization for Trajectory‐Based Deliveries
Authors: Wilson Byron , Gete Ermias
Published: August 2016

Introduction:

Couch‐gantry trajectory based deliveries are capable of producing high quality Stereotactic Radiosurgery (SRS) treatments in a time efficient manner. In this work we present two methods for treatment time optimization of these deliveries.

Methods:

Dosimetrically optimal plans were calculated by optimizing MLC and dose rates along a trajectory which encapsulates 4π geometry. This trajectory was used to benchmark time optimization methods. Two methods of treatment time optimization were developed in this study. The first of which relies on a trajectory which samples phase space variably dependent on a selected sampling frequency. Treatment plans were created with decreased sampling frequencies until the treatment quality was deleteriously effected and the most time efficient delivery was selected. The second method uses a gradient descent algorithm to remove time inefficient sections of a trajectory and subsequently re‐optimizes the MLC and dose rates to form a new, time optimized trajectory.

Results:

Both methods were capable of producing treatment plans which were dose equivalent to the benchmark 4π geometry plan. The methods reduced treatment time of 12Gy fractions by 18% and 13% for the first and second method respectively. Both methods had a more pronounced time saving benefits for 2Gy fractions, for which delivery time was decreased by 53% and 34% for the first and second method respectively.

Conclusion:

The methods presented were capable of producing highly conformal SRS treatment plans. These treatments took an average time of 109 seconds for fractionated deliveries and 394 seconds as single fraction deliveries.
Poster – 13: Evaluation of an in‐house CCD camera film dosimetry imaging system for small field deliveries
Authors: Lalonde Michel , Alexander Kevin , Olding Tim , Schreiner L. John , Kerr Andrew T.
Published: August 2016

Purpose:

Radiochromic film dosimetry is a standard technique used in clinics to verify modern conformal radiation therapy delivery, and sometimes in research to validate other dosimeters. We are using film as a standard for comparison as we improve high‐resolution three‐dimensional gel systems for small field dosimetry; however, precise film dosimetry can be technically challenging. We report here measurements for fractionated stereotactic radiation therapy (FSRT) delivered using volumetric modulated arc therapy (VMAT) to investigate the accuracy and reproducibility of film measurements with a novel in‐house readout system. We show that radiochromic film can accurately and reproducibly validate FSRT deliveries and also benchmark our gel dosimetry work.

Methods:

VMAT FSRT plans for metastases alone (PTVMET) and whole brain plus metastases (WB+PTVMET) were delivered onto a multi‐configurational phantom with a sheet of EBT3 Gafchromic film inserted mid‐plane. A dose of 400 cGy was prescribed to 4 small PTVMET structures in the phantom, while a WB structure was prescribed a dose of 200 cGy in the WB+PTVMET iterations. Doses generated from film readout with our in‐house system were compared to treatment planned doses. Each delivery was repeated multiple times to assess reproducibility.

Results and Conclusions:

The reproducibility of film optical density readout was excellent throughout all experiments. Doses measured from the film agreed well with plans for the WB+PTVMET delivery. But, film doses for PTVMET only deliveries were significantly below planned doses. This discrepancy is due to stray/scattered light perturbations in our system during readout. Corrections schemes will be presented.
Poster ‐ 15: Air kerma rate measurements using a cylindrical free‐air ionization chamber on the 05B1‐1 beamline at the Canadian Light Source
Authors: Anderson Danielle , Siegbahn Albert , Fallone Gino , Warkentin Brad
Published: August 2016

Purpose:

The BioMedical Imaging and Therapy (BMIT) beamlines at the Canadian Light Source offer the opportunity for investigating novel imaging and therapy applications of synchrotron radiation. A necessary component in advancing this research, and in progressing toward clinical applications, is the availability of accurate dosimetry that is traceable to a standards institution. However, dosimetry in this setting is challenging. These beams are typically small, non‐uniform, and highly intense. This work describes air kerma rate measurements on a BMIT beamline using a free‐air ionization chamber (FAC).

Methods:

The measurements were taken at the 05B1‐1 beamline (∼8 – 100 keV) for several beam qualities with mean energies between 20.0 and 84.0 keV. The Victoreen Model 480 cylindrical FAC, with a specially fabricated 0.52 mm diameter aperture, was used to measure air kerma rates. The required correction factors were determined using a variety of methods: tabulated data, measurements, theoretical calculations and Monte Carlo simulations (EGSnrc user code egs_fac).

Results:

The experimental air kerma rates measured between 0.270 ± 13.6% and 312 ± 2.7% Gy/min. At lower energies (low filtration), the most impactful correction factors were those for ion recombination and for x‐ray attenuation.

Conclusions:

These measurements marked the first absolute dosimetry performed at the BMIT beamlines. The experimental and Monte Carlo methods developed will allow air kerma rates to be measured under other experimental conditions, provide a benchmark to which other dosimeters will be compared, and provide a reference for imaging and therapy research programs on this beamline.
Poster ‐ 18: New features in EGSnrc for photon cross sections
Authors: Ali Elsayed , Mainegra‐Hing Ernesto , Rogers David W.O.
Published: August 2016

Purpose:

To implement two new features in the EGSnrc Monte Carlo system. The first is an option to account for photonuclear attenuation, which can contribute a few percent to the total cross section at the higher end of the energy range of interest to medical physics. The second is an option to use exact NIST XCOM photon cross sections.

Methods:

For the first feature, the photonuclear total cross sections are generated from the IAEA evaluated data. In the current, first‐order implementation, after a photonuclear event, there is no energy deposition or secondary particle generation. The implementation is validated against deterministic calculations and experimental measurements of transmission signals. For the second feature, before this work, if the user explicitly requested XCOM photon cross sections, EGSnrc still used its own internal incoherent scattering cross sections. These differ by up to 2% from XCOM data between 30 keV and 40 MeV. After this work, exact XCOM incoherent scattering cross sections are an available option. Minor interpolation artifacts in pair and triplet XCOM cross sections are also addressed. The default for photon cross section in EGSnrc is XCOM except for the new incoherent scattering cross sections, which have to be explicitly requested. The photonuclear, incoherent, pair and triplet data from this work are available for elements and compounds for photon energies from 1 keV to 100 GeV.

Results:

Both features are implemented and validated in EGSnrc.Conclusions: The two features are part of the standard EGSnrc distribution as of version 4.2.3.2.
Poster ‐ 34: Clinical Implementation of Prone Breast Treatment
Authors: Jiang Runqing , Fleming Katrina , Kobeleva Sofya , Osei Ernest
Published: August 2016

Purpose:

Prone breast treatment is used to reduce acute and late toxicities for large or pendulous breast patients. This study developed and implemented the clinical workflow of prone breast radiotherapy treatment.

Methods:

Varian kVue Access360™ Prone Breast Couchtop was used as prone breast board. The treatment planning (TP)is performed in Eclipse TP system. TP comparisons between supine deep inspiration breathing hold (DIBH) and prone breast; prone forward field‐in‐field (FinF) planning and inverse IMRT planning were performed and discussed. For the daily setup, breast coverage was assessed in the room using light field and MV imaging was used at day 1 and weekly.

Results:

The first ten patients are CT scanned and planned both supine and prone. The coverage was all excellent for supine DIBH plan and prone breast plan. The plan in the prone position demonstrated improvements in lung sparing comparing to the DIBH plan. Both forward FinF plan and inverse IMRT plan achieved acceptable coverage of the breast, and heart dose is comparable. Considering the daily setup variations and MLC leakage, forward FinF plan was recommended for routine clinical use. The procedure has been tested in phantom and patients were treated clinically.

Conclusions:

Prone breast irradiation has been advocated for women with large pendulous breasts in order to decrease acute and late toxicities. The workflow for prone breast radiation therapy has been developed and the technique is ready to treat patients.
Poster ‐ 37: Pre‐clinical geometric, dosimetric and timing assessment of head and neck OARs using an in‐house atlas‐based auto‐segmentation (ABAS) tool
Authors: Khawandanh Eman , McVicar Nevin , Duzenli Cheryl
Published: August 2016

Purpose:

This study aims to validate the geometric and dosimetric performance of our in‐house ABAS tool using manual inter‐observer variation as benchmark data.

Materials and methods:

An in‐house ABAS constructed, using MIM MaestroTM version 6.5, from 36 previously treated head and neck cases. 15 OARs of eight nasopharynx patients were segmented via three observers from the same institution and using the in‐house ABAS. Percentage of volume differences (ΔV%,), degree of overlap (DICE), distance‐to‐agreement and the standard deviation of absolute dose difference ΔD SD(Gy) among the eight cases [ΔDmax SD(Gy) for serial organs and ΔDmean SD(Gy) for parallel organs] were compared between the manual segmentation and original ABAS contours for each OAR.

Results:

The geometric results indicated that ABAS ΔV% was within 1SD from the manual segmentation. DICE showed that manual segmentation marginally outperformed ABAS in the delineation of parotid glands, submandibular glands, and laryngopharynx, but ABSA performed as well as the manual segmentation or better for all other structures. The distance‐to‐agreement was <1.5 cm for 87% of ABAS structures. From a dosimetric perspective, only ABAS salivary glands demonstrated higher ΔD SD(Gy) compared to manual segmentation. For all other structures ABAS results were similar or better than the manual segmentation. The average time to segment a complete H&N OAR set was <3minutes versus 30minutes for manual segmentation.

Conclusion:

ABAS is a practical time‐saving tool. This study indicated up 90% time‐saving of the operator time per case. ABAS geometric and dosimetric results were within ±1SD inter‐observer variation for most of the structures.
Poster ‐ 54: Development and Evaluation of Normal Tissue Objective Parameters and Avoidance Regions for Prostate Bed VMAT Treatments
Authors: Hudon Luc , Pierce Greg , Roumeliotis Michael
Published: August 2016

Purpose:

A retrospective study was conducted to determine optimal NTO parameters on five patients that were treated with radical prostate doses of 66 Gy in 33 fractions to the prostate bed. The purpose of this work is to evaluate the effectiveness of various NTO settings and also provide insight into whether the use of multiple sparing techniques is beneficial or redundant for a given site.

Methods:

The effect of varying the NTO parameters were systematically examined in conjunction with the option of an avoidance region: a “ring” structure around the planning target volume. Within each of these groups, four plans were made; three with varying NTO settings as well as a fourth control plan not using the NTO. The three NTO settings used were the Varian default values, the automatic setting (a selectable option in the NTO function), and a developed set of test parameters (Manual NTO).

Results:

The site‐specific NTO plans showed the greatest improvement regardless of whether they were used in combination with the ring structure. The most striking improvement in OAR sparing occurred when using the Manual NTO settings without the ring structure. In this setting, the average reduction in mean bladder dose was 473 cGy. The automatic NTO and Varian default settings produced improvements of 146 cGy and 12 cGy, respectively.

Conclusion:

The use of site‐specific NTO parameters produced plans with marked improvement to normal tissue sparing in comparison to plans using the Varian default settings or the automatic NTO.
Poster ‐ 56: Preliminary comparison of FF‐ and FFF‐VMAT for prostate plans with higher rectal dose
Authors: Liu Baochang , Darko Johnson , Osei Ernest
Published: August 2016

Purpose:

A recent retrospective study found 53 patients previously treated to 78Gy/39 using flattened filtered (FF) 6X‐VMAT at GRRCC had rectal DVH more than one standard deviation higher than the average. This study was to investigate if using 6FFFor10FFF beams could reduce these DVHs without compromising target coverage.

Methods:

Twenty patients’ plans were re‐planed with 2‐arc 6X‐VMAT, 6FFF‐VMAT and 10FFF‐VMAT using the Eclipse TPS following departmental protocol. All plans had the same optimization and normalization, and were evaluated against the acceptance criteria from the QUANTEC and Emami. Statistical differences in the mean dose to OARs (Dm) and PTV homogeneity index (HI) between energies were tested using the paired sample Wilcoxon signed rank statistical method (p<0.05). Beam delivery accuracy was checked on five patients using portal dosimetry (PD).

Results:

The PTV HI for the 10FFF shows no statistical difference from the 6X. All the OARs, except left femoral head with 6FFF, have significantly lower Dm using 6FFF and 10FFF. There is no difference in the maximum doses to rectum and bladder and are limited by the prescribed doses. Measurements show good agreements in the gamma evaluation (3%/3mm) for all energies.

Conclusion:

This preliminary study shows that doses to the OARs are reduced using 10FFF for the same target coverage. The plans using 6FFF result in lower doses to some OARs, and statistically different PTV HI. All plans showed very good agreement with measurements.
Poster ‐ 57: Statistical analysis of setup correction for radical IMRT lung patients on a treatment couchtop with six degrees of freedom
Authors: Cisa‐Pare Elisabeth , Ali Elsayed , Nyiri Balazs
Published: August 2016

Purpose:

To characterize the distributions of setup corrections for radical IMRT lung patients treated on a couchtop with six degrees of freedom (6DOF).

Methods:

Translational and rotational setup corrections were retrospectively analyzed for patients treated on the HexaPODTM 6DOF couchtop. Conventional and hypo‐fractioned radical IMRT lung treatments were included, for a total of 152 patients and 2,042 fractions. The distribution of setup corrections was analyzed for each DOF. Potential correlations between pairs of corrections were examined and possible causes identified. Intra‐patient variability of setup corrections was characterized.

Results:

For lateral, longitudinal and vertical setup corrections, the mean ± 1 S.D. (in mm) were: −0.6 ± 3.8, 2.8 ± 5.1, and 1.1 ± 3.9. Each of the three means is statistically significant from the theoretical population mean of zero (p<0.01). For rotations, the means were within 0.1° from zero, with a standard deviation of 1.3°. Moderate correlation (r = −0.45) was observed between longitudinal and pitch corrections, which can be caused by changes in the spinal column position, to which registration is mostly done. The standard deviation for intra‐patient corrections varies among patients: 2 – 10 mm for translations and 0.5 – 3° for rotations. Intra‐patient variability in translations has a positive correlation with that in rotations.

Conclusions:

In 6DOF setup corrections for lung patients, systematic translational corrections were observed, with moderate correlation between longitudinal and pitch corrections. Careful setups and custom immobilization may help reduce such offsets, correlations, and intra‐patient setup variability.
Sci‐Fri AM: Quality, Safety, and Professional Issues 07: Global Medical Physics Efforts: Closing the Gap
Authors: Van Dyk Jacob (Jake)
Published: August 2016

Purpose:

There is an increasing awareness of the disparity in Medical Physics needs between high income countries (HICs) and low‐to‐middle income countries (LMICs). This is especially evident with the growing incidence of cancer in LMICs. Projections from the recent Lancet Oncology Commission on Expanding Global Access to Radiotherapy indicate that an additional 22,000 Medical Physicists will be required by 2035 to provide uniform access to radiation therapy globally. This paper addresses possibilities and challenges associated with closing the Medical Physics gap between HICs and LMICs.

Methods:

Medical Physics and Oncology related organizations involved in providing support to enhance cancer therapy in LMICs were reviewed, especially as related to education, training and human resource development.

Results:

More than 35 organizations involved in addressing the cancer crisis in LMICs were found. Of these, 16 involve Medical Physics activities, with 7 being specific Medical Physics‐related organizations. Ten of the 16 are involved in some LMIC activities with 6 having a major emphasis on LMIC contexts.

Conclusions:

The development of Medical Physics human resource capacity is a major challenge for LMICs. Fifty‐five countries have no radiation therapy capabilities and by implication no capacity to train Medical Physicists. Overt attention with structured and altruistic actions by HIC contexts will help make inroads into the LMIC needs. Clear options throughout career structures in support of global health considerations combined with strong partnerships between interested parties in HICs and LMICs will enhance the development of safe and resource‐appropriate strategies for advancing Medical Physics capabilities.
Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 08: Retrospective Dose Accumulation Workflow in Head and Neck Cancer Patients Using RayStation 4.5.2
Authors: Wong Olive , Chan Biu , Moseley Joanne , McNiven Andrea , Lindsay Patricia , Bissonnette Jean‐Pierre , Waldron John , Giuliani Meredith , Zhang Beibei
Published: August 2016

Purpose:

We have developed a semi‐automated dose accumulation workflow for Head and Neck Cancer (HNC) patients to evaluate volumetric and dosimetric changes that take place during radiotherapy. This work will be used to assess how dosimetric changes affect both toxicity and disease control, hence inform the feasibility and design of a prospective HNC adaptive trial.

Methods:

RayStation 4.5.2 features deformable image registration (DIR), where structures already defined on the planning CT image set can be deformably mapped onto cone‐beam computed tomography (CBCT) images, accounting for daily treatment set‐up shifts and changes in patient anatomy. The daily delivered dose can be calculated on each CBCT and mapped back to the planning CT to allow dose accumulation. The process is partially automated using Python scripts developed in collaboration with RaySearch.

Results:

To date we have performed dose accumulation on 18 HNC patients treated at our institution during 2013–2015 under REB approval. Our semi‐automated process establishes clinical feasibility. Generally, dose accumulation for the entire treatment course of one case takes 60–120 minutes: importing all CBCTs requires 20–30 minutes as each patient has 30 to 40 treated fractions; image registration and dose accumulation require 60–90 minutes. This is in contrast to the process without automated scripts where dose accumulation alone would take 3–5 hours.

Conclusions:

We have developed a reliable workflow for retrospective dose tracking in HNC using RayStation. The process has been validated for HNC patients treated on both Elekta and Varian linacs with CBCTs acquired on XVI and OBI platforms respectively.
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 01: Optimization of an organic field effect transistor for radiation dosimetry measurements
Authors: Syme Alasdair
Published: August 2016

Purpose:

To use Monte Carlo simulations to optimize the design of an organic field effect transistor (OFET) to maximize water‐equivalence across the diagnostic and therapeutic photon energy ranges.

Methods:

DOSXYZnrc was used to simulate transport of mono‐energetic photon beams through OFETs. Dose was scored in the dielectric region of devices and used for evaluating the response of the device relative to water. Two designs were considered: 1. a bottom‐gate device on a substrate of polyethylene terephthalate (PET) with an aluminum gate, a dielectric layer of either PMMA or CYTOP (a fluorocarbon) and an organic semiconductor (pentacene). 2. a symmetric bilayer design was employed in which two polymer layers (PET and CYTOP) were deposited both below the gate and above the semiconductor to improve water‐equivalence and reduce directional dependence. The relative thickness of the layers was optimized to maximize water‐equivalence.

Results:

Without the bilayer, water‐equivalence was diminished relative to OFETs with the symmetric bilayer at low photon energies (below 80 keV). The bilayer's composition was designed to have one layer with an effective atomic number larger than that of water and the other with an effective atomic number lower than that of water. For the particular materials used in this study, a PET layer 0.1mm thick coupled with a CYTOP layer of 900 nm provided a device with a water‐equivalence within 3% between 20 keV and 5 MeV.

Conclusions:

organic electronic devices hold tremendous potential as water‐equivalent dosimeters that could be used in a wide range of applications without recalibration.
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 02: Dosimetric effects of gold nanoparticle surface coatings
Authors: Koger Brandon , Kirkby Charles
Published: August 2016

Introduction:

Gold nanoparticles (GNPs) can enhance radiation therapy within a tumour, increasing local energy deposition under irradiation, but experimental evidence suggests the enhancement is not as large as predicted by dose enhancement alone. Many studies neglect to account for surface coatings that are frequently used to optimize GNP uptake and biological distribution. This study uses Monte Carlo methods to investigate the consequences on local dose enhancement due to including these surface coatings.

Methods:

Using the PENELOPE Monte Carlo code system, GNP irradiation was simulated both with and without surface coatings of polyethylene glycol (PEG) of various molecular weights. Dose was scored to the gold, coating, and surrounding water, and the dosimetric differences between these scenarios were examined.

Results:

The simulated PEG coating absorbs a large portion of the energy that would otherwise be deposited in the medium. The mean dose to water was reduced by up to 2.5, 3.5, and 4.5% for GNPs of diameters 50, 20, and 10 nm, respectively. This effect was more pronounced for smaller GNPs, thicker coatings, and low photon source energies where the enhancement due to GNPs is the greatest. The molecular weight of the coating material did not have a significant impact on the dose.

Conclusions:

The inclusion of a coating material in GNP enhanced radiation may reduce the dose enhancement due to the nanoparticles. Both the composition and size of the coating play a role in the level of this reduction and should be considered carefully.
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 04: On 3D Fabrication of Phantoms and Experimental Verification of Patient Dose Computation Algorithms
Authors: Khan Rao , Zavan Rodolfo , McGeachy Philip , Madamesila Joseph , Villarreal‐Barajas Jose Eduardo
Published: August 2016

Purpose:

Transport based dose calculation algorithm Acuros XB (AXB) has been shown to accurately account for heterogeneities mostly through comparisons with Monte Carlo simulations. This study aims at providing additional experimental verification for AXB for flattened and unflattened clinical energies in low density phantoms of the same material.

Materials and Methods:

Polystyrene slabs were created using a bench‐top 3D printer. Six slabs were printed at varying densities from 0.23 g/cm3 to 0.68 g/cm3, corresponding to different density humanoid tissues. The slabs were used to form different single and multilayer geometries. Dose was calculated with AXB 11.0.31 for 6MV, 15MV flattened and 6FFF (flattening filter free) energies for field sizes of 2×2 cm2 and 5×5 cm2. The phantoms containing radiochromic EBT3 films were irradiated. Absolute dose profiles and 2D gamma analyses were performed for 96 dose planes.

Results:

For all single slab, multislab configurations and energies, absolute dose differences between the AXB calculation and film measurements remained <3% for both fields, with slightly poor disagreement in penumbra. The gamma index at 2% / 2mm averaged 98% in all combinations of fields, phantoms and photon energies.

Conclusions:

The transport based dose algorithm AXB is in good agreement with the experimental measurements for small field sizes using 6MV, 6FFF and 15MV beams adjacent to low density heterogeneous media. This work provides sufficient experimental ground to support the use of AXB for heterogeneous dose calculation purposes.
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 09: Stability of a water calorimetry system as a primary standard for absorbed dose to water
Authors: Cojocaru Claudiu , Mui Bryan , McEwen Malcolm , Ross Carl , Klassen Norman , Marchington David
Published: August 2016

Purpose:

To investigate the stability of a water calorimetry system as a primary standard for absorbed dose to water using measurements performed in cobalt‐60 and high‐energy linac photon beams over a span of more than a decade.

Methods:

Calorimetry measures adsorbed dose directly by recording the amount of heat created when ionizing radiation passes through matter. The radiation‐induced temperature rise was measured using two thermistors calibrated against the NRC temperature primary standard, using an AC bridge with lock‐in amplifier for precise measurement. The calorimeter system was operated under thermal equilibrium at 4 °C (to eliminate convection) with drifts in water temperature less than 0.1 mK/min. Seven water vessels of various designs were used to make repeated measurements over the course of 17 years.

Results:

The standard uncertainty achieved for a set of ten calorimeter measurements (4 Gy delivered) was generally well below 0.15 % while the variation between multiple sets for a given vessel was consistent with this value. The long‐term stability of the system combined with inter‐vessel variations indicated that there was good control of the radiochemistry (chemical heat defect).

Conclusions:

The measurements performed over a period of several years showed that the combined water calorimeters showed stability at +/− 0.25 % level. Thus, rather than relying on a particular vessel as an artifact one can realize the Gray through the more generalized method of combining a glass vessel, high‐purity water and thermistor probes. This provides increased robustness in the dissemination of absorbed dose to Canadian users.
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 12: Suitability of plan class specific reference fields for estimating dosimeter correction factors for small clinical CyberKnife fields
Authors: Vandervoort Eric , Christiansen Eric , Belec Jason , Muir Bryan
Published: August 2016

Purpose:

The purpose of this work is to investigate the utility of plan class specific reference (PCSR) fields for predicting dosimeter response within isocentric and non‐isocentric composite clinical fields using the smallest fields employed by the CyberKnife radiosurgery system.

Methods:

Monte Carlo dosimeter response correction factors (CFs) were calculated for a plastic scintillator and microchamber dosimeter in 21 clinical fields and 9 candidate plan‐class PCSR fields which employ the 5, 7.5 and 10 mm diameter collimators. Measurements were performed in 5 PCSR fields to confirm the predicted relative response of detectors in the same field.

Results:

Ratios of corrected measured dose in the PCSR fields agree to within 1% of unity. Calculated CFs for isocentric fields agree within 1.5% of those for PCSR fields. Large and variable microchamber CFs are required for non‐isocentric fields, with differences as high as 5% between different clinical fields in the same plan class and 4% within the same field depending on the point of measurement. Non‐isocentric PCSR fields constructed to have relatively homogenous dose over a region larger than the detector have very different ion chamber CFs from clinical fields. The plastic scintillator detector has much more consistent response within each plan class but still require 3–4% corrections in some fields.

Conclusions:

While the PCSR field concept is useful for small isocentric fields, this approach may not be appropriate for non‐isocentric clinical fields which exhibit large and variable ion chamber CFs which differ significantly from CFs for homogenous field PCSRs.
Teaching astronomy with dry erase whiteboards
Authors: Slater Timothy F.
Published: August 2016

In the quest to become a great astronomy teacher, one carefully considers what might be the best textbook, what might be the best homework collection and grading system, which classroom policies promote an active learning environment, and which teaching inclinations and strategies might work best with this year’s students. But what about teaching equipment? As you are thinking about next year’s teaching hardware needs, a surprisingly effective tool to consider adding to your cabinet that consistently encourages more active learning is a stack of small dry erase whiteboards.
Response to Comment on “A bacterium that degrades and assimilates poly(ethylene terephthalate)”
Authors: Yoshida Shosuke , Hiraga Kazumi , Takehana Toshihiko , Taniguchi Ikuo , Yamaji Hironao , Maeda Yasuhito , Toyohara Kiyotsuna , Miyamoto Kenji , Kimura Yoshiharu , Oda Kohei
Published: August 2016

Yang
et al
. suggest that the use of low-crystallinity poly(ethylene terephthalate) (PET) exaggerates our results. However, the primary focus of our study was identifying an organism capable of the biological degradation and assimilation of PET, regardless of its crystallinity. We provide additional PET depolymerization data that further support several other lines of data showing PET assimilation by growing cells of
Ideonella sakaiensis
.
How neuroinflammation contributes to neurodegeneration
Authors: Ransohoff Richard M.
Published: August 2016

Neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and frontotemporal lobar dementia are among the most pressing problems of developed societies with aging populations. Neurons carry out essential functions such as signal transmission and network integration in the central nervous system and are the main targets of neurodegenerative disease. In this Review, I address how the neuron’s environment also contributes to neurodegeneration. Maintaining an optimal milieu for neuronal function rests with supportive cells termed glia and the blood-brain barrier. Accumulating evidence suggests that neurodegeneration occurs in part because the environment is affected during disease in a cascade of processes collectively termed neuroinflammation. These observations indicate that therapies targeting glial cells might provide benefit for those afflicted by neurodegenerative disorders.
Fighting poverty with data
Authors: Blumenstock Joshua Evan
Published: August 2016

Machine learning algorithms measure and target poverty
Now you see me too
Authors: Öhrström Lars
Published: August 2016

Attaching chiral molecules to a chiral framework allows their molecular structures to be determined
DDB1 Stimulates Viral Transcription of Hepatitis B Virus via HBx-Independent Mechanisms
Authors: Kim Woohyun , Lee Sooyoung , Son Yeongnam , Ko Chunkyu , Ryu Wang-Shick
Published: August 2016

HBx, a small regulatory protein of hepatitis B virus (HBV), augments viral DNA replication by stimulating viral transcription. Among numerous reported HBx-binding proteins, DDB1 has drawn attention, because DDB1 acts as a substrate receptor of the Cul4-DDB1 ubiquitin E3 ligase. Previous work reported that the DDB1-HBx interaction is indispensable for HBx-stimulated viral DNA replication, suggesting that the Cul4-DDB1 ubiquitin E3 ligase might target cellular restriction factors for ubiquitination and proteasomal degradation. To gain further insight into the DDB1-HBx interaction, we generated HBx mutants deficient for DDB1 binding (i.e., R96A, L98A, and G99A) and examined whether they support HBx-stimulated viral DNA replication. In contrast to data from previous reports, our results showed that the HBx mutants deficient for DDB1 binding supported viral DNA replication to nearly wild-type levels, revealing that the DDB1-HBx interaction is largely dispensable for HBx-stimulated viral DNA replication. Instead, we found that DDB1 directly stimulates viral transcription regardless of HBx expression. Through an HBV infection study, importantly, we demonstrated that DDB1 stimulates viral transcription from covalently closed circular DNA, a physiological template for viral transcription. Overall, we concluded that DDB1 stimulates viral transcription via a mechanism that does not involve an interaction with HBx.

IMPORTANCE
DDB1 constitutes a cullin-based ubiquitin E3 ligase, where DDB1 serves as an adaptor linking the cullin scaffold to the substrate receptor. Previous findings that the DDB1-binding ability of HBx is essential for HBx-stimulated viral DNA replication led to the hypothesis that HBx could downregulate host restriction factors that limit HBV replication through the cullin ubiquitin E3 ligase that requires the DDB1-HBx interaction. Consistent with this hypothesis, recent work identified Smc5/6 as a host restriction factor that is regulated by the viral cullin ubiquitin E3 ligase. In contrast, here we found that the DDB1-HBx interaction is largely dispensable for HBx-stimulated viral DNA replication. Instead, our results clearly showed that DDB1, regardless of HBx expression, enhances viral transcription. Overall, besides its role in the viral cullin ubiquitin E3 ligase, DDB1 itself stimulates viral transcription via HBx-independent mechanisms.