bluuebunny/crossref_metadata_2025 huggingface dataset:
Night Becomes Day: Carnival, Contested Spaces, and the Black Movement in Bahia
Authors: Williamson Kenneth
Published: July 2012

This article details the cultural politics surrounding carnival in Salvador, Bahia, Brazil, between 1995 and 1999, including the experiences and meanings of carnival, the struggle over Afro‐Brazilian culture, and wealth generated from carnival. The black movement utilizes carnival as a highly visible site of contestation and protest against racism in Brazil. However, the movement simultaneously struggles with issues of co‐optation, especially by African carnival groups, demonstrating the tensions in the interrelationship between culture and politics. Black movement activists’ stories and experiences reveal the micropolitics of the movement and individuals engaged in politics and identity.
Attenuation of Gas Pulsation in a Reciprocating Compressor Piping System by Using a Volume-Choke-Volume Filter
Authors: Liu Boxiang , Feng Jianmei , Wang Zhongzhen , Peng Xueyuan
Published: July 2012

This paper presents an investigation of the use of a volume-choke-volume low-pass filter to achieve gas pulsation attenuation in a reciprocating compressor piping system, with a focus on its frequency response characteristics and influence on the actual attenuation effects. A three-dimensional acoustic model of the gas pulsation was established for a compressor discharge piping system with and without the volume-choke-volume filter, based on which the gas column natural frequencies of the piping system and the pressure wave profiles were predicted by means of the finite element method. The model was validated by comparing the predicted results with the experimental data. The results showed that the characteristic frequency of the filter was sensitive to both diameter and length of the choke but independent of the parameters of the piping beyond the filter. It is worth noting that the characteristic frequency of the filter constituted one order of the gas column natural frequencies of the piping system with the filter. The pressure pulsation levels in the piping system downstream of the filter could be significantly attenuated especially for the pulsation components at frequencies above the filter’s characteristic frequency. The measured peak-to-peak pressure pulsation at the outlet of the filter was approximately 61.7% lower than that of the surge bottle with the same volume.
The Effect of Intake Valve Deactivation on Lean Stratified Charge Combustion at an Idling Condition of a Spark Ignition Direct Injection Engine
Authors: Grover Ronald O. , Chang Junseok , Masters Edward R. , Najt Paul M. , Singh Aditya
Published: July 2012

A combined experimental and analytical study was carried out to understand the improvement in combustion performance of a four-valve spark ignition direct injection (SIDI) wall-guided engine operating at lean, stratified idle with enhanced in-cylinder charge motion by deactivating one of the two intake valves. A fully warmed-up engine was operated at low speed, light load by injecting the fuel from a pressure-swirl injector during the compression stroke to produce a stratified fuel cloud surrounding the spark plug at the time of ignition. Steady state flow-bench measurements and computational fluid dynamics (CFD) calculations showed that valve deactivation primarily increased the in-cylinder swirl intensity as compared with opening both intake valves. Engine dynamometer measurements showed an increase in charge motion led to improved combustion stability, increased combustion efficiency, lower fuel consumption, and higher dilution tolerance. A CFD study was conducted using in-house models of spray and combustion to simulate the engine operating with and without valve deactivation. The computations demonstrated that the improved combustion was primarily driven by higher laminar flame speeds through enhanced mixing of internal residual gases, better containment of the fuel cloud within the piston bowl, and higher postflame diffusion burn rates during the initial, main, and late stages of the combustion process, respectively.
Stability Analysis and Control of Supercavitating Vehicles With Advection Delay
Authors: A. Hassouneh Munther , Nguyen Vincent , Balachandran Balakumar , H. Abed Eyad
Published: July 2012

A pitch-plane model of a supercavitating vehicle is developed to account for the time delay in the propagation of the cavitator action from the vehicle nose to the vehicle aft. This time delay is an advection delay, which is on the order of the vehicle length divided by its speed. Unlike previous models with time-delay effects, in the present model, the effect of cavity rotation during forward motion is incorporated. Stability analyses and feedback control designs are carried out using this model. It is found that the open-loop system with and without the time delay is unstable. Feedback control laws that stabilize the delay-free system model are found to be ineffective in the presence of the time delay. The authors show that the delay leads to destabilization of the supercavitating vehicle dynamics in the sense that an operation at a stable trim condition is replaced by a stable limit-cycle motion that is commonly referred to as tail-slap. Feedback control designs are carried out by taking into account the time delay, and it is demonstrated that the supercavitating vehicle can be stabilized at trim conditions inside and outside the cavity. By using numerical studies of the nonlinear delay-dependent pitch-plane model of the supercavitating vehicle, the effectiveness of the new control designs are demonstrated.
Passive Effusion Cooling in a Rectangular S-Bend Diffuser
Authors: Ng B. C. N. , Birk A. M.
Published: July 2012

The experimental study considered passive effusion cooling in an S-bend diffusing passage in which ambient cool air was drawn naturally into the S-bend passage with subatmospheric flow distributions. Seven-hole pressure probes were used to measure the test section’s inlet and outlet flow conditions which were used to evaluate the performance of the S-bend diffuser. Back-pressure, outlet flow-fields, and wall pressure distributions were investigated to study the effects of effusion cooling on the pressure recovery performance of the S-bend diffuser. The study revealed a substantial back-pressure penalty and wall pressure distribution alteration in the S-bend passage with full coverage effusion cooling. The outlet diffuser was shown to be not as effective with effusion cooling. The findings highlighted the importance of the design of effusion holes locations in complex flow passages.
Tension-Compression Fatigue of a SiC/SiC Ceramic Matrix Composite at Elevated Temperature
Authors: Ruggles-Wrenn M. B. , Jones T. P.
Published: July 2012

Tension-compression fatigue behavior of a nonoxide ceramic composite with a multilayered matrix was investigated at 1200 °C in laboratory air. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in an eight-harness-satin weave (8HSW). Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Tension-compression fatigue behavior was studied for fatigue stresses ranging from 80 to 200 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was −1.0. Fatigue run-out was defined as 2 × 105 cycles. Fatigue limit was 80 MPa. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. The material retained 100% of its tensile strength. Reductions in tensile modulus and in compressive modulus were negligible. Composite microstructure, as well as damage and failure mechanisms were investigated.
Mutually beneficial doping of tellurium and nitrogen in ZnO films grown by metal-organic chemical vapor deposition
Authors: Tang Kun , Gu Shulin , Ye Jiandong , Zhu Shunming , Huang Shimin , Gu Ran , Zhang Rong , Shi Yi , Zheng Youdou
Published: July 2012

The advantages of tellurium-nitrogen (Te-N) codoping are investigated in ZnO films grown by metal-organic chemical vapor deposition. Te incorporation gives aid in enhancing the N solubility by lowering its formation energy while N addition helps to stabilize the substituted Te on O sites with the phase-segregated ZnTe crystallites suppressed by forming the N-Zn-Te structures in the N-doped ZnTexO1−x. Carbon related impurities, commonly existing in N-doped ZnO and acting as compensating centers for holes, are fully eliminated by the Te-N codoping. The codoping technique also lowers the energy level of the NO acceptors and leads to realizing N-doped ZnTexO1−x films with holes as major carriers.
Poster — Thur Eve — 32: Water tank referenced calibration method for detector array devices
Authors: Foottit C , Gerig L
Published: July 2012

Introduction: Detector array devices, such as the I'mRT Matrixx (IBA Dosimetry), provide a means of evaluating beam profiles with respect to gantry for a range of dose rates and monitor units. The relative calibration of these devices is typically highly susceptible to even relatively small variations in beam output. An alternative method is proposed here, which directly references the device detector response to water tank data. Methods: The Matrixx response was measured at the four cardinal angles for three devices. A calibration factor was determined for each orientation of the Matrixx device by dividing a water tank measured profile by the Matrixx response for the in‐plane and cross‐plane detectors. A geometric mean of each orientation was used as the estimate of the calibration coefficient. Results: Before calibration, the three‐detector average of the deviation from the profile measured in the water tank centered on each of the horns was 0.4% (SD 0.2%); applying the calibration procedure reduced this to 0.1% (SD 0.1%). The energy independence of the proposed relative calibration was also confirmed. A comparison of the linac output for relatively short Matrixx acquisitions to the longer water tank acquisition suggested some difference. This difference was mitigated by averaging. Conclusions: The proposed water tank reference calibration procedure is an effective means of determining the relative calibration of a detector array and mitigates the effect of compound error by avoiding the recursive algorithm of typical calibration methods. In addition it has the benefit of being directly relatable to commissioning beam data.
Poster — Thur Eve — 37: Improved clustering MLC leaf‐sequencing algorithm for step‐and‐shoot IMRT
Authors: Jing J , Lin H , Chow J
Published: July 2012

This study examines how to reduce the complexity of fluence map generated using an improved clustering leaf‐sequencing method, and evaluates such method in step‐and‐shoot intensity‐modulated radiotherapy (IMRT). Based on the current equal‐space grouping algorithm for multileaf collimator (MLC) leaf sequence, we proposed an improved K‐means grouping algorithm which can replace the stratification routine in the program of existing leaf sequence. The improved algorithm can be thought of as a gradient descent procedure, which begins at starting cluster centroids, and iteratively updates these centroids to decrease the objective function. The K‐means always converge to a local minimum depending on the starting cluster centroids. The K‐means algorithm continuously updates cluster centroids until the local minimum is reached. We compare the leaf‐sequencing results in term of numerical values from the improved K‐means and equal‐space grouping algorithm. A representative 1D intensity map from a clinical treatment plan was investigated and optimized by the K‐means and equal‐space grouping algorithm. It was found that the K‐means algorithm decreased the dose square error from 53.67 to 35.27. Moreover, the normalized square differences of the equal‐space and K‐means algorithm are equal to 2881 and 1244, respectively. The results demonstrated an improvement in accuracy achievable by allowing the fluence map to be defined in an optimal way rather than using the pre‐defined criteria. Therefore, the K‐means leaf‐sequencing algorithm can better simulate the distributions of the input fluence data compared to the traditional grouping algorithm in step‐and‐shoot IMRT.
Poster — Thur Eve — 41: Effect of beam symmetry on enhanced dynamic wedge quality assurance and tolerance levels
Authors: Meyer T , Hudson A
Published: July 2012

Wedged fields are common in three dimensional conformal radiation therapy and require appropriate quality assurance (QA). Currently, our centre calculates the angle of enhanced dynamic wedge (EDW) deliveries with the PROFILER at a monthly frequency but Canadian guidelines on the recommended QA of enhanced dynamic wedges are not available yet. TG‐142 recommendations include monthly validation of the central axis wedge factors with only annual verification of wedge profiles. Our monthly QA results have demonstrated a sensitivity of the calculated EDW angle to open beam symmetry. The goal of this work is to compare wedge angle and direct profile comparison as QA measures of EDW delivery and determine appropriate parameter tolerances. The impact of open field symmetry variations on EDW profiles was determined by varying beam symmetry with a test potentiometer and measuring the resulting EDW beam profile with the PROFILER. A calculated wedge angle and direct profile comparison were used to describe the deviations in EDW deliveries. The impact of the deviations on typical plans incorporating wedged fields was evaluated by constructing ‘equivalent wedges' to the profile deviations using mixed 60 degree and open field beams and performing plan comparisons in Eclipse. Beam symmetry was observed to have a significant impact on wedge angle for small angle wedges, with a 1% symmetry tolerance allowing a 3.4 degree range of wedge angles for a nominal 10 degree wedge. Direct profile comparison allows a more consistent definition of a dose based tolerance range to be applied without angle dependent tolerances.
Poster — Thur Eve — 48: An inexpensive and convenient phantom for quality assurance in image guidance based radiosurgery
Authors: Soisson E
Published: July 2012

This work describes the design and use of an inexpensive phantom designed for precision measurements in radiosurgery quality assurance. The main features of this simple phantom include its solid water construction, interchangeable ion chamber holders and film registration system, thus allowing for measurement of small fields with several detectors using the same phantom. The entire phantom was constructed using one 30cm × 30cm × 3cm slab of solid water. The phantom contains a slot that allows for the placement of two small volume ion chambers (liquid and A1SL) via custom inserts near the center of the phantom. In addition, the plug can be filled for film measurements. The phantom can be split down the center to allow for the placement of a film. As opposed to registering film to room based markers, such as lasers, the phantom contains radio‐opaque fiducials that puncture the film while also providing a method to register the film images to exported dose planes. In addition to the markers used for film registration, the phantom contains several external beebees that can be used to avoid ambiguity in image registration when using image guidance for setup. This simple phantom contains many features of other much more expensive phantoms designed for this purpose and has been found to be very useful clinically and in departmental research. The key elements of this phantom could be included in several other designs allowing it to be reproduced in other centers.
Poster — Thur Eve — 67: Clinical results of deep inspiration breath hold radiation treatment for the left breast patients
Authors: Jiang R , Zhan L , Gopaul D , Osei E
Published: July 2012

Adjuvant radiotherapy for left breast cancers increases local tumor control, but also increases the risk of radiation‐induced cardiac disease. Deep Inspiration Breath Hold (DIBH) can minimize dose to the heart for left breast patients where the heart is within the tangential field. In this study, we evaluated the dosimetric benefit of DIBH technique comparing to free breathing (FB) radiotherapy for left breast cancer patients. Five patients with left breast cancer treated with DIBH technique were selected randomly. The CT scans of breath hold (BH) and FB were taken for every DIBH patient. Standard clinical DIBH intensity‐modulated radiotherapy (IMRT) plans were generated with BH scan dataset using the Varian Eclipse TP system. The prescription dose is 4250 cGy in 16 fractions. The BH plan was copied to the FB scan dataset and shifted accordingly to have the same coverage for the breast tissue, and the dose was re‐calculated. Dose‐volume histograms (DVH) of the heart and lung; mean dose and maximum dose of the heart were calculated and compared from the BH and FB plans for every patient. The lung volume is increased during BH and hence the heart is moved out of the field, resulting in the lower heart maximum dose. The mean dose is almost less than 1 Gy for all BH plans. The average mean heart dose is 0.8 Gy for BH plan compared to 1.6 Gy for FB plan. Patients benefit significantly from DIBH technique due to the very low heart dose.
Poster — Thur Eve — 69: Electron beam dosimetry in heterogeneous phantoms using the MAGIC normoxic polymer gel
Authors: Nedaie HA , Ghahraman AR , Bolouri B , Arbabi A
Published: July 2012

Recently, radiation sensitive polymer gels are being used as a reliable dosimetry method for three‐dimensional (3D) verification of radiation doses in clinical use. Some properties of gel dosimeters have made them useful in verifying complex situations in electron therapy. The aim of this study was to experimentally evaluate the influence of tissue inhomogeneities on electron beam dose distributions by use of polymer gel dosimetry. Another purpose was to evaluate the appropriateness of polymer gels for electron beam dosimetry applications. A cylindrical phantom filled with MAGIC polymer gel with a polyacrilic wall (ρ = 1.18 g.cm−3) was placed in a Perspex water‐filled tank exactly underneath the bone inhomogeneity region .Then, the slab phantom was irradiated with a dose of 5Gy of 8MeV electrons to measure the dose distribution beyond the heterogeneity region. Afterwards, another cylindrical gel phantom similar to the above was used and irradiated with the same dose of 15 MeV electrons to measure the dose distribution beyond the same heterogeneity region. The same mentioned setup was repeated for measurement of the dose distribution beneath the air heterogeneity and homogenous phantom. The results of gel dosimetry under bone inhomogeneity have shown a reduction in dose. This is related to the high mass stopping and mass scattering powers of bone tissue. In addition, dose enhancement is seen laterally near the bone‐tissue interface, due to increased side scattering of electrons. Hot and cold scatter lobes under heterogeneity regions are other effects that can be seen. The results of gel dosimetry under the air inhomogeneity have shown an increase in dose. This is related to the low mass stopping and mass scattering powers of the air cavity. When a high energy beam passes through a low‐density medium or an air cavity, electronic equilibrium is lost along the central axis of the beam .The dose rebuild up is a consequence of this electronic disequilibrium. An overall good agreement was found between measurements with gel and with a diode detector for the single beam experiment. Electron dose distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavities which are related to mass stopping and mass scattering powers of heterogeneous materials.
Poster — Thur Eve — 70: Quantification of tumour dose enhancement at kilo‐voltage energies due to the presence of gold nanoparticles during radiation therapy: EGSnrcMP Monte Carlo study
Authors: Fleck A , Jiang R , Schaly B , Charland P , Osei Et
Published: July 2012

One of the greatest challenges in radiation therapy is the ability to deliver a lethal dose of radiation to a tumour while sparing the surrounding normal tissues. In theory, the dose delivered to a tumour during photon‐based radiation therapy can be enhanced by loading high atomic number (Z) materials into the tumour, which results in greater photoelectric absorption and hence increased photoelectron fluence within the tumour than in surrounding tissues. The EGSnrcMP Monte Carlo code, together with DOSXYZnrc, a three‐dimensional voxel dose calculation module has been used to study the macroscopic dose enhancement factor (MDEF) in a tumour infused with gold nanoparticles at the kilo‐voltage energies. We observed that gold nanoparticles infused in a tumour irradiated with kilo‐voltage energies has the potential to enhance the tumour dose by a factor ranging from 0.25 to about 5 depending on the mean energy of the beam and the concentration of gold nanoparticles in the tumour. The increase in dose can be attributed to the significant increase in the photoelectron fluence within the tumour loaded with gold particles during the irradiation. Future studies will involve the characterization of the MDEF at megavoltage energies.
Poster — Thur Eve — 74: A set of tests designed for electron dose calculation algorithm verification during a treatment planning system upgrade
Authors: Wang Y , Nielsen M , MacPherson MS
Published: July 2012

A set of tests were designed to verify an electron algorithm effectively and quickly during a treatment planning system upgrade. Based on TG‐53 report's suggestion and the assumption that the algorithm is well commissioned before the upgrade, the tests spot‐check the output factors, depth doses, off‐axis doses and treatment field sizes. The field sizes of 4×4, 6×6, 10×10, 15×15, 20×20 and 25×25 are to be tested. Four test plans are created for each field size, i.e., for open field, for extended SSD, for shaped field, and for bolus field. Fixed MU setting is recommended to avoid a possible plan normalization issue. The parameters to be recorded and compared include doses at dmax, R50 and Rp along central axis, which contain output and depth dose information, doses at four off‐axis points in dmax plane, which contain off‐axis dose and beam symmetry information, and FWHMs at dmax. For the plans other than open field only doses at dmax are checked. The tests were performed successfully during a planning system upgrade. The whole test can be completed in approximately 12 hours if the workload is distributed into multiple task carriers. It was found that most of the data agree very well between the old and the new version of the algorithm while some of the Rp or R50 doses deviated more than other data, which prompted a depth dose check. PDD comparisons were performed for the involved fields and it was found there were less than 0.5 mm PDD shifts occurred.
Poster — Thur Eve — 75: Towards MR only simulation: MR based digitally reconstructed radiograph of head and neck
Authors: Yu H , Mah K , Balogh J
Published: July 2012

Purpose: To develop a practical method to obtain bony structures from Magnetic Resonance (MR) images and to create MR‐ based digitally reconstructed radiographs (DRR) for MR only simulation. Methods and Materials: Using T1‐weighted MR images, air regions including the sinuses and the airway in the head and neck were manually contoured. The bone and soft tissue masks were automatically generated based on the statistical data calculated from the air contour and MR intensities. “CT like” MR images were generated by mapping the MR intensities of the voxels within these masks into the CT number ranges of these tissues. The MR‐based DRRs created from “CT like” MR images were quantitatively evaluated using the co‐registered MR and CT images of 10 stereotactic radiosurgery CNS patients. Ten anatomical control points, set on the contours of the skull segmented using a threshold of 300 HU were used to determine the differences in distance between MR‐based DRRs and CT‐based DRRs, and to evaluate the geometrical accuracy of MR‐based DRRs. Results: The bony structures were visible in the MR‐based DRRs. The mean geometric difference and standard deviation between the ten anatomical control points on MR‐ based and CT‐based DRRs were −0.03±1.11 mm (including uncertainty of image fusion). The maximum distance difference was 1.67mm. Conclusions: The study provides a practical method to generate MR‐ based DRRs from MR‐only simulations of the head and neck regions. The image quality and anatomical accuracy of MR‐based DRRs is comparable to that of CT‐based DRRs.
Sci—Fri AM: Imaging — 01: Feasibility of estimating choline kinase activity with kinetic modeling of 18F‐fluorocholine pet imaging of prostate cancer
Authors: Blais AR , Lee T‐Y
Published: July 2012

Prostate cancer (PCa) detection and delineation remains a challenge for medical imaging. Studies have shown 18F‐Fluorocholine (FCH) PET imaging to be a promising modality in the detection of recurrent PCa. Detection of denovo PCa is more challenging, as lesions such as benign prostatic hyperplasia (BPH) may adversely affect the sensitivity and specificity of the modality. PCa and BPH have been shown to exhibit similar uptake of FCH, yet it has been shown that phosphocholine levels are much more elevated in PCa compared to BPH. Therefore, it would be useful to measure the activity of phosphorylation via choline kinase (k3) in order to differentiate PCa from BPH. This work examines the feasibility of using a compartmental model to estimate k3 with dynamic 18F‐Fluorocholine PET imaging. JSim software [1] was used to simulate the compartmental model for FCH exchange. A simulated tissue curve was generated using predefined parameters and the model's ability to estimate these parameters through fitting of the simulated tissue curve with and without noise was investigated. The fitting procedure was performed using the non‐negative least squares algorithm in MATLAB after the equation governing fitting was linearized. In the noiseless case, the model was able to accurately identify the values of each rate parameter. For the noisy case with an SNR of 10:1, the mean estimated k3 for 10,000 runs had a coefficient of variation of 14.9%. The kinetic model shows promise for quantifying k3, which would allow the differentiation of malignant and benign tumours of the prostate.
Sci—Fri AM: Imaging — 05: Cone‐beam computed tomography for breast biopsy analysis: Simulations
Authors: Laamanen C , LeClair R
Published: July 2012

Purpose: To determine the feasibility and potential utility of cone beam CT on breast biopsies. Methods: CBCT simulations were done with a setup which emulates an MX‐20 digital specimen radiography system (Faxitron X‐Ray Corporation, Chicago, IL), albeit a DQE = 1 was assumed. The phantom consisted of a 5mm diameter cylinder with a length of 5mm, made up of a homogeneous 50:50 mixture of fibrous and fatty tissue. Small cancerous spheres (lesions) with diameters ranging from 5 to 500 μm were embedded. Projections were acquired at magnification 5 using 26 kV‐0.3 mA‐3.8 sec beams. Images were reconstructed using a varied number of projections (50, 100, 150, 300). Values of contrast and SNR were calculated between the lesions and nearby regions. Noise was estimated by generating 10 images for each task. Scatter was found to be negligible. Results: The 50 μm spheres were only visible when at least 150 projections were used, but the 100 μm ones were visible regardless of the number. SNR increased with the number of projections, whereas contrast was insensitive. For ≥100 μm spheres contrast ranged from 0.26 on the outer radial edge to 0.28 nearer the center. The SNRs for 100 μm spheres were above 5 for reconstructions composed of ≥100 projections. Cancerous lesions within a fibrous biopsy may be detectable. Conclusions: The findings from this simulation study suggest that CBCT for breast biopsy characterization via the MX‐20 system could be of potential use to see structures on the order of 100 μm.
Sci—Fri AM: Imaging — 06: The role of body mass and gender in atlas construction for attenuation correction in PET/MRI
Authors: Patrick J , Marshall H , Sabondjian E , Butler J , Rachinsky I , Thompson T , Théberge J , Prato F , Stodilka R
Published: July 2012

Attenuation correction (AC) in PET/MRI is difficult as there is no clear relationship between MR signal and 511 keV attenuation coefficients (μ) as there is with CT. One approach is to register a pre‐defined atlas of μ to the PET/MRI for AC. However, the design of the atlas may strongly influence the quantitative accuracy of the AC. Here we compare 3 different atlas design approaches and evaluate their performance in an oncology patient population. The 3 strategies were: use of BMI‐dependent atlases; use of gender‐dependent atlases, and use of a gender‐ and sex‐independent atlas. Seventeen patients were imaged with FDG PET/CT and subsequently scanned with 3T MRI. MR and PET/CT images were coregistered, CT scans converted to μ‐maps, and the resulting MRI/μ‐map paired data were used to construct 6 atlases: averaged male and female atlases, averaged BMI‐specific atlases (obese >30, overweight 25–29.9, Normal 18.5–24.9), and a single atlas comprised of all patients averaged together. The atlases were then used for PET AC for patients not included in the construction of the atlas in a leave‐one‐out manner. Resulting PET images were compared to each other and to the gold‐standard CT‐based PET reconstructions across all voxels and tissue‐specific regions (soft‐tissue, bone, lung). Sex‐specific atlases yielded best results (average relative percent error over the 3 VOIs = 0.4509) & BMI‐based atlases yielded highest average relative percent error at 0.9340. In all cases, highest errors were in the VOIs located in the livers.
Sci—Fri AM: Imaging — 07: Symmetric geometric transfer matrix partial volume correction technique for emission tomography: Principle, validation, and robustness
Authors: Sattarivand M , Kusano M , Poon I , Caldwell C
Published: July 2012

Partial volume correction (PVC) is often needed to correct for limited spatial resolution in quantitative Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) studies. In conventional region‐based PVC methods, spill over between regions segmented from coregistered computed tomography (CT) or magnetic resonance (MR) images is accounted for by calculating regional spread functions (RSFs) in a geometric transfer matrix (GTM) framework. This paper describes a new analytically derived symmetric GTM (sGTM) method that considers spill over between RSFs rather than between regions. The sGTM is mathematically equivalent to Labbe's method, however it is region‐based rather than voxel‐based and it avoids handling large matrices. The sGTM method was validated using an MR‐based 3D digital brain phantom and a physical phantom containing spheres 5 mm to 30 mm in diameter. The sGTM method was compared to the GTM method in terms of accuracy, precision, noise propagation, and robustness, i.e. effects of mis‐registration or point spread function (PSF) estimation errors. The results showed that the sGTM method has accuracy similar to that of the GTM method, and within 5% of the true value. However, the sGTM method showed better precision and noise propagation than the GTM method, especially for spheres smaller than 13 mm. Moreover, the sGTM method was more robust than the GTM method when misregistration or errors in estimates of PSF occurred. In conclusion, the sGTM method was analytically derived and validated and shown to exhibit better noise characteristics and robustness compared to the GTM method.
Sci—Fri PM: Delivery — 03: Spine SBRT: Treating multiple vertebrae using cone‐beam CT image‐guidance and the hexapod robotic couch
Authors: Hyde D , Sangha A , Korol R , Lochray F , Sahgal A
Published: July 2012

Purpose: The intent of spinal SBRT is to maximize the biological effective dose and improve local control, while sparing the adjacent spinal cord. We report on the spinal SBRT positional accuracy for multiple, consecutive vertebrae in a single course, using the Elekta Synergy‐S and BodyFIX immobilization systems. Methods: After initial patient adjustment, verification cone‐beam CT (CBCT) images were acquired before, during and after treatment. These images were used to assess immobilization and correct any misalignment exceeding 1 mm or 1°, in all six degrees‐of‐freedom using the HexaPOD robotic couch. This analysis is based on 415 verification images from 67 consecutive courses of treatment. These treatment courses comprised 25 single thoracic vertebrae, 16 multiple thoracic vertebrae, 20 single lumbar vertebrae and 6 multiple lumbar vertebrae. Results: The absolute intra‐fraction motion averaged over all directions (±std dev.) for the T‐single, T‐multiple, L‐Single and L‐Multiple was 0.54 (±0.73) mm, 0.54 (±0.88) mm, 0.36 (±0.57) mm, and 0.47 (±0.63) mm respectively. The percentage that exceeded the 1.5 mm planning margin was 3.8%, 4.0%, 1.0% and 0.85% respectively. T‐spine treatments were out‐of‐tolerance more frequently than the L‐spine. There was a statistically significant difference between single and multiple lumbar treatments (unpaired t‐test, p<0.01), but this was not clinically significant as 99% were within our 1.5 mm margin. Conclusions: Near‐rigid immobilization with the acquisition of intra‐fraction CBCT images and the correction of misalignments in all six degrees‐of‐freedom provides the necessary precision to safely perform SBRT of consecutive spinal metastases within one course of treatment.
Sci—Fri PM: Delivery — 05: A complete set of VMAT machine‐specific QA tests using EPID
Authors: Mestrovic A
Published: July 2012

During a VMAT (Volumetric Modulated Arc Therapy) radiation delivery, various machine parameters (gantry position and speed, MLC leaves position, dose rate, etc) have to be highly synchronized and coordinated. To ensure that all of the machine components are effectively operating together requires unique machine‐specific quality assurance (QA) tests. The purpose of this work is to describe a complete set of VMAT machine‐specific QA tests using Electronic Portal Imaging Device (EPID). To address the need for VMAT machine‐specific QA tests, Varian has recommended 6 EPID‐based tests for commissioning and QA of RapidArc™ capable machines. Recent studies have identified that these Varian tests do not define a complete set of tests needed for adequate commissioning and machine‐specific QA of RapidArc machines. The goal of this work is twofold: a) to report and discuss the results of the original 6 Varian's EPID‐based tests, and b) to extend the original set by adding 2 more EPID‐based tests, which results in a more complete and comprehensive set of tests. We have demonstrated that the Varian EPID‐based QA tests can be used to verify that the synchronization of Dose Rate, Gantry Speed and MLC Leaves speed is generally to within 1.5% during a RapidArc delivery. Also, the gantry rotation does not have any significant effect on MLC leaves positional accuracy during a RapidArc delivery. Finally, we have introduced a new EPID‐based QA test, which can be used to verify that the angular accuracy of the gantry position during a RapidArc delivery is to within ∼1 degree.
Sci—Fri PM: Delivery — 06: A generalized solution to the wide field array calibration method
Authors: Nyiri B , Gerig L
Published: July 2012

Multi detector arrays are commonly used in radiation oncology for IMRT and Linac QA. The calibration of detector arrays is usually based on the wide field calibration technique. Unfortunately small beam changes between measurements will result in large error propagation. The present work introduces a generalized modified version of the wide field calibration method, robust against measurement to measurement variation. Our generalized framework uses an unlimited number of measurement pairs, n geometric positions providing n(n−1)/2 pairs. We solve this large over determined linear system using least squares with gradient method. Measurements were made on an Elekta synergy 6 MV beam with two IBA Matrixx detectors, each containing a 32 × 32 array (1024) of vented pixel ionization chambers. Data acquisition was by the IBA Omnipro Advance software, version 1.2 running in the “ONLINE” cine mode with a 10 sec integration time. Continuous beam sampling (10 seconds long) measured over 10 minutes demonstrated why consistent calibration using the conventional wide field calibration is a challenge. Overall signal changes of 1.6%, flatness changes of 0.3% and the beam symmetry changes of 0.2% over the full 10 minute beam‐on time were observed. For the purpose of testing and demonstration of our method, we have chosen to make measurements in 5 geometric orientations relative to the beam, including 1 reference position, 2 rotations and 2 translations. With our method we were able to calibrate all 1024 detectors to better than 0.6% total uncertainty as demonstrated against inter and intra MatriXX comparison.
Sci—Fri PM: Delivery — 10: Megavoltage x‐ray imaging detector based on cerenkov effect
Authors: Teymurazyan A , Pang G
Published: July 2012

A Monte Carlo simulation was used to study imaging and dosimetric characteristics of a novel design of a megavoltage (MV) x‐ray imaging detector. The proposed detector consists of a matrix of optical fibers aligned with the incident x‐rays and coupled to an active matrix flat‐panel imager (AMFPI) for image readout. The new design relies on Cerenkov effect for MV x‐ray imaging and is named CPID (for Cerenkov Portal Imaging Device). When MV x‐rays are incident on CPID, they interact within the volume of the detector primarily via Compton effect and pair‐production, resulting in electrons and positrons. From these charged particles, those with sufficient energy, trigger production of optical light via Cerenkov effect. The light that is generated in the optical fibre cores within the acceptance angle of the fibers is guided towards the AMFPI. Properties, such as detection efficiency, modulation transfer function, zero frequency detective quantum efficiency (DQE), and energy response of the detector, have been investigated. It has been shown that the proposed detector can have a zero‐frequency DQE more than an order of magnitude higher than that of current electronic portal imaging device (EPID) systems and yet a spatial resolution comparable to that of video‐based EPIDs. In additional the proposed detector is less sensitive to scattered x‐rays than current EPIDs.
Sci—Sat AM: Brachy — 03: Feasibility study of the determination of absorbed dose to water using a fricke based system
Authors: Gamal I El , Cojocaru C , Ross C , Marchington D , McEwen M
Published: July 2012

By measuring the dose to water directly a metrology standard, independent of air kerma, can be developed to make the basis of HDR brachytherapy dosimetry consistent with current dosimetry methods for external radiation beams. The Fricke dosimeter system, a liquid chemical dosimeter, provides a means of measuring the absorbed dose rate to water directly by measuring the radiation‐induced change in absorption of the Fricke solution. In an attempt to measure the absorbed dose to water directly for a 192Ir HDR brachytherapy source a ring shaped Fricke holder was constructed from PMMA, essentially following the work of Austerlitz et al. (Med. Phys. 2008). Benchmark measurements conducted in a 60Co beam yielded a standard uncertainty in the absorption reading of 0.16 %, comparable with previous results in the literature. Measurements of the standard uncertainty of the control (unirradiated) solution using the holder yielded 0.2 %, indicating good process control and minimal contamination from the holder itself. However, it was found that the holder sealing method (to allow measurements in a water phantom) significantly contaminated the Fricke solution, resulting in an excessive background reading. Irradiations were therefore conducted in air to determine the feasibility of the procedure. Irradiations with a 17 GBq source gave a standard uncertainty of approximately 0.5 %, indicating that the target uncertainty of 1.5% for the measurement of absorbed dose to water using a Fricke‐based primary standard is achievable. This would be comparable with calorimeter‐based systems currently being developed.
Sci—Sat AM: Brachy — 04: Neutron production around a radiation therapy linac bunker ‐ monte carlo simulations and physical measurements
Authors: Khatchadourian R , Davis S , Evans M , Licea A , Seuntjens J , Kildea J
Published: July 2012

Photoneutrons are a major component of the equivalent dose in the maze and near the door of linac bunkers. Physical measurements and Monte Carlo (MC) calculations of neutron dose are key for validating bunker design with respect to health regulations. We attempted to use bubble detectors and a 3He neutron spectrometer to measure neutron equivalent dose and neutron spectra in the maze and near the door of one of our bunkers. We also ran MC simulations with MCNP5 to measure the neutron fluence in the same region. Using a point source of neutrons, a Clinac 1800 linac operating at 10 MV was simulated and the fluence measured at various locations of interest. We describe the challenges faced when measuring dose with bubble detectors in the maze and the complexity of photoneutron spectrometry with linacs operating in pulsed mode. Finally, we report on the development of a userfriendly GUI for shielding calculations based on the NCRP 151 formalism.
Sci—Sat AM: Brachy — 05: Comprehensive web‐based QA in radiation oncology
Authors: Kildea J , Parker W
Published: July 2012

Innovation/Impact: We describe the web‐based QA infrastructure under development and in use within our paperless radiation oncology clinic. Our framework comprises a centralized web‐server that facilitates simultaneous and seamless access to multiple databases within the clinic. All activities, including treatment planning, patient appointments and machine quality control/maintenance, are accessible via a single internal webpage with various software tools and metrics employed for QA and monitoring. We believe that our framework is representative of the direction in which modern radiation oncology departments are moving; namely paperless operation with centralized data access for patient‐specific QA and statistical process control.
Sci—Sat AM: Brachy — 09: Permanent seed re‐implantation using image guidance for composite dose planning
Authors: Meyer T , Sia M , Husain S , Smith W
Published: July 2012

Treatment outcome has been associated with dosimetric implant quality assessed in a postplan. Uncertainties during the implant and in the period before postplan evaluation lead to dosimetric deviations from the original treatment plan. The observed range of postplan results can include patients with dosimetry below recommended levels. Further treatment options may be considered to boost the delivered dose and a second seed implant is one way to accomplish this. This work describes the development of a procedure to plan and deliver a second seed implant and an evaluation of the dosimetric improvement. A patient with a post‐plan D90 of 124 Gy was offered a second seed implant 21 weeks after the initial implant. A total dose of 163 Gy was prescribed due to radiobiological considerations for the time between implants. A volume study was performed 2 weeks before the implant and variable angle images of the seeds from the first implant were obtained to reconstruct the original seed coordinates. The second implant was planned considering the total composite physical dose distribution by forward planning additional seeds onto the original implant coordinates. The additional seeds were manually added to a new plan on the volume study images at the planned coordinates and delivered as a typical preplanned implant. Post‐plan evaluation four weeks after the second implant showed a D90 of 177 Gy and a V100 of 92.7%. These results demonstrate the effective use of a second seed implant with image guided composite planning to improve dosimetric implant quality.
High-Salt Stress Conditions Increase the pAW63 Transfer Frequency in Bacillus thuringiensis
Authors: Beuls Elise , Modrie Pauline , Deserranno Cï¿½dric , Mahillon Jacques
Published: July 2012

Conjugation experiments with
Bacillus thuringiensis
and transfer kinetics demonstrated that salt stress has a positive impact on plasmid transfer efficiency. Compared to standard osmotic conditions (0.5% NaCl), plasmid transfer occurred more rapidly, and at higher frequencies (>100-fold), when bacteria were exposed to a high-salt stress (5% NaCl) in liquid brain heart infusion (BHI). Under milder salt conditions (2.5% NaCl), only a 10-fold effect was observed in Luria-Bertani broth and no difference was detected in BHI. These observations are particularly relevant in the scope of potential gene exchanges among members of the
Bacillus cereus
group, which includes food-borne contaminants and pathogens.
Regulatable Vectors for Environmental Gene Expression in Alphaproteobacteria
Authors: Tett Adrian J. , Rudder Steven J. , Bourdï¿½s Alexandre , Karunakaran Ramakrishnan , Poole Philip S.
Published: July 2012

Two expression vectors utilizing the inducible taurine promoter (
tauAp
) were developed. Plasmid pLMB51 is a stable low-copy vector enabling expression in the environment and
in planta
. The higher copy number pLMB509 enables BD restriction-independent cloning, expression, and purification of polyhistidine-tagged proteins.
Roles of Four Putative DEAD-Box RNA Helicase Genes in Growth of Listeria monocytogenes EGD-e under Heat, pH, Osmotic, Ethanol, and Oxidative Stress Conditions
Authors: Markkula Annukka , Lindstrï¿½m Miia , Johansson Per , Bjï¿½rkroth Johanna , Korkeala Hannu
Published: July 2012

To examine the role of the four putative DEAD-box RNA helicase genes ofListeria monocytogenesEGD-e in stress tolerance, the growth of the Δlmo0866, Δlmo1246, Δlmo1450, and Δlmo1722deletion mutant strains at 42.5ï¿½C, at pH 5.6 or pH 9.4, in 6% NaCl, in 3.5% ethanol, and in 5 mM H2O2was studied. Restricted growth of the Δlmo0866deletion mutant strain in 3.5% ethanol suggests that Lmo0866 contributes to ethanol stress tolerance ofL. monocytogenesEGD-e. The Δlmo1450mutant strain showed negligible growth at 42.5ï¿½C, at pH 9.4, and in 5 mM H2O2and a lower maximum growth temperature than the wild-type EGD-e, suggesting that Lmo1450 is involved in the tolerance ofL. monocytogenesEGD-e to heat, alkali, and oxidative stresses. The altered stress tolerance of the Δlmo0866and Δlmo1450deletion mutant strains did not correlate with changes in relative expression levels oflmo0866andlmo1450genes under corresponding stresses, suggesting that Lmo0866- and Lmo1450-dependent tolerance to heat, alkali, ethanol, or oxidative stress is not regulated at the transcriptional level. Growth of the Δlmo1246and Δlmo1722deletion mutant strains did not differ from that of the wild-type EGD-e under any of the conditions tested, suggesting that Lmo1246 and Lmo1722 have no roles in the growth ofL. monocytogenesEGD-e under heat, pH, osmotic, ethanol, or oxidative stress. This study shows that the putative DEAD-box RNA helicase geneslmo0866andlmo1450play important roles in tolerance ofL. monocytogenesEGD-e to ethanol, heat, alkali, and oxidative stresses.
Biological Role of Pigment Production for the Bacterial Phytopathogen Pantoea stewartii subsp. stewartii
Authors: Mohammadi Mojtaba , Burbank Lindsey , Roper M. Caroline
Published: July 2012

Pantoea stewartii
subsp.
stewartii
, the causal agent of Stewart's wilt of sweet corn, produces a yellow carotenoid pigment. A nonpigmented mutant was selected from a bank of mutants generated by random transposon mutagenesis. The transposon insertion site was mapped to the
crtB
gene, encoding a putative phytoene synthase, an enzyme involved in the early steps of carotenoid biosynthesis. We demonstrate here that the carotenoid pigment imparts protection against UV radiation and also contributes to the complete antioxidant pathway of
P. stewartii
. Moreover, production of this pigment is regulated by the EsaI/EsaR quorum-sensing system and significantly contributes to the virulence of the pathogen
in planta
.