bluuebunny/crossref_metadata_2025 huggingface dataset:
Sci—Thur PM: YIS — 09: ROC Analysis of Metabolomics Data Sets for Cancer Screening
Authors: Moroz J , Turner J , Slupsky C , Fallone BG , Syme A
Published: August 2010

Disease processes are known to alter the metabolic pathways of affected cells and tissues in an organism. This perturbation of the steady state can lead to quantifiable changes in metabolites found in biofluids such as urine, blood or saliva. The objective of this work was to identify robust patterns of change in the metabolic profile of mouse urine as a group of experimental animals transitioned from healthy to tumour bearing. Samples were collected for one week before tumour cell injections and for a period of four weeks after injection. An age‐matched group of control mice was profiled to investigate the effects of age and non‐tumour related experimental procedures. Samples were analyzed using an 800 MHz NMR spectrometer and profiled using the Chenomx software platform. A total of 40 metabolites were evaluated in each sample. The paired t‐test was used to identify statistically significant changes (controlled for multiple hypothesis testing) in individual metabolites and ratios of metabolite pairs. Partial least squares discriminant analysis was used to identify more complicated relationships between metabolites. Of the 40 individual metabolites, 16 changed in a significant manner that was not also observed in the controls. Of the 780 metabolite ratios, 126 were significant. To investigate potential clinical utility, population distributions were subjected to ROC curve analysis. Individual metabolite‐based results produced areas under the curve (AUC) as high as 0.770, ratios produced AUCs as high as 0.937 and multivariate models produced AUC values as high as 0.942. AUC values larger than 0.9 are considered excellent.
Poster — Thur Eve — 01: Dynamic Aperture Optimization in MERT Using Direct Aperture Optimization
Authors: Alexander A , Soisson E , DeBlois F , Seuntjens J
Published: August 2010

The advantage of modulated electron radiation therapy (MERT) comes from the defined electron range and sharp fall‐off offered with electron beams, combined with complex inverse planning techniques to conform dose to the target and reduce dose to organs at risk (OAR) beyond the target. Recent studies have evaluated the feasibility of various electron collimator devices for shallow tumor treatments. Despite the promising MERT studies, a MERT system comparable to IMRT is not commercailly available. In this work we investigate a dynamic aperture optimization process, which dynamically optimizes the aperture shapes and weights using direct aperture optimization (DAO) and is applicable to the McGill MERT delivery process using the Few‐Leaf‐Electron‐Collimator (FLEC). This study presents the optimization code (DADAO), and a plan comparison to commercially available photon beam optimization algorithms using a basic target and organ at risk geometry. A FLEC‐DADAO plan was benchmarked to plans generated from TomoTherapy and Varian Eclipse IMRT and RapidArc in order to establish a baseline level of confidence. Results were analyzed using dose volume histograms (DVH) and isodose plots. The DADAO plan was comparable to the clinical plans, competitive in its ability to reduce the dose to OAR but weaker in its ability to highly conform the dose to the target objectives. The DADAO code for MERT demonstrates potential to optimize electron planning and reduce the low‐dose irradiated volume including the low dose to the OAR at a slight cost in target coverage as compared to photon techniques.
Poster — Thur Eve — 04: The Line Spread Function Measurement of a Novel Transmission Detector
Authors: Asuni G , Rickey D , McCurdy B
Published: August 2010

Measurement‐based dose verification of planned intensity modulated radiotherapy (IMRT) fields requires a detector with good spatial resolution. A novel, transmission detector array has been recently developed by IBA Dosimetry (Germany) as an IMRT quality assurance tool. To characterize the detector system performance for verification of IMRT fluence, the line spread function (LSF) of a single ion chamber in the detector in a clinical 6 MV photon beam was measured with a narrow slit of width 0.25 mm. The LSF of the detector was obtained by laterally translating it in 0.5 mm steps underneath the slit, from the center to 16 mm distance from the center in the cross‐plane direction. The measured signal was corrected for background and leakage. The FWHM of the LSF for the single chamber was found to be 4.2 mm, which is comparable to the chamber size of 3.8 mm. The MTF of the detector system is a sinc function and with a first zero crossing of the MTF at spatial frequency of 0.25 lp/mm. This compares well to the value of 0.15 lp/mm found for the PTW (Germany) 2D‐ARRAY type 10024, also used for dose verification of IMRT fluence. We have successfully measured the LSF for a new novel transmission detector using a narrow slit method and a clinical 6MV photon beam. The transmission detector was found to have a better first zero crossing of the MTF compared to the 2D‐ARRAY type 10024. Research partly sponsored by IBA Dosimetry.
Poster — Thur Eve — 11: Evaluation of the Performance of a Positron Emission Based Tumour‐Tracking Technique
Authors: Chamberland M , Soleimani M , Wassenaar R , Spencer B , Xu T
Published: August 2010

The delivery accuracy of radiotherapy treatments remains limited by tumor motion due to patient breathing. We present a simulation study and experimental evaluation of a technique called PeTrack that can track tumour location in real‐time. Position sensitive detectors record annihilation coincidence events from fiducial positron emission markers implanted in or around the tumour. It uses an expectation‐maximization clustering algorithm to track the position of the markers and a linear extrapolation method for motion prediction. We assessed the performance of the tracking using a clinical positron emission tomography system with the markers moving in different patterns. We also evaluated the performance of the tracking for stationary markers using a prototype PeTrack detector. In the experimental study with the PET scanner, the data was fitted to two theoretical curves. The root mean square error (RMSE) was 0.43 mm in x and 0.46 mm in y for a sinusoidal movement pattern. The RMSE was 0.64 mm in x for motion following animal breathing data. The linear extrapolation method for motion prediction yielded an average prediction error of 1.1 mm in the experimental study, with a prediction error of 2.3 mm at a 95% confidence level. Using the prototype PeTrack detector, the tracking precision was found to be 0.16 mm in x, 0.20 mm in y and 0.21 mm in z. We conclude that PeTrack can track tumour motion in real‐time and improve the delivery accuracy of radiotherapy.
Poster — Thur Eve — 17: Effect of Heterogeneities Due to Kilo‐Voltage Photon Beam Energy in Small‐Animal Irradiation: A Monte Carlo Evaluation
Authors: Chow J , Lindsay P , Leung M , Jaffray D
Published: August 2010

This study evaluated the effect of tissue heterogeneities due to photon beams in the kilo‐voltage energy range in small‐animal irradiation. Monte Carlo (MC) simulation (EGSnrc code) was used. Three MC mouse phantoms were generated from a single mouse CT image set. These phantoms were generated by overriding the relative electron density of no voxels (heterogeneous), all voxels (homogeneous) and the bone voxels (bone homogeneous) to one. Phase‐space files of the 100 and 225 kVp photon beams produced by a small animal irradiator were generated using BEAMnrc. A 360 deg photon arc was simulated for treatment of the lung, and 3D dose calculations were carried out for the three phantom geometries. The resulting dose profiles for the different phantoms and beam energies were compared. It was found that the 225 kVp photon beams have a better conformai dose distribution than the 100 kVp. The bone doses in the heterogeneous mouse phantom were about 4 – 5 (100 kVp) and 2 (225 kVp) times higher when compared to the homogeneous phantom. However, the lung dose does not vary significantly between the heterogeneous, homogeneous and bone homogeneous phantoms for either the 100 or 225 kVp photon beams. We concluded that bone dose enhancement was found when 100 and 225 kVp photon beams were used in small‐animal irradiation. This dosimetric effect due to the presence of the bone heterogeneity was more significant than the lung heterogeneity, and such bone dose enhancement does not occur in the typical patient's radiotherapy using the MV photon beams.
Poster — Thur Eve — 20: Fine Tuning the Source Parameters of a Varian 6 MV BEAMnrc Model through the Simulation of Small Jaw Collimated Photon Fields
Authors: Cranmer‐Sargison G , Sidhu NP , Thwaites DI
Published: August 2010

Purpose: The goal of this work was to finalize the electron source parameters of a Varian 6 MV BEAMnrc model through the simulation of jaw collimated small fields. Methods and Materials: For nominal field sizes of 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 cm profile data was acquired in water using a stereotactic field diode (SFD) and EBT2 film. To achieve a positional error below ± 0.01 cm a stepper motor driven linear actuator device was incorporated into the Wellhofer water tank. At electron energies of 6.0, 6.1 and 6.2 MeV the spatial distribution of the electrons incident on the target was modelled as a Gaussian. The FWHM was decreased in steps of 0.010 cm from 0.150 to 0.100 cm. DOSXYZnrc simulations were run and profile data extracted for comparison. Results: The SFD and EBT2 profile data were found to be in good agreement with small differences believed to be the result of non‐uniformities inherent to the film. In all cases the measured field sizes were found to be smaller than the nominal and the simulated field sizes adjusted accordingly. At a FWHM = 0.150 cm the penumbral width was much too broad and the smallest field widths wider than experiment. As the FWHM was decreased from 0.150 to 0.110 cm the fit became progressively better, yet worsened at a FWHM = 0.100 cm for all but the smallest field size. Conclusion: Small jaw collimated fields can be used to fine tune the electron source parameters used in a BEAMnrc linac model.
Poster — Thur Eve — 21: Monte Carlo Simulation of X‐Ray Scatter in Diagnostic Range with EGSnrc and GEANT4
Authors: Cui C , Elbakri IA , Ingleby HR , Lippuner J
Published: August 2010

In diagnostic x‐ray imaging, the attenuation of matter to x‐rays is substantially due to Compton and Rayleigh scattering in low Z materials. Consequently, the contrast of the x‐ray images is degraded by scattered photons. Because the total coherent scatter cross‐section is only about 10% of total Compton scatter cross‐section, Compton scatter plays a crucial role in x‐ray image quality. The x‐ray scatter effect can be corrected with experimentally measured or simulated data to improve image quality. It is necessary to acquire accurate x‐ray scatter information. Monte Carlo simulation is an important way of acquiring the x‐ray scatter information and the only practical way to analyze the Compton and Rayleigh scatter separately. However, due to the different ways of modeling the physics and various approximations in different Monte Carlo simulation packages, inconsistent simulation results have been observed. Using the Monte Carlo simulation packages of EGSnrc and GEANT4 we investigated the effects of the electron‐binding effects on the simulated x‐ray scattering in the diagnostic range. It is found that the Compton scatter and Rayleigh scatter are significantly different when simulated with different simulation packages and different physics models, e.g. with or without electron binding effect simulated. These differences are probably due to the ways the scattering process is modeled in the Monte Carlo simulation packages. Because the crucial role of simulated x‐ray scatter in scatter correcting in diagnostic imaging, improved modeling to the x‐ray scatter process in the Monte Carlo simulation package is desired.
Poster — Thur Eve — 22: Monte Carlo Inverse Planning and Site‐Specific Integration in HDR Brachytherapy
Authors: D'Amours M , Poon E , Pouliot J , Dagnaul A , Verhaegen F , Beaulieu L
Published: August 2010

Purpose: In HDR brachytherapy, the presences of air gaps, bones and applicator are neglected in the TG43 dose calculation algorithm and therefore no commercial treatment planning system (TPS) can take into account these factors. This approximation could cause major dosimetric divergences. This work demonstrates the combine use of Monte Carlo (MC) dose calculations with inverse planning based on simulated annealing in order to incorporate heterogeneities at the optimization stage in brachytherapy. Materials and Method: Each DK consists in an independent simulation with a full representation of the setup: CT‐based reconstruction of the patient anatomy and applicator model in Geant4. Two different HDR source model were used for the study: Nucletron's 192Ir microSelectron and the axxent electronic source (Xoft inc.), for 50 kVp. This method is tested with two different anatomies. The first one is an interstitial breast treatment and the second case is a rectum applicator boost. A research version of the inverse planning algorithm IPSA was chosen as the optimization method. IPSA reads and analyzes the DKs, replacing the TG43 formula for the cost function evaluation. Results: The impact of the water approximation is found to be energy dependent, with a greater effect for the x‐ray source compared to Iridium. For the breast case, an underdosage of 5.4 % versus 2% on the CTV V100 is found. These deviations are corrected using the MC approach. Conclusion: This novel technique is shown to improve the dosimetry and the planning in HDR brachytherapy.
Poster — Thur Eve — 23: Artificial Electron Disequilibrium Due to Inaccurate Cone‐Beam CT Data for Adaptive Lung Radiation Therapy
Authors: Disher B , Hajdok G , Wang A , Craig J , Gaede S , Battista J
Published: August 2010

Cone‐beam computed tomography (CBCT) is becoming a clinically useful imaging modality for image‐guided adaptive radiation therapy. The Varian On‐Board Imaging system (Varian Medical Systems Inc., Palo Alto California) uses a 125 kVp source, emitting a conical x‐ray beam, and a flat‐panel amorphous silicon detector. Unfortunately, CBCT images are prone to artifacts such as those caused by acceptance of x‐ray scatter from the patient at the detector plane, intra‐fraction motion, and x‐ray spectral “beam‐hardening”. Previous studies indicate that large dose inaccuracies occur when using CBCT lung images for adaptive dose computations, compared to other treatment sites with less tissue heterogeneity. We have compared dose distributions calculated using CBCT and 4‐dimensional (4D) time‐averaged CT (Philips Inc., Cleveland, OH) lung images of the same patient. Using 6MV fields, an under‐dosage of 55Gy was predicted for the CBCT planned target volume, compared to 60Gy predicted by the 4DCT based plan. CT number profiles from CBCT and 4DCT lung images revealed many undervalued pixels in the CBCT data, some corresponding to vacuum (−1000HU)! Monte Carlo simulations of dose deposition, using a water and lung slab geometry, were used to study the effects of ultra‐low density on the 3D dose distribution. It was found that a specific transition‐density induces lateral electron disequilibrium, and causes an undervaluation of dose in mid‐lung, along the central axis of the beam. Thus, CBCT images containing depressed CT number values in lung caused an artificial electron disequilibrium problem, which can be misinterpreted in adaptive treatment re‐planning.
Poster — Thur Eve — 25: Improving the Accuracy of Electrometer Calibrations
Authors: Downton B
Published: August 2010

For many years, the Ionizing Radiation Standards (IRS) group, NRC, has maintained the capacity to calibrate high‐quality electrometers used for radiation therapy. In particular, electrometer calibrations have now become a necessary part of the recently introduced MV X‐ray calibration service. With a growing interest in electrometer calibrations, the IRS electrometer calibration facility was due for revamping and upgrading. In 2008, instability in the IRS electrometer calibration system was observed during a period of high humidity. Troubleshooting suggested that the high humidity was causing high leakage currents, but it was difficult to obtain evidence of leakage occurring at any specific location since the leakage currents were small (pA or even fA). Desiccation of the calibrated standard capacitors dramatically improved the overall system performance, so the eventual solution involved isolation of the calibrated standard capacitors using a humidity controlled cabinet. Additional improvements included changing most of the connectors in the system from coaxial BNC to two‐lug triaxial bayonet type (TRB), and designing a 3‐stage filter to allow calibrations of newer current‐based electrometers. The result is an electrometer calibration facility that is unaffected by humidity and very stable, allowing year‐round calibrations for any of the electrometer models commonly encountered.
Poster — Thur Eve — 27: Investigation of the Influence of Different Encapsulating Material on 170Tm Brachytherapy Source Spectra
Authors: Enger S , D'Amours M , Aizier A , Beaulieu L
Published: August 2010

The purpose of this work was to investigate the influence of the encapsulating material on different part of the 170Tm decay spectra. A hypothetical 170Tm source with the Flexisource brachytherapy encapsulation was used in the simulations. The active core of the source is a pure thulium cylinder with a length of 3.5 mm, a radius of 0.3 mm and covered with a stainless‐steel or a pure gold cylinder. The length of the capsule is 5 mm, the inner radius is 3.0 mm and the outer radius 0.425 mm. Simulations were performed with and without taking the source encapsulation into account. The simulation utilized GEANT4 Monte Carlo code version 9.2. For the stainless‐steel encapsulation 95.5% of the total brems Strahlung is produced inside the core, 3.8% in the capsule and less than 1% in the water. For the gold capsule 85% is produced inside the core, 14.2% inside the gold capsule and negligible amount (<1%) in water. The range of the beta particles decreases with 1.1 mm with the stainless‐steel encapsulation but the tissue will still receive dose from the beta particles up to 3 mm from the source. The gold encapsulation, if present, absorbs most of the electrons and attenuates low energy photons. The mean energy of the photons escaping the core and the stainless‐steel capsule is 113 keV while for gold capsule the mean energy is 160 keV. TG43 parameters in both cases are extracted.
Poster — Thur Eve — 29: Determination of Contrast Agent Concentration in Tortuous Blood Vessels Using Measured MRI Phase Changes and Fourier‐Based Field Inhomogeneity Equations
Authors: Foottit C , Cron G , Hogan M , Nguyen T , Cameron I
Published: August 2010

There has been considerable research effort into obtaining quantitative measures of perfusion using dynamic contrast‐enhanced MRI. Absolute quantification of the arterial input function (AIF) and/or venous output function (VOF) in major blood vessels improves perfusion estimates, however reliable techniques for doing so are lacking. Using changes in phase (Δφ) in blood vessels is thought to be the best way to quantify the AIF or VOF. However, it is not yet clear how best to deal with the susceptibility physics when the blood vessels have a complex geometry. We propose a methodology for obtaining absolute quantification of the AIF or VOF using a Fourier‐based calculation of field inhomogeneities, in order to convert Δφ to absolute contrast agent concentration, regardless of the blood vessel geometry. This methodology was tested in an aqueous phantom system. The experimentally measured Δφ was divided by the expected Δφ on a pixel by pixel basis. Ideally, this ratio should be one. Considering all pixels in the phantom tubing, the measured Δφ divided by expected Δφ had a mean value of 1.02 and standard deviation of 0.172. The Fourier‐based calculation can therefore successfully predict Δφ and thus can be used to account for the effect of the vessel geometry and orientation in the conversion of MR phase to contrast agent concentration. The methodology is thus promising for making absolute measurements of the AIF or VOF.
Poster — Thur Eve — 31: Optimum Frequency of Spatial Registration in Image Guided Radiation Therapy for TMI
Authors: Garcia LM , Wilkins D , Gerig LH , Nyiri B , Raaphorst P
Published: August 2010

Purpose: To assess the influence of the frequency of spatial registration in total marrow irradiation using Helical Tomotherapy to correct for intrafraction variations. Methods: The analysis was performed using TCP and NTCP models in a phantom study. Different cases were investigated: one treatment per fraction (no‐junction), and splitting the treatment along Y‐axis (SUP‐INF direction) into 2 or 3 independent sub‐treatments (one/two‐junction), which allows 2 or 3 spatial registrations per treatment fraction. Linearly increasing margins were added to expand the CTV (ribs and spine) and OARs (lungs) with increasing distance from the registration point (iPTV and iPRV). Margin increases of 5, 10 and 15 mm were analyzed. The prescription was for 95% of the iPTV to receive 20 Gy. Results: The dose to the iPRVs was reduced when the treatment was split; D20 to lung was 22, 16.2 and 13.4 Gy for no‐junction, one‐junction and two‐junction cases respectively. However the dose received by the iPTV also decreased; the volume of the iPTV receiving the prescription was 93.9%, 90.5% and 88.4% respectively. The probability of uncomplicated cure TCP(1‐NTCP) increased 3% from no‐junction to two‐junction cases for a maximum margin of 5 mm. The corresponding difference for maximum margin of 15 mm was 22%. Larger margins combined with splitting the treatment to perform additional patient registrations showed benefit, mainly due to lower NTCP. Conclusion: Increasing uncertainties can be reduced by splitting large treatments and realigning the patient prior to each sub‐treatment. This technique reduces the NTCP and marginal misses of the PTV.
Poster — Thur Eve — 39: Dosimetric Evaluation of Bulk Electron Density Based Treatment Planning in IMRT Head and Neck Patients: Can It Be Used for MRI‐Based Planning?
Authors: Karotki A , Mah K , Meijer G , Meltsner M
Published: August 2010

One limitation of using MRI alone for radiation planning is the lack of electron density for dose calculation. We evaluated the dosimetric accuracy of using bulk density overrides as a substitute for CT‐derived densities in IMRT treatment planning for head and neck cancer. Ten clinically‐approved, CT‐based treatment plans were used for this study. Three dose distributions were calculated for each treatment plan. The first calculation used CT‐derived density as a basis for heterogeneity correction. The second calculation assumed a homogeneous patient density of 1 g/cm3. For the third dose calculation we contoured bones and air cavities and assigned them a uniform density of 1.5 g/cm3 and 0 g/cm3, respectively. The remaining tissue was assigned a density of 1 g/cm3. All three calculations utilized identical beam parameters (angles, segments and MUs). Actual MR images were not used for contouring to avoid effects of gradient distortion and volumetric uncertainties associated with them. All calculations were done using the Collapsed Cone Superposition algorithm in the Pinnacle3 treatment planning system. Our results show that the assignment of bulk density to bones and air cavities was a feasible approach to IMRT treatment planning for head and neck patients. In almost all cases, the dosimetric results were within 2% of the treatment plans based on CT‐derived density. This method may overcome the lack of electron density information in MR‐based planning. The use of homogeneous geometry, while simpler and less time consuming, resulted in unacceptably high errors in the dose distribution compared to the nominal plan. This research project is supported by Philips Medical Systems.
Poster — Thur Eve — 43: Clinical Evaluation of an Atlas Based Auto‐Segmentation Application for Auto‐Contouring Pelvic Targets and OARs
Authors: Kamta G Lagmago , Buckley L , Henderson E
Published: August 2010

The use of volumetric image data sets in radiotherapy treatment planning has become standard practice and requires an accurate delineation of anatomical structures, a tedious and time consuming task. This has lead to the development of auto‐segmentation approaches for contouring anatomical structures on CT data sets. In this work, we evaluate the accuracy of the ABAS software package (Atlas Based Auto‐Segmentation, version 1.1.0, CMS, Inc, The Elekta Group) for contouring pelvic organs relevant to radiotherapy. The evaluation is based on randomly selected CT data sets of 8 patients treated in our clinic for pelvic malignancies, in which relevant organs have been manually contoured by an oncologist. Each of the 8 CT data sets is used as an atlas to generate contours on all other sets. The resulting ABAS‐generated contours are compared to oncologists ones by means of the Dice coefficient. We find that contours generated by ABAS are best and will require no editing for bony structures such as the femoral heads and the pelvis. For the prostate, bladder and the rectum, ABAS contours are acceptable but will require some editing. However, for the prostate, the presence of fiducial implants could lead to streaking artifacts that degrade the quality of ABAS‐generated contours. For smaller organs with low tissue contrasts such as seminal vesicles and iliac nodes, ABAS results are poor and will lead to no time savings in the radiotherapy process. Finally for organs for which ABAS works well it is quite robust against the variability of the atlas.
Poster — Thur Eve — 44: Short Term Development Effects of Gafchromic EBT2 Film
Authors: Lamey M , Field C , McKenzie M , Fallone BG
Published: August 2010

Introduction: Gafchromic external beam therapy (EBT)2 is used in our clinic to verify the delivery of Tomotherapy patient plans. We have investigated the short term development effects of Gafchromic film up to 16 hours after irradiation. The importance of the scan position of the film along the active region of a Vidar Pro Dosimetry scanner is also studied. Materials/Methods: An EBT2 film is placed between two halves of a cylindrical phantom. A calibration plan which delivers dose in 13 predefined regions on the film is delivered on a Tomotherapy Hi‐ART 2 (Tomotherapy Inc., Madison WI) system. A point dose is taken within the phantom and used to determine the film irradiation response. The film was scanned using a Vidar Pro Dosimetry Advantage (Vidar, Herndon, VA, USA) scanner. The film was scanned after irradiation at times ranging from 5 minutes to 16 hours. The importance of the film position along the scanner active region was investigated by scanning the film under two conditions: at the edge of the scanner and at the middle of the scanner. Results/Discussion: One hour after irradiation the film had developed to 98.5 % of the measured OD at 16 hours, while after 2 hours, the film had developed to approximately 99 % of the measured OD at 16 hours. Specific to our calibration file setup, we measured a difference of 4.7 % in the 54 cGy region. This large difference could be important when using film to determine the acceptance of patient plans.
Poster — Thur Eve — 45: Three‐Dimensional US Probe Localization by Single Perspective Pose Estimation
Authors: Lang P , Seslija P , Habets D , Chu M , Holdsworth D , Peters T
Published: August 2010

Purpose: Intra‐operative fluoroscopy and transesophageal (TEE) ultrasound are imaging modalities commonly used in many cardiac procedures, including trans‐catheter aortic valve replacement. Fluoroscopy‐to‐ultrasound registration would enhance conventional image guidance by providing a common frame of reference in which both modalities can be viewed. An important component of this registration is 3D localization of the TEE probe with respect to the fluoroscopic image. Traditional approaches to this problem employed magnetic tracking systems, however these systems are hindered by metallic distortions and restrictive patient access within the operating room. Methods: Two 2D‐to‐3D registration techniques, a point‐based and intensity‐based technique, were implemented. These registration techniques determine the 3D pose of the TEE probe directly from single‐perspective fluoroscopy images, which facilitates the localization of both the probe and fluoroscopic image in a common frame of reference. In vitro experiments were performed to assess the accuracy of each registration technique. Measured displacements were compared against mechanical translation/rotation tables, utilized to provide a gold standard. Results: Maximum root‐mean‐square displacement and rotation errors were found to be 0.58mm, 0.32° and 2.29mm, 3.76° for point‐based and intensity‐based tracking techniques, respectively. The accuracy of the point‐based registration technique is significantly higher than the intensity‐based technique, but requires the use of a rigid tracking attachment. Conclusion: Localization of the TEE from single‐perspective fluoroscopy images provides an accurate means of intra‐operative fluoroscopy‐to‐ultrasound registration, and does not significantly interrupt the regular workflow within the operating room.
Poster — Thur Eve — 46: Image‐Based Scoring of Radiation Injury in Lung: Analysis of Sources of Uncertainties
Authors: Lee S , Stroian G , Seuntjens J
Published: August 2010

We are studying the robustness and uncertainties of an automated method for quantifying radiotherapy‐induced lung injury from CT images and delineate its relationship with radiation dose at different post‐radiation (post‐RT) time points. Methods: Using multi‐resolution affine optimization technique, post‐RT diagnostic CT images were registered to planning CT images. Following the registration and patient tissue‐based CT calibration, a change in physical density at each voxel position of the planning CT was evaluated and voxels which density change is considered pathological were segmented as injury. Retrospective dose calculations using anisotropic analytical algorithm (AAA) and Monte‐Carlo (MC) were performed. The segmented injury was spatially correlated to the dose distributions to deduce a patient‐specific dose‐response relationship for radiation‐induced injury. Results: We found the probability of injury as a function of dose and post‐treatment time was patient‐specific. Due to the inaccuracy of the affine registration, the injury segmentation was manually corrected for the misalignment of normal tissue features, which gave rise to a case‐dependent uncertainty of up to 10%. Inter‐patient variability in CT calibration contributed 4% or less to the uncertainty on the probability. Finally, dose calculation from MC simulation occasionally yielded a significantly modified complication probability compared to AAA model suggesting that dose calculation accuracy is important for the investigation on dose‐response of lung injury. Conclusion: The presented method provided a quantitative approach for dose‐response analysis in normal lung tissues if the accuracy in image registration and dose calculation can be assured and will provide better options to complication‐driven treatment planning.
Poster — Thur Eve — 48: Comparison of Organ Doses and Effective Dose with PCXMC and Phantom Measurements for Neonates
Authors: Ma H , Omotayo A , King J , Elbakri IA
Published: August 2010

Monte Carlo (MC) simulations and phantoms measurements are essential methods to estimate patient dose in radiography. We compared organ and effective doses determined using the PCXMC 2.0 MC software with TLD phantom measurements for newborn patients. We used high sensitivity TLD's (TLD‐100H, Harshaw) for organ dose measurements using the ATOM 703D anthropomorphic newborn phantom. TLD's were calibrated, annealed and then placed in pre‐drilled slots at various locations in the phantom representing several internal organs. The thorax and abdomen of the phantom were exposed at techniques similar to those used in the neonatal intensive care unit. The charge read‐out form the TLD's was then converted to organ doses form which an effective dose value was calculated. This value was then compared to that obtained from PCXMC 2.0 (STUK, Finland) by using the same exposure and patient parameters. The Effective dose values were 20.88μSv and 21.10μSv for phantom and PCXMC calculations respectively, yielding a 1.05% difference. Organ doses also showed good agreement. Organs partially exposed or outside of the primary beam showed higher discrepancies. Overall, both methods are useful for dose optimization studies but PCXMC has an advantage in terms of the amount of time and effort required to generate dose estimates.
Poster — Thur Eve — 52: Head and Neck IMRT Complexity Characterization and Prediction of Deliverability Using the Modulation Complexity Score
Authors: McNiven AL , Davidson MTM , Sharpe MB , Purdie TG
Published: August 2010

Intensity modulated radiation therapy (IMRT) is often referred to as being highly complex, but the definition of complexity can be varied. A single metric, the modulation complexity score (MCS), has previously been developed to quantify IMRT complexity. The purpose of this study is to evaluate the use of MCS in the characterization of segmentation complexity and beam deliverability in the context of head and neck IMRT. Fifty treatment plans were evaluated by calculating the MCS per beam. Patient‐specific measurements were obtained as part of the standard IMRT QA process using a diode array and retrospective analysis was completed using various gamma analysis criteria. The MCS, as well as single beam parameters (e.g. number of MU or control points), were compared to dosimetric results. 375 individual treatment beams were analyzed, with an average MCS of 0.245 (range: −0.338 – 0.754) and 125 MU on average (range: 32 to 295). All beams had >90% of diodes passing the standard gamma analysis (3%/3mm) with an average of 98%. There was a linear relationship between the number of MU and the MCS score (r2=0.75). The relationship between pass rate and complexity (characterized by MCS or MU) is not simple, however it may be possible to predict good dosimetric results based on the plan complexity. In conjunction with the ability to compile complexity statistics for specific treatment sites or protocols, MCS could impact the radiation therapy process at many points, including during planning, plan evaluation and QA.
Poster — Thur Eve — 54: Discrete Point Spread Functions for Electronic Portal Imaging Devices
Authors: Nichita E , Ostapiak O , Farrell T
Published: August 2010

EPID images are related to the fluence by a (possibly position‐dependent) Point Spread Function (PSF), or kernel. So far, work concerning finding the PSF for a certain EPID has relied on continuous representations. Since the EPID image itself corresponds to a discrete pixel grid, an interesting problem is to find a discrete PSF and do so based only on measurements, without resorting to Monte Carlo simulations. The present work concerns a method for finding such a discrete kernel for the simple case when the kernel is translation‐ and rotation‐invariant. The method relies on minimizing the difference, in a least‐squares sense, between the true acquired image and the image obtained with the calculated kernel. The method was tested using a simulated fluence and EPID image corresponding to a uniform rectangular field. The EPID image was generated by convolving the fluence with a known PSF. The developed algorithm was then tested by comparing the PSF shape produced by the algorithm (based on the image and fluence) with the actual PSF shape used to construct the EPID image. The two were found to match perfectly. A second test was performed by introducing a random error, uniformly distributed in the (−10%, +10%) interval, into the fluence used as input for the algorithm and then reconstructing the EPID image using the calculated PSF. The difference between the “true” EPID image and the reconstructed one was found to be smaller than 0.1% for the simulated field that was studied.
Poster — Thur Eve — 58: Beam Orientation Optimization for IMRT Treatment Planning Using PARETO
Authors: Potrebko P , McCurdy B , Fiege J , Champion H , Cull A
Published: August 2010

Intensity‐modulated radiation therapy (IMRT) treatment planning requires tradeoffs to be made between delivering a prescribed dose to the planning target volume (PTV) and sparing the organ's‐at‐risk (OARs). Traditionally in clinical practice, treatment planners manually optimize beam orientations, objectives, and/or weights in a time‐consuming, trial‐and‐error process to find some acceptable compromise, with no guarantee that this solution is actually optimal. We propose a novel and powerful fluence and beam orientation optimization package for radiotherapy optimization, called PARETO (Pareto‐Aware Radiotherapy Evolutionary Treatment Optimization), which consists of a multi‐objective genetic algorithm capable of optimizing several objective functions simultaneously and mapping the structure of their trade‐off surface efficiently and in detail. Fitness functions, based on mean dose for the OARs and PTV, as well as fluence gradients are optimized. PARETO intelligently varies all beam orientations and beam fluence to simultaneously optimize all objectives. Over many generations, the entire family of Pareto‐optimal treatment plans, spanning a multi‐dimensional trade‐off surface, is mapped out. Pareto‐optimal solutions are stored in a database and trade‐offs between the competing objectives can be visualized graphically and explored. The efficacy of the solutions provided by PARETO was evaluated using a commercial treatment planning system with five coplanar IMRT treatment plans for a homogenous phantom consisting of three OARs surrounding a central PTV. This work demonstrated that the fitness functions within PARETO have a strong correlation to the dose distribution. Thus, from many Pareto‐optimal plans, the clinician may select the plan which they decide is the most appropriate multi‐objective compromise for a patient.
The Nonphagocytic NADPH Oxidase Duox1 Mediates a Positive Feedback Loop During T Cell Receptor Signaling
Authors: Kwon Jaeyul , Shatynski Kristen E. , Chen Haiyan , Morand Stanislas , de Deken Xavier , Miot Françoise , Leto Thomas L. , Williams Mark S.
Published: August 2010

Reactive oxygen species enhance T cell receptor signaling by promoting the phosphorylation of a proximal kinase.
HCMV-Encoded Chemokine Receptor US28 Mediates Proliferative Signaling Through the IL-6–STAT3 Axis
Authors: Slinger Erik , Maussang David , Schreiber Andreas , Siderius Marco , Rahbar Afsar , Fraile-Ramos Alberto , Lira Sergio A. , Söderberg-Nauclér Cecilia , Smit Martine J.
Published: August 2010

A viral G protein–coupled receptor may initiate a positive feedback loop to promote tumor proliferation and vascularization.
Astrocytes, ATP, Brainstem, and Breathing
Authors: Stern Peter R.
Published: August 2010

Central nervous system glial cells are key players in the chemo-reflex essential for breathing.
Mycobacterium bovisBCG-Specific Th17 Cells Confer Partial Protection againstMycobacterium tuberculosisInfection in the Absence of Gamma Interferon
Authors: Wozniak Teresa M. , Saunders Bernadette M. , Ryan Anthony A. , Britton Warwick J.
Published: August 2010

Protective immunity against tuberculosis (TB) requires the integrated response of a network of lymphocytes. Both gamma interferon (IFN-γ)- and interleukin 17 (IL-17)-secreting CD4+T cells have been identified in subjects with latent TB infection and during experimentalMycobacterium tuberculosisinfection, but the contribution of Th17 cells to protective immunity is unclear. To examine their protective effectsin vivo, we transferred mycobacterium-specific IL-17- and IFN-γ-secreting CD4+T cells isolated fromM. tuberculosisBCG-immunized IL-12p40−/−and IFN-γ−/−or wild-type mice, respectively, intoM. tuberculosis-infected IL-12p40−/−or RAG−/−mice. In the absence of IL-12 and IL-23, neither IL-17-secreting (Th17) nor IFN-γ-secreting (Th1) BCG-specific T cells expanded or provided protection againstM. tuberculosis. In RAG−/−recipients with an intact IL-12/IL-23 axis, both Th17 and Th1 cells were activated and induced significant protection againstM. tuberculosis. The reduction in the bacterial load following transfer of IFN-γ−/−Th17 cells was associated with significant prolongation of survival compared to recipients of naïve IFN-γ−/−T cells. This effect was at the cost of an increased inflammatory infiltrate characterized by an excess of neutrophils. Therefore, Th17 cells can provide IFN-γ-independent protection againstM. tuberculosis, and this effect may contribute to the early control ofM. tuberculosisinfection.
Treatment of coil embolization failed recurrent giant basilar tip aneurysms with bypass and surgical occlusion
Authors: Ramanathan Dinesh , Ciporen Jeremy , Ghodke Basavaraj , Ellenbogen Richard G , Sekhar Laligam N
Published: August 2010

Giant basilar tip aneurysms are a challenge to treat because of the complex anatomy and critical vessels that arise in this region. For large aneurysms, with multiple recurrences after coiling, when microsurgical clipping is not possible, a bypass to the posterior cerebral artery (PCA) can be helpful in providing definitive treatment. Two patients with giant basilar tip aneurysms were treated with bypass to the PCA. One patient had a microsurgical clipping and the other had a proximal occlusion of the basilar artery along with the bypass. Long-term angiographic and clinical follow-up was obtained. One patient had marked improvement in symptoms and a stable aneurysm remnant and the other patient had complete occlusion. Surgical treatment with a bypass to the PCA, with clipping of the aneurysm or proximal ligation of the basilar artery can be an effective treatment option for giant basilar tip aneurysms.
INPUT-OUTPUT RELATION OF LINEAR SYSTEMS BY USING COMPLEX WAVELET PACKET TRANSFORM
Authors: OSAKE MASAAKI , NAKANO KAZUSHI , TABARU TETSUYA , SHIN SEIICHI
Published: August 2010

This paper is concerned with an input-output relation of linear systems when using the complex wavelet packet transform. In general, the linear relation between input-output is guaranteed by the following two conditions: (1) the mother wavelet has a better frequency resolution, and (2) the real and imaginary parts in the mother wavelet consist of a Hilbert transform pair. The complex wavelet satisfying the above conditions has been used for demonstrating the linear relation. In this paper, a complex wavelet packet transform is applied for improving the frequency resolution. The validity of our approach is shown through a numerical experiment.
FIRM-LEVEL ENTREPRENEURSHIP: THE ROLE OF PROACTIVENESS, INNOVATIVENESS AND STRATEGIC RENEWAL IN THE CREATION AND EXPLORATION OF OPPORTUNITIES
Authors: KREISER PATRICK , MARINO LOUIS , DAVIS JUSTIN , TANG ZHI , LEE CHOONWOO
Published: August 2010

Recent research suggests that existing conceptualizations of firm-level entrepreneurship may not be sufficient in fully explaining the construct. The primary purpose of this study is to explore the fundamental dimensions underlying firm-level entrepreneurship and to empirically test a model depicting the hierarchical relationship between these various dimensions. It is argued that proactiveness, innovativeness and strategic renewal represent the primary dimensions of firm-level entrepreneurship. Three hypotheses are developed, specifying the role each of these three dimensions plays in the creation and exploitation of environmental opportunities. Utilizing data collected from 250 small-to-medium sized enterprises (SMEs) in South Korea, the empirical results suggest proactiveness positively impacts firms' perceptions of environmental opportunities, and these organizations then utilize innovativeness and strategic renewal in an effort to capture these perceived opportunities. The paper concludes with a discussion of the implications of our study for managerial practice and theory building.
Calibration and Evaluation of Fixed and Mobile Relay-Based System Level Simulator
Authors: Mumtaz Shahid , Tu Le Thanh , Saidul Kazi , Gameiro Atílio
Published: August 2010

Future wireless communication systems are expected to provide more stable and higher data rate transmissions in the whole OFDMA networks, but the mobile stations (MSs) in the cell boundary experience poor spectral efficiency due to the path loss from the transmitting antenna and interference from adjacent cells. Therefore, satisfying QoS (Quality of Service) requirements of each MS at the cell boundary has been an important issue. To resolve this spectral efficiency problem at the cell boundary, deploying relay stations has been actively considered. As multihop/relay has complex interactions between the routing and medium access control decisions, the extent to which analytical expressions can be used to explore its benefits is limited. Consequently, simulations tend to be the preferred way of assessing the performance of relays. In this paper, we evaluate the performance of relay-assisted OFDMA networks by means of system level simulator (SLS). We consistently observed that the throughput is increased and the outage is decreased in the relay-assisted OFDMA network, which is converted to range extension without any capacity penalty, for the realistic range of values of the propagation and other system parameters investigated.
Blood Glucose Levels and Performance in a Sports Camp for Adolescents with Type 1 Diabetes Mellitus: A Field Study
Authors: Kelly Dylan , Hamilton Jill K. , Riddell Michael C.
Published: August 2010

Background. Acute hypo- and hyperglycemia causes cognitive and psychomotor impairment in individuals with type 1 diabetes mellitus (T1DM) that may affect sports performance.Objective. To quantify the effect of concurrent and antecedent blood glucose concentrations on sports skills and cognitive performance in youth with T1DM attending a sports camp.Design/Methods. 28 youth (ages 6–17 years) attending a sports camp carried out multiple skill-based tests (tennis, basketball, or soccer skills) with glucose monitoring over 4 days. Glucose levels at the time of testing were categorized as (a) hypoglycemic (<3.6 mM); (b) within an acceptable glycemic range (3.6–13.9 mM); or (c) hyperglycemic (>13.9 mM).Results. Overall, sports performance skill was~20% lower when glucose concentrations were hypoglycemic compared to either acceptable or hyperglycemic at the time of skill testing (). During Stroop testing, “reading” and “color recognition” also degraded during hypoglycemia, while “interference” scores improved (). Nocturnal hypoglycemia was present in 66% of subjects, lasting an average of 84 minutes, but this did not affect sports skill performance the following day.Conclusions. Mild hypoglycemia markedly reduces sports skill performance and cognition in young athletes with T1DM.
Therapeutic Improvement of Scarring: Mechanisms of Scarless and Scar‐Forming Healing and Approaches to the Discovery of New Treatments
Authors: Occleston Nick L. , Metcalfe Anthony D. , Boanas Adam , Burgoyne Nicholas J. , Nield Kerry , O′Kane Sharon , Ferguson Mark W. J.
Published: August 2010

Scarring in the skin after trauma, surgery, burn or sports injury is a major medical problem, often resulting in loss of function, restriction of tissue movement and adverse psychological effects. Whilst various studies have utilised a range of model systems that have increased our understanding of the pathways and processes underlying scar formation, they have typically not translated to the development of effective therapeutic approaches for scar management. Existing treatments are unreliable and unpredictable and there are no prescription drugs for the prevention or treatment of dermal scarring. As a consequence, scar improvement still remains an area of clear medical need. Here we describe the basic science of scar‐free and scar‐forming healing, the utility of pre‐clinical model systems, their translation to humans, and our pioneering approach to the discovery and development of therapeutic approaches for the prophylactic improvement of scarring in man