bluuebunny/crossref_metadata_2025 huggingface dataset:
Muscular adaptations after two different volumes of blood flow‐restricted training
Authors: Martín‐Hernández J. , Marín P. J. , Menéndez H. , Ferrero C. , Loenneke J. P. , Herrero A. J.
Published: December 2012

This study aimed to gain an insight into the adaptations of muscle strength and skeletal muscle thickness after two different volumes of blood flow restriction training (BFRT), and compare them with high‐intensity training. The sample was divided into four groups: low‐volume, low‐intensity BFRT (BFRT LV); high‐volume, low‐intensity BFRT (BFRT HV); traditional high‐intensity resistance training (HIT); and a control group, which maintained their routine activities (CON). Leg extension one repetition maximum (1RM), isokinetic peak knee extension, and flexion torques at 60°/s and 180°/s as well as muscle thickness of the rectus femoris (RF) and vastus lateralis (VL) were assessed at baseline and after 5 weeks of training BFRT LV (7.03%, P < 0.05), BFRT HV (6.24%, P < 0.05) and HIT (18.86%, P < 0.001) groups increased 1RM performance, while no changes were observed in the CON group. Muscle thickness of the RF and VL was increased irrespective of the training group (7.5%, P < 0.001; and 9.9%, P < 0.001, respectively). We conclude that doubling the exercise volume with BFRT causes no further benefit with muscular size or strength. Although similar increases in muscle thickness were observed between training groups, HIT increased 1RM performance to a greater extent compared to either volume of BFRT.
Saddlepoint approximations for the sum of independent non‐identically distributed binomial random variables
Authors: Eisinga Rob , Te Grotenhuis Manfred , Pelzer Ben
Published: December 2012

We discuss saddlepoint approximations to the distribution of the sum of independent non‐identically distributed binomial random variables. We examine the accuracy of the saddlepoint methods for a sum of 10 binomials with different sets of parameter values. The numerical results indicate that the saddlepoint approximations provide very accurate estimates for the probability mass function and the right‐tail probabilities for the cumulative distribution function of the sum.
Access and Equity in Greenspace Provision: A Comparison of Methods to Assess the Impacts of Greening Vacant Land
Authors: Heckert Megan
Published: December 2012

This research explores three methods of measuring access to greenspace in Philadelphia and their implications for assessing equity in access based on race and socioeconomic status. These three methods are then used to assess the impacts of a vacant land greening program which turns vacant lots into temporary greenspaces. This research explores the differences between findings when access to greenspace is measured based on distance to any greenspace, total amount of greenspace to which residents have access, or a hybrid measure in which access is determined based on proximity to a threshold amount of greenspace. Not only do assessments of equity differ between the three approaches, but so do determinations of the impact of greening vacant land. Blacks, Hispanics and renters are more likely to live close to a public greenspace than whites or homeowners, but live in proximity to smaller overall amounts of greenspace. Greening vacant land increases the proportion of all residents who live within walking distance of a greenspace and lessens but does not eliminate differences in total greenspace access. The greatest effects of greening vacant land are seen in addressing differences in relative likelihood of having access to a threshold amount of greenspace.
Tuberculous hepatitis in renal transplant recipients following alemtuzumab induction therapy
Authors: Bosch W. , Poowanawittayakom N. , Chaikriangkrai K. , Mendez J. , Hellinger W.C. , Gonwa T.A. , Krishna M. , Pungpapong S.
Published: December 2012

Mycobacterium tuberculosis infection is one of many opportunistic infections in renal transplant recipients, arising either from reactivation of latent infection or de novo infection, occasionally donor derived. M. tuberculosis hepatitis has never been reported in patients who have received alemtuzumab as part of their renal transplant management. We describe 2 patients who underwent deceased‐donor renal transplantation following alemtuzumab induction therapy and presented with a febrile syndrome, subsequently diagnosed as tuberculous hepatitis, one with disseminated disease. Both responded well to treatment without significant side effects, resulting in excellent graft function. The importance of chemoprophylaxis should be emphasized to minimize the risk of developing active tuberculosis in patients with latent tuberculosis infection undergoing solid organ transplantation.
Endogenous GSK‐3/Shaggy Regulates Bidirectional Axonal Transport of the Amyloid Precursor Protein
Authors: Weaver Carole , Leidel Christina , Szpankowski Lukasz , Farley Nicole M. , Shubeita George T. , Goldstein Lawrence S. B.
Published: December 2012

Neurons rely on microtubule (MT) motor proteins such as kinesin‐1 and dynein to transport essential cargos between the cell body and axon terminus. Defective axonal transport causes abnormal axonal cargo accumulations and is connected to neurodegenerative diseases, including Alzheimer's disease (AD). Glycogen synthase kinase 3 (GSK‐3) has been proposed to be a central player in AD and to regulate axonal transport by the MT motor protein kinesin‐1. Using genetic, biochemical and biophysical approaches in Drosophila melanogaster, we find that endogenous GSK‐3 is a required negative regulator of both kinesin‐1‐mediated and dynein‐mediated axonal transport of the amyloid precursor protein (APP), a key contributor to AD pathology. GSK‐3 also regulates transport of an unrelated cargo, embryonic lipid droplets. By measuring the forces motors generate in vivo, we find that GSK‐3 regulates transport by altering the activity of kinesin‐1 motors but not their binding to the cargo. These findings reveal a new relationship between GSK‐3 and APP, and demonstrate that endogenous GSK‐3 is an essential in vivo regulator of bidirectional APP transport in axons and lipid droplets in embryos. Furthermore, they point to a new regulatory mechanism in which GSK‐3 controls the number of active motors that are moving a cargo.
An Orchestrated Program Regulating Secretory Pathway Genes and Cargos by the Transmembrane Transcription Factor CREB‐H
Authors: Barbosa Sónia , Fasanella Giovanna , Carreira Suzanne , Llarena Marta , Fox Rebecca , Barreca Cristina , Andrew Deborah , O'Hare Peter
Published: December 2012

CREB3 proteins comprise a set of ER‐localized bZip transcription factors defined by the presence of a transmembrane domain. They are regulated by inter‐compartmental transport, Golgi cleavage and nuclear transport where they promote appropriate transcriptional responses. Although CREB3 proteins play key roles in differentiation, inflammation and metabolism, a general framework relating their defining features to these diverse activities is lacking. We identify unique features of CREB3 organization including the ATB domain, which we show it is essential for transcriptional activity. This domain is absent in all other human bZip factors, but conserved in Drosophila CREBA, which controls secretory pathway genes (SPGs). Furthermore, each of the five human CREB3 factors was capable of activating SPGs in Drosophila, dependent upon the ATB domain. Expression of the CREB3 protein, CREB‐H, in 293 cells, upregulated genes involved in secretory capacity, extracellular matrix formation and lipid metabolism and increased secretion of specific cargos. In liver cells, which normally express CREB‐H, the active form specifically induced secretion of apolipoproteins, including ApoA‐IV, ApoAI, consistent with data implicating CREB‐H in metabolic homeostasis. Based on these data and other recent studies, we propose a general role for the CREB3 family in regulating secretory capacity, with particular relevance to specialized cargos.
Colonization of Butchers with Livestock‐Associated Methicillin‐Resistant Staphylococcus aureus
Authors: Boost M. , Ho J. , Guardabassi L. , O'Donoghue M.
Published: December 2012

Reports have documented colonization of swine in Europe, North America and more recently in China with livestock‐associated methicillin‐resistant Staphylococcus aureus (LA‐MRSA). Contamination of pig farmers, veterinarians and abattoir workers with these strains has been observed. However, although contamination levels of 10% of retail pork were reported from the Netherlands and Canada, there are limited data of contamination rates of workers handling raw meat. We investigated the rates of MRSA contamination of local butchers working in wet markets, where recently slaughtered pigs are cut up. Nasal swabs collected from 300 pork butchers at markets throughout Hong Kong were enriched in brain heart infusion broth with 5% salt and cultured on MRSASelect®. Isolates were confirmed as Staphylococcus aureus and susceptibility testing performed. The presence of mecA was confirmed, SCCmec and spa type determined and relatedness investigated by PFGE. Subjects completed a questionnaire on MRSA carriage risk factors. Seventeen samples (5.6%) yielded MRSA, 15 harbouring SCCmec IVb. Ten strains were t899 (CC9), previously reported from local pig carcasses. Five strains were healthcare associated: SCCmec type II, t701(CC6), colonizing two subjects at the same establishment, and single isolates of t008 (CC8), t002 (CC5) and t123 (CC45). The remaining isolates were t359 (CC97), previously reported from buffaloes, and t375 (CC5), reported from bovine milk. None of these butchers reported recent hospitalization or a healthcare worker in the family. Two had recently received antibiotics, one for a skin infection. Four reported wound infections within the last year. All were exposed to meat for >9 h per day. Carriage of MRSA was higher in butchers than in the general community. Although five strains were probably of healthcare origin, the high incidence of t899 (CC9) suggests that cross‐contamination from pork occurs frequently. Washing of hands after touching raw pork is advised.
Sci—Wed PM: Delivery—02: Characterization and Clinical Evaluation of RADPOS 4D in vivo Dosimetry System
Authors: Cherpak AJ , Cygler JE , Andrusyk S , Pantarotto J , MacRae R , Lochrin C , Perry G
Published: December 2012

A novel 4D in vivo dosimetry system, RADPOS, has recently been developed. The system combines a MOSFET dosimeter with an electromagnetic positioning sensor and is currently used in a clinical trial to determine its potential for application in external beam treatments. The probe is small (1.3 mm diameter) and can be used either on patient skin or inside natural body cavities as a real time treatment verification tool providing immediate feedback about patient motion and the accuracy of the delivered dose. Preliminary tests have shown that the RADPOS has dosimetric characteristics similar to microMOSFET detectors, when the last one is used alone. The system can measure displacements with an accuracy ranging from (1.1–1.3) mm, within a volume defined by the coordinates: , , and , related to the transmitter. The stability of the RADPOS position readout is within 0.21 ± 0.07 mm and is not affected by the linac beam. The clinical trial involves lung cancer patients treated with external beam radiotherapy. Four RADPOS detectors are positioned at marked points on the patients' abdomen and chest during an initial 4DCT and subsequent treatment fractions. Position coordinates of the sensors are read in real time and compared to determine deviation from initial breathing patterns measured during the 4DCT. Total dose is read at the end of each fraction. Initial clinical results show that the RADPOS system can measure the amplitude and period of the patients breathing pattern and can provide a means to identify corresponding changes in dose.
Sci—Wed PM: Delivery—03: Commissioning of DAVID —”Device for Advanced Verification of IMRT Deliveries”
Authors: Badragan G , Badragan I , Ramani R , Duzenli C , Giovanetti M
Published: December 2012

The ”Device for Advanced Verification of IMRT Deliveries” — DAVID is a transparent, segmented, multi‐wire ionization chamber. It attaches to the accessory holder of the gantry. Each wire is centered to the field defined by a leaf pair. The integrated signal measured in each wire is related to the dose delivered to the patient by the modulated incident beam. Thus, at this time DAVID is the only device able to measure an undisturbed signal, related only to Linac parameters. The software compares the signals measured during the radiotherapy session to a reference acquired during the pre‐treatment QA process. DAVID is intended for documenting the radiation delivery constancy of conformal plans, IMRT (Step & Shoot and Sliding window) and RapidArc techniques in real time, during patient treatment. Though not originally intended, DAVID has the potential to perform a number of Linac Physics QA tests. DAVID is a new product in North America. Currently only two are in use, one in New York and the other in Abbotsford, Canada. In order to employ effectively DAVID for routine clinical use, we performed a comprehensive set of measurements. The list includes transmission factors, signal reproducibility with field size and gantry angle, daily setup error of the device, field edge position sensitivity, dose rate signal dependence, EDW constancy, dosimetric leaf gap, picket fence and preliminary work on IMRT verification. All measured data was processed by statistical methods. Our results show that the DAVID system is an effective tool for monitoring IMRT delivery consistency.
Sci—Wed PM: Delivery—05: SBRT of Spinal Lesions Utilizing the Elekta Beam Modulator, Hexapod Couch and BodyFIX Systems
Authors: Hyde D , Basran PS , Pang G , Lochray F , Sahgal A
Published: December 2012

Stereotactic body radiation therapy (SBRT) of the spine involves a high biologic effective dose to the target, while sparing the adjacent spinal cord. With a prescription of 24 Gy in 2–3 fractions (25 Gy in 5 fractions for re‐treatments) and the maximum point dose to the spinal cord limited to 1000–1400 cGy, the target coverage may be compromised to respect the cord dose limit. Due to these tight margins, our centre performs SBRT with the BodyFIX immobilization system, using the Elekta Synergy Beam Modulator and cone‐beam CT (CBCT) for registration with the planning image using automatic grey value alignment. We initially used the Elekta Precise couch to setup the patient using 3 translations. The Hexapod couch is now used to precisely setup the patient using all six degrees of freedom. Intra‐fraction motion is assessed and corrected by means of a mid‐treatment CBCT. To date we have treated 13 spinal lesions with the BodyFIX system. For the 10 spinal lesions (totaling 36 fractions) treated prior to the installation of the Hexapod, the mid‐treatment translational and rotational errors (average absolute deviation) were determined to be less than 0.8 mm and 1.2 degrees. For the 3 spinal lesions (totaling 9 fractions) treated since the Hexapod installation, correction of all six degrees of freedom has resulted in mean mid‐treatment translational and rotational errors of less than 0.9 mm and 0.7 degrees. Consequently, CBCT image‐guidance and the Elekta Hexapod couch are capable of providing precise patient setup, while the BodyFIX system ensures minimal intra‐fraction motion.
Sci—Wed PM: Delivery—06: Management of Intra‐Fraction Organ Motion: First Performance Evaluation of an Experimental Dynamic Tumor Tracking System
Authors: Oelfke U , Tacke M , Kraus A , Nill S
Published: December 2012

The management of intra‐fraction organ motion is an area of active research in medical radiation physics. We present the development of a technical platform that allows a dynamic real‐time adaptation of radiation fields to moving radiation targets with a multi‐leaf collimator. The system consists of a dynamical control‐loop for an experimental MLC160 integrated with an ARTISTE linear accelerator. The information about the real‐time tumor position is taken directly from potentiometers that steer the movement of phantoms in the iso‐centric reference frame of the linear accelerator. As a second input the real‐time signal of the 4D‐tumor tracking device of CalypsoMedical Inc. can be employed. The performance of the system is evaluated by experimental studies with two moving phantoms: i) 2‐dimensional movements of the radiation target are simulated by a block of RW3 slabs that moves perpendicular to the treatment beam with different amplitudes for each direction of motion ii) an anatomically shaped lung phantom for which a solid tumor of RW3 is embedded in a low‐density material can be moved periodically in the cranial‐caudal direction with different amplitudes and frequencies. The irradiation of both phantoms can be analyzed by film dosimetry. The geometrical accuracy of the radiation field adaptation was measured with an EPID and gafchromic films imbedded into the phantoms. In a first test we have determined the latency of the complete system to approximately 500 ms; however a geometrical tracking accuracy within few millimeters could be established for periodical target movements of 2–4 cm amplitudes and characteristic breathing frequencies.
Sci—Wed PM: Delivery—09: Automatic Contrast Enhancement on Electronic Portal Images Based on Human Visual System Properties
Authors: Bonneau P , Branzan Albu A , Hilts M
Published: December 2012

Image Guided Radiation Therapy (IGRT) is one of the most efficient ways to treat prostate cancer. It is well‐known that Electronic Portal Images (EPI) acquired prior to the radiation therapy are of poor quality due to the low radiation dose. Several image parameters need to be manually adjusted in order to be able to visualize and localize the fiducial markers (FMs) seeds at the beginning of each day of treatment. This localization process is essential for the proper alignment of the patient. In this paper, we propose a novel technique for automatic image enhancement. There are many challenges involved in the automation of the image enhancement for FM seed detection. An automated enhancement algorithm is image and noise dependant. The level of noise in an input image and global image properties such as average contrast and intensity vary significantly between different patients and even for the same patient between different image acquisition sessions. Moreover, the small size of the targets (the FM seeds) makes it very difficult to distinguish them from noise, and hence to enhance them. Our approach addresses these challenges by using a contrast enhancement scheme based on properties of the human visual system (HVS). The rationale behind considering this approach lies in the ability of the HVS to adapt to detect objects of small size under low contrast and noise conditions. Our main contribution lies in the automatic set‐up of the parameters based upon a maxima search over a contrast metric.
Sci—Wed PM: Delivery—10: Optical CT‐based Gel Dosimetry in Image Guided Adaptive Radiation Therapy
Authors: Olding T , Darko J , Schreiner LJ
Published: December 2012

Three dimensional gel dosimetry has become more clinically practical with the development of normoxic and less toxic polymer gels and of new accessible imaging techniques for dose readout. In this paper we describe the application of NIPAM polymer and Fricke xylenol (FXG) gels to image‐guided adaptive radiation therapy (IGART). The gel dosimetry was performed with a commercial optical CT imager. The first investigation was the validation of cone‐beam CT (CBCT) based patient localization and repositioning being implemented into our clinic. Gel dosimeters inserted in a phantom mimicking prostate cancer treatment, were processed and irradiated with and without required repositioning, and the dose delivery compared to treatment plans. In the second study, FXG dosimetry was used to determine the dose reduction from a CBCT upgrade on Varian linacs. In both experiments 3D dose data sets were obtained. The IGART repositioning gel experiments clearly showed when the process was followed as intended or when it failed. Without repositioning there were large volumes of disagreement between planned and measured dose distributions, with repositioning a 3D gamma comparison gave good agreement with > 95% of the voxels in agreement. The gel dosimetry of the changes with the upgrade to OBI Advanced confirmed a dose reduction of ∼90%. These results indicate that gel dosimetry provides features for IGART validation not available with conventional dosimeters. In particular, since a gel dosimetry phantom can be put through an IGART process as a patient, the whole process can be tested and validated in a regular quality control program.
Sci—Wed PM: Delivery—11: Dosimetric Properties of an EPID for Real‐Time Dose Verification
Authors: McCurdy BMC , Greer PB
Published: December 2012

PURPOSE: Dosimetric properties of an amorphous‐silicon electronic portal imaging device (EPID) operated in a real‐time acquisition mode were investigated. This mode will be essential for time‐resolved dose verification of dynamic‐IMRT and arc‐IMRT. METHODS: The EPID was used in continuous acquisition mode, where individual sequential image frames are acquired in real‐time. Properties studied include dose linearity and reproducibility. Summed continuous acquisition mode results were also compared to dose results using the well‐studied integrated acquisition mode, for example treatment deliveries including dynamic‐IMRT and single‐arc‐IMRT. Comparison was made using percentage dose difference of in‐field pixels (pixels >10% of maximum signal). Temporally‐resolved EPID response was also compared to that of ion‐chamber data for selected points in the deliveries. RESULTS: Using continuous acquisition mode, EPID response was not linear with dose, with response approximately corresponding to 1–1.5 missed images per irradiation. Reproducibility of EPID response improved with increasing MU. Analysis of the example irradiations revealed summed continuous acquisition mode compared well to integrated acquisition mode, within 2% of maximum dose for more than 95% of in‐field pixels. Time resolved EPID data compared well to ion chamber data, with dose increases/decreases overlying each other. CONCLUSION: Continuous acquisition mode is suited for time‐resolved dosimetry applications including single‐arc‐IMRT and dynamic IMRT, giving comparable dose results to the integrated acquisition mode. Linearity and reproducibility should be adequate for clinical applications although caution should be used in low MU work. Time‐resolved EPID dose information also compared well to time‐resolved ion‐chamber measurements.
Poster — Wed Eve—02: Monte Carlo Dose Calculation of Critical Organs in MDR Cs‐137 Afterloading Intracavitary Brachytherapy
Authors: Owrangi AM , Masudiefar M , Jaberi R , Ghahramani F , Clarkson R , Chow JCL
Published: December 2012

The aim of this study is to perform Monte Carlo dose calculations on two critical organs, bladder and rectum, by considering the effects of applicator attenuation for three different applicator diameters of the Selectron/MDR intracavitary brachytherapy system. Three different pelvic phantoms, with a gynecological cylinder, were used to simulate the treatments. Dosimetric measurements were carried out in five different positions in the rectum and one position in the bladder using p‐type diode detectors. The absorbed doses at clinical points in the phantoms were calculated using the MCNP5 Monte Carlo code and the PLATO commercial treatment planning system (TPS). It was found that the dose‐rate constant for the pellet source was with uncertainty within 1.33% compared to the latest published data. In all cases, results of the Monte Carlo based calculations agreed better with measured doses than those of the PLATO TPS, with the maximum deviation occurring for the 3 cm diameter applicator in the rectum. The largest discrepancy seen in this study, between measured dose and the TPS calculated dose, was 7.1%. The Monte Carlo calculation, for the same position, had a dose discrepancy of 3.0%. The average deviation between the PLATO TPS calculated doses and measured doses was approximately double what was seen between the Monte Carlo results and measured doses. This is due to the absence of the applicator attenuation effect in the PLATO TPS. Therefore, Monte Carlo simulation can be considered a more accurate dose calculation method in this study.
Poster — Wed Eve—04: Dosimetric Effects of Seed Delivery Error and Ultrasound Probe Deformation During Prostate Brachytherapy
Authors: Meyer T , Kay I
Published: December 2012

Permanent seed prostate brachytherapy post plan dosimetry often shows significant deterioration from the treatment plan, commonly attributed to a large number of effects and implant uncertainties. The purpose of this study is to determine the amount of probe deformation and the dosimetric effects of seed delivery errors for typical clinical implants. A C‐arm was used to take variable angle images of clinical implants immediately after the last needle was delivered, with the patient and ultrasound remaining in the treatment position, and again after the ultrasound probe had been removed from the patients. Three dimensional seed coordinates were reconstructed for each of the variable angle image sets. Dosimetry comparison between the treatment plan D90 (mean 196 Gy) and the planning contours with seed coordinates immediately post‐implant showed a mean reduction of 48 Gy (range 44 Gy to 64 Gy) attributable to delivery accuracy. A rigid body registration was performed between seed coordinates to remove overall gland motion and residual seed coordinates were compared to observe seed motion due to probe deformation. The residual seed motion showed non‐random deformational patterns, but was small in magnitude (mean 1.1 mm, range 0.2 mm – 4.4 mm) and showed less impact on D90, although values were dependent on contour volume. These results demonstrate that much of the reduced dosimetry observed at post‐plan occurs in the operating room where technical advances or changes in the implant procedure may improve results.
Poster — Wed Eve—05: Experimental Verification of Dose Calculation and Delivery for the Flexitron HDR Brachytherapy System
Authors: Patel D , Mei X , Kerr A , Joshi CP
Published: December 2012

A Flexitron High Dose Rate brachytherapy system has been installed recently in our center including a Flexiplan treatment planning system (TPS) and a 40‐channel Flexitron treatment delivery unit (TDU) with an Ir‐192 Flexisource. The primary objective of this work was to validate the dose calculated by the Flexiplan TPS through dose delivery on the Flexitron TDU. Comparisons of measured and calculated doses are presented for three scenarios: single and multiple dwell positions in a single catheter, and an optimized seven catheter single plane implant (). For the single catheter delivery, point dose measurements were performed using a 0.01cc ionization chamber. For the single plane implant, thermo‐luminescent dosimeters (TLDs) and a 2D ion chamber array (I'mRT MatriXX, Scanditronix) were used for absolute and relative dose measurements respectively. The measured point doses for the single and multiple dwell points in a single catheter agree with the Flexiplan calculated doses to within ≤5%. For the single plane multiple catheter implant, TLD measured and Flexiplan calculated doses agree within ≤3%. The relative 2D dose distribution obtained with the MatriXX agrees to within ≤1% with the Flexiplan dose distribution except in the region near the edges of the single plane implant. A 4–6% dose difference is observed around the edges, where there is a high dose gradient, and is attributed to volume averaging effect resulting from the finite size of the ion chamber. The agreement between planned and delivered doses is acceptable considering the appreciable effect of small positional uncertainties on measured dose.
Poster — Wed Eve—08: Effectiveness RMI‐156 Mammography Accreditation Phantom in Evaluating Digital Mammography Systems
Authors: Rajapakshe R
Published: December 2012

PURPOSE: Evaluation of the Effectiveness RMI‐156 Mammography Accreditation Phantom in Digital Mammography METHOD AND MATERIALS: Modulation Transfer Function (MTF) and Signal Difference‐to‐Noise Ratio (SDNR) are considered to be the quantitative image quality matrices that can be used to characterize image quality in digital mammography. However there is no established information regarding the acceptable values for these quantities. This is further complicated by the fact that different detector technologies (pixel size, DQE etc.) are used in digital mammography. Recent experience with two different digital mammography systems (incorporating different digital detectors) from the same manufacturer indicated that the RMI‐156 phantom image quality is better suited for clinical evaluation and comparison of digital mammography systems. RESULTS: SDNR values for a 1 mm disk placed on a 4 cm Lucite phantom for Siemens Novation (70 μm pixel) and Inspiration (85 μm pixel) were calculated to be 3.0 and 3.2 respectively during acceptance testing. However, the evaluation of RMI‐156 phantom image from both systems indicated the image from Inspiration system with higher SDNR had inferior image quality. The Inspiration system was therefore re‐calibrated to increase exposure factors by 33% leading to a new SDNR value of 3.5. This clearly demonstrated that SDNR and MTF measures are not yet established for digital mammography systems for acceptance testing and that RMI‐156 phantom can still be used for digital mammography system evaluations. CONCLUSION: RMI‐156 mammography accreditation phantom is found to be a better image quality indicator in comparing and calibrating digital mammography systems than SDNR and MTF estimates.
Poster — Wed Eve—09: Quest for a “Gold Standard” for Breast Density Evaluation
Authors: Uyaniker B , Rajapakshe R , Gordon P , Silver S
Published: December 2012

We have examined the breast density evaluation process using commonly employed methods, visual BIRADS estimate, standard thresholding method (Cumulus) and a newly developed automatic assessment algorithm (Bden) in order to obtain clues for a “gold standard” for breast density estimation. According to these results the experts were in exact agreement for 23 out of 36 images, corresponding to the 63.9 % of the total sample and kappa statistics with indicates the proportion of the chance agreement (expected) is as 30.9 %. Agreement between the two experts found to be less than 70%. It was always possible to include a given image one class lower or higher. Furthermore, systematical shifts in the BIRADS category estimates between the readers have been noticed. The results obtained, although within a limited sample and from only one patient population, indicate that it is difficult to obtain a gold standard using the visual method as judgment plays an important role. Furthermore, there exist systematical shifts in the BIRADS category estimates between the observers. As a result, assessments given by different observers or obtained at a later time are not easily comparable. Hence, there may be even no “gold standard” unless a new scale of breast density using an automated method is defined.
Poster — Wed Eve—10: An X‐Ray Attenuation Approach to Breast Density for Full Field Digital Mammography
Authors: Uyaniker B , Rajapakshe R , Baxter P
Published: December 2012

Mammography, in principal, is x‐ray imaging with high resolution and contrast and based on the fact that the intensity of the x‐ray radiation reduced different amount as it traverses different matter. Starting from this basic definition we have explored the possibility of using x‐ray attenuation for quantitative determination of the density of the sample along the path of the x‐ray beam, which in our case corresponds to the product of the breast thickness and actual density of the breast. We have observed that x‐ray attenuation is strongly correlated with the percent breast density and developed a simple method based on this simple physical principle in order to estimate the percent breast density from digital mammography images. Comparison of the results with the radiologist evaluation for breast density demonstrates the applicability of the x‐ray attenuation measurements to determine breast density using a physical model without any assumptions.
Poster — Wed Eve—11: Pinhole Image Characterization of X‐Ray Tube Focal Spots using Storage Phosphor Imaging Technology
Authors: Johns PC , Schulze JSC
Published: December 2012

The x‐ray tube focal spot is a key determinant of the resolution of an imaging system. Although system resolution can be assessed using bar pattern test objects, a pinhole image provides the point‐spread function due to the focal spot and complete information on the radiation source distribution. The NEMA standard protocol specifies no‐screen film for pinhole imaging, but in the digital age this is problematic. We investigated use of a medium‐resolution storage phosphor imaging system, similar to a hospital CR system. An x‐ray tube with 15° target angle and nominal 1.0 and 2.0 mm focal spots was assessed using a 0.075 mm diameter commercial pinhole and a storage phosphor system. The screen resolves nearly . Its blur of about 0.2 mm is comparable to the pinhole aperture size projected onto the image receptor by the radiographic magnification, , used. A simple expression is obtained which corrects a distance measured in the digital image of the focal spot for both pinhole blur and screen blur to yield the true focal spot dimension. For the x‐ray tube assessed, focal spot size was independent of current, and decreased very slightly with increased potential. A second tube, mounted for research purposes to foreshorten the focal spot to an effective angle of 2.2°, was also assessed. In both tubes, the two focal spots superimposed but were not centered on each other. A medium‐resolution storage phosphor imaging system can adequately replace no‐screen film in pinhole imaging and is much more convenient.
Poster — Wed Eve—12: Initial Experiments in Monoenergetic X‐Ray Scatter Imaging at the BioMedical Imaging and Therapy facility of the Canadian Light Source
Authors: Johns PC , Bewer BE , Chapman LD
Published: December 2012

In projection x‐ray imaging, in the absence of a grid scattered x‐ray photons from the patient out‐number primary photons at the image receptor by as much as 10:1. Scattered radiation can significantly degrade projection contrast and signal‐to‐noise ratio in conventional projection imaging, but can also be used as a source of additional information about the patient or object examined. In principle, a raster scan by a primary pencil beam and two‐dimensional scatter field detector could be used to acquire the scatter information. Simultaneous measurements would reduce acquisition time. Here we report on our first investigations of using a fan beam. We used a monoenergetic radiation beam at the BioMedical Imaging and Therapy (BMIT) facility at the Canadian Light Source (CLS) synchrotron (Saskatoon, Saskatchewan). X rays of approximately 40 keV produced by the 05B1–1 bend magnet beamline were used with Computed Radiography plates as the detector. The fan beam was 1.1 mm thick by 10.6 cm wide. The circularly‐symmetric diffraction patterns of water, plastics, and porcine tissue samples were sampled outside of the fan plane. Signal processing based on cross‐correlation of the scatter field with arc patterns was investigated as a means to provide approximate localization of materials in the fan plane. A more sophisticated signal‐processing approach and/or collimation strategy will likely be necessary.
Poster — Wed Eve—13: Evaluation of Spectroscopic Compton Tomography Approach at 55 keV
Authors: Chighvinadze T , Pistorius S
Published: December 2012

The feasibility of reconstructing 2D electron density () images has been studied. The spectroscopic measurement of Compton scattered photons in a single projection computed tomography (CT) fan beam geometry at 55 keV was investigated. Images were reconstructed by backprojecting over circular paths. A line of energy sensitive detectors was placed outside of periphery of the primary x‐ray fan beam to record the number of scattered photons. The forward problem was simulated in Matlab using analytical equations containing the Klein‐Nishina scattering cross sections, electron density of the object and the solid angle between the point of scattering and the detector. A narrow energy spectrum was needed to achieve good resolution. As the FWHM of the incident spectrum increases, the location where the scatterer can be detected with high precision, decreases. The spatial resolution varies across the image and areas of higher spatial resolution are those which exhibit small angle scattering to the detectors close to the source. Thus various target/filter combinations were studied. The optimal spectrum can be generated by an x‐ray tube operated at 90 kVp with a tungsten target and filter consisting of 0.5mm tungsten and 1.2mm erbium. A point source and ideal detectors were used and no multiple scatter or attenuation was considered. Electron densities were reconstructed using this approach for two phantoms and good qualitative results were obtained. Our ultimate goal is to produce 3D images from scattered photons in a multi‐projection cone‐beam breast CT geometry.
Poster — Wed Eve—14: Real‐Time MR Imaging for Angioplasty
Authors: MacDonald ME , Stafford RB , Frayne R
Published: December 2012

Angioplasty has been demonstrated as an effective treatment for cardiovascular diseases such as carotid stenosis, having similar patient outcomes to the once dominant endarectomy technique. Angioplasty is an attractive choice, as it is much less invasive. However, angioplasty procedures are hinged on the guidance of catheters through the vascular system, and imaging is required for this process. X‐ray is almost always used for these types of interventions, but has several noted drawbacks, including the exposure of ionizing radiation to both patients and staff. Magnetic resonance (MR) imaging has been used in previous experiments at different centres and overcomes some of the problems associated with X‐ray imaging. Here, we propose a real‐time imaging system, for use in catheter guiding applications, and look at parameters and techniques that will increase the overall frame rate displayed to an in‐room monitor. By modifying a fast gradient recalled echo (FGRE) sequence, and ported data directly to an image reconstruction station, implemented on an iMac computer, images are reconstructed and display in real time. By using algorithms such as variable rate k‐space acquisition (varking), multi‐phase array coils, reducing the number of phase‐encode lines, and reducing the analog to digital converter (ADC) sampling rate, frame rate was improved from ∼1 Hz to ∼5Hz. Analysis of images, pre‐ and post‐optimization, yield comparable quality by inspection, and an improved SNR from 45 to 160. This system has been designed to perform MR angioplasty procedures, which will the next step in our research project using animal models.
Poster — Wed Eve—16: Optoacoustic Detection of Tissue Thermal Damage
Authors: Whelan W , Arsenault M , MacPhee M , Kolios M
Published: December 2012

Minimally invasive thermal therapy has been investigated as an alternative treatment modality for solid tumours including breast, liver and prostate. Thermal therapy is typically delivered as a single‐fraction, stand‐alone therapy. It involves heating tissues to greater than 55 C over a period of a few minutes, which results in coagulative necrosis. It can potentially achieve highly conformal 3D coagulation volumes, exhibits sharp demarcation between treated and spared tissues, and tissue effects can be observed and thus potentially controlled in real time. This paper describes a new approach to guiding the progress of thermal therapy using optoacoustics, a technique which combines the high optical contrast and high resolution associated with near‐infrared optical imaging and ultrasound imaging, respectively. In this study, thermal lesions were induced in bovine liver ex vivo via non‐contact single fiber laser heating at 810 nm. Optoacoustic signals were obtained using an optoacoustic imaging system comprised of an Nd:YAG pumped Titanium‐Sapphire laser delivering 6 ns pulses and an annular array of 8, 4 MHz transducers. Optoacoustic signal increased up to 2.5 fold with heating times from 1 to 6 minutes. Furthermore, tissue coagulation was clearly visible in the optoacoustic images compared to the surrounding native tissue. The results demonstrate that optoacoustic signals are sensitive to changes in tissue optical and mechanical properties that occur when tissues are thermally damaged, and, hence, optoacoustic imaging may be a suitable candidate for guiding thermal therapy delivery.
Poster — Wed Eve—17: Detrimental Dose: A Proposed Metric to Score Incidents in Radiation Therapy
Authors: Carlone M , MacPherson M
Published: December 2012

Public awareness of radiation therapy is increasing, and incidents related to radiation therapy delivery are receiving increased public scrutiny. There is a growing interest within the professional community in systems for reporting errors in radiation therapy and communicating their significance. Many of the reporting systems proposed to‐date use decision trees to stratify incidents according to differing levels of severity, with the result that it is difficult to compare incidents between disparate systems. We propose a new metric that uses absorbed dose as a basis for estimating the anticipated detriment of a radiation therapy error in much the same way as dose is used to determine risk in radiation protection. The formulation takes into account the magnitude of the dose error and the volume of tissue unintentionally irradiated, modified by dimensionless quantities that account for tissue response (Tissue Sensitivity) and patient‐specific quality of life factors (Severity Index). The resulting quantity, which we have termed “Detrimental Dose”, should be applicable to describing the severity of an adverse event regardless of the magnitude of the error. Using specific examples of recent radiation therapy incidents, we illustrate how this new metric can be used to estimate the severity of a misadministration of dose. We believe that such a system can provide a unified framework for reporting and assessment of radiation therapy errors.
Poster — Wed Eve—20: Evolving Standards of Education and Training in Medical Physics in Six Regions of the World
Authors: Kulkarni N
Published: December 2012

Significant resources are allocated for applying Medical Physics to health care. State‐ of‐ the‐ art technological developments have made this discipline valuable in early diagnosis and treatment of many diseases, particularly cancer. There is a dire need to harmonize the standards of practice in order to cope with modern technology. This should be done by optimising education and training (E & T) in Medical Physics across various countries. With experiences gained from the successes and failures in this field, standards of practice have evolved in the developed as well as the developing countries, but at different rates. Considerations of regional economic conditions and priorities have led to increased gaps in these standards of practice. This discussion focuses on the status of E&T in Africa, South East Asia, Australia, Europe, Middle East, and North America. The evolution of standards in different regions is examined with due consideration to regionally‐influenced factors. Suggestions have been made to optimise rather than equalise the standards.
Poster — Wed Eve—21: 2D CBCT Dosimetry Using XR‐QA Model GAFCHROMIC Film
Authors: Tomic N , Seuntjens J , DeBlois F , Devic S
Published: December 2012

We describe a 2D reference dosimetry system for dose measurements during cone‐beam computed tomograpfy (CBCT) scans using on‐board imager (OBI) on Varian Clinac‐iX linear accelerator that employs XR‐QA radiochromic film model, specifically designed for measurements at low energy photons. We report on surface doses and percent depth dose (PDDs) measurements during clinical CBCT scans on a humanoid Rando phantom. Response of XR‐QA model radiochromic film reference dosimetry system was calibrated in terms of air kerma in air. Pieces of XR‐QA films were taped on surface of the Rando phantom for surface dose, and XR‐QA film strips placed between Rando slices for PDDs measurements, during CBCT scans for different sites and CBCT protocols. Spatial dosimetry was performed using an Epson Expression 10000XL document scanner. Change in optical reflectance of unexposed film was subtracted from the exposed one to obtain final netR, which was converted to dose using previously determined calibration curve. Our measurements show that skin dose ranges from 0.07 cGy in Low Dose Head to 4.64 cGy in Pelvis Spot Light CBCT protocol, with uncertainty of 2% at higher doses, rising to 4% at 0.5 cGy and 12% at the lowest measured dose. Film strip profile measurements show different dose distributions depending on the CBCT mode used and the anatomical site imaged. The main advantage of the described system for dose measurements during CBCT scans is that it does not require a priori knowledge of the backscatter factors while providing 2D reference dosimetry at low kVp photon beams.
Poster — Wed Eve—22: Measurement of Imaging and Treatment Time Delays in Gated Radiotherapy
Authors: Smith W , Becker N
Published: December 2012

In gated radiotherapy, the accuracy of treatment delivery is determined by the accuracy with which both the imaging and treatment beams are gated. The time delay is the time between when the markers enter or leave the specified position range for amplitude based gating, or phase for phase based gating, and when an image is obtained or linear accelerator beam starts or ceases delivery. We measured time delay for three fluoroscopy systems and three linear accelerator treatment beams, varying gating type (amplitude vs. phase), beam energy, dose rate, and period. In the system we studied, the treatment beam was turned on and off later than expected by 0.08 ± 0.03s (1 SD). Retrospectively gated fluoroscopy systems had time delays in the opposite direction, indicating the images appeared to have been acquired earlier than they had in reality. The average beam on imaging time delays were −0.04 ± 0.05s (amplitude,), −0.11 ± 0.04s (phase); while the average beam off imaging time delays were −0.18 ± 0.08s (amplitude) and −0.15 ± 0.04s (phase). In this case, the asynchronous time delays for the imaging and treatment systems add linearly. We measure and model the effect of asynchronous time delays on gated deliveries and discuss their implications.