bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of helical tomotherapy machine using EPR/alanine dosimetry
Authors: Perichon Nicolas , Garcia Tristan , François Pascal , Lourenço Valérie , Lesven Caroline , Bordy Jean‐Marc 
Published: March 2011

Purpose:Current codes of practice for clinical reference dosimetry of high‐energy photon beams in conventional radiotherapy recommend using a square field, with the detector at a reference depth of 10 cm in water and 100 cm source to surface distance (SSD) (AAPM TG‐51) or 100 cm source‐to‐axis distance (SAD) (IAEA TRS‐398). However, the maximum field size of a helical tomotherapy (HT) machine is defined at 85 cm SAD. These nonstandard conditions prevent a direct implementation of these protocols. The purpose of this study is twofold: To check the absorbed dose in water and dose rate calibration of a tomotherapy unit as well as the accuracy of the tomotherapy treatment planning system (TPS) calculations for a specific test case.Method:Both topics are based on the use of electron paramagnetic resonance (EPR) using alanine as transfer dosimeter between the Laboratoire National Henri Becquerel (LNHB) reference beam and the Institut Curie's HT beam. Irradiations performed in the LNHB reference beam allowed setting up the calibration method, which was then implemented and tested at the LNHB 6 MV linac x‐ray beam, resulting in a deviation of 1.6% (at a 1% standard uncertainty) relative to the reference value determined with the standard IAEA TRS‐398 protocol.Results:HT beam dose rate estimation shows a difference of 2% with the value stated by the manufacturer at a 2% standard uncertainty. A 4% deviation between measured dose and the calculation from the tomotherapy TPS was found. The latter was originated by an inadequate representation of the phantom CT‐scan values and, consequently, mass densities within the phantom. This difference has been explained by the mass density values given by the CT‐scan and used by the TPS which were not the true ones. Once corrected using Monte Carlo N‐Particle simulations to validate the accuracy of this process, the difference between corrected TPS calculations and alanine measured dose values was then found to be around 2% (with 2% standard uncertainty on TPS doses and 1.5% standard uncertainty on EPR measurements).Conclusion:Beam dose rate estimation results were found to be in good agreement with the reference value given by the manufacturer at 2% standard uncertainty. Moreover, the dose determination method was set up with a deviation around 2% (at a 2% standard uncertainty).
Optimizing magnetite nanoparticles for mass sensitivity in magnetic particle imaging
Authors: Ferguson R. Matthew , Minard Kevin R. , Khandhar Amit P. , Krishnan Kannan M. 
Published: March 2011

Purpose:Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, the authors explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency.Methods:Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally using a custom‐built MPI transceiver designed to detect the third harmonic of MNP magnetization. The driving field amplitude and frequency were chosen to be suitable for imaging small animals. Experimental results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution and size‐dependent magnetic relaxation.Results:The experimental results show a clear variation in the MPI signal intensity as a function of MNP diameter that is in agreement with simulated results. A maximum in the plot of MPI signal vs MNP size indicates there is a particular size that is optimal for the chosen.Conclusions:The authors observed that MNPs 15 nm in diameter generate maximum signal amplitude in MPI experiments at 250 kHz. The authors expect the physical basis for this result, the change in magnetic relaxation with MNP size, will impact MPI under other experimental conditions.
Novel detector design for reducing intercell x‐ray cross‐talk in the variable resolution x‐ray CT scanner: A Monte Carlo study
Authors: Arabi Hosein , Asl Ali Reza Kamali , Ay Mohammad Reza , Zaidi Habib 
Published: March 2011

Purpose:The variable resolution x‐ray (VRX) CT scanner provides substantial improvement in the spatial resolution by matching the scanner's field of view (FOV) to the size of the object being imaged. Intercell x‐ray cross‐talk is one of the most important factors limiting the spatial resolution of the VRX detector. In this work, a new cell arrangement in the VRX detector is suggested to decrease the intercell x‐ray cross‐talk. The idea is to orient the detector cells toward the opening end of the detector.Methods:Monte Carlo simulations were used for performance assessment of the oriented cell detector design. Previously published design parameters and simulation results of x‐ray cross‐talk for the VRX detector were used for model validation using theGATE Monte Carlo package. In the first step, the intercell x‐ray cross‐talk of the actual VRX detector model was calculated as a function of the FOV. The obtained results indicated an optimum cell orientation angle of 28° to minimize the x‐ray cross‐talk in the VRX detector. Thereafter, the intercell x‐ray cross‐talk in the oriented cell detector was modeled and quantified.Results:The intercell x‐ray cross‐talk in the actual detector model was considerably high, reaching up to 12% at FOVs from 24 to 38 cm. The x‐ray cross‐talk in the oriented cell detector was less than 5% for all possible FOVs, except 40 cm (maximum FOV). The oriented cell detector could provide considerable decrease in the intercell x‐ray cross‐talk for the VRX detector, thus leading to significant improvement in the spatial resolution and reduction in the spatial resolution nonuniformity across the detector length.Conclusions:The proposed oriented cell detector is the first dedicated detector design for the VRX CT scanners. Application of this concept to multislice and flat‐panel VRX detectors would also result in higher spatial resolution.
Epp: A C++ EGSnrc user code for x‐ray imaging and scattering simulations
Authors: Lippuner Jonas , Elbakri Idris A. , Cui Congwu , Ingleby Harry R. 
Published: March 2011

Purpose:Easy particle propagation (Epp) is a user code for the EGSnrc code package based on theC++ class library egspp. A main feature of egspp (and Epp) is the ability to use analytical objects to construct simulation geometries. The authors developed Epp to facilitate the simulation of x‐ray imaging geometries, especially in the case of scatter studies. While direct use of egspp requires knowledge of C++, Epp requires no programming experience.Methods:Epp's features include calculation of dose deposited in a voxelized phantom and photon propagation to a user‐defined imaging plane. Projection images of primary, single Rayleigh scattered, single Compton scattered, and multiple scattered photons may be generated. Epp input files can be nested, allowing for the construction of complex simulation geometries from more basic components. To demonstrate the imaging features of Epp, the authors simulate 38 keV x rays from a point source propagating through a water cylinder 12 cm in diameter, using both analytical and voxelized representations of the cylinder. The simulation generates projection images of primary and scattered photons at a user‐defined imaging plane. The authors also simulate dose scoring in the voxelized version of the phantom in both Epp and DOSXYZnrc and examine the accuracy of Epp using the Kawrakow–Fippel test.Results:The results of the imaging simulations with Epp using voxelized and analytical descriptions of the water cylinder agree within 1%. The results of the Kawrakow–Fippel test suggest good agreement between Epp and DOSXYZnrc.Conclusions:Epp provides the user with useful features, including the ability to build complex geometries from simpler ones and the ability to generate images of scattered and primary photons. There is no inherent computational time saving arising from Epp, except for those arising from egspp's ability to use analytical representations of simulation geometries. Epp agrees with DOSXYZnrc in dose calculation, since they are both based on the well‐validated standard EGSnrc radiation transport physics model.
Minimax optimization for handling range and setup uncertainties in proton therapy
Authors: Fredriksson Albin , Forsgren Anders , Hårdemark Björn 
Published: March 2011

Purpose:Intensity modulated proton therapy (IMPT) is sensitive to errors, mainly due to high stopping power dependency and steep beam dose gradients. Conventional margins are often insufficient to ensure robustness of treatment plans. In this article, a method is developed that takes the uncertainties into account during the plan optimization.Methods:Dose contributions for a number of range and setup errors are calculated and a minimax optimization is performed. The minimax optimization aims at minimizing the penalty of the worst case scenario. Any optimization function from conventional treatment planning can be utilized by the method. By considering only scenarios that are physically realizable, the unnecessary conservativeness of other robust optimization methods is avoided. Minimax optimization is related to stochastic programming by the more general minimax stochastic programming formulation, which enables accounting for uncertainties in the probability distributions of the errors.Results:The minimax optimization method is applied to a lung case, a paraspinal case with titanium implants, and a prostate case. It is compared to conventional methods that use margins, single field uniform dose (SFUD), and material override (MO) to handle the uncertainties. For the lung case, the minimax method and the SFUD with MO method yield robust target coverage. The minimax method yields better sparing of the lung than the other methods. For the paraspinal case, the minimax method yields more robust target coverage and better sparing of the spinal cord than the other methods. For the prostate case, the minimax method and the SFUD method yield robust target coverage and the minimax method yields better sparing of the rectum than the other methods.Conclusions:Minimax optimization provides robust target coverage without sacrificing the sparing of healthy tissues, even in the presence of low density lung tissue and high density titanium implants. Conventional methods using margins, SFUD, and MO do not utilize the full potential of IMPT and deliver unnecessarily high doses to healthy tissues.
Dosimetry protocol for the forthcoming clinical trials in synchrotron stereotactic radiation therapy (SSRT)
Authors: Prezado Y. , Vautrin M. , Martínez‐Rovira I. , Bravin A. , Estève F. , Elleaume H. , Berkvens P. , Adam J. F. 
Published: March 2011

Purpose:An adequate dosimetry protocol for synchrotron radiation and the specific features of the ID17 Biomedical Beamline at the European Synchrotron Radiation Facility are essential for the preparation of the forthcoming clinical trials in the synchrotron stereotactic radiation therapy (SSRT). The main aim of this work is the definition of a suitable protocol based on standards of dose absorbed to water. It must allow measuring the absolute dose with an uncertainty within the recommended limits for patient treatment of 2%–5%.Methods:Absolute dosimetry is performed with a thimble ionization chamber (PTW semiflex 31002) whose center is positioned at equivalent depth in water. Since the available synchrotron beam at the ESRF Biomedical Beamline has a maximum height of 3 mm, a scanning method was employed to mimic a uniform exposition of the ionization chamber. The scanning method has been shown to be equivalent to a broad beam irradiation. Different correction factors have been assessed by using Monte Carlo simulations.Results:The absolute dose absorbed to water at 80 keV was measured in reference conditions with a 2% global uncertainty, within the recommended limits. The dose rate was determined to be in the range between 14 and 18 Gy/min, that is to say, a factor two to three times higher than the 6 Gy/min achievable in RapidArc or VMAT machines. The dose absorbed to water was also measured in a RW3 solid water phantom. This phantom is suitable for quality assurance purposes since less than 2% average difference with respect to the water phantom measurements was found. In addition, output factors were assessed for different field sizes.Conclusions:A dosimetry protocol adequate for the specific features of the SSRT technique has been developed. This protocol allows measuring the absolute dose absorbed to water with an accuracy of 2%. It is therefore satisfactory for patient treatment.
Model‐based optoacoustic inversions with incomplete projection data
Authors: Buehler Andreas , Rosenthal Amir , Jetzfellner Thomas , Dima Alexander , Razansky Daniel , Ntziachristos Vasilis 
Published: March 2011

Purpose:Optoacoustic imaging is an emerging noninvasive imaging modality that can resolve optical contrast through several millimeters to centimeters of tissue with diffraction‐limited resolution of ultrasound. Yet, quantified reconstruction of tissue absorption maps requires optoacoustic signals to be collected from as many locations around the object as possible. In many tomographic imaging scenarios, however, only limited‐view or partial projection data are available, which has been shown to generate image artifacts and overall loss of quantification accuracy.Methods:In this article, the recently introduced interpolated‐matrix‐model optoacoustic inversion method is tested in different limited‐view scenarios and compared to the standard backprojection algorithm. Both direct (TGSVD) and iterative (PLSQR) regularization methods are proposed to improve the accuracy of image reconstructions with their performance tested on simulated and experimental data.Results:While for full‐view tomographic data the model‐based inversion has been generally shown to attain higher reconstruction accuracy compared to backprojection algorithms, the incomplete tomographic datasets lead to ill‐conditioned forward matrices and, consequently, to error‐prone inversions, with strong artifacts following a distinct ripple‐type pattern. The proposed regularization techniques are shown to stabilize the inversion and eliminate the artifacts.Conclusions:Overall, it has been determined that the regularized interpolated‐matrix‐model‐based optoacoustic inversions show higher accuracy than reconstructions with the standard backprojection algorithm. Finally, the combination of model‐based inversion with PLSQR or TGSVD regularization methods can lead to an accurate reconstruction of limited‐projection angle optoacoustic data and practical systems for optoacoustic imaging in many realistic cases where the full‐view dataset is unavailable.
A novel lateral disequilibrium inclusive (LDI) pencil‐beam based dose calculation algorithm: Evaluation in inhomogeneous phantoms and comparison with Monte Carlo calculations
Authors: Wertz Hansjoerg , Jahnke Lennart , Schneider Frank , Polednik Martin , Fleckenstein Jens , Lohr Frank , Wenz Frederik 
Published: March 2011

Purpose:Pencil‐beam (PB) based dose calculation for treatment planning is limited by inaccuracies in regions of tissue inhomogeneities, particularly in situations with lateral electron disequilibrium as is present at tissue/lung interfaces. To overcome these limitations, a new “lateral disequilibrium inclusive” (LDI) PB based calculation algorithm was introduced. In this study, the authors evaluated the accuracy of the new model by film and ionization chamber measurements and Monte Carlo simulations.Methods:To validate the performance of the newLDI algorithm implemented in Corvus 09®, eight test plans were generated on inhomogeneous thorax and pelvis phantoms. In addition, three plans were calculated with a simple effective path length (EPL) algorithm on the inhomogeneous thorax phantom. To simulate homogeneous tissues, four test plans were evaluated in homogeneous phantoms (homogeneous dose calculation).Results:The mean pixel pass rates and standard deviations of the gamma 4%/4 mm test for the film measurements were for the plans calculated with LDI, for the plans calculated with EPL, and for the homogeneous plans. Ionization chamber measurements and Monte Carlo simulations confirmed the high accuracy of the new algorithm (dose deviations ; gamma 3%/3 mm )Conclusions:LDI represents an accurate and fast dose calculation algorithm for treatment planning.
Phosphatidylinositol 3-Kinase Signaling Delays Sendai Virus-Induced Apoptosis by Preventing XIAP Degradation
Authors: White Christine L. , Chattopadhyay Saurabh , Sen Ganes C. 
Published: March 2011

ABSTRACT

Sendai virus (SeV) infection causes apoptosis, which is manifested only late after infection; however, inhibition of phosphatidylinositol 3-kinase (PI3K) dramatically accelerates the process. We report here that rapid apoptosis uses the same mitochondrial apoptotic pathway as slow apoptosis. Cytoplasmic cytochrome
c
(cyt
c
) was released early in both cases, but the antiapoptotic protein XIAP prevented early activation of the caspases in cells with active PI3K. When the enzyme was inhibited, XIAP was degraded rapidly in infected cells, allowing cyt
c
to cause caspase activation and early apoptosis. Thus, SeV infection-mediated apoptosis is temporally regulated by the prevention of XIAP degradation by PI3K.
Treatment of a Human Papillomavirus Type 31b-Positive Cell Line with Benzo[a]Pyrene Increases Viral Titer through Activation of the Erk1/2 Signaling Pathway
Authors: Bowser Brian S. , Alam Samina , Meyers Craig 
Published: March 2011

ABSTRACTNumerous epidemiological studies have implicated cigarette smoking as a cofactor in the progression to cervical cancer. Tobacco-associated hydrocarbons have been found in cervical mucus, suggesting a possible interaction with human papillomavirus (HPV)-infected cells. The polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) is a major component of cigarette smoke condensate that has received significant attention due to its ability to induce carcinogenesis. We have previously demonstrated by conventional methods for determining viral titer that high concentrations of BaP increase HPV31b titers within the context of organotypic raft cultures compared with the level for vehicle controls. However, a definitive mechanism for explaining this increase in viral titer was lacking. Here, we show that BaP treatment activates the Ras-Raf-Mek1/2-Erk1/2 signaling pathway. The importance of Erk1/2 pathway activation to the BaP-mediated increase in viral titer was determined by Erk pathway inhibition with multiple Erk1/2 pathway inhibitors. Finally, BaP treatment activated p90RSK and its downstream target CDK1. These data indicate that the Erk1/2 signaling pathway plays an important role in mediating the response to BaP treatment that ultimately leads to increased viral titers.
Regulation of Antinucleoprotein IgG by Systemic Vaccination and Its Effect on Influenza Virus Clearance
Authors: LaMere Mark W. , Moquin Amy , Lee F. Eun-Hyung , Misra Ravi S. , Blair Patrick J. , Haynes Laura , Randall Troy D. , Lund Frances E. , Kaminski Denise A. 
Published: March 2011

ABSTRACTSeasonal influenza epidemics recur due to antigenic drift of envelope glycoprotein antigens and immune evasion of circulating viruses. Additionally, antigenic shift can lead to influenza pandemics. Thus, a universal vaccine that protects against multiple influenza virus strains could alleviate the continuing impact of this virus on human health. In mice, accelerated clearance of a new viral strain (cross-protection) can be elicited by prior infection (heterosubtypic immunity) or by immunization with the highly conserved internal nucleoprotein (NP). Both heterosubtypic immunity and NP-immune protection require antibody production. Here, we show that systemic immunization with NP readily accelerated clearance of a 2009 pandemic H1N1 influenza virus isolate in an antibody-dependent manner. However, human immunization with trivalent inactivated influenza virus vaccine (TIV) only rarely and modestly boosted existing levels of anti-NP IgG. Similar results were observed in mice, although the reaction could be enhanced with adjuvants, by adjusting the stoichiometry among NP and other vaccine components, and by increasing the interval between TIV prime and boost. Importantly, mouse heterosubtypic immunity that had waned over several months could be enhanced by injecting purified anti-NP IgG or by boosting with NP protein, correlating with a long-lived increase in anti-NP antibody titers. Thus, current immunization strategies poorly induce NP-immune antibody that is nonetheless capable of contributing to long-lived cross-protection. The high conservation of NP antigen and the known longevity of antibody responses suggest that the antiviral activity of anti-NP IgG may provide a critically needed component of a universal influenza vaccine.
Role of Nrf2 in Host Defense against Influenza Virus in Cigarette Smoke-Exposed Mice
Authors: Yageta Yuichi , Ishii Yukio , Morishima Yuko , Masuko Hironori , Ano Satoshi , Yamadori Tadahiro , Itoh Ken , Takeuchi Kaoru , Yamamoto Masayuki , Hizawa Nobuyuki 
Published: March 2011

ABSTRACT

Influenza virus is a common respiratory tract viral infection. Although influenza can be fatal in patients with chronic pulmonary diseases such as chronic obstructive pulmonary disease, its pathogenesis is not fully understood. The Nrf2-mediated antioxidant system is essential to protect the lungs from oxidative injury and inflammation. In the present study, we investigated the role of Nrf2 in protection against influenza virus-induced pulmonary inflammation after cigarette smoke exposure with both
in vitro
and
in vivo
approaches. For
in vitro
analyses, peritoneal macrophages isolated from wild-type and
Nrf2
-deficient mice were treated with poly(I:C) and/or cigarette smoke extract. For
in vivo
analysis, these mice were infected with influenza A virus with or without exposure to cigarette smoke. In
Nrf2
-deficient macrophages, NF-κB activation and the induction of its target inflammatory genes were enhanced after costimulation with cigarette smoke extract and poly(I:C) compared with wild-type macrophages. The induction of antioxidant genes was observed for the lungs of wild-type mice but not those of
Nrf2
-deficient mice after cigarette smoke exposure. Cigarette smoke-exposed
Nrf2
-deficient mice showed higher rates of mortality than did wild-type mice after influenza virus infection, with enhanced peribronchial inflammation, lung permeability damage, and mucus hypersecretion. Lung oxidant levels and NF-κB-mediated inflammatory gene expression in the lungs were also enhanced in
Nrf2
-deficient mice. Our data indicate that the antioxidant pathway controlled by Nrf2 is pivotal for protection against the development of influenza virus-induced pulmonary inflammation and injury under oxidative conditions.