bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy dependence and dose response of Gafchromic EBT2 film over a wide range of photon, electron, and proton beam energies
Authors: Arjomandy Bijan , Tailor Ramesh , Anand Aman , Sahoo Narayan , Gillin Michael , Prado Karl , Vicic Milos 
Published: April 2010

Purpose:Since the Gafchromic film EBT has been recently replaced by the newer model EBT2, its characterization, especially energy dependence, has become critically important. The energy dependence of the dose response of Gafchromic EBT2 film is evaluated for a broad range of energies from different radiation sources used in radiation therapy.Methods:The beams used for this study comprised of kilovoltage x rays (75, 125, and 250 kVp), gamma (662 KeV), gamma (1.17–1.33 MeV), megavoltage x rays (6 and 18 MV), electron beams (6 and 20 MeV), and proton beams (100 and 250 MeV). The film's response to each of the above energies was measured over the dose range of 0.4–10 Gy, which corresponds to optical densities ranging from 0.05 to 0.74 for the film reader used.Results:The energy dependence of EBT2 was found to be relatively small within measurement uncertainties for all energies and modalities.Conclusion:For relative and absolute dosimetry of radiation therapy beams, the weak energy dependence of the EBT2 makes it most suitable for clinical use compared to other films.
Validation of an image simulation technique for two computed radiography systems: An application to neonatal imaging
Authors: Smans Kristien , Vandenbroucke Dirk , Pauwels Herman , Struelens Lara , Vanhavere Filip , Bosmans Hilde 
Published: April 2010

Purpose:The purpose of this study is to develop a computer model to simulate the image acquisition for two computed radiography (CR) imaging systems used for neonatal chest imaging: (1) The Agfa ADC Compact, a flying spot reader with powder phosphor image plates (MD 40.0); and (2) the Agfa DX‐S, a line‐scanning CR reader with needle crystal phosphor image plates (HD 5.0). The model was then applied to compare the image quality of the two CR imaging systems.Methods:Monte Carlo techniques were used to simulate the transport of primary and scattered x rays in digital x‐ray systems. The output of the Monte Carlo program was an image representing the energy absorbed in the detector material. This image was then modified using physical characteristics of the CR imaging systems to account for the signal intensity variations due to the heel effect along the anode‐cathode axis, the spatial resolution characteristics of the imaging system, and the various sources of image noise. The simulation was performed for typical acquisition parameters of neonatal chest x‐ray examinations. To evaluate the computer model, the authors compared the threshold‐contrast detectability in simulated and experimentally acquired images of a contrast‐detail phantom. Threshold‐contrast curves were computed using a commercially available scoring program.Results:The threshold‐contrast curves of the simulated and experimentally acquired images show good agreement; for the two CR systems, 93% of the threshold diameters calculated from the simulated images fell within the confidence intervals of the threshold diameter calculated from the experimentally assessed images. Moreover, the superiority of needle based CR plates for neonatal imaging was confirmed.Conclusions:The good agreement between simulated and experimental acquired results indicates that the computer model is accurate.
MR‐based attenuation correction for hybrid PET‐MR brain imaging systems using deformable image registration
Authors: Schreibmann Eduard , Nye Jonathon A. , Schuster David M. , Martin Diego R. , Votaw John , Fox Tim 
Published: April 2010

Purpose:Realization of combined positron emission tomography (PET)—magnetic resonance (MR) scanners has the potential to significantly change healthcare and revolutionize clinical practice as it allows, simultaneously, visualization of molecular imaging and anatomical imaging. PET‐MR, acquired in one imaging study, will likely become the advanced imaging modality of choice for neurological studies, certain forms of cancer, stroke, and the emerging study of stem cell therapy. A challenge toward the implementation and operation of combined PET‐MR scanners is that attenuation corrections maps are not directly available due to space and cost constraints. This article presents a method to obtain accurate patient‐specific PET attenuation coefficients maps in head imaging by warping an atlas computed tomography (CT) data set to the patient‐specific MR data set using a deformable registration model.Methods:A multimodality optical flow deformable model has been developed that establishes a voxel‐to‐voxel correspondence between the CT atlas and patient MR images. Once the mapping is established, the atlas is warped with the deformation field obtained by the registration to create a simulated CT image study that matches the patient anatomy, which could be used for attenuation correction.Results:To evaluate the accuracy of the deformable‐based attenuation correction, 17 clinical brain tumor cases were studied using acquired MR‐CT images. A simulated CT was compared to the patient's true CT to assess geometrical accuracy of the deformation module as well as voxel‐to‐voxel comparison of Hounsfield units (HUs). In all cases, mapping from the atlas CT to the individual MR was achieved with geometrical accuracy as judged using quantitative inspection tools. The mean distance between simulated and true CT external contour and bony anatomy was 1.26 and 2.15 mm, respectively. In terms of HU unit comparison, the mean voxel‐to‐voxel difference was less than 2 HU for all cases.Conclusions:Attenuation correction for hybrid PET‐MR scanners was easily achieved by individualizing an atlas CT to the MR data set using a deformable model without requiring user interaction. The method provided clinical accuracy while eliminating the need for an additional CT scan for PET attenuation correction.
Skeletal dosimetry in a voxel‐based rat phantom for internal exposures to photons and electrons
Authors: Xie Tianwu , Han Dao , Liu Yang , Sun Wenjuan , Liu Qian 
Published: April 2010

Purpose:The skeleton makes a significant contribution to the whole body absorbed dose evaluation of rats, since the bone marrow and bone surface in the skeleton express high radiosensitivity and are considered to be important dose‐limiting tissues. The bone marrow can be categorized as red bone marrow (RBM) and yellow bone marrow (YBM). It is important to investigate the bone marrow in skeletal dosimetry.Methods:Cryosectional color images of the skeleton of a 156 g rat were segmented into mineral bone (including cortical bone and trabecular bone), RBM, and YBM. These three tissue types were identified at 40 different bone sites and integrated into a previously developed voxel‐based rat computational phantom. Photon and electron skeletal absorbed fractions were then calculated using the MCNPX Monte Carlo code.Results:Absorbed fraction (AF) and specific absorbed fraction (SAF) for mineral bone, RBM, and YBM at the 40 different bone sites were established for monoenergetic photon and electron sources placed in 18 organs and seven bone sites. Discrete photon energy was varied from 0.01 to 5.0 MeV in 21 discrete steps, while 21 discrete electron energies were studied, from 0.1 to 10.0 MeV. The trends and values found were consistent with the results of other researchers [M. G. Stabin, T. E. Peterson, G. E. Holburn, and M. A. Emmons, “Voxel‐based mouse and rat models for internal dose calculations,” J. Nucl. Med. 47, 655–659 (2006)]. ‐factors for the radionuclides , , , , and , located in 18 organs and seven bone sites for the skeleton, were calculated and are provided in detail.Conclusions:For internal dose calculations, the AF data reveal that the mineral bone in the rat skeletal system is responsible for significant attenuation of gamma rays, especially at low energies. The photon SAF curves of RBM show that, for photon energies greater than 0.6 MeV, there is an increase in secondary photons emitted from the mineral bone as photon energy increases. The SAF values calculated in this study can also be used to determine the absorbed dose to the skeletal system of rats. The‐factors generated here will be useful in preclinical targeted radiotherapy experiments.
Brushed permanent magnet DC MLC motor operation in an external magnetic field
Authors: Yun J. , St. Aubin J. , Rathee S. , Fallone B. G. 
Published: April 2010

Purpose:Linac‐MR systems for real‐time image‐guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac‐MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed.Methods:The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics).Results:In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to. The carriage motor tolerated up to field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of .Conclusions:The current Varian MLC system motors can be used for real‐time image‐guided radiotherapy coupled to a linac‐MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac‐MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required.
Planning tools for modulated electron radiotherapy
Authors: Surucu Murat , Klein Eric E. , Mamalui‐Hunter Maria , Mansur David B. , Low Daniel A. 
Published: April 2010

Purpose:To develop tools to plan modulated electron radiotherapy (MERT) and to compare the MERT plans to conventional or intensity modulated radiotherapy (IMRT) treatment plans.Methods:Monte Carlo dose calculations of electron fields shaped with the inherent photon multileaf collimators (MLCs) were investigated in this study. Treatment plans for four postmastectomy breast cancer patients were generated using MERT. The distances from the patient skin surfaces to the distal planning target volume surfaces were computed along the beam axis direction to determine the physical depth. Electron beam energies were selected to provide target coverage at these depths and energy bins were generated. A custom built MERT treatment planning graphical user interface (MERTgui) was used to shape the electron bins into deliverable electron segments. Monte Carlo dose distribution simulations were performed using the MLC‐defined segments generated from the MERTgui. A custom built superpositiongui was used to combine doses for each segment using relative weights and final MERT treatment plans were compared to the conventional or IMRT treatment plans. In addition, a demonstration of combined MERT and IMRT treatment plans was performed.Results:The MERT treatment plans provided acceptable target organ coverage in all cases. Relative to 3D conventional or IMRT treatment plans, the MERT plans predicted lower heart doses in all cases; average of the heart of all plans was reduced from 14.1 to 3.3 Gy. The contralateral breast and contralateral lung doses decreased substantially with MERT planning compared to IMRT (on average, contralateral breast heart was reduced from 8.7 to 0.7 Gy and contralateral lung was reduced from 8.4 to 1.2 Gy with MERT). Ipsilateral lung was lower with MERT than with the conventional plans (44.6 vs 29.2 Gy with MERT), but greater when compared against IMRT treatment plans (25.4 vs 28.9 Gy with MERT). A MERT and IMRT combination plan was generated to benefit from the complementary advantages of MERT and IMRT, resulting in satisfactory target coverage and reduced organ at risk doses.Conclusions:MERT tools can facilitate treatment planning and provide plans for treatment of shallow targets such as the postmastectomy chest wall.
Computerized image analysis: Texture‐field orientation method for pectoral muscle identification on MLO‐view mammograms
Authors: Zhou Chuan , Wei Jun , Chan Heang‐Ping , Paramagul Chintana , Hadjiiski Lubomir M. , Sahiner Berkman , Douglas Julie A. 
Published: April 2010

Purpose:To develop a new texture‐field orientation (TFO) method that combinesa priori knowledge, local and global information for the automated identification of pectoral muscle on mammograms.Methods:The authors designed a gradient‐based directional kernel (GDK) filter to enhance the linear texture structures, and a gradient‐based texture analysis to extract a texture orientation image that represented the dominant texture orientation at each pixel. The texture orientation image was enhanced by a second GDK filter for ridge point extraction. The extracted ridge points were validated and the ridges that were less likely to lie on the pectoral boundary were removed automatically. A shortest‐path finding method was used to generate a probability image that represented the likelihood that each remaining ridge point lay on the true pectoral boundary. Finally, the pectoral boundary was tracked by searching for the ridge points with the highest probability lying on the pectoral boundary. A data set of 130 MLO‐view digitized film mammograms (DFMs) from 65 patients was used to train the TFO algorithm. An independent data set of 637 MLO‐view DFMs from 562 patients was used to evaluate its performance. Another independent data set of 92 MLO‐view full field digital mammograms (FFDMs) from 92 patients was used to assess the adaptability of the TFO algorithm to FFDMs. The pectoral boundary detection accuracy of the TFO method was quantified by comparison with an experienced radiologist's manually drawn pectoral boundary using three performance metrics: The percent overlap area (POA), the Hausdorff distance (Hdist), and the average distance (AvgDist).Results:The mean and standard deviation of POA, Hdist, and AvgDist were, , and , respectively. For the POA measure, 91.5%, 97.3%, and 98.9% of the computer detected pectoral muscles had POA larger than 90%, 85%, and 80%, respectively. For the distance measures, 85.4% and 98.0% of the computer detected pectoral boundaries had Hdist within 5 and 10 mm, respectively, and 99.4% of computer detected pectoral muscle boundaries had AvgDist within 5 mm from the radiologist's manually drawn boundaries.Conclusions:The pectoral muscle on DFMs can be detected accurately by the automated TFO method. The preliminary study of applying the same pectoral muscle identification algorithm to FFDMs without retraining demonstrates that the TFO method is reasonably robust against the differences in the image properties between the digitized and digital mammograms.
Eruption-related lahars and sedimentation response downstream of Mount Hood
Authors: Pierson Thomas C. , Scott William E. , Vallance James W. , Pringle Patrick T. 
Published: April 2010

Abstract
Late Holocene dome-building eruptions at Mount Hood during the Timberline and Old Maid eruptive periods resulted in numerous dome-collapse pyroclastic flows and lahars that moved large volumes of volcaniclastic sediment into temporary storage in headwater canyons of the Sandy River. During each eruptive period, accelerated sediment loading to the river through erosion and remobilization of volcanic fragmental debris resulted in very high sediment-transport rates in the Sandy River during rain- and snowmelt-induced floods. Large sediment loads in excess of the river's transport capacity led to channel aggradation, channel widening, and change to a braided channel form in the lowermost reach of the river, between 61 and 87 km downstream from the volcano. The post-eruption sediment load moved as a broad bed-material wave, which in the case of the Old Maid eruption took ~2 decades to crest 83 km downstream. Maximum post-eruption aggradation levels of at least 28 and 23 m were achieved in response to Timberline and Old Maid eruptions. In each case, downstream aggradation cycles were initiated by lahars, but the bulk of the aggradation was achieved by fluvial sediment transport and deposition. When the high rates of sediment supply began to diminish, the river degraded, incising the channel fills and forming progressively lower sets of degradational terraces. A variety of debris-flow, hyperconcentrated-flow, and fluvial (upper and lower flow regime) deposits record the downstream passage of the sediment waves that were initiated by these eruptions. The deposits also presage a hazard that may be faced by communities along the Sandy River when volcanic activity at Mount Hood resumes.
Cataclysms and controversy—Aspects of the geomorphology of the Columbia River Gorge
Authors: O’Connor Jim E. , Burns Scott F. 
Published: April 2010

Abstract
Landslides and floods of lava and water tremendously affected the Columbia River during its long history of transecting the Cascade Volcanic Arc. This field trip touches on aspects of the resulting geology of the scenic Columbia River Gorge, including the river-blocking Bonneville landslide of ~550 years ago and the great late-Pleistocene Missoula floods. Not only did these events create great landscapes, but they inspired great geologists. Mid-nineteenth century observations of the Columbia River and Pacific Northwest by James Dwight Dana and John Strong Newberry helped germinate the “school of fluvial” erosion later expanded upon by the southwestern United States topographic and geologic surveys. Later work on features related to the Missoula floods framed the career of J Harlen Bretz in one of the great geologic controversies of the twentieth century.
The dynamic landscape on the north flank of Mount St. Helens
Authors: Austin Steven A. 
Published: April 2010

Abstract
The dynamic landscape on the north flank of Mount St. Helens includes the largest debris avalanche deposit to accumulate within human history, covering more than 45 km2 on the upper North Fork of the Toutle River on 18 May 1980. Most land-forms on the debris avalanche are now relatively stable and only affected significantly by geomorphic processes exceeding certain energy thresholds. Following the debris avalanche, the most significant landscape-forming event has been the mudflow of 19 March 1982. This mudflow overtopped the rim of the largest explosion pit, formed and deepened channels, and largely formed the present landscape of the debris avalanche surface. Now that the power of geomorphic processes has diminished, only finer sediment is being moved. Channels are armored with coarser clasts, and valleys are plugging with sediment. Hikers can observe the new landscape from two selected overlooks. Johnston Ridge Observatory is the staging area for a recommended roundtrip hike of 13.6 km (8.4 mi).
Hydrogeology of the Columbia River Basalt Group in the northern Willamette Valley, Oregon
Authors: Burt Walter , Conlon Terrence , Tolan Terry L. , Wells Ray E. , Melady Jason 
Published: April 2010

ABSTRACT
Basalt flows of the Columbia River Basalt Group (CRBG) host a series of regionally extensive aquifers between western Idaho and the Pacific Ocean that serve as an important source for domestic, municipal, agricultural, and industrial water supply throughout much of this area, and are the sole source for some communities in the Willamette Valley. Rapid growth and increased pumping have resulted in significant water level declines in some locales in the Willamette Valley, forcing some communities to develop other water sources, and/or develop aquifer storage and recovery projects to store water in CRBG aquifers.
The CRBG generally consists of multiple concordant, tabular sheet flows. The primary water-bearing horizons within the CRBG are associated the vesicular and/ or brecciated flow top and flow bottom (pillow/hyaloclastite) structures that form the interflow zone between two flows. The interiors of the CRBG flows typically have limited vertical permeability and act as aquitards, creating a series of layered confined aquifers. The dominant groundwater flow pathway in the CRBG aquifer system is along these individual, laterally extensive, interflow zones. Tectonic structures may modify the dominant flow regime in the CRBG by offsetting or otherwise disturbing originally laterally continuous interflow zones. Faults result in a wide spectrum of effects on flow in the CRBG aquifers depending on the nature of the fault.
The hydraulic properties inherent to CRBG aquifers, including high degree of confinement, low bulk permeability and limited recharge have led to overdraft conditions in many areas. Conversely, these characteristics create favorable conditions for aquifer storage and recovery system development in the central Willamette Valley and Tualatin Basin.
Anadromy in Arctic populations of lake trout (Salvelinus namaycush): otolith microchemistry, stable isotopes, and comparisons with Arctic char (Salvelinus alpinus)
Authors: Swanson Heidi K. , Kidd Karen A. , Babaluk John A. , Wastle Rick J. , Yang Panseok P. , Halden Norman M. , Reist James D. 
Published: April 2010

In the family Salmonidae, lake trout ( Salvelinus namaycush ) are considered the least tolerant of salt water. There are, however, sporadic reports of lake trout in coastal, brackish habitats in the Canadian Arctic. Otolith microchemistry analyses conducted on lake trout and Arctic char ( Salvelinus alpinus ) from four Arctic lakes in the West Kitikmeot region of Nunavut, Canada, revealed that 37 of 135 (27%) lake trout made annual marine migrations. Anadromous lake trout were in significantly better condition (K = 1.17) and had significantly higher C:N ratios (3.71) than resident lake trout (K = 1.05 and C:N = 3.34). Anadromous lake trout also had significantly higher δ15N (mean = 16.4‰), δ13C (mean = –22.3‰), and δ34S (mean = 13.43‰) isotope ratios than resident lake trout (means = 12.84‰, –26.21‰, and 1.93‰ for δ15N, δ13C, and δ34S, respectively); results were similar for Arctic char and agree with results from previous studies. Mean age of first migration for lake trout was 13 years, which was significantly older than that for Arctic char (5 years). This could be a reflection of size-dependent salinity tolerance in lake trout, but further research is required. These are the first detailed scientific data documenting anadromy in lake trout.