bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytokeratin expression in squamous cell carcinoma arising from hidradenitis suppurativa (acne inversa)
Authors: Kurokawa Ichiro , Nishimura Keisuke , Yamanaka Kei‐ichi , Mizutani Hitoshi , Tsubura Airo , Revuz Jean
Published: December 2006

Abstract:  We have studied cytokeratin (CK) expression in two cases of well‐differentiated and poorly differentiated squamous cell carcinoma (SCC) arising from hidradenitis suppurativa (HS) (acne inversa). In both cases, type A (infundibular‐like keratinized) epithelia were observed. In type A epithelia, CK 1 and 10 expressions were decreased, and CK 14 and 17 were detectable in the whole layers. CK 7, 8, 15, 16 and 18 were not detected in type A epithelia. In tumor nests of well‐differentiated SCC, CK 1 and 10 expressions were downregulated, and CK 14 expression was upregulated. In tumor nests of poorly differentiated SCC, CK 1 and 10 were not expressed, but simple epithelial keratins (CK 8, 18 and 19) were expressed. These changes of CK expression are related to malignant transformation from the sinus tract (type A epithelium) in HS to SCC.
Peripheral Modulation of Dopaminergic Receptors Affects Erectile Responses in Rats
Authors: El‐Din Mahmoud Mohy , Senbel Amira M. , Daabees Tahia T. , Sharabi Fouad M.
Published: December 2006

Abstract: Clinical observations have suggested that dopaminergic mechanisms are involved in the regulation of male sexual responses, including erection. Apomorphine was initially reported to exert its erectogenic effects by modifying central dopaminergic activity. This study aimed primarily at evaluating and investigating the effect of apomorphine on erectile functions in rats and its potential effects on the cardiovascular system, as well as the possible role of dopaminergic stimulation in the peripheral control of erection. Measurement of intracavernosal pressure changes elicited by electrical stimulation of the cavernosal nerve in anaesthetized rats and mating tests were used. SCH23390, the D1receptor antagonist, attenuated penile response to electrical stimulation. Intravenous administration of apomorphine in low dose (100 µg/kg), but not in high dose, significantly potentiated erectile responses to electrical stimulation. Intracavernosally injected apomorphine (50 µg/kg) significantly potentiated the filling rate of the corpora cavernosa 5 min. after injection, and did not induce erection in absence of electrical stimulation. In addition, apomorphine amplified the male sexual and copulatory behaviour by reducing ejaculation, mount and intromission latencies, and significantly increasing the number of ejaculations per session. However, apomorphine produced rapid and long‐lasting hypotension and potentiated the hypotension and tachycardia associated with nerve‐stimulated penile erection. Our results suggest that D1‐dopaminergic receptors may be functionally involved in the peripheral mediation of penile erection. Apomorphine may amplify sexual and copulatory behaviour and may also, by a complementary role, amplify neurogenically mediated erections by acting in the periphery.
Inclusion of Sliding Friction in Contact Dynamics Model for Helical Gears
Authors: He Song , Gunda Rajendra , Singh Rajendra
Published: December 2006

This paper proposes a new analytical model for helical gears that characterizes the contact plane dynamics and captures the velocity reversal at the pitch line due to sliding friction. First, the tooth stiffness density function along the contact lines is calculated by using a finite element code. Analytical formulations are then derived for the multidimensional mesh forces and moments. Contact zones for multiple tooth pairs in contact are identified, and the associated integration algorithms are derived. A new 12-degree-of-freedom, linear time-varying model with sliding friction is then developed. It includes rotational and translational motions along the line-of-action, off-line-of-action, and axial directions. The methodology is also illustrated by predicting time and frequency domain results for several values of the coefficient of friction.
Dose point kernel for boron‐11 decay and the cellular values in boron neutron capture therapy
Authors: Ma Yunzhi , Geng JinPeng , Gao Song , Bao Shanglian
Published: December 2006

The study of the radiobiology of boron neutron capture therapy is based on the cellular level dosimetry of boron‐10's thermal neutron capture reaction , in which one helium‐4 ion and one lithium‐7 ion are spawned. Because of the chemical preference of boron‐10 carrier molecules, the dose is heterogeneously distributed in cells. In the present work, the (scaled) dose point kernel of boron‐11 decay, called ‐DPK, was calculated by GEANT4 Monte Carlo simulation code. The DPK curve drops suddenly at the radius of , the continuous slowing down approximation (CSDA) range of a lithium‐7 ion. Then, after a slight ascending, the curve decreases to near zero when the radius goes beyond , which is the CSDA range of a helium‐4 ion. With the DPK data, values for nuclei and cells with the boron‐10 on the cell surface are calculated for different combinations of cell and nucleus sizes. The value for a cell radius of and a nucleus radius of is slightly larger than the value published by Tung et al. [Appl. Radiat. Isot. 61, 739–743 (2004)]. This result is potentially more accurate than the published value since it includes the contribution of a lithium‐7 ion as well as the alpha particle.
Investigations of different kilovoltage x‐ray energy for three‐dimensional converging stereotactic radiotherapy system: Monte Carlo simulations with CT data
Authors: Deloar Hossain M. , Kunieda Etsuo , Kawase Takatsugu , Tsunoo Takanori , Saitoh Hidetoshi , Ozaki Masahiro , Saito Kimiaki , Takagi Shunji , Sato Osamu , Fujisaki Tatsuya , Myojoyama Atsushi , Sorell Graham
Published: December 2006

We are investigating three‐dimensional converging stereotactic radiotherapy (3DCSRT) with suitable medium‐energy x rays as treatment for small lung tumors with better dose homogeneity at the target. A computed tomography (CT) system dedicated for non‐coplanar converging radiotherapy was simulated with BEAMnrc (EGS4) Monte‐Carlo code for x‐ray energy of 147.5, 200, 300, and 500 kilovoltage (kVp). The system was validated by comparing calculated and measured percentage of depth dose in a water phantom for the energy of 120 and. A thorax phantom and CT data from lung tumorswere used to compare dose homogeneities of kVp energies with MV energies of 4, 6, and. Three non‐coplanar arcs (and) around the center of the target were employed. The Monte Carlo dose data format was converted to the XiO RTP format to compare dose homogeneity, differential, and integral dose volume histograms of kVp and MV energies. In terms of dose homogeneity and DVHs, dose distributions at the target of all kVp energies with the thorax phantom were better than MV energies, with mean dose absorption at the ribs (human data) of 100%, 85%, 50%, 30% for 147.5, 200, 300, and, respectively. Considering dose distributions and reduction of the enhanced dose absorption at the ribs, a minimum ofis suitable for the lung kVp 3DCSRT system.
Characterization of the susceptibility artifact around a prostate brachytherapy seed in MRI
Authors: Wachowicz K. , Thomas S. D. , Fallone B. G.
Published: December 2006

Magnetic distortions surrounding a typical brachytherapy seed (IMC6711, within a clinical magnetic resonance imager were modeled for a number of different seed orientations with respect to the main magnetic field. From these distortion maps, simulated images were produced. The simulated images were then compared to images experimentally acquired using a spin echo technique on a Philips magnetic resonance imaging scanner. The modeled images were found to conform very well to those acquired experimentally, thus allowing one to establish where the seed is positioned within the complex image distortion patterns. The artifact patterns were dependent on the orientation of the seed with the main magnetic field, as well as the direction of the read encode gradient. While all imaging schemes which employ a unidirectional linear read encode trajectory should produce the artifacts modeled in this article, sequences other than spin echo may produce additional artifacts. Gradient echo and steady‐state free precession imaging techniques were also performed on the seed for comparison.
Computerized detection of vertebral compression fractures on lateral chest radiographs: Preliminary results with a tool for early detection of osteoporosis
Authors: Kasai Satoshi , Li Feng , Shiraishi Junji , Li Qiang , Doi Kunio
Published: December 2006

Vertebral fracture (or vertebral deformity) is a very common outcome of osteoporosis, which is one of the major public health concerns in the world. Early detection of vertebral fractures is important because timely pharmacologic intervention can reduce the risk of subsequent additional fractures. Chest radiographs are used routinely for detection of lung and heart diseases, and vertebral fractures can be visible on lateral chest radiographs. However, investigators noted that about 50% of vertebral fractures visible on lateral chest radiographs were underdiagnosed or under‐reported, even when the fractures were severe. Therefore, our goal was to develop a computerized method for detection of vertebral fractures on lateral chest radiographs in order to assist radiologists’ image interpretation and thus allow the early diagnosis of osteoporosis. The cases used in this study were 20 patients with severe vertebral fractures and 118 patients without fractures, as confirmed by the consensus of two radiologists. Radiologists identified the locations of fractured vertebrae, and they provided morphometric data on the vertebral shape for evaluation of the accuracy of detecting vertebral end plates by computer. In our computerized method, a curved search area, which included a number of vertebral end plates, was first extracted automatically, and was straightened so that vertebral end plates became oriented horizontally. Edge candidates were enhanced by use of a horizontal line‐enhancement filter in the straightened image, and a multiple thresholding technique, followed by feature analysis, was used for identification of the vertebral end plates. The height of each vertebra was determined from locations of identified vertebral end plates, and fractured vertebrae were detected by comparison of the measured vertebral height with the expected height. The sensitivity of our computerized method for detection of fracture cases was 95% (19/20), with 1.03 (139/135) false‐positive fractures per image. The accuracy of identifying vertebral end plates, marked by radiologists in a morphometric study, was 76.6% (400/522) and 70.9% (420/592) for cases used for training and those for testing, respectively. We prepared 32 additional fracture cases for a validation test, and we examined the detection accuracy of our computerized method. The sensitivity for these cases was 75% (24/32) at 1.03 (33/32) false‐positive fractures per image. Our preliminary results show that the automated computerized scheme for detecting vertebral fractures on lateral chest radiographs has the potential to assist radiologists in detecting vertebral fractures.
Monte Carlo modelling of a‐Si EPID response: The effect of spectral variations with field size and position
Authors: Parent Laure , Seco Joao , Evans Phil M. , Fielding Andrew , Dance David R.
Published: December 2006

This study focused on predicting the electronic portal imaging device (EPID) image of intensity modulated radiation treatment (IMRT) fields in the absence of attenuation material in the beam with Monte Carlo methods. As IMRT treatments consist of a series of segments of various sizes that are not always delivered on the central axis, large spectral variations may be observed between the segments. The effect of these spectral variations on the EPID response was studied with fields of various sizes and off‐axis positions. A detailed description of the EPID was implemented in a Monte Carlo model. The EPID model was validated by comparing the EPID output factors for field sizes between and at the isocenter. The Monte Carlo simulations agreed with the measurements to within 1.5%. The Monte Carlo model succeeded in predicting the EPID response at the center of the fields of various sizes and offsets to within 1% of the measurements. Large variations (up to 29%) of the EPID response were observed between the various offsets. The EPID response increased with field size and with field offset for most cases. The Monte Carlo model was then used to predict the image of a simple test IMRT field delivered on the beam axis and with an offset. A variation of EPID response up to 28% was found between the on‐ and off‐axis delivery. Finally, two clinical IMRT fields were simulated and compared to the measurements. For all IMRT fields, simulations and measurements agreed within 3%— for 98% of the pixels. The spectral variations were quantified by extracting from the spectra at the center of the fields the total photon yield , the photon yield below , and the percentage of photons below . For the studied cases, a correlation was shown between the EPID response variation and , , and .
Automated detection of a prostate stent in electronic portal images
Authors: Carl Jesper , Nielsen Henning , Nielsen Jane , Lund Bente , Larsen Erik Hoejkjaer
Published: December 2006

Planning target volumes (PTV) in fractionated radiotherapy still have to be outlined with wide margins to the clinical target volume due to uncertainties arising from daily shift of the prostate position. A recently proposed new method of visualization of the prostate is based on insertion of a thermo‐expandable stent. The current study proposes a new detection algorithm for automated detection of the stent in electronic portal images. The algorithm is based on the stent having a cylindrical shape with a fixed diameter, which was used as the basis for an automated detection algorithm. The automated method uses enhancement of lines combined with a grayscale morphology operation that looks for enhanced pixels separated with a distance similar to the diameter of the stent. The images in this study are all from prostate cancer patients treated with radiotherapy in a previous study. Images of a stent inserted in a humanoid phantom demonstrated a localization accuracy of 0.4– which equals the pixel size in the image. The automated detection of the stent was compared to manual detection in 71 pairs of orthogonal images taken in nine patients. The algorithm was successful in 67 of 71 pairs of images. The method is fast, has a high success rate, good accuracy, and has a potential for unsupervised localization of the prostate before radiotherapy, which would enable automated repositioning before treatment and allow for the use of very tight PTV margins.
A fast tube of response ray‐tracer
Authors: Schretter Colas
Published: December 2006

A ray‐tracing algorithm is proposed to quickly approximate volumes of intersection between an arbitrary tube of response and a voxel array. The method is based on the idea of the Wu antialiased line tracer that is well known in the computer graphics community. However, our method works in three dimensions and supports arbitrary symmetrical response profile functions. The inner loop implementation does not use any conditional branching and is aware of low‐level optimization strategies. The running speed of a fast incremental Siddon routine appears to be about 60% slower than our algorithm.
Using fluence separation to account for energy spectra dependence in computing dosimetric EPID images for IMRT fields
Authors: Li Weidong , Siebers Jeffrey V. , Moore Joseph A.
Published: December 2006

This study develops a method to improve the dosimetric accuracy of computed images for an amorphous silicon flat‐panel imager. Radially dependent kernels derived from Monte Carlo simulations are convolved with the treatment‐planning system's energy fluence. Multileaf collimator (MLC) beam hardening is accounted for by having separate kernels for open and blocked portions of MLC fields. Field‐size‐dependent output factors are used to account for the field‐size dependence of scatter within the imager. Gamma analysis was used to evaluate open and sliding window test fields and intensity modulated patient fields. For each tested field, at least 99.6% of the points had with a 3%, 3‐mm criteria. With a 2%, 2‐mm criteria, between 81% and 100% of points had . Patient intensity modulated test fields had 94%–100% of the points with with a 2%, 2‐mm criteria for all six fields tested. This study demonstrates that including the dependencies of kernel and fluence on radius and beam hardening in the convolution improves its accuracy compared with the use of radial and beam‐hardening independent kernels; it also demonstrates that the resultant accuracy of the convolution method is sufficient for pretreatment, intensity modulated patient field verification.
On relating the generalized equivalent uniform dose formalism to the linear‐quadratic model
Authors: Djajaputra David , Wu Qiuwen
Published: December 2006

Two main approaches are commonly used in the literature for computing the equivalent uniform dose (EUD) in radiotherapy. The first approach is based on the cell‐survival curve as defined in the linear‐quadratic model. The second approach assumes that EUD can be computed as the generalized mean of the dose distribution with an appropriate fitting parameter. We have analyzed the connection between these two formalisms by deriving explicit formulas for the EUD which are applicable to normal distributions. From these formulas we have established an explicit connection between the two formalisms. We found that the EUD parameter has strong dependence on the parameters that characterize the distribution, namely the mean dose and the standard deviation around the mean. By computing the corresponding parameters for clinical dose distributions, which in general do not follow the normal distribution, we have shown that our results are also applicable to actual dose distributions. Our analysis suggests that caution should be used in using generalized EUD approach for reporting and analyzing dose distributions.
Thick, segmented ‐photodiode detector for cone beam megavoltage CT: A Monte Carlo study of system design parameters
Authors: Monajemi T. T. , Fallone B. G. , Rathee S.
Published: December 2006

Megavoltage (MV) imaging detectors have been the focus of research by many groups in recent years. We have been working with segmented crystals in contact with photodiodes in our lab. The present study uses both x‐ray and optical photon transport Monte Carlo simulations to analyze the effects of scintillation crystal height, septa material, beam divergence, and beam spectrum on the modulation transfer function, MTF and zero frequency detective quantum efficiency, DQE(0), of a theoretical area detector. The theoretical detector is comprised of tall, segmented crystals and two dimensional photodiode arrays with a pitch of and a fill factor of 72%. Increasing the crystal height above does not result in an improvement in the DQE(0) if the reflection coefficient of the septa is less than 0.8. For a reflection coefficient of 0.975 for the septa, there is a continual gain in the DQE(0) up to tall crystals. Similar calculations show that employing a 3.5 MV beam without a flattening filter increases the DQE(0) for tall crystals by 9% compared to a typical beam with a flattening filter. The severe degradations due to beam divergence on MTF are quantified and suggest the use of focused detectors in MV imaging. It is found that when the effect of optical photons is considered, the presence of divergence can appear as a shift in the location of the input signal as well as loss of spatial resolution.
Important considerations for radiochromic film dosimetry with flatbed CCD scanners and EBT film
Authors: Lynch Bart D. , Kozelka Jakub , Ranade Manisha K. , Li Jonathan G. , Simon William E. , Dempsey James F.
Published: December 2006

In this study, we present three significant artifacts that have the potential to negatively impact the accuracy and precision of film dosimetry measurements made using EBT radiochromic film when read out with CCD flatbed scanners. Films were scanned using three commonly employed instruments: a Macbeth TD932 spot densitometer, an Epson Expression 1680 CCD array scanner, and a Microtek ScanMaker i900 CCD array scanner. For the two scanners we assessed the variation in optical density (OD) of EBT film with scanning bed position, angular rotation of the film with respect to the scan line direction, and temperature inside the scanner due to repeated scanning. Scanning uniform radiochromic films demonstrated a distinct bowing effect in profiles in the direction of the CCD array with a nonuniformity of up to 17%. Profiles along a direction orthogonal to the CCD array demonstrated a 7% variation. A strong angular dependence was found in measurements made with the flatbed scanners; the effect could not be reproduced with the spot densitometer. An IMRT quality assurance film was scanned twice rotating the film between the scans. For films scanned on the Epson scanner, up to 12% variation was observed in unirradiated EBT films rotated between and , which decreased to approximately 8% for EBT films irradiated to . Variations of up to 80% were observed for films scanned with the Microtek scanner. The scanners were found to significantly increase the film temperature with repeated scanning. Film temperature between 18 and caused OD changes of approximately 7%. Considering these effects, we recommend adherence to a strict scanning protocol that includes: maintaining the orientation of films scanned on flatbed scanners, limiting scanning to the central portion of the scanner bed, and limiting the number of consecutive scans to minimize changes in OD caused by film heating.
Dose and image quality for a cone‐beam C‐arm CT system
Authors: Fahrig Rebecca , Dixon Robert , Payne Thomas , Morin Richard L. , Ganguly Arundhuti , Strobel Norbert
Published: December 2006

We assess dose and image quality of a state‐of‐the‐art angiographic C‐arm system (Axiom Artis dTA, Siemens Medical Solutions, Forchheim, Germany) for three‐dimensional neuro‐imaging at various dose levels and tube voltages and an associated measurement method. Unlike conventional CT, the beam length covers the entire phantom, hence, the concept of computed tomography dose index (CTDI) is not the metric of choice, and one can revert to conventional dosimetry methods by directly measuring the dose at various points using a small ion chamber. This method allows us to define and compute a new dose metric that is appropriate for a direct comparison with the familiar of conventional CT. A perception study involving the CATPHAN 600 indicates that one can expect to see at least the inset with 0.5% nominal contrast at the recommended head‐scan dose when using tube voltages ranging from to . When analyzing the impact of tube voltage on image quality at a fixed dose, we found that lower tube voltages gave improved low contrast detectability for small‐diameter objects. The relationships between kVp, image noise, dose, and contrast perception are discussed.
Modeling granular phosphor screens by Monte Carlo methods
Authors: Liaparinos Panagiotis F. , Kandarakis Ioannis S. , Cavouras Dionisis A. , Delis Harry B. , Panayiotakis George S.
Published: December 2006

The intrinsic phosphor properties are of significant importance for the performance of phosphor screens used in medical imaging systems. In previous analytical‐theoretical and Monte Carlo studies on granular phosphor materials, values of optical properties, and light interaction cross sections were found by fitting to experimental data. These values were then employed for the assessment of phosphor screen imaging performance. However, it was found that, depending on the experimental technique and fitting methodology, the optical parameters of a specific phosphor material varied within a wide range of values, i.e., variations of light scattering with respect to light absorption coefficients were often observed for the same phosphor material. In this study, x‐ray and light transport within granular phosphor materials was studied by developing a computational model using Monte Carlo methods. The model was based on the intrinsic physical characteristics of the phosphor. Input values required to feed the model can be easily obtained from tabulated data. The complex refractive index was introduced and microscopic probabilities for light interactions were produced, using Mie scattering theory. Model validation was carried out by comparing model results on x‐ray and light parameters (x‐ray absorption, statistical fluctuations in the x‐ray to light conversion process, number of emitted light photons, output light spatial distribution) with previous published experimental data on phosphor material (Kodak Min‐R screen). Results showed the dependence of the modulation transfer function (MTF) on phosphor grain size and material packing density. It was predicted that granular screens of high packing density and small grain size may exhibit considerably better resolution and light emission properties than the conventional screens, under similar conditions (x‐ray incident energy, screen thickness).
Robustness and complexity of a minimally invasive vascular intervention simulation system
Authors: Alderliesten Tanja , Konings Maurits K. , Niessen Wiro J.
Published: December 2006

Minimally invasive vascular interventions offer advantages over open surgery. Thorough training is needed to master the skills required to correctly perform these minimally invasive interventions. Simulation is becoming a potential alternative for training. We have developed the foundation, i.e., the algorithmics and models, for a minimally invasive vascular intervention simulation system focusing on guide‐wire manipulations. In this article we address the robustness, accuracy, and complexity of this foundation using a phantom. To this end the theory on which the simulation is based is used to formulate constraints on the simulation parameters. Furthermore, the parameter space has been explored in order to optimize the trade‐off we are facing: accuracy versus speed of the simulation. A physical experiment setup has been designed that allows us to obtain ground‐truth data. The accuracy of the simulation has been determined by comparing physical experimental results with various simulations. For multiple combinations of parameter settings the simulation supplies a guide‐wire configuration with a root‐mean‐square error around . The results show that the speed of the simulation is still an issue and needs to be improved. Nevertheless, the results also indicate that the developed algorithms and models are a robust foundation to build a simulation system on.
Direct aperture deformation: An interfraction image guidance strategy
Authors: Feng Yuanming , Castro‐Pareja Carlos , Shekhar Raj , Yu Cedric
Published: December 2006

A new scheme, called direct aperture deformation (DAD), for online correction of interfraction geometric uncertainties under volumetric imaging guidance is presented. Using deformable image registration, the three‐dimensional geometric transformation matrix can be derived that associates the planning image set and the images acquired on the day of treatment. Rather than replanning or moving the patient, we use the deformation matrix to morph the treatment apertures as a potential online correction method. A proof‐of‐principle study using an intensity‐modulated radiation therapy plan for a prostate cancer patient was conducted. The method, procedure, and algorithm of DAD are described. The dose‐volume histograms from the original plan, reoptimized plan, and rigid‐body translation plan are compared with the ones from the DAD plan. The study showed the feasibility of the DAD as a general method for both target dislocation and deformation. As compared with using couch translation to move the patient, DAD is capable of correcting both target dislocation and deformations. As compared with reoptimization, online correction using the DAD scheme could be completed within a few minutes rather than tens of minutes and the speed gain would be at a very small cost of plan quality.
Clinical assessment of three‐dimensional ultrasound prostate localization for external beam radiotherapy
Authors: Orton Nigel P. , Jaradat Hazim A. , Tomé Wolfgang A.
Published: December 2006

Three‐dimensional ultrasound localization has been performed for external beam prostate treatments at our institution since September 2001. This article presents data from the daily shifts for 221 patients and 5005 fractions, and the results of tests performed to assess the system's performance under clinical conditions. Three tests are presented: (1) To measure the accuracy of the shifts, eight patients treated on a helical tomotherapy machine were localized daily using both ultrasound (US) and a megavoltage computed tomography (MVCT) scan. Comparison of the shifts showed that US localization improved alignment for six of the eight patients when compared to alignment using skin marks alone. The mean US‐MVCT vector for these six patients was , compared to between the MVCT and the skin marks. The other two patients were identified as poor candidates for US prior to their first treatment fraction. (2) To assess the extent of intrafraction motion, US localization was repeated after treatment for six patients and a total of 29 fractions. The mean intrafraction prostate shift was , and the shift was within the localization uncertainty [Tomé et al., Med. Phys. 29, 1781–1788 (2002); in New Technologies in Radiotion Oncology, edited by W. Schlegel, T. Bortfelde, and A. Grosu (Springer, Berlin, 2005)] of the system for 25 of 29 fractions. (3) To assess the interuser variation in shifts, four experienced operators independently localized five patients for five consecutive fractions. The standard deviation of the users’ shifts was found to be approximately the same as the system's localization uncertainty. For shifts larger than the system localization uncertainty, the standard deviation of the users’ shifts was nearly always much smaller than the mean shift. Taken together with the results of the US‐MVCT comparison, this indicates that the shifts improved patient localization despite differences between users.
Efficient projection and backprojection scheme for spherically symmetric basis functions in divergent beam geometry
Authors: Ziegler Andy , Köhler Thomas , Nielsen Tim , Proksa Roland
Published: December 2006

In cone‐beam transmission tomography the measurements are performed with a divergent beam of x‐rays. The reconstruction with iterative methods is an approach that offers the possibility to reconstruct the corresponding images directly from these measurements. Another approach based on spherically symmetric basis functions (blobs) has been reported with results demonstrating a better image quality for iterative reconstruction algorithms. When combining the two approaches (i.e., using blobs in iterative cone‐beam reconstruction of divergent rays) the problem of blob sampling without introducing aliasing must be addressed. One solution to this problem is to select a blob size large enough to ensure a sufficient sampling, but this prevents a high resolution reconstruction, which is not desired. Another solution is a heuristic low‐pass filtering, which removes this aliasing, but neglects the different contributions of blobs to the absorption depending on the spatial position in the volume and, therefore, cannot achieve the best image quality. This article presents a model of sampling the blobs which is motivated by the beam geometry. It can be used for high resolution reconstruction and can be implemented efficiently.
Intensity modulated radiation therapy with irregular multileaf collimated field: A dosimetric study on the penumbra region with different leaf stepping patterns
Authors: Chow James C. L. , Grigorov Grigor N. , Jiang Runqing
Published: December 2006

Using a Varian 21 EX linear accelerator with a multileaf collimator (MLC) of 120 leaves, the penumbra regions of beam profiles within an irregular multileaf collimated fields were studied. MLC fields with different leaf stepping angles from 21.8° to 68.2° were used. Beam profiles in different directions: (1) along the cross‐line and in‐line axis, (2) along the leaf stepping edges of the field, and (3) parallel to the stepping edges but in the middle of the field, were measured and calculated using Kodak XV radiographic film and Pinnacle3 treatment planning system version 7.4f. These beam profiles were measured and calculated at source to axis distance= with of solid water slab on top. On the one hand, for both cross‐line and in‐line beam profiles, the penumbra widths of 20%–80% did not vary with the leaf stepping angles and were about . On the other hand, the penumbra widths of 10%–90% of the above two profiles varied with the stepping angles and had maximum widths of about (cross‐line) and (in‐line) for stepping angles of 38.7° and 51.3°, respectively. For profiles crossing the “rippled” stepping edges of the field, the penumbra widths (10%–90%) at the regions between two opposite leaves (i.e., profile end at the jaw position) decreased with the stepping angles. At the penumbra regions between two leaf edges with the tongue‐and‐groove structure of the same bank (i.e., profile end at the jaw position), the penumbra widths increased with the stepping angles. When the penumbra widths were measured between two opposite leaf edges and at corners between two leaves, the widths first decreased with the stepping angles and then increased beyond the minimum width point at stepping angle of 45°. The penumbra width (10%–90%) measured at the leaf edge was larger than that at the corner. For the beam profiles calculated using Pinnacle3, it is found that the results agreed well with the measurements along the cross‐line and in‐line axis, while there was a deviation for the profiles along the leaf stepping edge of the field compared to the film measurements. The measured results in this study can help us to understand the dosimetric effect of the leaf stepping (due to finite leaf width), tongue‐and‐groove and rounded leaf end structure in the penumbra region of an irregular MLC field. A more dedicated penumbra model can be developed for the treatment planning system.
Radiative transport in fluorescence‐enhanced frequency domain photon migration
Authors: Rasmussen John C. , Joshi Amit , Pan Tianshu , Wareing Todd , McGhee John , Sevick‐Muraca Eva M.
Published: December 2006

Small animal optical tomography has significant, but potential application for streamlining drug discovery and pre‐clinical investigation of drug candidates. However, accurate modeling of photon propagation in small animal volumes is critical to quantitatively obtain accurate tomographic images. Herein we present solutions from a robust fluorescence‐enhanced, frequency domain radiative transport equation (RTE) solver with unique attributes that facilitate its deployment within tomographic algorithms. Specifically, the coupled equations describing time‐dependent excitation and emission light transport are solved using discrete ordinates angular differencing along with linear discontinuous finite‐element spatial differencing on unstructured tetrahedral grids. Source iteration in conjunction with diffusion synthetic acceleration is used to iteratively solve the resulting system of equations. This RTE solver can accurately and efficiently predict ballistic as well as diffusion limited transport regimes which could simultaneously exist in small animals. Furthermore, the solver provides accurate solutions on unstructured, tetrahedral grids with relatively large element sizes as compared to commonly employed solvers that use step differencing. The predictions of the solver are validated by a series of frequency‐domain, phantom measurements with optical properties ranging from diffusion limited to transport limited propagation. Our results demonstrate that the RTE solution consistently matches measurements made under both diffusion and transport‐limited conditions. This work demonstrates the use of an appropriate RTE solver for deployment in small animal optical tomography.
Monte Carlo simulations of dose near a nonradioactive gold seed
Authors: Chow James C. L. , Grigorov Grigor N.
Published: December 2006

The relative doses and hot/cold spot positions around a non‐radioactive gold seed, irradiated by a 6 or photon beam in water, were calculated using Monte Carlo simulation. Phase space files of 6 and photon beams with a field size of were generated by a Varian 21 EX linear accelerator using the EGSnrc and BEAMnrc code. The seed was positioned at the isocenter in a water phantom with source‐to‐axis . For the single beam geometry, the relative doses (normalized to the dose at distance above the isocenter) at the upstream seed surface were calculated to be 1.64 and 1.56 for the 6 and beams respectively when the central beam axis (CAX) is parallel to the width of the seed. These doses were slightly higher than those (1.58 and 1.52 for 6 and beams respectively) calculated when the CAX is perpendicular to the width of the seed. Compared to the relative dose profiles with the same beam geometry without the seed in the water phantom, the presence of the seed affects the dose distribution at about distance beyond both the upstream and downstream seed surface. For a pair of opposing beams with equal and unequal beam weight, the hot and cold spots of both opposing beams were mixed. For a photon arc around the longitudinal axis of the seed, the relative dose profile along the width of the seed was similar to that of the opposing beam pair, except the former geometry has a larger dose gradient near the seed surface. In this study, selected results from our simulation were compared to previous measurements using film dosimetry.
Multiobjective optimization with a modified simulated annealing algorithm for external beam radiotherapy treatment planning
Authors: Aubry Jean‐François , Beaulieu Frédéric , Sévigny Caroline , Beaulieu Luc , Tremblay Daniel
Published: December 2006

Inverse planning in external beam radiotherapy often requires a scalar objective function that incorporates importance factors to mimic the planner's preferences between conflicting objectives. Defining those importance factors is not straightforward, and frequently leads to an iterative process in which the importance factors become variables of the optimization problem. In order to avoid this drawback of inverse planning, optimization using algorithms more suited to multiobjective optimization, such as evolutionary algorithms, has been suggested. However, much inverse planning software, including one based on simulated annealing developed at our institution, does not include multiobjective‐oriented algorithms. This work investigates the performance of a modified simulated annealing algorithm used to drive aperture‐based intensity‐modulated radiotherapy inverse planning software in a multiobjective optimization framework. For a few test cases involving gastric cancer patients, the use of this new algorithm leads to an increase in optimization speed of a little more than a factor of 2 over a conventional simulated annealing algorithm, while giving a close approximation of the solutions produced by a standard simulated annealing. A simple graphical user interface designed to facilitate the decision‐making process that follows an optimization is also presented.
An EGSnrc investigation of the correction factor for ion chambers in kilovoltage x rays
Authors: La Russa Daniel J. , Rogers D. W. O.
Published: December 2006

As part of the standard practice for obtaining consistent ion chamber measurements with cavities open to the surrounding atmosphere, the raw measured response is corrected to the response at a reference temperature and pressure using the standard temperature‐pressure correction factor . In this study, the EGSnrc Monte Carlo code was used to investigate the validity of the correction factor for kilovoltage x rays incident on various geometrically distinct ion chambers. The calculated ‐corrected chamber response deviated by over 2% relative to expected values for a spectrum incident on a graphite thimble chamber at an air density typical of Mexico City. The relative deviation from the expected response was much worse for a large spherical graphite chamber, exceeding 16% at an air density of ( at ) for the same beam energy. The breakdown of the correction factor was also observed for a mammography spectrum incident on two mammography chambers. For beams, the correction factor behaved as expected. For day‐to‐day variations in pressure, only a negligible of the correction factor was observed with low x‐ray energies. Factors contributing to the breakdown of the correction factor at low x‐ray energies and large pressure variations, such as the range of electrons, the material of the wall, the chamber dimensions and air‐photon interactions, are discussed in depth.
2D/3D Image fusion for accurate target localization and evaluation of a mask based stereotactic system in fractionated stereotactic radiotherapy of cranial lesions
Authors: Jin Jian‐Yue , Ryu Samuel , Faber Kathleen , Mikkelsen Tom , Chen Qing , Li Shidong , Movsas Benjamin
Published: December 2006

The purpose of this study was to evaluate the accuracy of a two‐dimensional (2D) to three‐dimensional (3D) image‐fusion‐guided target localization system and a mask based stereotactic system for fractionated stereotactic radiotherapy (FSRT) of cranial lesions. A commercial x‐ray image guidance system originally developed for extracranial radiosurgery was used for FSRT of cranial lesions. The localization accuracy was quantitatively evaluated with an anthropomorphic head phantom implanted with eight small radiopaque markers (BBs) in different locations. The accuracy and its clinical reliability were also qualitatively evaluated for a total of 127 fractions in 12 patients with both kV x‐ray images and MV portal films. The image‐guided system was then used as a standard to evaluate the overall uncertainty and reproducibility of the head mask based stereotactic system in these patients. The phantom study demonstrated that the maximal random error of the image‐guided target localization was in each direction in terms of the 95% confidence interval (CI). The systematic error varied with measurement methods. It was approximately , mainly in the longitudinal direction, for the kV x‐ray method. There was a systematic difference, primarily in the lateral direction, between the kV x‐ray and the MV portal methods. The patient study suggested that the accuracy of the image‐guided system in patients was comparable to that in the phantom. The overall uncertainty of the mask system was , and the reproducibility was in terms of 95% CI. The study demonstrated that the image guidance system provides accurate and precise target positioning.
Histocompatible Embryonic Stem Cells by Parthenogenesis
Authors: Kim Kitai , Lerou Paul , Yabuuchi Akiko , Lengerke Claudia , Ng Kitwa , West Jason , Kirby Andrew , Daly Mark J. , Daley George Q.
Published: December 2006

Genetically matched pluripotent embryonic stem (ES) cells generated via nuclear transfer or parthenogenesis (pES cells) are a potential source of histocompatible cells and tissues for transplantation. After parthenogenetic activation of murine oocytes and interruption of meiosis I or II, we isolated and genotyped pES cells and characterized those that carried the full complement of major histocompatibility complex (MHC) antigens of the oocyte donor. Differentiated tissues from these pES cells engrafted in immunocompetent MHC-matched mouse recipients, demonstrating that selected pES cells can serve as a source of histocompatible tissues for transplantation.
Polymorphic Secreted Kinases Are Key Virulence Factors in Toxoplasmosis
Authors: Saeij J. P. J. , Boyle J. P. , Coller S. , Taylor S. , Sibley L. D. , Brooke-Powell E. T. , Ajioka J. W. , Boothroyd J. C.
Published: December 2006

The majority of known
Toxoplasma gondii
isolates from Europe and North America belong to three clonal lines that differ dramatically in their virulence, depending on the host. To identify the responsible genes, we mapped virulence in F
1
progeny derived from crosses between type II and type III strains, which we introduced into mice. Five virulence (
VIR
) loci were thus identified, and for two of these, genetic complementation showed that a predicted protein kinase (ROP18 and ROP16, respectively) is the key molecule. Both are hypervariable rhoptry proteins that are secreted into the host cell upon invasion. These results suggest that secreted kinases unique to the Apicomplexa are crucial in the host-pathogen interaction.
Separation of Marine Bacteria according to Buoyant Density by Use of the Density-Dependent Cell Sorting Method
Authors: Inoue Katsuyuki , Nishimura Masahiko , Nayak Binaya B. , Kogure Kazuhiro
Published: December 2006

The purpose of this study was to test whether some phylogenetic groups of natural marine bacteria have unique buoyant densities that allow them to be separated by the density-dependent cell sorting (DDCS) method. We first concentrated a natural bacterial assemblage to collect sufficient numbers of cells. They were separated into three fractions by DDCS, and the community structure in each was clarified by fluorescence in situ hybridization. The cells of
Archaea
tended to appear in the high-density fraction, whereas those of
Cytophaga-Flavobacterium-Bacteroides
were in the low-density fraction. We also calculated the sedimentation velocities of three typical marine bacteria (low density, middle density, and high density) using their buoyant density. The sedimentation velocities were approximately 10, 20, and 30 μm h
−1
; these velocities have ecological implications when the heterogeneity of bacteria is considered at a microscale. To our knowledge, this is the first report on the buoyant density of natural marine bacteria.
Role of Host Nutrition in Symbiont Regulation: Impact of Dietary Nitrogen on Proliferation of Obligate and Facultative Bacterial Endosymbionts of the Pea Aphid
Acyrthosiphon pisum
Authors: Wilkinson T. L. , Koga R. , Fukatsu T.
Published: December 2006

The impact of host nutrition on symbiont regulation in the pea aphid
Acyrthosiphon pisum
was investigated. The population density of the obligate symbiont
Buchnera aphidicola
positively correlated with dietary nitrogen levels. In contrast, the population density of the facultative symbiont
Serratia symbiotica
increased in aphids reared on low-nitrogen diets, indicating distinct regulatory mechanisms in the same insect host.