bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐E‐330A‐03: Reduction of Ring Artifacts in Cone Beam CT: Artifact Detection and Correction for Flat Panel Imagers
Authors: Altunbas M , Shaw C , Chen L 
Published: July 2006

Purpose: Defective pixels in a flat panel detector may be characterized by a nonlinear signal response drastically different from those in the neighboring pixels. They could lead to ring artifacts in cone beam CT. In this presentation, we will describe and demonstrate the use of a filter based calibration technique to detect these pixels. In addition, we will employ this technique as a flat field correction method to correct nonlinear signal response. Methods and Materials: To force the signal responses of all pixels to vary smoothly without sudden changes, we acquired images at fixed mAs but with various filtrations. Each filtered image is fitted to a smooth surface whose values are close to those of normal pixels but vary smoothly in the image. The ratios of the surface fit values to the original values were then computed on a pixel‐by‐pixel basis and used to map pixel values during subsequent image acquisition. This mapping would compensate for the nonlinear signal response associated with the defective pixels thus eliminating the ring artifacts. Using the surface fits as the reference, defective pixels were detected by automatic thresholding. Results: Using filter based calibration, defective (∼0.035 %) pixels were successfully detected and corrected for. Therefore, ring artifacts were largely eliminated in cone beam CT images. A reduction in patterned noise artifacts in the projection images was also observed. The automated surface fitting procedure was found to be robust. Conclusions: Although the conventional flat field correction addresses non‐uniform response across the detector, artifacts may still form as the pixel response varies with the beam quality and signal intensity. The filter based calibration procedure was successfully used to detect and correct for these artifacts.This work was supported in part by a research grant EB00117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI.
TH‐E‐224A‐03: Orientation, Position, and Temperature Dependence On Optical Density Measurements When Using Sensitive Radiochromic Film and Fluorescent CCD Scanner
Authors: Lynch B , Kozelka J , Ranade M , Li J , Simon W , Dempsey J 
Published: July 2006

Purpose: We report systematic artifacts that were found to occur when scanning a commercial radiochromic film (RCF) (GAFCHROMIC EBT) with a charge‐coupled device (CCD) film scanner. Potential systematic sources of optical density (OD) measurement error were found be related to film orientation with respect to the scanner bed, film position on the scanner bed, and film temperature from repeated scanning. Method and Materials: We investigated the use of two flatbed CCD scanners that have been previously reported for use with the RCF, as well as two point densitometers that measure diffuse OD. Change in OD with film orientation was studied with small uniformly irradiated RCFs that were rotated and repeatedly scanned. A RCF from an IMRT QA measurement was scanned in portrait and landscape orientations to assess the magnitude of possible clinical errors. Film uniformity was assessed by evaluating profiles in the scan direction for large RCFs with graded uniform ODs produced by exposure to sunlight. A thermocouple was placed on the bed of a CCD scanner RCF was repeatedly scanned while recording temperature. Results: Sinusoidal variations of 15% were observed for rotating film measurements made with one CCD scanner (Epson) and 80% for the other (Microtek). The point densitometers did not demonstrate any variation with rotation. Changes in temperature in the range of 18–34°C lead to OD changes as large as 7%. The edges of the CCD scan beds demonstrated non‐uniformities as large as 15%. Conclusion: Care must be taken to avoid these systematic errors when using RCF for clinical dosimetry. We recommend: maintaining the orientation of films; scanning in the central portion of the scanner bed; and limiting the number of consecutive scans.This work was supported by NCI grants R01‐CA‐100636 and N43‐CM‐52214, Department of Health and Human Services Contract No HHSN261200522014C, and by Sun Nuclear Corporation.
TH‐E‐224A‐05: Absorbed Radiation Dose Measurement with a μK‐Resolution Ultrasonic Thermometer
Authors: Malyarenko E , Heyman J , Guy S , Chen‐Mayer H , Tosh R 
Published: July 2006

Purpose: To develop a μK‐resolution ultrasonic thermometer for non‐invasive measurements of absorbed radiation dose in water and to characterize the intensity profile of radiation beams used for medical treatment. Method and Materials: Subtle temperature changes in water were measured by monitoring the phase of an ultrasonic disturbance propagating in it. The current system includes a thermally insulated water tank, an ultrasonic transducer, a frequency counter, and a Pulsed Phase‐Locked Loop connected to a PC. The alpha‐prototype was initially tested and characterized experimentally with time‐controlled light pulses, and was subsequently evaluated with radiation heating from a therapy‐level Co‐60 source. The system was subjected to 30 one‐minute, 50% duty cycle radiation exposures; the temperature history was recorded and analyzed. Results: Preliminary Fourier analysis of the temperature changes caused by periodic radiation heating showed that the absorbed dose rate corresponds to 1.80 Gy/min, deduced from a 0.43 mK (±3% 1) per cycle temperature rise in water. The estimated nominal dose rate at 81.6 cm from the source and 3.2 cm below the water surface is estimated to be 1.65 Gy/min. The discrepancy can be attributed to the non‐standard water tank size and incomplete temperature calibration of the alpha prototype at test time. We expect to resolve these issues by equipping the system with a standard water tank and implementing a more advanced calibration procedure. Conclusions: The alpha prototype has been tested in Co‐60 radiation and produced reasonable results. The feedback from these tests has recently been incorporated into the design of a beta prototype. The new system routinely detects less than 10 μK temperature changes in water and shows great promise for precise dose measurements and beam profile characterization. The new calibration procedure does not require external sensors and makes the system more portable and fully self‐contained.Research sponsored by NIST.
Sci‐Thur PM Therapy‐01: 6MV Photon dMLC IMRT: Near Surface Dose with Oblique Incidence
Authors: Popescu C , Beckham W , Bush K 
Published: July 2006

The purpose of the study was to investigate absorbed dose in the build up region for oblique intensity modulated 6MV beams. For locally advanced breast carcinoma using multi‐field IMRT it is imperative to know with good precision the dose at the surface. This study intended to determine the effect of IMRT on the surface dose compared with open beams, to benchmark our Monte Carlo algorithm (BEAMnrc) in the build up region for clinical implementation and to characterize the dose calculation accuracy of our treatment planning system (Eclipse ™ 7.3) at the surface and depths up to dmax.Measurements were performed in solid water using a parallel plate ionization chamber for a 10 × 10 cm2 open field, 1 cm slit and a typical breast IMRT treatment field, both delivered with sliding window technique at 00°, 350° and 700° angles of incidence. Compared with the open field the 1cm gap sliding window decreased the surface dose up to 10% for normal incidence and up to 5% for 70° incidence. The measured depth‐dose curves along the central axis are in excellent agreement within 2% of the Monte Carlo simulations. The TPS using the pencil beam algorithm overestimates the dose at the surface by a factor of 3 at normal incidence for both open and IMRT fields. The TPS does not take into account the increase in the surface dose due to oblique incidence. Monte Carlo can be used to calculate with accuracy the surface dose for a clinical multi‐ field IMRT plan.
Sci‐Thur PM Therapy‐08: Intra and Inter Observer Variability and Systematic Error in Prostate Delineation
Authors: Gerig L , Gao Z , Eapen L , Wilkin D , Morash C , Wassef Y 
Published: July 2006

Individual sub‐processes of external beam radiation therapy can affect patient outcome. Specifically geometric uncertainties play a major role in tumor control and normal tissue complications. It is known that tumor definition varies among different observers but importantly, at least to our knowledge, few studies have reported their findings against a true gold standard, most relying on the population average as the reference value. This work uses the Visible Human Project® data for a set of cross‐indexed CT and anatomical photographic digital images of a human male cadaver. We use the anatomical images to define a gold standard for the prostate as defined by a group of experts. Six radiation oncologists then repeatedly (20 times over several weeks) defined the prostate alone on the corresponding CT images allowing us to quantify inter and intra observer random and importantly to measure systematic error.Individual and population means were tested for systematic error against the gold standard. We found that the observers routinely over estimated the prostate volume, and that our intra and inter observer variability is not significantly different than that reported in the literature. Significantly we report a systematic error in target definition, with the physicians failing to include all of the posterior prostate volume near the rectum. In contrast the observers rarely missed true prostate volume in the left, right or anterior quadrants, but we observe a systematic error in that normal tissue anterior to the prostate was routinely included as target tissue.
Po‐Thur Eve General‐07: Dosimetry of Small Lung Lesions with EGSnrc Monte Carlo and Treatment Planning Systems
Authors: Darko J , Joshi C , Osei E , Halsall T , Salomons G , Kerr A 
Published: July 2006

Early stage lung cancer, presenting as a small solitary pulmonary mass, is treated with radiation when concurrent disease precludes a surgical option. These small lesions are usually surrounded by less dense normal lung, which affects the ability to deliver a homogenous dose to the target volume. In low‐density tissue, such as lung, there is increased transmission of photons. In addition, lateral scatter of electrons out of the beam can lead to increased penumbral width. The magnitude of these effects is known to be dependent on beam energy. Some of the commonly used commercial treatment planning systems have had limited success in predicting accurately dose distributions under these highly inhomogeneous conditions.We present a quantitative comparison between Monte Carlo simulation and commercial planning systems for a select range of clinically relevant target geometries and beam parameters. Small water equivalent cylindrical lung tumors of diameter 3 and 5 cm were incorporated within a CT dataset at different locations. A Parallel Opposed Pair (POP) field arrangement with 6MV or 15MV photons and variable field‐edge margins were considered. These plans were calculated using BEAMnrc Monte Carlo code and on two planning systems; ADAC Pinnacle III Version 7.4 and MDS Nordion Theraplan Plus v3.8.The analysis of dose profiles and DVH's show considerable and unique differences between Monte Carlo and the results from each TPS within the tumor and at the junction between tumor and lung. For both planning systems, the severity of these errors, increases with photon energy, and decreases with field size.
Po‐Thur Eve General‐13: Commissioning a gated kV imaging system
Authors: Smith W , Spencer D 
Published: July 2006

The recent expansion in the use of breathing gating systems of various types necessitates the development of methods to efficiently evaluate them. An ideal commissioning procedure would not require extensive specialized equipment, would allow multiple measurements to be made quickly and easily, and be capable of detecting errors at levels which could conceivably be important in treatment situations. In this study, a simple method to evaluate timing accuracy and precision for gated kV imaging was developed, and used to evaluate the Brainlab ExactTracGating ™ kV imaging system.The phantom used has a moving platform and a set of IR markers moved in a sinusoidal vertical motion by a cam milled with 0.001 inch accuracy. A 1mm thick lead sheet with a 3 mm diameter hole was placed under the moving platform. Kodak PP‐L film was placed on the moving platform and kV images were obtained at 5%, 50% and 95% gating levels with each of the two tubes. Ten measurements for each tube could be easily made on a single 11×17 inch film. The measurement was repeated for periods between 1.5 and 5 seconds, and with a platform moving close to a sine function with an amplitude of 2.1cm. This commissioning system was capable of detecting systematic timing errors of less than 40 ms, but none were observed. The standard deviation in timing accuracy was measured under difficult physiological conditions (3 second period, 2 cm amplitude of motion) and found to be about 0.03 cm, which corresponds to 30 ms.
Sci‐Fri AM General‐10: An Apparent Threshold Dose Effect in Radiochromic Gel Dosimeters
Authors: Babic S , Battista J , Jordan K 
Published: July 2006

Purpose: To identify the chemical and or physical cause of a threshold dose in the low dose response of FXG gel dosimeters.Methods: Gels were prepared by mixing stock solutions of ferrous‐ammonium‐sulphate and different chemical supplies of xylenol‐orange (XO) together with sulfuric acid into a solution of gelatin and distilled water. Concentrations of ferrous‐ammonium‐sulphate, XO and sulfuric acid were varied to identify one of these chemicals as a source of impurities potentially causing the threshold dose effect. Samples in 1 or 10cm acrylic cuvettes were irradiated to doses between 0–5Gy. Optical transmissions were measured through the samples and referenced to water at 589 and 543nm, respectively, using an absorption spectrophotometer. This procedure was repeated for gelatin‐free FX solutions and with gel containing varying concentrations of ferric‐ammonium‐sulphate.Results: The threshold dose decreased to 0.20±0.05 Gy using reagent grade XO. There was no correlation between threshold dose and varying concentrations of ferrous and sulphuric acid although decreasing the XO concentration from 0.05 to 0.025mM lowered the threshold dose by a factor of two. Gelatin‐free FX solutions showed a threshold dose. Using a ferric concentration of 7.5uM decreased the threshold dose to 0.04±0.03 Gy. The threshold dose effect was not present at 543nm.Conclusions: Chemical impurities are not responsible for the threshold dose. The “apparent” threshold dose is caused by the production of different Fe(III)i:XOj species (each with their own respective spectral absorptivity). These species are formed at different dose levels and sensitivity to detecting these species requires optimization of the readout wavelength.
Sci‐Sat AM (2) Therapy‐03: Characterization of Intermediate Energy X‐Ray Photons (0.2–1.0 MeV) for stereotactic radiosurgery: experimental demonstration of reduced radiological penumbra
Authors: Keller B , O'Malley L , Beachey D , Presutti J , Pignol JP 
Published: July 2006

Introduction: Stereotactic radiosurgery is used to treat intracranial lesions with a high degree of accuracy. At the present time, x‐ray energies at or above Co‐60 gamma rays are used. We hypothesize that intermediate energy x‐ray photons (IEP's), combined with small field sizes, produce a reduced radiological penumbra leading to a sharper dose gradient. The purpose of this work is three‐fold: 1.) to produce IEP's using a medical linear accelerator 2.) to characterize the x‐ray energy 3.) to demonstrate reduced radiological penumbra for IEP's compared to 6MV x‐rays.Materials & Methods: A Siemens linear accelerator was modified to produce IEP's. PDD versus depth measurements were done in solid water using a Markus parallel plate ionization chamber (PTW Freiburg) at SSD=100cm for a 2×2cm2 field size. Monte Carlo computer simulations were done using MCNP‐4C. A penumbra measurement device was constructed to examine radiological penumbra for various photon energies, field sizes and depths. Film (Gafchromic EBT) was used to record field edge profiles. These films were scanned using a digital microscope (spatial resolution of 1.87 microns/pixel). Film irradiations were done using SSD=100cm, depth= 2cm, FS=1.1cm2.Results: For the IEP's, PDD values were 55.4%(surface), 62.6%(5cm), and 34.7%(10cm). Monte Carlo simulations suggest a nominal x‐ray energy of 800kV. The 80%–20% penumbra widths were 2.10mm (6MV) and 0.345mm (IEP's).Conclusions: A novel intermediate energy x‐ray beam (800kV) has been produced using a linear accelerator. There is more than a 5‐fold reduction in radiological penumbra for the IEP's versus 6MV x‐rays for the small field size examined.
Role of Narrow Mountains in Large-Scale Organization of Asian Monsoon Convection*
Authors: Xie Shang-Ping , Xu Haiming , Saji N. H. , Wang Yuqing , Liu W. Timothy 
Published: July 2006

Abstract
The Asian summer monsoon is organized into distinct convection centers, but the mechanism for this organization is not well understood. Analysis of new satellite observations reveals that narrow mountain ranges are an important organizing agent anchoring monsoon convection centers on the windward side. The Bay of Bengal convection, in particular, features the heaviest precipitation on its eastern coast because of orographic lifting as the southwest monsoon impinges on the coastal mountains of Myanmar (also known as Burma). This is in contrast to the widely held view that this convection is centered over the open ocean as implied by coarse-resolution datasets, a view that would require an entirely different explanation for its formation. Narrow in width and modest in height (≤1 km), these mountains are hardly mentioned in conceptual depictions of the large-scale monsoon and poorly represented in global climate models. The numerical simulations of this study show that orographic rainbands are not a local phenomenon but exert far-reaching effects on the continental-scale monsoon. The realization that these overlooked geographical features are an important element of the Asian monsoon has important implications for studying the monsoon in the past, present, and future.
Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison
Authors: Friedlingstein P. , Cox P. , Betts R. , Bopp L. , von Bloh W. , Brovkin V. , Cadule P. , Doney S. , Eby M. , Fung I. , Bala G. , John J. , Jones C. , Joos F. , Kato T. , Kawamiya M. , Knorr W. , Lindsay K. , Matthews H. D. , Raddatz T. , Rayner P. , Reick C. , Roeckner E. , Schnitzler K.-G. , Schnur R. , Strassmann K. , Weaver A. J. , Yoshikawa C. , Zeng N. 
Published: July 2006

Abstract
Eleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C.
All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.
Altered B-cell receptor signaling kinetics distinguish human follicular lymphoma B cells from tumor-infiltrating nonmalignant B cells
Authors: Irish Jonathan M. , Czerwinski Debra K. , Nolan Garry P. , Levy Ronald 
Published: July 2006

Abstract
The B-cell receptor (BCR) transmits life and death signals throughout B-cell development, and altered BCR signaling may be required for survival of B-lymphoma cells. We used single-cell signaling profiles to compare follicular lymphoma (FL) B cells and nonmalignant host B cells within individual patient biopsies and identified BCR-mediated signaling events specific to lymphoma B cells. Expression of CD20, Bcl-2, and BCR light chain isotype (κ or λ) distinguished FL tumor B-cell and nontumor host B-cell subsets within FL patient biopsies. BCR-mediated signaling via phosphorylation of Btk, Syk, Erk1/2, and p38 occurred more rapidly in tumor B cells from FL samples than in infiltrating nontumor B cells, achieved greater levels of per-cell signaling, and sustained this level of signaling for hours longer than nontumor B cells. The timing and magnitude of BCR-mediated signaling in nontumor B cells within an FL sample instead resembled that observed in mature B cells from the peripheral blood of healthy subjects. BCR signaling pathways that are potentiated specifically in lymphoma cells should provide new targets for therapeutic attention.
Gene transfer of cytidine deaminase protects myelopoiesis from cytidine analogs in an in vivo murine transplant model
Authors: Rattmann Ina , Kleff Veronika , Sorg Ursula R. , Bardenheuer Walter , Brueckner Annette , Hilger Ralf A. , Opalka Bertram , Seeber Siegfried , Flasshove Michael , Moritz Thomas 
Published: July 2006

AbstractHematopoietic stem cell gene transfer of the drug-resistance gene cytidine deaminase (CDD) protecting cells from the cytotoxic cytidine analogs cytarabine and gemcitabine was investigated in a murine transplant model. Following transplantation of CDD-transduced cells and cytarabine application (500 mg/kg; days 1-4; intraperitoneally) significant myeloprotection was demonstrated with nadir counts of peripheral blood granulocytes and thrombocytes of 2.9 ± 0.6/nL versus 0.7 ± 0.1/nL (P < .001) and 509 ± 147/nL versus 80 ± 9/nL (P = .008), respectively (CDD versus control). Protection also was observed from otherwise lethal gemcitabine treatment (250 mg/kg; days 1-3). Stable levels of gene-marked cells in primary and secondary recipients were demonstrated for up to 9 months, and whereas CDD overexpression clearly reduced B- and T-lymphocyte numbers, no major toxicity was observed in the myeloid compartment. Despite the profound myeloprotective properties, however, CDD overexpression did not allow for pharmacologic enrichment of transduced hematopoiesis in our model. Thus, in summary, our data establish CDD as a drug-resistance gene highly suitable for myeloprotective purposes, which, given the lack of selection observed in our hands, might best be used in combination with selectable drugresistance genes such as MGMT (P140K) or MDR1.