bluuebunny/crossref_metadata_2025 huggingface dataset:
Burial grounds’ impact on groundwater and public health: an overview
Authors: Oliveira Bruna , Quinteiro Paula , Caetano Carla , Nadais Helena , Arroja Luís , Ferreira da Silva Eduardo , Senos Matias Manuel
Published: June 2012

The most common practice for disposal of dead bodies is inhumation in soil, which favours interactions with the surrounding environment and returns nutrients to the life cycle. However, when the burial ground is located where hydrogeological, geological and climatic conditions are not favourable to the process, contamination of soils and groundwater may occur, and decomposition may be inhibited, leading to social, economic and political problems. The most critical parameters when assessing the pollution potential of a burial ground are inhumation depth, geological formation, depth of the water table, density of inhumations, soil type and climate. Considering that, this paper presents an overview of the potential threat that cemeteries can pose, analysing and discussing the influence of the main variables causing environmental impacts and public health risks.
Sub‐ and suprathreshold adaptation currents have opposite effects on frequency tuning
Authors: Deemyad Tara , Kroeger Jens , Chacron Maurice J.
Published: June 2012

Key points

We provide the first experimental evidence that sub‐ and suprathreshold adaptation currents, despite having similar effects on spike frequency adaptation, have opposite effects on frequency tuning.

Through a combination of computational analysis and mathematical modelling, we reveal how the differential activation properties of these currents can lead to differential effects on the neuronal transfer function.

Our findings challenge the common assumption that spike frequency adaptation always attenuates the neural response to low frequency stimuli, and instead suggest that spike frequency adaptation and frequency tuning can be regulated independently of one another.

Abstract  Natural stimuli are often characterized by statistics that can vary over orders of magnitude. Experiments have shown that sensory neurons continuously adapt their responses to changes in these statistics, thereby optimizing information transmission. However, such adaptation can also alter the neuronal transfer function by attenuating if not eliminating responses to the low frequency components of time varying stimuli, which can create ambiguity in the neural code. We recorded from electrosensory pyramidal neurons before and after pharmacological inactivation of either calcium‐activated (IAHP) or KCNQ voltage‐gated potassium currents (IM). We found that blocking each current decreased adaptation in a similar fashion but led to opposite changes in the neuronal transfer function. Indeed, blocking IAHP increased while blocking IM instead decreased the response to low temporal frequencies. To understand this surprising result, we built a mathematical model incorporating each channel type. This model predicted that these differential effects could be accounted for by differential activation properties. Our results show that the mechanisms that mediate adaptation can either increase or decrease the response to low frequency stimuli. As such, they suggest that the nervous system resolves ambiguity resulting from adaptation through independent control of adaptation and the neuronal transfer function.
Double Diffusion From a Heated Sphere in an Infinite Porous Medium
Authors: Ganapathy R.
Published: June 2012

Free convective heat and mass transfer from a sphere of constant temperature and concentration buried in an unbounded porous medium is studied analytically assuming the validity of the Darcy flow model. Using a regular perturbation analysis, transient and steady-state solutions have been obtained in the form of series expansions in terms of a thermal Rayleigh number, which is based on the temperature of the heated sphere and the medium permeability. The results are exemplified by drawing the streamlines at various times. Of special significance is the emergence of a downward flow in the transient state when the two buoyancy mechanisms are opposed. These results apply as well to the case of buoyancy-induced flows from a sphere generating simultaneously two different chemical components.
Study of silica nano-pattern erosion in H2SO4-H2O2 mixture using spectroscopic ellipsometry
Authors: Yu Zhaoning , Kurataka Nobuo , Tran Hieu , Gauzner Gene
Published: June 2012

To overcome the difficulty in measuring the extremely slow erosion of transparent silica, we apply spectroscopic ellipsometry (SE) optical critical dimension measurements on a subwavelength surface relief grating instead of a blank silica substrate. By analyzing the nano-grating SE spectra, we find that the H2SO4-H2O2 Piranha cleaning widely used for organic contaminants removal also etches silica slowly—up to a molecular monolayer is partially removed from the silica surface by each cleaning cycle. Based on these findings, we conclude that silica dissolution is an important factor to be considered in applications such as template cleaning in nanoimprint lithography.
SU‐C‐BRA‐01: 4D Cone‐Beam CT Acquisition Using Respiratory Phase Predication Technique
Authors: Yan P , Zhou L , Li Z , Chi Y , Chang J , Chao C
Published: June 2012

Purpose: Respiration‐correlated CBCT reduces respiratory motion artifacts at the cost of increased view‐aliasing artifacts due to the gaps in projection data that are sorted to other phases. Respiratory‐gated acquisitions can cover the full scanning range but is inefficient (∼5 minutes per phase). In this study, we developed a 4D CBCT acquisition method using respiratory phase predication technique that can potentially acquire full projection data for each phase within a clinically acceptable (∼10 minutes or less) time. Methods: The proposed 4D CBCT continuously scans the target until sufficient number of projections is acquired for all phases. The respiratory phase predication technique consists of the following iterative steps: (1) training using respiratory signal for the first few (e.g., five) breathing cycles; (2) initial optimization of the gantry rotation speed; (3) adaptive control of the rotation speed and image acquisition during the scan (4) sorting the projection images into different phases. The method was validated using the 4D XCAT digital lung phantom with the motion driven by a sinusoid wave and a real patient respiration signal acquired with RPM system. CBCT images were reconstructed for each phase using the simultaneous arithmetic reconstruction technique and compared with the mixed‐phase reconstruction. Results: Sufficient projection images (an angular interval less than 1 degree) were acquired for all 10 phases after 10 gantry rotations. The acquisition time was estimated from 10–12 minutes assuming each gantry rotation took ∼1 minute. The CBCT images reconstructed from the mixed‐phase projections were blurred in comparison to those for individual phases. Conclusion: A respiratory prediction technique for 4D CBCT has been developed and validated with real patient breathing pattern. We plan to further reduce the number of gantry rotations and therefore the scanning time by improving the control of adaptive image acquisition and taking advantage of data redundancy as in 4D CT.
SU‐C‐213CD‐06: Quantitative Assessment of 4D Cone‐Beam CT Based Image Guidance for Patient Positioning in Precision Radiotherapy
Authors: Gopal A , Lee S , Mittauer K , Kahler D , Lu B , Samant S
Published: June 2012

Purpose: To evaluate the precision of 4D cone‐beam CT as an image guidance tool for stereotactic body radiotherapy using intensity modulated arc or fixed gantry radiotherapy in sites with significant intrafraction tumor motionMethods: 4D cone‐beam CT (4D‐CBCT) is a recent innovation that has the potential to significantly improve the precision of highly conformai radiotherapy treatments. The performance of a commercial Elekta Synergy X‐ray Volume Imager (XVI) 4D‐CBCT system was quantitatively analyzed using a motor driven respiration phantom for a series of uniform and irregular breathing patterns. The quality of image guidance was assessed based on the precision of the 4D‐CBCT registration obtained from the XVI system with respect to the known motion of the respiration phantom (Quasar ModusQA). The quality of the registration was evaluated with various scan acquisition settings for field size, projection arc, gantry speed, etc., to develop an optimized image guidance protocol for 4D treatment sites. Results: The results indicated that the 4D‐CBCT registration shifts were in good overall agreement with the actual phantom motion. After rigid registration corrections using static regions of the phantom to eliminate systematic shifts, the respiration amplitudes were accurately reflected to within 1–3 mm for most breathing patterns, which is well within the expected uncertainty of registration algorithms as well as the amplitude and phase variability of the motor control. However, position differences in individual phase comparisons were found to be as high as 8–10 mm. We also observed that the larger field settings (m20) for the 4D‐CBCT acquisition rendered comparable accuracy to smaller vendor recommended fields (S20). Conclusions: The accuracy of 4D‐CBCT based patient positioning for treatment sites with significant respiratory motion was verified along with its potential to facilitate greater precision for dose convergence in hyperfractionated radiotherapy as well as to evaluate the feasibility of respiration gated radiotherapy.
SU‐C‐217A‐03: Position Sensitivity of Calculated Dose‐Length‐Product‐To‐Effective‐ Dose Conversion Factors in Computed Tomography Examination
Authors: Gao Y , Ding A , Caracappa P , Xu X
Published: June 2012

Purpose: To quantify the sensitivity of Dose Length Product to Effective Dose conversion factors (k‐factors) to scan length and position. Methods: To convert the recorded Dose Length Product (DLP) to an estimate of Effective Dose (E), a set of conversion factors, known as k‐factors, are used. These published k‐factors were developed for a limited set of standard protocols with fixed scan lengths, and most are based on stylized models of the human body. Using realistic models of male and female (RPI‐AM and RPI‐AF) and a validated model of the CT source, Monte Carlo simulations are preformed to calculate the dose to each organ on a slice‐by‐slice basis. For each slice, the organ doses are converted into ‘local' k‐factors. Over a full scan length, the effective doses from the individual slices and the DLPs are summed, so the k‐factor for the scan is equivalent to the average of the local k‐factors in the scan range. Results: Simulations of 1‐cm thick CT slices were performed over the entire range of the torso for the RPI‐AM and RPI‐AF phantoms. The local k‐factors calculated range from a minimum of 0.0128 in the upper shoulder region (above most of the radio‐sensitive organs of the chest), to a maximum of 0.0369 in the region around the female gonads. The calculated k‐factor for a standard chest scan was 0.0289, which compares favorably to published values. However, the k‐factor decreases as the scan range is expanded. Consequently, a chest scan that is only 10 cm longer would have a k‐factor 18% lower when compared to the standard protocol. Conclusion: By improving the understanding of the sensitivity of k‐factors to scan length and position, more accurate estimates of effective dose from CT examination can be provided without sacrificing the efficiency and simplicity that k‐factors provide. This project was funded by National Institutes of Health (National Institute of Biomédical Imaging and Bioengineering R42EB010404).
SU‐C‐218‐06: Evaluation of a CT‐Based, Semi‐Automated Lung Mass Estimation Method Under Varying Acquisition Conditions
Authors: Busse N , Erwin W , Pan T
Published: June 2012

Purpose: To evaluate a simple, semi‐automated lung mass estimation method on CT scans from a variety of acquisition techniques for mass correction of MIRD dose estimates. Methods: CT scans from ten patients undergoing stereotactic body radiation therapy treatment planning on a GE DST PET/CT scanner were analyzed retrospectively. For each patient, free‐ breathing (FB) and respiratory gated 4D‐CT scans were acquired. 4D‐CT scans were reconstructed and sorted into ten phases representing one complete respiratory cycle. An average CT (ACT) was derived from the ten phase reconstructions. Half the patients also had breath‐hold (BH) scans. Scans were analyzed using Osirix MD's V 1.3 (Pixmeo, Geneva Switzerland) Grow Region segmentation tool. Lung volume; average lung, tissue (∼lcm ROI in the descending aorta), and air (∼1 cm ROI in the trachea) HU's were recorded for each acquisition type. Lung mass was calculated by assuming each voxel is a linear combination of only air and tissue. The fraction of total lung volume consisting of lung tissue is assumed to be (lung HU ‐ air HU) / (tissue HU ‐ air HU), and mass = total volume X fraction X 1 g/cm3. Results: 4D‐CT mass estimates showed variability, with a minimum at end‐expiration and a maximum just after end‐inspiration. ACT generally produced the highest estimate. FB and BH estimates were near the median. Conclusions: Although calculated mass increased with increasing total lung volume, the difference between minimum and maximum population means in the 4D‐CT data was 5.5%. FB and BH estimates fell within that 5.5%, while the ACT mean was 9.8% above the global mean. The range of estimated masses (524 g to 977 g) suggests the value of lung mass estimates for more patient‐specific MIRD dose assessment. Excluding ACT, the results indicate that any of the acquisition techniques can provide a reasonable lung mass estimate. This work was supported in part by a residency grant from the AAPM.
SU‐D‐BRCD‐01: Evaluation of Zebra Multi‐Layer Ionization Chamber System for Patient Treatment Field and Machine QA for Spot Scanning and Passive Scattering Proton Beams
Authors: Dhanesar S , Sahoo N , Taylor M , Song X , Poenisch F , Summers P , Li H , Zhu X R , Gillin M
Published: June 2012

Purpose: To evaluate Zebra multi‐layer ionization chamber system for patient treatment field and machine QA for spot scanning proton beams (SSPB) and passive scattering proton beams (PSPB). Methods: Zebra dose measurement system (IBA Dosimetry), consisting of 180 parallel platechambers with 2 mm detector spacing, was used for measuring proton beamdepth dose curves (DDC) for spread out Bragg peaks (SOBP) and single spot pristine Bragg peaks (PBP). The measurements were performed for 100 to 250 MeV PSPB and 89.2 to 221.8 MeV SSPB using the Hitachi ProBeat synchrotron based delivery system. An in‐house Matlab based analysis software was used to compare the Zebra measured DDC with those measured by the Markus chamber in a PTW water tank (MC‐WT). Several verification plans in the water phantom were created for patient treatment fields using the Eclipse treatment planning system (TPS). The DDC for individual verification fields were measured using the Zebra andcomparisons were made with the TPS calculations. Results: The dosedifferences between the Zebra and MC‐WT measurements in the plateau regions of the DDC are within 2% for various energies of PSPB, but are larger than 2% at the sharp dose distal gradient regions. The values for distal penumbra widths, range and SOBP widths from Zebra and MC‐WT measurements agree within 0.5 mm, 1.5 mm, and 2 mm, respectively. The Zebra measured values of the range of the single spots also agreed within 1 mm with their established values from other measurements. The Zebra measured DDC of verification plan of patient treatment fields showed goodagreement with those from the TPS. Conclusions: Our investigation shows that Zebra can be useful for fast and reasonably accurate measurements of the DDC of pristine and spread‐out Bragg peaks of both spot scanning and passive scattering proton beams.
SU‐D‐BRCD‐03: Spectroscopic Characterization of a 6 MV Linear Accelerator Field Using Compton Spectrometry Measurements and Monte Carlo Techniques
Authors: Bartol L , DeWerd L
Published: June 2012

Purpose: Effective treatment planning for radiotherapy is dependent on accurate spectra determination; however, direct measurements of spectra arecomplicated by fluence rates that exceed detection system limitations. This work demonstrates the potential to use a Compton scattering technique to measure the spectrum of a 6MV linac. These spectra are further characterized using Monte Carlo (MC) simulations. Methods: A high‐purity germanium detector was used to measure the photon spectrum scattered at35 degrees from the central axis of 3cmx3cm and lOcmxlOcm 6MV fields from a Varian linac. Photons were scattered using aluminum rods positioned at isocenter, and were admitted to the detector through a 30cm‐long collimating aperture. The measured Compton‐scattered spectra were corrected for background. An MC model of the linac was developed in MCNP5 to calculate central‐ and off‐axis spectra. The model geometry was verified by comparisons with percentage depth‐dose and profilemeasurements. The spectroscopic effect of the mean energy, radius, and divergence of the electron beam incident on the target was tested for twofield sizes. Results: The count rate of the scattered beam increased with field size and scattering rod diameter. Preliminary measurements indicate that the spectrum was shifted to lower energies using this technique; however, the signal‐to‐noise ratio was poor due to leakage and room scatter. MC simulations demonstrate that the central‐ and off‐axis spectra were sensitive to changes in mean electron energy; however, changes in beam diameter and angular divergence did not substantially affect either the central‐ or off‐axis spectra. Conclusions: This work demonstrates that the spectrum from a 6MV linac can be measured using Compton spectrometry. Further work is required to increase the signal‐to‐noise ratio and correct fordetector response. MC simulations indicate that the spectra were sensitive to variations in the parameters used to define the primary electron beam incident on the target.
SU‐D‐BRCD‐04: Validation of Film Dosimetry in the Dose Build‐Up Region
Authors: Corradini N , Presilla S , Sassowsky M , Schombourg M
Published: June 2012

Purpose: To establish a film dosimetric method for high‐resolution measurement in the dose build‐up region. Methods: Percent depth dose (PDD) curves were measured in water for TomoTherapy using Gafchromic EBT2 films. Depth dose measurements were also performed using Standard Imaging A1SL and PTW PinPoint ionization chambers, as well as a PTW DiodeE detector. The film and detector measurements were then compared to Monte Carlo (MC) simulation data computed using PENELOPE. An in‐ house support apparatus was constructed to hold the films parallel to the beam central axis while being suspended in the water, simultaneously demarcating the water surface on the film. The films were converted to dose using a corrected net optical density method involving the red and blue color channels of an Epson Expression 10000XL scanner. Film analysis was performed using ImageJ software and MATLAB code developed in clinic. Results: In our film method, a systematic shift of 1.2mm downstream is seen for the sample of five films, with good reproducibility within the sample (s=0.3mm). The film measurements showed a mean PDD difference of 0.3% (s=0.4%) with a maximum of 1.3% from that of MC between depths of 0.5mm to 20mm. The average film dose measured at the water surface (d=0mm) was 13.1% greater than that calculated by MC. EBT2 film shows much better agreement with MC in the dose build‐up region than the ionization chamber and detector measurements. Conclusions: This study demonstrates the capability of EBT2 films for simple and accurate superficial dose measurements. A suspected reason for the systematic shift in film alignment is attributed to difficulty in determining water surface due to the meniscus that forms at the film. Funded by SSRMP Research Grant 2011
SU‐D‐BRB‐03: Prediction of Tumor Outcomes Through Wavelet Image Fusion and Texture Analysis of PET/MR Imaging
Authors: Vallières M , Freeman C R. , Skamene S R. , Naqa I El
Published: June 2012

Purpose: To investigate the combination of PET/MR image features for the early prediction of tumor metastases to the lungs in soft‐tissue sarcoma (STS) cancer. Methods: A dataset of 24 patients with histologically proven STS was used in this study. All patients underwent pre‐treatment FDG‐PET and MR scans, which comprised of T1 and T2‐fat suppression weighted (T2FS) sequences. The patients had a median follow‐up period of 36 months (range: 6–69 months). Eight patients developed metastases to the lungs.Tumors were contoured on the T2FS scans by an expert physician. Fusion of the co‐registered FDG‐PET/MR scans was performed using a wavelet transform technique. A SUV feature (SUVmax) from the FDG‐PET scans and 6 texture features from the co‐occurrence matrix of the fused scans were extracted from the tumor region and correlation with the clinical endpoint of metastases to the lungs was investigated. Statistical analysis was performed using Spearman's rank correlation (rs) and multivariable logistic regression. Results: The highest univariate prediction was found on FDG‐PET/T2FS fused scans analyzed using the texture features “Sum‐Mean” and “Variance”. These two fused scan—texture feature combinations reached rs = −0.6838 (p = 0.0003). In comparison, SUVmax reached rs = −0.6257 (p = 0.0011). The highest multivariate prediction was found with the following 3‐ parameter model: −3.15*SUVmax − 5.37*FDG‐PET/T2FS‐Sum‐Mean + 0.57*FDG‐PET/T1‐Variance. This model reached rs = 0.7977 (p = 0.000005). Conclusions: This work indicates the potential of PET/MR texture features of tumors as complementary metrics to existing prognostic factors. Substantial improvement in terms of prediction of metastases to the lungs in STS cancer was found with the combination of texture features from fused FDG‐PET/MR scans. Potentially, this could improve patients' outcomes by allowing better adaptation of treatments. Future work will involve evaluation of the robustness of the proposed method and validation on a larger set of patients.
SU‐D‐BRB‐04: FDG‐PET Histogram Distances: Novel Predictors of Tumor Response to Chemoradiotherapy
Authors: Tan S , Zhang H , Kligerman S , Chen W , Kim G , Feigenberg S , D'Souza W , Suntharalingam M , Lu W
Published: June 2012

Purpose: To examine the accuracy of FGD‐PET histogram distances as predictors of pathologic tumor response to chemo‐radiotherapy (CRT) in esophageal cancer. Methods: Twenty patients were included. A rigid registration was used to align the post‐CRT PET/CT with the pre‐CRT PET/CT images. The primary tumor was delineated using a region‐growing algorithm with a threshold of SUV = 2.5 on the pre‐CRT PET. Two histograms of SUVs within the tumor were constructed on the pre‐CRT PET and registered post‐CRT PET, respectively. The differences between the two histograms reflected changes in the SUV distribution and were therefore potential predictors of tumor response. The differences were quantitatively measured by histogram distances using 12 bin‐to‐bin and 8 cross‐bin algorithms. The accuracy of histogram distances in predicting pathologic tumor response to CRT was measured using the area under ROC curve (AUC), prediction accuracy, and the Mann‐Whitney tests, in comparison with traditional PET response measures and texture features. Results:Cross‐bin histogram distances were shown to be significant (p<0.05) predictors of pathologic tumor response. They were more accurate than bin‐ to‐bin histogram distances (not significant). The most accurate cross‐bin histogram distances were: Quadratic‐Chi distance (AUC=0.89, accuracy=80%, p=0.003), Earth Mover distance (AUC=0.83,accuracy=80%, p=0.014), diffusion distance (AUC = 0.82, accuracy=85%, p=0.02) and Match distance (AUC = 0.79, accuracy=80%, p=0.03). This family of novel predictors were more accurate than traditional PET response measures using SUVmax (AUC=0.76, accuracy=75%, p=0.05), SUVpeak (AUC=0.74, accuracy=70%, p=0.08), Total Glycolytic Volume (AUC=0.76, accuracy=70%, p=0.05), as well as texture features based on the cooccurrence matrix (Inertia: AUC=0.85, accuracy=80%, p=0.01). Conclusions: The cross‐bin histogram distances characterized changes in the SUV distribution within a tumor and showed high accuracy for the prediction of pathologic response to CRT in esophageal cancer. This workwas supported in part by the National Cancer Institute Grant R21 CA131979.
SU‐D‐BRA‐03: Simultaneous MV‐KV Imaging for Intra‐Fractional Motion Management during Volume Modulated Arc Therapy (VMAT) Delivery on the Varian TrueBeam
Authors: Hunt M , Regmi R , Zhang P , Pham H , Wang P , Xiong J , Morf D , Mageras G
Published: June 2012

Purpose: To evaluate a MV‐kV intra‐fractional imaging technique for use during volume modulated arc therapy (VMAT) with the Varian TrueBeam. Methods: MV‐kV image pairs were acquired intra‐fractionally during VMAT delivery. kV images (11 fps) were acquired throughout delivery using a standard pre‐programmed imaging template. MV images (9.5 fps) were acquired simultaneously by deploying the EPID and passively collecting the resulting images using Varian proprietary software, iTools Capture. Localization accuracy was evaluated by imaging a Rando phantom implanted with 3 fiducials while moving the couch according to XML‐ programmed trajectories simulating typical prostate and respiratory motion. VMAT delivery was done using a single 360 degree arc in TrueBeam Developer mode. The effect on accuracy of total MU and gantry speed was studied. To improve image quality, MV frame averaging was performed and the MV and kV images were then registered to their corresponding DRRs using in‐house registration software. From these 2D registrations, the 3D position at each MV‐kV acquisition point was determined. Results: Between 130 and 390 MV‐kV pairs were acquired for each delivery. The mean difference between planned couch and measured fiducial 3D positions with prostate motion was less than 0.03 cm in each direction (SD 0.03 cm). Neither gantry speed nor MU significantly impacted accuracy. for respiratory motion, the mean difference between planned and measured position was less than 0.04 cm. Standard deviation averaged 0.06 cm but increased to 0.12 cm with large instantaneous motion and less MV dose per frame. MV frame averaging and inaccuracies in MV image gantry angle determination also affected accuracy, particularly with significant motion. Conclusions: With high quality MV imaging, MV‐kV localization techniques can be highly accurate, even in the presence of significant motion. As clinical MV‐kV methods become available, such techniques can provide an efficient and accurate method for monitoring intra‐fractional motion. This work was partially supported through a research agreement with Varian Medical Systems, Palo Alto, CA
SU‐D‐213CD‐01: 4D Ultrasound Calibration for Radiotherapy Guidance Using Automatic Intramodality Image Registration
Authors: Schlosser J , Kirmizibayrak C , Shamdasani V , Metz S , Hristov D
Published: June 2012

Purpose: In prior work we developed a robotic system providing real‐time soft‐tissue ultrasound (US) volumes during radiotherapy beam delivery. for image guidance, the US volumes must be transformed to the linear accelerator reference frame. In this work we propose and characterize a new method of calibrating 4D US volumes based on automatic intramodality image registration. Methods: A dynamic navigation link was used to port 3D US volumes from a Philips iU22 xMatrix machine to a PC in real‐time. Sixty volumetric (3D) US images of a pelvic phantom were collected from various probe positions while the transducer's pose was monitored by an optical tracking system. US volumes were automatically registered to the first US volume using normalized mutual information. A system of equations was formulated and solved for the US probe‐to‐image transformation using the registration transformations and the optical tracking information. Accuracy of the US calibration was assessed on eight additional US volumes with two separate methods. In the first method, a set of three fiducial markers implanted in the phantom was manually selected in each volume by three individual readers. Selected marker locations were reconstructed in the stationary camera frame, and for each marker, mean distance to the reconstructed centroid was measured. In the second method, a bladder structure was semi‐automatically segmented in each image volume. Mean distance between bladders segmented in a reference volume and the other seven volumes was computed. Calibration accuracy was also investigated as a function of the number of calibration images used. Results: Mean error for the fiducial marker reconstruction was 2.3 mm. Mean distance error between segmented structures was 1.1 mm. The proposed calibration method typically converged with less than 20 images. Conclusion: Automatic image registration facilitates fast and simple US spatial calibration with accuracy under 2.3 mm using any US phantom. This work is supported in part by the Stanford University BioX program and by Philips Medical. Two of the authors of the abstract are employed by Philips Medical.
SU‐D‐217BCD‐03: Impact of Jaw Width on the Megavoltage Computed Tomography Image Quality and Imaging Dose with Helical Tomotherapy
Authors: Chao M , Corry P
Published: June 2012

Purpose: On‐treatment megavoltage computed tomography on Helical Tomotherapy (Accuray Inc., Sunnyvale, CA) is critical for image guided radiotherapy. A strategy was developed to assess the impact of various jaw widths on image quality and imaging dose with Tomotherapy. Methods: A cheese phantom (Gammex RMI, Middleton, WI) made of water equivalent materials was employed in this study. Three sets of measurements were independently carried out. Firstly, in the imaging dose measurement, the phantom was placed on the couch and aligned with a stationary green laser and beam isocenter. The measurement point was 10 mm up from the cente of the phantom. Three slices on either side of the middle slice were selected. Secondly, two inserts with different rows of holes of various sizes were placed inside the phantom for image contrast and resolution investigation. Lastly, twelve density inserts were placed into the outer holes in the phantom for measurement of the image value to density table (IVDT). A comparison of imaging dose, image resolution and contrast, IVDT table between different jaw configurations was performed to evaluate the imaging system. Results: Imaging dose was 2.93 cGy with a jaw size of one mm as opposed to 1.62 cGy with a four mm jaw, both of which are below the vendor's requirement: 3 cGy. However, image quality is improved significantly with the smaller jaw. Four lines of holes can be readily identified on images using smaller jaw while only three lines visible with the larger jaw. Image contrast is similarly enhanced when reducing the jaw size. On average CT numbers are 6% higher with the smaller jaw than those obtained with the larger one. Conclusions: Significant improvement in image quality is achieved with the smaller jaw field in Tomotherapy while the imaging dose is kept at a clinically acceptable level.
SU‐D‐217BCD‐05: Analytic Determination of Size of Water Cylinder Absorbing Equal Radiation Dose as a System of Concentric Cylinders of Arbitrary Composition: Application for Pediatric CT
Authors: Bakalyar D
Published: June 2012

Purpose: To develop analytic formulae for calculating absorbed dose to a system of concentric cylinders and to use this to determine the size of water cylinder which would absorb the same dose in a matching field. Appropriate scaling of radiation output to patient size is of particular interest in pediatric CT (TG204). Methods: For a given CT scanner output, absorbed dose increases as patient size decreases. Analytic functions can calculate the dose delivered to systems of concentric cylinders of varying size and composition. In particular these functions provide useful insight when considering examinations in body regions with large variations in attenuation, such as the chest (which can be modeled as concentric cylinders of heart, lung, rib and soft tissue). Iterative calculations rapidly determine the size water cylinder required to absorb the same dose in matching radiation fields. More general findings put limits on some of the methods for determining size specific dose estimates (SSDE). Results: For the simple chest model, in the absence of scatter or bow tie filter considerations, the equivalent water phantom would have a diameter of just over half the chest equivalent concentric cylinder phantom. A more general Result is that in the limit of very small size, the absorbed dose in a fixed irradiating field depends only on mass attenuation coefficient. Conclusions: The concentric cylinder model developed can be used to study the scaling of radiation dose with patient size. In particular, the water phantom absorbing the same dose as the chest region has only about half the diameter. An important conclusion is that in the limit of small size, absorbed dose depends on mass attenuation coefficient only and that in this limit an equivalent water phantom does not exist.
SU‐D‐217BCD‐06: Evaluation of Effective Dose during Neuro 3‐D Imaging Using a C‐Arm Cone‐Beam CT System
Authors: Wang C , Ferrell A , Nguyen G , Toncheva G , Jiang X , Haynes W , Enterline D , Smith T , Yoshizumi T
Published: June 2012

Purpose: The purpose of this study was three‐fold: 1) to estimate the organ doses and effective dose (ED) for patients undergoing neuro 3D‐imaging protocols, 2) to study the effect of beam collimation on ED, and 3) to derive protocol‐specific DAP‐to‐ED conversion factors. Methods: A cone‐beam CT system (Philips Allura Xper FD20/20) was used to measure the organ doses for seven neuro imaging protocols. Two data sets were obtained: seven protocols with uncollimated beam (FOV: entire head) and four with beam collimation (FOV: roughly from the base to the top of the skull). Measurements were performed on an adult male anthropomorphic phantom (CIRS, Norfolk, VA) with 20 MOSFET detectors (Best Medical Canada, Ottawa, Canada) placed in selected organs. The dose area product (DAP) values were recorded from console. The ED values were computed by multiplying measured organ doses to corresponding ICRP 103 tissue weighting factors. Results: For seven protocols with uncollimated setting, the EDs ranged from 0.16 mSv to 1.6 mSv, and the DAP‐to‐ED conversion factors range from 0.037 to 0.17 mSv/Gy/cm2. For four protocols with beam collimation, the ED was reduced approximately by a factor of 2, and the DAP‐to‐ED conversion factors by approximately 30%. Conclusions: We have measured ED for standard adult neuro imaging protocols in a 3‐D rotational angiography system. Our results provide a simple means of ED estimation using DAP values from console in the C‐arm cone‐beam CT system. Research was funded in part by Philips Healthcare, the Netherlands.
SU‐D‐217A‐02: Effects of Enegy‐Window Width and Spectral Effective Energy on Estimation of Gamma Camera Deadtime Using the Decay Method
Authors: Silosky M , Kappadath S
Published: June 2012

Purpose: Assessment of count‐rate performance (CRP) is part of routine quality assurance (QA) for gamma cameras. Manufacturers often specify deadtime (t) based on the NEMA decay method (NEMA 1‐2007). The spectral conditions prescribed by NEMA are often difficult to duplicate during routine clinical QA testing and the appropriate energy window is poorly defined. The objective of this investigation is to evaluate the effects of energy‐window selection and spectral conditions on estimates of t using the NEMA decay method. Methods: CRP was evaluated intrinsically over a period of 48 hours with Tc‐99m for two Siemens Symbia gamma camera detectors using the NEMA decay method. CRP measurement was repeated with varying amounts of scattering material (0–8 cm of acrylic) placed between the source and detectors to transform the incident spectrum. CRP measurements were also repeated using different photopeak‐window widths (2–75%) as well as an open energy‐window. The CRP data were fit to the paralyzable detector model via non‐linear least‐squares minimization to estimate t. Results: Estimates of t increased linearly with decreasing spectral effective energy. The effective energy was varied from 142‐to‐99 keV, which consequently altered the estimates of t by ∼0.095μs or 21% (p<0.01). Additionally, estimates of t increased as a power‐law when the fraction of measured counts in the photopeak window decreased relative to open‐window (total) counts. The ratio photopeak‐window counts to open‐ window counts were varied from 1‐to‐0.12 which consequently altered the estimates of t by ∼8μs or 180%. The estimated change in t between 15% and 20% photopeak window is —0.13μs or 12.5%. Repeat measurements demonstrated that estimates of t using the decay method are precise to <2%. Conclusions: Deadtime (t) determined using the decay method varied significantly with the spectral effective energy and photopeak‐window width. Careful attention to measurement conditions are imperative when measuring t using the decay method for comparison against manufacturer's specifications or trending as part of routine QA program.
SU‐D‐217A‐03: Nuclear Medicine Uniformity Assessment Using 2D Noise Power Spectrum
Authors: Nelson J , Christianson O , Harkness B , Madsen M , Mah E , Thomas S , Zaidi H , Samei E
Published: June 2012

Purpose: Nuclear medicine quality control programs require daily evaluation for the presence of potential non‐uniformities by commonly utilizing a traditional pixel value‐based assessment (Integral CFOVUniformity). While this method effectively captures regional non‐ uniformities in the image, it does not adequately reflect subtle periodic structures that are visually apparent and clinically unacceptable, therefore requiring the need for additional visual inspection of the image. The goal of this project was to develop a new uniformity assessment metric by targetingstructural patterns and more closely correlating with visual inspection. Methods: The new quantitative uniformity assessment metric is based on the 2D Noise Power Spectrum (NPS). A full 2D NPS was performed on each image. The NPS was thresholded to remove quantum noise and further filtered by the visual response function. A score, the Structure Noise Index (SNI), was then applied to each based on the average magnitude of the structured noise in the processed image. To verify the validity of the new metric, 50 daily uniformity images with varying degrees of visual structured and non‐structured non‐uniformity were scored by 5 expert nuclear medicine physicists. The correlation between the visual score and SNI were assessed. The Integral CFOV was also compared against the visual score. Results: Our new SNI assessment metric compared to the Integral CFOV showed in increase in sensitivity from 67% to 100% in correctly identifying structured non‐uniformities. The overall positive predictive value also increased from 55% to 72%. Conclusions: Our new uniformity metric correlates much more closely with visual assessment of structured non‐ uniform NM images than the traditional pixel‐based method. Using this new metric in conjunction with the traditional pixel value‐based assessment will allow a more accurate quantitative assessment of nuclear medicineuniformity.
SU‐D‐217A‐04: Evaluation of the Spatial Concordance Between the Intratumoral Patterns of 18F‐FLT and 18F‐FDG Uptake in a Small Animal Tumor Model
Authors: Bass C , Axente M , He J , Sundaresan G , Hirsch J , Hugo G , Zweit J , Pugachev A
Published: June 2012

Purpose: PET imaging allows for the visualization of tumor microenvironment and identification of aggressive or radioresistant tumor subvolumes that can be targeted with an escalated radiation dose. Multiple PET tracers have been developed for visualization of different aspects of tumor microenvironment; however, the spatial distribution of tracers in tumors is equally affected by tumor tissue viability and tracer delivery limitations. Given these issues and the low resolution associated with PET imaging, two different PET tracers can produce very similar images. Therefore, it is important to demonstrate that a novel PET tracer does provide additional useful information to that obtained with other tracers. This study investigates the added value of performing 18F‐FLT PET imaging as well as 18F‐FDG imaging. Methods: Head and neck tumor xenografts grown in nude mice were used to study intratumoral tracerdistributions. 18F‐FDG and 18F‐FLT PET images were obtained on subsequent days using a small animal PET/CT. Pinnacle 9 was used to deformably register the CT image from the FLT PET/CT to the FDG PET/CT image set. The generated deformation was applied to the FLT PET image to achieve an unbiased FLT to FDG PET image registration. The Pearson correlation coefficient between FDG and FLT was calculated voxel‐ by‐voxel within a tumor contour. Overlap analysis of thresholded tracer distributions was carried out by comparing Dice similarity coefficients. Results: Both SQ20B and FaDu tumors showed a moderate voxel‐by‐voxel correlation between FDG and FLT intratumoral patterns of uptake with an average rho value of .56 and .63 respectively (range .37–.76) despite significant differences in tumor morphology. The average volumes under thedice coefficient surface for SQ20B and FaDu tumors were not significantly different. Conclusions: Despite being equally affected by the issues of tracer delivery, necrosis and PET resolution, FDG and FLT PET images displayed an observable difference at clinically relevant thresholds.
SU‐D‐218‐02: 4D‐MRI Based on Body Area (BA) Surrogate and Sagittal Image Acquisition
Authors: Qin Y , Chang Z , Segars W , Yin F , Cai J
Published: June 2012

Purpose: 4D‐MRI based on body area (BA) surrogate using axial image acquisition has been demonstrated. Since respiratory motion mostly occurs in the superior‐inferior (SI) direction, it is expected that sagittal acquisition may provide more robust and accurate breathing signal than axial acquisition. The aim of this study was to investigate the feasibility of extracting breathing signals from sagittal images using BA surrogate and its application in 4D‐MRI. Methods: 7 human subjects were imaged continuously in a single (n=5) or multiple (n=2) sagittal planes using a steady‐state precession sequence. Imaging parameters were: TR/TE, 3.7ms/1.21ms; Matrix, 256×166; FOV, 350×300mm; flip angle, 52°; slice thickness, 5mm; frame rate: ∼3 frames/s. Imaging time per slice is 2 minutes for single slice acquisition and ∼10 seconds for multi‐slice acquisition. Breathing signals were generated for all subjects by tracking the change of BA. The multi‐slice sagittal acquisition was performed on a MRI‐ compatible motion phantom with a cylindrical gel target and was simulated on a 4D digital human phantom. Breathing signals were extracted from the sagittal images using the BA surrogate. Respiratory phases were calculated. 4D‐MRI of both phantoms were retrospectively reconstructed based on the respiratory phases. Results: Breathing signals extracted from both single slice and multi‐slice sagittal acquisitions showed stable and well‐ characterized patterns. 4D‐MRI of the physical phantom showed clear sinusoidal motion of the gel target in all three planes with minimal artifacts. Simulated ‘4D‐MRI’ of the 4D digital phantom matched well with original images: the mean absolute difference in motion amplitude of the ‘tumor’ was 0.4±0.3mm. Small artifacts of discontinuity were observed in the SI direction in certain phases. Conclusions: It is feasible to extract breathing signals from sagittal images for 4D‐MRI application. Further investigation is needed to test whether sagittal acquisition is more robust and accurate than axial acquisition for breathing signal extraction.
SU‐D‐218‐04: Evaluation of the Performance of the Solid State X‐Ray Image Intensifier (SSXII) Using Generalized Metrics
Authors: Gupta S , Huang Y , Jain A , Bednarek D , Rudin S
Published: June 2012

Purpose: To evaluate the performance of the Solid State X‐ray Image Intensifier (SSXII) using generalized linear‐system metrics and to study the effect of different scatter fractions, object magnifications, and focal spots onits performance. Methods: The SSXII is a high‐resolution and high‐ sensitivity region‐of‐interest x‐ray imaging detector that provides real‐timeimaging with low instrumentation noise. To evaluate the total system performance for a clinical environment, we used generalized metrics that include the effects of scattered radiation, finite focal‐spot size, and geometric unsharpness. For comparison, a commercial standard flat‐panel detector (FPD) was used. The focal‐spot MTF was obtained by taking theFourier Transform of the point‐spread function of x‐ray pin‐hole images. The detector MTF was measured using the standard edge method. The scatter MTF was simulated with a theoretical model. We have calculated the GMTF and GDQE for the SSXII and FPD. Three focal‐spots (small, medium, and large), different object magnifications and scatter fractions were used for the GMTF and GDQE comparison. Results: The GMTF andthe GDQE were shown to be degraded significantly from that of the detectoralone at the higher spatial frequencies because of blur due to the finite sizeof the focal‐spot, and at the lower frequencies because of scatter. Furthermore, the degradation increases even more as the focal‐spot size,object magnification and scatter fraction increases. The GMTF and the GDQE for the FPD were similar to those of the SSXII at lower frequencies, but were limited to frequencies below its 2.5 cycles/mm Nyquist frequency due to the 194‐micron pixel size compared to the 18.9 cycles/mm Nyquist frequency of the 26.4‐micron pixel‐size SSXII. Conclusions: This work demonstrates that the SSXII and the FPD have similar performance at thelower spatial frequencies, whereas, the SSXII demonstrates superior performance over the FPD at higher frequencies. Supported in part by: NIH Grants R01‐EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp.
SU‐D‐218‐06: Acceleration of Optical Photon Monte Carlo Simulations Using the Macro Monte Carlo Method
Authors: Jacqmin D
Published: June 2012

Purpose: The purpose of this work is to demonstrate that optical photon Monte Carlo simulations via a photon transport code called MCML can be accelerated using macro Monte Carlo (MMC) techniques. Methods: MCML was modified to incorporate the macro Monte Carlo radiation transport method. The original MCML uses scattering, absorption, reflection and refraction physics to transport optical photons through multi‐layered geometries. The code determines transmission, reflection and absorption for the layered geometry specified by the user. To make the code run faster, the MMC version of MCML uses large, multi‐interaction steps in regions that are homogeneous. These large steps are pre‐computed and stored in a database with many step sizes, materials and photon energies. The MMC version of MCML determines whether large MMC steps or traditional Monte Carlo should be used depending on the photon's current location inthe geometry. Results: The MMC version of MCML was tested against the original MCML code for a number of simple test geometries. It was also tested in anatomical geometries that are often uses in optical photon modeling. This includes skin and skull geometries. In each case, the reflection and transmission results from each code differed by less than 0.5%. The absorption data produced by each code also differed by less than 0.5% in most cases, and never differed by more than 2%. The MMC version of MCML runs between 1–3 times as many particles per unit time comparedto MCML, depending on the geometry. Conclusions: Applying Macro Monte Carlo methods to MCML produces a faster code without compromising accuracy. The speed‐gains are greatest in geometries thathave regions that are large relative to the mean scattering length for photons in that region. This work has the potential to accelerate light modeling for both photodynamic therapy and near‐infrared spectroscopic imaging.