bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐I‐22: Measurement and Correction of Sagging Shifts in KV Cone‐Beam CT From An On‐Board Imaging System
Authors: Ali I , Ahmad S
Published: July 2008

Purpose: To evaluate the effects of sagging on mechanical isocenter accuracy and image quality of kV cone‐beam CT (CBCT) and to develop a pre‐processing algorithm for removing these effects from on‐board‐imaging (OBI). Method and Materials: OBI sagging shifts were measured by scanning a cubical phantom with a 2 mm metal marker. The metal marker was aligned with radiation isocenter and its position was tracked in cone‐beam projections using normalized cross‐correlation image registration algorithm of kV CBCT system. The position of the marker was determined by 650 projections of a CBCT scan over an angular range from 0°–360°. To remove sagging shifts, projections were corrected to reconstruct CBCT images using Feldkamp back projection. The marker center of the cubical phantom in the corrected CBCT reconstructed images was used to determine OBI isocenter. The CATPHAN from phantom lab was used to compare image quality parameters such as blurring, uniformity and linearity for CBCT images before and after OBI sagging shift corrections. Results: We found that sagging affects localization accuracy of the OBI isocenter and image quality in CBCT. The marker position shifts about ± 2 mm over 360° range due to sagging and this produces about 1.4 mm isocenter shift in CBCT reconstructed from projections before correction for sagging. CBCT numbers vary by about 1% in full‐fan scans and up to 3.5% in half‐fan scans. Blurring and spatial distortion artifacts are produced in CBCT before correction of OBI sagging shifts. Conclusion: Sagging of the kV OBI system produces a systematic isocenter shift of CBCT. Further, sagging shifts lead to image artifacts such as spatial distortion, blurring, degradation of soft tissue contrast, position resolution, variation in CBCT number linearity and uniformity. Correction of OBI sagging in cone‐beam projections prior to CBCT reconstruction provides more accurate isocenter localization and improves image quality.
SU‐GG‐I‐29: Comparison of Spatial Resolution Properties for Three Cone‐Beam CT Systems Using An Aluminum Wire Phantom
Authors: Shen Y , Liu X , Chen L , Lai C , Han T , Wang T , Shaw C
Published: July 2008

Purpose: To evaluate and compare the spatial resolution properties of three different cone beam CT systems using an aluminum wire phantom. Method and Materials: A wire phantom was constructed to evaluate and compare different cone‐beam CT systems for their spatial resolution. The phantom contains 12 aluminum wires of various sizes (51, 76, 102, 127, 152, 178, 203, 229, 254, 279, 305, and 356 μm in diameter) suspended in air in the axial direction and positioned along a 7.2 cm diameter circle around the rotating axis. The wire phantom was imaged with cone‐beam CT systems using three different detectors: an aSi/aSe flat panel detector (Anrad FPD14), an aSi/CsI flat panel detector (Varian PaxScan 4030CB) and a CCD/CsI detector (Hamamatsu C4742). Images were acquired in both continuous and pulsed x‐ray modes and in various binning modes (1×1, 2×2, 3×3 and 4×4). 300 projection images were acquired over 360° for each scan. Feldkamp's filtered backprojection algorithm with a pure ramp filter was used for 3D reconstruction. Results: Careful examination of the reconstructed images shows that wires as small as 100 μm were resolved with Anrad and Varian detectors. However, despite the smaller pixel size of the Anrad detector, images obtained with the Varian detector showed slightly better quality. It was found that binning did not affect the visibility but degraded quality was observed with increased binning size. Due to motion blur, images obtained with continuous x‐rays showed lower spatial resolution. Conclusion: It was found that the spatial resolution of cone‐beam CT system does not solely depend on detector's resolution. Using pulse mode X‐ray shows a better performance in cone‐beam CT system than continuous mode.

This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐GG‐I‐33: A General Three‐Material Quantification Method Using Dual‐Energy CT Imaging
Authors: Liu X , Yu L , Primak A , McCollough C
Published: July 2008

Purpose: To propose a general method to quantify the density, atomic number, and mass fraction of three materials using only two energies levels (kVp settings), and evaluate its performance with quantitative simulations. Method and Materials: It is well known that dual‐energy CT can accurately quantify the density and atomic number for two materials in a two‐material object. This is possible because the dual‐energy CT technique provides two spectrally different measurements. For an object with three constituents, an additional measurement is required to solve the dual‐energy equations that now have three unknown values. Under certain conditions, a third physical measurement is not needed to solve for the three unknowns. One such solution is to assume that each material has a constant volume when mixed together, which provides an additional equation regarding the mixture's density. However, the constant volume assumption is not always true. Here, we calculate the mixture's density based on the mass attenuation coefficient, which can be expressed using the effective atomic number and density of the mixture. Then, we use the calculated density of the mixture to solve for the mass fractions of the three materials. To evaluate this method, we made numerical simulations using different densities of hydroxyapatite (HA: ). The developed algorithm is applied to the images and the chemical elements Ca, P, and are quantified. Results: The numerical simulation results indicate that the proposed method can accurately calculate the effective atomic number, density, and mass fractions of the constituents of a mixture for up to three different materials. Conclusion: The proposed algorithm is a general material‐decomposition method for dual‐energy CT. The number of materials which can be quantified is up to three. Conflict of Interest: CHM and ANP: Research grants from Siemens Medical Solutions.
SU‐GG‐I‐36: Measuring CT Incident Flux Using CT Sinogram Data
Authors: Massoumzadeh P , Whiting B
Published: July 2008

Purpose: The value of incident flux in a multi detector CT scanner is necessary to model noise properties of a CT scan. A novel method is proposed to determine the incident flux of any clinical CT scan by utilizing direct exposure (air) regions of the sinogram data. Method and Materials: 17 clinical patient scans, with tube current modulation on (11 scans) and off (6 scans), were collected from three sixteen‐row scanners at different locations. In addition a non‐symmetric object (skull with contrast) was scanned with two mAs settings (low and high), and with tube modulation on and off. Air regions of sinogram data were segmented by setting a threshold and collecting samples of direct exposures. Meanwhile, the extracted data were normalized using predetermined information about Case‐a: the bowtie profile, or Case‐b: the bowtie profile and the tube current (which was extracted from the header of CT sinogram data file). The variance of the gradient of the selected points of normalized data in transmission space as a function of gantry angle was obtained, which is inversely proportional to the incident flux. With this innovative method the result of Case‐a is proportional to the tube current, and the result of Case‐b is a constant scaling factor(K) relating incident flux to tube current for a given CT scanner. Results: The rms relative error between predicted and measured K was found to be 2.2%. The standard deviation in the value of K was 4.5%, indicating the scan‐to‐scan variation in flux scaling for an individual scanner. Computing a mean inter‐scanner variation indicates calibration of individual scanners is required to achieve simulation noise accuracies less than 5%. Conclusion: Utilizing this method, the incident flux or scaling factor characterizing incident flux for particular CT scanner can be computed.
SU‐GG‐I‐41: Accurate Determination of Dynamic Perfusion CT Point Doses in a Rando Phantom: The Importance of the Proper Orientation and Location of the TLD Chips in the Axial Segments
Authors: Goerner F , Al‐Senan R , Giantsoudi D , Hatab M
Published: July 2008

Purpose: As the patient table does not move during a cerebral perfusion CT study, the CTDI is not a true representation of dose to specific points in the scan volume and point dose methods are more appropriate. Our goal was to investigate the dose profile across both the width and length of the anthropomorphic phantom slices and to investigate the dependency of location and direction of the TLD chips. Method and Materials: A total of 78 LiF TLDs measuring 3×3×0.8 mm were placed in the middle holes in the anterior, posterior and middle of the 2nd and 3rd slices of the Alderson‐Rando head phantom. They were each filled with 10 TLDs placed parallel to the phantom slices with a 1.3 mm gap between them. Additionally, TLDs were loaded in two orientations in the location of the orbits in the 3rd slice: parallel and perpendicular to the phantom slice. Results: There was up to a 61% difference in dose readings from the TLDs placed at the top and those placed at the bottom of the phantom's 25 mm slice containing the orbits. Rando slices 2 and 3 which were exposed during the perfusion study exhibited variations of .24%–533% between the anterior and posterior parts. The dose gradients for both slices will be presented. In addition, there was a statistically significant difference between how the TLDs were oriented in the phantom holes. Those placed in an axial direction exhibited higher doses than those placed in a sagittal or coronal direction. Conclusion: There is considerable difference in dose between the anterior and posterior of each phantom slice examined as well as between the top and bottom location. Reports of perfusion or interventional CT dose studies using TLDs in anthropomorphic phantoms should clearly specify the location and orientation of the TLD chips.
SU‐GG‐I‐42: An Anthropomorphic Adult Physical Phantom and Fiber Optic Coupled Point Dosimetry System for the Measurement of Effective and Average Organ Doses of CT Patients
Authors: Hintenlang D , Moloney W , Winslow J
Published: July 2008

Purpose: Advances in computed tomography (CT) acquisition techniques, primarily multi‐detector CT (MDCT) and cone beam CT (CBCT), make it highly desirable to develop measurement techniques that provide a more physically meaningful measurement of patient dose than the traditional CT dose index (CTDI). The goal of this work was to accurately quantify the organ doses delivered to adult patients during CT exams as a fundamental tool for developing patient dose histories. Method and Materials: A tissue‐equivalent anthropomorphic adult phantom based on a tomographic data set was developed and fabricated at the University of Florida. The adult phantom's physical and radiological parameters are designed to mimic ICRP reference man, and include tissue‐equivalent materials for soft tissue, bone, and lung. Fiber optic‐coupled (FOC) dosimeters, which have been calibrated and characterized across the CT energy range, provide point dose measurements for multiple organ locations. The combination of phantom and FOC dosimeters establishes a dosimetry system to characterize both internal organ doses and effective dose. Results: The calibrated point detector system provides remote, real‐time dose measurements and in conjunction with the adult physical phantom allows for the quantification of absorbed organ dose measurements for a wide range of MDCT acquisition protocols. Average organ doses were quantified for the prostate, kidneys, liver, and lungs. The point dosimeter measurement illustrates the significant dose contributions that originate from scattering outside of tissue regions represented by the 15 cm length of CTDI phantoms. FOC dosimeters permit the dose to be displayed as a function of longitudinal position for a variety of scan parameters, aiding in the interpretation of dose comparisons. Conclusion: FOC dosimeters demonstrate high sensitivity, reproducibility, excellent dose linearity, and combined with their small physical size permit accurate point‐dose measurements. The organ doses vary significantly from interpretations of the CTDI, depending strongly on position and scan volume.
SU‐GG‐I‐43: Measurement of Radiation, Scatter and CTDIw From the Toshiba 320‐Slice CT Scanner with and Without Shielding
Authors: Patton P , Davis J , Orrison W , Hanson E , Cadwalader J
Published: July 2008

Scattered radiation has the potential to deliver high radiation doses to operators located within the scanning room during computed tomographic (CT) guided procedures. Measurements were made to determine the scatter radiation exposure from a 320‐slice Toshiba CT scanner. Additionally, the scatter radiation was measured after applying a lead‐fee shielding drape adjacent to the scanning areas to determine the effects on scatter radiation. The ACR CTDI head and body phantoms were used to measure the CTDIw for the adult head, the adult abdominal, and the pediatric abdominal protocols. Measurements indicate that, when similar scan protocols are used, a reduction of exposure is observed when using the 320‐slice scanner. Furthermore, scatter radiation is significantly reduced by using the lead‐free shielding drape.
SU‐GG‐I‐51: The Effect of Number of Projections On the Accuracy of Volumetric Data Reconstructed Using Digital Tomosynthesis
Authors: Sarkar V , Shi C , Papanikolaou N
Published: July 2008

Purpose: To investigate the effect of the number of projections used as source data on the volume of objects recreated by tomosynthesis when using the shift‐and‐add algorithm. Method and Materials: A phantom was created in Matlab to represent a cube of water within which a cube, sphere and cylinder of bone were inserted. The phantom was imported into the Pinnacle treatment planning system and DRRs were produced at every degree from 340° to 20°. Different volumetric reconstructions were performed by using 2 to 41 of these DRRs. Slices were created every 2.5 mm and imported into Pinnacle to be contoured for the volume of each object to be determined. Results: For the cube and cylinder, the volume calculated from the contours grew closer to the true volume as the number of projections used was increased, with the calculated volume agreeing with the true volume when nine projections were used to recreate the object. For the sphere, the volume oscillated about a value that is much larger than the real volume and never reached the true value. Conclusion: Due to the nature of the shift‐and‐add algorithm, it is easier to determine the presence of an object on a slice if it has a uniform signal. Thus presence of the cylinder and cube on a slice was determined by ensuring no ghosting was present around the object. However, the sphere, which has an inherently varying signal on a two‐dimensional projection, made it much harder to decide whether a slice contains the full object or if it is being partially smeared out, explaining the erroneous volumes from the contours. Therefore, while as few as seven projections are enough to identify the volume of certain objects, different reconstruction algorithms may be required to be used to the reconstruction of any arbitrary object.
SU‐GG‐I‐55: Comparison of Viewing Angle Performance and Observer Performance of Different Types of Liquid Crystal Displays
Authors: Hatanaka S , Morishita J , Higashida Y , Hiwasa T
Published: July 2008

Purpose: Liquid crystal displays (LCDs) have a number of advantages over cathode ray tubes and conventional viewers based on film. However, it is nown that the performance of LCDs varies by viewing angle. The purpose of this study was to compare the angular performance and effects on observer performance in different types of LCDs, namely a general purpose LCD for personal computers and one especially designed for medical use. Method and Materials: Two types of LCDs were used in this study, an in‐plane switching (IPS) technology display especially designed for medical use and a general‐purpose twisted nematic (TN) technology display. We measured the luminance responses and contrast ratios for the two types of LCDs at different viewing angles (−60 degrees to 60 degrees). Furthermore, observer performance at various viewing angles in the horizontal direction for the medical display was also examined by eight observers based on contrast‐detail diagrams. Results: The two types of LCDs showed notable variations in luminance and contrast ratios as a function of the viewing angle. Results obtained in different directions (horizontal, vertical and diagonal directions) indicated different contrast ratios. Acceptable viewing angles in terms of the contrast ratio were much smaller in each direction than those for nominal viewing angles in the specifications provided by the manufacturers. Acceptable viewing angles of the medical‐grade display in the horizontal and vertical directions were broader than those of the general purpose display. There was no significant difference in observer performance between 0 and 40 degrees. On the other hand, our results showed a statistically significant difference in observer performance between 0 and 60 degrees. Conclusion: Contrast ratio and luminance response showed notable variations with different viewing angles and different types of LCD. More importantly, the detection of contrast‐detail materials of the LCD monitor was influenced by viewing angles.
SU‐GG‐I‐57: A Mutlidetector CT Model Using BEAMnrc/DOSXYZnrc Code for Estimating Radiation Doses: Phantom Study
Authors: Chiang‐Hsieh CC , Tsai HY , Tung CJ , Chao TC
Published: July 2008

Purpose: Most of Monte Carlo based methods to estimate radiation dose in computed tomography (CT) were performed using MCNP or EGS codes. However, They can't really simulate the CT source, such as the x‐ray tube and the bowtie filter. The purpose of this study is to verify the feasibility of using BEAMnrc/DOSXYZnrc code to develop a real multidetector CT (MDCT) model and estimate radiation doses based on CT image voxelized phantoms. Method and Materials: A Siemens Somatom Sensation 64 MDCT scanner system was established to achieve the objective in this study. Detailed inner structures of the MDCT source were constructed by component modules in the BEAMnrc/DOSXYZnrc code to simulate the x‐ray tube, filtrations, bowtie filter, collimators and geometry factors. Furthermore, simulated CT source results, such as spectra, off axis ratio (OAR), half‐value layer, and radiation beam profiles, were compared with the measured results. Next, utilizing cylindrical and anthropomorphic phantom calculate CTDI and organ dose in the single axial and helical scan. Results: The simulated x‐ray spectra have been compared with those in Xcom5r calculations and they agreed with each other. Comparisons between simulated and experimental results for the lateral in‐air OAR, half value layer, and the radiation beam profiles were completed and the differences were within 3%. The CT dose index (CTDI) in air, in phantoms and organ dose have been simulated and calculated to confirm with measurements. Conclusion: This study illustrates the feasibility to extend the BEAMnrc/DOSXYZnrc code to model MDCT sources. The X‐ray tube and bowtie filter model really constructed by the BEAMnrc code. Future works devote to simulating specific patients' organ doses and effective doses in CT examinations.
SU‐GG‐I‐67: Assessment of Gamma Dose Rate in City of Kermanshah
Authors: Hosseinabad M Tavakoli , Kodamoradi E
Published: July 2008

Purpose: Environmental natural radiation measurement is of great importance and interest especially for human health. The induction of genetic disorder and cancer appears to be the most important in an exposed population. Method and Materials: Measurements of background gamma rays were performed using a mini‐rad environmental survey meter at 25 different locations around the city of Kermanshah (a city in the west of Iran). The measurements were also performed at two different time of day one in the morning and the other in the afternoon. At each location and time measurement were repeated for five times and the mean was considered as the background dose at that location. Results and Conclusion: Comparison between the measured results in the morning and afternoon have not shown any significant difference (P>0.95). The maximum and minimum obtained results were 2.63 mSv/y and 1.49 mSv/y respectively. From the total measurement at 25 sites mean and SD background radiation dose to the population is 2.24±0.25 mSv. It is about 2.5 times of the world average total external exposure cosmic rays and terrestrial gamma rays dose reported by UNSCEAR.

Keywords: Background radiation, Ionizing radiation, low level radiation, Environment radiation.
SU‐GG‐I‐68: Dosimetryc Study to Voxel Model Applied to Carciac Procedures in Nuclear Medicine
Authors: Hoff G , Cassola V , da Silva A
Published: July 2008

Purpose: The objective of this study is to realize a computational dosimetry on a simplified model of miocardic perfusion, considering the usual different ways to describe the spectra emitted for Tc‐99m. Method and Materials: The GEANT4 code was used to simulate two geometries: the radial dose distribution from an isotropic point source described by the three spectra, modeled with photon emission from the center of a 1.3‐m‐diam sphere of muscle tissue; and a second considering an uniform distribution of Tc‐99m in the heart muscle of the adult male voxel model MAX, to take the organs dose distribution. The different ways to describe the spectra emitted for Tc‐99m was: monoenergetic spectrum of 140 keV; three photons emissions spectrum (2.1, 141 and 143 keV) and total spectrum (including characteristics x‐rays and Auger electrons). Results: For distance low than 1 cm from the point source the radial dose distribution is higher for total spectrum. The radiation dose in a sphere with 0.01 mm defined at the center of the sphere of muscle was 0.369 mGy Bq1 h1 (total spectrum), 0.276 mGy Bq1 h1 (three photon spectrum), and 0.005 mGy Bq1 h1 (monoenergetic spectrum). This data shown that include Auger electrons, characteristic x‐rays, and low energy gamma give a significant contribution to total energy deposition. This results corroborates the simulations realized using the voxel model. The data variation shown that monoenergetic and three gamma spectra, comparing to total spectra simulated, produce a decrease on absorbed dose on cardiac tissue of 19.2% and 7.1%, respectively. Conclusion: The results shown that the combined transport of electrons Auger and characteristics x‐rays of the Tc‐99m increase the radiation dose, especially on organs/tissues closer to those have had absorbed the radiopharmaceuticals. This study indicates the importance on describe the complete radiopharmaceuticals spectrum on dosimetric simulations in Nuclear Medicine.
SU‐GG‐I‐69: An Attempt to Establish Regional Diagnostic Reference Levels for CT Scanners in India
Authors: Livingstone R , Dinakaran P
Published: July 2008

Purpose: To establish regional diagnostic reference levels for CT scanners from a survey in Tamil Nadu, South India. Method and Materials: A regional survey of 71 CT scanners in a few districts in Tamil Nadu was done over a period of one year as a part of an ongoing Atomic Energy Regulatory Board (AERB) funded project. The survey included dissemination of necessary data involving exposure parameters and radiation doses used routinely in each centre. Dose estimation in CT scanners was performed using a 32 cm CT dose index (CTDI) acrylic body phantom and a 10cc pencil ion chamber. Weighted CTDI (CTDIw) and effective doses were calculated using observed CTDI values. An attempt to establish regional diagnostic reference levels was made by adopting results from a local dose reference level obtained from the host institution where the study was conducted. Results: Out of the 71 CT scanners surveyed, 24 were conventional, 29 spiral and 18 multidetectors. The mean CTDIw values for biphasic abdominal CT using corresponding routine institutional protocols would be 14.55 mGy, 12.6 mGy and 17.18 mGy for conventional, spiral and multidetector CT scanners respectively. The third quartile values of effective dose for biphasic abdominal CT from the regional dose survey would be 17.15 mSv (range: 5.36 mSv – 46.81 mSv), 14.83 mSv (range: 3.68 mSv – 25.63 mSv) and 20.37 mSv (range: 4.31 mSv – 47.08 mSv) for conventional, spiral and multidetector CT scanners respectively. Conclusion: Regional diagnostic reference levels for body CT examinations could be established from prior knowledge of the local reference levels obtained. The wide variation of dose levels observed from various centres could contribute extensively to the population dose in the region in concern.
SU‐GG‐I‐72: Characterization and Use of XRCT Radiochromic Film for CT Radiation Profile
Authors: Ohuchi H , Abe M
Published: July 2008

Purpose: To quantify and evaluate the use of the self‐developing Gafchromic XRCT film for its implementation in routine CT QA. Method and Materials: The film was examined for several properties including delivered dose, dose sensitivity, and energy dependence. The digital image data of the film was taken by scanning using a flatbed color image scanner with a reflective mode. Radiochromic films (RCFs) are known to have microscopic and macroscopic non‐uniformities. These variations in the response make the optical S/N (signal‐to‐noise ratio) lower, resulting in lower film sensitivity. To mitigate the effects of RCF nonuniform response, a self‐developed optical common‐mode rejection (CMR) scheme was applied. The optical CMR can improve the dosimetric sensitivity limit of a RCF through use of a set of color components, e.g. red and green outputs from an RGB color scanner. The response of the XRCT films to delivered dose ranging from 0.3 mGy to 120 mGy for tube voltages of 80 to 120 kV was analyzed by using an optical CMR scheme and the results were compared with those obtained by the conventional analysis using the red output. Dose profiles were obtained using the XRCT film based on an Aquilion 64 CT scanner. Results: No energy dependence was observed for tube voltages of 80 to 120 kV. The dose‐response curve showed that the XRCT film response is nonlinear, then, a second‐order polynomial fit was applied to the curve. When analyzed by using the optical CMR, excellent agreement between predicted and measured optical densities was obtained in the low range less than 1 mGy, while those with the conventional analysis did not show a consistency with a fit. Conclusion: This work indicates that this RCF film possesses unique and good characteristics which allows for its use in routine CT QA.
SU‐GG‐I‐83: Temporal Filtering of Noise in Low‐Dose X‐Ray Fluoroscopy
Authors: Wang J , Zhu L , Chai A , Xing L
Published: July 2008

Purpose: To improve quality of low‐dose X‐ray fluoroscopic images using statistics‐based restoration algorithm so that the patient fluoroscopy can be performed with much reduced radiation dose. Method and Materials: We first studied the noise properties of low‐dose X‐ray fluoroscopic images through repeated measurements using a Varian Acuity simulator. Noise in X‐ray fluoroscopic images can be modeled as Poisson noise plus background electronic Gaussian noise and the mean‐variance of the noise can be described by an analytical formula. Based on the noise model in fluoroscopic images, a penalized weighted least‐squares (PWLS) objective function was constructed to restore fluoroscopic images acquired with low mAs protocol. Furthermore, the Karhunen‐Loève (KL) transform was utilized to consider correlations among neighboring frames of fluoroscopy. The KL transform manipulates a sequence of correlated measurements into an uncorrelated, ordered principle component series and, therefore, provides a unique means for de‐correlation, feature extraction and noise reduction. After the KL transform, the regularization parameter in PWLS criterion will be inverse proportional to its corresponding eigenvalue. Such a choice is favorable because the regularization parameter varies adaptively according to the signal‐to‐noise ratio of that component. A smaller KL eigenvalue is associated with a component having a lower SNR; therefore, a larger regularization value should be used to penalize this noisier data. Results: We tested the proposed K‐L domain PWLS noise reduction algorithm using an anthropomorphic chest phantom. Low‐dose fluoroscopic images were acquired with X‐ray tube current of 10 mA and duration of x‐ray pulse 2 ms. In the image restored by the proposed KL domain PWLS algorithm, noise is greatly suppressed while fine structures are well preserved. Conclusion: Experiment studies show that image quality of low‐dose X‐ray fluoroscopic image can be dramatically improved by using statistics‐based temporal filtration. The proposed noise reduction technique shows potential for dose reduction of X‐ray fluoroscopy.
SU‐GG‐I‐90: A Surface Reconstruction and Smoothing‐Based Re‐Contouring Algorithm for Target Volumes in Radiotherapy Treatment Planning
Authors: Liu D , Chetty I
Published: July 2008

Purpose: To develop an automatic re‐contouring approach for tumor volumes via surface reconstruction and smoothing. The method overcomes the limitations of traditional methods used in 3D volume reconstruction which can be quite irregular, leading to non‐physical beam intensities during inverse‐planning. Method and Materials: Stacks of contours are extracted from DICOM RS files which are exported from the treatment planning system. Surface models are generated from the contours via a surface reconstruction algorithm. The surface reconstruction algorithm contains two steps. First, contours are triangulated and medial axes are computed. Then, contours on adjacent cross sections are joined to create a surface. Gaussian and other surface smoothing operators are applied to the surface models. The smoothed models are re‐sliced with CT planes to produce new contours. Results: The Gaussian surface smoothing operator is an excellent smoothing tool but suffers from the volume shrinkage problem. To circumvent this problem, a volume‐preserving surface smoothing operation is implemented (Taubin's surface smoothing algorithm), which uses a non‐shrinking variant of the Gaussian smoothing algorithm. As noted in the figures, the method, applied to prostate volumes, shows good correspondence between the smoothed and original volumes. The mean 3D vector distance between the smoothed and original surfaces was 0.6 mm (RMS = 0.8 mm) for an example case. Conclusion: The proposed surface‐based reconstruction algorithm produces more physically realistic, smooth target volumes in 3D while maintaining the overall structure of the original volume. Future work will include the implementation and evaluation of other surface smoothing operators as well the incorporation of the smoothed 3D volumes into treatment planning to assess the impact on inverse‐planned fluence maps and IMRT dose distributions.
SU‐GG‐I‐96: Improvements for Fully Automatic Lung Segmentation From RT Planning Scans
Authors: Anane A , Boettger T
Published: July 2008

Purpose: Segmentation of pulmonary X‐ray computed tomography (CT) images is a primordial step to most pulmonary image analysis applications. Many approaches have been presented in the past mainly focusing on lung extraction from high resolution CT data. Looking towards RT planning one has often to deal with low image quality, artifacts and pathological changes of the anatomy. We present a fully automatic method for delineation of the lungs and the trachea in three‐dimensional RT planning scans for thorax and breast patients. Method and Materials: The method consists of several steps. First, lung region is extracted automatically computing an optimal threshold method. Then, the trachea is separated from the lungs by fast marching. Next left and right lungs are separated in each slice by computing a minimal path in the area where separation is suspected from the information of the neighboring slices. Finally the 3D segmentations of the left and right lungs are refined running the random walker algorithm with foreground and background seeds automatically calculated from the intensity‐based pre‐segmentation. Results: Processing time is below one minute and does not require any user input. Several 3D CT Datasets from different patients were used to evaluate the methods. The algorithms can segment the trachea and separate the left and right lung. In comparison to previous publications stability could be improved. Still in some cases result are not satisfying, e.g. trachea segmentation reaches into the lungs and lesions or emphysema are not included in the lung segmentations. Conclusion: The presented algorithm allows for fully automatic lung segmentation. One major improvement could be to employ a shape model as recently published by other groups as a shape‐constrained segmentation method could help to overcome the observed problems with exclusion of pathologies.
SU‐GG‐I‐111: Activity Concentration Degradation in Positron Emission Tomography of Objects in Motion
Authors: Riegel A , Mawlawi O , Pan T
Published: July 2008

Purpose: To determine the functional form of activity concentration degradation for objects in motion scanned with positron emission tomography (PET). Method and Materials: A computational model was developed to simulate the behavior of spherical objects moving sinusoidally. Sinusoidal probability density functions (PDFs) of varying lengths were convolved with a noise‐free disk, producing blurred, elongated shapes of the disk similar to those observed in PET imaging of thoracic lesions. Maximum values of the convolved images were determined, plotted as a function of PDF length, and fit using least squares criteria. PET scans of a NEMA IEC phantom oscillating sinusoidally were performed to compare with model results. Motion amplitudes varied from 0 cm to 3 cm at 0.5 cm intervals. The period of the oscillation was 4 s. No background activity was present. Each scan was acquired to 15 million counts to minimize statistical fluctuation. Maximum activity concentrations were determined for each sphere at each motion amplitude and fit using least squares criteria. The functional forms which best fit the data from the model and phantom data were compared. Results: Model results suggest the degradation due to motion follows a logarithmic decline (R2 = 0.99) after the amplitude exceeds the diameter of the object. Before this extent is reached, no degradation was observed. Phantom results support model predictions: The functional form which fit the phantom data best was a natural logarithm of motion amplitude (R2 = 0.97 for sphere diameter 1.3 cm, R2 = 0.99 for sphere diameter 1.0 cm). Conclusion: Motion degradation of activity concentration follows a logarithmic function of motion extent. Modeling motion degradation could lead to development of a recovery coefficient for motion analogous to the recovery coefficient used to correct for partial volume averaging.
SU‐GG‐J‐34: Aperture Design of Two‐Dimensional MLC Motion for Dose‐Rate‐Regulated Tracking
Authors: Han‐Oh Y , Yi B , Gui M , Berman BL , Yu C
Published: July 2008

Purpose: Real‐time adaptive tumor tracking called Dose‐Rate‐Regulated Tracking (DRRT) is based on a preprogrammed MLC sequence and real‐time dose‐rate modulation. We have developed an algorithm for designing the MLC sequence reflecting 2‐D MLC motion. MLC apertures were designed from 4D‐CT images, and the algorithm was tested in the 3‐D phantom. Method and Materials: The 2‐D MLC motion and the corresponding tumor shape are derived from ten‐breathing bins of 4D‐CT. The closed MLC leaves that are not participating in the beam aperture are programmed to remain in motion to minimize leaf‐end leakage. This feathering motion is intended to spread the leakage dose to the normal tissue beneath the closed MLC leaves. We performed phantom studies with a 3‐D Phantom (Washington Univ.) for two cases: (1) a circular moving target (2) a patient's lung tumor in the lower lobe. The results of these two measurements were compared with those for the case of a static beam aperture and a static phantom (static‐static case). The accuracy of the 2‐D MLC sequence was determined by γ analysis with those for the static‐static case. The effectiveness of the feathering motion was quantified with the leakage dose normalized to the maximum dose measured by the film. Results and Conclusion: For both of the above cases, the γ analysis showed that 95% of the pixels are less than 1 for 3 % and 3 mm criteria. The feathering motion reduced the leaf‐end‐leakage dose from ∼15% to ∼7%. A careful design of the MLC‐leaf sequence done in advance can not only facilitate real‐time tumor tracking, but also reduce the dose to healthy tissue, and thus can lead to improved results using DRRT.
SU‐GG‐J‐42: Automatic Contour Delineation On Cone Beam CT (CBCT) and Verification
Authors: Chi Y , Liang J , Zhang T , Yan D
Published: July 2008

Purpose: Patient anatomy manifested on cone beam CT(CBCT) image is useful for treatment localization, however, automatic organ segmentation on CBCT is challenging and its accuracy needs to be established. The purpose of this study is to quantify the accuracy of automatic contour delineation on CBCT using weekly helical CT (HCT) and daily CBCT images.Method and Materials: Images from 5 head and neck IMRT patients were used in this study. Each patient had 5 to 6 weekly HCTs and daily CBCTs. Those images are registered to planning HCT using a freeform deformable image registration algorithm. Contours were automatically generated for both HCTs and CBCTs using planning contours and registered displacement. The resulting contours on weekly HCT were used as reference, and compared to contours on CBCT with respect to ROI volume, ROI center coordinate, and ROI surface discrepancy. The ROI surface discrepancy was determined using distance transform of ROI masks. Results: GTV, left parotid, right parotid and mandible, are selected for comparison. GTV volume discrepancy in percentage is −2.8±6.1%, ranging from −9.8% to 11.5 %. GTV volume discrepancy in magnitude is −2.3±3.6cc, ranging from −7.8 to 3.8cc. Volume discrepancies for left parotid, right parotid, and mandible are −6.7±4.7%, −3.6±4.1%, −4.3±5.0% in percentage respectively, and −1.3±1.1cc, −3.2±3.6cc, −0.8±1.0cc in magnitude. The mean difference in ROI centers for all organs is less than 2mm with a maximum of 4mm. Surface discrepancy of GTV, left parotid, right parotid, and mandible are −0.33±1.8mm, −0.28±1.1mm, −0.32±0.9mm, and −0.28±0.9mm respectively. Conclusion: Most of contours from CBCT has slightly smaller volume but all show excellent match to those from HCT, with most surface discrepancy within image voxel size. Further investigations on quantifying dosimetric effect of the geometry uncertainty are underway. Conflict of Interest: Support in part by NCI Grant — CA091020.
SU‐GG‐J‐65: Decision Making in Daily Or Weekly Volumetric Imaging Guidance Based On Case Studies
Authors: Sheng K , Chow J , Read P
Published: July 2008

Purpose: Daily volumetric imaging provides accurate patient positioning at the cost of imaging dose and lengthened treatment time. In order to assess the necessity of these images for well immobilized head‐and‐neck cancer patients from a risk management point‐of‐view, magnitudes of set up errors corrected by TomoTherapy MVCT on a daily or weekly basis are analyzed. The impact of these errors on the delivered dose to the tumor and organs‐at‐risk (OAR) is calculated. Method and Materials: The set up errors of 6 nasal cavity and 4 nasopharyngeal cancer patients were retrospectively analyzed. Each patient had MVCT guided daily repositioning. The new dose volume histogram (DVH) and equivalent uniform dose (EUD) for planning target volume (PTV) and OARs were calculated for hypothetical scenarios where no imaging guidance (IG) or weekly image guidance (WIG) took place. Results: The mean total set up error if treated without daily IG was 3.6±1.0 mm, which can be reduced to 1.7±0.6 mm if a WIG was performed. The geometrical uncertainties from the absence of image guidance resulted in a reduction of mean PTV EUD dose by 2.1±1.0%, which can be reduced to 1.4±1.0% with WIG. The EUD of OARs increased 1.8±2.0Gy or 0.8±1.3Gy without or with WIG respectively. For the organ showing the most dosimetric impact from the image guidance, the probability of having 6 or 8 Gy of deviation was 10% and 2 % respectively. These probabilities were reduced by more than four fold if weekly IG was performed. Conclusion: Without daily IG, the mean patient position uncertainty has relatively small impacts on the mean PTV and OAR dosimetry, which can be further reduced approximately by half using weekly IG. The frequency of the IG can therefore be determined by the deviation probability function of the most critical OAR and its limiting tolerance dose.
SU‐GG‐J‐69: Development of a Programmable Moving Phantom for the Verification of 4D Dose Delivery
Authors: Yoon J , Chung J , Lee J , Jung W , Suh T
Published: July 2008

Purpose: To develop a programmable moving phantom to simulate internal organ motion and investigate the impact of the respiratory motion on dose delivery by comparison with phantom measurements. Method and Materials: A moving phantom system was constructed to simulate internal organ motion. The system consists of a motion system and an acrylic phantom. A mechanical cam is responsible for the motion in the anterior‐posterior direction. A worm gear allows 1‐D linear motion in the superior‐inferior direction. The acrylic phantom has lung and prostate inserts including a film cassette and an ion chamber. The motion control system was composed of two AC servo motors, a controller and a PC‐based motion program. The motion control program was implemented to move the phantom insert with a non‐linear (sinusoidal or irregular) motion according to a user‐defined motion profile. The user‐defined motion profile can be generated in a spreadsheet either by calculation using an analytic model or by acquisition of real patient data. An external stereo camera was used to acquire the motion data for verification. Results: User‐defined motion trajectory can be produced using the programmable moving phantom with an accuracy of 0.5 mm. Although a period for motion update is 10ms, camera measurement result indicates that the resulting motion profile was smooth enough to simulate internal organ motion with the help of an interpolator in the motion controller. Conclusion: This work indicates the prospect for 4D patient specific QA using the programmable phantom with a patient internal organ motion data. Real 4D dose verification could be achieved with independent 3‐axis moving mechanics. Conflict of Interest: This work was supported by a grant of Seoul R&BD Program (10550).
SU‐GG‐J‐70: Development of An Image‐Guided Conformal Small Animal Irradiation Platform
Authors: Lindsay P , Ansell S , Moseley D , Jelveh S , Hill R , Jaffray D
Published: July 2008

Purpose: To develop an image‐guided conformal small animal irradiation system for pre‐clinical studies. The initial dosimetric and imaging properties of the system have been characterized. Method and Materials: The system consists of a 225 kVp x‐ray tube (GE Isovolt, maximum power 3 kW, focal spot=0.4mm–3.0mm), and 20.5×20.5 cm amorphous silicon flat panel detector (512×512 pixels, 7 frames‐per‐second) mounted on a rotating gantry. The system can rotate 360°, at a maximum speed of 3 RPM. The source‐isocenter distance is 31 cm, and the source‐imager distance is 62 cm. Cone‐beam CT images are generated from projections over half or full rotation, and reconstructed using filtered‐back projection. A motorized stage allows translational movement of specimen. Initial dosimetric characterization of the system has been done using EBT Gafchromic film in a solid water phantom at 2 cm depth. The unit is free standing and self‐shielded. Results: The maximum dose rate achievable at isocenter is 4.5 Gy/min for 220 kVp unfiltered beam, and 2 Gy/min for 220 kVp beam with 0.5mm added Cu filtration (HVL = 1.0mm Cu). The maximum dose rate for 100 kVp is 2.5 Gy/min (unfiltered) and 1.5 Gy/min with 2mm added Al filtration (HVL = 3.1 mm Al). Cone‐beam CT images are generated with a resolution of 0.2×0.2×0.2 mm. Conclusion: Image‐guided conformal pre‐clinical irradiation systems will enable novel translational research in radiation oncology and radiobiology. The presented system has been demonstrated to provide the dose rate, mechanical stability and image‐guidance capabilities necessary to facilitate such research.
SU‐GG‐J‐90: Ex Post Facto Addition of Headframes to DICOM Image Sets for Radiosurgery Treatment Planning
Authors: Wiant D , Rossmeisl J , Robertson J , Bourland J
Published: July 2008

Purpose: To facilitate Gamma Knife™ stereotactic radiosurgery (GK‐SRS) headframe placement and pre‐planning using pre‐existing DICOM images, for a canine radiosurgery clinical trial. Method and Materials: Software has been developed and tested for virtual GK‐SRS headframe placement using pre‐existing images obtained for diagnostic or other purposes. The Matlab‐based software allows for user‐interactive graphical positioning of the headframe or manual entry of headframe position relative to the clinical image coordinate system. Six degrees of freedom (translations and rotations) are enabled. The process was tested by matching the graphically added (virtual) fiducial markers to the true fiducial markers obtained from headframe image sets having known translations and rotations. Results: GK‐SRS fiducials can be virtually positioned either graphically or manually and then written to a new combined set of DICOM images for export to the GK‐SRS planning system. Frame placement accuracy is estimated at 1mm (∼ 1 voxel), dependent on the base image pixel resolution. GK‐SRS treatment plans can be developed prior to the treatment day to optimize both frame placement (e.g. ideal location) and treatment (e.g. dose location). Conclusion: Adding GK‐SRS fiducials to a DICOM image set allows possible headframe positions to be evaluated and enables transfer of the modified image set to the GK‐SRS planning system for definition of potential stereotactic coordinate systems. Viability of GK‐SRS can then be assessed with an initial treatment plan, without the patient present, to demonstrate treatment feasibility and increase efficiency on the treatment day. These tools, with slight modifications, serve a similar purpose for human GK‐SRS patients, allowing off‐site cases to be initially evaluated and pre‐planned, to aid in both treatment optimization as well as treatment day efficiency.

Supported in part by the Wake Forest University TRADONC program NCI T‐32 CA113267 and by the Wake Forest University Translational Science Institute.