bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐I‐92: Semi‐Automatic Structure Delineation Using Deformable Image Registration
Authors: Michalski D , Huq M , Heron D
Published: July 2008

Purpose: To determine the applicability of the semi‐automatic organ and tumor contouring method based on the elastic registration of CT images. Method and Materials: Five CT scans of thorax used for treatment planning of lung cancer patients were employed for this study. The GTV and esophagus were the structures of interest. The CT slice where a structure firsts appears is manually contoured and the last slice with the structure is identified. The initial contour is cascaded to the last slice via a consecutive image registration. The method uses the space‐zooming technique based on the Gaussian pyramid. The deformation field obtained at a given pyramid level is interpolated to the next level using B‐splines. The deformed images are interpolated by means of backward reconstruction. The image registration is based on an image differential optical motion estimation. The software is implemented in C programming language. The data are extracted from dicom files with Matlab scripts. Results: Ideally the initial slice with a structure of interest is delineated and the method allows to complete the entire volume automatically up to its final Ct slice. For cases with a significant structural change between slices like volume partitioning, a human intervention is required to contour the problematic cross‐section. The contours migration was deemed to provide acceptable results. The final inspection and contour examination of the entire volume is still required to validate structures. The robustness of the method for average case might be tuned with with algorithm's parameters. Conclusion: The described method works for cases for which there is no drastic topological change between slices of the structure of interest. The method deals with cases for which threshold‐based segmentation techniques have difficulties due to similar values of CT numbers of the adjacent structures.
SU‐GG‐I‐94: Analysis of Breathing Pattern for Radiotherapy by Studying Diaphragm Trajectory
Authors: Dou X , Wu X , Xing L , Bayouth J
Published: July 2008

Purpose: Understanding breathing patterns would help in designing a patient‐specific treatment plan. This work pursues a robust means finding individual breathing patterns by studying diaphragm motion. To our best knowledge, no previous work utilized an automated 4‐D image segmentation technique for analyzing diaphragm motion. Method and Materials: In this study we intend to accurately segment the diaphragm from 4‐D image datasets to analyze breathing patterns. The core of the problem is to develop an effective 4‐D surface segmentation method for diaphragm. We developed a novel 4‐D optimal surface detection method capable of simultaneously detecting diaphragm over the entire respiration cycle. The optimality is controlled by cost functions designed for surfaces and by several geometric constraints defining the surface smoothness and position changes between phases. The problem is solved by transforming it into computing a minimum s‐t cut in a derived arc‐weighted directed graph. Gradient Vector Flow (GVF) is incorporated into cost function design to allow flexible initialization of the diaphragm surface and to encourage convergence to boundary concavities. A pre‐segmentation of the diaphragm in one phase is used as initial surfaces for all other phases. We implemented our algorithm and experimented on 7 sets of 4‐D chest/abdomen CT images. Dome point of the diaphragm in the first phase is found and those in the remaining phases within a neighborhood are detected to generate the diaphragm trajectory. Results: Our method converges quickly and yields highly accurate contouring results by visual examination. The diaphragm trajectory over the breathing cycle can then be computed from the segmentation result. Conclusion: We developed a novel 4‐D surface segmentation method for accurate detection of diaphragm over the entire respiration cycle from 4‐D CT image data. The breathing pattern can then be analyzed from the motion of diaphragm. The method helps in developing patient‐specific treatment plan.
SU‐GG‐I‐95: Simpler and Faster Watershed Medical Image Segmentation Algorithm
Authors: Kum O , Lee H , Kim J , Song T , Park K , Han Y
Published: July 2008

Purpose: A watershed medical image segmentation method has a drawback of producing a region for each local minimum, resulting in oversegmentation. To alleviate this problem, a post merging process such as a hybrid graph merging algorithm is used, which impedes interactive segmentation with a graphical user interface. An effective watershed algorithm without a post merging process is proposed. Method and Materials: Our algorithm, as the preprocessing, includes the edge‐preserving noise reduction and gradient‐based boundary sharpening steps. Because the initial oversegmentation depends on the gradient image intensity variations, the noise reduction algorithm can reduce the problem appreciably. A well‐known statistical edge‐preserving noise reduction algorithm is implemented to preserve the boundaries of the image objects which have different physiological properties. Gradient‐based boundary sharpening stage follows the novel edge‐preserving noise reduction step. Boundary sharpening process combined with watershed segmentation results in an effective watershed algorithm without a post merging process. The combination of the standard gradient values with two cross operators makes the edges sharper and thinner. A threshold value is controlled interactively with a steppedup graphical user interface in the boundary sharpening process. Results: We applied the method to both CT and MR images. Interactive real time medical image segmentation was possible with a graphical user interface. Threshold values were manipulated interactively with a mouse to get an appropriate segmentation of the abdomen CT image. It was also confirmed that this method produced the same segmentations as those of hybrid‐merging algorithm for the MR brain images. Conclusion: In the gradient‐based watershed, computing time is negligible and storage requirement can be reduced appreciably because a post hybrid merging algorithm is not necessary. Moreover, interactive real time segmentation is possible with the steppedup graphical user interface.
SU‐GG‐I‐99: Validation and Comparison of 3D Image Registration Approaches for Adaptive IMRT in Head‐And‐Neck Cancer
Authors: Li H , Thorstad W , Zhu J , Wu B , Yang D , Low D , Lu W
Published: July 2008

Purpose: 3D image registration is a key component in image‐guided adaptive radiotherapy. It is imperative that the accuracy of a registration method is assured prior to clinical implementation. However, registration validation is scarcely covered in the literature. In this work, we validated and compared seven registration methods for CT/MRI and MRI/MRI fusion in adaptive radiotherapy treatment planning of head‐and‐neck tumors. Method and Materials: A planning CT image and an MRI image were acquired before the treatment and seven weekly MRIs acquired during an IMRT head‐and neck cancer treatment. Seven methods including intensity‐based, surface‐based, landmark‐based, manual, and non‐rigid registrations were applied to align 2 pairs of CT/MRI, and 8 pairs of MRI/MRI datasets. For each registration, eight anatomic landmarks were identified in each image. The distance between the transformed landmark position and the manually determined position was calculated. The registration accuracy was estimated by the mean distance. Results: The mean distances between CT/MRI and MRI/MRI landmarks were approximately 2.0 mm. For CT/MRI registration, intensity‐based registration plus manual adjustment performed the best with the smallest registration error of 1.2 mm. Non‐rigid and manual methods both had small errors of 1.5 mm. Surface‐based and landmark‐based methods had larger errors of 3.3 mm and 2.4 mm, respectively. For MRI/MRI registration, non‐rigid methods had the smallest registration error of 1.3 mm. Similarly, surface‐based and landmark‐based methods had larger errors of 2.8 mm and 2.9 mm, respectively. Non‐rigid method and landmark‐based methods had the greatest registration error variances. Conclusion: We qualitatively and quantitatively evaluated seven methods on CT‐MRI and MRI‐MRI registration for head‐and‐neck patient. Careful and quantitative evaluation of the registration accuracy is important for the identification of the optimized registration method, the application of multimodality imaging in treatment planning, and the daily image guidance in treatment delivery.
SU‐GG‐I‐112: PET Imaging of Heterogeneous Tumors: An Investigation of the Influence of Motion On Recovered Activity
Authors: McCall K , Barbee D , Kissick M , Jeraj R
Published: July 2008

Purpose: As multi‐day PET studies become part of targeted therapy planning and treatment assessment, it is important to characterize how positioning errors affect observed tumor heterogeneity. We have characterized the uncertainty in recovered‐activity in PET‐imaging of heterogeneous tumors as a function of axial position. Method and Materials: Recovery coefficient (RC) is ratio of maximum activity‐concentration to the true specific activity in an object. The uncertainty in RC was quantified by RCerror: the quotient . We measured RCerrors for a GE Discovery LS PET/CT scanner with an axial detector width of 4.25mm. A Heterogeneous‐tumor phantom, containing three spheres (15mm, 10mm, 5mm diameter), was scanned as the phantom was moved axially in 1mm intervals. RCerror of the spheres were determined in images reconstructed by iterative ordered subset expectation maximization (OSEM) and filtered backprojection (FBP) algorithms. The clinical effect was investigated using head and neck cancer (HN) patients imaged on this scanner. 18FLT‐PET images of patients were thresholded into three levels of relative uptake, and segmented into connected sub‐regions. We simulated multi‐scan studies and calculated the changes in SUV that result from repositioning the patient. Results: OSEM reconstruction provided more accurate recovery of activity in the spheres when compared to FBP. However, uncertainty of these OSEM values was larger, as RCerrors were 27%, 8% and 4% for the 5mm, 10mm and 15mm spheres respectively. In contrast, RCerrors were 10%, 8% and 3% for FBP. The effects of RCerrors were examined in clinical images; a positioning error of 5‐degree tilt caused 23% decrease in correlation within the tumor region of patient 1 and 12% in patient 2. Conclusion: Uncertainty in the RC depends on object diameter, reconstruction algorithm, and axial‐displacement. However, heterogeneities in FBP images of consecutive PET studies would be less susceptible to errors related to the axial positioning of tumors.
SU‐GG‐I‐117: Diffusion Tensor Imaging Analysis in Temporal Lobe Epilepsy Using Image Registration
Authors: Juh R , Suh T
Published: July 2008

Purpose: Diffusion tensor imaging (DTI) can provide information regarding early pathological changes, such as neuronal cellular changes in gray matter or demyelination in white matter tracts. Statistical analysis and deformable registration can be performed to compare changes in a group of patients and control. In this study we investigated whether the seizure focus in patients with temporal lobe epilepsy (TLE) can be identified compared to controls. Method and Materials: Ten control (36±7y) with no history of neurological disease, and 10 TLE patients (30±10y) diagnosed with temporal lobe epilepsy were included in this study. The ADC and FA maps acquired from each patient was compared to the normal group data, and also the whole patient group was compared to the control group on a voxel based analysis and deformable registration. Results: The three of ten patients, a well localized region in the temporal lobe gray matter was found to show significantly increased ADC, which might be associated with the seizure focus. As the long‐term seizure may damage the tissues, the involved areas may show changes in DTI. Every patient showed a different pattern, some with a well‐localized focus with increased ADC which might be associated with seizure focus. The FA maps were also analyzed, however no significant changes were found localized in the white matter, rather in the same gray matter area, suggesting that the effect was mediated from ADC changes. Conclusion: The SPM analysis of ADC maps acquired from each individual patient compared to a normal group might provide a means of accurately identifying focal abnormalities prior to more invasive diagnostic procedures and possible epilepsy surgery. The occult epileptogenic regions may be identified using voxel‐based statistical analysis of ADC.
SU‐GG‐I‐118: A Novel Method of MRI Correlate with Electron Density Information for Radiotherapy Treatment Planning
Authors: Tsai CH , Chuang CS , Chi KW
Published: July 2008

Purpose: MRI (Magnetic Resonance Image) provided excellent soft tissue resolution and functional images for treatment target delineation. For MRI based treatment planning, electron density of the organ or structures of interest were manual assigned. In this study, we developed a new method to correlate MRI images with electron density information for radiotherapy treatment planning dose calculation. Method and Materials: We implement a neural‐network structure with two MRI sequences inputs and the output end correlates with CT images that belong to the same patient to be a training target. The iterative training process was designed to keep the best fit parameters of neural‐network in order to enlarge the similarity between Neural‐Network outputs and CT images. After the training process, MR images can be converted into a Homemade CT like image (HCT) for radiotherapy treatment plan dose calculation. The real CT □CT with union density and HCT were compared and analyzed with their characteristics for radiotherapy dose calculation. Results: Our HCT provides more precise, convenient and heterogeneous dose distribution than manual assigned or union density for MRI‐only treatment plans. The Monitor Unit calculated from prescribe dose was within ± 3% when compared with CT based treatment planning. Conclusion: A novel method of MRI correlates with electron density information for Treatment Planning dose calculation purpose was purposed. The converting algorithm was created by a nonlinear method, and searching for solutions using numerical approaching.
SU‐GG‐I‐120: Improved BOLD Signal Detectability of Short Breath Holding Duration at 3T: A Comparison with 1.5T
Authors: Kuan W , Hsu Y , Lim K , Liu H
Published: July 2008

Purpose: Hypercapnia stresses such as breath holding (BH) have been showed to result in vasodilatation. Karstrup compared cerebrovascular reactivity between inhalation and BH, and found good correlation in BOLD intensity changes. This suggested possibility of using a simple BH task to evaluate abnormal vasomotor functions in clinical. A previous study has focused on the detectability of BOLD signal changes during short BH durations at 1.5 T and found a 10‐s BH could be detected but a 20‐s is suggested for clinical applications. As the 3T scanners recently became more available, we re‐evaluated this issue and aimed to find optimal BH duration for clinical use at 3 T. Method and Materials: A T2* gradient‐echo EPI sequence was used for BOLD measurements at a 3T scanner. Imaging parameters were TR/TE/flip angle= 3000ms/35ms/90°. Five BH duration, from 5 to 30 s, were experimented. To quantitatively examine BOLD responses, a convolution model was used to fit the time curves. Maximum signal change, FWHM and onset time (defined as the time to the first half maximum) were determined from the fitted curve and compared with the previously published results for 1.5 T. To explore the number of voxels with significant BOLD signal changes (p<0.05, corrected), a correlation analysis was applied. Results: Our result shows the fractional activation volume increases with the BH duration and reaches the plateau at 15‐s which is earlier than the data for 1.5T. Conclusion: Our results suggested the BOLD imaging at 3T was more sensitive for detecting BH induced cerebrovacular reactivity than at 1.5 T. The BH duration of 15 s or above is recommended for clinical use at 3 T, which is an improvement from 20‐s BH at 1.5 T.
SU‐GG‐I‐122: ACR MRI Accreditation Equipment Performance Evaluation for Various Scanner Settings
Authors: Liu Yu
Published: July 2008

Purpose: ACR MRI Accreditation program was created a decade ago for assessing performance by various facilities. Accreditation was voluntary at that time. Recently many stand‐alone MRI imaging centers/clinics seek accreditation because it is now mandatory by some insurance companies. For ACR MRI physics survey/system performance evaluation, it is closely correlated with the equipment performance. It is a challenging task to survey a variety of magnets in different field strength, configurations, and with many software versions/optional packages. The purpose of this work is to summarize ACR MR system evaluation and ACR phantom test experience. Method and Materials: GE, Siemens, Philips, and Hitachi's MRI magnets, in fixed or mobile setup, ranging from 0.3T, 0.7T, 1.0T, 1.5T, to 3.0T are surveyed. Both ACR and site T1/T2 scan protocols are used. Results: It is found that when an MRI scanner is properly maintained, geometric accuracy, slice thickness accuracy, and percent signal ghosting is usually within the limit regardless of fixed or mobile setup, or field strength of the magnet. However, intensity uniformity and low contrast detectability are most demanding for very low field (<0.5T) and 3.0T magnets. At a low magnetic field, it is caused by low signal to noise ratio. For a 3.0T magnet, it is caused by low RF penetration at high field strength, and a much higher acceptable limit for low contrast detectability. In some cases, site protocol for T1 and T2 pulse sequences is required to pass the ACR phantom test. Conclusion: The ACR MRI phantom testing items are designed for different scanner performance criteria. When a testing result is out of the ACR acceptable limit, it is important for the physicist to recognize whether the phantom is not setup properly, or it is caused by scan parameter selection, or a service call is necessary.
SU‐GG‐I‐127: Multiple Stepped Magnetic Field Technique Applied to Enhance the Resolution of Electron Spin Echo Oxygen Imaging (ESEOI) at 250MHz
Authors: Seifi P , Epel B , Sundramoorthy S , Mailer C , Halpern H
Published: July 2008

Purpose: The knowledge of local partial oxygen pressure (pO2) in malignant tumors is important due to the effect of hypoxia, or low oxygen concentration on tumor aggressiveness and response to radiation therapy. Three dimensional ESEOI is one of the few noninvasive modalities that provide a quantitative, spatially resolved measure of pO2 inside tumor. The spatial resolution is defined by the gradient field magnitude and therefore is limited by the imager frequency bandwidth. By using the multiple magnetic field B0 technique (MB0) we have extended the effective bandwidth of the imager and acquired images with better spatial resolution. Method and Materials: A phantom with the same spin probe (OX063H) used for small animal imaging was also employed in this study. Our pulse imager design allows us to use high microwave power and achieve frequency bandwidth of 20MHz. This bandwidth is sufficient to image a 2cm long sample using 50 mT/m gradient in the single B0 (SB0) technique. In the MB0 technique, the same experiment is repeated at multiple B0 values to increase the efficient acquisition bandwidth. Results: Using SB0 and MB0 methods, we obtained 3D images of our phantom with spatial resolution of 0.5mm. This is a large improvement compared to the 1.4mm resolution for current ESEOI protocol and 1.3mm resolution of continuous wave EPROI, both used in small animal imaging. The measured T2 uncertainty was about 5%. Conclusion: The MB0 method was found to be technically more complicated than the SB0 method but less susceptible to instrumental limitations in applying larger gradient fields. These results pave the way for high resolution ESEOI in small animal imaging. This makes ESEOI a more powerful tool for understanding the tumor physiology based on 3D pO2 imaging.
SU‐GG‐I‐130: An Evaluation of Image Quality and Dose for a Hologic Selenia Digital Mammography System with a Tungsten Anode X‐Ray Tube
Authors: Schueler B , Fetterly K
Published: July 2008

Purpose: Image quality and breast dose for an amorphous selenium detector digital mammography system with a tungsten (W) anode x‐ray tube and rhodium (Rh) and silver (Ag) filters were compared to an equivalent model system with a molybdenum (Mo) anode x‐ray tube and Mo and Rh filters. Method and Materials: Signal difference to noise ratio (SDNR) and mean glandular dose (MGD) were measured for 4, 6 and 8‐cm thick breast equivalent material slabs and an aluminum contrast object. Values were compared over a range of kVp and mAs selections for Mo/Mo, Mo/Rh, W/Rh and W/Ag anode/filter combinations. The kVp selection that resulted in the highest SDNR for each thickness and anode/filter combination was determined. SDNR at the optimum kVp for each anode/filter was then compared. The automatic exposure control (AEC) selections for the W and Mo system were also compared with regards to SDNR and MGD. Results: W/Rh was found to produce the highest SDNR over a wide MGD range, followed by W/Ag, Mo/Rh and Mo/Mo. The W anode system provided a 30–35% improvement in SDNR for the same breast dose as compared to the Mo anode system. When the SDNR of the W anode and M anode systems are matched, the W anode system resulted in a 40–50% reduction in MGD. Using the W anode system default AEC for selection of exposure parameters, a 7–25% improvement in SDNR and a 10–30% reduction in MGD was achieved, as compared to the Mo anode system. Conclusion: The W anode system provides superior image quality for the same breast dose. The default AEC for this system provides a compromise between image quality improvement and decreased dose as compared to the Mo anode system.
SU‐GG‐I‐131: Non‐Primary to Primary Ratio Measurements in a Digital Breast Tomosynthesis System
Authors: Shen S , Mainprize J , Mawdsley G , Yaffe M
Published: July 2008

Purpose: For a breast tomosynthesis system using a stationary detector, a standard mammographic anti‐scatter grid cannot be used. As a result, scatter and off‐focal radiation are expected to be high and will negatively impact reconstructed image quality. In addition, phosphor‐based systems can suffer from glare which will further degrade the image. The goal of this project is to quantify the “non‐primary” sources of signal as a function of projection angle to provide information for potential image correction in the tomosynthesis reconstruction. Method and Materials: The scatter, off‐focal and glare components will be evaluated in terms of a non‐primary to primary ratio (NPR). Using a series of tantalum apertures of increasing size, we measured the primary and off‐focal components, and scatter/glare in an open beam. The NPR was then evaluated over typical tomosynthesis projection angles (0° to 25°) for a range of thicknesses of plastic phantoms. Results: The off‐focal to primary ratio is measured to be 0.091. The NPR at 0° was calculated as 0.44, 0.82, and 1.2 for 2, 4 and 6 cm phantoms. A small angular dependence is seen in the NPR, increasing at higher angles. The NPR can be reasonably predicted by an empirical model of NPR versus effective thickness with a maximum error in NPR of 0.022 (4.9% error) over a range of 0° to 20°. At 25° the NPR appeared to increase sharply (5%–9.5% greater than the empirical model). Conclusion: The NPR appears to be weakly dependent on projection angle up to about 20°. Further investigation will involve extending the measurements to a range of kV and filter combinations, and to elucidate the mechanism for increased NPR at highly oblique angles (>20°). Conflict of Interest (only if applicable): Our lab has a research agreement with GE Healthcare regarding several topics in breast imaging.
SU‐GG‐J‐35: Application of a Direct Scatter Correction Algorithm to EPID‐Based Megavoltage Cone‐Beam CT
Authors: Sramek B , Waggener R
Published: July 2008

Purpose: To investigate the application of the Scatter and Primary Estimation from Collimator Shadows (SPECS) scatter correction algorithm to EPID‐based megavoltage cone‐beam CT imaging, and to characterize the qualitative and quantitative effect of algorithm parameter choice on image correction. Method and Materials: A series of EPID projection images were acquired through 200 degree gantry rotation around a 15cm diameter quality assurance test phantom. Using the reconstructed CT images of the sensitometry and uniformity inserts, five SPECS algorithm parameters were tested and the effects on cupping artifacts, contrast‐to‐noise ratio, root mean square error and CT number accuracy were determined. Nominal parameter combinations were then applied to anthropomorphic phantom reconstructions. Results: The algorithm parameter used to define the collimator edge was found to have the largest impact on image reconstruction quality in comparison to the other parameters studied. An investigation of approximately 800 parameter combinations yielded a nominal set of five parameters, which when applied to the reconstruction of the uniformity insert reduced the cupping artifact to less than one percent. Application of the nominal algorithm parameters to the sensitometry insert reconstruction produced improvements in reconstructed CT number in Teflon by 125%, acrylic by 100%, and low‐density polyethylene by 75%, with a slight improvement in the contrast‐to‐noise ratio of acrylic to water. In the anthropomorphic head phantom reconstruction, the average CT number of bone increased from 200 to 670, while the average CT number of soft tissue increased from −200 to −30. Conclusion: This work outlines the application of the SPECS algorithm as an option for scatter correction in EPID‐based megavoltage cone‐beam CT imaging. The algorithm was found to provide a reduction in cupping artifacts and improvement in CT number reconstruction using scatter information derived directly from projection data, without necessitating additional modeling of system and patient‐specific geometrical conditions.
SU‐GG‐J‐37: Assessing Image Guided Radiation Therapy Targeting Accuracy: Coincidence Of Imaging System Isocenter With Treatment Machine Mechanical And Radiation Isocenters
Authors: Saleh H , Pokhrel D , Williamson J
Published: July 2008

Purpose: The purpose of this study is to introduce a method for quantifying the accuracy of linac and imaging system isocenters and demonstrate its use by measuring the targeting of two kilovoltage (kV) imaging systems, and one gantry mounted megavoltage Electronic Portal Imaging Device (EPID). One is the kV imaging system (OBI) integrated with the linear accelerator which supports radiographic and cone beam CT imaging. The other system is the BrainLab Exac Trac stand alone fixed to the treatment room ceiling and floor. Method and Materials: A cylindrical Lucite phantom was designed and fabricated to perform this study. The cylindrical phantom is 20 cm in diameter and 20 cm long. The phantom contains 13 radio‐opaque fiducial markers. A 5 mm spherical marker is positioned at the center of the cylinder. The phantom was imaged and the CT data sets were imported to two planning systems. Treatment beams were placed and both 3D data sets and isocenter information were transferred to the Linac delivery and imaging workstations. For each imaging system, phantom was initially positioned according to machine cross‐hair. Then images were acquired and measured shifts were applied to precisely position the phantom. Then, Winston‐Lutz test was performed for different gantry and collimator configuration. The radiation beam was collimated by a tray‐mounted 30 mm diameter circular collimator. Results: The radius of spherical volume in which all isocenter intersect or lie was measured. For EPID, OBI, CBCT, and Exac Trac, the radius is: 0.54 mm, 1.4 mm, 1.7 mm and 1.46 mm respectively. From the Winston‐Lutz analysis, the average isocenter deviation from all angles is 1.18 ± 0.28 mm. Conclusion: The error in mechanical, radiation and imaging isocenter is about one millimeter. Regardless what imaging system is used for patient setup, it is important to incorporate this systematic error in any planning margins.
SU‐GG‐J‐38: Assessment of Conebeam CT Image Quality in the Presence of An Electromagnetic Tracking System
Authors: Santanam L , Esthappan J , Noel C , Mutic S , Goddu S , Parikh P , Low D
Published: July 2008

Purpose: A novel electromagnetic tracking system is being used for real‐time tracking during treatment delivery. On board cone‐beam CT imaging is routinely being used for real‐time imaging and localization. Concurrent use of these two modalities might prove beneficial for correlating imaging and tracking information. The purpose of this study is to investigate the effect of the presence of the electromagnetic tracking system on the CBCT image quality. Method and Materials: A commercial CT performance phantom (Catphan, Phantom Laboratory, Salem, NY) containing various image quality assessment tools was imaged using a kilovoltage on‐board cone‐beam CT system (Varian Medical Systems, Palo Alto). An electromagnetic tracking system (Calypso® 4D Localization System, Calypso Medical, Seattle, WA) uses an electromagnetic array for tracking transponder positions. The imaging quality assessment phantom was imaged with and without the electromagnetic tracking system in place. To quantify the effect on the image quality, the CT number accuracy, spatial integrity, image uniformity, high and low contrast resolution were compared. Results: CT number accuracy, spatial linearity and high contrast resolution were unaffected by the presence of the array. The visibility of the 1% cylindrical low contrast resolution targets was 15 mm and 7 mm for with and without the array respectively. The inherent streaking artifacts degraded the low contrast image quality significantly.

Conclusion: Presence of an electromagnetic array significantly degrades CBCT low contrast resolution while other image performance parameters are minimally affected. For imaging human anatomy, algorithms to improve image quality may need to be developed. Conflict of Interest: This work is supported in part from a grant from Calypso Medical Systems.
SU‐GG‐J‐41: Automated Estimation of a Tumor Region and Its Displacement On EPID Cine Images Without Implanted Markers in Lung Stereotactic Body Radiotherapy
Authors: Arimura H , Egashira Y , Shioyama Y , Nakamura K , Yoshidome S , Shigeo A , Nomoto S , Honda H , Higashida Y , Onizuka Y , Terashima H
Published: July 2008

Purpose: The purpose of this study was to develop a method for automated estimation of a lung tumor region and its displacement on an electronic portal imaging device (EPID) during lung stereotactic body radiotherapy (SBRT) without implanted markers. Method and Materials: Our method for automated estimation of the tumor region and its displacement was based on a template matching technique with cross‐correlation coefficient between a target template image and each consecutive portal (CP) image, which was acquired in cine mode with the EPID in each treatment. Each target region was segmented in the first EPID cine image, which was referred to as the reference portal (RP) image, based on a multiple‐gray level thresholding technique and a region growing technique, and then a target template image was extracted as “a tumor template”. The displacement vector of a target was determined from the position in which the target template image took the maximum cross‐correlation value within the CP image. EPID images with 512×384 pixels (pixel size: 0.56 mm) were acquired in a cine mode at a sampling rate of 0.5 frame/sec by using x‐ray energies of 4, 6, or 10 MV on linear accelerators. We applied our proposed method to EPID cine images of 12 cases (ages: 51–83, mean: 73) with a non‐small cell lung cancer. Results: For 12 cases, the target displacements obtained by our method agreed with those determined by the manual method by a mean correlation value of 0.839. Each tumor region segmented by our proposed method was overlapped by 60% on average with that determined by the manual method. Conclusion: This preliminary result suggested that our proposed method may be useful for estimating of displacements of target positions without implanted markers in lung SBRT.
SU‐GG‐J‐51: Comparison Between Siemens Standard MV‐CBCT and the Investigational Imaging Beam‐Line MV‐CBCT
Authors: Beltran C , Faddegon B , Bani‐Hashemi A
Published: July 2008

Purpose: To compare the image quality and dose delivered between the standard Siemens MV‐CBCT and an investigational Imaging Beam Line. Method and Materials: Several MV‐CBCT images of a heterogeneity phantom were acquired using the standard 6MV treatment beam on a Siemens Oncor machine. Subsequently, modifications were made to the linear accelerator. The major modifications consisted of replacing the Tungsten target with Carbon, removing the flattening filter and decreasing the beam energy by 25%. The modified imaging beam line (IBL) replaced the highest energy electron treatment beam. Additional MV‐CBCT images were acquired with the IBL. The 6MV beam and IBL were modeled in the treatment planning system and ion chamber measurements were made to ensure proper dose calculations. Results: Standard MV‐CBCTs with isocenter doses of 9.1, 4.9, 3.0, and 1.1cGy were acquired for the 30cm diameter heterogeneity phantom. A 6.1cGy standard MV‐CBCT was acquired for an 18cm diameter heterogeneity phantom. IBL MV‐CBCTs with isocenter doses of 2.2, 1.8, 1.3, 0.9, and 0.4 cGy were acquired for the 30cm diameter phantom. An IBL MV‐CBCT image of 0.6, 1.2, and 3.0cGy was acquired for the 18cm phantom. The contrast and signal to noise ratio (SNR) of the 9.1cGy standard MV‐CBCT is similar to the 2.2cGy IBL MV‐CBCT for the 30cm phantom. For the 18cm phantom, the 6.1cGy standard MV‐CBCT and 1.2cGy IBL MV‐CBCT have similar contrast and SNR. Conclusion: The IBL produces a similar CBCT image quality to the standard method with a reduction in dose by at least a factor of four to five. Conflict of Interest: Supported in part by Siemens Medical USA.
SU‐GG‐J‐60: Constructing a 6 MV Radiotherapy Accelerator with Integrated 1.5T MRI functionality: Status Report
Authors: Raaymakers BW , Lagendijk JJW , Raaijmakers AJE , Kerkhof EM , van der Put R , Kok JGM , van Dijk I , van Vulpen M , Overweg J , Brown K
Published: July 2008

Radiotherapy is increasingly dependent on image data for treatmentpreparation, delivery, response assessment and follow‐up. In collaboration with Elekta, Crawley, UK and Philips, Best, The Netherlands, we are constructing a hybrid 1.5T MRI radiotherapy system. This system facilitates real‐time, soft‐tissue based image guidance during delivery as well as treatment response assesment. The preceeding technical feasibility study led to a design in which the 6MV accelerator can rotate in a ring around the MRI in the mid‐transversal plane. The magnet design is adjusted in order to minimise the magnetic interference and to minimise the absorption of the beam. The prototype is planned for autumn 2008. The aim is to demonstrate MRI guided radiation with sub‐mm precision. The prototype will initially be static: the accelerator will be in a fixed lateral position. The treatment room preparation will be discussed including: creation of entrance route in bunker, faraday cage, cooling and electrical connections for in‐room MRI peripherals and passive magnetic room‐shielding to minimise magnetic interference with neighbouring clinical accelerators. The current Geant4 Monte Carlo simulations on the accelerator output and radiation dosimetry will be verified in the prototype. Geant4 simulations were also used to find suitable IMRT solutions in the presence of a 1.5T field, these will be evaluated experimentally. System related issues addressed will be the radiofrequency interference between the MRI and the accelerator, the geometric correction of images dedicated for this system and the geometrical coupling of the MRI and accelerator coordinate system. Also the automatic, on‐line target definition on MRI and the clinical benefit of MRI guidance will be discussed.
SU‐GG‐J‐67: Detection of Gold Fluorescence X‐Rays for the In‐Vivo Quantification of Gold Concentration During Gold Nanoparticle‐Aided Radiation Therapy (GNRT)
Authors: Siddiqi A , Cheong S , Cho S
Published: July 2008

Purpose: To determine the concentration of gold (Au) nanoparticles presented within the tumor during in vivo demonstration of tumor dose enhancement by detecting gold fluorescence x‐rays. Method and Materials: Gold nanoparticle solution of 1% by weight in saline was prepared using commercially available gold nanoparticles with 1.9 nm core diameter. A cylindrical sample container (2.5 cm in diameter and 5.0 cm in height) was irradiated with 110 kVp and 200 mA x‐rays from conventional radiotherapy simulator for 40 seconds with 1 cm × 1 cm x‐ray beam at 85 cm source‐to‐surface distance (SSD) and spectrum was obtained using either Si‐PIN or CdTe photodiode detector using a container‐to‐detector geometry to minimize unwanted photons entering the detector. Results: The spectrum collected using the Si detector successfully captured the Au Lα and Lβ fluorescence lines at 9.7 and 11.4 keV, respectively, well above the background. Au K lines could not be measured with Si‐PIN photodiode due to Si‐PIN detection inefficiency above 60 keV. To capture the Au K lines, CdTe photodiode detector was employed which has high detection efficiency for energy range of Au K lines. The spectrum collected using CdTe detector clearly showed the Au Kα2, Kα1, and Kβ lines corresponding to energies of 67.0, 68.8, and 77.9 keV, respectively. Conclusion: The magnitude of obtained Kα fluorescence signal (i.e. greater than 50% above all background scattering) is very encouraging considering the tested gold concentration. With more sophisticated geometry to minimize scattered photons reaching the detector, Au fluorescence output from K lines can be used to measure even lower concentrations of gold nanoparticles. Fluorescence output as a function of Au concentration can be developed to accurately measure gold nanoparticle concentration.
SU‐GG‐J‐76: Dosimetric Consequences of Patient Setup Decisions in Image‐Guided Procedures Based On Soft‐Tissue Fiducials for Imaging
Authors: Dieterich S , Schlaefer A
Published: July 2008

Purpose: The purpose of this work is to demonstrate the dosimetric consequences of patient setup and tracking technique decisions for 4D adaptive SBRT treatments. Method and Materials: Clinical fiducial tracking scenarios of 450 SBRT cases, 120 of them treated with 4D adaptive SBRT, were analyzed and classified into different case scenarios. A flowchart was created to systematically display each clinical tracking scenario and the decision options. Based on the flowchart, scenarios which could cause a deviation from delivered dose to planned dose were identified. For these situations, each tracking decision was evaluated for dosimetric impact by simulating the situation in treatment planning software using a patient CT and an artificially created elliptical tumor. Results: Only two clinical scenarios were identified as having dosimetric consequences. One scenario contains tumors which rotate significantly (>5 degrees) during the respiratory cycles. For rotations smaller than 5 degrees we saw no differences in the DVH than non‐rotating tumors. For tumors with rotation angles larger than 6 degrees, the DVH shows increasing, but still small, tumor underdose. The second scenario with potential dosimetry changes was a small rotational change (<5 degrees) of the tumor position relative to the global patient position. Our calculations show that changing the global patient position to move the tumor into the treatment field did change the DVH, because the SSD and obliquity of incoming beams changes. A third tracking scenario was identified in which a repeat simulation is necessary. Conclusion: Fiducial setup and rotational tumor tracking decisions for SBRT treatments were classified. Dosimetric impact was studied for the two relevant class decisions. A class of patients which needed re‐CT was identified. Our flowchart and dosimetry studies will help in the future to systematically identify and address soft‐tissue fiducial tracking scenarios and choice of tracking technique for SBRT.
SU‐GG‐J‐84: Evaluation of Comparing Daily Ultrasound Images with a Reference Ultrasound Image for Prostate Localization
Authors: Brandner E , Specht R , Bahri S , Poltinnikov I , Huq M
Published: July 2008

Purpose: To evaluate if acquiring an ultrasound image at the time of CT simulation for comparison with daily ultrasound images improves daily localization of prostates. Method and Materials: Resonant Medical's® ultrasound localization system was installed and implemented in our clinic. The technique relies on acquiring a 3D ultrasound image at the time of CT simulation for daily comparison whereas other ultrasound localization techniques compare daily ultrasound images to the original CT image. Treatment planning is done on the CT. DRRs are also constructed from the CT, and fiducials implanted in the prostate are outlined on the DRRs. Each day a 3D ultrasound image was acquired and compared to the ultrasound that was acquired at the time of CT simulation. Daily, if the ultrasound image was approved by the physician, the couch was shifted to align the current prostate location with its location at the time of simulation. After the ultrasound, ports were taken as often as prescribed by the physician. The fiducial locations as seen in the ports were compared to their locations on the DRRs. Any necessary shifts were made to align the fiducials. Following the treatments, an analysis was made of the ultrasound localization as compared to the fiducial localization. 22 patients had 7 or more days in which both ultrasound and ports of fiducials were acquired and are included in this analysis. Results: The measured average difference between the ultrasound localization and the localization based on ports of fiducials is 7.2 mm. This is comparable to what is reported in literature for other ultrasound localization techniques. Conclusion: Using a 3D ultrasound image acquired at the time of CT simulation does not improve ultrasound localization accuracy as compared to techniques that compare daily ultrasound images to the simulation CT for localization.
SU‐GG‐J‐88: Evaluation of Patient Setup Accuracy for Targeted Marrow Irradiation with Image‐Guided Helical Tomotherapy
Authors: Han C , Liu A , Schultheiss T , Wong J
Published: July 2008

Purpose: Targeted marrow irradiation (TMI) using intensity‐modulated fields could allow dose escalation while limiting radiation toxicities to critical organs for patients who traditionally would receive total body irradiation. In this study, we evaluated patient setup uncertainties and the efficacy of our image‐guided setup techniques for TMI treatments based on helical tomotherapy megavoltage CT image registrations. Method and materials: We analyzed image registrations from 206 treatment fractions for 26 TMI patients. Prior to each treatment fraction, two MVCT scans were performed encompassing the head & neck region and the pelvic region, respectively. image registrations were performed for each scan. The two image registrations were averaged to correct patient setup errors. Results: In the head & neck region, the mean and standard deviation (SD) of setup corrections was 3.5±6.4 mm in the RL direction, −2.4±5.3 mm in the SI direction, −0.7±5.8 mm in the AP direction, and 0±1.2° in roll. In the pelvic region, it was 1.5±7.7 mm in the RL direction, −3.7±5.6 mm in the SI direction, 2.1±5.7 mm in the AP direction, and 0±1.1° in roll. After the two registrations were averaged, it was 2.5±6.6 mm in the RL direction, −3.1±5.1 mm in the SI direction, 0.7±5.1 mm in the AP direction, and 0±0.8° in roll. The residual setup errors in the head & neck region had mean and SD of 1.0±2.5 mm in the RL direction, 0.7±1.9 mm in the SI direction, −1.4±2.7 mm in the AP direction, and 0±0.8° in roll. Conclusion: The two‐scan technique ensured that the superior and inferior portions of the patient bony structure were properly set up in most cases. In cases when the residual setup errors were significant, the superior and inferior segments should be treated separately with separate setup corrections to ensure adequate target volume coverage.
SU‐GG‐J‐93: Feasibility Study On Artifact Reduction Using Dual Energy Digital Tomosynthesis
Authors: Baydush A , Godfrey D , Segars W
Published: July 2008

Purpose: We propose a simulation study to examine the feasibility of incorporating dual energy (DE) subtraction with digital tomosynthesis (DTS) to help reduce DTS reconstruction artifacts. Method and Materials: We have previously investigated the incorporation of DTS into radiation therapy for patient localization and found the initial results promising. Due to the limited sampling of the Fourier space, high contrast signals, such as bone, tend to bleed into other slices of the reconstruction. These artifacts could be misconstrued or reduce the conspicuity of low‐contrast signals, especially in the lungs. For this simulation study, an advanced 4D NURBS based Cardiac‐Torso (NCAT) phantom, which includes a detailed whole‐body anatomy of organs including the lungs, airway tree, heart, and vessels, was used. When combined with advanced models of the imaging process, the NCAT phantom can produce realistic imaging data. For this study, a unique x‐ray projection algorithm developed specifically for the NCAT phantom was used to generate limited angle projection data for DTS reconstruction. 81 images were acquired over a 40 degree arc. The breathing cycle was set to simulate breath‐hold imaging. Data sets were generated using spectra of 80 and 120 kVp. For this study, dual energy subtraction (DES) was performed on these two sets of limited angle images to remove the overlying bony anatomy. The resulting images were then reconstructed using a modified filtered back projection technique. This DE‐DTS volume was then visually compared to a standard DTS reconstruction of the 120 kVp data set. Results: The removal of the overlying bony anatomy of the chest in the DE‐DTS images helps to reduce the high contrast artifacts present in the standard DTS reconstruction. Conclusion: This feasibility study demonstrates that DE‐DTS imaging may provide increased visualization of low contrast regions in the chest by reducing high contrast DTS reconstruction artifacts.