bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐C‐WAB‐04: Auto‐Contouring Accuracy in the Presence of a Rectal Balloon
Authors: Godley A , Stockham A , Stephans K
Published: July 2013

Purpose: To determine if the presence of rectal balloons improves the accuracy of prostate and rectum auto‐contouring on kV cone‐beam CTs (CBCTs). Methods: Seven patients undergoing five fraction prostate SBRT were selected. Rectal balloons were placed and consistently inflated at simulation and treatment to increase organ stability and reproducibility. All five pre‐treatment CBCTs were contoured using ABAS (Elekta) which deformably registers the plan CT or previous CBCTs to the current CBCT and then morphs their contours according to this deformation field. Six patients undergoing 40 fraction prostate IMRT without rectal balloons were also chosen. Nine fractions each were contoured similarly with ABAS. All scans were manually contoured by a physician and Dice Coefficient (DC) calculated between the physician and auto‐contours as our measure of accuracy. Results: Average accuracy of auto‐to physician rectal contours significantly improved with rectal balloons from DC of 0.85 to 0.91 (P<0.0001). The prostate contour accuracy also improved from DC 0.84 to 0.88 (P=0.0016). Balloons reduced variability between the plan and treatment image, allowing the registration to successfully recover the deformation and morph the contours. Bladder filling is the overriding factor in its auto‐contouring, so its accuracy is not affected by the rectal balloon, DC 0.91 with, 0.92 without. Prostate auto‐contouring was more accurate than the intra‐observer agreement DC of 0.83, and consistent with the bladder agreement of 0.92. The rectal balloon significantly boosted intra‐observer agreement from 0.85 to 0.97 (P<0.001). This is higher than auto‐contouring accuracy, indicating it could be further improved. Visually the tissue air boundary is clear but CBCTs have a scan dependent, ∼5 mm border of rapidly rising intensity that currently confounds the deformation. Auto‐contours are produced in ∼20 seconds. Conclusion: The use of rectal balloons significantly improves the accuracy of prostate and rectum auto‐contours on daily CBCTs, enabling online adaptive therapy. A research version of ABAS was provided by Elekta AB, Stockholm, Sweden
SU‐C‐WAB‐07: Normalized Distance Discordance (DD): A Quantitative and Position‐Specific Metric to Evaluate the Uncertainty of Inter‐and Intra‐Patient Deformable Registrations
Authors: Saleh Z , Apte A , Sharp G , Wang Y , Deasy J
Published: July 2013

Purpose: Quantitative tools to estimate the uncertainty in deformable image registration are lacking. Distance discordance(DD) is a quantity that we have defined, and is an estimate of the mean error (measured in terms of distance) due to deformable image registration. This abstract presents a refined method of estimating distance discordance that improves accuracy. Methods: Starting from an arbitrary reference image [i] in a set of images [1…n], voxels are traced from any two moving images [j] and [k] that happened to be registered at the same voxel on [i] to other reference images in the image set. The difference between each pair of points is recorded in the Cartesian coordinate system (dx,dy,dz). The mean of the difference (, , ) is subtracted from the original difference in order to calculate the unbiased distance between these pair of points and which corresponded to distance discordance metric. Experiments using this new approach were evaluated in a set of 8 different head and neck patients. Results: The 3D spatial map of the mean DD metric showed a variation among anatomical sites in the head and neck region. Regions of high contrast (bones) showed a lower mean DD value (2—13 mm) while regions of low contrast (soft tissue) had a larger mean DD value (6—19 mm). The shape of the dose discordance histogram (DDH) for some anatomical structures followed a log normal distribution with a long tail while others had irregular shape. Conclusion: The updated DD metric gives an unbiased measure of the spatial uncertainty in image registration in the absence of a ground truth. For instance, the DD maps can be used to set a level of confidence for dose accumulation in adaptive radiotherapy. However, the DD metric provides a necessary but not a sufficient condition to ensure good registration. Partially supported by NIH grant R01 CA85181; href=http://soundfrost.org/>download free<
SU‐C‐141‐03: Assessing ITV and PTV Coverage for Mobile Tumors with Real‐Time Fluoroscopy Imaging
Authors: Mooney K , Chen S , Feigenberg S , D' Souza W
Published: July 2013

Purpose: To evaluate the appropriateness of the internal target volume (ITV) and planning target volume (PTV) generated based on 4DCT simulation using real‐time kV fluoroscopic imaging. Methods: 4DCT scans of a moving (3D) phantom with implanted fiducials were acquired using three‐dimensional lung tumor locations derived from Cyberknife Synchrony system log files. Data from 5 patients consisting of tumor trajectories derived from the Synchrony model and from three different treatment fractions were used in this analysis. All patients in this study had a peak‐to‐peak respiratory amplitude between 7–15mm. The fiducials were contoured on ten phases of the 4DCT scans, and ITVs and PTVs (ITV+5mm) were created for each marker. Fluoroscopic images were acquired for all trajectories at a rate of 15Hz for 20–30 seconds in two imaging planes: anterior‐posterior and lateral. The markers were tracked using the Varian Intra‐fraction Motion Review (IMR) software, using a reference movie frame in which marker locations were matched against their corresponding positions on the DRR. The tracked marker positions were classified as within the ITV, between the ITV and the PTV, and outside the PTV in each frame. Results: The fiducial was detected inside of the ITV in 82.4% (71.7%) of frames in the lateral plane (AP plane), between the ITV and PTV in 17.4% (28.0%) of lateral (AP) frames, and detected outside the PTV in 0.2% (0.3%) of lateral (AP) frames. When the marker was between the ITV and the PTV, the distance from marker to ITV was >3mm in 21% (27%) in lateral (AP) plane images. Conclusion: We have developed a method to quantify the degree to which the planned ITV and PTV encompass the extent of tumor motion. The tumor was detected outside of the ITV more often in the AP‐plane of imaging, and detected within the PTV in nearly all cases. Varian Medical Systems
SU‐C‐141‐05: Impact of Respiratory‐Correlated CT Reconstruction Algorithms in the Choice of Margin Definition for Free Breathing Lung Treatment
Authors: Thengumpallil S , Germond J‐F , Matzinger O , Bourhis J , Bochud F , Moeckli R
Published: July 2013

Purpose: To investigate the impact of phase‐and amplitude‐based reconstruction algorithms in 4D treatment margin strategies in presence of respiratory irregularities. Methods: 4D CT images of Dynamic Thorax Phantom were acquired and the respiratory signal was tracked by the belt. Three irregular breathing patterns were simulated: amplitude, frequency, and combined amplitude and frequency variations. 4D CT image artifacts were analyzed for the phase‐and amplitude based reconstruction algorithms. To assess the impact of the 4D CT image artifacts on the dose distribution, twelve plans (three simulated breathing models for the two reconstruction algorithms and for the two margins strategies) were calculated with a Monte Carlo based TPS. The lung tumor was delineated according to the mid ventilation and the ITV‐based strategy. All the plans were evaluated for Dmin, Dmax, Dmean, homogeneity index and conformity index. Results: The amplitude‐based reconstruction shows a significant reduction of artifacts compared to the phase‐based only for breathing amplitude variations. Most of the observed artifacts are image blurring and incomplete structures. The dosimetric analysis shows that the mid‐ventilation strategy provides better tumor coverage than the ITV‐based strategy. In the mid‐ventilation strategy the selected phase is close to the exhale phase which is less subject to motion artifacts. In the ITV‐based strategy the influence of motion artifacts is more pronounced due to the contribution of different phases and leads to a blurred dose distribution. Conclusion: Amplitude‐based reconstruction algorithm reduces image distortions in the particular case of amplitude variations but not when frequency variations are present. Based on the impact of image artifacts on the definition of margin strategies we showed that the mid‐ventilation strategy is more robust than the ITV‐based strategy. The ITV‐based strategy is more prone to image artifacts which cause significant degradation in the dose distribution compare to the mid ventilation.
SU‐C‐141‐06: Registration Accuracy with Four‐Dimensional Cone‐Beam CT for Lung Cancer Treatment
Authors: Haga A , Kotoku J , Kida S , Masutani Y , Yamashita H , Takahashi W , Imae T , Nakagawa K
Published: July 2013

Purpose: A four‐dimensional (4D) cone‐beam CT (CBCT) is widely implemented in the image‐guided radiation therapy (IGRT) for lung cancer treatment. Recently, we established a verifying system using in‐treatment 4D CBCT acquired during Volumetric Modulated Arc Therapy (VMAT). With this system, we assess the registration accuracy with pre‐treatment 4D CBCT for IGRT. Methods: Fifteen lung cancer patients treated with single‐arc VMAT were selected in this study. The breathing condition of all patients was constrained with a stereotactic body frame (ELEKTA) accompanied by abdominal compression plate. The gross tumor volumes were contoured on 10 CT datasets from 4D CT (TOSHIBA and ANZAI) and merged into internal target volumes (ITVs). The planning target volume (PTV) margin was isotropically taken as 5 mm. The patient registration was performed by an Elekta x‐ray volume imaging functionality version 4.5 (XVI ver.4.5), which allows to use 4D CBCT respiratory sorting for registration. The VMAT treatment was performed with simultaneous acquisition of the kV projection images. The in‐treatment 4D CBCT was reconstructed by in‐house software. The reconstructed images were exported to a treatment planning system. To assess set‐up errors and respiratory motion, the displacement of tumors between the planning ITV and the shadow of the tumor in in‐treatment 4D CBCT images was measured in CC, left‐right (LR), and anterior‐posterior (AP) directions. Results: The average displacements between the ITV and the actual tumor location during treatment were 0.24 +/− 0.45, 0.19 +/− 0.46, and 0.42 +/− 0.43 mm for the CC, LR, and AP directions, respectively. The discrepancy in each phase did not exceed 3 mm in any direction. Conclusion: With in‐treatment 4D CBCT, which is a direct method for quantitatively assessing the intrafractional location, we confirmed that the required PTV margins were 3 mm when the registration was performed using pre‐treatment 4D CBCT. This work was supported by JSPS KAKENHI 22791176.
SU‐C‐141‐07: A Mass‐Conserving 4D XCAT Phantom Enabling Normal Tissue Deformable Dose Accumulation
Authors: Williams C , Mishra P , Seco J , St. James S , Wagar M , Mak R , Berbeco R , Lewis J
Published: July 2013

Purpose: The XCAT phantom is a realistic 4D digital torso phantom that is widely used in imaging and therapy research. However, lung mass is not conserved between respiratory phases of the phantom, making detailed dosimetric simulations unphysical. A framework is presented for enforcing local mass conservation in the XCAT lung and is combined with a dose calculation algorithm to create a tool for dose accumulation studies. As an application of this technique, the impact of irregular breathing on 4DCT‐based predictions of accumulated lung dose is assessed. Methods: A displacement vector field (DVF) between a respiratory state and a reference image is directly determined from the XCAT motion model and its divergence is used to correct the lung density. A series of phantoms with regular and irregular breathing (based on patient data) are generated and corrected. Monte Carlo simulations of conventional and SBRT treatments are performed, and the dose is deformed and accumulated. A 4DCT is simulated for the irregular breathing patient, and the 4DCT dose calculation is compared with the full accumulated delivered dose. Results: The presented framework successfully conserves mass in the XCAT lung. The spatial distribution of the lung dose was qualitatively changed by the use of mass conservation; however the DVH does not change significantly. The comparison of the delivered dose with the 4DCT‐based prediction shows similar lung metric results, however dose differences of 10% can be seen in different regions of the lung. Conclusion: The XCAT phantom has been successfully modified so that it conserves lung mass during respiration, enabling it to be used as a tool to perform dose accumulation studies in the lung without relying on deformable image registration. These studies can reveal potentially significant differences between the predicted dose and the actual delivered dose. The software is freely available from the authors. The project described was supported, in part, by an RSNA Research Scholar Grant and Award Number R21CA156068 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the RSNA, National Cancer Institute or the National Institutes of Health.
SU‐C‐103‐01: An Optical Tracking and Positioning System for Proton Therapy
Authors: Hsi W , Laws A , Schreuder A
Published: July 2013

Purpose: An optical tracking and positioning system (OTPS) for proton therapy was developed to study the characteristics of robotic couch movement and the trend of inter‐fractional displacements on positioning patients treated for prostate or brain cancers. Methods: For patient localization, required movements of couch must be precisely executed. Commercial robotic couch with software‐driven six‐degree isocentric freedom was utilized in our clinic. To align couch rotating center within 1 mm to proton beam, movements of couch without or with patient loads were accurately measured within 0.5 mm without and by the OTPS; including a stereoscopically infrared camera and rigid body tools. To investigate large 10 mm inter‐fractional couch displacements with 5.0 mm standard deviation (S.D.) observed on one patient using head mask for immobilization, a mathematic formula, referred to as 3PtTrack method, was developed for studying the trend of inter‐fractional patient movements within head mask. Results: Typical 4.0 mm circular couch displacements were measured at horizontal plane while displacements were 2.0 mm at vertical plane; however, large 20 mm circular displacements were observed at Procure first clinic couch. After applying software‐driven ISO alignment, residual displacements at couch rotation were 0.3 mm. 85% of movements with patient loads on couch were within 0.5 mm to required values at horizontal plane. The 3PtTrack method could place daily QA device to required location within 0.5mm over a period of 3 months. Movements within mask were found to be similar (both less 5.0 mm with 2.0 mm S.D.) for two patients with largely different couch displacements. Conclusion: The couch rotation was well aligned to proton beam by using OTPS. Movements with patient loads were accurately executed. Large couch displacements presented an issue of fixation on head mask to couch, while smaller movement measured by 3PtTrack indicate that patients still moved with masks.
SU‐C‐103‐02: Localization Accuracy of a Novel Prone Breast Stereotactic Immobilization and Localization System
Authors: Mutaf Y , Yu C , Nichols E , Yi B , Prado K , D' Souza W , Regine W , Feigenberg S
Published: July 2013

Purpose: The GammaPodTM stereotactic radiotherapy device incorporates a novel stereotactic immobilization system and a fiducial based localization frame for the breast. We present the localization accuracy achieved with this stereotactic system through an IRB approved prospective protocol. Methods: GammaPodTM target localization is achieved using a dual layered immobilization breast cup under a negative pressure which has a built‐in stereotactic frame. Patient CT scans were attained using a pivoted patient loader which automatically lowers the patient from a vertical position to a horizontal prone‐lying position. We then performed two CT scans 30 minutes apart, simulating the pre‐treatment imaging and treatment sessions. The patient is disconnected from the patient loader after the first scan, but the immobilization cup remains on the breast under 150 mmHg of negative pressure until the end of the second scan. Evaluation of target localization was carried out via previously implanted surgical clips (two to five) and superficially positioned markers (three to seven). Scans were performed with 1 mm CT slice thickness. Results: The first 9 patients' results are presented with a total of 25 patients expected. Two patients were excluded due to improper fitting of the breast cup and patient comfort; one patient was excluded due to loss of breast cup pressure between the two scans. In the remaining six patients, the spatial reproducibility of internal markers was found to be 1.2 ± 1.0 mm (range 0.3−3.7) in between the two scans while the external marker positions differed by 0.9 ± 0.9 mm (range 0.1−3.9). The intrinsic accuracy of the stereotactic localization system found to be 0.1 ± 0.1 mm. Conclusion: The GammaPodTM target localization system is a unique approach to breast immobilization employing stereotactic principles. Preliminary results of this study suggest that the overall localization uncertainty of this system is 2.8 mm (95% CL).

C. Yu and W. Regine have financial interests in Xcision Medical Systems.
SU‐C‐103‐03: Online CBCT Guided Prostate Cancer Radiotherapy: Is 3 Mm Target Margin Adequate?
Authors: Qin A , Sun Y , Liang J , Tyagi N , Yan D
Published: July 2013

Purpose: Evaluation of treatment dose for daily CBCT guided prostate cancer radiotherapy. Methods: 25 prostate cancer patients treated using daily IGRT with the total dose 64Gy in 20 fractions were retrospectively studied. IMRT plan was created with 3 mm CTV to PTV margin, where CTV was defined as prostate alone for low risk patients and prostate plus seminal vesicles for intermediate or high risk patients. Daily CBCT was performed before delivery for target (prostate with implanted radio‐markers) localization and translational correction. Additional CBCT was taken immediately after the treatment, and used in the treatment dose construction. For each patient, deformable registration between the pre‐treatment helical CT and the post‐treatment CBCTs was performed. The treatment dose in each organ was accumulated using the displacement vector field and the daily dose recalculated on daily CBCT. Dose‐volume parameters, as well as EUD, from both the planned and delivered doses for the CTV, rectum and bladder were used in the evaluation. Results: Evaluation of 11 patients, 4 low risk and 7 intermediate/high risk, has been completed so far. The EUD for CTV was in [61.0%, 100.3%] of the planned target dose with mean±sd = 93.7±11.4%, D99 in [77.9%, 100.1%] with mean±sd = 91.9±5.9%, D95 in [93.8%, 100.5%] with mean±sd = 97.1±2.3%. Large target dose reduction (> 10% on the CTV EUD) occurred for two patients(> 15%), and both appeared at the posterior and superior edges of the CTV. For rectum, the treatment EDU is in [80.0%, 96.8%], with mean±sd = 88.8±6.1%. The bladder EUD is in [98.1%, 131.1%] with mean±sd = 112.1±10.2%. Conclusion: The evaluation shows that 3 mm target margin is inadequate to compensate for intra‐treatment target motion in the prostate cancer treatment with daily CBCT guided target localization and correction. More than 15% of patients could have marginal missing without a validated intra‐treatment motion management. This research is partially supported by Elekta R&D fund.
SU‐C‐134‐04: Accuracy of Material Decomposition Calculations by Gemstone Spectral Imaging
Authors: Scott A , Zhou Y , Allahverdian J
Published: July 2013

Purpose: To measure energy‐specific CT number and effective Z accuracy for a variety of simulated tissues and to measure iodine concentration accuracy, using Gemstone Spectral Imaging (GSI). Methods: We used a GE CT 750HD scanner and CIRS electron density phantom; the phantom is solid water with inserts simulating lung, bone, and soft tissues and has a syringe insert for iodine solutions. We used the GE GSI‐49 protocol to scan and the GSI Viewer software to calculate effective Z, iodine concentration, and CT number between 40 and 140 keV. CIRS provided the mass density, true effective Z, and elemental composition of each phantom material and true CT numbers at matching energies were calculated using XCOM. Results: The deviations between measured and calculated CT numbers varied from ‐ 610 HU (dense bone at 40 keV) to almost 0 HU (liver at 100 keV). For most materials the greatest divergence occurred at 40 keV and decreased with increasing energy to a stable error at 80 or 90 keV. The dense bone and lung had the greatest deviation, which did not stabilize until 130 or 140 keV. The calculated effective Z was accurate for trabecular bone and muscle, but with errors of approximately 10% for dense bone, breast, liver, and adipose tissue (GSI cannot measure Z for lung). Iodine concentrations were accurate within 10% for 38 mgI/cc and lower concentrations. Conclusion: Our results show large inaccuracies in CT number for dense bone and lessened accuracy for most materials at energies less than 80 keV, but the RMS error is reduced by a factor of 2 – 4 when using 80+ keV data only. The effective Z of each material was within approximately 10%. Iodine concentration accuracy was within 10% for the lower concentrations. Altogether, clinical applications requiring 1–5% accuracy may not be feasible.
SU‐C‐116‐06: Evaluation of Image Quality in Digital Mammography and Digital Breast Tomosynthesis: Phantom Observer Study From American College of Radiology Imaging Network PA 4006
Authors: Thomas M , Matsutani Y , Conant E , Maidment A
Published: July 2013

Purpose: Determine contributing factors for image quality in 2D and 3D from comparison of phantom scores and image acquisition parameters. Methods: Tomosynthesis 2D and 3D quality assurance images of the ACR Mammography Accreditation Phantom were obtained as part of the American College of Radiology Imaging Network PA‐4006 trial. Imaging was performed on Selenia Dimensions (Hologic, Bedford MA) systems at the Hospital of the University of Pennsylvania (n=176) and Einstein Medical Center, Philadelphia, PA (n=70). Four trained observers scored all available images according to manufacturer's instructions; image order was randomized by case number and modality for each observer. For tomosynthesis, observers selected the slice level maximizing conspicuity. Paired t‐test compared FFDM and DBT cumulative scores by site, multivariate regression related device parameters to image quality, and multi‐observer Kappa assessed interobserver agreement. Results: Fiber scores were higher for 3D than 2D at site B (p<0.001) with no difference at site A. Speck and mass scores were greater for 2D than 3D at both sites (p<0.001). At site A, regression analysis demonstrated positive correlation of exposure (mAs) with 2D mass, 3D fiber and 3D mass scores; no significant correlations were found for site B. Absolute level of interobserver agreement was highest for specks, followed by fibers and masses. There was substantially lower inter‐observer agreement for specks in 3D than 2D; the agreement between 2D and 3D for fibers and masses did not change significantly. Conclusion: Phantom scores differed significantly between 2D and 3D imaging; fibers were better visualized in 3D, while specks and masses were better visualized in 2D. Observers stated that scoring specks in 3D was more challenging; this is supported by the observation that inter‐observer agreement was significantly poorer in 3D than 2D only for specks. There are many factors that influence scoring. While phantom score was partially predicted by exposure, other factors were involved.
SU‐E‐I‐10: Dose Measurement Methodology for Dental Cone‐Beam CT
Authors: Deman P , Atwal P , Duzenli C , Thakur Y , Ford N
Published: July 2013

Purpose: Dental Cone Beam CT (CBCT) was introduced to perform 3D high resolution imaging at lower dose than multi‐slice CT (MSCT). No consensus has been found to measure the dose delivered by this equipment, unlike the CTDI measurement used for the narrow beam MSCT. The goal of this study is to determine the suitability of the dosimetry methods published in AAPM Report 111 for dental equipment. Methods: A protocol derived from one proposed by Dixon et al. was applied to dose measurements of MSCT, dental CBCT (small and large fields of view) and a dental panoramic system. The CTDI protocol was also performed on the MSCT to compare both methods under different scanning conditions. Experiments were executed to characterize the dose distribution using a thimble ionization chamber (dose free‐in‐air, dose in a CTDI phantom) and gafchromic film (beam profiles, dose in an anthropomorphic phantom). Experiments were performed on the CBCT with a CTDI head phantom alone and with the head phantom placed on a body phantom to measure the importance of scattered radiation due to the chest. Results: The dose measured in the centre of the phantom and field of view from the large field of view dental CBCT (11.4 mGy/100mAs) is 2 times lower than that of MSCT (20.7 mGy/100mAs) for the same FOV, but approximately 20 times higher than for a panoramic system (0.6 mGy/100mA.s). The impact of scattered radiation due to the chest phantom measured with the Dixon et al. method was not significant. The dose distributions measured with the PMMA phantom and the anthropomorphic phantom were similar. Conclusion: Although the dose delivered by the dental CBCT was reduced by a factor of 2 compared to MSCT for the same field of view, it is approximately 20 times higher than the dose delivered by the panoramic system.
SU‐E‐I‐13: Theoretical Modeling of the Variations of CT Number Distributions for Mobile Targets in Cone‐Beam Computed Tomographic Imaging
Authors: Ali I , Alsbou N , Algan O , Herman T , Ahmad S
Published: July 2013

Purpose: To investigate quantitatively variations in CT number distributions of mobile targets in cone‐beam CT (CBCT) imaging. A mathematical model was developed to predict variations in the CT number distributions and their dependence on motion parameters of mobile targets. Materials and Methods: CBCT images were acquired for three targets manufactured from homogenous water‐equivalent gel inserted into a commercial mobile thorax phantom. The phantom moved with controlled cyclic motion patterns in one‐dimension along the superior‐inferior direction to simulate patient respiratory motion. Profiles of the CT number distributions of the static and mobile targets were obtained using CBCT images. Mathematical modeling was developed to predict the variations in CT number distributions and their dependence on the motion parameters of targets moving in one‐dimension using CBCT imaging. Results: The mathematical model of CT number distributions of mobile targets in CBCT reproduced the measured CT number distributions and predicted their dependence on the target size and phantom motion parameters such as speed, amplitude, phase and frequency. The extension of the CT number distribution increased linearly with range of motion in the direction of motion. Motion frequency and phase play important role in spatial and level variations of the CT number distributions. The CT number levels of the mobile targets were smeared over a longer distribution and CT number level dropped in comparison with the distribution of stationary targets. Conclusion: The CT number distributions varied considerably with motion in CBCT. The mathematical model of CT number distribution for mobile targets developed in this work predicted well variations in the measured CT number profiles and their dependence on motion parameters. The CT number distributions spread‐out along the direction of motion and CT number level decreased. This quantitative characterization of motion artifacts on CT number distributions in CBCT may have potential application in diagnostic imaging and radiotherapy.
SU‐E‐I‐14: Improvement of Four Dimensional Cone Beam CT Image Quality with Iterative Reconstruction
Authors: Kida S , Nakano M , Masutani Y , Nakagawa K , Haga A
Published: July 2013

Purpose: Four‐dimensional cone beam CT (4D‐CBCT) is well known as powerful modality for image guided radiation therapy. Conventionally, it is reconstructed by sorting the X‐ray projection images into each respiratory phase according to a breathing signal using the FDK algorithm. This usually leads to inadequate number of projections in each phase, resulting in low quality 4D‐CBCT images with obvious streaking artifacts. We tried to improve the image quality for 4D CBCT using iterative reconstruction method (ML‐convex) and compared with the images by FDK in SNR of the reconstructed images. Methods: We used ML‐convex algorithm, which has the ability to reconstruct CBCT images from a few number of noisy x‐ray projections by taking knowledge of x‐ray photon statistics into account. We compared the image quality of 4D CBCT by ML‐convex with that by FDK using projection images acquired with different rotational speeds by XVI 5.0 (Elekta). Projection images were sorted by 10 phases for both reconstruction algorithms. A phantom study and patient study were performed. The convergence rate and reconstruction accuracy were evaluated using Catphan‐600 physical phantom. Results: Image quality of 4D‐CBCT is substantially enhanced by the ML‐convex algorithm. Streaking artifacts, commonly presented in the image reconstructed by FDK algorithm, are almost suppressed in spite of the small number of projections. Quantitative evaluations indicated that, compared with the FDK results, ML‐convex method improves signal‐to‐noise‐ratio (SNR) and reconstructed more accurate CT value. Conclusion: The ML‐convex algorithm yielded images with higher SNR and more accurate CT value than those produced by FDK algorithm. This Result will enable us to apply 4D CBCT by ML‐convex algorithm to Image Guided Adaptive Radiation Therapy and patient daily CBCT‐based treatment localization in real clinical environments with the higher computational efficiency.
SU‐E‐I‐15: To Study the Feasibility of Contouring the Planning Organ at Risk Volume for Heart Based On KV‐CBCT Images
Authors: Gong G , Liu C , Yin Y
Published: July 2013

Purpose: To study the feasibility of contouring heart planning organ at risk volume (PRV) on KV ‐ Cone‐beam CT images,and measure the margins for the PRV of heart based on planning CT images. Methods: 15 early stage non‐small cell lung cancer (NSCLC) patients accepted radiotherapy in our hospital were selected. For every case,KV‐CBCT scan was achieved before every fraction treatment to correct the setup error,and the first 10 serious CBCT images were selected in present research. After contouring the heart on CBCT images according to the same standard,compared the differences of heart between CT and KV‐CBCT,analyzed the reproducibility of contouring the heart on different serious CBCT images,measured the margins in different axial direction from heart on planning CT to CBCT. Results: The heart volume of planning CT was smaller than CBCTs with statistical difference (p<0.05), and the volumes based on different serious CBCT images were similar for every patient (p>0.05). The coincidence of the hearts region on the same anatomical section between the first serious CBCT and others serious could reach to (0.985±0.020) without statistical significant difference (p>0.05). The mean margins for heart from planning CT to CBCT was (10.5 ± 2.8mm) in left direction, (5.9 ± 2.8mm) in right direction, (2.2 ± 1.6mm) in head direction, (3.3 ± 2.2mm) in foot direction, (6.7 ± 1.1mm) in the anterior direction, (4.5mm ± 2.5mm) less in the posterior direction; respectively. Conclusion: The PRV of heart contouring based on KV‐CBCT was feasible with good reproducibility. If there were no CBCT,11mm in left direction,6mm in right direction,3mm in head‐foot direction,7mm in the anterior direction, and 5mm in posterior direction should be applied to obtain the PRV of heart.
SU‐E‐I‐20: Simulated Multi‐Protocol CT Imaging with Patient‐Derived Numerical Phantom Towards Patient‐Specific Scan Protocol Optimization
Authors: Yang Z , Jin H , Kim J
Published: July 2013

Purpose: Optimizing scan protocols for individual patients and exam of interest is clinically demanding, and yet challenging task. This study presents a simulated CT imaging technique with patient‐derived numerical phantom which enables exploration of combination of protocols that might lead to a condition for dose‐effective and acceptable image quality without repeated scanning patient with multiple protocols. Method: From a wholebody patient CT scan, 24 different tissue types were segmented semi‐automatically. Spectral attenuation properties of tissue types were referenced from NIST, and natural state density of each tissue was referenced from the literature. X‐ray spectra of various KVp were generated by using an existing TASMIP model. Projection/filtered‐backprojection process in fan‐beam geometry taking quantum noise into account were computed to generate simulated CT images for any combination of KVp, mAs, and slice thickness. In order to mimic real CT images, filter kernels were derived from measured MTFs of a commercial CT(Sensation 16, Siemens). Developed technique was used for generating multi‐protocol CT images of 5 different KVp (120, 110, 100, 90, 80 KVp) and varying mAs to assess the feasibility of patient‐specific optimization of CT protocol that might lead to minimum achievable dose while preserving diagnostic image quality. For quality evaluation, CNR was calculated on ROIs placed on liver and adipose tissues. Result:Noise and texture appearance of the simulated CT image resembled sufficiently to the real CT images from commercial CT system. Multiple combinations of KVp and mAs were found to yield comparable CNR(10.7 ∼ 11.5) while reducing patient dose by 25%. Conclusion: Proposed method could generate simulated multi‐protocol CT images of patient‐derived phantoms, which has a potential for use in optimizing the patient‐specific scan protocol. The research was supported by the Converging Research Center Program through the Ministry of Education, Science and Technology (2012K001498)
SU‐E‐I‐22: Performance Evaluation of a Commercial CMOS Detector for Dynamic High‐Resolution Imaging
Authors: Jain A , Ionita C , Bednarek D , Rudin S
Published: July 2013

Purpose: Present state‐of‐the art flat‐panel detectors have limitations in terms of noise and resolution for dynamic imaging. With recent developments, CMOS‐based detectors show promise to fulfill the ever increasing need for better image quality. Here, we evaluated a CMOS‐based detector by measuring its sensitivity, MTF, DQE and INEE. Methods: The detector (Hamamatsu Model # C10901D‐40) featured 12‐bit image acquisition, CsI phosphor, 100 μm detector pixel pitch and an active area of 9.7cm × 6.7cm and had a maximum frame rate of 30 fps. The sensitivity and instrumentation noise equivalent exposure (INEE) were calculated using flat‐field images taken at various exposures (4.2 μR to 334 μR). The detector resolution was evaluated by measuring the modulation transfer function (MTF) using a tilted edge. The noise power spectra (NPS) and detective quantum efficiency (DQE) were measured using the RQA5 spectrum for three different exposures (4.2 μR, 16.5 μR and 174 μR). Results: The signal vs. exposure curve showed excellent linearity of the detector and the sensitivity of the detector was found to be 5.8 DN/μR. The slope and the intercept of the variance vs. exposure curve were used to calculate the INEE of the detector, which was found to be 7.46 μR The measured MTF values were 0.61, 0.21 and 0.07 at 10%, 50% and 90% of the Nyquist frequency of 5 cycles/mm. The corresponding values of the DQE at these indicated frequencies were 0.47(0.56), 0.19(0.32) and 0.03(0.09) at 4.2 μR (16.5 μR). Conclusion: The imaging performance of Hamamatsu detector was evaluated in terms of sensitivity, linear system metrics and INEE. The INEE of this detector appears higher than desirable for fluoroscopy, but the detector shows good DQE at high exposure when the effect of the high instrumentation noise is not significant.(Support: NIH grants R01EB002873 and R01EB008425) NIH grants R01EB002873 and R01EB008425
SU‐E‐I‐25: Extension of a Real‐Time Skin Dose Tracking System to Include Pediatric Fluoroscopic Cardiac Procedures
Authors: Rana V , Bednarek D , Wu J , Rudin S
Published: July 2013

Purpose: To develop pediatric graphic models for a real‐time skin dose‐tracking system (DTS) and to verify the accuracy of dose and dose‐rate determination with these models for cardiac projections. Methods: A system has been developed to track skin dose during fluoroscopic interventional procedures and to provide a graphic representation of the cumulative dose distribution in real time. Accurate operation of the DTS has been verified for adult patient graphic models. To extend the application of this software to pediatric procedures, a series of 3D pediatric patient graphic models has been developed with varying heights ranging from 60 to 128 cm and with three weight ranges for each height. An open‐source software application was used for graphic development while a commercial software package was used to pose the models with arms up or down. The appropriate graphic model is selected by the operator at the beginning of the procedure to closely match the patient. To verify correct dose calculation for these models, exposures were made for typical cardiac projections using a water‐filled phantom with AP and lateral dimensions of 12 and 19 cm, respectively, corresponding to the torso of a 20 kg child. Dose (rate) was measured at the center of the field using a 6 cc ionization chamber and the readings compared to those calculated by the DTS. Results: The DTS displayed values of cumulative skin dose and of dose rate agreed with the values measured with an ionization chamber within 2 percent over a range of RAO/LAO and CRA/CAU projections on a cardiac C‐arm unit. Conclusion: The patient model size range for the DTS software has been extended to include pediatric patients down to 60 cm in height and 12 kg in weight and the DTS has been shown to be able to accurately track the skin dose for such models. Research supported in part by Toshiba Medical Systems and NIH Grant 2R01EB002873.
SU‐E‐I‐26: When Is High Level‐Control Fluoroscopy Not High Dose‐Rate Fluoroscopy?
Authors: Bednarek D , PazLozada J , Rudin S
Published: July 2013

Purpose: To examine the logic of the current use of high level control (HLC) mode as set up on many fluoroscopic systems. Methods: Use of HLC requires special means of activation and a continuous audible alarm and implies a higher dose rate of fluoroscopy. To examine if this implication is true in practice, we performed a survey of the entrance air kerma to an abdomen phantom as well as the maximum air kerma for a number of fluoroscopic machines operated under automatic exposure‐rate control using standard (non‐HLC) fluoroscopy and HLC fluoroscopy modes. Measurements were made using the abdomen phantom of the ACR Radiography / Fluoroscopy Accreditation Program with the ionization chamber placed either 15 cm from isocenter or at the FDA compliance point. For the maximum dose rate determination a 3 mm thick sheet of lead was placed over the phantom. The results presented are for 7 different mobile and fixed c‐arm units operated in available protocol and magnification modes. Results: For the abdomen phantom, the machines showed widely different entrance air kerma rates and response to changes in exposure mode and protocols. Our survey found: c‐arm units which gave a lower dose rate under HLC fluoroscopy than standard fluoroscopy when used with the abdomen phantom; units for which the HLC dose rate for some protocols was less than for standard fluoroscopy with other protocols; and units which did not exceed 88 mGy/min for some protocols even with lead in the beam when operating under HLC. In all cases, the audible alarm signaled HLC fluoroscopy with the implication of high dose rate. Conclusion: The audible alarm activated by HLC can be misleading and counterproductive since dose rates under HLC can be lower than standard fluoroscopy on the same machine. HLC does not always mean high doserate fluoroscopy. JP was supported by the Fulbright Scholar Program.
SU‐E‐I‐31: Moving From Image Intensifier to Flat Panel Detector in Interventional Radiology: Initial Experiences in a Tertiary Referral Center in India
Authors: Livingstone R , Keshava S
Published: July 2013

Purpose: To audit radiation doses imparted to patients from interventional procedures performed in image intensifier and flat panel based interventional systems in a tertiary referral center in India. Methods: Forty cerebral angiographies were performed using Siemens Multistar top Image intensifier (II) and nine using Artis Zee flat panel detector (FPD) based angiographic systems. Dose area product (DAP) meter was used to measure dose imparted to patients during interventional procedures. Dose audit involved assessment of radiation dose, exposure parameters and image quality relevant to the examination. Copper filtration of 0.2mm was selected in the II based system, whereas 0.6mm copper filters were selected in FPD system. Subjective evaluation of image quality was performed by the interventionalists performing the procedure. Results: The mean DAP values for cerebral angiography using II and FPD systems were 127.5 (32.96 to 366.47) and 94.6 (26.31 to 228.68) Gy cm2 respectively. Dose reduction of about 26 % without sacrificing diagnostic information was achieved using FPD compared to the II system. Conclusion: It is necessary to orient the interventional staff to strictly adhere to low dose protocols so that inadvertent selection of preset protocols may impart high doses to patients. Further data collection on several other interventions is necessary in order set reference levels for Indian adult. At present using low dose protocols involving high filtration does not degrade image quality and are suggestive for use in FPD systems for the Indian adult.
SU‐E‐I‐33: QC in CT by Automated Monitoring of Key Performance Indicators: A Ten Month Study
Authors: Nowik P , Bujila R , Andersson H , Jonsson C
Published: July 2013

Purpose: To develop a method of performing routine periodical QC of CT systems by automatically analyzing key performance indicators (KPI) obtainable from scanning manufacturers' QC phantoms making it possible to follow a CT scanners performance between annual tests (e.g., on a daily basis). Methods: A KPI pertains to a measurable or determinable parameter that is influenced by other underlying parameters, where a stable KPI implies that the underlying parameters are stable as well. KPIs were identified and verified by studying and mapping out the relationship between established QC parameters used in annual testing. The KPIs include positioning, noise, uniformity, homogeneity, CT number of water and CT number of air. An application that automatically analyzes phantom images sent to a DICOM receiver was developed (MonitorCT). CT technologists send scans of a QC phantom to the developed application on a daily basis. Results: 290 daily QC scans, from two CT scanners, have been collected and analyzed during ten months. A systematic offset of circa 3mm from the scanner isocenter has been observed in the positioning test, which is under investigation. Noise, uniformity and homogeneity tests have been within specified tolerances during the data collection period. The CT numbers have trended outside of both MonitorCT and vendor tolerances which was caught using the developed method, which would not have been noticed otherwise until annual tests were performed. Consequently, actions could be taken promptly (water calibration). Conclusion: Automated monitoring of KPIs is a powerful tool that can, with little effort, be used to supplement established QC methodologies. Medical physicists, or other concerned parties, are able to obtain an indication of the current and historical (trends) status of a CT system so that actions can be taken directly to ensure the quality of CT examinations and patient safety.
SU‐E‐I‐39: Experimental Study On the Performance of the OMAR CT Artifact Correction Algorithm Near Titanium and Stainless Steel
Authors: Schoenfeld A , Crilly R , Poppe B , Laub W
Published: July 2013

Purpose: Implants with high atomic numbers produce star‐like artifacts in CT‐images. When coupled in pairs, a black window appears in between. The Philips OMAR algorithm approaches these artifacts by post processing the images. In this study, measurements were performed with radiochromic EBT2 films in order to verify, whether the OMAR algorithm contributes to the accuracy of treatment plans in implant regions. Methods: Two sets of titanium and stainless steel rods with diameters of 1inch and 0.5inch were centered in a water phantom either single or in pairs. The phantom was scanned in a Philips Bigbore Brilliance scanner, which provides the OMAR correction algorithm. A set of uncorrected CT data was kept in addition to the post processed data. The treatment plans were calculated with AAA in Eclipse. The Hounsfield units in the volume of the metal rods were set to match the relative electron density with the conversion table extended accordingly. A 10×12 field at 90 degrees gantry rotation and 400MU was calculated using on a 1mm grid. The plans were irradiated using a Varian Novalis‐TX linac with EBT3 films placed on the sides of the single rod setup or between the rods in the two rod setups. The FilmQA Pro Software was used for evaluation of the films. Results: With one inhomogeneity present in the phantom, the difference between the plans based on the uncorrected data and the plans based on the post processed data is small. With paired inhomogeneities and the associated increased artifact, the difference becomes more significant and the OMAR algorithm improves the accuracy. High Z scattering effects cause considerable deviation from the planned dose profiles near the rods. Conclusion: The OMAR‐algorithm improves the accuracy of the dose calculations. The dose profiles across implant regions are calculated accurately, if the Hounsfield units are defined accordingly.