bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐C‐110‐05: Analysis of Intra‐ and Inter‐Fractional Range Variations to Fiducials in Proton Radiotherapy of Liver Tumors
Authors: Rubinstein A , Chen G , Mori S , Hong T , Wolfgang J
Published: November 2011

Purpose: To quantify radiological pathlength variations to fiducials in proton beam treatment of liver tumors. Methods: Serial 4DCT scans of 10 patients with primary liver tumors were analyzed. The water equivalent pathlength (WEL) was quantified from entrance surface to radio‐opaque clips 1) for different respiratory phases 2) for serial 4DCT scans 3) for each treatment angle (typically AP or PA and a single lateral field) 4) for different immobilization methods. WEL measurements to fiducials is well defined, Vs range to the distal surface of a deformably registered target, but results in fewer measurements (typically 3 clips). A statistical analysis of the mean range variations and spread is performed. Results: AP range at T50 to clips is reproducible from day to day with a mean variation of 1.8mm, SD 1.3mm. Lateral field range variations from day to day at T50 were 1.3mm SD 2.6mm. Range variations at inhale were more variable, with AP T00 mean WEL variation of 3.5mm SD 4.4mm and lateral mean variations of 3.2mm SD 1.7mm. An 8mm lateral range variation was observed in one patient. Range variation during respiration was also studied. The mean AP and lateral range variation was 3mm SD 2.4 and 4.1 mm SD 2.1mm. A 13mm variation was observed in one patient, and attributed to clip motion during respiration without significant change in the entrance surface. Conclusions: Several sources of range uncertainty are routinely included in treatment range determination for proton therapy. These include uncertainties in CT HU numbers, relative stopping powers of tissues, compensator misalignment, etc. Organ motion is explicitly taken into account in the aperture plane, but not in the beam direction. This study elucidates the magnitude and causes of range variations to well defined points. Inclusion of this uncertainty should be considered in determining treatment range.

The project described was supported by Award Number P01CA021239 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
SU‐C‐211‐01: First Results from a Preclinical X‐Ray Phase‐Contrast CT Scanner
Authors: Tapfer A , Bech M , Pauwels B , Liu X , Bruyndonckx P , Sasov A , Kenntner J , Mohr J , Walter M , Schulz J , Pfeiffer F
Published: November 2011

Purpose: One of the main limitations of absorption‐based x‐ray imaging of biomedical specimen is the weak soft‐tissue contrast. This limitation can be addressed by phase‐sensitive imaging methods facilitating considerably improved density resolution. During the last decades various approaches have been investigated ‐ amongst them grating‐based interferometric methods with laboratory x‐ray sources. As a first step towards clinical applications, we have developed a grating‐based compact preclinical phase‐contrast CT scanner, from which we present the first commissioning results. Methods: The grating interferometer translates a small local refraction signal of x‐rays in the sample to intensity modulations that can be detected with a conventional x‐ray detector. Using a generalized filtered backprojection based reconstruction algorithm to account for the cone‐beam geometry, phase‐sensitive tomographic imaging of whole rodents is possible. A first phantom study was performed to investigate the performance, quantitativeness and accuracy of phase‐contrast and absorption‐based computed tomography scans. These scans yield the three‐dimensional distribution of attenuation coefficient mu and refractive index decrement delta of the different liquids contained in the phantom. Further performance experiments were conducted to assess the rotation stability and to optimize the phase‐contrast acquisition protocol of the compact gantry system. Results: The experimental phantom data for mu and delta match accurately with tabulated data, and demonstrate that the compact gantry performs well in both absorption and phase contrast. In addition, first imaging results from small‐animal models will be presented. Conclusions: We show results of the first implementation of phase‐contrast imaging into a compact, rotating x‐ray CT gantry system. We believe that this work represents an important milestone in translating phase‐contrast from bench to bedside.
SU‐C‐301‐01: Methodological Improvements in Voxel‐Based Analysis of Diffusion Tensor Imaging: Applications to Study the Impact of APOE on White Matter Integrity
Authors: Newlander S , Sinha U
Published: November 2011

Purpose: We utilize the DTI indices of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) to investigate 14 normal subjects with the specific genes that increase (APOE e2) and that decrease (APOE e4) the age of onset of Alzhiemerˈs Disease. Methods: DTI acquisitions were performed in clinically acceptable scan times and thus had a low signal‐to‐noise ratio. The DTI data was denoised with a total variation regularization algorithm prior to affine and nonlinear registration to generate a common reference frame for the image volumes of all subjects. Region of interest (ROI), voxel‐based analysis (VBA), and tract based spatial statistics (TBSS) were performed on the aligned ADC and FA maps to identify differences in the cohorts segregated by these alleles as well as segregated by mean age of the group. Results: VBA on the denoised tensor data identified regions of reduced FA (primarily in the genu which was confirmed by ROI analysis) in the APOE e4 cohort compared to the APOE e2 cohort. The most consistent results were obtained for VBA using the denoised tensor and anisotropic smoothing prior to statistical testing. In contrast, isotropic smoothing identified regional differences for small filter sizes alone, emphasizing that this method introduces bias in FA values for higher smoothing kernel sizes. TBSS did not identify any regional differences in the white matter tracts and this may be related to the small localized area of change (found by VBA and ROI methods) that may not be detectable when analyzing voxels averaged normal to the tract. Conclusions: The current findings are consistent with the age trajectories of the transverse relaxation rate studies of APOE ε2 and ε4 cohorts. The relaxometry study confirms the current DTI study that the late myelinating regions such as the genu are more susceptible to age‐related myelin breakdown and this was associated with APOE status.
SU‐C‐301‐03: A Spatially Distributed X‐Ray Source Array for High Resolution Digital Breast Tomosynthesis
Authors: Qian X , Yang G , Sultana S , Gidcumb E , Tucker A , Spronk D , Sprenger F , Lu J , Zhou O
Published: November 2011

Purpose: The current digital breast tomosynthesis (DBT) scanners are based on regular full‐field digital mammography systems and require partial isocentric motion of an x‐ray tube over certain angular range to record the projection views needed for reconstruction. This prolongs scanning time and degrades imaging quality due to motion blur. The purpose of this study is to evaluate the feasibility of improving spatial resolution and scanning speed of the current DBT device by replacing mammography tube with a stationary carbon nanotube (CNT) based x‐ray source array. Methods: A spatially distributed multi‐beam field emission x‐ray (MBFEX) source array was designed for DBT. Electrostatic simulations were carried out to design the electron focusing optics to achieve the desired x‐ray focal spot size. Finite element analysis was performed to determine the x‐ray source anode heat load. A control electronic system was developed to scan and to regulate the imaging dose from each beam by compensating the driving voltages and by modulating the exposure time from each beam. The x‐ray flux, lifetime, focal spot size, variation between different beams, etc were characterized. Results: A MBFEX source array with 31 individually controllable beams covering 30 degrees viewing angle was fabricated. It is operated up to 50KVp anode voltage and 30mA tube current per beam at an effective focal size comparable to that of the traditional mammography tube. Consistency in the beam‐to‐beam performance was achieved by optimizing the CNT cathodes and by electronic compensation. Tomosynthesis images of a breast phantom were obtained using the new source array. Conclusions: These preliminary results demonstrate the feasibility of CNT x‐ray source array for stationary DBT to eliminate image blurring from tube motion. With a fast detector the device can provide a higher spatial resolution at a reduced imaging time compared to the current rotating gantry DBT systems.

This research is currently supported by the following grants：NCI Grant No. U54CA119343, NIH R01 Grant No. CA134598‐01 and the University Cancer Research Fund at the University of North Carolina. Dr. Xin Qian, was supported by a fellowship from DoD Grant No. BC087505.
SU‐C‐220‐01: Comparative MTF and DQE Performance of Wireless Digital Image Receptors
Authors: Murphy S , Christianson O , Samei E
Published: November 2011

Purpose: Two new wireless digital receptors were evaluated and compared with a conventional flat‐panel using the International Electrotechnical Commission formalism (IEC 62220‐1) for measuring modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) using two filtration schemes. Methods: Raw images were acquired for three image receptors (Pixium 4600, Trixell; DRX‐1C and DRX‐1, Carestream Health, Inc.) using a radiographic system with a well‐characterized output (Philips Super80 CP, Philips Healthcare). Free in‐air exposures were measured using a calibrated radiation meter (Unfors Mult‐ O‐Meter Type 407, Unfors Instruments AB). Additional aluminum filtration (and a new alternative combined copper‐aluminum filtration) were used to conform the x‐ray output to IEC‐specified beam quality definitions RQA5 and RQA9. Testing was performed to exclude lag effects. Assessment of the DR systems followed the IEC 62220‐1 formalism. Each detector was irradiated with RQA5 and RQA9 open beams with each filtration at increasing photon fluence to determine the system conversion function. The normal exposure level (XN) was set at 1.0 mR to the detector surface. The NPS was evaluated at XN/2, XN, and at 2XN. The prescribed edge test device was used to evaluate the MTF. The DQE was then calculated from the MTF and NPS functions. Results: All three DR systems demonstrated similar MTFs at most frequency ranges, while the DRX‐1 showed lower values near the cutoff of approximately 3.5 cycles/mm. At each exposure, the Pixium 4600 and DRX‐1C demonstrated similar NPS curves that indicated better noise performance than the DRX‐1. Zero‐frequency DQEs for Pixium 4600, DRX‐1C, and DRX‐1 were approximately 63%, 74%, and 38% for RQA5 and 42%, 50%, and 28% for RQA9, respectively. Conclusion: In terms of DQE performance, the DRX‐1C image receptor is superior to the Pixium 4600 and DRX‐1. Wireless DR receptors offer high‐quality alternatives to CR for portable imaging applications.

Supported in part by Carestream Health, Inc. (Rochester, NY)
SU‐C‐220‐02: A High Efficiency Grid System for Abdominal Radiography
Authors: Gauntt D , Barnes G
Published: November 2011

Purpose: To improve scatter control in abdominal radiography.Methods: A crossed grid system was constructed and consists of a stationary low ratio, high strip density conventional grid (8:1, 60 lines/cm) positioned above and with its septa orthogonal to the septa of a novel high ratio, air interspace, coarse strip density scanning grid (15:1, 2.0 lines/cm). The latter has articulating grid slats; during an exposure the slats remain focused on the x‐ray focal spot. To suppress grid line artifacts, a trapezoidal x‐ray exposure was generated and coupled with the movement of the scanning grid. This effectively eliminates grid line artifacts for small grid movements. The grid DQE was measured for 4 grid configurations: the crossed grid system, the scanning grid alone, a stationary 15:1 conventional grid, and no grid. The measurements were made with standard CsI flat panel detector and a variety of acrylic thicknesses and x‐ray tube potentials.Results: In all cases the DQEgrid measured with the various grid systems was markedly better (130% to 580%) than that measured without a grid. The performance of the crossed grid system was 6% to 120% better than the conventional 15:1 grid. The scanning grid system performed 22% better (20 cm acrylic, 60 kVp) to 6% worse (40 cm acrylic, 120 kVp) than the crossed grid system. While subtle gridline artifacts are present in flat‐field images, the artifacts are invisible in images of anthropomorphic phantoms Conclusions: A high efficiency scanning grid system has been designed and constructed. The system requires only a short grid movement during an exposure to suppress grid line artifacts. It can be used with or without a crossed conventional low ratio grid. In either case, its dose efficiency in controlling scatter is markedly superior that of a high quality, high ratio conventional stationary grid.

The authors are co‐owners of X‐Ray Imaging Innovations, which has developed this technology, and are co‐inventors of U.S. Patent 6,795,529, which covers this technology
SU‐C‐220‐03: Texture‐Based Identification of Pathologic Change on Temporally Subtracted Radiographic Chest Images
Authors: Armato S , Lee M , Yu G , MacMahon H
Published: November 2011

Purpose: Temporal subtraction images created from sequential chest radiographs provide a tool for the enhanced visualization of pathologic change. Although these images provide valuable information to radiologists, the presence of misregistration artifacts could confound the appreciation of actual pathologic change regions. The purpose of this study was to develop a method for the automated identification of pathologic change depicted on temporal subtraction images using a texture‐based classification framework.Methods: Eighty‐eight temporal subtraction images derived from the posteroanterior chest radiographs of 49 patients were created using an existing temporal subtraction algorithm. With the corresponding computed tomography (CT) scan as a reference, an experienced radiologist manually outlined all regions of pathologic change on each subtraction image to provide the “truth.” Generated with each subtraction image was a corresponding “lung mask” image that defined the spatial extent of the lung fields within the image. Candidate pathologic change regions were segmented within the lung mask using a gray‐level thresholding technique, and morphological features computed for each region (e.g., area, circularity, perimeter) were used to reduce false positives. Texture features extracted from a 64×64‐pixel region of interest (ROI) placed over the centroid of each remaining candidate within the subtraction image were input to an automated linear discriminant classifier, which was trained using the regions of actual change outlined by the radiologist. Performance was evaluated using receiver operating characteristic (ROC) analysis.Results: A resubstitution classifier training/testing paradigm applied to the set of change region candidates yielded an area‐under‐the‐ROC‐curve value (Az) of 0.75. A 10‐fold cross validation training/testing paradigm for evaluating “truth” regions yielded Az=0.88 Conclusions: This study demonstrates the potential for texture features to distinguish regions of pathologic change from misregistration artifacts on temporal subtraction images of the chest. Future work will seek to improve the extraction of initial region candidates.

Disclosure statement: SGA and HM receive royalties and licensing fees through the University of Chicago related to computer‐aided diagnosis. HM is a consultant for Riverain Medical.
SU‐D‐BRB‐02: Monte Carlo Modeling of the Gamma Knife Perfexion
Authors: Best R , Bennett M , Gersh J , Wiant D , Bourland J
Published: November 2011

Purpose: For dosimetric and research irradiation studies, we have implemented a Monte Carlo (MC) dose computation model based on the physical and radiological characteristics of the Gamma Knife Perfexion (GK PFX) using the Penelope MC dosimetry codes. GK dosimetric aspects examined include: 1) output factors (OF) for each of the three GK collimator sizes (4, 8, 16 mm), 2) OFs for each source row and collimator size, and 3) dose distribution profiles. Methods: Vendor proprietary information facilitated our modeling of the GK PFX irradiation geometry, which was mathematically defined within Penelope. MC simulations were carried out on a Linux cluster. 3D dose distributions were analyzed using Matlab. A 16 cm diameter dosimetry sphere was modeled with a virtual detector volume at its center. Detector volume varied from 33 to 590 mm̂3 to study detector volume effects. A single source per row was modeled for five rows for each collimator (15 beams modeled). Single‐source dose distributions were rotated about the z‐axis of the axially symmetric geometry and summed to simulate all 192 sources. Results: Good agreement is found for row‐ and total‐output factors (greatest deviation <2% for the 4 mm collimator) compared to reference values. Simulated and measured full‐width at half‐ max values of 3D dose distribution profiles show sub‐millimeter differences (0.4 mm, 4 and 8 mm collimators; 0.9 mm, 16 mm collimator). There is excellent agreement for integrated profile shapes. Conclusions: Detailed geometric representations (radiation source, device components) of the GK PFX are required for high fidelity MC simulations. Calculated GK PFX OF values are dependent on the simulated detector volume size (4 mm OF most dependent). Our model shows strong agreement for the GK PFX OFs and dose profile shapes compared to reference values.

Acknowledgement: Non‐disclosure agreement for proprietary information with Elekta AB. No financial contribution.
SU‐D‐BRC‐06: Multimodality Assessment of Response to Combined Chemoradiation and Anti‐Angiogenic Therapy with CuATSM‐PET, FLT‐PET, and Contrast‐Enhanced CT Imaging
Authors: Nyflot M , Simoncic U , Harari P , Perlman S , Jeraj R
Published: November 2011

Purpose: The integration of molecular therapies into chemoradiation treatments has motivated improved tools for treatment assessment. We used hypoxia, proliferation, and perfusion imaging techniques for multimodality response assessment in patients receiving combined therapy. Methods: Ten HNSCC patients received anti‐angiogenic therapy (Avastin). After three weeks, patients began chemoradiation and continued Avastin. Patients were imaged at baseline, after Avastin monotherapy, and during combined therapy. Imaging modalities were CuATSM‐PET (tumor hypoxia), FLT‐ PET (proliferation), dynamic FLT‐PET (FLT kinetics) and dynamic contrast‐enhanced CT (perfusion). Mean SUV was calculated from PET data and dynamic FLT data were analyzed for kinetics with a two‐compartment, four‐parameter model. DCE‐CT data were analyzed with GE Advantage software. Paired t‐tests were used to evaluate tumor response and mean imaging values were correlated with Pearsonˈs R.Results: After Avastin monotherapy, significant decreases were measured in CuATSM_SUV (p=0.05), FLT_SUV (p<0.01), FLT_Ki (p<0.01), and CT_Enhancement (p<0.01). During combined therapy, further decreases were measured in CuATSM_SUV and FLT_SUV (p=0.05, p<0.001). Across the study, significant correlations were found between CuATSM_SUV and CT_BloodVolume (R=0.72), CT_BloodFlow (R=0.59), and FLT_K1 (R=0.53). Additionally, FLT_Ki was significantly correlated to FLT_SUV (R=0.80) and CT_Enhancement (R=0.50) Conclusions: Multimodality imaging has been used to identify clinically relevant tumor characteristics over the course of therapy. Significant decrease in tumor proliferation suggests effective combination of Avastin and chemoradiotherapy, and FLT imaging endpoints could potentially be used to optimize combined therapy. Decrease in hypoxia was also measured, and given the established prognostic value of hypoxia, mid‐therapy hypoxic status is another potential therapeutic endpoint. Decrease in CT_Enhancement after Avastin may indicate reduction in vascular permeability, and correlation between CuATSM_SUV and perfusion‐related parameters such as FLT_K1, CT_BloodVolume, and CT_BloodFlow suggests further importance of vascular status in effectiveness of combined therapies. As outcome data becomes available, these imaging biomarkers could eventually be used to personalize delivery of combined therapy.

Study supported in part by Genentech
SU‐D‐214‐03: Experience with Using Treatment Volume for Quality Assurance of HDR Treatment Plans
Authors: Wilkinson D , Kolar M
Published: November 2011

Purpose: To assess the usefulness of treatment volume (V100) in patient specific HDR treatment plan quality assurance. Methods: The Nucletron Plato and Oncentra treatment planning systems were used in this study. Results from both film‐based 2D and CT‐based 3D planning have been included. Plots of time x activity/dose (T*A/D) versus V100 were constructed for various “fixed” geometry systems such as vaginal cylinders (n=167), endobronchial and esophageal tubes, (n=79) and tandem/ring systems (n=352; pt A dosimetry) as well as for larger interstitial volume implants (n=25). For single catheter applicators, plots of V100 as a function of active length (AL) or treating distance (d) were also made. Results: The T*A/D vs V100 plots for the fixed systems above were all very linear (r2 of at least 0.98); a slight improvement in some cases was noted when a second order polynomial was used to fit the data. The volume implant data were best fit with a second order polynomial (r2 = 0.98). For a given treating distance, V100 not surprisingly was a linear function of active length (2.5 to 17 cm) for single or quasi‐single (2 or 3 catheter esophagus) line applicators. We found that V100 values were extremely consistent for a given treating distance and active length (e.g. 36.64 ± 0.45 cm3 for d= 1.5 cm and AL = 4 cm). For tandem/ring applicators, V100 values could achieve similar consistency only if considerable care was taken in defining the catheters. Conclusion: Volume data provide a simple, fast and consistent method of checking new treatment plans against historic data (representative samples of which need to be independently verified). For simple applicators, both the V100 and the value of T*A/D may be used for this comparison.
SU‐D‐301‐04: Development of a Simple Method for Measuring the DQE of An X‐Ray Imaging System with Unspecified Characteristic Response
Authors: McDonald M , Kim H , Henry J , Cunningham I
Published: November 2011

Purpose: To develop a method of measuring the detective quantum efficiency (DQE) of an x‐ray imaging system with unspecified characteristic response for use in a hospital quality assurance program. Methods: Measurement of the DQE of radiographic systems in a hospital setting is made difficult by the fact that many systems have a non‐linear or unspecified characteristic response curve. This makes it difficult to determine the detector signal as a function of a number of incident x‐ray quanta as required to linearize the system response. We solve this problem with what we call a “neutral attenuator” method that uses a copper stepwedge to attenuate the beam and incorporate a theoretical correction for spectral beam hardening effects. Using a standardized spectrum (IEC 61267 RQA‐5, 7.1mm hvl), a copper stepwedge consisting of 5 steps with transmissions ranging from 0.94 to 0.01 was placed in the beam to determine the characteristic curve. The method was validated by comparing a conventional (IEC 62220‐1) DQE assessment with the DQE obtained using our method based on both raw (linear) and processed (non‐linear) image data from a General Electric Revolution Xrd Q/i detector. Results: The DQE obtained using the conventional method had a zero‐frequency value of 0.49 with an estimated uncertainty of 0.03. Our new method generated a value of 0.50 using raw image data and 0.47 using processed image data. Conclusions: A simple method has been developed to determine the DQE of an x‐ray system that can be used on both linear image data and non‐linear image data. While not IEC 62220‐1 compliant, it is simple enough to be incorporated into a hospital quality assurance program.
SU‐E‐E‐07: Radcalc IMRT Plan Verification vs. Mapcheck IMRT Plan Verification
Authors: Pierno J , Hamilton C , Kanumalla S
Published: November 2011

Purpose: To compare the accuracy of the RadCalc (LifeLine Software) IMRT plan verification module to the MapCHECK (Sun Nuclear) IMRT Treatment Plan verification system.Methods: A group of 47 patients were randomly selected to compare the accuracy of the two methods of IMRT verification. IMRT treatment plans were created using the Eclipse treatment planning system (Varian Medical Systems) Version 8.6. For the MapCHECK, a verification plan was created in Eclipse and all beams were calculated with one gantry and collimator angle and exported to the MapCHECK software. The plan was delivered to the MapCHECK device using a Varian 21EX. The data sets were compared in the MapCHECK software with a percent difference of 3% and a distance to agreement of 3mm. For the RadCalc software a calculation point was added to the plan, the plan was approved and exported to RadCalc. The plan was then calculated within the RadCalc software Version 7.0. MUˈs for all fields were examined and the percent difference for the calculation point was reviewed.Results: Both methods were utilized on all selected patients and the results then compared. The MapCHECK data sets averaged a percent difference of 1.27% from the planned dose with an average of 99.29% of the points passing. The RadCalc data sets averaged a percent difference of 1.05%. Conclusions: It was determined that the RadCalc IMRT verification module can be directly substituted for the MapCHECK IMRT Treatment Plan verification system with no loss in verification accuracy. The RadCalc module provides equivalent plan verification for smaller plan size (i.e. under 20.0 cm × 20.0 cm), while providing superior results for large field IMRT due to the field size limits inherent to the MapCHECK device.
SU‐E‐E‐10: The Leadership Journey ‐ From the Classrom to the Clinic
Authors: Barra R
Published: November 2011

This 50‐minute session will share practical application leadership tips to help ensure a successful and cohesive team. Whether you are a new leader, a seasoned veteran or wanting to step into leadership, everyone will grow in their influence as we unpack and examine principles from the leadership toolkit. Purpose: Most Physicists come from a clinical background and are sometimes put into leadership roles with minimal training on how to lead a team. This 50‐minute session will share practical application leadership tips to help ensure a successful and cohesive team. Whether you are a new leader, a seasoned veteran or wanting to step into leadership, everyone will grow in their influence as we unpack and examine principles from the leadership toolkit. Methods: 1. Expanding Your Influence Beyond Your Title Influence doesnˈt merely coincide with position. Leadership and management are separate qualities. As you grow your leadership you can leverage influence beyond your title and authority lines. 2. Coaching 101 Youˈve been put in charge. They gave you the keys to the car. You have the responsibility for making your team better. What next? 3. Vision Casting He who thinks he leads and has no followers is simply taking a walk. How do you get past the cliché to actually moving in the same direction? We will focus on building a collaborative vision where new and seasoned team members can have ownership in the present and future direction of the department. Results: A team which functions in a positive and effective manner. Team members and leaders are enjoying their work place better because they have ownership in the direction of the department. Conclusions: The quality of leadership in the team will effect the performance of a department in a positive or negative manner. As we improve our clinical education and team building skills, we our best equipped to take others on the journey of building a well functioning team.
SU‐E‐E‐11: Results from the Tomotherapy Daily QA Using the Rotational Therapy Phantom
Authors: Jaradat H , Freeman K
Published: November 2011

Purpose: In this study we will present results from the daily QA program used to monitor the tomotherapy machine over a period of eight months. Methods: The daily QA uses the Rotational Therapy Phantom, Gammex 507 (RTP). The RTP system allows for checking the rotational output, energy, gantry speed, gantry position, MLC‐Gantry position synchrony and beam profile constancies. All of these tests are done within one five‐minute procedure to check these metrics on the tomotherapy machine. The measurements are done using two ion chambers connected to the TomoElectrometer in rate collection mode. Daily QA data is analyzed using the Rotational Therapy Phantom Software (RTPS) to compare the constancy of these metrics relative to a standard set. The Daily QA protocol runs a dynamic MLC, five‐identical‐rotation procedure with a period of 40 seconds per rotation. Results: Measurements are taken using the TomoElectrometer with a sample time of 200ms, because the procedure utilizes dynamic MLC and rotational gantry, the procedure allows the software to detect variations in the output rate, energy constancies, gantry speed, position and MLC/Gantry position synchrony at the same rate. This work will present examples of these variations including evidence on gantry position/MLC asynchrony of up to 2 seconds. This corresponds to 18 degrees or 2.55 projections. Conclusions: Using the RTPS for daily QA on tomotherapy system shows that the system can run with up to 2 seconds (18 degrees) asynchrony between the MLC and the gantry position. This 18 degree discrepancy between the plan and the actual delivery could result in significant clinical outcome for a wide range of treatment sites, such as prostate, H&N, Lung and Brain treatments.

Work is currently being done to expand the application of the RTPS to be applicable on the Varian and Elekta rotational therapy modalities.

Kennith Freeman is an employee of Gammex Inc.
SU‐E‐E‐18: Stereotactic Treatment of Multiple Targets Using Sngle Isocenter: Planning, Dosimetric and Delivery Advantages
Authors: Shtraus N , Schifter D , Alani S , Tempelhof H , Matceyevsky D , Gez E , Corn B , Kanner A
Published: November 2011

Purpose: To evaluate the relative plan quality of single‐isocenter vs. multi‐isocenter for radiosurgical treatment of multiple brain metastases Methods: Ten patients referred to stereotactic radiosurgery treatment for 2–3 lesions in the brain. Two stereotactic radiosurgery plans were generated for each patient, First Plan using static beams and arcs for multi isocenter treatment plan and a second plan with one isocenter covering all lesions using static beams All plans were generated using ergo++ software on Elekta synergy‐s with beam modulator 16×21 cm with 4mm interdigitating leaves. Plans were normalized to deliver a prescription dose to the 80% isodose‐line Results: All plans were judged clinically acceptable, and no significant differences for OAR were observed in the dosimetry parameters. Nevertheless patient with different size of lesions and proximity to OAR had a different prescription dose which lead to much higher dose at the center of the lesion in the single iso plan compare to the multi isocenter plan and still kept very tight dose cover and gradient, in some cases the maximum dose was higher by 20% and average machine on time was 43.6± 9.58% higher, respectively Conclusions: Our initial results suggest that single‐isocenter plans can be utilized to deliver conformity equivalent to that of multiple isocenter techniques. Single isocenter radiosurgery for multiple targets can be efficiently delivered, and requiring less than one‐half the beam time required for multiple isocenter set ups.
SU‐E‐I‐05: Implementation Analysis of a Mammographic Computer‐Aided Diagnostic (CAD) System
Authors: Alam M. Sadegh Riyahi , Riyahi‐Alam Nader
Published: November 2011

Purpose: Computer‐aided diagnostic (CAD) system can assist radiologists by detecting breast abnormalities in early stage. Hence, the need for designing and analysis of an interactive a CAD system facilitated with such a reliable interface proper to diagnose breast cancer on mammograms becomes apparent. Methods: The base hardware system regarded for this purpose includes one digitizer, high speed computer could connecting to PACS by DICOM format, while this system has been designed in Visual C++. Net environment using Microsoft Access based Database(ODBC). Based on these requirements, evaluation, analysis and designing of the technical details for implementing a developed mammographic CAD system including three software programming sections of (a) Patient Information, (b) Viewer & General Image Processing and (c)CAD section as the main part of the system has been accomplished in thus study. Results: a) The “Patient Information Dialog” designed for saving full patient information, thumbnail images, storing text report, printing reports, b) The “Viewer & General image Processing sections” designed to display four mammogram breast views (RCC‐RMLO‐LCC‐LMLO) in one window, background removing using histogram, ROI determination, contrast/windowing/thresholding, histogram‐equalization, edge detection using desire different kernels‐filtering and c)CAD system as the main part includes processing and diagnostic algorithm for detecting breast abnormalities by using wavelet and fuzzy logic algorithm, developed earlier by this group, finally with 16 conventional Template for Clinical reports are the main parts of the designed system. Conclusions: The provided MammoCAD system in this article could overcome drawbacks of the interpretation of a large volume of images produced in conventional screening mammography. The detection of suspicious cancers or possibility of malignancies will be analyzed by the software, hence, increasing sensitivity and accuracy of the algorithm can help to decrease the number of cancers that is hard to diagnose and also to prevent unnecessary biopsies for breast cancer diagnosis.
SU‐E‐I‐29: A Prior Information Based Total‐Variation Digital Tomosynthesis Reconstruction Algorithm
Authors: Jian Y , Cai J , Yin F
Published: November 2011

Purpose: To develop a total‐variation (TV) based compressive sensing image reconstruction algorithm using a set of limited‐angle projections by applying a prior image information to enhance the image quality and anatomic information of current Four‐dimensiona Digital Tomosynthesis (4D‐DTS). In the iterative algorithm, both TV regularization and Bspline deformation field are included to accurately reconstruct 4D‐DTS images in order to reduce imaging dose. Methods: For 4D Cone Beam Computed Tomography (4D‐CBCT), images of different phases share similar anatomical struture, and their difference can be used as sparseness prior in the 4D‐DTS reconstruction. The Bspline tensor transforms the reference image to fit the target image, and is regulated by TV penalty terms in the cost function of the unconstrained optimization problem. Nonlinear conjugate gradient method is applied to solve the unconstrained problem. Results: Several phase pairs of 4D‐CBCT are used examples. With voxel per region sets 50, the algorithm can have the most similarity with the target image with the fastest convergence. By decreasing Bspline resolution, the deformation will be become more flexible while losing some accuracy of registration. The similarity between target image and resulted image can be tuned by regularization factor, which will enable us to determine how much additional information is needed to build the new image volume. The integrated built CPU and GPU platform provides the acceleration tools of forward/backward projection and Bspline coefficients calculation for large‐scale 4D‐CBCT data in the iteration process, which is 100 times faster than using only software method. Conclusions: The performance of the algorithm is determined by two built‐in parameters in the algorithm: Bspline Resolution and Regulization Factor, whose tuning can favor different edge and resolution performances or fidelity and similarity to the target measurements, and also determine the flexibility and accuracy during the registration.

Research sponsored by Varian Medical System.
SU‐E‐I‐31: CT Metal Artifact Reduction by Constrained Optimization with a Model‐Based Scanning Scheme
Authors: Zhang X , Xing L
Published: November 2011

Purpose: The streak artifacts caused by metal implants have been recognized as a “missing data” problem that limits various applications of CT imaging, such as target delineation and accurate dose calculation. How to deal with the missing data is essential in metal artifact problems. In this work we want to investigate a method that can minimize the missing information and reconstruct images with significantly reduced metal artifacts. Methods: A penalized‐weighted‐least‐squares method is first used to accurately identify the metal objects in image space. Based on this prior knowledge, a new model‐based scanning scheme is designed by shifting the object center during a CBCT scan to avoid the metal regions and reduce the missing projections. An iterative algorithm based on constrained optimization is then used for the image reconstruction. It minimizes a quadratic edge‐preserving smoothness measure function of the image, subject to the constraint that the estimated projection data is within a specified tolerance of the available metal‐shadow‐excluded projection data, with image non‐negativity enforced. The algorithm is evaluated using a numerical QA phantom (350×350×16, 1 mm3, only central slice considered) with simulated Poisson noise in the projections. The new scanning scheme is modified over a conventional half‐fan scanning geometry with source‐to‐axis and source‐to‐detector distances of 100 cm and 150 cm, respectively. Total 339 views projection data are simulated over 360° rotation. Results: Studies showed that the constrained optimization with the model‐based scanning data has superior performance compared with analytical FDK reconstruction and other iterative reconstructions. It significantly suppressed metal artifacts in the presence of noise. Profile comparisons and RMSE measurements also suggested that the model‐based scanning scheme can effectively reduce the missing information and yield better images. Conclusions: The proposed algorithm can be used to significantly reduce metal artifacts to produce clinically acceptable image for current on‐board CBCT image systems.
SU‐E‐I‐40: Reconstruction of Sparse Images from Few‐View Cone‐Beam Data
Authors: Han X , Bian J , Eaker D , Kline T , Sidky E , Ritman E , Pan X
Published: November 2011

Purpose: In current cone‐beam CT imaging, one acquires data at hundreds of views, at the cost of a non‐negligible amount of radiation dose as well as prolonged scanning time. Enabled by advanced, iterative algorithms, progress has recently been made on image reconstruction from sparse‐view data, which can potentially reduce imaging radiation dose and scanning time. For cases where data are highly sparse, such as when only a few (e.g. <10) projections are available, accurate image reconstruction becomes challenging. However, prior knowledge of the imaged subject such as sparse structures may be utilized to improve reconstruction fidelity. In this work, we investigated the incorporation of image sparsity into the framework of novel iterative algorithms for few‐view image reconstruction of sparse objects. Methods: We incorporated image sparsity by combining the hard‐thresholding technique into the framework of the adaptive‐steepest‐descent‐POCS (ASD‐POCS) algorithm. We performed simulation studies by using a numerical artery phantom, and real‐data studies by using micro‐CT data of a human coronary artery specimen. The number of projections under study ranged from 3 to 10. A number of quantitative metrics were used to evaluate the image‐reconstruction performance. Results: Images of numerical phantoms and the real coronary artery specimen were accurately reconstructed from as few as <5 projections. Quantitative metrics showed that the quality of few‐view image reconstruction using the proposed algorithm is comparable to that of image reconstruction using existing algorithms from data acquired at 360 to 720 views. Conclusions: We have demonstrated that by incorporating appropriate image‐sparsity information into novel iterative algorithms, CBCT images can be reconstructed accurately from a few projections. The proposed technique may potentially be used for in‐vivo and in‐vitro coronary artery imaging.
SU‐E‐I‐42: Variations of the Chromaticity in Gray‐Scale Images Displayed on Different Liquid‐Crystal Display Monitors
Authors: Akamine H , Awamoto S , Miyazaki H , Nakamura Y , Hashimoto N , Morishita J
Published: November 2011

Purpose: Purpose in this study was to investigate variations of the chromaticity in gray‐scale images displayed on different liquid‐crystal display (LCD) monitors at different illuminance. Method and Materials:Four color LCD monitors (RX210, 240 cd/m2, two‐megapixel, Eizo Nanao), and four monochrome LCD monitors (G31, 450 cd/m2, three‐megapixel, Eizo Nanao) were used in this study. These LCDs have various operating hours ranging from 4,000 hours to 23,000 hours. The chromaticity in gray‐scale images with 18 different luminance levels was measured by use of the BN test patterns (JESRA X‐0093‐2010) and a chromameter (CS‐200:KONICA MINOLTA). Distances in CIE uˈvˈ color space, delta uˈvˈ, for all possible pairs of LCD monitors were calculated based on AAPM TG‐18 guideline. The chromaticity of the LCDs was measured at different illuminance (0, 30, and 560 lux). Variations of the chromaticity at different illuminance compared to 0 lux were examined using delta uˈvˈ. Results: Delta uˈvˈ for all possible pairs of LCD monitors did not exceed 0.01. Delta uˈvˈ of the monochrome and the color LCDs indicated greater differences than those for different color LCDs or different monochrome LCDs. There was no difference of chromaticity depending on the operating hours. When illuminance increased, the chromaticity varied on every LCD. Although delta uˈvˈ between 0 lux and 560 lux exceeded 0.01 at low‐luminance levels of 30 cd/m2 or less, delta uˈvˈ between 0 and 30 lux did not exceed 0.01. Conclusions: Variations of the chromaticity for all possible pairs of LCD monitors used in this study were less than 0.01. We found that the chromaticity varied on every LCD with increasing illuminance.
SU‐E‐I‐47: Characterization of Beryllium Oxide Optically Stimulated Luminescence Detectors for Use in Diagnostic Radiology
Authors: Eller S , Rodriguez M , Ruan C , Yukihara E
Published: November 2011

Purpose: To determine the response of beryllium oxide (BeO) optically stimulated luminescence (OSL) detectors in diagnostic radiology and to develop a protocol for proper handling and readout. Methods: The BeO OSL detectors used in this study are ∼4.7 mm × ∼4.7 mm × 0.5 mm chips and weigh ∼32 mg each (Thermalox 995, Brush Ceramic Products, Brush Wellman, Inc.). Detectors were annealed at 700 °C for 15 minutes prior to irradiation and protected from light. The dose response, minimum detectable dose, and reproducibility were determined using 90Sr/90Y beta sources. Clinical irradiations were performed at OUHSC with a radiographic unit (Proteus XR/a, GE Healthcare). An 6 cm3 ionization chamber (model 10X5‐6, Radcal Corporation), A12O3:C OSLDs (Luxel™, Landuaer, Inc.), and LiF:Mg,Ti (TLD‐100, Thermo Fisher Scientific, Inc.) were also used for comparison. The relative response of each type of detector was determined by varying the preset tube voltage of the radiographic unit from 50–130 kVp. The OSL and TL signals were read using a Riso/ TL/OSL‐DA‐15 automated reader (Riso/ National Laboratory), which uses continuous blue stimulation for the OSL measurements. Results: BeO was found to be very sensitive, with a minimum detectable dose of ∼20 μGy using the Riso/ OSL reader. The dose response is linear up to ∼5 Gy, and the reproducibility using a proper methodology is less than 1.2 %. BeO under‐responds to low energy photons by a factor less than 20% relative to 130 kVp, whereas Luxel™ over‐responds to low energy photons by a factor less than 40% relative to 130 kVp. Conclusions: This study demonstrates the dosimetric properties of BeO for applications in diagnostic radiology and indicates that BeO may require energy correction factors to be applied.

Stephen Eller was supported by ProCure Treatment Centers, Inc.
SU‐E‐I‐54: A Database for Estimating Scanner‐Specific CT Organ Dose
Authors: Rupcich F , Schmidt T
Published: November 2011

Purpose: To develop a database for estimating scanner‐specific organ dose in a voxelized patient model for any spectral shape and angular tube current modulation setting. The database enables the estimation of organ dose for both existing and novel acquisition techniques without requiring Monte Carlo simulations. Methods: The transport of monoenergetic photons through three phantoms was simulated with the PENELOPE Monte Carlo radiation transport routines at 5 – 150 keV in 1 keV increments at 1000 projections in 0.36 degree increments. The source‐to‐detector distance for each simulation was 100 cm, with a source‐to‐isocenter distance of 50 cm. The lateral and axial extents of the detector were 100 cm and 16 cm respectively, while the detector pixel resolution was 0.25 mm. The first phantom was a 0.5 mm resolution anthropomorphic voxelized female phantom, while the other two phantoms were standard head and chest CTDI cylinders modeled using mathematical quadrics. Results: The simulations resulted in a normalized dose deposition table for numerous organs quantifying the typical dose deposited in the organ per emitted photon for each energy level and projection angle. The values in this table can be multiplied by an incident spectrum and number of photons at each projection angle and summed across all energies and angles to estimate the total organ dose. Similarly, the CTDIvol for a particular acquisition can be estimated from the dose deposition tables for the CTDI phantoms. The estimated CTDIvol can be used along with a physical CTDIvol measurement to convert the organ dose calculated from the database to a scanner specific estimate. Conclusions: The proposed database and procedure enable the estimation of scanner‐specific organ dose for CT scans utilizing any spectral shape and angular tube current modulation scheme without requiring Monte Carlo simulations.

This project is funded in part by the US Food and Drug Administration, Office of Womenˈs Health (OWH), and by the Oak Ridge Institute of Science and Engineering (ORISE). Performance of Monte Carlo simulations were made possible by NSF grant OCI‐0923037.