bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐D‐BRC‐04: Comparison of Tumor Shrinkage in Proton and Photon Therapy of Lung Cancer
Authors: Chen YP , Zhang L , Liao Z , Komaki R , Cox J , Balter P , Mohan R , Dong L
Published: November 2011

Purpose: To compare tumor shrinkage in IMRT and proton therapy for locally advanced non‐small cell lung cancer. Methods: Twenty‐four patients enrolled in randomized clinical trial were selected in this study. Patients were randomly assigned to either IMRT or proton therapy when adequate target coverage and mean lung dose constraints can be met. The relative biological effectiveness (RBE) for proton therapy was assumed to be 1.1. There are three prescription dose levels allowed by the protocol, but all patients selected for this analysis received 74 Gy (RBE) in 37 fractions. All patients received weekly 4DCT scans to assess their anatomical changes. To minimize the impact of motion, the primary gross tumor volume (GTVp) and clinical target volume (CTV) were defined on the expiration phase of the 4DCT. In‐house developed deformable registration software was used to propagate the planning GTVp and CTV to the end of expiration phase of weekly 4DCT scans. One proton patient received breath‐hold gated treatment and the target volumes were assessed on the breath‐hold weekly CT. To minimize the impact of variable time delay between simulation and the start of treatment, we normalized tumor shrinkages to the first available weekly 4DCT, assuming no drastic change during the first week of treatment. Results: Although individual patient exhibited quite different shrinkage patterns, the average shrinkage for each treatment group was strikingly similar. The average GTVp shrinkage was 23% in IMRT and 23% in Proton at the end of treatment. The average CTV shrinkage was 11 % in IMRT and 8% in Proton, respectively. Conclusions: The average tumor shrinkage for patients receiving proton therapy and IMRT was remarkably similar, suggesting the adequacy of using RBE value of 1.1 for lung cancer proton therapy. Supported in part by NCI P01 CA021239
SU‐D‐214‐02: Quality Assurance Tool for Radiation Therapy Patients: Peer Review System Design and Implementation
Authors: Kapoor R , Le A , Palta J
Published: November 2011

Purpose: To demonstrate the efficacy of a peer review system (PRS) for remote quality assurance in radiation oncology. The PRS is a Web‐based system which allows radiation oncologists to share anonymous treatment plans (imaging, structure sets, and dose distributions) with peer reviewers for their feedback. Methods: We have developed a DICOM‐RT compliant PRS that can store patient images and treatment planning data. The PRS infrastructure consisting of three components: Gateway, Web Server and Web Viewer, which is developed with current Web technology, utilizing .NET framework and Silverlight plug‐in for web interface. The patient data can be visualized through a Web browser and distributed across multiple locations by the local area network and the Internet. The submitter uses the Gateway to anomymize patient data, chooses a reviewer from the master list, adds annotations and messages and submits patient data for review via the PRS Web Server. Upon receiving the data from the submitter, the reviewer is notified via email and prompted to review the submitted treatment plan from the Web Viewer simply by clicking on the embedded URL. The PRS Web Server has built‐in functionality to keep track of reviewer comments communication between submitter and reviewers. Results: The system was evaluated at two facilities with different treatment planning systems (Varian Eclipse v.8.9 and Philips Pinnacle v.9.0). The CT images and related DICOM‐RT objects for several different patients from each facility were successfully submitted and reviewed using the prototype PRS. Conclusions: The PRS has been successfully pilot‐tested for remote peer‐review of treatment planning data. The PRS allows radiation oncology service providers access to treatment planning data from any location and an ability to review it in an interactive and collaborative manner. The broader implementation of the PRS in clinical settings will improve the quality and safety of radiation therapy.
SU‐D‐214‐04: Accuracy of the Dose Calculation Algorithm of a Commercially Availale Fluence Based IMRT QA Software
Authors: Esquivel C , Zalman T , Fitzpatrick M , Vazquez‐Quino L , Gutiérrez A , Papanikolaou N , Stathakis S
Published: November 2011

Purpose: In this study we attempt to evaluate the accuracy of the dose calculation algorithm available in the DosimetryCheck quality control system used for patient specific IMRT QA. Methods: Slab geometries including inhomogeneities and ten (n=10) lung and head and neck patientsˈ plans from Pinnacle3 (ver. 9.0) and Eclipse (ver. 10.0) treatment planning systems (TPS) were evaluated. Fluence measurements acquired using an Varian aSi1000 electronic portal imaging device (EPID). The measurements consisted of open fields of various size and photon energy for the slab geometry plans and of integrated images for each patient. The EPID images were imported in the Dosimetry Check software. The corresponding plans including CT images, structures and doses were exported to the Dosimetry Check software. The software then used the imported measured fluence of each field to calculate the dose to the patient. The same fluence was also used in Pinnacle3 and Eclipse to calculate the dose to the patient. Results: Discrepancies were observed between the Dosimetry Check and the TPS EPID based calculation for the slab geometry tests with inhomogeneities. The highest discrepancies were observed, as expected, for small fields of high energy. The gamma index values between the TPS fluence based calculations and the Dosimetry Check ranged from 85–98% for the patient cases. Point dose differences of 2–15% were observed for both lung and head and neck plans. Conclusions: Fluence based dose reconstruction using patient geometry is an invaluable tool. However, it is known that the pencil beam algorithm is not able to predict the dose accurately in the presence of inhomogeneities as in the case of head neck and lung and users are advised to use caution when evaluating IMRT QA plans with inhomogeneities. On the other hand, the effect of inhomogeneities is much less profound for pelvic, abdominal and brain cases.
SU‐D‐214‐05: RTMetrix: Web‐Based Dashboard for Automated Data Mining of Record and Verify (R&V) Systems for Efficiency and Quality
Authors: Fox T , Jiang X , Elder E
Published: November 2011

Purpose: Record and verify (R&V) systems are used by most radiation oncology practices for storing the technical treatment planning and delivery data for radiation therapy patients. We have developed an automated quality assurance (QA) method with web‐based dashboards and automated quality and efficiency analysis of the technical planning and treatment delivery process. Methods: Custom software was developed (RTMetrix) to mine the R&V database and provide real‐time analysis of treatment planning and delivery data. RTMetrix was developed using object‐oriented web development software along with a relational database for storing supplemental data associated with the R&V database. It is a read‐only web application system using the R&V data associated with each patient to reconstruct clinical workflows and assess quality of the treatment delivery process. Three main web‐based dashboards with a notification messaging system have been initially developed in areas of treatment delivery, image‐ guided radiation therapy (IGRT) and physics‐based QA tools. Results: The workflow using RTMetrix is straightforward for physicians and physicists by providing the information in standard web browsers. Using RTMetrix, a web query is provided to calculate the real‐time statistics for each physicianˈs IGRT review status including the time taken to perform the review. Another web query in the system provides the average room time over any time period including one day to 10 years. An example of using room time review during the past year revealed that the use of breast patients and pediatric patients required more than 15‐minute treatment times. The final dashboard is the automated QA of the patients treated during the clinic each day. This dashboard provides an additional daily audit of the R&V system using AAPM TG‐40 chart checking rules. Conclusions: RTMetrix provides a platform for easily mining the R&V system for quality and efficiency analysis of radiation oncology departments.
SU‐D‐110‐01: A Method for 2D‐To‐4D Sorting of Dynamic MRI to Derive an Anatomic Representation of the Average Breathing Cycle
Authors: Tryggestad E , Flammang A , Roland T , Shea S , Wong J
Published: November 2011

Purpose: Beneficial “4D” treatment planning and delivery methods, most of which are under development, rely on robust characterizations of motion. Implementation of these 4D methods may be hindered by deficiencies in current pre‐treatment imaging. 4D‐CT is the current standard for deriving patient‐specific margins. However, 4D‐CT is sub‐optimal because it represents a single‐cycle “snapshot” motion per slice location which results in slice‐to‐slice inconsistencies for variable breathing. Moreover, 4D‐CT involves ionizing radiation. MRI is not thusly encumbered. We have developed a 2D‐to‐4D sorting technique for dynamic MRI to derive an average‐breathing‐cycle anatomic representation for radiotherapy planning. Methods: Healthy lung and abdominal volunteers were imaged continuously for 10–30 minutes with balanced steady‐state free precession (bSSFP) and/or half‐Fourier single‐shot turbo spin echo (HASTE) on a 1.5T MRI system (MAGNETOM Espree, Siemens). 3D volumes were scanned in sagittal or coronal planes by changing the slice location per frame. Voxels were 2×2×5 mm3 and sequence parameters were adjusted to achieve repetition times of 200–300 ms. Synchronous with image acquisition, an external respiratory trace was collected at 50 Hz. Results: A two‐step sorting technique based on the respiratory trace was developed. In the first step, all frames per slice location and phase bin were averaged, producing an “average 4D‐MRI.” From this we derived corresponding “standard deviation 4D‐MRI.” Frame averaging resulted in blurring. In the second step, raw frames were compared to the set of images per slice location from the average 4D‐MRI; a normalized cross‐correlation scoring criterion over a user‐selected rectangular ROI indicated the best‐matching respiratory phase anatomically. The subset of best‐matching raw frames per slice location and phase were averaged to produce a final representation with improved contrast. Conclusions: Dynamic MRI shows great promise as a potential standard for motion management. Future efforts will involve modifications to the bSSFP sequence for significant improvements in speed.

This work has received research personnel support from Siemens
SU‐D‐110‐03: A New Phantom Allowing Realistic Non‐Uniform Activity Distributions for PET Quantification
Authors: Kirov A S , Sculley E , Schmidtlein C R , Siman W , Kandel B , Zdenek R , Schwar R , Ayzenberg G , Yorke E , Schöder H , Humm J L , Amols H I
Published: November 2011

Purpose: To develop and test the design of a new phantom, which is capable of producing experimental models of realistic activity distributions as observed in PET patients, for the evaluation of PET quantification accuracy and image segmentation algorithms. Methods: A phantom is constructed from thin plastic foils, less than 0.1 mm thick, which are cut along computer generated contours derived from the activity distribution of a large tumor in a patient PET scan. These sheets are used to displace activity inside a rectangular non‐uniform activity (NonU) cell (11.6 × 11.4 × 10.1 cm3), filled with a single activity solution of 18F‐ fluorodeoxyglucose (FDG), thus producing a non‐uniform activity distribution with variable activity gradients within a single PET slice or across multiple slices. The NonU cell is centered in a larger cylinder containing background activity. Corrections for omitted or deformed plastic sheets and for trapped air bubbles are applied to recover the known reference activity distribution. The phantom is tested in three different PET/CT scanners and the obtained images are compared to the known reference activity for different slices. Results: The resulting images retain the features of the selected region of interest of the original PET images of a patient tumor and agree well with the known activity distribution in the phantom. Differences between the known reference activity and the PET scan were found to be strongly dependent on registration and are less than 30% for more than 65% of the voxels for most of the tested slices. Conclusions: Using the NonU phantom to produce images of known activity distributions derived from clinically realistic activity configurations will aid in more accurate testing of PET quantification accuracy and in the development of image reconstruction, artifact correction and image segmentation algorithms. Improvements of the phantom design based on the test results are suggested.
SU‐D‐110‐05: MR‐Based Dose Calculation for Prostate Radiotherapy Using Atlas‐ Based Auto‐Segmentation
Authors: Lambert J , Dowling J , Menk F , Parker J , Capp A , Denham J , Salvado O , Greer PB
Published: November 2011

Purpose: A method that could enable dose calculations to be performed using magnetic resonance (MR) images for conventional treatment planning and adaptive planning using MR‐accelerator systems would be to apply bulk electron densities to the MR images. However currently bone must be manually segmented making this impractical. This work develops and tests an atlas‐based method to automatically segment bone on pelvic MR images for dose calculations. Methods: An MR whole‐pelvic atlas was created using manually delineated scans from 39 patients. Atlas‐based pelvic‐bone auto‐segmentations were then created for 25 patient scans using deformable image registration of the atlas to each patients scan with a leave‐one‐out atlas approach. These and corresponding expert manual segmentations were compared using the Dice similarity coefficient. Bone was assigned a density of 1.19 g/cm3 and all other tissues a water equivalent density. Treatment plans were generated on the whole‐pelvis MR images and doses compared for the manual and auto‐segmented bone plans. Results: The average Dice coefficient was 0.83 (standard deviation = 0.05). The average manual bone volume was 834.6 cm3 compared to the atlas based average volume of 840.0 cm3, with a mean difference of 5.4 cm3 (0.64%). The average ICRU point dose calculated on the MR images using the atlas‐based bone segmentations was 0.2% lower (standard deviation 0.3%) than the dose calculated using the manual bone segmentations. Conclusions: The atlas based method for auto‐segmentation of pelvic bone enables MR‐based prostate radiotherapy dose calculations for treatment and adaptive planning.

This work was partially funded by a Cancer Council New South Wales Grant RG07‐06
SU‐D‐110‐06: Delineation of Target Volume Based on FDG PET‐CT Images and Its Effect on Tumor and Normal Tissue Doses
Authors: De La Fuente Herman T , Ortega H , Thompson S , Herman T , Ahmad S
Published: November 2011

Purpose: To evaluate the effect of FDG PET‐CT imaging on target volume definition, inter and intra observer perceptions, and on tumor and normal tissue doses. Methods: The positron emission tomography with fluorine‐18‐ fluorodeoxyglucose (18F‐FDG) radiopharmaceutical and computed tomography (CT) combined provide structural and functional information for the definition of tumor and radio‐resistant regions that can be treated to high doses. This study uses data from twenty patients who had CT and PET imaging for treatment plan preparation. Treatment plans used non‐opposing co‐planar beams of four to seven fields. The prescribed dose was 70.2 Gy in 39 fractions. Physicians H and T independently delineated tumor volumes on CT and PET‐CT images and treatment plans were generated. Doses to CT contoured structures were obtained from plans that were originally planned based on contoured PET‐CT fused images. Tumor volumes of PET‐ CT and CT were compared by an index of agreement (IA). The intra and inter observer variations on tumor delineation, mean, minimum and maximum tumor doses, and percent differences in uninvolved lung doses were compared. Results: The mean intra observer IA value was approximately 0.50 for both physicians. The mean inter observer IA value was 0.45 and 0.52 for CT and fused PET‐CT tumor outlining respectively. The percent differences in average minimum and mean tumor doses for PET‐CT and CT plans were 60.1% and 8.1% respectively for physician H, and 78.4% and 11.7% respectively for physician T. The uninvolved lung mean dose variations for PET‐CT and CT plans were 5.6% and 1.9% for physicians H and T respectively, and between both physicians the differences were 9.6% and 12.7% for PET‐CT and CT plans respectively. Conclusions: The volumes created on PET‐CT images by two experienced physicians were greatly different compared to volumes created on CT only, resulting in extreme differences in calculated doses.
SU‐D‐301‐01: Performance Limits of Large Area Poly‐Si X‐Ray Imagers Employing In‐Pixel Amplification
Authors: El‐Mohri Y , Liang A , Koniczek M , Antonuk L , Zhao Q , Jiang H
Published: November 2011

Purpose: Active matrix flat‐panel imagers (AMFPIs) — based on amorphous silicon thin‐film transistors (TFTs) — have been developed for a wide variety of x‐ray imaging applications at diagnostic energies. However, under conditions of low exposure or small pixel sizes, the additive electronic noise associated with readout of the pixel signal of these imagers leads to relatively low levels of signal‐to‐noise ratio — resulting in significant loss of detective quantum efficiency (DQE) and image quality. An increasingly promising approach for overcoming such limitations involves the incorporation of in‐pixel amplification circuits, referred to as active pixel (AP) architectures, based on low‐temperature polycrystalline silicon (poly‐ Si) TFTs. Methods: Theoretical performance limits for additive noise and DQE for large area imagers employing various AP designs have been explored. The methodology involves SPICE simulations of pixel circuits in an array environment employing realistic inputs for signal, as well as noise derived from individual poly‐Si TFT test devices. Pixel circuit noise performance derived from these simulations, along with other imaging parameters, are input to cascaded systems models for calculations of the corresponding DQE performance. Results: For large area imagers employing architectures comprising one‐ and two‐stage in‐pixel amplification, the calculations suggest that the effect of additive noise can be significantly diminished, leading to substantial improvement in DQE compared to that of conventional AMFPIs, especially at the low exposures associated with fluoroscopy. Such improved performance is largely maintained even for more sophisticated pixel designs incorporating additional features such as higher frame rate and selectable amplification gain. Conclusions: Active pixel imagers based on poly‐Si TFTs offer a potential alternative to conventional AMFPIs for overcoming the decline of DQE at low exposures in fluoroscopy. The combination of detailed circuit simulations and cascaded systems modeling provides a powerful tool for guiding the development of future generations of ever more sophisticated imagers.

Work Supported by NIH grant R01‐EB000558
SU‐D‐301‐03: Next‐Generation Angiography: A Theoretical Comparison of Signal and Noise in Photon‐Counting and Dual‐Energy Approaches
Authors: Tanguay J , Cunningham I
Published: November 2011

Purpose: Energy‐resolving photon‐counting (EPC) x‐ray detectors are being developed in a number of research laboratories around the world. An exciting prospect for these detectors is the ability to suppress non‐iodinated structures in an angiographic image without motion artifacts that limit the use of conventional digital subtraction angiography (DSA). However, dual‐energy technology also has the potential to provide background‐removed angiograms without motion artifacts. We develop a general theoretical framework for estimating image signal and noise in background‐suppression techniques in angiography and use it to directly compare image quality in dual‐energy angiography (DEA) with image quality anticipated using EPC detectors Methods: We developed a method for estimating iodine signal and noise in a general background‐removal technique that uses either energy‐ integrating or EPC x‐ray detectors. We applied the developed framework to the task of separating iodine from soft tissue using DEA with low and high applied tube voltages of 50 kV and 80 kV, respectively, and energy‐resolved angiography (ERA) with a 70‐kV applied tube voltage and an EPC detector with three energy bins. We compared the signal‐difference‐to‐noise ratio (SDNR) in an iodine specific image that could be obtained with each technique. We compared the theoretical predictions to calculations obtained using Monte Carlo simulations of the same imaging task. Results: Under the imaging conditions considered, SDNR obtained using ERA is only higher than that obtained using DEA by a factor of 1.1. The theoretical SDNR predictions compared very well with results from the Monte Carlo calculations for both DEA and ERA. Conclusions: We found that, for the task of isolating iodine in soft‐tissue, SDNR obtained with ERA is only greater than that obtained with DEA by 10 % for the same patient entrance exposure. This suggests that research resources may be better spent on developing dual energy methods by improving detectors for dual‐energy applications.
SU‐D‐301‐05: Angular Dependency of the Slice Sensitivity Profile in Tomographic Breast Imaging
Authors: Nosratieh A , Yang K , Boone J
Published: November 2011

Purpose: To study the effect of angular acquisition on the slice sensitivity profile (SSP) in tomographic breast imaging, for both breast CT and tomosynthesis. Methods: Brass disks (0.025 mm thick) ranging in diameter from 2.5–20 mm were placed within mammography phantoms of varying thicknesses (3–6 cm). The disks were imaged using a prototype digital tomosynthesis system (Selenia Dimensions, Hologic Corporation, Bedford, Ma). The tomosynthesis system acquires images over an angular acquisition range of 15‐degrees. The same brass disks were used to measure the SSP in breast CT, using a 14cm‐diameter cylindrical polyethylene phantom. The bCT angular range spanned from 15 to 360‐degrees. A subset of the projection images were reconstructed with a filtered back projection algorithm to simulate limited‐angle acquisition. The SSP was determined by measuring the mean gray‐scale (GS) in the tomographic images along the z axis of the scan corresponding to the disk position. Normalized profiles of the background‐corrected mean GS values were generated as a function of the distance away from the detector. The full‐width at half maximum (FWHM) GS intensity was determined. Results: As the angular acquisition range increases, the SSP narrows and results in a smaller FWHM value. The FWHM values of the SSP for the smallest disk at (2.5 mm‐diameter) were 8.6 mm, 4.2 mm, and 0.8 mm for 15, 40, and 180 degrees, respectively. Conclusions: Limited angle tomography results in a broadening of the SSP, inversely proportional to the angular range of acquisition. The SSP approaches a minimum as the angular coverage exceeds 180 degrees.

One author receives funding from Hologic (Bedford, Mass).
SU‐D‐301‐06: Impact of Non‐Stationarity in Breast Tomosynthesis on Task‐Based Imaging Performance
Authors: Richard S , Samei E
Published: November 2011

Purpose: Reconstructed tomosynthesis data is known to exhibit non‐stationarity, (i.e., the pixel mean and standard deviation depends on location), which is expected to impact our ability to accurately assess imaging performance. The purpose of this study was to characterize the magnitude and impact of non‐stationarity on various imaging tasks. Method and Materials:A phantom consisting of an array of 15 aluminum oxide beads was constructed to measure the 3D modulation transfer function (MTF) across a range of locations in the breast. Similarly, a uniform breast phantom was used to measure the noise‐power spectrum (NPS) across the same range of locations. Simulated tomosynthesis and real tomosynthesis images were acquired to characterize independently the impact of non‐stationarity on quantum and anatomical noise measurements and the impact of scatter on non‐stationarity. The MTF and NPS were compared across locations in terms of measures of sharpness and noise and furthermore combined with a task function to measure task‐based performance indices including the detection, localization, and size estimation of a 4 mm mass. The variability and range of the indices were characterized across the different regions of the breast. Results: The 3D MTF and NPS varied in shape and orientation across location. The measure of sharpness and noise was found to vary by 3% and 2%, respectively, from the center to the edge (located 4 cm from center). The task‐based performance also depended on location, with 4% variation for a detection task and 3% variation for a size estimation task. Overall, variation was mostly along the lateral direction of the breast. Conclusions: This work provides guidelines for the application of Fourier‐based metrics in breast tomosyntehsis. While the shape and orientation of the 3D MTF and NPS are dependent on location, variability of the task‐based performance indices was found to be minimal.
SU‐D‐220‐01: Hybrid X‐Ray/Ultrasound Imaging Approach for Patient Positioning and Real‐Time Tracking in IGRT
Authors: Schlosser J , Salisbury K , Xing L , Hristov D
Published: November 2011

Purpose: Projection x‐ray imaging and telerobotic diagnostic ultrasound can complement each other as image guided radiation therapy (IGRT) tools. The purpose of this study was to develop and evaluate an IGRT system and workflow that integrates these two modalities for patient positioning and real‐time tracking. Methods: In the designed workflow, pre‐treatment positioning is performed by stereoscopic x‐ray imaging of target surrogates, such as implanted fiducial markers. When the target is in position, a reference soft‐tissue ultrasound image of the target is acquired using a novel telerobotic ultrasound system. During treatment beam delivery, the ultrasound system continuously acquires spatially localized soft tissue images concurrently with the acquisition of megavoltage (MV) x‐ray cine images from the treatment beam. Target position is monitored in real‐time using both modalities. Ultrasound monitoring signals result from comparison of the reference image template to the current ultrasound image using cross correlation based techniques. X‐ray monitoring signals rely on tracking fiducial markers visible in the MV images. To evaluate the approach experimentally, an intensity modulated radiation therapy (IMRT) plan for a tissue‐mimicking multi‐modality phantom with implanted gold markers was simulated. The phantom was placed on a motion stage, and target shifts before and during treatment were simulated. Results: Target displacements were monitored in real‐time by the ultrasound system and detected below 3 mm. The displacements were subsequently confirmed with kV x‐ray localization, and the target was repositioned. During IMRT delivery, view of fiducial markers was blocked by multi‐leaf collimator leaves in some MV cine images. Ultrasound complemented MV image tracking by successfully monitoring the target during periods of marker blockage. Conclusions: Strengths of x‐ray and ultrasound modalities may be combined to achieve an IGRT system capable of (1) absolute pre‐treatment patient positioning, and (2) robust real‐time displacement monitoring during beam delivery without additional dose to the patient.
SU‐D‐220‐04: 3D US Imaging Combined with Active Breathing Control as a New Solution for IGRT in SBRT of Liver Lesions
Authors: Bloemen E , Meer S , Visser P , Buijsen J , Steenbakkers I , Lammering G , Verhaegen F
Published: November 2011

Purpose: To establish the use of 3D ultrasound (US) combined with Active Breathing Control (ABC) for IGRT in liver lesions. Methods: A 3D US device was used. An US probe was redesigned to obtain optimal probe tracking conditions for IGRT of the liver. At the treatment planning stage a reference US scan was performed in mid‐ventilation, with the aid of an ABC system. US and mid‐ventilation CT images were fused, the lesion was contoured and beams and isocenter from the treatment planning system were imported. Prior to each treatment an US scan in mid‐ventilation was acquired. The current position of the lesion was compared to its reference position. The resulting 3D US shift was compared to the EPI shift. Results: Due to breathing the liver deforms and the relationship between the lesion and surrogates, used as an assisting tool for US image segmentation, changes. The treatment plan is based on the 50% expiration CT images. Ideally, the IGRT method should guide the lesion to the same position as the planned position. In this study we demonstrated that the combination of US scanning and ABC optimized our image quality and resulted in a smaller inter‐ and intra‐observariation of image segmentation. We demonstrated a significant difference between US and EPI image guidance, demonstrating that IGRT based on bone structures alone is not sufficient. Conclusions: Accurate IGRT in SBRT of liver lesions, using US imaging in combination with ABC is feasible. It allows accurate positioning of liver lesions in the treatment beams.
SU‐E‐E‐03: Advantageous Liver Sparing by Non‐Coplanar Volumetric Modulated Arc Therapy to Intrahepatic Malignancy: A Dosimetric and Feasibility Study
Authors: Tsai Yi‐Chun
Published: November 2011

Purpose: Volumetric modulated arc therapy (VMAT) has been an evolving technique with improved conformity, normal organ sparing, and the additional freedom of non‐coplanar beam design as compared to helical tomotherapy. This study was to compare the dose‐volume liver sparing effect between coplanar (C) with and without non‐coplanar (NC) design for volumetric modulated arc therapy (VMAT), and to verify the delivery accuracy in patients with liver malignancy treated by the integrated NC‐VMAT. Methods: Sixteen patients with intrahepatic malignancies were planned with VMAT using coplanar with and without the additional non‐coplanar beams. All the prescribed doses were normalized to the fraction size of 2 Gy. The dose‐volume data of liver were calculated by the total liver minus the gross tumor volume. The mean dose, volume fraction receiving more than certain dose x Gy (Vx), and effective volume of liver (Veff) were compared with paired Student t test. Seven patients treated by the integrated NC‐VMAT were verified for dose accuracy using 2‐dimensional array method (MapCheck2). Results: With comparable target coverage, NC‐VMAT provided significantly better liver sparing effect than C‐VMAT in mean dose (16.52±7.8 Gy vs. 17.9±8.9 Gy, p=0.02), V5 (50.3±15.2% vs. 53.8±16.6%, p=0.02), V10 (33.1±10.8% vs. 35.3±13.1%, p=0.08), V20 (24.6±10.3% vs. 26.6±12.2%, p=0.04), V30 (20.1±10.3% vs. 22.0±11.9%, p=0.02), and Veff (9.6±5.2% vs. 10.6±5.9%., p=0.03), respectively. Among the 7 patients treated by NC‐VMAT with the average delivery time of 368±105 seconds, All but one patient with the dose accuracy met the 3%/3mm criteria of more than 95%, and all patients completed the treatment with no more than grade 2 liver toxicity. Conclusions: Liver is a sensitive organ to even low‐dose irradiation, is located asymmetrically in the abdomen, and has irregular shape. NC‐VMAT may be advantageous in liver sparing and feasible for the accurate delivery.
SU‐E‐E‐04: The Doctor of Medical Physics, a New Professional Degree
Authors: Kubricht W
Published: November 2011

Purpose: In the last 2 to 3 decades, rapid changes have occurred in the fields of radiology oncology prompting a need to rethink training required for medical physicists. It is clear that traditional approaches of obtaining an academic M.S. or Ph.D. degree, coupled with minimal on‐the‐job training, have not produced an acceptable success rate for credentialing by the American Board or Radiology (ABR). As a result, the ABR has taken steps to define required training criteria prior to examination in an attempt to resolve this matter. Methods: In 2006, initial steps began at Texas Tech University to design a new doctoral degree to prepare students to successfully enter and compete in the field of medical physics. This 5‐year degree, the Doctor of Medical Physics, is a clinical degree patterned after the MD degree. This is a new degree program that is complimentary to and not competitive with traditional M.S. and Ph.D. degrees designed to prepare students for academic careers. The Doctor of Medical Physics is appropriate for those physicists who wish to focus their careers in clinical medical physics in an interactive role with their physician colleagues. The first year is indeed the first year of medical school, with the second and third years focused on an interdisciplinary didactic program including physics, biology, mathematics, and related topics. Years 4 and 5 include a structured residency program with graduation contingent on successful completion of the written ABR Examinations. The opportunity exists for a final fellowship year as the student prepares for the oral boards. Results: In 2010, this degree was approved by the Southern Association of Colleges and Schools, Commission on Colleges (SACS‐COC) and by Texas Higher Education Coordinating Board. Conclusions: Other schools in Texas are in various stages of implementing similar degree programs.
SU‐E‐E‐05: The Compute Cloud, a Massive Computing Resource for Patient‐Independent Monte Carlo Dose Calculations and Other Medical Physics Applications
Authors: Constantin M , Sawkey D , Mansfield S , Svatos M
Published: November 2011

Purpose: Massive computing resources are needed to generate an extensive linac phase‐space (PHSP) database for different radiotherapy beams that could serve as a starting point for several user‐applications, such as patient‐dependent dose calculations or Monte‐Carlo‐based quality assurance procedures. The goal of this project is to disseminate our knowledge about performing patient‐independent Monte‐Carlo dose calculations on the Amazon Elastic Compute Cloud (EC2) and educate medical physicists on technical aspects such as simulation instance management and cluster coordination while ensuring data security for a low CPU cost. Methods: Amazon‐Web‐Services, along with Google, Microsoft, IBM, etc, offers resizable compute capacity in the cloud changing the economics of computing by eliminating the server fixed expenses. A cost‐efficient elastic cluster is available for a wide users community who can perform Monte Carlo simulations or other numerical applications using Amazon Machine Images. These virtual machines can be configured to work in a particular scientific environment, i.e. GEANT4 or PENELOPE. GEANT4 patient‐independent dose simulations were launched in parallel on EC2 using high CPU extra‐large spot instances (7 GB of memory, 8 virtual cores at 2.13 to 2.44GHz). Data storage was performed using the Simple Storage Service (S3). The S3 Organizer was used to upload the simulation or download multiple files. The 4‐layer EC2 security system, composed of the host/guest operating systems, Firewall, and signed secret access keys, ensures data privacy. Results: A local script was set‐up to launch multiple dose calculation instances on EC2 and automatically save the results on S3. Geant4‐application development, testing, and debugging were performed on a local workstation, along with data analysis and comparison with experiment. IAEA‐compliant patient‐independent PHSP files were generated and dose calculations were successfully validated against experiment. Conclusions: Cloud computing offers a low‐cost alternative for improved radiotherapy planning and optimization algorithms by enabling beam transport and Monte Carlo‐based dose calculations.

Work supported by Varian Medical Systems
SU‐E‐E‐06: The New ABR Exam: What Have We Done to Change the Way We Teach Physics to Residents?
Authors: Kanal K , Dickinson R , Zamora D , Stewart B
Published: November 2011

Purpose: Our purpose is to develop a new physics course integrated with radiology clinical content and practice to prepare radiology residents to take the new American Board of Radiology (ABR) diagnostic radiology exam that went into effect on July 2010. Methods: Our old physics course was taught over a period of one year, and consisted mainly of lectures taught from an imaging physics textbook. We now offer a two year course that primarily uses the RSNA/AAPM physics modules supplemented with other resources such as the AAPM physics curriculum and AAPM/RSNA physics tutorials. Various physics topics will be discussed in a non‐serial order so that the residents develop an understanding of a breadth of topics in the first year. Each class session requires assigned reading or review before class. During class, we focus on important and relevant concepts from the assigned reading. We meet with the residents every other week and have one scheduled clinical lecture a month. The clinical lecture may come in the form of a radiologist teaching physics with emphasis on clinical relevance, a lab demonstrating physics concepts, a show and tell of radiology equipment, or a guest speaker from another institution. We are using audience response systems to encourage participation and discussion, and using tag‐team teaching to generate interest and discuss clinically relevant questions and answers. We have also redesigned the physics course website to make it more user‐friendly. Results: We donˈt know yet. Only time and the success of our residents taking the board exam in 2013 will demonstrate whether the new format is working Conclusions: We anticipate that the new format will work, but this is only possible providing time and effort is expended by physicists in making changes to the old teaching methods to benefit the residents and the radiology community as a whole.
SU‐E‐E‐09: On‐Line Target Localization with Stereotactic Body Frame and Cone Beam CT for Accelerated Partial Breast Irradiation
Authors: Zhu J
Published: November 2011

Purpose: On‐line target localization with Cone Beam CT (CBCT) alone has the limitation that the detected offsets of patient tilt and spin cannot be corrected. This causes not only the geometric but also dosimetric quality compromise to the accelerated Partial Breast Irradiation. In this work, the stereotactic body frame was used for tuning the patient tilt and spin by means of its equipped air bags. The resultant geometric and dosimetric improvements were presented. Methods: On each treatment fraction, patient setup for accelerated Partial Breast Irradiation was initially performed based on the stereotactic body frame. CBCT images were acquired and registered with planning CT images to match the breast and the cavity. Offsets of patient position in the anterior‐posterior, lateral, longitudinal as well as the couch rotation were corrected by controlling the linear accelerator. Patient tilt and spin were corrected by justifying the air cushion of the stereotactic body frame. Geometric and dosimetric improvements were evaluated by calculating the physic depths and the depth doses of all treatment fields based on the CBCT images with and without patient tilt and spin justification. Results: The average magnitude of corrections to patient tilt and spin are 2.4 ±1.2 degree and 3.6 ±2.3 degree (2 patients, 20 fractions). Without tilt and spin justification, the average physic depths of all treatment fields were off by 12±7.5mm which causes depth doses off by 6.5±2.1%. Conclusions: Combining the stereotactic body frame with the Cone Beam CT for accelerated Partial Breast Irradiation demonstrated the ability to improve the quality of dose delivery. It can be implemented as routine procedure in clinic.
SU‐E‐E‐13: Validation and Testing of the Integrity and Consistency of Overall Performance of Tomotherapy System
Authors: Jones Q , Jones Q
Published: November 2011

Purpose: T o validate and test the integrity and consistency of the overall Tomotherapy system in delivering of an IMRT plan, producing of a Plan Adaptive from its MVCT scan, dose delivered to MVCT scan, and matching and shifting of a patient positioning using its MVCT scan. Methods: The phantom was constructed with a solid water slab on the bottom, an IˈmRT MatriXX in between, and another solid water slab on the top. A Tomotherapy plan was created that contained a target volume in the middle of the phantom and 2 volumes of interest on the lateral and posterior of the target area and was optimized to deliver a prescription dose to the target while minimize the dose to the volumes of interest. A DQA plan was then created and delivered to the phantom to compare the planned and the delivered doses. The phantom was positioned on the treatment couch and scanned to verify the MVCT system in matching and shifting the phantom accordingly to the positioning offset position. The scan dose was also measured from the MVCT scan of the phantom. The MVCT image dataset was then used to create a Plan Adaptive to compare the verification dose and the planning dose. Results: Measuring and analyzing of the delivered dose to an ionization array of the same phantom and IMRT plan on a routine basic can validate and detect the discrepancy of consistency of the Tomotherapy system. Conclusions: This QA routine indicates the acceptable application of an ionization array in testing the overall performance of the Tomotherapy system. Further recommendation includes incorporating an inhomogeneity phantom system such as mix the slabs with lighter and/or heavier density material. This QA routine can also be used on other Linacs.
SU‐E‐E‐14: Fabrication of Divergent Wax Based Tissue Compensators for Head and Neck Radiotherapy
Authors: Srinivas C , Shenoy K , Shenoy V , Kulal B , Ravichandran R , Supe S
Published: November 2011

Purpose: Tissue obliquity is a common problem in conventional radiotherapy to head and neck region. This results in generation of hot spots and non‐uniformity of dose in the planned treatment volumes. Ellis compensators made of non divergent aluminum metal rods have been suggested. The purpose of this study is to develop a divergent wax based tissue compensator (DWTC) to address tissue obliquity and verify it dosimetrically before clinical implementation. Methods: A method is developed for a photon field of size 20 cm × 20 cm from a telecobalt machine having Source Skin Distance (SSD) of 80 cm and Source Diaphragm Distance (SDD) of 45 cm. A jig was made with 3 Perspex sheets kept at specified distances which were perforated to allow radial divergence of metal spokes (depicting pencil beams) to pass through. Dose compensator is fabricated with dental wax based on the measured tissue thickness variations in different planes. Patient anatomy was reproduced on a POP which was placed at the bottom of the jig and a divergent compensator was developed at the top of the jig by placing wax on the upper end of the metal spokes. The efficacy of DWTC in the treatment plane was confirmed with Imatrix device using a wedge shaped and two semi neck water phantoms with and without compensators. Results: The profiles with and without compensator verified by Imatrix device showed adequate tissue compensation for clinical purposes. The uniformity of the dose in the treatment region is well within 3%, 3mm criteria (dose evaluation parameter). Conclusions: The method developed for DWTC could be adopted for a linear accelerator with different SSD and SDD. The entire process of making a DWTC is simple, accurate and can be easily fabricated.
SU‐E‐E‐15: Combined IMRT and 3D Plan Improves Results of Lung Exposure in Radiation Treatment of Lung Cancer Patinets
Authors: Shtraus N , Meir Y , Schifter D , Corn B , Soyfer S
Published: November 2011

Purpose: Lung Cancer represents the major reason for mortality in the modern society. The disease is usually diagnosed in the advanced stage. External beam radiation therapy is the essential component in the treatment of stage 3 Non Small Cell and Small Cell Lung cancer patients. IMRT proved as preferred technique above conformal 3 D in term of sparing lung tissue and subsequent radiation pneumonitis. In our work we investigated the impact of innovate technique of combination of 3 D and IMRT on dose distribution in centrally located lung cancer patients. The rational of combination is based on the inability of IMRT technique to provide the oppositional fields arrangement desired in order to avoid the additional lung tissue Methods: Three treatment plans were generated for seven patients with lung cancer. For every patient 3 D conformal, IMRT and combined 3D and IMRT plans were compared for V5, V10, V20, V 30 and mean dose of the lung DVH, maximal dose to the esophagus and spinal cord Results: The DVH of the lung in three comparative plans for 3D, IMRT and combined plans for the total lung ‐GTV was as follow: V5‐63.2±8.6%, 63.9± 9.2%, 56.6± 11.4%; V10‐53.07± 10.1, 52.3± 11.2, 38.8± 9.6; V20‐27.6± 6.7, 31.1± 7.0, 20.6± 2.3; V30‐14.3±4.6, 13.36± 0.37, 14.96± 1.22 respectively. The maximal doses to esophagus was 53.21± 3.05, 54.4± 4.67, 52.3± 4.5 Gy respectively. Maximal dose to the spinal cord was 42.5± 2.9, 39.58± 1.2 and 43.7± 4.5 Gy respectively Conclusions: Combined 3 D and IMRT technique results in better lung tissue sparing comparing to other treatment plans
SU‐E‐E‐17: Experience with Helical TomoTherapy Commissioning and Quality Assurance of Twin Peaks Linac vs. Earlier Models
Authors: Movahed A , Rabbani B
Published: November 2011

Purpose: To evaluate the differences and stability of Twin Peaks linac in TomoTherapy system. Methods: In general, the following checks are performed prior to using a new x‐ray machine for radiotherapy treatment: acceptance testing, dosimetric commissioning, plan verification, quality assurance procedures, radiation and interlocks safety. The beam modeling of TomoTherapy machine involves four steps: (I) static beam profiles, (II) helical data, (III) MLC data and (IV) IMRT plan verification. The commissioning of the Twin Peak accelerator was conducted with a physicist from the TomoTherapy Inc. Results: Our experience and data comparison is based on commissioning results of this unit equipped with TomoTherapyˈs new Twin Peaks linac and the earlier version of Tomoˈs conventional linac and on nine month of clinical usage. The photon beam spectrum of helical Tomotherapy in the treatment mode has approximately a maximum energy of 5.7 MeV. Our experience with Twin Peaks yielded about 5.2 MeV. Similarly earlier units operate with a dose rate of about 850 cGy/min at the isocenter. Our unitˈs dose rate is about 835cGy/min. During nine months period, deterioration of the target was not observed compared to the earlier models. The dimensional characteristics of the Twin Peak LINAC have maintained the same SAD specification, and spot size capability. There was no difference in the beam performance of units with the two different types of LINAC. Details of the data will be presented Conclusions: Based on acceptance tests and commissioning of Twin Peaks linac helical TomoTherapy Hi Art system and nine months of clinical usage, we found out that the energy and dose rate are lower than the earlier version linacs. The target behavior and profile shoulder curves unlike the other earlier linac have not shown so far any changes. Overall, it is a much better target and improved technology versus the earlier version.