bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐BRB‐02: Independent Two‐Dimensional Dose Validation for TomoTherapy
Authors: He W , Chang S , Chen W , Baikadi M , Tsang C , Peters C , Brereton H
Published: November 2011

Purpose: To develop a two‐dimensional (2D) dose calculation software for helical tomotherapy with absolute dose validation capability. Methods: This in‐house software takes advantage of archived patient treatment planning documents, initial coordinates of red and green lasers, central coronal plane slice numbers of the Cheese phantom, and clinical dosimetric functions. A tomotherapy DQA plan has to be generated and archived first. The software performs an independent absolute dose check to the tomotherapy plan. The software calculates the 2D dose map of the central coronal plane of the Cheese phantom, and the 2D map is narrowed into a 3.2cm×3.1cm rectangular on the plane to save calculation duration. Doses of points on the plane are calculated with 1 mm resolution, so that a total of 992 points are calculated for each patient case. The center of the 2D square is the cross point of red lasers, which is the center of the Cheese phantom by default. The 2D dose map calculated is thereafter compared with the planned one, which is a 3D dose matrix from the DQA plan. Gamma index is then calculated with 3mm and 5% criteria. Results: The newly developed software has been tested on ten tomotherapy patients (cases of 1 pancreas, 2 brain, 1 stomach, 1 lung, 1 head & neck, 3 prostate, and 1 esophagus). The gamma distributions are all passed with a minimum ratio of 95%. Conclusions: An in‐house independent dose calculation software for helical tomotherapy has been developed to independently validates 2D doses with gamma index. Gamma in this software is calculated by comparing the 2D calculation to 3D doses, which makes the introduced method more superior than normal IMRT or tomotherapy QA. Validation of the software on more cases and more tomotherapy units is necessary.
WE‐C‐BRB‐07: Influence of MLC Width on Intensity Modulated Plans
Authors: Mihailidis D , Mallah J , plants M , Kagadis G
Published: November 2011

Purpose: This study presents a comprehensive dosimetrtic comparison between all the MLC systems that may be used for treatment planning in IMRT and SBRT. The clear clinical benefits of smaller MLC leaf widths, in the presence of IMRT, are questionable we found. We underline the importance of dosimetric benchmarking of IMRT. Methods: The RPC H&N and TG‐119 phantoms and several clinical cases, were planned successively for NovalisTX (2.5mm), Synergy‐BM(4mm), Artiste(5mm), Varian(5mm), and Primus (10mm) within the same planning system and multi‐6MV beam arrangements. The Primus was successfully benchmarked against the RPC and the TG‐119 phantoms and was used as reference. IMRT was utilized with same optimization parameters for all MLC systems, respectively. The target coverage was evaluated via a conformity index (CI) and the OAR sparing was evaluated from the dose to a “Ring” structure created around the target. Comparisons based on dose distributions, DVHs and gEUD for all plans were performed. Results: Surprisingly, we noticed no difference in TV coverage and sparing of OARs. Furthermore, the isodose distributions and DVHs for the RPC and TG‐119 phantoms show no major dosimetric gains for the smaller MLC widths, the cord for the RPC phantom received lower doses with the 1cm MLC system (our benchmark reference), for the same TV coverage across the systems. For the clinical cases, all systems gave comparable TV coverage and sparing of the OARs, with the Primus MLC system again, to provide slightly better conformity (lower CI). This better dose conformity is the reason that the dose fall‐off within the “Ring” structure is higher, for the Primus system. Conclusions: This study is the first that comprehensively compares the majority of todayˈs MLC systems and has shown no significant indication that smaller MLC widths can lead to optimal plans, when multi‐field IMRT techniques are used for planning.
WE‐C‐BRB‐09: Volumetric Modulated Arc Therapy Based Total Marrow Irradiation and Dosimetry Verification
Authors: Liang Y , Mell L , Kim G
Published: November 2011

Purpose: This study develops treatment planning and a comprehensive dosimetry verification procedure for volumetric modulated arc therapy(VMAT) based total marrow irradiation(TMI), a form of targeted total body irradiation(TBI). Methods: The simulation CT of 3 patients treated with TBI were used. Planning was done with Eclipse treatment planning system(Varian Medical Systems, CA). Planning volume(PTV) was defined as skeletal bone, rib, and sternum, with 3mm margin, from head to mid‐femur. In total marrow and lymphoid irradiation(TMLI), PTV is expanded to include spleen and major lymph nodes. The mandible, maxillary bones and forearms were excluded. The dose prescription was 12Gy in 6 fractions. The PTV is divided into head‐and‐neck(H&N), chest and pelvis regions. Correspondingly, there is separate plan for each region, composed of 2∼3 arcs/fields with multiple isocenters along patient axial direction. The 2D dosimetry verification was conducted with EBT2 Gafchromic film(International Specialty Products, NJ) for gamma evaluation and ion chamber for absolute point dose measurement, using a IMRT phantom(Computerized Imaging Reference Systems, VA) and RIT software(Radiological Imaging Technology, CO), with emphasis of junction area between neighboring plans for hot/cold spots. We further conduct volumetric dose verification with electronic portal imaging devices and DosimetryCheck program(Math resolutions, MD). The gamma evaluation criteria were 5% absolute point dose difference and 3mm distance to agreement. Results: More than 90% of PTV is covered by 100% of prescribed dose. Compared to TBI, average dose reduction on critical organs are: lung(10%), kidney(53%), liver(48%), Eyes(69%), and heart(51%). Junction areas show average 98% gamma passing rate and 3% absolute dose difference; volumetric portal dosimetry show average 91% gamma passing rate and 2% absolute dose difference, compared to plan dose. Conclusions: Adequate target dose coverage and reduced normal organ dose are observed. A comprehensive dosimetry verification procedure is developed. The initial results are encouraging and warrant further investigation towards clinical implementation.
WE‐C‐BRB‐12: Moving from Gamma Based to Patient DVH Based IMRT QA
Authors: Zhen Heming , Nelms Bejamin E. , Tomé Wolfgang A.
Published: November 2011

Purpose: In this work we study 1) the correlation between patient DVH deviations and 3D gamma passing rate of the whole patient volume, 2) the correlation between patient DVH deviations and gamma passing rates of each corresponding ROI, and 3) the capability of an software/algorithm that predicts patient DVH deviations based on planar QA result. Methods: 96 unique “imperfect” step‐and‐shoot IMRT plans were generated by applying 4 different types of error—induced beam models on 24 clinical Head/Neck patients. The doses in each patient as well as QA phantom were then recalculated using an error‐free beam model to simulate the real delivery. The degree of induced errors was tuned to result in planar QA results that are commonly achieved in clinics. Clinically relevant patient DVH deviations, as well as 3D Gamma passing rates for both the whole patient volume and each corresponding ROI were derived by comparing the “delivered” and planed patient dose. Predicted patient DVH deviations were generated by perturbing planned dose based on simulated results of per beam planar QA in a phantom, using a commercial software/algorithm. Results: Weak to moderate correlation were found between clinically important patient DVH metrics (CTV‐D95, parotid Dmean, spinal cord D1cc, and larynx Dmean) and 3D patient gamma passing rate (3%/3mm, 2%/2mm, 1%/1mm) for whole patient volume as well as for each corresponding ROI. Predicted DVH deviations were in good agreement with actual DVH deviations. Conclusions: Gamma passing rate, even calculated in 3D for each specific ROI in real patient, has limited power in predicting clinical impact in terms of patient DVH deviations. The software/algorithm has potential to accurately predict these DVH deviations using the plan information and phantom planar QA results. Moving from Gamma based to patient DVH based IMRT QA appears to be both necessary and possible, and is therefore suggested.

This is an unfunded work however one of the authors (Dr. Benjamin E. Nelms) serves as a consultant to the vendor (Sun Nuclear, Melbourne, FL) of the software that is used in this study.
WE‐C‐214‐03: ECCK — A Computer System of Automate Patient Chart Checking
Authors: Yang D , Wu Y , Yaddanapudi S , Rangaraj D , Goddu S , Brame S , Mutic S
Published: November 2011

Purpose: ECCK (Electronic Chart ChecKing) is a clinical computer system (software and database) designed to improve quality, efficiency, and frequency of patient chart checking. The goal is to use computer programs to automatically review patient treatment data and to highlight discrepancies and potential concerns through color‐coded reports and email messages. Methods: ECCK contains a dedicated PC workstation, a separate database server and a data storage server. It integrates many different technologies, including SQL database, data structure design, DICOM, PACS, dynamic HTML, javascript, MATLAB, C++ and image processing. ECCK contains 200+ MATLAB programs, many C++ programs, DHTML design templates, style sheets, javascript programs and design documents. Most ECCK programs run on the ECCK workstation. Patient data are obtained from the treatment planning system and oncology information system (OIS) server in both native format and DICOM format, and analyzed according to predefined rules with logical conditions. Reports, generated in DHTML format, are stored on the storage server and indexed in database. A standalone report‐browser program is run by users on any computer in the department. Other features include OIS database querying and offline document browsing. Results: ECCK functionality is purpose dependent and varies for therapists, physicians, and physicists. For physics, ECCK checks patient prescriptions, beam parameters, setup parameters, fractionation schedules, treatment calendar, treatment records, beam delivery history, existing of mandatory documents and images, etc. Conclusions: ECCK is useful to reduce the repetitive routine work of users, and to improve the speed and accuracy of chart checking. ECCK enables increased frequency of patient chart audits, and allows verification tasks which are not easily performed by humans. While human is the ultimate expert, ECCK ensures a consistent amount of quality in the chart checking process which is otherwise impossible to maintain.
WE‐C‐214‐04: ADQ — A Software Tool That Automatically, Autonomously, Intelligently and Instantly Verify Patient Radiation Therapy Beam Deliveries
Authors: Wu Y , Mutic S , Rangaraj D , Yaddanapudi S , Brame S , LaBrash J , Yang D
Published: November 2011

Purpose: To effectively mitigate errors in IMRT radiation therapy delivery, all beams, all fractions, for all patients should be checked in vivo, immediately, automatically, autonomously and intelligently for integrity, quality and safety. For this purpose, ADQ or Automatic Dynalog QA, is implemented for instant and automatic patient delivery beam verification. Methods: ADQ contains multiple functional modules. DICOM receiver program is developed in C++ to receive DICOM‐RT Plans from treatment planning systems, process data and save to database. The verification tool is implemented in MATLAB that automatically validates beam parameters (gantry angle, collimator angle and positions, MLC positions, fluence maps, etc.) between the treatment plans and recorded dynamic MLC log files, generate reports for each treatment session, and send out alert emails for detected urgent problems. Report reviewer is implemented in C++ that enables physicists to review, comment and confirm reports. ADQ programs use own database and Mosaiq R&V database. Simple, automatic and no human intervention is needed unless an error is detected. Results: ADQ is running to generate near real‐time QA reports for every treatment date. DICOM receiver is running 24 hours to collect plans. Report reviewer deployed through network facilitates easy access to reports. All IMRT beams delivered to the patients are checked for a period of four months to study the reliability, MLC performance, false positive rate and importantly identify true positive. More than 80000 thousand beams from 4 different Linacs were analyzed up‐to‐date. Conclusions: We developed new software tools to improve the RT treatment QA by automatic checking patient treatment beam delivery records for each patient and each treatment session. Report data achieved in database can be easily used for further studies, for example, analysis of MLC leaf failures.
WE‐C‐214‐05: A Quantification of the Effectiveness of Standard QA Measures at Preventing Errors in Radiation Therapy and the Promise of in Vivo EPID‐Based Portal Dosimetry
Authors: Ford E , Terezakis S , Yang Y , Harris K , Mutic S
Published: November 2011

Purpose: We analyze the ability of standard quality assurance (QA) checks in radiation therapy to prevent errors commonly observed in the course of clinical operations. Methods and Materials: Near‐miss and error reports were collected over a 3‐year period by means of voluntary reporting systems at two academic medical centers. We analyzed 250 near‐misses, events that did not affect patients but which had the potential to do harm with at least “moderate side effects” (level 3 or greater on the French ASN scale) if they had not been detected prior to treatment. We determined which of these events could be detected by 13 commonly employed QA measures, including but not limited to physician plan review, physics chart check, port films, cone‐beam CT. We then determined which events could have been detected by in vivo portal dosimetry with an electronic portal imaging device (EPID). Results: QA checks vary greatly in their ability to detect reported errors. Port films, one of the most effective measures in place, had a 53% detection efficiency, while pre‐treatment IMRT QA had a detection efficiency close to 0%. EPID‐dosimetry had a detection rate of 83%. In some cases, EPID‐dosimetry would have detected errors which were introduced after the initial IMRT QA. Conclusions: No single QA check currently employed is 100% effective at detecting common errors. Most checks currently in use are less than 50% effective. By contrast, the data indicate that in vivo EPID‐dosimetry may be substantially more effective. Further work is needed to determine if these patterns hold across multiple institutions.

Pilot research grant from Elekta Inc.
WE‐C‐214‐07: A Global Digital Benchmark and QA Data Center for Radiotherapy Quality Assurance
Authors: Xiao Y , Hurksman C , Cui Y , Doemer A , Brown N , Salehpour M , Mallah J , Mihailidis D , Palta J , Salter B , Galvin J , Moran J
Published: November 2011

Purpose: To establish a centralized database platform for radiotherapy quality assurance (QA). This can be an interactive platform where physicists can download digital benchmark cases from, perform radiotherapy planning and QA measurements with various planning and delivery systems, and upload the results. Data retrieval and analysis functions can then be developed for the quality assessment of the radiation plan and measurement in the context of prior data with similar planning, delivery and measurement technologies. Data mining of the system can in turn generate quantitative guidance for clinical trial QA requirements that have the optimum combination of stringent mandates and realistic accommodations. Methods: Built upon prior experience of Task Group(TG) 119 from IMRT workgroup of AAPM, and digital data phantoms from EORTC, these groups collaborate with clinical trial work group of AAPM and advanced technology consortium (ATC) to establish a virtual QA environment within National Biomedical Imaging Archive (NBIA). Digital phantoms from TG 119 and EORTC dosimetric evaluation with DICOM image, structures, plan and dose were uploaded to the virtual QA environment for the established community to download and perform evaluation of basic dosimetric parameters including, structure volumes, geometric location of structure center, designated points on dose volume histogram (DVH). Nine different treatment planning or related systems with various versions are included in these evaluations. Results: Volume variations among versions of these nine systems are 2.7%, 4.2%, 14.7%, 4.7% for prostate PTV, prostate, rectum and bladder respectively. DVH reading differences are 0.1%, 2.4% and 1.5% for prostate D95, rectum D30 and bladder D30. DVH reading differences for cube 10 are 1%, 86% and 100% for V0, V20 and V30 respectively. Conclusions: A virtual QA environment has been established within NBIA for radiation oncology inter‐system and inter‐institution QA. Initial testing in reading geometric and dosimetric parameters identified significant variations among systems.
WE‐C‐110‐02: Influence of ASIR on Spatial Resolution: A Study for Objects of Varying Contrast Levels
Authors: Zhang D , Li X , Liu B
Published: November 2011

Purpose: Since the introduction of Adaptive Statistical Iterative Reconstruction (ASIR), multiple studies have been conducted to demonstrate its potential in noise reduction and dose saving. On the other hand, the influence of ASIR on system resolution has not been fully studied: high contrast measurements such as MTF and bar patterns could not explain the blurring effect of ASIR on low contrast objects, and an objective evaluation on the system resolution for objects of different contrast levels is missing. Here we tried to fill this gap. Methods: A novel method is proposed under the assumption that the effect of ASIR on low contrast images can be characterized by transfer functions, which can be determined from noise power spectra acquired with and without ASIR. To verify the effectiveness of this method, synthesized images were obtained by filtering low contrast FBP images with the transfer functions, and were then compared with ASIR images. For objects with intermediate contrasts, the effect of ASIR was studied by mimicking objects of the same geometry but different contrast levels through partial volume effect. A thin tungsten wire was imaged with its length covering different portions of the slice thickness, and then profiles and FWHM were obtained to compare the resolving power of the system. Results: Agreement between the synthesized images and ASIR images verified the effectiveness of the proposed method. For 10 cm DFOV and SS100, ASIRˈs blurring effect on low contrast images was measured as 0.5 lp/cm drop on the 5% MTF. For ASIR images of the tungsten wire with 30–500 HU signal difference, the FWHM of the wire varied with a COV of 2.23%, showing that ASIR did not significantly change the system resolution on intermediate‐contrast objects. Conclusions: ASIRˈs blurring effect on objects of varying contrast levels could be objectively determined using the proposed methods.
WE‐C‐110‐03: A Performance Comparison between Prior Image Constrained Compressed Sensing and ASiR in Pediatric CT
Authors: Tang J , Chen G‐H
Published: November 2011

Purpose: To compare denoising performance between the Prior Image Constrained Compressed Sensing (PICCS) method and a commercially available technique, Adaptive Statistical Iterative Reconstruction (ASiR). Methods: Pediatric abdominal CT data sets were acquired using a GE VCT scanner and retrospectively analyzed in this study. ASiR was applied to the FBP reconstructed images to reduce noise. Similarly, the PICCS reconstruction method was also applied to the same data set to reduce noise. To enable PICCS reconstruction, each FBP‐reconstructed image was forward‐projected to generate a fully‐sampled synthesized projection data set; additionally, it was low‐pass filtered to generate a low‐noise prior image. The forward‐projected data and the low‐pass filtered image were fed into the PICCS reconstruction method to generate a high spatial resolution and low noise image. Nine ROIs (two were in fat, four in soft tissue, three were in air) were used to measure the standard deviation of the noise. The difference images between the FBP image and the PICCS/ASiR images were calculated for visually evaluating the edge degradation. Results: PICCS reduced the noise standard deviation roughly by a factor of 2 for all the measured ROIs. 80% ASiR could achieve a similar noise reduction factor for fat and soft tissues. The noise in air regions in ASiR images was not reduced. Residual anatomical structures were observed in the difference images between FBP and 80% ASiR, while they were barely observable in the difference images between FBP and PICCS. Conclusions: PICCS can be used to reduce the noise by a factor of 2 in pediatric CT while preserving the edges. With the same noise reduction factor, PICCS can better preserve edges than ASiR. The noise reduction of ASiR is selective: it does not work in air regions, while the noise reduction of PICCS is uniform.
WE‐C‐110‐04: Local Dose Constraints in Fluence Field Modulated CT
Authors: Bartolac S , Graham S , Siewerdsen J , Jaffray D
Published: November 2011

Purpose: Fluence field modulated computed tomography (FFMCT) presents a new paradigm for CT imaging. Spatial modulation of the x‐ray fluence field, whereby the fluence pattern can change independently for each projection, can potentially meet user‐prescribed, regionally‐varying image quality objectives, while reducing radiation exposure to the patient. This work studies the potential to meet image quality objectives while limiting dose to local regions of interest via FFMCT. Methods: All experiments were carried out in simulation using cylindrical and anthropomorphic phantoms. Fluence patterns were optimized to meet prescribed signal‐to‐noise ratio (SNR) criteria using a simulated annealing method with dose constraints on locally defined regions of interest. Optimizations were repeated using different weighting factors on the local dose constraints. Resulting SNR and dose distributions were compared to those of a fixed bowtie filtered fluence pattern. Results: Results using FFMCT had superior agreement with the target SNR objectives and resulted in integral dose reductions of up to 50% when compared to results using bowtie filtered fluence fields. Increasing the relative weight of the local dose constraint resulted in further dose reductions (30–40% integral dose) to local regions of interest, with some tradeoff in SNR where overlap between the target low dose regions occurred with target high SNR regions of interest. Conclusions: These results support the hypothesis that FFMCT has the potential to meet prescribed image quality objectives, while decreasing radiation dose to the patient. They also indicate that fluence field modulation may be optimized to prioritize dose reduction to local regions of interest when attempting to meet particular noise objectives.
WE‐C‐110‐07: Estimation of CT Radiation Profile Width Using an LED‐Based Optically Stimulated Luminescence System
Authors: Ruan C , Rodriguez M , Hu Y , Ahmad S , Yukihara E
Published: November 2011

Purpose: To evaluate the feasibility and accuracy of an LED‐based Optically Stimulated Luminescence (OSL) system for measuring computed tomography (CT) radiation profile width. Methods: The OSL detector strips used consisted of a layer of Al2O3 :C powder incorporated into a plastic tape. The strips were 150 mm long with a width of 4–5 mm and thickness of 0.3 mm. The 64‐slice CT dose profiles were measured by irradiating the OSL strips both free‐in‐air and inside the PMMA head and body phantoms. Three separate OSL strip measurements were performed for each scan condition. The exposed strips were then read out using a custom built LED‐based reader system, which operated for 150 mm in 0.25 mm steps, providing 600 data points along the OSL strip in 60 sec. The width of the CT radiation profiles was determined from the full width half maximum (FWHM) at different nominal beam collimations. The results were compared to those obtained from digitized film profiles and ionization chamber point measurements (0.3 cc ionization chamber). Results: By comparing the FWHM values of OSL and digitized film measured free‐in‐air, the system accuracy was verified with results < ± 2.2% for nominal beam widths of 5, 10, 20 and 40 mm. The relative OSL response as a function of phantom positions was verified by comparing the FWHM values in phantom measurements using OSL and ionization chamber. The results agreed well within 7.6%. Conclusions: The proposed method of using an LED‐based OSL system to determine the FWHM of the CT radiation profile has a high accuracy and shows good agreement with the conventional film measurements and the more advanced point‐dose methodology proposed by TG 111. Combined with the simple calibration, it gives this work a great potential to be used in routine clinical quality assurance check.
WE‐C‐110‐08: A Novel Phantom for CT Performance Assessment: Towards a Task‐Based Measure of Image Quality
Authors: Richard S , Samei E
Published: November 2011

Purpose: The advent of CT iterative reconstructions in the clinic has posed an increasing challenge on the community in our ability to assess image quality due to increased non‐stationarity and non‐linearity of reconstructed images. The purpose of this study is to investigate the potential of a novel phantom aimed to enable a robust assessment of image quality of CT images including iterative reconstructions. Method and Materials: A cylindrical phantom was built from a series of slabs with removable rings to simulate diffrerent patient sizes. The “noise slab” consists of a uniform piece of acrylic for the noise‐power spectrum (NPS) measurement. The “resolution slab” consists of an array of spheres of various materials to simulate a range of contrast levels found in CT images. Each set of spheres can be used to measure the modulation transfer function (MTF) as a function contrast, dose, and location. The “dose slab” enables the incorporation of ion chambers, while the last slab contains cylindrical inserts for CNR measurements. The phantom was scanned on a 64 slice CT and reconstructed with filtered‐back projection (FBP) and a model‐based iterative reconstruction algorithm (MBIR). Images were used to derive the relevant image quality and dose metrics. Results: The NPS measurement enabled the characterization of different textures between FBP and MBIR. Contrast and dose were found to have a significant impact on the MTF for the MBIR data. The task‐based detectability index computed from the MTF and NPS agreed qualitatively with image quality and yielded quantitative estimation of dose reduction provided with iterative reconstruction algorithms. Conclusions: Initial results showed that a phantom can be used to measure imaging performance of non‐linear reconstruction algorithms. Results suggested that a task‐based approach to system performance assessment may be essential to properly compare image quality between different protocols when employing iterative reconstruction algorithms.

The authors have received funding support from GE healthcare.
WE‐C‐110‐09: A Theoretical Model for Calculating MDCT Beam‐Shaping Filter Geometry: Comparison of Calculated Attenuation Profile and Monte‐Carlo Simulated Transmission Spectra to Measurements
Authors: Stiller W , Veloza LS , Pahn G , Kauczor H‐U
Published: November 2011

Purpose: MDCT beam‐shaping filters modulate X‐ray intensity across the fan beam, reducing patientsˈ skin dose while homogenizing detector statistics. A simple theoretical model for calculating beam‐shaping filter geometry has been developed; and for calculated attenuation profiles Monte‐ Carlo (MC) simulated transmission spectra have been compared to measured X‐ray spectra. Methods: Based on the assumption that X‐ray intensity after transmission through a given set of a beam‐shaping filter and a cylindrical object of homogeneous composition is equal for all fan angles, a theoretical beam‐shaping filter geometry has been calculated. For a set of fan angles (0°–21° relative to central ray of the fan), transmission spectra were simulated for calculated filter geometry using a Geant4 MC simulation. Simulated spectra have been compared to fan‐angle dependent measurements of MDCT X‐ray spectra (120kVp) acquired using a Compton spectrometer. Additionally, the initial assumption of equalized X‐ray intensity after beam transmission through a set of shaping filter and homogeneous cylindrical phantom was checked by simulating resulting detector signal. Results: Comparison of measured transmission spectra to those resulting from simulation of a beam‐shaping filter geometry estimated using the proposed theoretical model yields maximum differences below ±2.0% for all fan angles. K‐lines of simulated and measured spectra match well and are in agreement with theoretical values for tungsten anodes. Measured and simulated filter transmission and mean X‐ray energy after filter passage are also in good agreement. For the modeled filter geometry the initial assumption of signal homogenization could be validated through simulation. Conclusions: Comparison of measured transmission spectra to those simulated for a beam‐shaping filter geometry estimated using the proposed theoretical model reveals excellent qualitative and quantitative agreement. Thus the proposed method can be used for calculating reliable estimates of MDCT beam‐shaping filter geometry instead of having to rely on manufacturersˈ data or resort to time‐consuming measurements.

This research project is in part funded by the German Federal Ministry of Education and Research (BMBF) within the collaboration project: “Innovative Methods for the Optimization of Radiological Applications in Biomedical Imaging”, grant number 02NUK008G.
WE‐C‐220‐02: Development of a Miniature Ultrasonic Device for Conformal Cyclocoagulation : From Transducer Design to Early Clinical Trials
Authors: Lafon C , Aptel F , Charrel T , Birer A , Chavrier F , Chapelon JY , Romano F , Denis P
Published: November 2011

In the 80s, HIFU were successfully tested for treating refractory glaucoma (Lizzi et al.). However, more clinically feasible laser‐based approaches are now considered to be the gold standard. The new proposed ultrasonic device aims to perform a conformal, partial and fast thermal ablation of the ciliary body for reducing the production of aqueous humor and intraocular pressure (IOP).

Numerical simulations and anatomical constraints were considered for designing the device. Itis made of six cylindrical transducersoperating at 21MHz for modulating and producing sharp zones of ablation. In vitro tests and animal experimentation on rabbits were performed for characterization purpose.Each transducer generated sequentially an ultrasonic beam at an acoustical power of 2W for 3s. Significant decreases of IOP were obtained in vivo and no adverse effects were evidenced on histology. The feasibility, the tolerance and the efficacy of the treatment of refractory glaucoma were assessed during a clinical pilot study on eight patients. The absence of side‐effects and the significant decrease of IOP, up 45% six months after treatment, proved the clinical relevance of this new device for treating refractory glaucoma.

Glaucoma is a very frequent ophthalmologic disease. An increase of the intraocular pressure (IOP) results in mechanical damage over the retina and the optical nerve.
WE‐C‐220‐03: Lessons Learned: Creating a Dedicated Focused Ultrasound Surgery Program
Authors: Schlesinger D , Benedict S , Sheehan J , Larner J
Published: November 2011

MR‐guided focused ultrasound surgery (MRgFUS) is an emerging technology with the potential to disrupt traditional treatment techniques across a wide variety of surgical and medical disciplines. Proposed applications for MRgFUS are multiplying quickly and include indications as diverse as tumor ablation, thrombolysis, hemostasis, reversible blood‐brain barrier disruption, targeted drug delivery, gene therapy, and neuromodulation. Interest in MRgFUS is quickly increasing, however the desire to find new potential treatment indications may be outpacing work on developing “best practices” for designing new centers, organizing clinical teams, and defining standards for treatment quality and reporting. The University of Virginia recently started up one of the first programs in the world designed from the ground up specifically for the purpose of MR‐guided focused ultrasound surgery. The lessons learned during this process, both positive and negative, may be valuable to the ongoing discussion of best practices. This lecture will provide an overview of the UVA experience, including center design, construction, and administrative organization, and funding /revenue, and program startup. A particular focus will be on the clinical startup experience, and how this might be improved with a more formal risk‐based process analysis.

Learning objectives:

1. To understand the rationale for a stand‐alone FUS center versus a center created out of existing resources in the medical center.

2. To understand the design features of the center, as well as the challenges that had to be overcome in the design and construction of the center.

3. To understand the multidisciplinary organization of the center and how inter‐department conflicts are managed.

4. To understand the expectations vs. reality of the center regarding the distribution of treatment indications, the effort required to start clinical trials, and the ability to collect clinical revenue.

5. To understand the centerˈs experience during clinical startup, and the successes and challenges faced by the center when trying to refine clinical processes and develop standards for quality assurance.

Funding Support, Disclosures, and Conflict of Interest: The Focused Ultrasound Center at the University of Virginia has received funding for development and research from the following: The Focused Ultrasound Surgery Foundation, the Commonwealth of Virginia, InSightec Ltd., and the General Electric Co.
WE‐D‐220‐03: The Effect of Object Speed on the Performance of 3D Speckle Tracking Using a 3D Swept‐Volume Probe for the Purpose of Ultrasound‐Guided Radiotherapy
Authors: Harris E , Miller N , Bamber J , Evans P
Published: November 2011

Purpose: This study investigated how object speed affects 3D speckle tracking accuracy and precision in the azimuthal and elevational directions when using a mechanically swept 3D ultrasound probe. Methods: A 3D probe was used to acquire B‐mode volumetric ultrasound images of a homogenous tissue‐mimicking ultrasound phantom. Object motion was simulated by moving the probe in the azimuthal and elevational directions using a translational stage with 3‐axis of motion whilst volumetric images were continuously acquired. To form volumetric images the transducer was mechanically swept back and forth and therefore object motion was prograde or retrograde to the transducerˈs sweep motion. Displacement between volumes was estimated using 3D correlation‐based speckle tracking of a region of interest (ROI) located at various positions within the phantom. We investigated tracking accuracy and precision for speed of 0 to 35 mm s‐1 for fixed displacements of 2mm and 4mm, for prograde and retrograde motion and as a function of depth. Results: For the azimuthal direction, both accuracy and precision were better than 0.1mm and 0.15mm for 2mm and 4mm displacements respectively and no significant correlation was found between accuracy and speed and between accuracy and depth. For the elevational direction and 2mm displacement, accuracy was 0.25mm and 0.3mm for prograde and retrograde motion respectively. Accuracy and precision were greatest at the elevational focus (60mm). For a 4mm elevational displacement with retrograde motion, accuracy and precision reduced with speed and tracking failure was observed at speeds > 14mms‐1, this was not observed for prograde motion. Conclusion: For mechanically swept 3D probes tracking in the elevational direction is poor for retrograde motion at speeds of greater than 14mms‐1. Thus for inter‐volume displacements greater than 2mm only prograde motion should be tracked which will decrease temporal resolution by a factor of 2.
WE‐D‐220‐05: Development of Autoscanning 3D Ultrasound Technology for Radiotherapy Simulation, Planning and IGRT
Authors: Lachaine M , Tremblay S , Lathuiliere F , Wallace H J , Falco T
Published: November 2011

Purpose: 3D ultrasound (3DUS) can be used to provide soft‐tissue visualization in both CT‐sim and treatment rooms. Fused CT/3DUS datasets provide complementary information for contouring, and 3DUS‐to‐3DUS comparisons are used for soft‐tissue based IGRT. To date, 2DUS probes have been used in combination with a position sensor to reconstruct images from a freehand sweep. In this work we describe the development of a mechanically sweeping autoscan probe for acquisition, with a focus on transperineal prostate imaging. Methods: A calibration algorithm was developed for reconstruction of 3D autoscan images in room coordinates. To ensure images are consistently centered, a Hall sensor was used to tag the central position of the sweep within the probe casing. The accuracy was measured by comparing 3DUS and CT images of the same phantom. Precision was measured by scanning a sphere within the phantom 32 times. The effect of treatment and CT radiation dose on probe homing was measured by delivering 8000 MU of 6 and 18 MV beams with the probe 1 cm outside of the field edge, as well as CT scans of the entire probe, between successive acquisitions. Preliminary patient images were acquired to show the feasibility of scanning prostates transperineally. Results: Accuracy of the system was found to be within 1 mm, and precision within 0.5 mm with 95% confidence. Neither CT nor treatment dose affected the spatial accuracy. Preliminary images showed feasibility of imaging the prostate and surrounding structures. Conclusions: A mechanically sweeping probe can reconstruct 3DUS images accurately and precisely in CT and treatment room coordinate systems and is not affected by radiation dose. Transperineal imaging of the prostate with the probe is shown to be feasible. Future work will enable continuous image acquisitions during treatment to track intrafractional motion of the prostate and critical structures.

All authors except H J. Wallace III are employed by Elekta/Resonant Medical
WE‐E‐224‐01: Preparing for ABR Board Exams
Authors: Stump K
Published: November 2011

The process of obtaining board certification in one of the specialties of Radiological Physics by the American Board of Radiology is a complex and often daunting experience. The candidateˈs first introduction to board certification is the Part I written examination, also known as the Initial Qualification Examination. There are two key components to successfully completing this examination. The first component is understanding the process and the eligibility requirements for the exam. The second is to prepare for and pass the examination. This talk will be divided into two sections to address each of these components individually. The first half of the talk will describe present and future requirements which must be met in order for the candidate to sit for the Part I examination. The second portion of the talk will cover the wide range of topics that will be covered on the exam and the overall exam procedure. This talk is not designed to be a complete review course for Part I of the ABR examination, while possible examination topics will be discussed, the focus of the presentation will be to provide an outline of exam material along with an introduction into the process and overall eligibility.

Educational Objectives

1. Understand the prerequisites and application process for the Initial Qualification Examination for the ABR Radiological Physics Board Certification.

2. Understand different pass levels for the examination.

3. Have a general understanding of possible examination topics and recommend appropriate study materials for the Part 1 examination.
WE‐E‐224‐03: Preparing for the ABR Radiological Physics Oral Board Exam
Authors: Becker S
Published: November 2011

Preparing for Part III (Oral Exam) of the ABR Therapy Physics boards is more than just studying as much material as possible. There will always be material that is missed and gaps in oneˈs knowledge. Therefore, in order to fill those gaps, it is crucial to understand how the parts of the material relate to each other and to the clinical experience. Part III presents its own challenges compared to the written exams. It requires not only knowledge of and experience with clinical procedures, but also the ability to explain orally how they are performed and what they mean. One must be able to easily and confidently respond to oral questions about all aspects of working in the clinic and clearly explain why those clinical methods and procedures are performed that way. This talk is not a comprehensive review of all required study material. Instead, it focuses on the required experiences, skill sets, and study methods that are needed to pass Part III of the board exam.

Educational Objectives:

1. Generate a list of clinical experiences needed for the exam

2. Understand how the study material and clinical experiences relate to each other

3. Learn how to effectively prepare for an oral style exam
WE‐E‐BRA‐01: Outcomes Modeling: General Review
Authors: Haken RK Ten
Published: November 2011

The use of mathematical models to summarized clinical or biological outcomes with respect to the distribution of dose throughout an organ or tissue has great appeal. At its best, the overall cumulative effects of all parts of a heterogeneously irradiated object could be summarized in terms of a clinically relevant outcome such as a normal tissue complication probability (NTCP).

Despite this appeal, integration of these concepts into mainstream treatment planning has been slow in coming. Parameterization of the models is conceptually simple, requiring input data consisting primarily of dose, volume and outcome information. However, uncertainties in accumulated total effective dose and differential irradiated volumes together with heterogeneities in biological responses can make these determinations difficult. At best, it has been possible to obtain broad “population” based model parameters for some organs for “groups of similarly‐treated patients”. In general, as used today, these models are not by themselves (i.e., without additional stratification factors) “predictive” of outcome for “individual” subjects, nor can their use be generally extrapolated to the treatment of populations with techniques that vary greatly from those originally used. However, disclaimers aside, their appeal remains great, and real progress has been made. In this part of the session some of the basic concepts associated with outcomes models will be presented. Examples will be given as to how the models accommodate the responses of different types of normal tissues. We will show how implementation of the models in evaluation or planning generally first requires reduction of a complex dose distribution (or DVH) into an equivalent “uniform” total (or partial) organ dose.

Objectives:

1. Understand the basis and statistical nature of standard NTCP models.

2. Recognized that dose distribution reduction remains a basic component of their implementation.

3. Appreciate, that as currently used, most results apply to “populations” of “similarly treated” patients.
WE‐E‐BRB‐02: Current IMRT QA Metrics Are Not Correlated with Clinically Relevant Dosimetric Errors in Prostate and Head Neck Treatments
Authors: Lawrence M , Wang S , Cullip T , Chang S
Published: November 2011

Purpose: To investigate if the degree of IMRT QA error characterized by the conventional metrics is correlated with clinically relevant dosimetric errors for prostate and head‐neck treatments. Methods: We examined 37 head‐neck and 41 prostate treatments, each had at least one field failed IMRT QA on MapCHECK judged by one of the standards — 95% passing rate at 3%/3mm, 5%/4mm, or 7%/5mm. The resulting deviation on target and critical normal‐structure doses was computed using in‐house TPS PlanUNC. PLanUNC reproduced the QA‐failed treatment plan using MapCheck‐measured beam characteristics. The modified plan represents the actual treatment that patient would receive if treatment (that failed QA) had been delivered. The degree of IMRT QA error was correlated with its dosimetric impact on minimum dose to 95% of the target volume [D95], mean and maximum doses to critical structures using Pearson correlation. A commercial software (3DVH) for 3D dosimetry study using MapCHECK QA data is also evaluated. Results: There is a lack of general correlation between QA passing rate and resulting error in PTV D95 and critical structures ((bladder, rectum, femur heads for prostate and brainstem, cord, parotids for head and neck) mean and max. dose (Pearson r value −0.146, range −0.519  0.130). More stringent QA criterion does not have better correlation with the 3D dosimetry error than less stringent criterion (r = −.154+/−0.15 for 3%/3mm, r= −1.93+/−0.192 for 5%/4mm, and r= −1.85+/− 0.14 for 7%/5mm). The IMRT QA errors for all cases studied, if left uncorrected, would lead to errors of 0.7% for the D95 (range −4.0–2.8%), 2.15% for the cord dose (−3.3–21.9%), and 0.6% (−9.5–4.9%) for all other critical structures. Conclusions:We observed no strong and consistent correlation between the degree of IMRT QA error and the degree of clinically relevant patient dose error.
WE‐E‐BRB‐03: Extracting Energy Fluence Distributions of X‐Rays Produced by Megavoltage Electron Beams Stopping in Thick Targets from Lateral Profiles Measured Using Ionization Chambers
Authors: Cojocaru C , Ross C , McEwen M , Faddegon B
Published: November 2011

Purpose: To develop a method of extracting energy fluence distributions of x‐rays produced by megavoltage electron beams stopping in thick targets from lateral profiles measured using ionization chambers. Methods: High accuracy x‐ray lateral profiles measured using various ionization chambers with a set of build‐up caps for a number of target materials were recently reported. It was possible to extract energy fluence distributions from these profiles by using Monte Carlo calculations. The conversion factor was calculated as the ratio between the MC calculated energy fluence (using FLURZnrc) and the MC calculated absorbed dose in the air cavity of the ionization chamber (using “cavity”) at each position. The “measured” energy fluence lateral distribution was then obtained by multiplying the measured absorbed dose with these coefficients point by point, for each build‐up cap. The geometry, beam and material properties were simulated with BEAMnrc. The “cavity” user code was used to score the absorbed dose in the ionization chamber air cavity per incident electron up to angles of 25°. The energy fluence calculations were performed using the EGSnrc user code FLURZnrc. Results: The conversion factors for the PMMA build‐up caps were different by up to 40 % from those for the hevimet caps. However, when converting to energy fluence, for all targets the agreement between the energy fluence distributions obtained with each of the six build‐up caps was better than 1 %. The final energy fluence distribution for a particular target was obtained by averaging the distributions obtained for all six build‐up caps. Conclusions: The present study showed that it is possible to extract energy fluence distributions from x‐ray lateral in‐air profiles measured using commonly used Farmer type ionization chambers with various build‐up caps. The uncertainty on the distributions was better than 1 %.

Partial support from NIH R01 CA104777‐01A2.