bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐110‐11: A Monte‐Carlo Based Software‐Bench for Performance Characterization of CT Reconstruction Algorithms
Authors: Noël P , Voigt J , Penchev P , Renger B , Rummeny E , Fiebich M
Published: November 2011

Purpose: The quantification of new computed tomography (CT) systems can be challenging with respect to image quality and diagnostic value. Especially for advanced algorithms, such as statistical reconstruction methods, the performance is more difficult to determine because of a larger set of parameters in combination with local dependences in the image domain. Thus, there is the need for a realistic software benchmarking to determine diagnostic performances. In this work, we present a software‐bench consisting of a Monte‐Carlo simulator (MCS) and a GPU‐based reconstruction‐engine for characterization of CT systems and reconstruction algorithms. Methods: The MCS is based on EGSnrc, which simulates the whole imaging system. The GPU‐based reconstruction‐engine is able to reconstruct different iterative and non‐iterative reconstruction algorithms. For initial results we simulated a flat‐panel detector‐based cone beam CT. The MCS determined the projection images of a cylindrical PMMA‐ Phantom. The 100mm diameter Phantom contains 9 cylindrical regions varying in size between 1mm and 10mm, and in density between ‐1000HU and 300HU. The simulated projection‐images are reconstructed with the FBP and the HYPR algorithms. Results: The system was configured and provided initial results. The influence of different parameters showed different image qualities for FBP and HYPR reconstructions, while HYPR revealed a superior performance. For example, when varying dose and detector‐configuration the soft‐tissue contrast and spatial resolution was improved by a factor of 2 or more. Conclusion: In this work, we show that the combination of a realistic simulation of projections and reconstruction algorithm is essential for characterization of new systems / algorithms. In particular, the correct simulations of the x‐ray interactions are crucial for characterization of image noise and spatial resolutions with respect to radiation dose. We see the need for systems such as ours to determine the clinical value of methods in combination with image quality measures and observer models.
WE‐C‐220‐01: Histotripsy without Cavitation
Authors: Crum L , Canney M , Bailey M , Khokhlova T , Khokhlova V , Sapozhnikov O , Kreider W , Simon J
Published: November 2011

Purpose: Histotripsy is an exciting new mechanism for ablating tissue in that it completely emulsifies tissue, leaving nothing behind but a liquid‐like slurry. Although clinical applications of this approach are still to be tested, it offers high promise for the use of High Intensity Focused Ultrasound (HIFU) for therapy. Accordingly to the conventional approach, short (microsecond‐length) pulses of very high amplitude ultrasound are used to induce intense cavitation, which mechanically disrupts the tissue. We have developed an approach that involves longer (millisecond‐length) pulses. These high amplitude pulses develop into shock waves that induce superheated boiling in the tissue, resulting in very efficient tissue emulsification. Methods. Experiments have been undertaken in a variety of tissues and tissue phantoms; we particularly prefer transparent tissue mimicking materials that permit high‐speed photography. Histotripsy lesions (essentially holes in tissue) were generated in these materials under acoustic exposures that have been reported in clinical applications. Imaging modalities include MR, ultrasound, and high‐speed photography. Results. When ultrasound imaging is used to examine HIFU‐induced, thermal‐lesion formation, the appearance of hyperechogenicity often occurs. Although this hyperechogenicity has typically been associated with the occurrence of cavitation, we have determined that cavitation seldom generates enough backscatter to be detectable; rather, hyperechogenicity is more often associated with boiling. In particular, we have observed that when the HIFU intensity is sufficiently high that shock formation occurs, boiling can occur in milliseconds. The appearance of a hyperechoic echo is an accurate focus monitoring technique. Modeling, using weak shock theory, supports this occurrence of boiling. The time‐to‐boil can accurately be predicted by modeling and is very reproducible. Conclusions: Histotripsy can be generated by shock‐wave‐induced boiling, an approach that offers many attractive features.
WE‐D‐220‐06: Sono‐Contrast Spectroscopy for Breast Cancer Diagnosis: Clinical Study Results
Authors: Yan K , Liao L , Yu Y
Published: November 2011

Purpose: to demonstrate the effectiveness of a non‐invasive multimodal sono‐contrast spectroscopy system in breast cancer diagnosis. Methods: This multimodal spectroscopy system combines three modules: diffuse reflectance spectroscopy (DRS), ultrasonography and low intensity focused ultrasound (LIFU). This multimodal system reports the optical functional difference in breast cancer and in normal tissue/benign lesion after transient LIFU stimulation of the vascular network. An IRB‐approved clinical study has been carried out to evaluate its diagnostic power. Currently 33 patients were enrolled with informed consent, grouped into histologically‐proven cancer, benign mass, and breast tissue, respectively. The ratio of intensities at wavelengths 685nm and 830nm was decomposed into low frequency and high frequency components using wavelet technique. Results: Comparison of the high‐frequency component showed that LIFU stimulated transitory fluctuation in non‐cancer tissue, but not in malignant tissue, as quantified in terms of the variance. The ratios of the variance during LIFU vs. baseline in cancer, benign and breast tissue are [mean (max/min/std)] 1.18 (2.04/0.60/0.45), 2.22 (2.74/1.51/0.54) and 3.21 (6.64/1.20/1.27), respectively. This suggests that the high‐frequency fluctuation was amplified in non‐cancer tissue during LIFU stimulation. Statistical analysis also reveals that these ratios of variance induced by LIFU are significantly different in cancer vs. non‐cancer (p=0.0007), and cancer vs. benign tissue (p=0.006). So far it has not suggested significant difference in benign vs. breast tissue (p=0.06). Conclusions: Current clinical results demonstrate the potential of the multimodal system in characterizing cancer vs. non‐cancer tissues. LIFU appears to exert more pronounced influence on blood flow in non‐cancer tissue than in breast cancer. This lack of response to LIFU in breast cancer is possibly due to its abnormal blood vasculature. The clinical study is ongoing to further assessing correlating factors, such as histological tissue types, hormone status (age), breast density, and to define the sensitivity and specificity of this promising technique.

This work is supported by National Cancer Institute grant R33‐CA107860.
WE‐E‐BRA‐02: Methodological Issues and Key Results in the QUANTEC 2010 Review of Radiation‐Induced Normal Tissue Toxicity
Authors: Deasy J , Bentzen S , Constine L , Eisbruch A , Jackson A , Marks L , Haken R Ten , Yorke E
Published: November 2011

The QUANTEC review of radiation‐induced normal tissue toxicity provides an attempt to synthesize published knowledge about normal tissue dose volume effects for many endpoints of clinical importance. In this review, I will briefly review the methods used by the QUANTEC group, limitations of the data, and some of the key findings. The QUANTEC reviews, although valuable, were constrained by several important limitations, for example: lack of access to the original data for joint analyses, differences in reporting methods, differences in dose calculation methods, differences in endpoint definitions, differences in endpoint measurement methods, etc. Despite these problems, some clinical recommendations have already been tested in separate data sets and shown to have validity. The solidity of the underlying data and clinical recommendations therefore necessarily varies. I will also briefly discuss recommended future directions to improve NTCP model predictions, including biomarker development, machine learning modeling, and pooled data analyses.

Educational goals include:

1. Understanding the main methods and structure of the QUANTEC reviews

2. Understanding the variability of the review results

3. Reviewing the main results, and caveats regarding their clinical use.
WE‐E‐BRC‐11: Towards Subject Specific Head and Neck Biomechanical Models Using Multi‐Level Multi‐Resolution and Inverse Consistent Registration Algorithms for Radiotherapy
Authors: Santhanam A , Min Y , Yang D , Terzopoulos D , Low D , Kupelian P
Published: November 2011

Purpose: The proposed work focuses on addressing the impact with which the patientˈs treatment delivery can be monitored and documented in real time taking into account the interfraction and intrafraction motion and effective optimizations for the treatment can be conceived and implemented. The first step towards establishing the radiation delivered to the head and neck tumor and the surrounding tissues in real‐time is the development of subject specific biomechanical head and neck models. The complexity in developing such a biomechanical model arises from the human musculoskeletal system, which includes approximately 57 articular bones and many more muscle actuators and their closed kinematic loops. Methods: We present a subject specific model, which is developed using cancer patientsˈ 3D CT scans (simulation CT, cone‐beam CT), a validated generic biomechanical model and registration algorithms that incorporate biomechanical properties from the generic model into the static patient anatomy to facilitate subject‐specific biomechanical model. For illustration purposes, we take as input a subject specific anatomy from a 3DCT acquired during the simulation stage. For analysis purposes, free‐form deformation (FFD), demons, the symmetric force demons, and optical flow (OF) registration methods are used within the multi‐level multi‐resolution (MLMR) and additional Inverse Consistency (MLMRIC) for comparing the registration accuracy. Once registered, the biomechanical generic model is warped using the registration results to closely fit the patient anatomy thereby facilitating a patient specific biomechanical model. Results: Validation studies showed that among the eight 3D registration methods, the MLMR symmetric demons registration is quantitatively more accurate as compared to the other methods and facilitates the development of a more appropriate subject specific biomechanical head and neck model. Conclusions: The development of subject specific biomechanical models is made possible by MLMR symmetric demons registration of generic validated biomechanical models to subject anatomy.
WE‐E‐301‐01: Practical Tips for VMAT Implementation
Authors: Galvin J , Yin F , Wu Q , Xiao Y
Published: November 2011

Volumetric modulated arc therapy (VMAT) is an arc‐based dose delivery approach that produces highly conformal dose distributions similar to those generated with static gantry intensity modulated radiation therapy. Like many existing IMRT approaches, this treatment technique can be delivered with a standard linear accelerator that is equipped with a conventional multileaf collimator (MLC). During arc beam delivery the dose rate, the speed of the gantry, and the position of the MLC leaves are varied dynamically. The AAPM has a working group, under the Therapy Physics Commitee of the Science Council, preparing a report that provides general guidelines and recommendations for safe, error‐free use of this new technology. This presentation will review the information in the report of the Therapy Emerging Technology Assessment Working Group (TETAWG). A major advantage of this IMRT approach is the speed of dose delivery. This makes VMAT ideally suited for meeting the challenges of delivering the higher daily doses that are necessary for the hypofractionated treatment techniques. All accelerator manufacturers that use a traditional rotating gantry geometry have implemented this technology, and an additional number of treatment planning systems are now available to handle this part of the VMAT dose delivery process. The development of this technology is rapid and there is a great need for clearly describing the overall QA requirements for VMAT. This presentation will address this need by discussing Acceptance Testing, Commissioning, and ongoing QA methodologies for VMAT.

Objectives:

1. To understand the Acceptance Testing procedure for a new VMAT delivery system, a retrofitted VMAT cability, or a VMAT threatment planing system

2. To understand the Commissioning process for the situations listed above

3. To understand the requirements for ongoing routine QA for VMAT
WE‐E‐220‐04: Focused Ultrasound Ablation of Tumour Hypoxic Tissue of Small Animals under PET and MRI Guidance
Authors: Chen X , Griffin R , Webber J , Corry P , Shafirstein G , Moros E
Published: November 2011

Purpose: Motivated by the need of alleviating tumor hypoxia‐related resistance to radiation therapy, we propose to develop a magnetic resonance imaging (MRI) guided focused ultrasound system (MRgFUS) incorporating positron emission tomography (PET) hypoxia imaging to detect and coagulate the hypoxic areas in mouse tumors before radiation treatment. We plan to use this system to test the hypothesis that thermal coagulation of evidently hypoxic regions of a tumor can improve radiotherapy outcome. Methods: A prototype system was established to seamlessly integrate the processes of PET imaging and MRgFUS ablation. It includes (1) A small animal specialized MR‐compatible FUS applicator using a spherically‐focused ultrasound transducer. (2) 18F‐ fluoromisonidazole microPET imaging (Siemens) to acquire and correlate the uptake of 18F‐miso tracers to hypoxic tissue in tumors. (3) A small animal positioning and immobilization device that is compatible both to PET and MRI, and can facilitate anesthesia supply, breathing sensor and FUS applicator. (4) An effective method to register PET images with MRI images so that the regions of hypoxic, necrotic, and normoxic tissue can be delineated within a tumor. (5) MRgFUS ablation of the segmented tumor hypoxic areas with the guidance of MRI‐acquired (7.0 T Bruker) temperature maps. To test the robustness of this system, we conducted in vivo experiments on six A/J mice bearing 4T1 tumors. Results: The tumor hypoxic regions can be clearly distinguished by 18F‐miso PET scans of mouse tumors with i.v. injection of 1 mCi/mouse and 1.5–2 hours of uptake. The positioning and immobilization device allowed accurate registration of PET and MRI images. Accurate targeting and heating (error <2 mm) was achieved with MRI‐temperature guidance (resolution: 0.2×0.5mm, per 4 s). Conclusions: The overall system/approach has proven the feasibility of PET+MRgFUS and should be useful in the study of combined treatment strategies incorporating radiation and thermal therapy using small animals.
WE‐E‐220‐07: Therapeutic Effects of Pulsed Focused Ultrasound Enhancement of Docetaxel Combined with Radiotherapy on Prostate Cancer In Vivo
Authors: Chen L , Mu Z , Chen X , Cvetkovic D , Pollack A , Ma C
Published: November 2011

Purpose: We demonstrated a significant increase of 3H‐docetaxel in the prostate tumor treated with pulsed focused ultrasound (pFUS). This study is to study the efficacy of the increased uptake of docetaxel (doc) by pFUS in prostate tumor growth delay in vivo in combination with radiotherapy (RT). Methods: LNCaP cells were grown in the prostates of nude mice. The tumor growth was monitored by MRI. Pulsed FUS treatment was performed using an ExAblate 2000 system with 1.5 T GE MR Scanner. When the tumor volume reached 36 ± 5.9 mm3, mice were randomly divided into 7 groups (n=5): (1) pFUS only; (2) RT only; (3) doc only; (4) doc + pFUS; (5) doc + RT; (6) doc + pFUS + RT; and (7) control. Animals involved with pFUS were treated with 1 MHz; 5W acoustic power for 60 sec with 50% duty cycle per sonication. Animals treated with doc received a dose of 5 mg/kg by tail vein injection. The doc injection was performed before the pFUS and RT treatments. For the RT treatment, animals were irradiated on a Cesium 137 irradiator with a 2 Gy dose. Animals were allowed to survive for 4 weeks post‐treatment. Tumor volumes were measured by MRI at 1 and 4 weeks post‐treatment. Results: Results showed an average reduction in the tumor volume by 59% for animals treated with doc only; 37% with RT only; 54% with pFUS+doc; 65.8% with RT+doc, and 72% with pFUS + doc + RT, respectively, compared with that in the control group. Conclusions: Triple combination therapies of doc, pFUS and RT may have a potential for the treatment of prostate cancer. Due to the large variations in tumor growth between individual animals more experiments are needed for better statistics and to find optimal treatment doses, parameters and fractionation schemes.
WE‐E‐220‐08: Image Based Microwave Focusing for Transcutaneous Therapy in Combination with Focused Ultrasound Heating
Authors: Stang J , Moghaddam M , Kripfgans O , Fowlkes J , Carson P
Published: November 2011

Purpose: In the current standard‐of‐care treatments for breast cancer, there remains a need for the reduction of local recurrence, harmful side effects, and cosmetic harm. high‐intensity focused ultrasound (HIFU) is generally effective but slow for large target areas and requires precise guidance. A combined microwave/ultrasound transcutaneous thermal therapy system is being developed for fast targeted or targeted plus diffuse treatment of breast cancer. Methods: In the microwave component, a cylindrical array of antennas operating at 915 MHz is used to focus continuous‐wave microwave energy transcutaneously into the pendent breast suspended in a coupling medium. The compatible HIFU system consists of two half shell arrays (Imasonic, Inc., Besancon, France) that allow close approach to the chest wall. In each case, prior studies provide breast tissue properties and distributions, for incorporation into multiphysics models. Time‐ reversal techniques are employed to find a solution (relative amplitudes and phase) for microwave focusing at a given location, and to precondition a weighted inverse solver that can optimize treatment planning for ablation at the tumor location while minimizing thermal dose elsewhere in the breast. Results: A full‐wave forward model of the microwave therapy array has been created and breast phantoms (E. Zastrow, //uwcem.ece.wisc.edu/MRIdatabase/) imported. Coupling of the electromagnetic energy deposition to the bioheat equation has been achieved using COMSOL Multiphysics, and a temperature map within the breast accounting for perfusion effects has been modeled. Studies of time‐reversal focusing results have shown that therapeutic levels of heat deposition with good targeting accuracy can be achieved using a twelve element array. Ultrasound beam patterns are close to predictions. Initial study of coupling agents compatible with both fields and with shared apertures is promising. Conclusions: Based on these encouraging results, the design and fabrication of adaptively focused combined laboratory systems are proceeding.

Supported in part by DOD/BCRP W81XWH‐10‐1‐0730.
WE‐G‐BRA‐03: Risk of Second Malignant Neoplasms Following VMAT and Proton Arc Therapy for Prostate Cancer
Authors: Rechner L , Howell R , Zhang R , Lee A , Newhauser W
Published: November 2011

Purpose: The risk of second malignant neoplasms (SMNs) following prostate radiotherapy is a concern due to the large population of survivors and decreasing age at diagnosis. It is known that parallel‐opposed beam proton therapy carries a lower risk than photon IMRT. However, a comparison of SMN risk following proton and photon arc therapies has not previously been reported. The purpose of this study was to predict the ratio of excess relative risk (RRR) of SMN incidence following proton arc therapy to that after VMAT. Additionally, we investigated the impact of margin size and the effect of risk‐minimized proton beam weighting on predicted RRR. Methods: Physician‐approved treatment plans were created for both modalities for three patients. Proton arc treatment plans were approximated with 16 equally spaced and uniformly weighted passively‐scattered proton beams, and VMAT plans were created with two 6‐MV arcs. Therapeutic dose was obtained with differential dose‐volume histograms from the treatment planning system, and stray dose was estimated from the literature or calculated with Monte Carlo simulations. Then, various risk models from the literature were applied to the total dose to span the likely dose‐risk relationship. Additional treatment plans were also investigated with varying margin size and risk‐minimized proton beam weighting, and their respective RRRs calculated. Results: The mean RRR ranged from 0.74 to 0.99, depending on risk model, suggesting a lower predicted risk of SMN following proton arc therapy. The additional treatment plans revealed that the RRR remained approximately constant with varying margin size, and that the predicted RRR was reduced by 12% using a risk‐minimized proton arc therapy planning technique. Conclusions: Proton arc therapy was found to provide an advantage over VMAT in regard to predicted risk of SMN following prostate radiotherapy. This advantage was independent of margin size and was amplified with risk‐optimized proton beam weighting.
WE‐G‐BRA‐07: Biological Modeling and Global Normal Lung Tissue Radiological Response in Patients Treated with Stereotactic Body Radiation Therapy for Lung Tumors
Authors: Diot Q , Kavanagh B , Stuhr K , Miften M
Published: November 2011

Purpose: To model the probability of normal lung tissue density change and obtain dose‐response curves restricted to observed change areas for patients with lung tumors who received stereotactic body radiation therapy (SBRT). Methods: 129 follow‐up CT scans for 36 patients who received SBRT between 2003 and 2009 with a maximum of 5 fractions and a median total dose of 54 Gy (range, 30–60) were analyzed. RT‐induced lung density changes were evaluated after fusion of planning CT scans with post‐RT follow‐up scans corresponding to interval periods of approximately 3, 6, 12, 18, and 24 months after treatment. Each follow‐up scan was manually reviewed and areas of visible density change were contoured. Scans were divided into regions receiving specific 10Gy dose‐bins. Voxel density changes belonging to contoured areas were averaged over each dose‐bin to obtain dose‐response curves (DRC). The occurrence of visible density change depending on the maximum dose to the tumor was also chosen as an end point to model the normal tissue complication probability (NTCP). Results: With an analysis restricted to area of visible change, the density change magnitude appeared to not depend much on the dose bin. The average density increase was smaller at 3 month (214HU), peaked at 6 months (322HU) and slightly decays thereafter without totally vanishing (300HU). This observed trend was similar using rigid or deformable registration. The maximum target dose for a 50% complication probability for changes >200HU was 80Gy according to the NTCP model. Conclusion: Although local correlations between dose and density increase have been reported for conventional and SBRT lung treatments, our analysis revealed a relatively uniform and stronger density response, while temporal density changes followed a previously reported density change trend (Palma 2010, IJROBP). These discrepancies were likely due to the restriction of the analysis to areas with actual density increase.
WE‐G‐BRA‐09: Risk of Radiation‐Induced Secondary Cancers in Paediatric Patients: A Comparison of Intensity Modulated Proton Therapy and Intensity Modulated Radiotherapy
Authors: Shin N , Laude C , Soisson E , ElNaqa I , Freeman C , Roberge D , Seuntjens J , Parker W
Published: November 2011

Purpose: To determine secondary cancer risk in paediatric patients treated with intensity modulated proton radiation therapy (IMPT) compared to IMRT. Methods: Proton therapy plans were created for fifteen patients previously treated with photon beam IMRT. IMPT plans were planned using the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA) with a scanned proton beam model. The proton plans were planned to the same prescription dose as the photon plans. Each proton plan consisted of one to three fields, depending on tumour location, and photon plan constraints were used as a guide for IMPT constraints. Proton and photon plans were compared for dose conformity, homogeneity, volumes of tissue receiving low doses, integral dose, and second cancer induction risk. Second cancer risk was determined using two methods. The relative risk of secondary cancer was found by applying a linear relationship between integral dose and relative risk of secondary cancer. The second approach used the organ equivalent dose concept to describe the dose in the body and then calculate the excess absolute risk (EAR) for solid cancers. Results: IMPT and IMRT plans had similar target conformity, homogeneity, near minimum, near maximum and median doses however IMPT plans had reduced integral dose and volumes of the body receiving low dose. IMPT plans resulted in a 0.313±0.098 smaller relative risk of secondary cancer than IMRT plans. The EAR of secondary cancer in the body 30 years after treatment was reduced by 20.89±9.56, 24.30±8.46 and 22.91±7.91 patients per 10000 patients per year for the linear, linear exponential and plateau dose‐response models respectively in IMPT compared to IMRT plans. Conclusions: Two methods were used to determine the risk of secondary cancers following radiation therapy in paediatric patients. Both methods indicated that IMPT results in a lower risk of secondary cancer than photon beam IMRT.
WE‐G‐BRB‐01: Safety and Quality Assurance in SRS and SBRT
Authors: Jaffray D , Benedict S , Solberg T
Published: November 2011

Stereotactic radiosurgery (SRS) has been an effective modality for the treatment of benign and malignant cranial disease for over 50 years. Increasingly, the stereotactic approach is being applied in a number of extracranial disease sites. Stereotactic body radiation therapy (SBRT) holds significant potential for improving tumor control rates across a range of locations and histologies. SRS / SBRT are fundamentally different from conventional radiotherapy in that the intent is to deliver an ablative dose that overcomes all of the abilities of a cancer cell to defend itself. It is inherently aggressive, much like a surgical approach, and therefore an increased rate of acute complications compared with conventional radiotherapy could be expected. Both SRS and SBRT require specialized technology, meticulous procedures, and dedicated personnel. Several recent high‐profile medical radiation events have generated considerable attention within the media, and serve to remind the profession that close attention to safety and ongoing quality improvement is a fundamental responsibility. The main aim of this symposium will be to address safety and quality in SRS and SBRT, highlighting the errors that have occurred in the past and determining how they can be minimized in a systematic way, starting from patient simulation, to planning and verification, immobilization and localization, delivery, and patient follow‐up, and to provide some recommendations for SRS / SBRT processes and procedures that may be beneficial in understanding and reducing risks inherent to the modalities. Specific issues to be addressed include:

‐ An overview of the accuracy requirements and the need for high levels of safety and quality in SRS/SBRT, as summarized in recent AAPM, ASTRO and ACR reports.

‐ Highlights from recent media events related to SRS, examining what went wrong and why; what could go wrong; and what nominal safety procedures, commissioning and routine QA and testing are needed for SRS and SBRT programs to ensure errors are minimized.

‐ Verification requirements for accurate image‐based localization and delivery in both rigid sites (e.g. CNS, spine) and moving targets (e.g. thorax (lung), liver, pancreas, etc.).
WE‐G‐BRC‐01: A Model for Clinically Focused Physics Education
Authors: Sprawls P , Monticciolo D , Sechopoulos I
Published: November 2011

Purpose: To provide a model for a comprehensive and collaborative program to enhance the effectiveness of physics education for residents in radiology. Methods and Materials: It is a major effort to address many of the existing challenges that exist today with physics education for radiology residents. Development of physics knowledge that will enhance clinical practice is best achieved through a synergistic combination of learning activities, each of which has specific values. The three specific elements of the progressive learning process are: 1. Class discussions on general topics conducted by physicists early in the residents program, 2. Focused learning activities in the clinical environment as residents begin specific clinical rotations coordinated by clinical faculty with on‐line modules or appropriate literature assignments, 3. Individual and group interactions, investigations, and study by residents. The physics faculty can enhance this phrase by providing study guides, learning objectives, and especially by participating in discussions and consultations. Results: The model relates to an evolution that is underway, in a variety of forms, in the various radiology residency programs and is actively being developed and applied by the authors. Fundamental to this evolution are existing challenges with scheduling, changes in the board examination process, and the rapidly increasing availability of web‐based resources. The two major sources at this time are the RSNA/AAPM modules and the resources provided by the Sprawls Educational Foundation both to provide high‐quality visuals for classroom discussion and modules for individual study. The content of these collections is currently being expanded. Conclusions: This model for clinically focused physics education for radiology residents provides a plan for highly effective programs that combine the values of three distinct types of learning activities to enhance physics education and utilizes the rapidly expanding web‐based resources to enhance human performance of both physics faculty and individual residents.
WE‐G‐BRC‐02: A Portable Optical CT Scanner for Interactive Teaching of Imaging Principles
Authors: Battista J , Miller J , Taylor R , Jordan K , MacDonald I
Published: November 2011

Purpose: To develop a portable scanner that demonstrates the principles of radiography and computed tomography (CT). Methods: The traditional methods for teaching the physics of medical imaging rely on lectures, followed by demonstrations on a clinical system that is not easily accessible or programmed for educational purposes. We have developed a scaled‐down portable CT imaging system suitable for interactive “real time” demonstrations using a laptop computer during a classroom or lab session. Our optical system uses light rays in lieu of x‐rays so that experiments can be conducted while posing no electrical or radiation hazards to instructors and students. The desk‐top CT imaging device will be supplied with a learning kit of experimental test phantoms, lab manuals, instructional videos, and specialized software that demonstrate 2D radiographic and 3D CT image reconstruction methods. These approaches are relevant to imaging systems used in digital diagnostic imaging and image‐guided therapy. Results: A low‐cost portable system (< $15,000) has been manufactured (http://www.deskcat.com/) to enrich the studentˈs learning experience and improve the retention of fundamental imaging concepts. Students learn about spatial resolution, contrast resolution, system linearity, image artifacts and they perform quantitative measurements in 3D space, using image visualization software tools and specialized test phantoms (7.2 cm diameter × 5.3 cm long). Early reaction from instructors and students alike has been very encouraging. Conclusions: This learning package should prove attractive to universities with medical physics programs in Departments of Physics, Medical Biophysics, or Biomedical Engineering, as well as Medical Schools with residency training programs (Medical Imaging, Radiation Oncology). The systemˈs modular nature allows extensions for future coverage of related topics such as nuclear and molecular SPECT imaging. Through future developments, it may also be possible to model the dose deposition patterns from intensity‐modulated radiotherapy beams using ultraviolet exposure of radiochromic gel volumes.

This research was sponsored by the Ministry of Research and Innovation, Government of Ontario, Canada (ORDCF Grant, OCITS Project) and by Modus Medical Devices as the industry partner. We also thank The University of Western Ontario for providing funding through its “Fellowship for Teaching Innovation”. This supported one of the authors (RT) during a summer studentship.
WE‐G‐BRC‐05: A Multidisciplinary Competency Certification Program for Specialized Procedures in Radiation Therapy
Authors: Brown D , Dunscombe P , Bayliss Y , Udowicz M
Published: November 2011

Purpose: To develop and implement a novel, multidisciplinary, web‐based competency certification program for specialized procedures in radiation therapy with the goals of improving standardization, safety, quality and communication within the clinical team. Methods: The certification program employs a variety of instructional and evaluation techniques. The introductory level consists of PowerPoint presentations with voice‐overs. Higher levels include links to significant recent publications in the specialty of interest. Participants are evaluated using on‐line quizzes and discipline‐specific competency checklists. Interdisciplinary collaboration is fostered by observation of colleagues performing their clinical roles. Results: The program comprises four levels with discipline specific tracks at the top three levels. Adequate performance on quizzes/competency checklists is a prerequisite for progression to the next level of certification. Level 1, an introductory level which is open to all members of the radiation treatment team including physics graduate students, residents and therapy students, comprises two hours of on‐line instruction. Level 2 is discipline specific and includes guided reading, with quizzes, cross‐disciplinary observation, and limited participation in clinical procedures. Level 3 includes more advanced guided reading, followed again by quizzes, and develops practical skills through supervised performance of a specified number of procedures. On satisfactory completion of Level 3 the participant is deemed an independent practitioner and teacher within their discipline. Level 4 is a maintenance of certification level that entails performance of a minimum number of procedures per year and documented on‐going professional development activities. Graduate students and physics and medical residents can also progress through the certification program to a level determined by their seniority and interest. The entire program, including presentations, quizzes, competency checklists, and readings, is available online through www.rtp‐learning‐centre.ca. Conclusions: The certification program offers a unique, simple, and flexible method of providing advanced education and training in specialized procedures to radiation medicine professionals.
WE‐G‐214‐05: Robotic Linac Adaptation (RLA) with a Novel Electron Gun Design for the In‐Line MRI‐Linac Configuration
Authors: Constantin D. , Holloway L. , Keall P. J. , Fahrig R.
Published: November 2011

Purpose: The emergence of MRI based guidance systems in radiation therapy has the potential for real‐time volumetric imaging and targeting. This work investigates a continuous delivery technique for an in‐line MRI‐linac system with a non‐MR‐shielded linac. Similar to the CyberKnife(TM) system the linac tracks the tumor motion and adapts its orientation in the fringe field of the magnet. Methods: An electron gun model resembling a plane capacitor is proposed to function with an unmodified Varian 600C linac. Space charge and electron transport simulations were used to characterize the electron gun‐linac system in the fringe field of a 0.5T open bore MRI scanner (GE Signa SP) at 0.18T. The assembly was displaced off the axis of symmetry and moved along the magnetic field lines to account for tumor motion and the beam characteristics of the systems were determined. Results: The minimum transverse rms emittance of the beam is ∼6.4 pi‐mm‐mrad 4.4mm away from the electron gun cathode with a current of 360mA. This compares favorably with the performance of a standard Pierce‐type gun placed at the same location in the magnet, which demonstrates significant reduction of current and/or emittance as high as 25 pi‐mm‐mrad. We show that the linac can be displaced off axis with minimal reduction in capture efficiency while maintaining low emittance if the linac is aligned with the field lines. The linac capture efficiency, the beam current at the gun exit, and the beam current at the linac exit were computed within the domain of linac motion. Conclusions: A specially designed electron gun‐linac assembly can function in the fringe field of a MRI magnet for various relative orientations of the linac with respect to the MR scanner. This technique allows the linac to simultaneously deliver dose and continuously track and adapt its position based on tumor motion.
WE‐G‐214‐09: Validation of 4D‐CT Pulmonary Ventilation Imaging: Characterization of the Reproducibility
Authors: Yamamoto T , Kabus S , Berg Jvon , Lorenz C , Loo B , Keall P
Published: November 2011

Purpose: A novel ventilation imaging method based on 4D‐CT has been applied to functional radiotherapy planning and assessing radiation‐induced ventilation changes. Understanding of its reproducibility is a prerequisite for such applications, however it has not been studied to date. The purpose of this study is to develop a method for validating 4D‐CT ventilation imaging through characterizing its reproducibility and show preliminary results. Methods: 4D‐CT ventilation images were created for three patients from repeat 4D‐CT scans at different time points, including two pre‐treatment (pre‐RT1 and pre‐RT2), one mid‐treatment (mid‐RT) and/or one post‐treatment (post‐RT). The reference (pre‐RT1) was compared with pre‐RT2 to quantify the temporal change in the absence of therapeutic intervention. Pre‐RT1 was also compared with mid‐RT and/or post‐RT to quantify the temporal change in the presence of therapeutic intervention. Finally, the Spearmanˈs voxel‐based correlations between pre‐RT1 and pre‐RT2 were compared to those between pre‐RT1 and mid‐RT or post‐RT to investigate the hypothesis: the temporal change in the absence of therapeutic intervention is smaller than that in the presence of therapeutic intervention. Results: Differences between the temporal changes in the absence and presence of therapeutic intervention were inconsistent. Regions of both agreement and disagreement were identified throughout the lung between pre‐RT1 and pre‐RT2, mid‐RT or post‐RT. The correlations with pre‐RT2 (absence) (range, 0.41–0.64) were slightly higher than or comparable to those with mid‐RT or post‐RT (presence) (range, 0.42–0.62). In general, the ventilation variations between pre‐RT1 and pre‐RT2 increased with increasing respiratory variations during the 4D‐CT acquisition. Conclusions: Preliminary results from a 3‐patient study suggest inconsistent differences between the temporal changes of 4D‐CT ventilation in the absence and presence of therapeutic intervention. Respiratory variations have been found to contribute to deteriorate the reproducibility. Ongoing studies focus on investigating more patients and spatial characteristics of the temporal changes.

SK, JB and CL are employees of Philips Research Europe.
WE‐G‐110‐02: A Cascaded Systems Model for Imaging Performance and Task‐Based Optimization in Dual‐Energy Cone‐Beam CT
Authors: Gang G , Prakash P , Zbijewski W , Stayman J , Siewerdsen J
Published: November 2011

Purpose: Optimization of dual‐energy (DE) tomographic imaging performance is challenged by the vast number of parameters to be considered. This work establishes a quantitative framework for theoretical analysis of noise‐power spectrum (NPS) and task‐based detectability in DE cone‐beam CT (DE‐CBCT). The model is compared to experimental results and applied to task‐based optimization of dual‐kVp selection and minimization of radiation dose. Methods: The model combines established methods for NPS propagation in DE imaging and CBCT, yielding a new framework for optimization of the DE‐CBCT imaging chain. The resulting DE‐CBCT NPS and noise‐equivalent quanta (NEQ) were derived to compute the detectability index for a variety of tasks in contrast‐enhanced musculoskeletal imaging. Theoretical calculations were validated against experimental measurements on a DE‐CBCT bench simulating the geometry of a CBCT prototype under development for musculoskeletal radiology. Optimization parameters included kVp pair, added filtration, dose allocation, etc. Results: The model provided tremendous insight in competing factors of DE‐CBCT performance. DE contrast (e.g., signal difference in 1 mm Ca or iodine to soft‐tissue) favored wide energy separation (e.g., [50/140] kVp) whereas NEQ degraded with kVp (e.g., maximized within the range considered at [65/100] kVp, with 0.6 mm Ag added to the latter). Detectability index quantitatively factored such tradeoffs in contrast and spatial‐frequency‐dependent noise along with the dose and imaging task — e.g., optimum at [65/105] kVp for a delta‐function iodine detection task. The model provided a quantitative guide to optimizing a broad scope of factors that would be difficult to consider through experimentation alone. Conclusions: A task‐based cascaded systems model establishes a new, quantitative framework for systematic optimization of DE‐CBCT imaging performance. The model combines established models shown to be of value in DE imaging and CBCT and should provide a valuable foundation for the development, optimization, and translation of high‐quality DE‐CBCT imaging techniques.

This work was supported by the National Institutes of Health Grant No. R01‐CA‐112163.
WE‐G‐110‐04: Finding the Optimal Thickness of Large Area Thin‐Film CdTe Detector under Diagnostic X‐Ray Beams
Authors: Jin X , Shvydka D , Parsai E
Published: November 2011

Purpose: Recent developments in large area photovoltaic applications of have moved cadmium telluride (CdTe) to the frontiers of thin‐film manufacturing, making the photoconductor a promising candidate for large‐area flat panel digital x‐ray detectors. We model thin‐film CdTe detector in direct detection configuration to find its intrinsic imaging characteristics, such as MTF (modulation transfer function), NPS (noise power spectrum), and DQE (detective quantum efficiency), as well as its electronic properties with the objective of determining the optimal thickness of CdTe. Material and Methods: The intrinsic imaging characteristics of thin‐film CdTe detector under diagnostic spectra were modeled with Monte Carlo simulation package, MCNP5. They were compared to those of other two photoconductors used in direct detection imaging, a‐Se and HgI2. The electronic properties of CdTe were studied with SCAPS simulation software, routinely used for photovoltaic device modeling. Results: While MTF decreases with increasing film thickness, the resultant DQE(f) increased with the thickness. The optimal thickness of CdTe under diagnostic x‐ray beams was found to be around 300μm, taking into account the resolution and detection efficiency factors. Although a‐Se shows better MTF under 80kVp, the DQE(f) of thin‐film CdTe is superior to that of a‐Se because of its much higher absorption efficiency. Electronic propertiesˈ study demonstrated that thin‐film CdTe device can provide adequate output under diagnostic x‐ray beams. We also found that increasing CdTe thickness beyond 300μm does not improve the output signal significantly. Conclusion: Our results show that the detector system based on thin‐film CdTe is capable of achieving high resolution as well as high quantum efficiency in diagnostic imaging applications. It also provides easily measurable signal output under this energy range. The optimal thickness of thin film CdTe for diagnostic x‐ray imaging is determined to be around 300μm.
WE‐G‐110‐09: Evaluation of Different Techniques for CT Radiation Profile Measurement
Authors: Ruan C , Jackson S , Hu Y , Ahmad S
Published: November 2011

Purpose: To demonstrate a procedure for using a Konica Minolta computed radiography (CR) system for the measurement of computed tomography (CT) radiation profiles and to compare this method with conventional and radiochromic film measurements. Methods: The exposure and processing conditions of a Konica Minolta CR reader system were characterized to establish the relationship between exposure in the imaging plate (IP) and pixel value. A 6 cc ionization chamber was exposed at the isocenter of a CT scanner using 80 kVp, 0.4s with various mA settings. CR images were processed in fix modes with various combinations of G and S values, establishing exposure and pixel value relationships. Optimal mA settings and processing parameters were selected to avoid the overexposure of the IP. The radiation profiles were collected using different collimation settings (40, 20, 10 and 5 mm) at 10 and 20 mA, respectively. The peak pixel value measured from the 10 mA profile was used to identify the location of 50% of maximal exposure in the 20 mA profile. The FWHM of the dose profile at different collimation beam widths can then be determined. The results were compared to those obtained from digitized conventional and radiochromic film profiles. Results: The optimal exposure (80 kVp, 0.4s, large body filter, 10 and 20 mA) and processing settings (fix mode with S = 5 and G = 1.81) were determined for CT radiation profile measurement. The FWHM results measured using this method agreed well within ±10% when compared to the conventional and radiochromic film results. Conclusions: The FWHM of CT radiation profiles can be accurately measured using a Konica Minolta CR system, when appropriate exposure technique and processing parameters are used. It has been proven to be a convenient and cost‐effective method for routine clinical quality assurance checks.
WE‐G‐211‐05: Advances in X‐Ray Luminescence Computed Tomography: Towards In‐Vivo Imaging of Radioluminescent Nanophosphors
Authors: Pratx G , Carpenter C , Sun C , Xing L
Published: November 2011

Purpose: Radioluminescent nanophosphors (RLNPs) show great promise for imaging biological processes in vivo, at the molecular level, and for enhancing the delivery of cytotoxic therapy within the target volume of a radiation treatment. As progress is made towards these goals, there is a need for an imaging modality that can quantitatively measure the distribution of RLNPs in vivo, with high sensitivity and spatial resolution. X‐ray luminescence computed tomography (XLCT) is best placed to meet all these requirements. In this scheme, collimated beams of X‐ray radiation selectively excite RLNPs, producing optical light within a narrowly‐defined volume. Optical measurements of the photons diffusing out of the subject can be interpreted as projective measurements and reconstructed into tomographic images. Methods: As a proof of concept, we built a prototype XLCT system and acquired projective data for near‐IR‐emitting RLNPs embedded in various phantoms. A novel reconstruction scheme that includes a model of light propagation in biological tissue was developed and evaluated on XLCT scans with sparse angular sampling. Results: Imaging in an optically‐diffusive medium shows that imaging performance is not affected by optical scatter; furthermore, the linear response of the reconstructed images suggests that XLCT is capable of quantitative imaging. Reconstruction that combines models of light and X‐ray propagation in tissue was found more accurate for sparsely‐sampled datasets. Conclusion: Based on phantom experiments, we found XLCT to be a feasible approach for imaging RLNPs tomographically. As we advance towards our goal of imaging RLNPs in live animals, we are designing and building a new imaging set‐up with improved X‐ray collimation and light collection efficiency.