bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐BRB‐04: MR Image Susceptibility Distortions: Quantification of Impact On the Radiation Treatment Planning of Cancer Sites
Authors: Stanescu T , Wachowicz K , Fallone B
Published: April 2010

Purpose: To investigate the impact of magnetic resonance (MR) image susceptibility‐induced distortions on radiation treatment planning (RTP) of cancer sites. Methods: We used a method relying on a) patient CT datasets are segmented into susceptibility relevant structures (soft‐tissue, bone, air), b) susceptibility masks are generated by assigning bulk values to volumes from a) and magnetic field numerical simulations are performed using finite difference methods, c) magnetic field distributions are converted into corresponding distortion fields applied to subsequently warp CT images, and d) CT‐based RT plans are generated and compared to corresponding CT+susceptibility plans, i.e. warped CT images. We used CT images instead of MR images to isolate the susceptibility effects. It is difficult to perform this analysis on MR images due to interference given by residual scanner‐related distortions (especially for large pelvic volumes), chemical shift artifacts, and CT‐MR image fusion errors. Results: The susceptibility distortions were determined for several cancer sites, i.e. brain, prostate, abdomen, and lung, for magnetic fields of 0.2T, 1.5T and 3.0T. The maximum distortion decreases with the increase of read gradient strength and the decrease of main magnetic field. The magnitude of susceptibility artifacts also depends on the anatomical structures' shape and their orientation with respect to the applied field. Evaluating RT plans, it was found that 0.2T susceptibility distortions do not alter the plan accuracy due to a reduced distortion levels (within image resolution). At higher fields and/or low gradient strengths the accuracy of the plans decreased significantly. Tumor target dose coverage was insufficient and critical structures were exposed to higher dose levels. Conclusions: The susceptibility distortions characteristic to several cancer sites were determined using numerical simulations and quantified for the RTP process. Depending on the scanning sequence, images may need correction to achieve spatial accuracy and ultimately ensure the efficiency of the RTP process.
WE‐C‐BRB‐05: Tracking of Thoracic Tumor Using EPID for Respiratory Gating Purposes: A Retrospective Feasibility Study
Authors: Schildkraut J , Gomez J , Singh A , Nazareth D , Malhotra H
Published: April 2010

Purpose: Conventional respiratory gating relies on an external surrogate which might provide suboptimal tracking of the tumor in many cases. In the present study, an attempt has been made to exploit the density differences between the tumor and its surrounding lung tissue to gate treatments directly using electronic portal imaging device [EPID]. Material & Methods: Varian Trilogy unit equipped with EPID [AS1000, resolution 1024×1024] was used. During treatment, a custom designed image acquisition template captured the portal images. The treatment plan along with the raw scan data and structures was also exported. DRRs for each field with the tumor [hereafter referred as nodule] projection overlaid on it, were also exported and were used as a shaped prior. Nodule was segmented in each portal image using a level set segmentation algorithm which includes an energy term that is minimized when the shape of the segmented region matches the shape prior. Results: The nodule segmentation algorithm was evaluated on a series of 20 portal images of a nodule located just above the diaphragm. The nodule has an average distance from the center of the portal of 5.68 mm with the standard deviation, minimum, and maximum distance of 1.79, 2.44, and 9.13 mm, respectively. The distance between the nodule and segmented region center was 1.98 mm and the standard deviation, minimum, and maximum distance being 0.96, 0.13, and 4.12 mm, respectively. The average & maximum position error between the portal and nodule center could be reduced by 35% & 45%, respectively, using the nodule segmentation algorithm. Present runtime of 4 seconds will be reduced to real‐time as the algorithm is being ported to graphic cards [GPUs]. Conclusion: The proposed method utilizes the tumor motion directly, thereby, eliminating an external surrogate system and its associated inaccuracies and offers promise for respiratory gating treatment delivery.
WE‐C‐BRC‐01: In Vivo Proton Beam Range Verification Using Spine MRI Changes
Authors: Gensheimer MF , Yock TI , Liebsch NJ , Sharp GC , Madan N , Grant PE , Paganetti H , Bortfeld T
Published: April 2010

Purpose: Uncertainty in the location of the distal dose edge is one of the main concerns about proton therapy. It leads to cautious treatment plans that partially neutralize the dosimetric advantage of protons. Vertebral bone marrow responds to radiation with fatty replacement that is visible on post‐treatment MRI. This presents a unique opportunity to visualize radiation effects in vivo. We have developed a method that uses spine MRI changes to precisely localize the distal dose edge in spinal proton radiation patients. Method and Materials: We carefully registered treatment planning CT scans and follow‐up T1‐weighted MRI scans from 10 proton spinal radiation patients. A radiation dose‐MRI signal intensity curve was created using the lateral beam penumbra in the sacrum. This curve was then used to quantitatively examine possible systematic or spatially varying proton range errors. Results: In the lateral penumbra there was a gradual increase in signal intensity with higher dose throughout the full dose range of 0–37.5 Gy. In the distal dose fall‐off region, the beam appeared to penetrate farther than planned in the central part of the vertebral bodies. The mean overshoot in five patients was 2.71 mm (95% confidence interval 1.13–4.28 mm). These errors are probably not clinically significant with current treatment planning procedures. Conclusion: We have demonstrated in vivo proton range verification based on post‐treatment spine MRI changes. Our analysis indicates that if range errors occur in spine treatments, their magnitude is at most a few millimeters in the majority of patients. It may be possible to extend our technique to MRI sequences that show early bone marrow changes. It could then be used for adaptive modification of spine radiation plans in order to reduce radiation dose to bone marrow and other normal tissues.
WE‐C‐BRC‐04: Predictive Power of Various PET Measures for Treatment Response Assessment
Authors: Vanderhoek M , Perlman S , Liu G , Jeraj R
Published: April 2010

Purpose: Assessment of treatment response in solid tumors is essential for disease management but typical response measures are limited and non‐robust. We compared the predictive power of several PET‐based measures in cancer patients receiving therapy. Method and Materials: Fourteen adult patients with advanced solid malignancies were treated with sunitinib malate, a molecular targeted agent. Using the cellular proliferation marker []FLT, whole‐body PET/CT scans were acquired pre‐, mid‐, and post‐treatment. Lesions were segmented on PET images and treatment response was assessed via percent change of the following measures: SUVmean, SUVmax, SUVpeak, SUVtotal, and PET defined tumor size: unidimensional, bidimensional, and volume. PET response assessment and clinical endpoint of therapy were used independently to classify patients into response categories: partial response (PR), stable disease (SD), or progressive disease (PD). Predictive power and robustness of PET measures were tested by varying response category cutoffs to generate ROC curves and Matthews correlation coefficients (MCC), a classification quality measure. Results: SUV measures demonstrated improved predictive power over PET defined size measures (MCCaverage: 0.27 vs. 0.21). Of all measures, SUVpeak was the most robust response predictor (MCCaverage: 0.30, MCCmax: 1.0), especially for prediction of PR. Of PET defined size measures, bidimensional size was the most robust response predictor. Changes in SUV measures pre‐ to mid‐treatment showed improved predictive power over pre‐ and mid‐ to post‐treatment changes (MCCaverage: 0.32, 0.27, and 0.22 respectively). Prediction of PR was vastly superior to that of SD and PD (MCCaverage: 0.44, 0.16, and 0.14 respectively). ROC analysis supported MCC results. Conclusion: Comparison of PET‐based measures revealed that SUV measures were more predictive of response than PET defined size measures. SUVpeak, a rarely used functional measure, demonstrated the most robust predictive power. Future treatment response studies should test and implement more robust measures, like SUVpeak, for improved response assessment.
WE‐C‐BRC‐07: Image Quality QA for Three Radiotherapy Cone‐Beam CT Systems
Authors: Doemer A , Perera H , Gingold E , Liu H , Fu L , Harrison A , Yu Y , Xiao Y
Published: April 2010

Purpose: With the increased presence of volumetric radiotherapy cone beam CT (RT‐CBCT) systems, the importance of high grade image quality is crucial to achieve daily image‐guided adaptive radiotherapy (IGART) capabilities. We subjected three commercially available RT‐CBCT systems to a battery of standard diagnostic image quality tests acquired under clinical conditions. This study reports on the evaluation of image qualities for RT‐CBCT's and a diagnostic CT. Methods and Materials: RT‐CBCT scans were performed on Elekta XVI, Nucletron Simulix, and Varian OBI Advanced Imaging using clinical pelvis scan settings on a CATPHAN Model 600. They were then compared to results from a GE Lightspeed CT scanner. The phantom contained modules allowing measurement of low contrast resolution, slice thickness, Hounsfield Unit (HU) sensitivity, spatial resolution, and image uniformity. Results: No CBCT system was able to detect any targets in the low contrast module. Six targets could be seen on diagnostic CT's. All RT‐CBCT systems had greater than 33% variations in slice thickness reconstruction. The HU sensitometry test showed absolute differences between accepted HU values and measured values for XVI and Simulix systems to be on average 6 times and 3 times the error seen in a diagnostic CT respectively. HU sensitivity for OBI is within 15% of a diagnostic CT. Both OBI and Simulix had spatial resolution twice that of XVI but were 3 lp/cm worse than a diagnostic CT. Measurements of image uniformity showed that all three RT‐CBCT systems have a standard deviation of HU values on the order of 10 times that of a diagnostic CT. Conclusions: The image qualities of three evaluated RT‐CBCT systems are relatively comparable, yet still inferior to those from helical CT. It is important to note that dosimetric settings can have a clear impact on image quality, and dose measurements were not done for this work.
WE‐C‐BRC‐08: A Method to Evaluate Region‐Specific Pulmonary Function Using 4D CT Images for Lung Cancer Patients Undergoing Radiation Therapy
Authors: Zhong H , Fragoso M , Patel S , Ajlouni M , Movsas B , Chetty I
Published: April 2010

Purpose: Collateral radiation exposure to healthy lung tissue during radiation therapy can result in changes in structural and biomechanical properties of the lung. These changes may cause various clinical symptoms. The purpose of this study was to develop a functional imaging technique to assess the lung's region‐specific ventilation and pressure during or after radiation treatment.

Method and Materials: With an in‐house developed finite element framework, a heterogeneous elastic model was developed for a lung patient and its Young's moduli were derived from a set of 4D CT images, acquired during radiation treatment. Each phase of the 4D dataset was registered, using deformable image registration (ITK demons algorithm) with the end‐inhale reference dataset. The resultant deformation matrix was used first to calculate the volumetric variation of each image voxel to generate a 3D ventilation image, and then to compute its corresponding transpulmonary pressure with the mechanical model. Results: Lung volumes on each phase of the acquired 4D dataset were compared with those derived from the deformed model, and were found to be within 1% of each other. The maximum ventilation occurs from phase 1 to phase 2, the earliest expiration phase. The average ventilation increased from 20.2% in phase 2 to 30.8% in phase 5 and their correspondent pressures increased from 1.57 Kpa to 2.25 Kpa. This result is generally consistent with published measurements. Conclusion: This study describes a theoretical approach to calculate the region‐specific ventilation and mechanical functions using deformable image registration. The method may be applied toward understanding how the mechanical properties of damaged lung differ from that of healthy lung tissue, and therefore it has potential applicability as a diagnostic indicator, as well as a tool for predicting radiation‐induced lung damages. Work is underway to correlate this approach with other traditional functional‐imaging modalities used to assess lung function.
WE‐D‐304A‐06: The Characterization of Iodinated‐Contrast Kinetics Using a Dynamic Breast Phantom
Authors: Huang S , Yang K , Packard N , Burkett G , Prionas N , Boone J
Published: April 2010

Purpose: To demonstrate the effectiveness of contrast‐enhanced dual energy mammography (CEDEM) in characterizing the contrast kinetic curve. Method and Materials: The acquisition of CEDEM was performed using a dedicated cone‐beam breast CT scanner in our laboratory, with the system operating in stationary imaging mode. CEDEM images were acquired with a filter combination of 0.2 mm Cu and 0.2 mm Sn at the same kVp. Previous studies in our group have shown that 55 kVp is the optimal technique factor to acquire high‐quality CEDEM images when imaging a 6‐cm, anatomical‐complex breast phantom. As an addition to the static breast phantom, a tumor perfusion chamber was designed and fabricated to simulate the contrast kinetics of breast tumors. The chamber is composed of a “leaky” vessel (soaker hose) and the tumor interstitial space (foam). The contrast kinetics was controlled by two peristaltic pumps, the “leakiness” of the soaker hose, and the permeability of the foam. When imaged experimentally, the tumor perfusion chamber was fixed in the middle of the static breast phantom. A sequence of CEDEM images were acquired with an initial bolus injection of 100 ml Visipaque®. The contrast kinetics was determined by evaluating the signal‐to‐noise ratio of each dual‐energy subtracted image as a function of time. Results: The CEDEM image sequence of the dynamic breast phantom was acquired at 55 kVp. The contrast kinetic curve was found to follow closely that of human subjects. The influence of the phantom parameters on the kinetic curve will be presented. The contrast kinetic curve modeling benign and malignant tumors using this phantom will be presented. Conclusion: The contrast kinetic curve was evaluated using a dynamic breast phantom. CEDEM was found to be effective in characterizing the contrast kinetic curve around breast tumors.
WE‐E‐BRB‐05: The Effects of Low Dose Regions On 3D IMRT QA Delivery Using a MatriXX 2D Array and MULTICUBE
Authors: Fox C , Sanford R
Published: April 2010

Purpose: IMRT quality assurance performed at treatment gantry angles using 2D arrays allows for the evaluation of rotational aspects of beam delivery. We investigate aspects of angular‐based IMRT QA that contribute to lower‐than‐average passing rates when compared to treatment planning calculations. Method and Materials: Planar dose profiles calculated on a CT of the IBA MatriXX 2D array device with the MULTICUBE phantom at iso‐center were exported from the Philips Pinnacle TPS. Beam angles of 0, 90, 180, and 270° were delivered using a Varian Clinac 2300iX. IBA OmniPro‐I'mRT software was used for analysis. Individual beams of 4×4 and 10×10 cm2 were compared to calculated profiles using gamma index criteria of 3 % and 3 mm. Additionally, composite profiles of 0 and 90° beams were assessed for each field size. Finally, IMRT‐delivered clinical beams were assessed. Results: The gamma index pass rates of individual 4×4 and 10×10 cm2 beams at 0° were greater than 98%. However, 90° beams were found to achieve below 90% pass rates, with the 4×4 being below 85%. The measured and calculated results compared worse in the exit dose region. Composite profiles of 0 and 90° beams agreed with calculated to within 98 % for both field sizes. Clinical IMRT beams showed good agreement in high‐dose regions, but passing rates in exit‐dose regions demonstrated reduced passing rates. Conclusion: An angular dependency is evident in the measurement of radiation fields when using the MatriXX device. Gamma index pass rates can show significant improvement through composite dose comparison. However, individual beam information can be lost, particularly the low‐dose beam exit contribution, when applying composite evaluation. This becomes important when considering the dose to organs‐at‐risk which lay in these low dose regions.
WE‐E‐303A‐01: Image‐Guided Therapies: Advances in Imaging, Modeling, and New Applications
Authors: Siewerdsen J , Hawkes D , Keall P
Published: April 2010

Recent advances in imaging technology, image modeling and registration, and advanced therapeutics offer the potential for precise, image‐guided therapies that will transform existing approaches to planning, intervention, adaptation, and monitoring of therapeutic response. Such therapies are marked by a dramatic increase in the application of image information from multiple modalities and demand accurate coregistration of morphological and functional information across a broad range of spatial and temporal scales. The scope of advanced therapeutic modalities enabled by such advances is broad, ranging from high‐precision image‐guided radiation therapy and surgery to minimally invasive target ablation, cell‐based therapies, and other forms of novel therapeutics. Moreover, the information acquired during the course of intervention will drive patterns of therapy delivery that are increasingly adaptive and patient‐specific. This symposium focuses on the scientific principles and recent advances in imaging, guidance, image modeling, registration, adaptation, and advanced therapy delivery techniques. Three speakers will present on topics central to such advancement: Dr. Siewerdsen will discuss principles of imaging performance, guidance, and the development and integration of new technologies for therapy guidance; Dr. Hawkes will address principles of rigid and deformable image registration, fusion, visualization, and augmented reality; finally, Dr. Keall will discuss the latest advances in imaging, adaptation, and novel treatment delivery techniques in image‐guided radiation therapy.

Learning Objectives:

1. Gain exposure to new developments in imaging technologies for image‐guided interventions.

2. Understand challenges in rigid and deformable image registration, fusion, and visualization.

3. Learn the latest advances in imaging, adaptation, and therapy delivery techniques in IGRT.
WE‐E‐210A‐03: 3D Carotid Ultrasound Imaging for Monitoring Carotid Atherosclerosis
Authors: Fenster A
Published: April 2010

Atherosclerosis is characterized by the development of plaques in the arterial wall, ultimately leading to heart attacks and strokes. Quantitative measurements of the progression and regression of carotid plaque burden are important in monitoring patients and evaluating new treatment options. 3D carotid ultrasound (3D US) has the potential to be an effective method to monitor the progression of carotid artery plaques in symptomatic and asymptomatic patients. To meet this challenge, we developed a 3D carotid US system that allows detailed studies of plaques in 3D. Our software includes 3D reconstruction, viewing, and segmentation of carotid plaques, surface morphology analysis, and registration software to allow quantitative tracking of plaque changes. We used our system to examine the detailed relationship between the 3D US‐based measurement of plaque volume, the 3D scanning parameters, volume measurement variability, and plaque surface morphology. In this paper, we describe the acquisition and reconstruction of 3D carotid US images, and extended concepts used in intima‐media thickness (IMT) measurements based on 2D images to a metric we call the 3D vessel‐wall‐plus‐plaque thickness (3D VWT), which is obtained by computing the distance between the carotid wall and lumen surfaces on a point‐by‐point basis in a 3D image of the carotid arteries. The VWT measurements can be superimposed on the arterial wall to produce the 3D VWT map. Since changes in plaque thickness is important in monitoring patients who are at risk for stroke, we also compute the change of VWT by comparing the 3D VWT maps obtained at two different times. To facilitate the visualization and interpretation of the 3D VWT and 3D VWT‐Change maps, we developed a technique to flatten these maps in an area‐preserving manner.

Learning Objectives:

1. Understand the limitations of conventional carotid ultrasound imaging

2. Understand the methods that can be used to overcome the limitations of the use of conventional ultrasound to monitor progression of carotid disease

3. Understand the advantages of 3D ultrasound images to monitor progression of carotid disease
TH‐B‐213A‐01: Risks From Occupational Radiation Exposures
Authors: Berrington A
Published: April 2010

Radiologists and radiologic technicians were among the earliest occupational groups to be exposed to ionizing radiation, and still constitute one of the largest groups of workers exposed to man‐made sources of radiation whilst at work. Studies of human populations exposed to acute, high doses of ionizing radiation have proved valuable in assessing the link between radiation and cancer and have been used to derive quantitative estimates of risk. However, the applicability of these estimates to the assessment of risks following fractionated or low level exposures remains uncertain. A number of epidemiologic studies have been conducted therefore to assess the potential risks from medical occupational exposure directly, including studies of radiologists in the UK, US and China and a cohort of radiologic technicians radiographers in the U.S.

This lecture will provide an overview of these epidemiological studies and their findings, as well as a description of a new study of physicians that perform fluoroscopically guided procedures that we are currently running at the National Cancer Institute. The use of cancer risk projection models that we have developed to estimate potential lifetime cancer risk following specified exposure histories will also be described with examples.

Learning Objectives:

1. Understand the strengths and limitations of the epidemiologic studies of medical radiation workers

2. Understand the strengths and limitations of risk projection models to estimate lifetime cancer risks from occupational radiation exposures
TH‐C‐BRD‐03: Kilovoltage Stereotactic Radiosurgery for Age Related Macula Degeneration: Assessment of Patient Effective Dose and Patient Specific Tissue Doses
Authors: Hanlon J , Lee C , Bolch W , Chell E , Gertner M , Hansen S
Published: April 2010

Purpose: Age‐related macula degeneration (AMD) is a leading cause of vision loss in the United States. Radiation therapy was initially explored as a treatment option in the 1990's, but has since been abandoned in favor of intraocular drug injections. Interest continues for stereotactic radiosurgery (SRS), an option that provides a noninvasive treatment for the wet form of AMD. Method and Materials: Two adult heads, male and female, were computationally modeled with Rhinoceros 4.0 using CT slice segmentation scaled to ICRP Publication 89 reference values. The head phantoms were voxelized and a three‐beam photon treatment (100 kVp) was modeled using the MCNPX radiation transport code to evaluate tissue dose and effective dose. Treatment was also simulated using the reference heads with changeable optic nerve positions based on individual patient variability seen in a head CT scan review. Results: A cumulative dose of 24 Gy to the macula (8 Gy per beam) yielded an effective dose of 0.28 mSv. The maximum doses to the most extreme patient specific optic nerve positions were evaluated using Dose Volume Histograms and found to be below the thresholds for serious complications, as were other reference tissues. Conclusion: The results of this study show that SRS is a safe option considering effective dose and tissue toxicity for a reference individual. Patient specific models will be created from the CT review and treatment will be modeled using MCNPX to establish certainty that this is a safe treatment option for all individuals considering other patient specific variations in anatomy.

This work was sponsored by Oraya Therapeutics.
TH‐C‐BRB‐02: Professional — SAM
Authors: Yester M
Published: April 2010

Currently, a common initiative in many fields is quality improvement. This endeavor is especially prominent in the medical community with concerns on patient safety and reduction of medical errors. As part of its certification oversight, the American Board of Medical Specialties (ABMS) has made QI one of the four sections of its Maintenance of Certification (MOC) process. This is particularly relevant to those medical physicists with time limited ABR certificates or for other ABR Diplomates voluntarily enrolled in the MOC program. One of the key aspects of The ABR expectation for Practice Quality Improvement (PQI), Part IV of the ABR MOC program, is that Diplomates provide evidence of an ongoing program of improvement of practice either as an individual or within the system the individual is employed. For physicists, this may seem somewhat nebulous due to the many duties and responsibilities in the clinical realm. For diagnostic physicists, this may seem even more undefined, especially for consultants. As a beginning dialogue related to PQI, suggestions for projects appropriate for physicists are presented. Another method for fulfillment of the PQI section is participation in society based PQI programs. Such programs are under development within AAPM and details on a program for diagnostic imaging physicists is presented.

Objectives: At the conclusion of the presentation, an individual will

1. Gain knowledge of the basic aspects of PQI as pertain to physicists.

2. Learn about examples of projects that would be acceptable for demonstration of PQI for physicists.

3. Learn about the development of a society based program for PQI for diagnostic imaging physicists within the AAPM.
TH‐C‐BRC‐05: A CMOS‐Based Digital Imager Integrated with An Orthovoltage X‐Ray Therapy Unit for Guidance of Precise Small Animal Irradiation
Authors: Wang Z , Saito N , Podgorsak MB
Published: April 2010

Purpose: Orthovoltage x‐ray units are commonly used in experimental irradiation of small animal models. However, the irradiation of targets that are deep‐seated within the animal is rather problematic without an image‐guidance system. This study was aimed at evaluating the use of a CMOS‐based portal‐imaging system to provide image‐guidance for small animal irradiation using an orthovoltage unit. Method and Materials: The imaging system consists of a CMOS‐based x‐ray sensor and a frame grabber connected to a PC. A fast frame rate (20 frame/sec, 50 ms/frame exposure, 96 m pixel size) was used to minimize image saturation due to the relatively high output of a typical therapeutic x‐ray unit (Phillips RT‐250). We first evaluated the imaging system with a contrast and resolution phantom. A pilot animal study with this system was then carried out for experimental thoracic irradiation of mice to induce pulmonary fibrosis. We used 75‐kVp beam for imaging, and 250‐kVp beam for the treatment, while keeping the same irradiation geometry setup. Based on image findings, radiation shields to protect the critical organs were custom‐made. Results: The 8‐mm diameter contrast discs in the testing phantom, with a minimum contrast of 0.9%, are all visible in the images. The spatial resolution based on bar‐pattern findings is at least 4.0 lp/mm. Mouse anatomical structures are clearly visible in the images. The portal images provided sufficient information for target localization and shield placement in the mice lung irradiation experiments. Conclusion: The CMOS‐based imaging system provides high quality images. It is convenient to use in comparison to the use of x‐ray films. We expect more accurate small animal irradiation results under the portal‐imaging guidance. Development of future applications of the imager may include multi‐directional imaging guidance and 3‐dimentional cone‐beam CT guidance for animal irradiation.

(Acknowledgment: Rad‐icon Imaging Corp. graciously provided the Shod‐o‐box™ imager for evaluation.)
TH‐C‐BRC‐09: Commissioning of a 3D MicroCT‐Based Small Animal Radiotherapy System
Authors: Rodriguez M , Zhou H , Jogani R , Nelson G , Keall P , Graves E
Published: April 2010

Purpose: We commissioned a novel microCT‐based kilovoltage 3D conformal radiotherapy system. A two‐stage, variable‐aperture collimator has been installed between the X‐ray source and the CT isocenter to confine the X‐ray beam, so that the system can be used for both imaging and treatment. Commissioning included alignment of the axes of the collimator and the X‐ray beam, measurement of the beam penumbra, measurement of the X‐ray beam dose rate in water, and measurement of the effective aperture size at isocenter. Method and Materials:
Images projected to gafchromic films placed at the isocenter and the microCT detector were analyzed by software developed for this commissioning, which provided quick and precise guidance for mechanical and control‐software adjustments. The penumbra was measured by fitting the beam profile to piece‐wise linear functions. The collimator‐beam alignment, the aperture ratio of the two stages, and the absolute aperture calibration were measured with known image pixel sizes. The attenuation was measured by comparing the signals in the shielded and the exposed areas in the images. Measurement of the dose rate in water was accomplished using solid water phantoms and film, calibrated using parallel ion chamber measurements. Results: The measured penumbra width was 0.5 mm, dictated primarily by the finite x‐ray source spot size. Alignment of the collimator and X‐ray beam alignment was achieved within 0.1 mm. The beam width precision was less than 0.05 mm, guaranteed by the stage‐aperture ratio and absolute beam‐width calibration. The measured attenuation was better than 99.85%. Conclusion: The 3D‐conformal‐animal‐radiation‐system commissioning has achieved the design goals that ensure the precise delivery of x‐ray beam to deep‐seated targets in experimental animals.

The techniques developed for the commissioning also provided reliable methods for future system quality assurance.
TH‐C‐303A‐03: Real‐Time Motion Detection of Prostate Target During Volumetric Arc Therapy Using Onboard Imaging Devices
Authors: Liu W , Wiersma R , Luxton G , Xing L
Published: April 2010

Purpose: To develop a real‐time prostate position monitoring technique for modern arc radiation therapy through novel usage of cine‐MV imaging together with as‐needed kV imaging. Methods and Materials: We divide the task of monitoring intrafraction prostate motion into two separate but related parts: (1) to detect potential target motion beyond a pre‐defined threshold and (2) to confirm whether it is beyond the threshold and how large the displacement is. By taking advantage of the gantry rotation during arc therapy, MV images from different viewing angles were used to stereoscopically evaluate the motion status of the prostate/marker and to allow us to detect potential over‐threshold displacement. If a potential over‐threshold event is detected by MV images, the onboard kV imager is turned on to confirm this through combined data from MV‐kV imaging. The position information acquired from combined MV‐kV data can be used as input for further motion management techniques. A Varian Trilogy linac with onboard kV imager was used to examine selected typical trajectories using a 4D motion phantom capable of moving in accordance with a pre‐programmed trajectory. Performance analysis of the proposed method has been done using 536 patient‐measured trajectories from 17 patients. Results: Prostate displacement beyond a set threshold (3mm) was detected for over 99.8% of the time with better than 1mm detection accuracy. Compared to other fluoroscopy‐based tracking techniques, kV usage is significantly reduced to on average of ∼15 times per arc delivery. Conclusions: Cine MV imaging during arc therapy provides a valuable tool for detecting non‐negligible intrafraction prostate motion with as‐needed low kV usage. Our motion detection method is distinguished from current motion monitoring techniques which seek to continuously and accurately localize a moving target. The proposed technique can be readily implemented with linacs equipped with EPID and onboard kV imaging devices.
TH‐C‐303A‐07: A Diaphragm Tracking Algorithm for Megavoltage Cone Beam CT Projection Data
Authors: Chen M , Siochi R
Published: April 2010

Purpose: To test a novel algorithm for diaphragm detection in 2D views of cone‐beam computed tomography (CBCT) raw data. Method and Materials: 6 Siemens megavoltage CBCT scans of lungs were analyzed. For each scan, a user identified the diaphragm apex in two full exhale and two full inhale views to determine exhale and inhale bounding points, respectively, in room coordinates. Projecting bounding points into other views creates opposite corners of a bounding rectangle that is enlarged to create a cost function region (CFR). A cost image is created by multiplying the gradients of the Gaussian filtered CFR with a gradient direction matching function, based on diaphragm contour training sets. The sum of cost image values along a parabolic path is V(a, x0, y0, t), where the parameter set (a, x0, y0, t) describes a parabola whose vertex is constrained within the bounding rectangle of the view at index t. Dynamic programming finds the path in this 4D parameter space that maximizes the sum of V, over all views, subject to smoothness constraints between adjacent views. The results were compared to the expert‐identified diaphragm apex. Errors were calculated in room coordinates as the root‐mean‐square distances between the expert's points and the parabola's vertices in all 200 views. Room coordinates were calculated by interpolated ray‐tracing. Results: The diaphragm was successfully detected in all 6 data sets, even for views with poor image quality and confounding objects. Each CBCT scan analysis (200 views) took about 35 seconds on a 2.66 GHz Intel quad‐core 2 CPU. The average cranio‐caudal position error was 1.58 ± 0.44 mm. Other directions were not assessed due to uncertainties in expert identification, so future studies will use anthropomorphic motion phantoms. Conclusion: The diaphragm detection algorithm is sufficiently quick and accurate for motion determination prior to radiation therapy.
TH‐C‐304A‐10: Computer‐Aided Measurement of Liver Volumes in CT by Means of Fast‐Marching and Level‐Set Segmentation
Authors: Suzuki K , Kohlbrenner R , Obajuluwa A , Epstein M , Garg S , Hori M , Baron R
Published: April 2010

Purpose: Measuring the liver volume by manual tracing of the liver boundary on arterial‐phase CT images is time‐consuming. Our purpose was to develop an automated liver extraction scheme based on a 3D level‐set segmentation technique for measuring liver volumes. Material and Methods: Hepatic CT scans of eighteen prospective liver donors were obtained under a liver transplant protocol. We developed an automated liver segmentation scheme for volumetry of the liver in CT. Our scheme consisted of five steps. First, a 3D anisotropic smoothing filter was applied to CT images for removing noise while preserving the structures in the liver, followed by an edge enhancement filter and a nonlinear gray‐scale enhancement filter for enhancing the liver boundary. By using the boundary‐enhanced image as a speed function, a 3D fast‐marching algorithm generated an initial surface that roughly estimated the shape of the liver. A 3D level‐set segmentation algorithm refined the initial surface so as to fit the liver boundary more accurately. Automated volumes were compared to manually determined liver volumes. Results: The mean liver volume obtained with our scheme was 1598 cc (range: 1002–2415 cc), whereas the mean manual volume was 1535 cc (range: 1007–2435 cc). The mean absolute difference between automated and manual volumes was 128 cc (9.5%). The two volumetrics reached an excellent agreement (the intra‐class correlation coefficient was 0.89) with no statistically significant difference (P=0.13). The processing time by the automated method was 2–5 min. per case (Intel, Xeon, 2.7 GHz), whereas that by manual segmentation was approximately 50–60 min. per case. Conclusion: CT liver volumetrics based on an automated scheme agreed excellently with manual volumetrics, and required substantially less completion time. Our automated scheme provides an efficient and accurate way of measuring liver volumes in CT; thus, it would be useful for radiologists in their measurement of liver volumes.
TH‐C‐210A‐02: Principles of Perfusion Measurement with CT
Authors: Gould R
Published: April 2010

CT has been used as a tool for determining blood perfusion to a diverse group of organ systems including the kidney, the lungs, the myocardium and the brain. Improvements in CT scanner design have improved and expanded capabilities for perfusion assessment, for example, faster scan times have enabled shorter sample duration and increased the number of samples that can be acquired per unit time. Greater x‐ray beam width in the Z‐axis and more rapid and controlled table movement have increased the coverage area. Gating techniques have reduced patient motion problems in some organs. However, perfusion studies remain challenging in many organs and in many patients. Artifacts, including beam hardening and streaking, and inherent limitations, including noise and partial volume effects, can limit the accuracy of measurements.

In this talk, methods for CT perfusion measurements will be reviewed. Developments in CT that have improved perfusion measurements will be discussed and sources of error will be described.

Learning Objectives:

1. Understand the principles of perfusion measurement with CT

2. Review the sources for error in perfusion measurements with CT
Effects of upper ocean sound-speed structure on deep acoustic shadow-zone arrivals at 500- and 1000-km range
Authors: Van Uffelen Lora J. , Worcester Peter F. , Dzieciuch Matthew A. , Rudnick Daniel L. , Colosi John A.
Published: April 2010

Deep acoustic shadow-zone arrivals observed in the late 1990s in the North Pacific Ocean reveal significant acoustic energy penetrating the geometric shadow. Comparisons of acoustic data obtained from vertical line arrays deployed in conjunction with 250-Hz acoustic sources at ranges of 500 and 1000 km from June to November 2004 in the North Pacific, with simulations incorporating scattering consistent with the Garrett–Munk internal-wave spectrum, are able to describe both the energy contained in and vertical extent of deep shadow-zone arrivals. Incoherent monthly averages of acoustic timefronts indicate that lower cusps associated with acoustic rays with shallow upper turning points (UTPs), where sound-speed structure is most variable and seasonally dependent, deepen from June to October as the summer thermocline develops. Surface-reflected rays, or those with near-surface UTPs, exhibit less scattering due to internal waves than in later months when the UTP deepens. Data collected in November exhibit dramatically more vertical extension than previous months. The depth to which timefronts extend is a complex combination of deterministic changes in the depths of the lower cusps as the range-average profiles evolve with seasonal change and of the amount of scattering, which depends on the mean vertical gradients at the depths of the UTPs.
The effect of oral articulation on the acoustic characteristics of nasalized vowels
Authors: Rong Panying , Kuehn David P.
Published: April 2010

To study the acoustic characteristics of nasalized vowels, the effects of velopharyngeal opening and oral articulation are considered. Based on vocal tract area functions for one American English speaker, spectral evolutions for the nasalization of three English vowels /a/, /i/, and /u/ were studied by simulating transfer functions for vowels with only velar movement, and for different nasal consonant-vowel utterances, which include both velar and oral movements. Simulations indicate extra nasal spectral poles and zeros and oral formant shifts as a result of the velopharyngeal opening and oral movements, respectively. In this sense, if oral articulation is coordinated with velar movement in such a way that nasal acoustic features are prominently attenuated, corresponding compensatory articulation can be developed to reduce hypernasality. This may be realized by (1) adjusting the articulatory placement for isolated nasalized vowels or by (2) changing the relative timing of coarticulatory movements for dynamic speech. The results demonstrate the effect of oral articulation on the acoustics of nasalized vowels. This effect allows oral articulation to compensate for velopharyngeal dysfunction, which may involve a constellation of speech production disorders resulting from anomalous velopharyngeal closure and which is usually accompanied by hypernasality and nasal emission of air.
Accuracy of formant measurement for synthesized vowels using the reassigned spectrogram and comparison with linear prediction
Authors: Fulop Sean A.
Published: April 2010

This brief report describes a small study which was undertaken with nine synthetic vowel tokens, in an effort to demonstrate the validity of the reassigned spectrogram as a formant measurement tool. The reassigned spectrogram’s performance is also compared with that of a typical pitch-asynchronous linear predictive analysis and is found to be superior. In this study, reassigned spectrograms were further processed to highlight the formants and then were used to measure these synthetic vowel formants generally to within 0.5% of their known true values, far surpassing the accuracy of a typical linear predictive analysis procedure which was inaccurate by as much as 17%. The overall accuracy of reassigned spectrographic formant measurement is thus demonstrated in these cases.
Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers
Authors: Le Crom Bénédicte , Castaings Michel
Published: April 2010

This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.
Graded activation of the intrinsic laryngeal muscles for vocal fold posturing
Authors: Chhetri Dinesh K. , Neubauer Juergen , Berry David A.
Published: April 2010

Previous investigations using in vivo models to study the role of intrinsic laryngeal muscles in phonation have used neuromuscular stimulation to study voice parameters. However, these studies used coarse stimulation techniques using limited levels of neuromuscular stimulation. In the current investigation, a technique for fine control of laryngeal posturing was developed using graded stimulation of the laryngeal nerves. Vocal fold strain history to graded stimulation and a methodology for establishing symmetric laryngeal activation is presented. This methodology has immediate applications for the study of laryngeal paralysis and paresis, as well as general questions of neuromuscular control of the larynx.
Identification of synthetic vowels based on a time-varying model of the vocal tract area function
Authors: Bunton Kate , Story Brad H.
Published: April 2010

The purpose of this study was to conduct an identification experiment with synthetic vowels based on the same sets of speaker-dependent area functions as in Bunton and Story [(2009) J. Acoust. Soc. Am. 125, 19–22], but with additional time-varying characteristics that are more representative of natural speech. The results indicated that vowels synthesized using an area function model that allows for time variation of the vocal tract shape and includes natural vowel durations were more accurately identified for 7 of 11 English vowels than those based on static area functions.
Insights into head-related transfer function: Spatial dimensionality and continuous representation
Authors: Zhang Wen , Abhayapala Thushara D. , Kennedy Rodney A. , Duraiswami Ramani
Published: April 2010

This paper studies head-related transfer function (HRTF) sampling and synthesis in a three-dimensional auditory scene based on a general modal decomposition of the HRTF in all frequency-range-angle domains. The main finding is that the HRTF decomposition with the derived spatial basis function modes can be well approximated by a finite number, which is defined as the spatial dimensionality of the HRTF. The dimensionality determines the minimum number of parameters to represent the HRTF corresponding to all directions and also the required spatial resolution in HRTF measurement. The general model is further developed to a continuous HRTF representation, in which the normalized spatial modes can achieve HRTF near-field and far-field representations in one formulation. The remaining HRTF spectral components are compactly represented using a Fourier spherical Bessel series, where the aim is to generate the HRTF with much higher spectral resolution in fewer parameters from typical measurements, which usually have limited spectral resolution constrained by sampling conditions. A low-computation algorithm is developed to obtain the model coefficients from the existing measurements. The HRTF synthesis using the proposed model is validated by three sets of data: (i) synthetic HRTFs from the spherical head model, (ii) the MIT KEMAR (Knowles Electronics Mannequin for Acoustics Research) data, and (iii) 45-subject CIPIC HRTF measurements.
A field study of the exposure-annoyance relationship of military shooting noise
Authors: Brink Mark , Wunderli Jean-Marc
Published: April 2010

This article reports a field study on noise annoyance from military shooting with small, midsize, and heavy weapons that was carried out among 1002 residents living near eight different training grounds of the Swiss army. The goal of the study was to derive the exposure-annoyance relationship for military shooting noise in communities in the vicinity of average military training grounds. Annoyance was determined in a telephone survey by means of the 5-point verbal and 11-point numerical annoyance scale recommended by the International Commission on Biological Effects of Noise. Exposure was calculated using acoustical source models of weapons and numbers of shots fired, as recorded by the army. Annoyance predictor variables investigated were LAE, LCE, LCE−LAE, number of shots above threshold, as well as individual moderators. Exposure-annoyance relationships were modeled by means of linear and logistic regression analyses. The sound exposure level LE of shooting noise better explained variations in annoyance than other operational and/or acoustical predictors. Annoyance on the 5-point scale was more closely related to noise exposure than expressed on the 11-point scale. The inclusion of the C-A frequency weighting difference as a second explaining variable, as suggested earlier, did not substantially enhance the predictability of high annoyance.