bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐BRC‐05: Use of FLT PET Imaging to Assess Tyrosine Kinase Inhibitor (TKI) Treatment Response
Authors: Jeraj R , Vanderhoek M , Simoncic U , Perlman S , Alberti D , Wilding G , Liu G
Published: April 2010

Background: Sunitinib (SU) is a tyrosine kinase inhibitor (TKI) with activity against VEGFR. During VEGFR TKI withdrawal, increased pain at sites of metastasis has been observed, which we hypothesize is due to the proliferative flare. []‐fluoro‐3′‐deoxy‐3′‐L‐fluorothymidine (FLT) PET imaging was used as a marker of treatment response, to assess the proliferative flare and to investigate perfusion and vascular status of the tumor. Methods: 14 patients with advanced solid malignancies have been enrolled. SU was given at the standard dose of 50 mg for 4 weeks, followed by a 2 week break. 90‐minute dynamic FLT PET/CT scans were obtained at the baseline, week 4, and week 6. 8 patients with adequate follow‐up time were classified in two groups: with clinical benefit (CB; progressive disease (PD)>6 mo) or without clinical benefit (noCB; PD<6 mo). Changes in the peak FLT standardized uptake value (SUVpeak) were calculated. In addition, FLT kinetic analysis was performed to extract perfusion and vasculature status of the tumor. Results: The differences in FLT uptake were significant between the two groups (CB: −20%, noCB: ∼0%). Interestingly, both groups exhibited a significant increase in SUVpeak during SU withdrawal, but with a significantly higher increase in the group without clinical benefit (CB: +20%, noCB: +50%). The kinetic analysis revealed significant differences in the perfusion at week 4 between the groups (CB: ∼0%, noCB: −40%), with no significant differences at the end of the treatment cycle. Conclusions: Change in SUVpeak was associated with the degree of clinical response. Proliferative increase in the target lesions during SU withdrawal was observed, and was higher for patients with poor clinical outcome.

Research sponsored in part by Pfizer.
WE‐C‐BRC‐06: Determining Changes to Tissues Irradiated During Proton Treatment Delivery by Measuring Secondary Prompt Gamma‐Ray Spectra
Authors: Polf J , Roeder B , Peterson S , Tabacaru G , Beddar S , Trache L
Published: April 2010

Purpose: Recent studies have investigated the use of secondary ‘prompt’ gamma‐rays emitted from patients during proton therapy as a possible method to verify dose delivery. The purpose of this study was to determine if the prompt gamma‐ray spectra emitted from biological tissues could be used as a method to analyze changes to tissues irradiated during proton treatment delivery. Method and Materials: We preformed measurements and Monte Carlo calculations of the prompt gamma emission spectra from tissue equivalent phantoms and tissue targets. The emission spectra from several types of tissue where characterized according to the emission lines from the individual elemental constituents of the target tissue. Next, we studied the individual emission lines from the tissue targets as a function of elemental concentration and density. Results: These results show that the prompt gamma emission lines from the major elemental components can be identified in the measured and calculated spectra. The intensities of these emission lines were found to be a function of concentration of each element and the physical density of the tissue. Conclusion: Based on the results of these preliminary studies, we conclude that it may be possible to determine both the atomic composition and physical density of irradiated tissues by measuring the prompt gamma ray spectra emitted during proton treatment delivery. Development of a technique to measure prompt emission spectra during daily treatment delivery would allow for the direct measurement of changes to irradiated tissues, such as changes to tumor hypoxia or tissue densities over the course of proton treatment delivery.
WE‐D‐304A‐03: Quantitative Image Analysis for Prognosis in Newly Diagnosed Breast Cancer Patients with Sonographically Normal Appearing Lymph Nodes
Authors: Drukker K , Sennett C , Giger M
Published: April 2010

Purpose: To investigate whether a computerized quantitative image analysis (QIA) system for diagnostic breast ultrasound can predict whether a breast cancer lesion has metastasized in patients with sonographically normal appearing axillary lymph nodes. Method and Materials: This study used a database of sonographic images of breast cancers in patients who presented with a single cancerous lesion and axillary lymph nodes that appeared normal on diagnostic breast ultrasound. The dataset contained images of 50 patients. In 20 patients, the breast cancer had metastasized and in 30 patients the cancer remained localized at the time of surgery. The truth regarding disease grade/pathology was obtained from the final breast surgery and lymphadectomy. Features including both lesion and parenchymal characteristics were calculated for each lesion. A leave‐one‐case‐out analysis was performed and each iteration stepwise feature selection was combined with the training of an LDA classifier for the task of distinguishing between cancerous lesions that metastasized and ones that remained localized. Results: In the leave‐one‐case‐out analysis, the most frequently selected combination consisted of 3 features. In this set, a single feature pertained to the lesion itself and the other 2 features described a difference between the lesion and the surrounding parenchyma. The features were the lesion echogenicity, the difference in echogenicity, and the difference in entropy. The LDA classifier yielded an area under the ROC curve (AUC value) of 0.80 (standard error 0.06) for the task of distinguishing between metastasized breast cancer index lesions and localized breast cancers. Conclusion: The QIA scheme obtained promising performance in this preliminary study and shows potential to diagnose metastatic disease. It is important to note that this study was performed using images only of patients for whom pre‐surgery imaging studies suggested that the breast cancer had remained localized.

Conflict of Interest: Grants NIH and DOE. Stockholder, grant, royalties Hologic.
WE‐D‐304A‐05: Analysis of Tumor Grade Breast Carcinoma Using Computer‐Extracted Morphological and Kinetic Features in DCE‐MRI
Authors: Bhooshan N , Giger M , Jansen S , Li H , Lan L , Newstead G
Published: April 2010

Purpose: An important prognostic marker in breast cancer is the histological grade of the breast tumor. Thus, the purpose of our study is to investigate the performance of computer‐extracted morphological and kinetic features in DCE‐MRI in distinguishing breast tumors with varying histological grades: Grade 1, Grade 2, and Grade 3. Materials and Methods: Breast MR images were obtained with a T1‐weighted SPGR sequence using Gd‐DTPA on a 1.5T GE MRI scanner. Each case has one precontrast and three to five postcontrast series at intervals of 68 seconds, and each series contains 60 coronal slices. The database contains 135 invasive ductal carcinoma (IDC) breast lesions including 21 Grade 1 lesions, 72 Grade 2 lesions, 42 Grade 3 lesions, and 133 benign lesions (no cysts). All lesions were verified pathologically. Each lesion was segmented and its characteristic kinetic curve was extracted using the fuzzy c‐means method. Textural, morphological, kinetic, and spatial enhancement variance features were extracted, and stepwise linear discriminant analysis using a Wilks lambda cost function in a round‐robin fashion was used for feature selection. The selected features were merged using Bayesian neural network, and the classification performance was evaluated using receiver‐operating characteristics (ROC) analysis. Results: We achieved AUC values of 0.80±0.05, 0.85±0.02, 0.75±0.06, 0.74±0.05, 0.75±0.06, and 0.60±0.05 for the classification tasks of Grade 1 vs. benign, malignant (Grades 1–3 lesions) vs. benign, Grade 1 vs. Grade 3 lesions, Grade 1 vs. Grades 2 and 3 lesions, Grade 1 vs. Grade 2, and Grade 2 vs. Grade 3, respectively. Conclusions: Computerized analyses of breast MR images have the potential to yield image‐based prognostic markers for breast carcinoma, specifically in distinguishing different histological grades of breast tumors.
WE‐D‐304A‐07: A Novel Stereo‐Scanning Tomosynthesis Scheme and Its Application in Image Guidance for Breast Radiotherapy
Authors: Zhang J , Yu C
Published: April 2010

Purpose: In conventional digital tomosynthesis (DTS), images are generated by scanning an x‐ray source and flat‐panel detector pair on a one‐dimensional trajectory. A novel stereo‐scanning tomosynthesis (STS) is proposed in which the x‐ray source is allowed to scan on a two‐dimensional (2D) surface. By allowing the x‐ray source to project from more stereo angles, the scanning scheme of STS provides more coverage in the spatial‐frequency domain of the object, consequently better image quality. Method and Materials: The feasibility and effectiveness of STS is corroborated by computer simulations, using a three‐dimensional (3D) numerical breast phantom in its natural shape. Iterative algorithm in the form of total variation regulated expectation maximization (TV‐EM) is developed for image reconstructions. A STS scheme is proposed as the image guidance method for prone‐position breast radiotherapy. Results: The STS images possess excellent image quality for online tumor targeting, superior to conventional DTS. STS outperforms DTS in restoring certain features of the object and reducing artifacts, due to its more frequency‐domain coverage. Conclusion: By allowing more general scanning trajectories than conventional DTS, STS may provide more flexible imaging geometry or/and better image quality, in various clinical tasks of image guided radiotherapy and diagnostic imaging.
WE‐D‐304A‐09: Characterization of Multi‐Beam Field Emission X‐Ray Source for Stationary Digital Breast Tomosynthesis
Authors: Qian X , Rajaram R , Yang G , Calderon‐Colon X , Phan T , Sultana S , Lalush D , Lu J , Zhou O
Published: April 2010

Purpose: The current prototype digital breast tomosynthesis (DBT) scanners are based on the regular full‐field digital mammography systems and require partial isocentric motion of a mammography x‐ray tube over certain angular range to record the projection views needed for reconstruction. This prolongs the scanning time and in turn degrades the imaging quality due to motion blur. We are developing a stationary DBT (s‐DBT) scanner to mitigate the above limitations. Method and Materials: The proposed s‐DBT system is based on the carbon nanotube multi‐pixel field emission x‐ray (MBFEX) technology demonstrated by our group. The pixilated and spatially distributed MBFEX source can generate x‐ray radiation from multiple views without any mechanical motion of the source, detector, or object. This enables the design of tomography systems with great flexibility in source configuration and imaging sequence. It further enables multiplexing imaging — simultaneously collection of multiple images using one detector. Results and Conclusions: To demonstrate the feasibility of the s‐DBT scanner, we have designed and constructed a proof‐of‐concept full‐field s‐DBT system. The configuration of the system, in terms of angular coverage, number of views, and dose, etc., closely resembles the Siemens DBT scanner for a more realistic comparison. In the Siemens DBT scanner, the x‐ray tube moves along an arc with the exposure points evenly distributed along the rotation route. Our s‐DBT scanner is designed with the MBFEX pixels positioned in a straight line parallel to the detector plane. We will report a detailed study on the design and the performance characteristics of the MBFEX source. In particular evaluation on key parameters including the x‐ray flux, the lifetime of the x‐ray source, effective x‐ray focal spot size, variation between different source, system spatial resolution, and x‐ray energy spectrum will be reported. These preliminary results demonstrate the feasibility of the proposed s‐DBT scanner.
WE‐D‐210A‐01: Design and Development of An Advanced PET System Built From Semiconductor Detectors
Authors: Levin Craig S
Published: April 2010

We are in the process of building a high performance positron emission tomography (PET) system for small animal research using a semiconductor detector material known as cadmium zinc telluride (CZT). If successful, this system will enable substantial improvements in the ability to detect, visualize, and quantify molecular‐based signatures of disease in vivo using PET. Unlike nearly all other PET system designs, which use scintillation detector technology, CZT directly collects electron‐hole pairs created from the absorption of a 511 keV annihilation photon. This approach has advantages both in terms of construction as well as performance of high resolution PET systems that we will describe in this presentation. We will also present other unusual features of the system design, results of detector spatial, energy, and temporal resolution measurements performed in the laboratory, image reconstruction strategies, as well as predicted system photon sensitivity, noise‐equivalent count rate, and reconstructed spatial resolution performance results obtained using Monte Carlo simulation studies.
WE‐E‐BRD‐01: Investigating Effects of Pelvic Bone Marrow Radiation Dose On Acute Hematologic Toxicity Using High Dimensional Data Analysis
Authors: Liang Y , Rose B , Lewis J , Yashar C , Mundt A , Mell L
Published: April 2010

Purpose: To develop a new method to investigate the effect of local pelvic bone marrow (BM) radiation dose on acute hematologic toxicity (HT) in cervical cancer patients undergoing concurrent chemoradiation therapy (CRT), with the ultimate goal of optimizing BM‐sparing radiation techniques. Method and Materials: We analyzed 24 cervical cancer patients treated with concurrent cisplatin (40mg/m2/week) and pelvic IMRT. The white blood cell count (WBC) nadir, defined as the lowest value occurring between the start of CRT and two weeks following IMRT, was used as the indicator of acute HT. The pelvic bone region included the os coxae, lower lumbar vertebrae, sacrum, acetabulae, and proximal femora. BM doses were standardized in two steps: pelvic bone registration followed by dose remapping. Simulation CT images were registered to a common (canonical) template using the optical flow based deformable image registration developed by Yang et al.[2]. The deformation field was used to remap the dose distribution back to the deformed pelvic bones. We generated a data structure called a “dose‐array” that reserves the spatial information of each dose value. The position of an element inside array can be used to trace its location in 3D. Results: Substantial variation of BM dose distribution among the 24 patients was observed. Patients were classified based on their WBC nadir value (⩾ vs. < 2000/μL) into two groups (n=15 vs. n=9, respectively), and the average pelvic BM 3‐D dose distribution was compared visually. Results suggested that patients receiving higher doses to the lower lumbar spine, upper sacrum, and medial ilium, were more likely to develop acute HT. Conclusion: We have developed a novel method to study the impact of BM radiation dose on acute HT. Our next step is to implement both unsupervised and supervised classification models to analyze radiation effects, for use in IMRT plan optimization.
WE‐E‐BRD‐04: GPU‐Based Implementation of Monte Carlo Superposition for Dose Calculation
Authors: Zhou B , Hu XS , Chen DZ , Yu C
Published: April 2010

Purpose To provide a fast and accurate dose calculation solution, a massively parallel version of a Monte Carlo superposition (MCS) method is developed on a computer with a Nvidia GTX260 graphics card. Method and Materials Graphics processing units (GPU) can be extremely powerful and economical in accelerating computationally intensive applications. However, the GPU memory structure can be too rigid for certain types of applications to realize its computation potential. The MCS method, by nature, is a memory‐intensive application since most of its operations are based on linear interpolation and table‐look‐up. To leverage the power of GPU, we modified a sequential MC algorithm and implemented a parallel version. The biggest challenge to our implementation is to how to arrange memory access sequences and increase temporal and spatial data locality. We introduced several techniques for handling this challenge, including stage‐based processing, photon grouping with respect to kernel index, etc. To match the hierarchy of GPU memory, data were carefully organized to minimize off‐chip memory accesses. A parallel thread‐safe random number generator was implemented to produce the necessary randomness required by the MC algorithm. Results Our GPU‐based implementation is based on fully optimized code and demonstrates a speedup of 25∼40 times over the CPU‐based single‐thread implementation. Although the speedup is significant, the research does reveal some inherent limitations on the GPU‐based implementation of the particular target MC algorithm. The most critical one is due to the conflicts between the GPU's SIMD (single‐instruction‐multiple‐data) architecture and the stochastic nature of the MC algorithm. Conclusion A massively parallel version of a MCS method is implemented on a computer powered by GTX260 GPU and a speedup up to 40X is observed. This indicates that a GPU‐based MC approach is viable and cost‐efficient for satisfying the increasing demands on computation power and accuracy by advanced radiation therapy technologies.
WE‐E‐BRD‐06: Validation of An MCNPX Monte Carlo Model of a Discrete‐Spot Scanning Beam Nozzle and Evaluation of the Beamlet Lateral Envelope of Low Doses
Authors: Sawakuchi G , Titt U , Mirkovic D , Zhu X , Sahoo N , Bues M , Ciangaru G , Poenisch F , Suzuki K , Arjomandy B , Gillin M , Mohan R
Published: April 2010

Purpose: To build and experimentally validate an accurate Monte Carlo (MC) model of a discrete spot scanning beam nozzle and to use this model to assess the dosimetric consequences of the “halo” dose (i.e., that due to scattering from beam line components and nuclear interactions). Method and Materials: An accurate model of the scanning nozzle at our institution was implemented using the MC system MCNPX version 2.5.0 according to the blueprints provided by the manufacturer of the proton therapy system (Hitachi Ltd., Tokyo, Japan). The MC model was validated against measurements of percentage depth doses (PDDs), lateral profiles in‐air (LPA) and in‐water (LPW), field size factors (FSFs), and spread out Bragg peaks. The validated MC model presented in this study was used to generate data for clinical configuration of our treatment planning system (TPS). Results: Distance to agreement between measured and simulated ranges, LPAs and LPWs were within 0.16 cm, 0.05 cm and 0.1 cm, respectively. Comparisons between measured FSFs and TPS predictions, which may not model the halo dose properly, reveled differences of up to 9.5%, whereas comparison with MC simulations showed maximum differences of 3.6%. We found that ion chambers with radius as large as 4.2 cm are insufficient to measure the integral energy deposition. Conclusion: Because of the halo dose, which broadens lateral sizes of the proton beamlets, care should be taken when measuring integral energy deposition for configuration of the TPSs. Furthermore, the halo dose must be properly modeled in the dose algorithm used by TPS for accurate prediction of scanned proton beam doses.
WE‐E‐BRD‐07: Algorithm for Accurate Computation of Doses From Large‐Angle Scattering of Scanned Proton Pencil Beams
Authors: Ciangaru G , Sahoo N , Zhu X , Sawakuchi G , Gillin M
Published: April 2010

Purpose: The purpose of this work was to find a technique to improve the accuracy of proton pencil beam dose computation for large scattering angles. Methods: The computed dose from an elementary pencil beam in the scattering medium, like water in our study, comes from a convolution integral of the proton fluence in air and the scattering distribution function in the medium. The incident proton beam profile in air, just outside the target medium, was modeled with a sum of up to three Gaussians fitted with measured data. The proton scattering in the medium, assumed to proceed through Coulomb interactions, was described using the classic Moliere distribution. The convolution integration was performed by a combination of analytical and numerical methods leading to a numerically manageable expression. Results: We compared measured and computed dose profiles at the 2 cm and at the Bragg peak depths for proton pencil beams with low and high energies. In all cases, profile calculations using just one Gaussian term for the beam fluence in air and the first Moliere term for the scattering distribution were in large disagreement with measurements at lateral distances beyond 10% profile falloff. At 2 cm depth in the water, the second and the third terms in Moliere distribution did not contribute significantly. On the other hand, the use of three Gaussians for the proton fluence in air produces nearly perfect agreement for lower energy protons and brings the agreement to within one order of magnitude for the higher proton energies. At Bragg peak depths, higher order Moliere terms are again insignificant for lower energy protons, but become important contributors for higher energy protons. Conclusions: The proposed procedure was shown to achieve a dramatic improvement in the accuracy of computed doses from proton pencil beams at large proton scattering angles.
WE‐E‐BRD‐08: Next‐Generation Deformable Patient Modeling for Monte Carlo Assessment of Organ Doses
Authors: Na Y , Zhang J , Xu X , Han B , Caracappa P
Published: April 2010

Purpose: Whole‐body patient models of various sizes and postures are needed for the assessment of organ doses in CT imaging, internal nuclear medicine and external‐beam radiation treatment procedures. This paper discusses a deformable mesh‐based modeling method to create patient‐specific phantoms that are morphed by changing to 5th‐ to 95th‐percentiles of body height and weight, as well as internal organ volume and masse. Method and Materials: The mesh‐based reference adult male and female phantoms were deformed by mainly two different percentile data: 1) the whole‐body size percentile data which were defined by the anthropometric parameters such as height and weight from the National Health and Nutrition Examination Survey (NHANES). 2) individual internal organ percentile data which were derived by the cumulative pattern analysis based on the International Commission on Radiological Protection (ICRP) 23 and 89 references. These mesh‐based percentile phantoms were converted into the voxel‐based phantoms. The final step is to link the voxel phantom with correct tissue density and elemental composition, so that radiation transport through the human‐body phantom was modeled correctly in a Monte Carlo code. Results: The whole‐body size percentile models have been created by the NHANES anthropometric data and the details of organ percentiles derived from ICRP references. The deformability of the RPI reference adult phantoms has been shown through the demonstration of percentiles‐ and postures‐specific adult models. Conclusion: A next generation deformable patient modeling method has been demonstrated. With the mesh deformation algorithms, the individual organs are able to be deformed to match the volumes and masses with desired organ percentiles. The flexible modeling allows patients to be represented in various sizes and postures for the purpose of Monte Carlo dose calculations. This study also identified the need for further research to develop method to run Monte Carlo calculations in mesh geometry directly.
WE‐E‐BRB‐02: Feasibility Study of Helical Tomotherapy for Dose Painting
Authors: Deveau M , Bowen S , Westerly D , Jeraj R
Published: April 2010

Purpose: Important limitations for dose painting are due to treatment planning and delivery constraints. The purpose of this study was to determine the sensitivity of dose conformity to optimization parameters using the clinical TomoTherapy Hi‐Art treatment planning system (TPS). Materials and Methods: Uptake data from a patient who underwent a []Cu‐ATSM PET/CT (surrogate of hypoxia) scan was retrospectively extracted for treatment planning. Extracted data was reformatted from voxel‐based to level‐based for compatibility with the Hi‐Art TPS. Optimized treatment plans were generated with physical objectives for each prescription sub‐volume modifying pitch, jaw width, modulation factor and iteration number. Effects of variations in plan parameters were simulated varying one physical parameter while keeping the other parameters unchanged. Avoidance structures were not used. The conformity of treatment plans to their non‐uniform prescriptions was evaluated via quality‐volume histograms (QVH) and percent receiving planned dose within 2 percent of prescription (Q0.98–1.02). Results: In general, the conformity of treatment plans to dose prescriptions was found to be adequate for delivery of dose painting plans. The conformity was better as the jaws decreased in width from 2.5 cm to 1.0 cm (Q0.98–1.02:64% vs 73%) and as the pitch increased from 0.122 to 0.443 (Q0.98–1.02:71% vs 73%). The effects on dose conformity of modulation factor and iteration number seem to be insensitive to change. Treatment delivery times varied from 5–11 minutes for changes in field width (2.5 cm to 1.0 cm) and from 11–25 minutes for changes in pitch (0.443 to 0.122). Conclusions: This investigation demonstrates the ability of the helical tomotherapy to create and deliver plans with non‐uniform dose distributions. Results indicate that agreement in prescription dose and planned dose distributions for all treatment plans are sensitive to physical parameter changes such as pitch and field width but insensitive to changes in modulation factor and iteration number.
WE‐E‐BRB‐03: Precision of Respiratory‐Gated Delivery of Synchrotron‐Based Proton Therapy
Authors: Tsunashima Y , Vedam S , Dong L , Umezawa M , Sakae T , Smith A , Balter P , Mohan R
Published: April 2010

Purpose: To investigate the precision of synchrotron based passively scattered respiratory gated delivery of proton irradiation. A simulation study was undertaken for the analysis of the residual target motion uncertainty during synchrotron based respiratory gated proton treatment. Method and Materials: In‐house software was developed to simulate a synchrotron based respiratory gated proton treatment. The interactions of respiratory motion traces (70 traces, 22 patients), respiratory gate threshold levels (10%, 20% and 30% duty cycle around peak exhalation) and synchrotron Tcyc patterns (fixed Tcyc =2.7, 3.0 ∼ 6.0 second, average patient breathing‐cycle and variable Tcyc) were plotted along the same time scale, similar to an oscilloscope display. Proton beam delivery within a gate threshold only occurred during a portion of each Tcyc pattern. A specific pattern of Tcyc acts as a “gate‐within‐a‐gate”, which produces a smaller effective gating window. Precision of respiratory gated proton delivery was analyzed by examining distribution of distance from the respiratory gate threshold where 95% of gated beam delivery (DGT95) occurred. Results: With shorter fixed Tcyc (< 4 sec), average DGT95 values were 0.30 cm, 0.23 cm and 0.17 cm respectively for 30%, 20% and 10% respiratory gate duty cycles. With longer fixed Tcycs (> 4 sec) average DGT95 values were 0.25 cm, 0.19 cm and 0.14 cm respectively for 30%, 20% and 10% respiratory gate duty cycles. With Tcyc ≈ average patient breathing cycle, average DGT95 values were 0.27 cm, 0.20 cm and 0.15 cm for 30%, 20% and 10% respiratory gate duty cycles. With variable Tcyc, DGT95 values were 0.21 cm, 0.17 cm and 0.14 cm for 30%, 20% and 10% respiratory gate duty cycles. Conclusion: Variable Tcyc mode offered the greatest precision of respiratory gated delivery for passively scattered synchrotron proton irradiation.
WE‐E‐BRB‐06: Optimization of Collimator Trajectory in Volumetric Modulated Arc Therapy: Development and Evaluation for Paraspinal SBRT
Authors: Zhang P , Happersett L , Yang Y , Mageras G , Hunt M
Published: April 2010

Purpose: To develop a collimator trajectory optimization paradigm for volumetric modulated arc therapy (VMAT) and evaluate this technique in paraspinal stereotactic body radiation therapy (SBRT). Method and Materials: We propose a novel VMAT paradigm, Coll‐VMAT, which integrates collimator rotation into the synchronization of gantry rotation, multileaf collimator (MLC) motion, and dose rate modulation. A principle component analysis (PCA) calculates the primary cord orientation using the cord contour projection on the beam's eye view for each gantry angle, thereafter determining a collimator angle such that MLC travel is parallel to the PCA‐derived direction. In this way, cord can be constantly blocked while minimizing resultant blocking of the planning target volume (PTV), and more MLC pairs are available for dose modulation. Standard VMAT optimization follows the geometry‐based collimator trajectory calculation, to obtain the optimal MLC position and monitor units (MU) at each gantry angle. Evaluation compares Coll‐VMAT‐optimized plans to standard VMAT and IMRT in 5 paraspinal SBRT patients. Prescription dose to the PTV is 24Gy while constraining the cord maximum dose to 14Gy. Plan evaluation statistics include PTV V22.8Gy, PTV D95%, cord mean dose, and total beam‐on time. Results: Collimator rotation in the five Coll‐VMAT plans ranges from 26°–54°, with a median of 40°. Patient‐averaged PTV V22.8Gy (94.6% with Coll‐VMAT vs 92.1% VMAT and 93.3% IMRT) and D95% (22.5Gy vs 21.4Gy and 22Gy) are higher, while cord mean dose is lower (9.8Gy vs 10.0Gy and 11.7Gy). Total beam‐on time is comparable to standard VMAT and substantially lower than IMRT (5164MU vs 4868MU and 13,283MU). Conclusion: The dosimetric advantage of Coll‐VMAT is significant especially for small targets. Collimator trajectory optimization provides an additional degree of freedom in VMAT optimization that can improve dosimetric quality of paraspinal SBRT compared to standard VMAT and IMRT. Conflict of Interest: Research agreement with Varian Corporation.
WE‐E‐BRB‐08: Motion and Delivery Management with Novel 4D‐Optimization
Authors: Nohadani O , Seco J , Bortfeld T
Published: April 2010

Purpose: Intensity modulated radiation therapy (IMRT) has the ability to deliver highly conformal dose distributions to tumors of complex shapes. However, motion uncertainties can substantially degrade the quality of an otherwise optimized treatment plan. We present a novel 4D‐optimization technique that exploits time effects and provides plans which are robust against tumor motion and warrant deliverability. Method and Materials: Our 4D‐optimization technique takes all registered breathing phases into account. All 4D CT data are conformally registered. To account for lung tissue inhomogeneities, we use Monte Carlo dose calculations. The 4D‐optimization method seeks to minimize the overall dose subject to i) lower bounds for tumor voxels and ii) upper bounds for remaining voxels, and iii) closeness of the beamlet intensities for neighboring phases. Results: Based on a clinical lung cancer case, our 4D‐optimization method delivers robust plans that significantly outperform the gating‐based optimal plans both in terms of target coverage as well as OAR sparing. In fact, the EUD to the PTV deviates only by 0.1% from the prescribed dose for our 4D method, whereas the gated EUD deviates by 2%. Moreover, since the 4D‐robust plan is quasi‐static and can be delivered over all breathing phases, it warrants for a reduction in delivery errors and is less sensitive to motion uncertainties. Note that gating is quite sensitive to the choice of the gated phase and, thus, requires enlarged margins. Furthermore, due to reduced number of segments needed, we report an increase in delivery efficiency. Conclusion: Our proposed 4D optimization method delivers plans that are robust against motion uncertainties. Moreover, the plan is also inherently robust against sequencing and delivery errors. Therefore, it allows to reduce margins on the ITV. The method outperforms gating both in dose coverage as well as delivery robustness and increases the delivery efficiency.
WE‐E‐304A‐01: Contrast Mechanism and Origin of Artifacts in Phase‐Sensitive X‐Ray Volumetric Imaging
Authors: Wu X , Yan A , Liu H
Published: April 2010

Purpose: Phase‐sensitive x‐ray volumetric imaging has great potential for tissue contrast enhancement and radiation dose reduction, compared to conventional tissue‐attenuation based x‐ray volumetric imaging. In order to achieve quantitative and artifact‐free phase sensitive volumetric imaging, one should quantify the formed phase contrast and find the origin of artifacts formed in phase‐sensitive volumetric imaging. Method and Materials: We incorporated x‐ray Fresnel diffraction into x‐ray projection acquisitions, and reconstructed volumetric images from these phase‐sensitive projections by the filtered backprojection method. A formula for the reconstructed tissue's apparent attenuation coefficients was derived for quantitative analysis. Computer simulations of phase sensitive 3D tomography were performed, and reconstructed 3D phantom tomograms were analyzed, and the artifacts associated with phase‐contrast were identified. In order to eliminate these artifacts, we performed phase retrievals based on the phase‐attenuation duality method for each projection, and these phase‐retrieved projections were then used for new 3D tomographic reconstructions. Results: The apparent linear attenuation coefficients in 3D tomograms were found each being the sum of three parts: the tissue linear attenuation coefficient, the scaled 3D Laplacian of tissue refraction index, and the artifact depending on global distributions of tissue attenuation coefficients and refraction indices. The simulated high‐resolution 3D images of phantoms exhibit severe artifacts as the upward and downward density over‐shootings and the streaks. The phase retrieval was shown very effective for removing these artifacts and accurately reconstructing tissue attenuation coefficients in phase‐sensitive 3D tomography. Conclusion: We clarified the contrast mechanism in phase‐sensitive volumetric imaging, found the quantitative contribution of the phase contrast in reconstructed 3D images, and revealed the origin of severe artifacts. The need of the phase‐retrievals for quantitative and artifact‐free phase sensitive volumetric imaging was clearly demonstrated.

Research supported in part by DoD Breast Cancer Research Program.
WE‐E‐304A‐03: An Energy‐Dispersive Technique to Measure Tissue X‐Ray Coherent Scattering Form Factors
Authors: King B , Johns P
Published: April 2010

Purpose: Data for the x‐ray scattering properties of tissues are needed for the development of x‐ray scatter imaging systems. Published amorphous material form factors from x‐ray diffractometer measurements vary significantly. An energy‐dispersive technique was developed to provide more accurate measurements. Method and Materials: The form factor is measured as a function of the momentum transfer argument where λ is the photon wavelength and θ is the scattering angle. Crystallographic diffractometers measure scattering versus θ at one wavelength (energy). Our method fixes θ and measures versus energy, using a high purity germanium spectrometer to measure the scattered polychromatic spectrum from a tungsten anode x‐ray tube. The target is moved laterally to measure the transmitted and scattered spectra without adjusting the x‐ray tube and detector. By taking the scatter to transmitted ratio bin‐to‐bin, the coherent scattering form factor is determined without adjustable parameters. Repeating with four θ values, the range 0.5 nm−1 < x < 12 nm−1 is obtained. Results: Measurements of the coherent scattering form factor of water and several plastics with our prototype system give good agreement for x > 7 nm−1 with the Independent Atom Model. This, together with general agreement at smaller x with published diffractometer data, is strong evidence that our measurement is accurate. The precision of our measurement has been thoroughly characterized and is approximately 10%. Conclusion: The energy‐dispersive technique measures over a wider x range than do diffractometers and does not require the use of arbitrary scaling constants. Our measurements are limited to 5 – 10% in x resolution at small θ but this is acceptable for tissue measurements. Resolution and precision will be improved by using rectangular apertures. Due to the advantages of the technique and to its thorough characterization, we expect the energy‐dispersive technique to provide definitive form factor results.
WE‐E‐304A‐04: Local Determination of Tissue Optical Properties: Reconstruction Based On Fiber‐Array Reflectance Profiles
Authors: Sheng C , Bonnerup C , Austerlitz C , Allison R , Sibata C
Published: April 2010

Quantitative evaluation of in vivo local tissue optical properties including scattering coefficient (μs), absorption coefficient (μa) and anisotropy (g) is often important in both photodiagnosis and phototherapy. In this study, a reflectance based fast technique was developed to determine the optical properties of turbid media using a linear‐array fiber bundle probe. Five 200 um collection fibers were linearly set along from the 200 um illumination fiber with center‐to‐center separation of 350 um. Spatial reflectance values were sequentially measured by spectrometer connected to a fiber‐switch. A model that relates the reflectance profiles to optical properties of a turbid medium was developed based on Monte Carlo simulations and phantom experiments. Simulation results at wavelength of 633 nm showed that μs′ (2∼40 cm−1) and μa (0∼5 cm−1) can be determined by reflectance spatial profiles. Intralipid and Nigrosin were used to simulate different reduced scattering coefficient (μs′) and absorption coefficient (μa) values within the same range as Monte Carlo simulation. Preliminary results show good correlation between known optical properties in tissue phantom and the measured optical properties, the average error for μs′ and μa was 7.8% and 6.6%, respectively. With same reduced scattering coefficient (μs′), changes in the absorption coefficient (μa) could be measured within 0.1 cm−1. Accurate extraction of tissue optical properties from in vivo measurements could have potential application in noninvasively superficial (pre)cancer detection and phototherapy planning.
WE‐E‐304A‐05: Acoustic Droplet Vaporization for Enhancement of High Intensity Focused Ultrasound Thermal Ablation
Authors: Zhang M , Haworth KJ , Swanson SD , Fabiilli ML , Kripfgans OD , Carson PL , Fowlkes JB
Published: April 2010

Purpose: Acoustic droplet vaporization (ADV) shows promise for the spatial control and acceleration of thermal lesion production. In this study, we investigated the hypothesis that ADV bubbles can substantially enhance HIFU ablation by increasing and controlling local energy absorption. Method and Materials: HIFU/ADV phantoms were made of polyacrylamide, egg white, degassed water and lipid‐coated perfluoropentane droplets (1.8 μm mean dia.). These egg white‐based phantoms (acoustic attenuation of 0.3 dB/cm at 1.44 MHz) were optically transparent, which allowed direct visualization of lesion formation during HIFU application. Phantoms were exposed in degassed water at 37°C to a focused ultrasound (1.44 MHz) with a focal intensity of 2000 W/cm2. Lesion volumes were measured by fluid displacement or T2 weighted MR imaging. Results: For 2‐s HIFU exposure on droplet‐containing phantoms (n = 5), apparent opacity changes were observed consistently, while no lesions were found in phantoms without droplets (n = 8). It was noted that the volume of the lesion with 2‐second HIFU exposure in droplet‐containing phantoms was comparable to that made by 5‐s exposure in the phantom without droplets. Lesion volumes (5‐s exposure) measured by MR imaging were found to be 45.5±5.5 (n=8), 102.5±13.5 (n=5), and 288.0±50.1μL (n=8) in phantoms of 0, 104, 105 droplets/mL, respectively. Conclusion: The presence of ADV bubbles reduced the acoustic energy for comparably sized lesion and increasing the speed of HIFU lesion formation. Our findings may address the pre‐focal heating problem in traditional HIFU ablation.
WE‐E‐210A‐01: Functional Cardiovascular MRI: Assessment, Visualization and Quantification of 3D Blood Flow Characteristics
Authors: Markl M
Published: April 2010

Magnetic Resonance Imaging (MRI) techniques provide a non‐invasive method for the highly accurate anatomic depiction of the heart and vessels. Most MR‐sequences demonstrate more or less significant sensitivity to flow and motion, which can lead to artifacts in many applications. The intrinsic motion sensitivity of MRI can, however, also be used to image vessels like in phase contrast (PC) MR‐angiography or to quantify blood flow and motion of tissue. Such techniques offer the unique possibility to acquire spatially registered functional information simultaneously with the morphological data within a single experiment. Characterizations of the dynamic components of blood flow and cardiovascular function provide insight into normal and pathological physiology and have made considerable progress in recent years

To synchronize flow or motion sensitive measurements with periodic tissue motion or pulsatile flow, data acquisition is typically gated to the cardiac cycle and time resolved (CINE) anatomical images are collected to depict the dynamics of tissue motion and blood flow during the cardiac cycle. Visualization and quantification of blood flow and tissue motion using PC MRI has been widely used in a number of applications. In addition to analyzing tissue motion such as left ventricular function, time‐resolved 2D PC MRI techniques have proven to be useful tools for the assessment of blood flow within the cardiovascular system.

Moreover, 3D spatial encoding offers the possibility of isotropic high spatial resolution and thus the ability to measure and visualize the temporal evolution of complex flow and motion patterns in a 3D‐volume. In this context, ECG synchronized and respiration controlled flow sensitive 3D MRI using 3‐directional velocity encoding (also termed ‘flow sensitive 4D MRI’) can be employed to detect and visualize global and local blood flow characteristics in targeted vascular regions (aorta, cranial arteries, carotid arteries, etc.). For the analysis and visualization of complex, three‐directional blood flow within a 3D volume, various visualization tools, including 2D vector‐fields, 3D streamlines and particle traces, have been reported. In addition more advanced data quantification strategies of directly measured (e.g. flow rates) or derived parameters (e.g. pressure difference maps, wall sheer stress, pulse wave velocity, etc.) are promising as new clinical markers for the characterization of cardiovascular disease.

This lecture will provide an overview of the MR imaging principles and advanced acquisition methods, data processing, flow visualization and quantification strategies, and clinical applications of flow sensitive MRI imaging.

Learning Objectives:

1. Understand the basic and advanced methods for flow measurements using MRI

2. Understand techniques for 3D flow visualization and quantification of blood flow and derived parameters

3. Understand the issues related to clinical applications of flow‐sensitive MRI
WE‐E‐213A‐01: Practical Aspects (and Pitfalls) of External Beam Photon Calibrations Using TG‐51
Authors: Curran B
Published: April 2010

Purpose: Since its publication in September, 1999 (Medical Physics 26(9), pp 1847–90), the TG‐51 calibration protocol has been implemented in most US institutions. This presentation, one part of a workshop session on practical aspects of treatment unit calibrations, will review the basics of TG‐51 calibrations for conventional linear accelerator beams. Methods and Materials: Using the TG‐51 publication as a guide, practical aspects of performing a TG‐51 calibration of a treatment unit will be described. Relevant definitions of the key parameters to be acquired, either through measurement or calculation, will be reviewed. Starting from the acquisition of valid absorbed‐dose to water calibration factor, methods for determining each of the parameters used in the TG‐51 calculation will be reviewed. Common techniques will be illustrated and some common mistakes will be discussed. Publicly available resources will be described. Methods for verifying the results of calibrations, particularly when spreadsheets or other calculations aids are utilized, will also be discussed.

Learning Objectives:

1. Review the basic implementation of TG‐51 for conventional external beam measurements.

2. Discuss practical aspects of the selection of ion chamber, electrometer and measurement conditions for TG‐51 calibrations.

3. Demonstrate some techniques for determining TG‐51 parameters such as Pion, Ppol, and kQ

4. Discuss some common mistakes and how to avoid them.
WE‐E‐213A‐02: Practical Aspects of Cyberknife Small Field Dosimetry
Authors: Dieterich S , Wang L
Published: April 2010

Small field dosimetry for Cyberknife is the most challenging aspects of machine commissioning and annual QA. Accurate reference dosimetry, relative output factors, TPR and OCR data form the baseline for accurate dose delivery. This presentation will give practical guidance on ways to achieve an accurate dosimetric measurement in a time‐efficient way.

First, a new reference dosimetry concept based on a recent publication by the IAEA Working group on “Small Field Dosimetry” will be introduced. This new concept explains how to approach reference dosimetry for radiation therapy machines which do not have a 10 cm × 10 cm field as required by TG51 or IAEA Report 398. Using an example, it will be explained how to calculate kQ for the 60 mm collimator. Suitable detectors for the reference dosimetry with the 60 mm collimator will be discussed. This will include a review of the measured dose dependency on chamber length for the non‐flattened field of Cyberknife based on recently published literature. A discussion on reference dosimetry for the IRIS collimator will conclude reference dosimetry.

Second, relative output factor measurements, focusing on collimators ⩽ 10 mm, will be introduced. The importance of checking the detector for correct inverse‐square law will be shown with a clinical example. Suitable detectors for output measurements are different from detectors used for reference dosimetry. Special consideration will be given to IRIS collimator output factors and their dependency on the accuracy of the mechanical field size tolerance.

This presentation will end with a section on measurements of the TPR and OCR data. Especially measuring OCR data for the IRIS collimator, which require 15 degree and 105 degree scans in addition to the in‐plane and cross‐plane scans, will be discussed. Data processing as well as tips & tricks to streamline the process will be given. Quality assurance and secondary dose verification processes as applicable to the dosimetry will be covered.

Learning Objectives:

1. Understanding the new IAEA “Small Field Dosimetry” Paradigm on reference field dosimetry.

2. Understanding which detector types are suitable for Cyberknife small field dosimetry, and why.

3. Understanding Cyberknife‐specific challenges.
TH‐A‐BRC‐01: Ultrasound Based IGRT
Authors: Salter B
Published: April 2010

While numerous image guidance tools have evolved in recent years, in‐room ultrasound (US) guidance remains a viable, efficient and still widely utilized tool for localization of prostate and other abdominal sites. In the presence of proper training and implementation, the method has been found to be an acceptably accurate, relatively inexpensive, non‐invasive method of localizing prostate that requires no delivered radiation dose. In this refresher course we will review the fundamentals of the US guidance process and discuss methods for implementation and ongoing QA of an effective US Guidance program.