bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐E‐9A‐01: Ultrasound Elasticity
Authors: Emelianov S , Hall T , Bouchard R
Published: July 2014

Principles and techniques of ultrasound‐based elasticity imaging will be presented, including quasistatic strain imaging, shear wave elasticity imaging, and their implementations in available systems. Deeper exploration of quasistatic methods, including elastic relaxation, and their applications, advantages, artifacts and limitations will be discussed. Transient elastography based on progressive and standing shear waves will be explained in more depth, along with applications, advantages, artifacts and limitations, as will measurement of complex elastic moduli. Comparisons will be made between ultrasound radiation force techniques, MR elastography, and the simple A mode plus mechanical plunger technique. Progress in efforts, such as that by the Quantitative Imaging Biomarkers Alliance, to reduce the differences in the elastic modulus reported by different commercial systems will be explained.

Dr. Hall is on an Advisory Board for Siemens Ultrasound and has a research collaboration with them, including joint funding by R01CA140271 for nonlinear elasticity imaging.

Learning Objectives:

Be reminded of the long history of palpation of tissue elasticity for critical medical diagnosis and the relatively recent advances to be able to image tissue strain in response to an applied force.

Understand the differences between shear wave speed elasticity measurement and imaging and understand the factors affecting measurement and image frame repletion rates.

Understand shear wave propagation effects that can affect measurements, such as essentially lack of propagation in fluids and boundary effects, so important in thin layers.

Know characteristics of available elasticity imaging phantoms, their uses and limitations.

Understand thermal and cavitational limitations affecting radiation force‐based shear wave imaging.

Have learning and references adequate to for you to use in teaching elasticity imaging to residents and technologists.

Be able to explain how elasticity measurement and imaging can contribute to diagnosis of breast and prostate cancer, staging of liver fibrosis, age estimation of deep veinous fhrombosis, confirmation of thermal lesions in the liver after RF ablation.
WE‐E‐16A‐01: Medical Physics Economics Update
Authors: Goodwin J , Dirksen B , White G
Published: July 2014

Radiology and Medical Physics reimbursement for Medicare services is constantly changing. In this presentation we will review the proposed reimbursement rules and levels for 2015 and compare them with those currently in effect for 2014. In addition, we will discuss the challenges that may lie ahead for the medical physics profession as the Centers for Medicare and Medicaid Services (CMS) moves away from a fee for service payment model and towards one of prospective payment.

Learning Objectives:

Understand the differences in the Medicare reimbursement systems for outpatient departments as opposed to physicians and free standing centers.

Learn the proposed Medicare rules for 2015 and how they may affect Radiology and Medical Physics revenues.

Be aware of possible long term changes in reimbursement and how they may affect our employers, our pocket books and our profession.
WE‐E‐BRE‐01: An Image‐Based Skeletal Dosimetry Model for the ICRP Reference Adult Female – Internal Electron Sources
Authors: O' Reilly S , Sinclair L , Maynard M , Rajon D , Wayson M , Marshall E , Bolch W
Published: July 2014

Purpose:

Limitations seen in previous skeletal dosimetry models, which are still employed in commonly used software today, include the lack of consideration of electron escape and cross‐fire from cortical bone, the modeling of infinite spongiosa, the disregard of the effect of varying cellularity on active marrow self‐irradiation, and the lack of use of the more recent ICRP definition of a 50 micron surrogate tissue region for the osteoprogenitor cells – shallow marrow. These limitations were addressed in the present dosimetry model.

Methods:

Electron transport was completed to determine specific absorbed fractions to active marrow and shallow marrow of the skeletal regions of the adult female. The bone macrostructure was obtained from the whole‐body hybrid computational phantom of the UF series of reference phantoms, while the bone microstructure was derived from microCT images of skeletal region samples taken from a 45 year‐old female cadaver. The target tissue regions were active marrow and shallow marrow. The source tissues were active marrow, inactive marrow, trabecular bone volume, trabecular bone surfaces, cortical bone volume and cortical bone surfaces. The marrow cellularity was varied from 10 to 100 percent for active marrow self‐irradiation. A total of 33 discrete electron energies, ranging from 1 keV to 10 MeV, were either simulated or modeled analytically.

Results:

The method of combining macro‐ and microstructure absorbed fractions calculated using MCNPX electron transport was found to yield results similar to those determined with the PIRT model for the UF adult male in the Hough et al. study.

Conclusion:

The calculated skeletal averaged absorbed fractions for each source‐target combination were found to follow similar trends of more recent dosimetry models (image‐based models) and did not follow current models used in nuclear medicine dosimetry at high energies (due to that models use of an infinite expanse of trabecular spongiosa).
WE‐E‐BRE‐04: Dual Focal Spot Dose Painting for Precision Preclinical Radiobiological Investigations
Authors: Stewart J , Lindsay P , Jaffray D
Published: July 2014

Purpose:

Recent progress in small animal radiotherapy systems has provided the foundation for delivering the heterogeneous, millimeter scale dose distributions demanded by preclinical radiobiology investigations. Despite advances in preclinical dose planning, delivery of highly heterogeneous dose distributions is constrained by the fixed collimation systems and large x‐ray focal spot common in small animal radiotherapy systems. This work proposes a dual focal spot dose optimization and delivery method with a large x‐ray focal spot used to deliver homogeneous dose regions and a small focal spot to paint spatially heterogeneous dose regions.

Methods:

Two‐dimensional dose kernels were measured for a 1 mm circular collimator with radiochromic film at 10 mm depth in a solid water phantom for the small and large x‐ray focal spots on a recently developed small animal microirradiator. These kernels were used in an optimization framework which segmented a desired dose distribution into low‐ and high‐spatial frequency regions for delivery by the large and small focal spot, respectively. For each region, the method determined an optimal set of stage positions and beam‐on times. The method was demonstrated by optimizing a bullseye pattern consisting of 0.75 mm radius circular target and 0.5 and 1.0 mm wide rings alternating between 0 and 2 Gy.

Results:

Compared to a large focal spot technique, the dual focal spot technique improved the optimized dose distribution: 69.2% of the optimized dose was within 0.5 Gy of the intended dose for the large focal spot, compared to 80.6% for the dual focal spot method. The dual focal spot design required 14.0 minutes of optimization, and will require 178.3 minutes for automated delivery.

Conclusion:

The dual focal spot optimization and delivery framework is a novel option for delivering conformal and heterogeneous dose distributions at the preclinical level and provides a new experimental option for unique radiobiological investigations.

Funding Support: this work is supported by funding the National Sciences and Engineering Research Council of Canada, and a Mitacs‐accelerate fellowship.

Conflict of Interest: Dr. Lindsay and Dr. Jaffray are listed as inventors of the small animal microirradiator described herein. This system has been licensed for commercial development.
WE‐E‐BRE‐12: Tumor Microenvironment Dynamics Following Radiation
Authors: Campos D , Niles D , Adamson E , Torres A , Kissick M , Eliceiri K , Kimple R
Published: July 2014

Purpose:

This work aims to understand the radiation‐induced interplay between tumor oxygenation and metabolic activity. These dynamics can potentially serve as biomarkers in assessing treatment response allowing for patient‐specific adaptive radiotherapy.

Methods:

Using patient‐derived xenografts of head and neck cancer we assessed tumor oxygenation via fiber‐optic probe monitored hemoglobin saturation and Blood Oxygen Level Dependent (BOLD) MRI. Measurements were taken before and after a 10 Gy dose of radiation. Changes in metabolic activity were measured via Fluorescence Lifetime IMaging (FLIM) with the appropriate controls following a 10 Gy dose of radiation. FLIM can non‐invasively monitor changes in fluorescence in response to the microenvironment including being able to detect free and bound states of the intrinsically fluorescent metabolite NADH (Nicotinamide Adenine Dinucleotide). With this information FLIM can accurately quantify the metabolic state of cells that have been radiated. To model the observed changes, a two‐compartment, source‐sink simulation relating hemoglobin saturation and metabolic activity was performed using MATLAB.

Results:

Hemoglobin saturation as measured by interstitial probe and BOLD‐MRI decreased by 30% within 15 minutes following radiation. FLIM demonstrated a decrease in the mean fluorescence lifetime of NADH by 100 ps following 10 Gy indicating a shift towards glycolytic pathways. Simulation of radiation‐induced alterations in tumor oxygenation demonstrated that these changes can be the result of changes in either vasculature or metabolic activity.

Conclusion:

Radiation induces significant changes in hemoglobin saturation and metabolic activity. These alterations occur on time scales approximately the duration of common radiation treatments. Further understanding these dynamics has important implications with regard to improvement of therapy and biomarkers of treatment response.
WE‐E‐17A‐03: FDG‐PET‐Based Radiomics to Predict Local Control and Survival Following Radiotherapy
Authors: Oh J , Apte A , Folkerts M , Kohutek Z , Wu A , Rimmer A , Lee N , Deasy J
Published: July 2014

Purpose:

An exploding field in cancer research is “radiomics,” based on the hypothesis that there is statistical (hidden) information in medical images that is prognostic or predictive of outcomes. Our group has developed an efficient pipeline to extract and analyze quantitative image features from medical images as related to outcomes or diagnosis. In this work, we summarize our previous studies with positron emission tomography (PET) images and show the potential of the use of radiomics for outcomes research.

Methods:

We analyzed two cancer datasets, each consisting of pre‐radiotherapy‐treatment PET scans: 163 T1‐2N0M0 non‐small cell lung cancer (NSCLC) patients and 174 head and neck (H&N) cancer patients with stage III–IV. The PET scans were converted to Computational Environment for Radiological Research (CERR) format, and CERR was used to generate 24 shape, texture, and intensity‐histogram based image features. Data‐mining and logistic regression methods were then used to model local failure (LF) and overall survival (OS). Unbiased estimates of performance were generated using leave‐one‐out cross‐validation (LOOCV).

Results:

For predicting LF, the models with biologically equivalent dose (BED) and TLG (metabolic tumor volume (MTV) x SUVmean) in NSCLC, and skewness and MTV in H&N, achieved the best performance with AUC=0.818 (p<0.0001) and AUC=0.826 (p=0.0002), respectively. For predicting OS, the models with kurtosis and volume in NSCLC and SUVmax and homogeneity in H&N achieved the best performance with AUC=0.706 (p<0.0001) and AUC=0.656 (p=0.0003), respectively. On LOOCV, all these models retained significant predictive power. Interestingly, MTV was highly correlated with LF in both sites.

Conclusion:

PET‐based imaged features are promising tools for improving treatment management decision making. Much more research is needed to identify optimal radiomics metrics and to correlate imaging phenotype with other clinical or genomic information.
WE‐E‐17A‐05: Complementary Prognostic Value of CT and 18F‐FDG PET Non‐Small Cell Lung Cancer Tumor Heterogeneity Features Quantified Through Texture Analysis
Authors: Desseroit M , Cheze Le Rest C , Tixier F , Majdoub M , Guillevin R , Perdrisot R , Visvikis D , Hatt M
Published: July 2014

Purpose:

Previous studies have shown that CT or 18F‐FDG PET intratumor heterogeneity features computed using texture analysis may have prognostic value in Non‐Small Cell Lung Cancer (NSCLC), but have been mostly investigated separately. The purpose of this study was to evaluate the potential added value with respect to prognosis regarding the combination of non‐enhanced CT and 18F‐FDG PET heterogeneity textural features on primary NSCLC tumors.

Methods:

One hundred patients with non‐metastatic NSCLC (stage I–III), treated with surgery and/or (chemo)radiotherapy, that underwent staging 18F‐FDG PET/CT images, were retrospectively included. Morphological tumor volumes were semi‐automatically delineated on non‐enhanced CT using 3D SlicerTM. Metabolically active tumor volumes (MATV) were automatically delineated on PET using the Fuzzy Locally Adaptive Bayesian (FLAB) method. Intratumoral tissue density and FDG uptake heterogeneities were quantified using texture parameters calculated from co‐occurrence, difference, and run‐length matrices. In addition to these textural features, first order histogram‐derived metrics were computed on the whole morphological CT tumor volume, as well as on sub‐volumes corresponding to fine, medium or coarse textures determined through various levels of LoG‐filtering. Association with survival regarding all extracted features was assessed using Cox regression for both univariate and multivariate analysis.

Results:

Several PET and CT heterogeneity features were prognostic factors of overall survival in the univariate analysis. CT histogram‐derived kurtosis and uniformity, as well as Low Grey‐level High Run Emphasis (LGHRE), and PET local entropy were independent prognostic factors. Combined with stage and MATV, they led to a powerful prognostic model (p<0.0001), with median survival of 49 vs. 12.6 months and a hazard ratio of 3.5.

Conclusion:

Intratumoral heterogeneity quantified through textural features extracted from both CT and FDG PET images have complementary and independent prognostic value in NSCLC.
WE‐E‐17A‐06: Assessing the Scale of Tumor Heterogeneity by Complete Hierarchical Segmentation On MRI
Authors: Gensheimer M , Trister A , Hawkins D , Ermoian R
Published: July 2014

Purpose:

In many cancers, intratumoral heterogeneity exists in vascular and genetic structure. We developed an algorithm which uses clinical imaging to interrogate different scales of heterogeneity. We hypothesize that heterogeneity of perfusion at large distance scales may correlate with propensity for disease recurrence. We applied the algorithm to initial diagnosis MRI of rhabdomyosarcoma patients to predict recurrence.

Methods:

The Spatial Heterogeneity Analysis by Recursive Partitioning (SHARP) algorithm recursively segments the tumor image. The tumor is repeatedly subdivided, with each dividing line chosen to maximize signal intensity difference between the two subregions. This process continues to the voxel level, producing segments at multiple scales. Heterogeneity is measured by comparing signal intensity histograms between each segmented region and the adjacent region. We measured the scales of contrast enhancement heterogeneity of the primary tumor in 18 rhabdomyosarcoma patients. Using Cox proportional hazards regression, we explored the influence of heterogeneity parameters on relapse‐free survival (RFS). To compare with existing methods, fractal and Haralick texture features were also calculated.

Results:

The complete segmentation produced by SHARP allows extraction of diverse features, including the amount of heterogeneity at various distance scales, the area of the tumor with the most heterogeneity at each scale, and for a given point in the tumor, the heterogeneity at different scales. 10/18 rhabdomyosarcoma patients suffered disease recurrence. On contrast‐enhanced MRI, larger scale of maximum signal intensity heterogeneity, relative to tumor diameter, predicted for shorter RFS (p=0.05). Fractal dimension, fractal fit, and three Haralick features did not predict RFS (p=0.09‐0.90).

Conclusion:

SHARP produces an automatic segmentation of tumor regions and reports the amount of heterogeneity at various distance scales. In rhabdomyosarcoma, RFS was shorter when the primary tumor exhibited larger scale of heterogeneity on contrast‐enhanced MRI. If validated on a larger dataset, this imaging biomarker could be useful to help personalize treatment.
WE‐E‐17A‐07: Patient‐Specific Mathematical Neuro‐Oncology: Biologically‐Informed Radiation Therapy and Imaging Physics
Authors: Swanson K , Corwin D , Rockne R
Published: July 2014

Purpose:

To demonstrate a method of generating patient‐specific, biologically‐guided radiation therapy (RT) plans and to quantify and predict response to RT in glioblastoma. We investigate the biological correlates and imaging physics driving T2‐MRI based response to radiation therapy using an MRI simulator.

Methods:

We have integrated a patient‐specific biomathematical model of glioblastoma proliferation, invasion and radiotherapy with a multiobjective evolutionary algorithm for intensity‐modulated RT optimization to construct individualized, biologically‐guided plans. Patient‐individualized simulations of the standard‐of‐care and optimized plans are compared in terms of several biological metrics quantified on MRI. An extension of the PI model is used to investigate the role of angiogenesis and its correlates in glioma response to therapy with the Proliferation‐Invasion‐Hypoxia‐ Necrosis‐Angiogenesis model (PIHNA). The PIHNA model is used with a brain tissue phantom to predict tumor‐induced vasogenic edema, tumor and tissue density that is used in a multi‐compartmental MRI signal equation for generation of simulated T2‐ weighted MRIs.

Results:

Applying a novel metric of treatment response (Days Gained) to the patient‐individualized simulation results predicted that the optimized RT plans would have a significant impact on delaying tumor progression, with Days Gained increases from 21% to 105%. For the T2‐ MRI simulations, initial validation tests compared average simulated T2 values for white matter, tumor, and peripheral edema to values cited in the literature. Simulated results closely match the characteristic T2 value for each tissue.

Conclusion:

Patient‐individualized simulations using the combination of a biomathematical model with an optimization algorithm for RT generated biologically‐guided doses that decreased normal tissue dose and increased therapeutic ratio with the potential to improve survival outcomes for treatment of glioblastoma. Simulated T2‐MRI is shown to be consistent with known physics of MRI and can be used to further investigate biological drivers of imaging‐based response to RT.
WE‐E‐17A‐09: Modulation of the Interstitial Fluid Pressure by High Intensity Focused Ultrasound as a Way to Alter Local Fluid and Solute Movement: Insights From a Mathematical Model
Authors: Sassaroli E , O' Neill B
Published: July 2014

Purpose:

To investigate and quantify the mechanisms responsible for the increased uptake of macromolecules observed in tissue exposed to pulsed high‐intensity focused ultrasound (HIFU) guided by MRI in preclinical studies.

Methods:

A mathematical model describing the transport of fluid and macromolecules in normal and tumor tissue is presented. The tissue is treated as a porous‐permeable, isotropic and linearly elastic medium. The model calculates the changes in the interstitial fluid pressure (IFP) and the interstitial fluid velocity (IFV) immediately after HIFU exposure. T2 weighted MR images taken a few minutes after a pulsed HIFU exposure of a rabbit thigh have been employed to estimate the fluid content in the tissue. A typical HIFU exposure is about 60s long and results in a temperature increase (hottest pixel) of about 140C as measured by MRI thermometry. The IFP and the IVF are then inserted into a macroscopic solute transport equation to determine the tissue concentration profiles of macromolecules. The model equations have been solved numerically using a finite element technique.

Results:

In both normal and tumor tissue, the model shows that in the focal region, immediately after HIFU exposure, there is a decrease in the IFP and the IVF is directed inward. Furthermore, the solution of the solute transport equation predicts a significant accumulation in the interstitium of large macromolecule solutes such as IgG which has a molecular weight of 150,000 Da.

Conclusion:

Efficient delivery of therapeutic agents in targeted tissues still remains a significant challenge in medicine. HIFU guided by MRI has been shown to improve targeted drug delivery in preclinical studies. The results of our simulation suggest improved fluid convection and macromolecule distribution during the initial lowering of the IFP resulting from HIFU exposure. This model offers valuable guidance for developing strategies that employ MRI‐guided HIFU for improving targeted drug delivery.
WE‐E‐17A‐10: Singular Value Decomposition Identifies Transcript Length Distribution Functions from DNA Microarray Data and Reveals Evolutionary Forces Globally Affecting Glioblastoma Multiforme Metabolism
Authors: Alter O
Published: July 2014

Purpose:

To search for evolutionary forces that might act upon eukaryotic mRNA transcript length, e.g., as a normal cell is transformed to a tumor cell.

Methods:

We use the singular value decomposition (SVD) to identify the length distribution functions of sets and subsets of human and yeast transcripts from profiles of mRNA abundance levels across gel electrophoresis migration distances that were previously measured by DNA microarrays. We show that the SVD identifies the transcript length distribution functions as “asymmetric generalized coherent states” from the DNA microarray data and with no a‐priori assumptions [Alter and Golub, Proc. Natl. Acad. Sci. USA 103 (32), pp. 11828‐11833 (2006); doi: 10.1073/pnas.0604756103].

Results:

Comparing subsets of human and yeast transcripts of the same gene ontology annotations, we find that in both disparate eukaryotes, transcripts involved in protein synthesis or mitochondrial metabolism are significantly shorter than typical, and in particular, significantly shorter than those involved in glucose metabolism. Comparing the subsets of human transcripts that are overexpressed in glioblastoma multiforme (GBM) or normal brain tissue samples from The Cancer Genome Atlas, we find that GBM maintains normal brain overexpression of significantly short transcripts, enriched in transcripts that are involved in protein synthesis or mitochondrial metabolism, but suppresses normal overexpression of significantly longer transcripts, enriched in transcripts that are involved in glucose metabolism and brain activity [Bertagnolli, Drake, Tennessen and Alter, PLoS One 8 (11), article e78913 (2013); doi: 10.1371/journal.pone.0078913].

Conclusion:

These global relations among transcript length, cellular metabolism and tumor development suggest a previously unrecognized physical mode for tumor and normal cells to differentially regulate metabolism in a transcript length‐dependent manner. The identified distribution functions support a previous hypothesis from mathematical modeling of evolutionary forces that act upon transcript length in the manner of the restoring force of the harmonic oscillator.

This research was supported by the Utah Science, Technology and Research (USTAR) Initiative, National Human Genome Research Institute (NHGRI) R01 Grant HG‐004302 and National Science Foundation (NSF) CAREER Award DMS‐0847173
WE‐E‐18A‐01: Large Area Avalanche Amorphous Selenium Sensors for Low Dose X‐Ray Imaging
Authors: Scheuermann J , Goldan A , Tousignant O , Leveille S , Zhao W
Published: July 2014

Purpose:

A large area indirect flat panel imager (FPI) with avalanche gain is being developed to achieve x‐ray quantum noise limited low dose imaging. It uses a thin optical sensing layer of amorphous selenium (a‐Se), known as High‐Gain Avalanche Rushing Photoconductor (HARP), to detect optical photons generated from a high resolution x‐ray scintillator. We will report initial results in the fabrication of a solid‐state HARP structure suitable for a large area FPI. Our objective is to establish the blocking layer structures and defect suppression mechanisms that provide stable and uniform avalanche gain.

Methods:

Samples were fabricated as follows: (1) ITO signal electrode. (2) Electron blocking layer. (3) A 15 micron layer of intrinsic a‐Se. (4) Transparent hole blocking layer. (5) Multiple semitransparent bias electrodes to investigate avalanche gain uniformity over a large area. The sample was exposed to 50ps optical excitation pulses through the bias electrode. Transient time of flight (TOF) and integrated charge was measured. A charge transport simulation was developed to investigate the effects of varying blocking layer charge carrier mobility on defect suppression, avalanche gain and temporal performance.

Results:

Avalanche gain of ∼200 was achieved experimentally with our multi‐layer HARP samples. Simulations using the experimental sensor structure produced the same magnitude of gain as a function of electric field. The simulation predicted that the high dark current at a point defect can be reduced by two orders of magnitude by blocking layer optimization which can prevent irreversible damage while normal operation remained unaffected.

Conclusion:

We presented the first solid state HARP structure directly scalable to a large area FPI. We have shown reproducible and uniform avalanche gain of 200. By reducing mobility of the blocking layers we can suppress defects and maintain stable avalanche. Future work will optimize the blocking layers to prevent lag and ghosting.
WE‐G‐18A‐06: Sinogram Restoration in Helical Cone‐Beam CT
Authors: Little K , Riviere P La
Published: July 2014

Purpose:

To extend CT sinogram restoration, which has been shown in 2D to reduce noise and to correct for geometric effects and other degradations at a low computational cost, from 2D to a 3D helical cone‐beam geometry.

Methods:

A method for calculating sinogram degradation coefficients for a helical cone‐beam geometry was proposed. These values were used to perform penalized‐likelihood sinogram restoration on simulated data that were generated from the FORBILD thorax phantom. Sinogram restorations were performed using both a quadratic penalty and the edge‐preserving Huber penalty. After sinogram restoration, Fourier‐based analytical methods were used to obtain reconstructions. Resolution‐variance trade‐offs were investigated for several locations within the reconstructions for the purpose of comparing sinogram restoration to no restoration. In order to compare potential differences, reconstructions were performed using different groups of neighbors in the penalty, two analytical reconstruction methods (Katsevich and single‐slice rebinning), and differing helical pitches.

Results:

The resolution‐variance properties of reconstructions restored using sinogram restoration with a Huber penalty outperformed those of reconstructions with no restoration. However, the use of a quadratic sinogram restoration penalty did not lead to an improvement over performing no restoration at the outer regions of the phantom. Application of the Huber penalty to neighbors both within a view and across views did not perform as well as only applying the penalty to neighbors within a view. General improvements in resolution‐variance properties using sinogram restoration with the Huber penalty were not dependent on the reconstruction method used or the magnitude of the helical pitch.

Conclusion:

Sinogram restoration for noise and degradation effects for helical cone‐beam CT is feasible and should be able to be applied to clinical data. When applied with the edge‐preserving Huber penalty, sinogram restoration leads to an improvement in resolution‐variance tradeoffs.
TH‐A‐16A‐01: Image Quality for the Radiation Oncology Physicist: Review of the Fundamentals and Implementation
Authors: Seibert J , Imbergamo P
Published: July 2014

The expansion and integration of diagnostic imaging technologies such as On Board Imaging (OBI) and Cone Beam Computed Tomography (CBCT) into radiation oncology has required radiation oncology physicists to be responsible for and become familiar with assessing image quality. Unfortunately many radiation oncology physicists have had little or no training or experience in measuring and assessing image quality. Many physicists have turned to automated QA analysis software without having a fundamental understanding of image quality measures. This session will review the basic image quality measures of imaging technologies used in the radiation oncology clinic, such as low contrast resolution, high contrast resolution, uniformity, noise, and contrast scale, and how to measure and assess them in a meaningful way. Additionally a discussion of the implementation of an image quality assurance program in compliance with Task Group recommendations will be presented along with the advantages and disadvantages of automated analysis methods.

Learning Objectives:

Review and understanding of the fundamentals of image quality.

Review and understanding of the basic image quality measures of imaging modalities used in the radiation oncology clinic.

Understand how to implement an image quality assurance program and to assess basic image quality measures in a meaningful way.
TH‐A‐BRF‐03: Evaluation of Synthetic CTs Generated Using MR‐SIM Data
Authors: Kim J , Glide‐Hurst C , Doemer A , Wen N , Chett I
Published: July 2014

Purpose:

To describe and evaluate a novel algorithm for generating synthetic CT images from MR‐SIM data for dose calculations in MR‐only treatment planning.

Methods:

A voxel‐based weighted summation method was implemented to generate synthetic CT (synCT) images. MR data were acquired using Philips 1.0T Panorama high‐field open MR‐SIM. Retrospective patient data from seven prostate patients and one brain patient (three lesions) enrolled in an IRB‐approved study were used. 3D T1‐weighted fast field echo and 3D T2‐weighted turbo spin echo sequences were utilized for all patients. A 3D balanced turbo field echo sequence using spectral presaturation with inversion recovery was acquired for prostate patients, but 3D ultra‐short echo time (UTE)‐DIXON was instead acquired for the brain patient to amplify bone signal for semi‐automatic bone segmentation. Weight optimization was performed using a training subset of patients. HU value differences between planning CT and synCTs were analyzed using mean absolute error (MAE). Original patient CT‐based treatment plans were mapped onto synCTs, dose was recalculated using original leaf motion and MU values, and DRRs were generated. Dosevolume metrics and gamma analysis were used for dosimetric evaluation.

Results:

Average whole‐body MAE of synCTs across all patients was 75+12 HU. In prostate cancer patients, average HU difference between planning and synCTs was 0.9±1.0% for soft tissue structures and 4.3±2.5% for bony structures. DRRs were generated from synCTs and qualitatively showed good geometric agreement with planning CT‐generated DRRs. D99, mean dose, and maximum dose to CTV calculated using the synCT remained within 1.2% of planning CT‐based dose calculations. All gamma analysis evaluated at 2%/2mm dose difference/distance to agreement) pass rates were greater than 95% with an average of 99.9±0.1% for prostate patients and 98.4±2.2% for three brain lesions.

Conclusion:

SynCTs were generated with clinically acceptable accuracy comparable to planning CTs, enabling dose computations for MR‐only simulation.

Research supported in part by a grant from Philips HealthCare (Best, Netherlands).
TH‐A‐BRF‐06: Optimal Timing for Ultrasound‐Activated Drug Delivery for Treatment of Prostate Cancer Under MR Guidance
Authors: Gupta R , Cvetkovic D , Wang B , Ma C , Chen L
Published: July 2014

Purpose:

To determine optimal timing for applying tumor targeted focused ultrasound (FUS) under MR guidance to release drugs from nanodroplets (ultrasound responsive, drug delivery vehicles) for effective treatment of prostate cancer.

Methods:

Poly lactide (PDLA) nanodroplets loaded with model drug {fluorescently labeled paclitaxel (FPTX)} were prepared using solid dispersion technique. Human prostate cancer, LNCaP cells were implanted orthotopically in prostates of male nude mice. Tumor bearing mice (n=3) were injected with 125 microlitre of 0.1% FPTX, 2% PDLA nanodroplets via tail‐vein. At 30min, 2h, 6h and 24h animals were anesthetized, blood was collected by eye bleed, then animals were sacrificed, tumor and organs were excised and weighted. One cut portion of the organ was homogenized, incubated in lysis buffer and centrifuged. Lysates were read using fluorescence spectrophotometer. Other portion was cut into sections for qualitative analysis using fluorescence microscope. Mice (n=3) were also injected with 0.1% FPTX solution (non encapsulated drug form) and mice (n=3) with no injections were used as controls.

Results:

Drug‐loaded nanodroplets shows more drug accumulation in tumor with maximum concentration of one third of injected dose after 2h of injection when compared with maximum concentration of less than one tenth of injected dose after 2h of injection for free drug. The time range 2h to 6h is considered optimum for applying FUS to activate drug release from nanodroplets, when maximum drug concentration is seen in tumor while low concentration is found in blood thus minimizing potential damage to blood vessels. Microscopy studies show consistency with quantitative data.

Conclusion:

Our prior in vivo studies have showed significant tumor growth delay when FUS is applied under MR imaging in combination with docetaxel loaded nanodroplets. Present work with model drug loaded nanodroplets indicates the potential for increasing prostate cancer treatment efficacy and providing preclinical data for using FUS‐mediated drug delivery under MR guidance.
TH‐A‐BRF‐07: Retrospective Reconstruction of 3D Radial MRI Data to Evaluate the Effect of Abdominal Compression On 4D Abdominal Organ Motion
Authors: Stemkens B , Tijssen R , Denis de Senneville B , Lagendijk J , van den Berg C
Published: July 2014

Purpose:

To assess the immobilization effect of an abdominal corset on the spatial and temporal motion characteristics of the pancreas and kidneys using a novel 4D‐MRI method.

Methods:

Four healthy subjects were scanned with and without a fiberglass corset on a 1.5T clinical MRI. For each subject the best fitting corset was chosen from a range of available corsets. For one subject a custom‐fit corset was used. The free‐breathing 4D‐MRI scan consisted of a balanced‐TFE sequence with radial in‐plane sampling (TE/TR=1.45ms/3.0ms, FA=30°, FOV=350×350×96mm3, voxelsize=2.0×2.0×4.0mm3, 30 dynamics, Tacq=10m17s). Turbo direction was along kz acquiring all kz lines within a single TFE shot (shot duration 93ms). A respiratory diaphragm navigator was interleaved with the TFE shots to acquire the breathing signal, which was used to retrospectively assign each k‐space segment to one of the ten respiratory phases. A 3D optical flow algorithm was used to estimate the non‐rigid displacement between the respiratory phases. The respiration frequency changes were assessed by means of power spectrum analysis (PSA) of the navigator signal.

Results:

Image quality was adequate for delineation and registration. Cranio‐caudal motion calculated by the 3D optical flow algorithm correlated with the navigator signal, but inter‐organ motion amplitude variation was observed between all organs. Motion reduction induced by the corset was primarily observed in the CC‐direction, but varied substantially across the subjects. Our method additionally showed that the antero‐posterior motion was slightly increased for both kidneys in all subjects (left: 1.2mm, right: 0.8mm). Visual inspection of PSA showed no trend in breathing frequency changes.

Conclusion:

We have demonstrated a novel, navigator based, freebreathing 4D‐MRI technique to assess the immobilization effect of abdominal compression in four healthy subjects. This technique can be clinically used to assess the effect of a custom‐fit corset on the motion of both tumor motion and surrounding organs at risk.
TH‐A‐BRF‐09: Integration of High‐Resolution MRSI Into Glioblastoma Treatment Planning
Authors: Schreibmann E , Cordova J , Shu H , Crocker I , Curran W , Holder C , Shim H
Published: July 2014

Purpose:

Identification of a metabolite signature that shows significant tumor cell infiltration into normal brain in regions that do not appear abnormal on standard MRI scans would be extremely useful for radiation oncologists to choose optimal regions of brain to treat, and to quantify response beyond the MacDonald criteria. We report on integration of high‐resolution magnetic resonance spectroscopic imaging (HR‐MRSI) with radiation dose escalation treatment planning to define and target regions at high risk for recurrence.

Methods:

We propose to supplement standard MRI with a special technique performed on an MRI scanner to measure the metabolite levels within defined volumes. Metabolite imaging was acquired using an advanced MRSI technique combining 3D echo‐planar spectroscopic imaging (EPSI) with parallel acquisition (GRAPPA) using a multichannel head coil that allows acquisition of whole brain metabolite maps with 108 μl resolution in 12 minutes implemented on a 3T MR scanner. Elevation in the ratio of two metabolites, choline (Cho, elevated in proliferating high‐grade gliomas) and N‐acetyl aspartate (NAA, a normal neuronal metabolite), was used to image infiltrating high‐grade glioma cells in vivo.

Results:

The metabolite images were co‐registered with standard contrast‐enhanced T1‐weighted MR images using in‐house registration software and imported into the treatment‐planning system. Regions with tumor infiltration are identified on the metabolic images and used to create adaptive IMRT plans that deliver a standard dose of 60 Gy to the standard target volume and an escalated dose of 75 Gy (or higher) to the most suspicious regions, identified as areas with elevated Cho/NAA ratio.

Conclusion:

We have implemented a state‐of‐the‐art HR‐MRSI technology that can generate metabolite maps of the entire brain in a clinically acceptable scan time, coupled with introduction of an imaging co‐registration/ analysis program that combines MRSI data with standard imaging studies in a clinically useful fashion.
TH‐A‐18C‐05: Scatter Reduction and Correction for Dual‐Source CBCT Using the Synchronized Moving Grid (SMOG) System
Authors: Chen Y , Zhang Y , Giles W , Jin J , Yin F , Ren L
Published: July 2014

Purpose:

to implement the newly developed synchronized moving grid (SMOG) system on a prototype dual‐source CBCT system to evaluate its efficacy for scatter reduction and correction under various settings, including different phantom size, grid ratio and image acquisition modes.

Methods:

A 1D grid was designed for each tube in our dual‐source CBCT system. Projections were acquired with the grid at different complementary positions from each scan angle and merged for reconstruction. The scatter signal was measured from the grid blocked area and the scatter distribution was estimated by using a cubic spline interpolated/extrapolated in each projection for scatter correction. The projections without grid were also acquired as the comparing group. Three sets of images were reconstructed from projections: a) without grid, b) with grid but without scatter correction and c) with grid and with scatter correction to evaluate CNR (contrast‐to‐noise ratio) and CT number linearity enhancement. The efficacy of the SMOG system was evaluated using CAT phantoms with different diameters (15cm, 20cm and 30cm), grids (grid ratios of 1:1 and 2:1) and acquisition modes (simultaneous: two tubes firing at the same time and sequential: only one tube firing in one rotation).

Results:

That scatter artifacts were substantially reduced with our scatter correction algorithm. CNR, degraded by the cross scatter in dual‐source system, were increased by 74%, 32% and 28% for phantom size of 15cm, 20cm and 30cm respectively after using scatter correction with 1:1 grid. And in 20 cm phantom case with simultaneous acquisition, the CT number linearity improved from 0.9969 to 0.9997. Higher grid ratio (more blocked area) resulted in better scatter artifact removal and CNR improvement at the cost of complexity and increased exposure.

Conclusion:

The SMOG system can effectively reduce the scatter artifacts and enhance CNR and CT number linearity for the dual‐source CBCT system.

This work was supported by NIH grant R01CA166948.
TH‐A‐18C‐06: A Scatter Elimination Scheme for Cone Beam CT Using An Oscillating Narrow Beam
Authors: Yan H , Xu Y , Folkerts M , Jia X , Jiang S
Published: July 2014

Purpose:

While cone beam CT (CBCT) has been widely used in image guided radiation therapy, its low image quality, primarily caused by scattered x‐rays, hinders advanced clinical applications, e.g., CBCT based on‐line adaptive re‐planning. We propose in this abstract a new scheme called oscillating narrow beam CBCT (ONB‐CBCT) to eliminate scatter signals.

Methods:

ONB‐CBCT consists of two major components. 1) Oscillating narrow beam (ONB) scan and 2) partitioned flat panel containing multiple individual detector strips and their own readouts. Both the beam oscillation and detector partition are along the superior‐inferior (SI) direction. During data acquisition, at a given projection, the narrow beam sweep through the detector region, and different portions of the detector acquires projection data in synchrony with the narrow beam. ONB can be generated by a rotating slit collimator design with conventional tube with single focal spot, or by directly using a new source with multiple focal spots. A proof‐of‐principle study via Monte Carlo simulation is conducted to demonstrate the feasibility of ONB‐CBCT.

Results:

As the beam becomes narrower, more and more scatter signals are eliminated. For the case with a bowtie filter and using 15 ONBs, the maximum and the average intensity error due to scatter are below 20 and 10 HU, respectively.

Conclusion:

ONB yields a narrowed exposure field at each snapshot and hence an inherently negligible scatter effect. Meanwhile, the individualized detector units guarantee high frame rate detection and hence a same large volume coverage as that in conventional CBCT. In summary, ONB‐CBCT is a promising design to achieve high‐quality CBCT imaging.

This study is supported in part by NIH (1R01CA154747‐01).
TH‐C‐18A‐11: Investigating the Minimum Scan Parameters Required to Generate Free‐Breathing Fast‐Helical CT Scans Without Motion‐Artifacts
Authors: Thomas D , Tan J , Neylon J , Dou T , Jani S , Lamb J , Low D
Published: July 2014

Purpose:

A recently proposed 4D‐CT protocol uses deformable registration of free‐breathing fast‐helical CT scans to generate a breathing motion model. In order to allow accurate registration, free‐breathing images are required to be free of doubling‐artifacts, which arise when tissue motion is greater than scan speed. This work identifies the minimum scanner parameters required to successfully generate free‐breathing fast‐helical scans without doubling‐artifacts.

Methods:

10 patients were imaged under free breathing conditions 25 times in alternating directions with a 64‐slice CT scanner using a low dose fast helical protocol. A high temporal resolution (0.1s) 4D‐CT was generated using a patient specific motion model and patient breathing waveforms, and used as the input for a scanner simulation. Forward projections were calculated using helical cone‐beam geometry (800 projections per rotation) and a GPU accelerated reconstruction algorithm was implemented. Various CT scanner detector widths and rotation times were simulated, and verified using a motion phantom. Doubling‐artifacts were quantified in patient images using structural similarity maps to determine the similarity between axial slices.

Results:

Increasing amounts of doubling‐artifacts were observed with increasing rotation times > 0.2s for 16×1mm slice scan geometry. No significant increase in doubling artifacts was observed for 64×1mm slice scan geometry up to 1.0s rotation time although blurring artifacts were observed >0.6s. Using a 16×1mm slice scan geometry, a rotation time of less than 0.3s (53mm/s scan speed) would be required to produce images of similar quality to a 64×1mm slice scan geometry.

Conclusion:

The current generation of 16 slice CT scanners, which are present in most Radiation Oncology departments, are not capable of generating free‐breathing sorting‐artifact‐free images in the majority of patients. The next generation of CT scanners should be capable of at least 53mm/s scan speed in order to use a fast‐helical 4D‐CT protocol to generate a motion‐artifact free 4D‐CT.

NIH R01CA096679
TH‐C‐12A‐01: Develop a Patient‐Specific QA Program for Radiation Therapy with On‐Board MRI
Authors: Li H , Rodriguez V , Green O , Hu Y , Kashani R , Wooten H , Yang D , Mutic S
Published: July 2014

Purpose:

This work describes development of the first patient‐specific quality assurance (QA) program for magnetic resonance imaging guided radiation therapy (MR‐IGRT).

Methods:

The program consisted of following components: 1) multipoint ionization chamber (IC) measurement using a 15 cm3 cubic phantom, 2) 2D stacked radiographic film dosimetry using a 30×30×20 cm3 phantom with multiple inserted ICs, 3) 3D ArcCHECK measurement with a centrally inserted IC, 4) machine delivery file verification, 5) 3D Monte‐Carlo dose re‐calculation with machine delivery file and phantom CT, 6) 2‐head mode delivery validation in case of a malfunctioning head, and 7) independent beam‐on time calculation for non‐IMRT fields. Both ADCL calibrated ICs and ArcCHECK were MRI compatible. Experimental data were analyzed for the first 10 patients treated at our institution.

Results:

The customized phantoms allowed measuring multiple points with ICs in one delivery. Absolute IC measurements were all within 3% in all phantom geometry/shape/material combinations. Despite known uncertainty associated with film dosimetry, passing rates greater than 90% were achieved in both absolute and composite modes using TG‐129 criteria. Due to the simultaneous irradiation by three radiation sources, ArcCHECK was used as a 3D relative dosimeter with angular and energy dependences uncorrected. 95–100% passing rates were obtained and the centrally inserted IC measurement assured that the overall dose normalization was within 3%. Machine delivery file verification and MC recalculated dose to the phantom results showed 98–100% passing rates, providing opportunity of moving from gamma passing rates to patient DVHbased QA metrics. Same results were obtained for the 2‐head delivery mode. Manual beam‐on time calculation for non‐IMRT fields showed better than 5% agreement.

Conclusion:

We have successfully developed the first MRIGRT patient specific QA program by adopting experimental and computational dosimetry methods that were developed in the past decade for other radiation therapy modalities.