bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐DE‐201‐10: Pitfalls When Using Ruby as An Inorganic Scintillator Detector for Ir‐192 Brachytherapy Dosimetry
Authors: Kertzscher G , Beddar S
Published: July 2016

Purpose:

To study the promising potential of inorganic scintillator detectors (ISDs) and investigate various unwanted luminescence properties which may compromise their accuracy.

Methods:

The ISDs were comprised of a ruby crystal coupled to a polymethyl methacrylate (PMMA) fiber‐optic cable and a charged coupled device camera. A new type of ISD was manufactured and included a long‐pass filter that was sandwiched between the crystal and the fiber‐optic cable. The purpose of the filter was to suppress the Cerenkov and fluorescence background light induced in the PMMA (the stem signal) from striking the ruby crystal, generating unwanted ruby excitation. A variety of experiments were performed to characterize the ruby based ISDs. The relative contribution of the induced ruby signal and the stem signal were quantified while exposing the detector and a bare fiber‐optic cable to a high dose rate (HDR) brachytherapy (BT) source, respectively. The unwanted ruby excitation was quantified while irradiating the fiber‐optic cable with the detector volume shielded. Other experiments addressed time‐dependent luminescence properties and a comparison to other commonly used organic scintillator detectors (BCF‐12, BCF‐60).

Results:

When the BT source dwelled 0.5 cm away from the fiber‐optic cable, the unwanted ruby excitation amounted to >5% of the total signal if the source‐distance from the scintillator was >7 cm. However, the unwanted excitation was suppressed to <1% if the ISD incorporated an optic filter. The stem signal was suppressed with a 20 nm band‐pass filter and was <3% as long as the source‐distance was <7 cm. The ruby based ISDs generated signal up to 20(40) times that of BCF‐12(BCF‐60).

Conclusion:

The study presents solutions to unwanted luminescence properties of ruby based ISDs for HDR BT. An optic filter should be sandwiched between the scintillator volume and the fiber‐optic cable to prevent the stem signal to excite the ruby crystal.
WE‐D‐BRB‐04: Clinical Applications of CBCT for Proton Therapy
Authors: Teo B.
Published: July 2016

The goal of this session is to review the physics of proton therapy, treatment planning techniques, and the use of volumetric imaging in proton therapy. The course material covers the physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for double scattering (DS), uniform scanning (US), and pencil beam scanning (PBS). The session covers the treatment planning strategies used in DS, US, and PBS for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. It introduces the audience to the current status of image guided proton therapy and clinical applications of CBCT for proton therapy. It outlines the importance of volumetric imaging in proton therapy.

Learning Objectives:

Gain knowledge in proton therapy physics, and treatment planning for proton therapy including intensity modulated proton therapy.

The current state of volumetric image guidance equipment in proton therapy.

Clinical applications of CBCT and its advantage over orthogonal imaging for proton therapy.

B. Teo, B.K Teo had received travel funds from IBA in 2015.
WE‐DE‐201‐12: Thermal and Dosimetric Properties of a Ferrite‐Based Thermo‐Brachytherapy Seed
Authors: Warrell G , Shvydka D , Parsai E I
Published: July 2016

Purpose:

The novel thermo‐brachytherapy (TB) seed provides a simple means of adding hyperthermia to LDR prostate permanent implant brachytherapy. The high blood perfusion rate (BPR) within the prostate motivates the use of the ferrite and conductive outer layer design for the seed cores. We describe the results of computational analyses of the thermal properties of this ferrite‐based TB seed in modelled patient‐specific anatomy, as well as studies of the interseed and scatter (ISA) effect.

Methods:

The anatomies (including the thermophysical properties of the main tissue types) and seed distributions of 6 prostate patients who had been treated with LDR brachytherapy seeds were modelled in the finite element analysis software COMSOL, using ferrite‐based TB and additional hyperthermia‐only (HT‐only) seeds. The resulting temperature distributions were compared to those computed for patient‐specific seed distributions, but in uniform anatomy with a constant blood perfusion rate. The ISA effect was quantified in the Monte Carlo software package MCNP5.

Results:

Compared with temperature distributions calculated in modelled uniform tissue, temperature distributions in the patient‐specific anatomy were higher and more heterogeneous. Moreover, the maximum temperature to the rectal wall was typically ∼1 °C greater for patient‐specific anatomy than for uniform anatomy. The ISA effect of the TB and HT‐only seeds caused a reduction in D90 similar to that found for previously‐investigated NiCu‐based seeds, but of a slightly smaller magnitude.

Conclusion:

The differences between temperature distributions computed for uniform and patient‐specific anatomy for ferrite‐based seeds are significant enough that heterogeneous anatomy should be considered. Both types of modelling indicate that ferrite‐based seeds provide sufficiently high and uniform hyperthermia to the prostate, without excessively heating surrounding tissues. The ISA effect of these seeds is slightly less than that for the previously‐presented NiCu‐based seeds.
WE‐D‐BRB‐00: Basics of Proton Therapy
Authors: Arjomandy Bijan , Hua Chia‐Ho
Published: July 2016

The goal of this session is to review the physics of proton therapy, treatment planning techniques, and the use of volumetric imaging in proton therapy. The course material covers the physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for double scattering (DS), uniform scanning (US), and pencil beam scanning (PBS). The session covers the treatment planning strategies used in DS, US, and PBS for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. It introduces the audience to the current status of image guided proton therapy and clinical applications of CBCT for proton therapy. It outlines the importance of volumetric imaging in proton therapy.

Learning Objectives:

Gain knowledge in proton therapy physics, and treatment planning for proton therapy including intensity modulated proton therapy.

The current state of volumetric image guidance equipment in proton therapy.

Clinical applications of CBCT and its advantage over orthogonal imaging for proton therapy.

B. Teo, B.K Teo had received travel funds from IBA in 2015.
WE‐DE‐BRA‐01: SCIENCE COUNCIL JUNIOR INVESTIGATOR COMPETITION WINNER: Acceleration of a Limited‐Angle Intrafraction Verification (LIVE) System Using Adaptive Prior Knowledge Based Image Estimation
Authors: Zhang Y , Yin F , Zhang Y , Ren L
Published: July 2016

Purpose:

To develop an adaptive prior knowledge based image estimation method to reduce the scan angle needed in the LIVE system to reconstruct 4D‐CBCT for intrafraction verification.

Methods:

The LIVE system has been previously proposed to reconstructs 4D volumetric images on‐the‐fly during arc treatment for intrafraction target verification and dose calculation. This system uses limited‐angle beam's eye view (BEV) MV cine images acquired from the treatment beam together with the orthogonally acquired limited‐angle kV projections to reconstruct 4D‐CBCT images for target verification during treatment. In this study, we developed an adaptive constrained free‐form deformation reconstruction technique in LIVE to further reduce the scanning angle needed to reconstruct the CBCT images. This technique uses free form deformation with energy minimization to deform prior images to estimate 4D‐CBCT based on projections acquired in limited angle (orthogonal 6°) during the treatment. Note that the prior images are adaptively updated using the latest CBCT images reconstructed by LIVE during treatment to utilize the continuity of patient motion.The 4D digital extended‐cardiac‐torso (XCAT) phantom was used to evaluate the efficacy of this technique with LIVE system. A lung patient was simulated with different scenario, including baseline drifts, amplitude change and phase shift. Limited‐angle orthogonal kV and beam's eye view (BEV) MV projections were generated for each scenario. The CBCT reconstructed by these projections were compared with the ground‐truth generated in XCAT.Volume‐percentage‐difference (VPD) and center‐of‐mass‐shift (COMS) were calculated between the reconstructed and the ground‐truth tumors to evaluate the reconstruction accuracy.

Results:

Using orthogonal‐view of 6° kV and BEV‐ MV projections, the VPD/COMS values were 12.7±4.0%/0.7±0.5 mm, 13.0±5.1%/0.8±0.5 mm, and 11.4±5.4%/0.5±0.3 mm for the three scenarios, respectively.

Conclusion:

The technique enables LIVE to accurately reconstruct 4D‐CBCT images using only orthogonal 6° angle, which greatly improves the efficiency and reduces dose of LIVE for intrafraction verification.
WE‐DE‐BRA‐03: Construction of An Ultrasound Guidance Platform for Image‐Guided Radiotherapy with the Intent to Treat Transitional Cell Carcinoma
Authors: Sick J , Rancilio N , Fulkerson C , LaPetina P , Poulson J , Knapp D , Stantz K
Published: July 2016

Purpose:

Ultrasound (US) is a noninvasive, nonradiographic imaging technique with high spatial and temporal resolution that can be used for localizing soft‐tissue structures and tumors in real‐time during radiotherapy (inter‐ and intra‐fraction). A detailed methodology integrating 3D‐US within RT is presented. This method is easier to adopt into current treatment protocol than current US based systems and reduces user variability for image acquisition, thus eliminating transducer induced changes that limit CT planning system.

Methods:

We designed an in‐house integrated US manipulator and platform to relate CT, 3D‐US and linear accelerator coordinate systems. To validate the platform, an agar‐based phantom with measured densities and speed‐of‐sound consistent with tissues surrounding the bladder, was rotated (0–45°) resulting in translations (up to 55mm) relative to the CT and US coordinate systems. After acquiring and integrating CT and US images into the treatment planning system, US‐to‐US and US‐to‐CT images were co‐registered to re‐align the phantom relative to the linear accelerator. Errors in the transformation matrix components were calculate to determine precision of this method under different patient positions.

Results:

Statistical errors from US‐US registrations for different patient orientations ranged from 0.06–1.66mm for x, y, and z translational components, and 0.00–1.05° for rotational components. Statistical errors from US‐CT registrations were 0.23–1.18mm for the x, y and z translational components, and 0.08–2.52° for the rotational components.

Conclusion:

Based on our result, this is consistent with currently used techniques for positioning prostate patients if couch re‐positioning is less than a 5 degree rotation. We are now testing this on a dog patient to obtain both inter and intra‐fractional positional errors. Additional design considerations include the future use of ultrasound‐based functionality (photoacoustics, radioacoustics, Doppler) to monitor blood flow and hypoxia and/or in‐vivo dosimetry for applications in other therapeutic techniques, such as hyperthermia, anti‐angiogenesis, and particle therapy.
WE‐DE‐BRA‐05: Monte Carlo Simulation of a Novel Multi‐Layer MV Imager
Authors: Myronakis M , Rottmann J , Hu Y , Wang A , Shedlock D , Morf D , Star‐Lack J , Berbeco R
Published: July 2016

Purpose:

To develop and validate a Monte Carlo (MC) model of a novel multi‐layer imager (MLI) for megavolt (MV) energy beams. The MC model will enable performance optimization of the MLI design for clinical applications including patient setup verification, tumor tracking and MVCBCT.

Methods:

The MLI is composed of four layers of converter, scintillator and light detector, each layer similar to the current clinical AS1200 detector (Varian Medical Systems, Inc). The MLI model was constructed using the Geant4 Application for Tomographic Emission (GATE v7.1) and includes interactions for x‐ray photons, charged particles and optical photons. Computational experiments were performed to assess Modulation Transfer Function (MTF), Detective Quantum Efficiency (DQE) and Noise Power Spectrum normalized by photon fluence and average detector signal (qNNPS). Results were compared with experimental measurements. The current work incorporates, in one model, the complete chain of events occurring in the imager; i.e. starting from x‐ray interaction to charged particle transport and energy deposition to subsequent generation, interactions and detection of optical photons.

Results:

There is good agreement between measured and simulated MTF, qNNPS and DQE values. Normalized root mean squared error (NRMSE) between measured and simulated values over all four layers was 2.18%, 2.43% and 6.05% for MTF, qNNPS and DQE respectively. The relative difference between simulated and measured values for qNNPS(0) was 1.68% and 1.57% for DQE(0). Current results were obtained using a 6MV Varian Truebeam™ spectrum.

Conclusion:

A comprehensive Monte Carlo model of the MLI prototype was developed to allow optimization of detector components. The model was assessed in terms of imaging performance using standard metrics (i.e. MTF, qNNPS, DQE). Good agreement was found between simulated and measured values. The model will be used to assess alternative detector constructions to facilitate advanced clinical imaging applications including MV‐CBCT and tumor tracking.

The project was supported, partially, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446‐01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.
WE‐DE‐BRA‐06: Evaluation of the Imaging Performance of a Novel Water‐Equivalent EPID
Authors: Blake SJ , Cheng J , Vial P , Lu M , Atakaramians S , Meikle S , Kuncic Z
Published: July 2016

Purpose:

To evaluate the megavoltage imaging performance of a novel, water‐equivalent electronic portal imaging device (EPID) developed for simultaneous imaging and dosimetry applications in radiotherapy.

Methods:

A novel EPID prototype based on active matrix flat panel imager technology has been developed by our group and previously reported to exhibit a water‐equivalent dose response. It was constructed by replacing all components above the photodiode detector in a standard clinical EPID (including the copper plate and phosphor screen) with a 15 × 15 cm2 array of plastic scintillator fibers. Individual fibers measured 0.5 × 0.5 × 30 mm3. Spatial resolution was evaluated experimentally relative to that of a standard EPID with the thin slit technique to measure the modulation transfer function (MTF) for 6 MV x‐ray beams. Monte Carlo (MC) EPID models were used to benchmark simulated MTFs against the measurements. The zero spatial frequency detective quantum efficiency (DQE(0)) was simulated for both EPID configurations and a preliminary optimization of the prototype was performed by evaluating DQE(0) as a function of fiber length up to 50 mm.

Results:

The MC‐simulated DQE(0) for the prototype EPID configuration was ∼7 times greater than that of the standard EPID. The prototype's DQE(0) also increased approximately linearly with fiber length, from ∼1% at 5 mm length to ∼11% at 50 mm length. The standard EPID MTF was greater than the prototype EPID's for all spatial frequencies, reflecting the trade off between x‐ray detection efficiency and spatial resolution with thick scintillators.

Conclusion:

This study offers promising evidence that a water‐equivalent EPID previously demonstrated for radiotherapy dosimetry may also be used for radiotherapy imaging applications. Future studies on optimising the detector design will be performed to develop a next‐generation prototype that offers improved megavoltage imaging performance, with the aim to at least match that of current clinical EPIDs.

Funding for this project was provided by an Australian Research Council Linkage Project grant (2015) between The University of Sydney, South Western Sydney Local Health District and Perkin‐Elmer Pty Ltd.
WE‐DE‐BRA‐07: Megavoltage Spectral Imaging with a Layered Detector
Authors: Myronakis M , Rottmann J , Hu Y , Wang A , Shedlock D , Morf D , Star‐Lack J , Berbeco R
Published: July 2016

Purpose:

The aim of the current work is to investigate the feasibility of megavoltage spectral imaging using a multiple layered detector for enhancement of low contrast detectability through material segmentation and discrimination (such as bone, markers and metal implants). Potentially the technique can be applied to improve detection and reduce dose in Megavoltage Cone Beam Computed Tomography (MV‐CBCT).

Methods:

Experiments were performed with a prototype multi‐layer imager (MLI) which has higher detective efficiency and lower noise characteristics than conventional Electronic Portal Imaging Devices (EPIDs). Images of a solid water phantom were acquired at 2.5 MV, 6MV and 6MV without flattening filter (FFF). The following materials were placed within a stack of solid water: aluminum, copper and gold. Material separation was assessed based on Contrast‐to‐Noise Ratio (CNR) of the weighted image, formed by a weighted subtraction of the images from two layers of the MLI. A range of weighting factors were investigated for material separation.

Results:

CNR can be minimized for each material by appropriate selection of the subtraction weighting factor. This is equivalent to a selective subtraction of specific materials from the image. Using multiple layers simultaneously also decreases the dose requirement and removes any registration errors. The minimum CNR for aluminum, copper and gold at the weighted image formed with 2.5MV was obtained at weighting factors equal to 0.92, 0.76 and 0.64 respectively. The corresponding values at 6MVFFF were 0.99, 0.92 and 0.78 respectively.

Conclusion:

In the current work, an MV spectral imaging feasibility study was attempted using a novel multi‐layer prototype EPID imager. Initial results suggest that material separation based on spectral differences between different layers is possible. This spectral imaging technique has potential advantages in MV‐CBCT for real‐time target tracking, patient set‐up imaging and adaptive radiotherapy.

The project was supported, partially, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446‐01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health
WE‐DE‐202‐03: Modeling of Biological Processes ‐ What Happens After Early Molecular Damage?
Authors: McMahon S.
Published: July 2016

Radiation therapy for the treatment of cancer has been established as a highly precise and effective way to eradicate a localized region of diseased tissue. To achieve further significant gains in the therapeutic ratio, we need to move towards biologically optimized treatment planning. To achieve this goal, we need to understand how the radiation‐type dependent patterns of induced energy depositions within the cell (physics) connect via molecular, cellular and tissue reactions to treatment outcome such as tumor control and undesirable effects on normal tissue.

Several computational biology approaches have been developed connecting physics to biology. Monte Carlo simulations are the most accurate method to calculate physical dose distributions at the nanometer scale, however simulations at the DNA scale are slow and repair processes are generally not simulated. Alternative models that rely on the random formation of individual DNA lesions within one or two turns of the DNA have been shown to reproduce the clusters of DNA lesions, including single strand breaks (SSBs), double strand breaks (DSBs) without the need for detailed track structure simulations. Efficient computational simulations of initial DNA damage induction facilitate computational modeling of DNA repair and other molecular and cellular processes. Mechanistic, multiscale models provide a useful conceptual framework to test biological hypotheses and help connect fundamental information about track structure and dosimetry at the sub‐cellular level to dose‐response effects on larger scales.

In this symposium we will learn about the current state of the art of computational approaches estimating radiation damage at the cellular and sub‐cellular scale. How can understanding the physics interactions at the DNA level be used to predict biological outcome? We will discuss if and how such calculations are relevant to advance our understanding of radiation damage and its repair, or, if the underlying biological processes are too complex for a mechanistic approach. Can computer simulations be used to guide future biological research? We will debate the feasibility of explaining biology from a physicists’ perspective.

Learning Objectives:

Understand the potential applications and limitations of computational methods for dose‐response modeling at the molecular, cellular and tissue levels

Learn about mechanism of action underlying the induction, repair and biological processing of damage to DNA and other constituents

Understand how effects and processes at one biological scale impact on biological processes and outcomes on other scales

J. Schuemann, NCI/NIH grantsS. McMahon, Funding: European Commission FP7 (grant EC FP7 MC‐IOF‐623630)
WE‐DE‐206‐03: MRI Image Formation ‐ Slice Selection, Phase Encoding, Frequency Encoding, K‐Space, SNR
Authors: Lin C.
Published: July 2016

Magnetic resonance imaging (MRI) has become an essential part of clinical imaging due to its ability to render high soft tissue contrast. Instead of ionizing radiation, MRI use strong magnetic field, radio frequency waves and field gradients to create diagnostic useful images. It can be used to image the anatomy and also functional and physiological activities within the human body. Knowledge of the basic physical principles underlying MRI acquisition is vitally important to successful image production and proper image interpretation.

This lecture will give an overview of the spin physics, imaging principle of MRI, the hardware of the MRI scanner, and various pulse sequences and their applications. It aims to provide a conceptual foundation to understand the image formation process of a clinical MRI scanner.

Learning Objectives:

Understand the origin of the MR signal and contrast from the spin physics level.

Understand the main hardware components of a MRI scanner and their purposes

Understand steps for MR image formation including spatial encoding and image reconstruction

Understand the main kinds of MR pulse sequences and their characteristics.
WE‐DE‐206‐04: MRI Pulse Sequences ‐ Spin Echo, Gradient Echo, EPI, Non‐Cartesia
Authors: Pooley R.
Published: July 2016

Magnetic resonance imaging (MRI) has become an essential part of clinical imaging due to its ability to render high soft tissue contrast. Instead of ionizing radiation, MRI use strong magnetic field, radio frequency waves and field gradients to create diagnostic useful images. It can be used to image the anatomy and also functional and physiological activities within the human body. Knowledge of the basic physical principles underlying MRI acquisition is vitally important to successful image production and proper image interpretation.

This lecture will give an overview of the spin physics, imaging principle of MRI, the hardware of the MRI scanner, and various pulse sequences and their applications. It aims to provide a conceptual foundation to understand the image formation process of a clinical MRI scanner.

Learning Objectives:

Understand the origin of the MR signal and contrast from the spin physics level.

Understand the main hardware components of a MRI scanner and their purposes

Understand steps for MR image formation including spatial encoding and image reconstruction

Understand the main kinds of MR pulse sequences and their characteristics.
WE‐DE‐209‐03: Spirometric Motion Management System
Authors: Hadley S.
Published: July 2016

Breast radiation therapy is associated with some risk of lung toxicity as well as cardiac toxicity for left‐sided cases. Radiation doses to the lung and heart can be reduced by using the deep inspiration breath hold (DIBH) technique, in which the patient is simulated and treated during the deep inspiration phase of the breathing cycle. During DIBH, the heart is usually displaced posteriorly, inferiorly, and to the right, effectively expanding the distance between the heart and the breast/chest wall. As a result, the distance between the medial treatment field border and heart/lung is increased. Also, in a majority of DIBH patients, the air drawn into the thoracic cavity increases the total lung volume.

The DIBH was discussed by an AAPM Task Group 10 years ago in the AAPM TG 76 report. However, DIBH is still not the standard of care in many clinics, which may be partially due to challenges associated with its implementation. Therefore, this seccion will focus primarily on how to clinically implement four different DIBH techniques: (1) Active Breathing Control, (2) Spirometric Motion Management, (3) 3D Surface Image‐Guided, and (4) Self‐held Breath Control with Respiratory Monitoring and Feedback Guidance.

Learning Objectives:

Describe the physical displacement of the heart and the change in lung volume during DIBH and discuss dosimetric consequences of those changes.

Provide an overview of the technical aspects.

Describe work flow for patient simulation and treatment.

Give an overview of commissioning and routine.

Provide practical tips for clinical implementation.
WE‐DE‐207B‐01: Optimization for Contrast‐Enhanced Spectral Mammography Based On Photon‐Counting Detectors
Authors: Ding H , Molloi S
Published: July 2016

Purpose:

To investigate the feasibility of optimizing the imaging parameters for contrast‐enhanced spectral mammography based on Si strip photon‐counting detectors.

Methods:

A computer simulation model using polyenergetic spectra from a tungsten anode x‐ray tube and a Si‐based photon‐counting detector was evaluated for contrast‐enhanced spectral mammography. The simulation traces the emission of photons from the x‐ray source, attenuation through the breast and subsequent absorption in the detector. The breast was modeled as a mixture of adipose and mammary gland tissues with a breast density of 30%. A 4 mm iodine signal with a concentration of 4 mg/ml was used to simulate the enhancement of a lesion. Quantum efficiency of the detector was calculated based on the effective attenuation length in the Si strips. The figure‐of‐merit (FOM), which was defined as the decomposed iodine signal‐to‐noise ratio (SNR) with respect to the square root of the mean glandular dose (MGD), was chosen to optimize the imaging parameters, in terms of beam energy, splitting energy, and pre‐filtrations for breast of various thicknesses and densities.

Results:

The optimal imaging parameters, which lead to the highest FOM, were found at a beam energy of 45 kVp with a splitting energy at 34 keV for an averaged breast thickness of 4 cm with a standard 0.75 mm Al pre‐filtration. The optimal tube voltage varied slightly from 46 to 44 kVp as the breast thickness increases from 2 to 8 cm. The optimal tube voltage decreased to 42 kVp when the Al pre‐filtration was increased to 3 mm.

Conclusion:

This simulation study predicted the optimal imaging parameters for application of photon‐counting spectral mammography to contrast‐enhanced imaging. The simulation results laid the ground work for future phantom and clinical studies.

Grant funding from Philips Medical Systems.
WE‐DE‐207B‐03: Influence of Local Anatomical Variations On Detection of Multifocal and Multicentric Breast Cancer
Authors: Wen G , Markey M , Park S
Published: July 2016

Purpose:

We employed a novel model observer to assess the impact of local anatomic variations on the detection of multiple breast tumors depicted on mammograms. We expect the study to be valuable for future task‐based assessments and optimizations of x‐ray based breast imaging techniques (e.g., digital breast tomosynthesis for diagnosis of multifocal multicentric breast cancer (MMBC)).

Methods:

Regions of interest (ROIs) from four different sets of clustered lumpy background simulations were extracted as the image background. A random number of circular Gaussians were inserted to simulate cases with multicentric lesions. The task of the model observer was to perform a multiple‐lesion detection task, making both image‐level and location‐specific detection decisions based on the overall information from individual ROIs and their interactions. The detectability at each of the possible signal location was measured using channelized Hotelling observers with a novel implementation of partial least squares channels. The power law exponent β of local anatomical noise power spectrum, and spatial covariances K within the ROIs were computed to represent local background variations. The relationships between β, K and the detectability were evaluated.

Results:

β and/or K were different across the ROIs. Location‐specific signal‐to‐noise ratio (SNR) results showed statistically significant correlations between β, K and the detectability. Specifically, a ROI with a higher value of β, and/or K with larger and more variable off‐diagonal elements was associated with a lower SNR at that ROI. These results also demonstrate the potential of the model observer to adapt to the variations in anatomical backgrounds.

Conclusion:

We conducted a model observer study to explore the influence of local anatomical backgrounds on detecting MMBC. The study suggests that the optimal imaging settings may need to be adjusted when the clinical task of interest changes (e.g., find only the largest tumor versus find every tumor).

This work is supported by National Science Foundation (NSF) Award CBET‐1445713.
WE‐DE‐207B‐08: Towards Standardization of X‐Ray Filters in Digital Mammography‐Enabled Breast Tomosynthesis Systems
Authors: Shrestha S , Vedantham S , Karellas A
Published: July 2016

Purpose:

In digital breast tomosynthesis (DBT) systems capable of digital mammography (DM), Al filters are used during DBT and K‐edge filters during DM. The potential for standardizing the x‐ray filters with Al, instead of K‐edge filters, was investigated with intent to reduce exposure duration and to promote a simpler system design.

Methods:

Analytical computations of the half‐value thickness (HVT) and the photon fluence per mAs (photons/mm2/mAs) for K‐edge filters (50µm Rh; 50µm Ag) were compared with Al filters of varying thickness. Two strategies for matching the HVT from K‐edge and Al filtered spectra were investigated: varying the kVp for fixed Al thickness, or varying the Al thickness at matched kVp. For both strategies, Al filters were an order of magnitude thicker than K‐edge filters. Hence, Monte Carlo simulations were conducted with the GEANT4 toolkit to determine if the scatter‐to‐primary ratio (SPR) and the point spread function of scatter (scatter PSF) differed between Al and K‐edge filters.

Results:

Results show the potential for replacing currently used Kedge filters with Al. For fixed Al thickness (700µm), ±1 kVp and +(1–3) kVp change, matched HVT of Rh and Ag filtered spectra. At matched kVp, Al thickness range (650,750)µm and (750,860)µm matched the HVT from Rh and Ag filtered spectra. Photon fluence/mAs with Al filters were 1.5–2.5 times higher, depending on kVp and Al thickness, compared to K‐edge filters. Although Al thickness was an order higher than K‐edge filters, neither the SPR nor the scatter PSF differed from K‐edge filters.

Conclusion:

The use of Al filters for digital mammography is potentially feasible. The increased fluence/mAs with Al could decrease exposure duration for the combined DBT+DM exam and simplify system design. Effect of x‐ray spectrum change due to Al filtration on radiation dose, signal, noise, contrast and related metrics are being investigated.

Funding support: Supported in part by NIH R21CA176470 and R01CA195512. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.
WE‐DE‐207B‐10: Library‐Based X‐Ray Scatter Correction for Dedicated Cone‐Beam Breast CT: Clinical Validation
Authors: Shi L , Vedantham S , Karellas A , Zhu L
Published: July 2016

Purpose:

Scatter contamination is detrimental to image quality in dedicated cone‐beam breast CT (CBBCT), resulting in cupping artifacts and loss of contrast in reconstructed images. Such effects impede visualization of breast lesions and the quantitative accuracy. Previously, we proposed a library‐based software approach to suppress scatter on CBBCT images. In this work, we quantify the efficacy and stability of this approach using datasets from 15 human subjects.

Methods:

A pre‐computed scatter library is generated using Monte Carlo simulations for semi‐ellipsoid breast models and homogeneous fibroglandular/adipose tissue mixture encompassing the range reported in literature. Projection datasets from 15 human subjects that cover 95 percentile of breast dimensions and fibroglandular volume fraction were included in the analysis. Our investigations indicate that it is sufficient to consider the breast dimensions alone and variation in fibroglandular fraction does not significantly affect the scatter‐to‐primary ratio. The breast diameter is measured from a first‐pass reconstruction; the appropriate scatter distribution is selected from the library; and, deformed by considering the discrepancy in total projection intensity between the clinical dataset and the simulated semi‐ellipsoidal breast. The deformed scatter‐distribution is subtracted from the measured projections for scatter correction. Spatial non‐uniformity (SNU) and contrast‐to‐noise ratio (CNR) were used as quantitative metrics to evaluate the results.

Results:

On the 15 patient cases, our method reduced the overall image spatial non‐uniformity (SNU) from 7.14%±2.94% (mean ± standard deviation) to 2.47%±0.68% in coronal view and from 10.14%±4.1% to 3.02% ±1.26% in sagittal view. The average contrast to noise ratio (CNR) improved by a factor of 1.49±0.40 in coronal view and by 2.12±1.54 in sagittal view.

Conclusion:

We demonstrate the robustness and effectiveness of a library‐based scatter correction method using patient datasets with large variability in breast dimensions and composition. The high computational efficiency and simplicity in implementation make this attractive for clinical implementation.

Supported partly by NIH R21EB019597, R21CA134128 and R01CA195512.The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
WE‐DE‐207B‐12: Scatter Correction for Dedicated Cone Beam Breast CT Based On a Forward Projection Model
Authors: Shi L , Vedantham S , Karellas A , Zhu L
Published: July 2016

Purpose:

The image quality of dedicated cone‐beam breast CT (CBBCT) is fundamentally limited by substantial x‐ray scatter contamination, resulting in cupping artifacts and contrast‐loss in reconstructed images. Such effects obscure the visibility of soft‐tissue lesions and calcifications, which hinders breast cancer detection and diagnosis. In this work, we propose to suppress x‐ray scatter in CBBCT images using a deterministic forward projection model.

Method:

We first use the 1st‐pass FDK‐reconstructed CBBCT images to segment fibroglandular and adipose tissue. Attenuation coefficients are assigned to the two tissues based on the x‐ray spectrum used for imaging acquisition, and is forward projected to simulate scatter‐free primary projections. We estimate the scatter by subtracting the simulated primary projection from the measured projection, and then the resultant scatter map is further refined by a Fourier‐domain fitting algorithm after discarding untrusted scatter information. The final scatter estimate is subtracted from the measured projection for effective scatter correction. In our implementation, the proposed scatter correction takes 0.5 seconds for each projection. The method was evaluated using the overall image spatial non‐uniformity (SNU) metric and the contrast‐to‐noise ratio (CNR) with 5 clinical datasets of BI‐RADS 4/5 subjects.

Results:

For the 5 clinical datasets, our method reduced the SNU from 7.79% to 1.68% in coronal view and from 6.71% to 3.20% in sagittal view. The average CNR is improved by a factor of 1.38 in coronal view and 1.26 in sagittal view.

Conclusion:

The proposed scatter correction approach requires no additional scans or prior images and uses a deterministic model for efficient calculation. Evaluation with clinical datasets demonstrates the feasibility and stability of the method. These features are attractive for clinical CBBCT and make our method distinct from other approaches.

Supported partly by NIH R21EB019597, R21CA134128 and R01CA195512.The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
WE‐C‐TOUR‐T‐01: Microdosimeters for Therapy
Authors: Das I.
Published: July 2016

Tour Leader: Indra Das, NYU Langone Medical Center, New York, NY

Tour Guides:

Hsui Ai, Indiana University School of Medicine, Indianapolis, IN

Paulina Galvis, NYU Langone Medical Center, New York, NY

Olga Volotoskova, NYU Langone Medical Center, New York, NY

Participating Vendors:

IBA

PTW – New York

RTI Electronics, Inc.

Standard Imaging, Inc.

Sun Nuclear Corporation

Small fields are increasing used in specialized radiation treatments such as Gammaknife, Cyberknife, Tomotherapy, IMRT, VMAT, SRS and SBRT. Due to small field size electron transport creates lateral electronic disequilibrium and thus dosimetry could be very difficult. Microdetectors are used for small field dosimetry which will be discussed in preface of this tour as below:

Understanding small field e.g. meaning and definition of small field

IAEA definition and approach

Characteristics of microdetectors in terms of perturbation, recombination, correction

Suitability of microdetectors in small field dosimetry
WE‐F‐204‐01: Some Lessons from a Career in Research
Authors: Mohan R.
Published: July 2016

In recent years heavy focus has been placed on clinical careers in medical physics, and the pathways to such careers are well‐known and well‐described. For the future advancement of the field of medical physics, it is necessary the focus also include research‐oriented careers. It is important for the younger generation of medical physicists to know that there are many career opportunities in research, and that it is quite possible to build a successful career in which research is a major component. We will hear from those who have already blazed a trail of success in academic and industry research careers in order to understand some of the most important decisions to make and skills to develop in order to be successful. Topics such as how to build a research program, how to develop your own lab, and how to initiate good collaborations are not generally taught explicitly but are integral to succeeding in a research career. Skills such as these are often best learned from the experiences of others. The challenges encountered in transitioning from graduate student to faculty member, securing the first grant, and moving into an industry research position will be highlighted and discussed.

Learning Objectives:

Identify career paths built on interest in research

Understand basic steps to starting and maintaining a research career

Identify differences between research careers in academia and industry

M. Giger, support by NIH and COI will be listed. J. Dempsey, ViewRay, Inc. has provided financial support for my research. R. Mohan, support from NIH.
WE‐FG‐206‐09: Association of Prostate Volumes with Restricted Diffusion and Prostate Cancer Aggressiveness
Authors: Tschudi Y
Published: July 2016

Purpose:

To create an automatic workflow for evaluation of thresholds of restricted diffusion, based on Apparent Diffusion Coefficient (ADC) values in multiparametric (mp)MRI of the prostate. To investigate the association of these volumes with biopsy Gleason Score (GS).

Methods:

Patients with prostate cancer, imaged on 3T Discovery MR750 (GE, Waukesha, WI) magnet were selected from departmental database based on the presence of mpMRI exam. All subsequent analyses were performed using Java plugins in MIM (MIM, Cleveland, Ohio). Prostate, peripheral zone (PZ) and urethra were contoured manually for each patient. The procedure defines three volumes on ADC in PZ, related to high (<T1 µm2/s), medium (<T2 µm2/s), and low risk (<T3 µm2/s), where T1<T2<T3. The thresholds for each patient were set 200 µm2/s apart, i.e. T2=T1+200 µm2/s and T3=T1+400 µm2/s. The thresholds were offset by 100 µm2/s for the transition zone (TZ). Pixels with ADC<400 µm2/s and within the urethra are excluded from the analysis. The correlations between (i) ADC volume sizes; and (ii) the fractions of the volumes from the prostate volume (ADC/Prostate) and GS were investigated with Spearman correlation.

Results:

mpMRIs from 139 the analysis. The correlations between (i) ADC volume sizes; and (ii) the fractions of the volumes from the prostate volume (ADC/Prostate) and GS were investigated with Spearman correlation.

Results:

mpMRIs from 139 selected patients with mpMRI acquired between May, 2012 and February, 2016, were analyzed. Six values for T1 were investigated starting from 750 to 950 µm2/s with step of 50 µm2/s. All correlations between ADC volumes and ADC/Prostate volumes and GS were significant. The following thresholds for PZ/TZ: 950/700, 1100/900 and 1200/1100 performed the best for high, mid and low risk. The correlation coefficients of of ADC high and ADC high/Prostate were 0.45 and 0.469 with p‐values <<0.00001.

Conclusion:

To the best of our knowledge, this is the first report which associates volumes of low diffusion and GS.
WE‐FG‐206‐11: Measuring Mechanical Biomarkers of Liver Tumors Using Tagged MRI
Authors: Xia X , Zhu M , Sun L , Sacks M , Genin G , Hu C , Guo L , Feng Y
Published: July 2016

Purpose:

Early detection of liver cancer improves patient prognosis dramatically. We propose a novel approach in which liver deformation is tracked during the cardiac cycle using tagged MRI. Strain concentrations that arise from material mismatches between the tumor and non‐tumor regions were compared in patients with liver tumors.

Methods:

Tagged MR images were acquired from four liver cancer patients in the coronal plane in a 3.0T scanner. In each cardiac cycle, a total of 25 time frames were acquired with a FOV of 289×359 mm2 and a resolution of 180×224. Lagrangian strain fields were calculated from displacement fields estimated from the tag lines using the HARP algorithm. Tumor and non‐tumor regions of interest (ROIs) were delineated manually by a trained physician. The non‐tumor ROI was defined as a region surrounding the tumor but away from the left lobe adjacent to the heart. A one‐tail paired T‐test was used to compare the strain distributions from the tumor and non‐tumor ROIs.

Results:

The strain fields reflected heterogeneity of liver mechanical properties and the nature of the loading. The left lobe had the highest strain magnitude because of its proximity to the heart. However, the maximum principal strain (E1) of the tumor ROI was significantly lower than that of the non‐tumor ROI.

Conclusion:

Cardiac contraction produced measureable strains in the liver, with statistically significant differences between tumor and non‐tumor ROIs. Lower strains in the tumor ROIs, observed for all patients, reflected the higher stiffness of the tumor, and showed the potential of using biomechanical properties as a biomarker for tumor diagnosis. Future work will focus on the question of whether tumors that are not visible to a trained physician can be identified using these strain fields.

Funding supports are provided by grant BK20140356 (YF) from Jiangsu Province, grant 61503267 (YF) from National Natural Science Foundation, and by grant K511701515 (YF) from Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
WE‐F‐209‐01: Radiation Safety Surveys in Diagnostic Imaging
Authors: Dillon C.
Published: July 2016

Over the past few years, numerous Accreditation Bodies, Regulatory Agencies, and State Regulations have implemented requirements for Radiation Safety Surveys following installation or modification to x‐ray rooms. The objective of this session is to review best practices in performing radiation safety surveys for both Therapy and Diagnostic installations, as well as a review of appropriate survey instruments.

This session will be appropriate for both therapy and imaging physicists who are looking to increase their working knowledge of radiation safety surveys.

Learning Objectives:

Identify Appropriate Survey Meters for Radiation Safety Surveys

Develop best practices for Radiation Safety Surveys for Therapy units that include common areas of concern.

Develop best practices for Radiation Safety Surveys of Diagnostic and Nuclear Medicine rooms.

Identify acceptable dose levels and the factors that affect the calculations associated with performing Radiation Safety Surveys.
WE‐F‐209‐02: Radiation Safety Surveys of Linear Accelerators
Authors: Martin M.
Published: July 2016

Over the past few years, numerous Accreditation Bodies, Regulatory Agencies, and State Regulations have implemented requirements for Radiation Safety Surveys following installation or modification to x‐ray rooms. The objective of this session is to review best practices in performing radiation safety surveys for both Therapy and Diagnostic installations, as well as a review of appropriate survey instruments.

This session will be appropriate for both therapy and imaging physicists who are looking to increase their working knowledge of radiation safety surveys.

Learning Objectives:

Identify Appropriate Survey Meters for Radiation Safety Surveys

Develop best practices for Radiation Safety Surveys for Therapy units that include common areas of concern.

Develop best practices for Radiation Safety Surveys of Diagnostic and Nuclear Medicine rooms.

Identify acceptable dose levels and the factors that affect the calculations associated with performing Radiation Safety Surveys.