bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐H‐201‐04: Panel Discussion Member
Authors: Dobbins J.
Published: July 2016

The New New Symposium is a symposium for members relatively new to the organization to learn about the organizational structure and operational procedures of the society; how decisions are made, how the council and committee leadership is appointed and operates, opportunities for volunteer involvement, and a brief overview of the services and efforts provided by the HQ staff and the website. Attendees will hear from council chairs, key staff and chairs, and members with volunteer experience.

After the symposium a social hour ensues with opportunities to interact with key AAPM members. The New Member Symposium is a (free) ticket option when you register online for the Annual Meeting. And don't forget registrants receive one (free) ticket for a beverage of your choice during the social afterwards.
TU‐H‐BRC‐05: Stereotactic Radiosurgery Optimized with Orthovoltage Beams
Authors: Fagerstrom J , Bender E , Culberson W
Published: July 2016

Purpose:

To achieve improved stereotactic radiosurgery (SRS) dose distributions using orthovoltage energy fluence modulation with inverse planning optimization techniques.

Methods:

A pencil beam model was used to calculate dose distributions from the institution's orthovoltage unit at 250 kVp. Kernels for the model were derived using Monte Carlo methods as well as measurements with radiochromic film. The orthovoltage photon spectra, modulated by varying thicknesses of attenuating material, were approximated using open‐source software. A genetic algorithm search heuristic routine was used to optimize added tungsten filtration thicknesses to approach rectangular function dose distributions at depth. Optimizations were performed for depths of 2.5, 5.0, and 7.5 cm, with cone sizes of 8, 10, and 12 mm.

Results:

Circularly‐symmetric tungsten filters were designed based on the results of the optimization, to modulate the orthovoltage beam across the aperture of an SRS cone collimator. For each depth and cone size combination examined, the beam flatness and 80–20% and 90–10% penumbrae were calculated for both standard, open cone‐collimated beams as well as for the optimized, filtered beams. For all configurations tested, the modulated beams were able to achieve improved penumbra widths and flatness statistics at depth, with flatness improving between 33 and 52%, and penumbrae improving between 18 and 25% for the modulated beams compared to the unmodulated beams.

Conclusion:

A methodology has been described that may be used to optimize the spatial distribution of added filtration material in an orthovoltage SRS beam to result in dose distributions at depth with improved flatness and penumbrae compared to standard open cones. This work provides the mathematical foundation for a novel, orthovoltage energy fluence‐modulated SRS system.
TU‐H‐BRC‐06: Temperature Simulation of Tungsten and W25Re Targets to Deliver High Dose Rate 10 MV Photons
Authors: Wang J , Trovati S , Loo B , Maxim P , Borchard P , Fahrig R
Published: July 2016

Purpose:

To study the impact of electron beam size, target thickness, and target temperature on the ability of the flattening filter‐free mode (FFF) treatment head to deliver high‐dose‐rate irradiations.

Methods:

The dose distribution and transient temperature of the X‐ray target under 10 MeV electron beam with pulse length of 5 microseconds, and repetition rate of 1000 Hz was studied. A MCNP model was built to calculate the percentage depth dose (PPD) distribution in a water phantom at a distance of 100 cm. ANSYS software was used to run heat transfer simulations. The PPD and temperature for both tungsten and W25Re targets for different electron beam sizes (FHWM 0.2, 0.5, 1 and 2 mm) and target thickness (0.2 to 2 mm) were studied.

Results:

Decreasing the target thickness from 1 mm to 0.5 mm, caused a surface dose increase about 10 percent. For both target materials, the peak temperature was about 1.6 times higher for 0.5 mm electron beam compared to the 1 mm beam after reaching their equilibrium. For increasing target thicknesses, the temperature rise caused by the first pulse is similar for all thicknesses, however the temperature difference for subsequent pulses becomes larger until a constant ratio is reached. The target peak temperature after reaching equilibrium can be calculated by adding the steady state temperature and the amplitude of the temperature oscillation.

Conclusion:

This work indicates the potential to obtain high dose rate irradiation by selecting target material, geometry and electron beam parameters. W25Re may not outperformed tungsten when the target is thick due to its relatively low thermal conductivity. The electron beam size only affects the target temperature but not the PPD. Thin target is preferred to obtain high dose rate and low target temperature, however, the resulting high surface dose is a major concern.

NIH funding:R21 EB015957‐01; DOD funding:W81XWH‐13‐1‐0165

BL, PM, PB, and RF are founders of TibaRay, Inc. BL is also a borad member. BL and PM have received research grants from Varian Medical System, Inc. and RaySearch Laboratory. RF is an employee of Siemens Healthcare GmbH
TU‐H‐BRA‐01: The Physics of High Power Radiofrequency Isolation in a Novel Compact Linear Accelerator Based MRI Guided Radiation Therapy System
Authors: Lamb J , Low D , Mutic S , Shvartsman S , Chmielewski T , Fought G , Sharma A , Dempsey J
Published: July 2016

Purpose:

To develop a method for isolating the radiofrequency waves emanating from linear accelerator components from the magnetic resonance imaging (MRI) system of an integrated MRI‐linac.

Methods:

An MRI‐guided radiation therapy system has been designed that integrates a linear accelerator with simultaneous MR imaging. The radiofrequency waves created by the accelerating process would degrade MR image quality, so a method for containing the radiofrequency waves and isolating the MR imager from them was developed. The linear accelerator radiofrequency modulator was placed outside the room, so a filter was designed to eliminate the radiofrequency corresponding to the proton Larmour frequency of 14.7 MHz. Placing the radiofrequency emitting components in a typical Faraday cage would have reduced the radiofrequency emissions, but the design would be susceptible to small gaps in the shield due to the efficiency of the Faraday cage reflecting internal radiofrequency emissions. To reduce internal radiofrequency reflections, the Faraday cage was lined with carbon fiber sheets. Carbon fiber has the property of attenuating the radiofrequency energy so that the overall radiofrequency field inside the Faraday cage is reduced, decreasing any radiofrequency energy emitted from small gaps in the cage walls.

Results:

Within a 1.2 MHz band centered on the Larmor frequency, the radiofrequency (RF) leakage from the Faraday cage was measured to be −90 dB with no RF on, −40 dB with the RF on and no shield, returning to −90 dB with the RF on and shields in place. The radiofrequency filter attenuated the linear accelerator modulator emissions in the 14.7 MHz band by 70 dB.

Conclusions:

One of the major challenges in designing a compact linear accelerator based MRI‐guided radiation therapy system, that of isolating the high power RF system from the MRI, has been solved. The measured radiofrequency emissions are sufficiently small to enable system integration.

This research was funded by ViewRay, Inc., Oakwood, OH
TU‐H‐BRA‐04: A Novel Superconducting Magnet Design for Optimized Patient Access and Minimal SSD for Use in a Linac‐MR Hybrid
Authors: Yaghoobpour Tari S , Wachowicz K , Fallone B
Published: July 2016

Purpose:

A prototype rotating hybrid MR imaging system and linac has been developed to allow for simultaneous imaging and radiation delivery parallel to B0. However, the design of a compact magnet capable of rotation in a small vault with sufficient patient access and a typical clinical source‐to‐surface distance (SSD) is challenging. This work presents a novel superconducting magnet design that allows for a reduced SSD and ample patient access by moving the superconducting coils to the side of the yoke. The yoke and pole‐plate structures are shaped to direct the magnetic flux appropriately.

Methods:

The surface of the pole plate for the magnet assembly is optimized. The magnetic field calculations required in this work are performed with the 3D finite element method software package Opera‐3D. Each tentative design strategy is virtually modeled in this software package and externally controlled by MATLAB, with its key geometries defined as variables. The particle swarm optimization algorithm is used to optimize the variables subject to the minimization of a cost function. At each iteration, Opera‐3D will solve the magnetic field solution over a field‐of‐view suitable for MR imaging and the degree of field uniformity will be assessed to calculate the value of the cost function associated with that iteration.

Results:

An optimized magnet assembly that generates a homogenous 0.2T magnetic field over an ellipsoid with large axis of 30 cm and small axes of 20 cm is obtained.

Conclusion:

The distinct features of this model are the minimal distance between the yoke's top and the isocentre and the improved patient access. On the other hand, having homogeneity over an ellipsoid give us a larger field‐of‐view, essential for geometric accuracy of the MRI system. The increase of B0 from 0.2T in the present model to 0.5T is the subject of future work.

Funding Sources: Alberta Innovates ‐ Health Solutions (AIHS)| Disclosure and Conflict of Interest: B. Gino Fallone is a co‐founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta biplanar linac MR for commercialization).
TU‐H‐BRA‐05: A System Design for Integration of An Interior MRI and a Linear Accelerator
Authors: Mao W , Wang G
Published: July 2016

Purpose:

MRI is a highly desirable modality to guide radiation therapy but it is difficult to combine a conventional MRI scanner directly with a linear accelerator (linac). An interior MRI (iMRI) concept has been proposed to acquire MRI images within a small field of view only covering targets and immediate surrounding tissues. The objective of this project is to design an interior MRI system to work with a linac using a magnet to provide a field around 0.2T in a cube of 20cm per side, and perform image reconstruction with a slightly inhomogeneous static magnetic fields.

Methods:

All the results are simulated using a commercially available software package, FARADY. In our design, a ring structure holds the iMRI system and also imbeds a linac treatment head. The ring is synchronized to the linac gantry rotation. Half of the ring is made of steel and becomes a magnetic flux return path (yoke) so that a strong magnetic field will be limited inside the iron circuit and fringe fields will be very weak. In order to increase the static magnetic field homogeneity, special steel magnet boots or tips were simulated. Three curved boots were designed based on two‐dimensional curves: arc, parabola and hyperbola.

Results:

Different boot surfaces modify magnetic field distributions differently. With the same pair of neodymium‐iron‐boron (NdFeB) magnets, the magnetic induction at the centers are 0.217T, 0.201T, 0.204T, and 0.212T for flat, arc, parabola and hyperbola boots, respectively. The hyperbola boots lead to the most homogeneous results, the static magnetic field deviations are within 0.5% in a cube of 20cm, and can be further improved using shimming techniques.

Conclusion:

This study supports the concept of an iMRI design. Successful development of iMRI will provide crucial information for tumor delineation in radiation therapy.
TU‐H‐202‐04: The VAMPIRE Challenge: Preliminary Results From a Multi‐Institutional Study of CT Ventilation Image Accuracy
Authors: Kipritidis J.
Published: July 2016

CT ventilation imaging is an exciting functional imaging modality that combines four‐dimensional computed tomography (4DCT) and deformable image registration (DIR) to provide exquisite ventilation maps of the lung. CT ventilation imaging can be used for:

Functional avoidance in thoracic radiation therapy,

Imaging longitudinal changes in regional lung function for treatment assessment and adaptation,

Image‐assisted diagnosis of non‐oncologic respiratory diseases.

CT ventilation imaging uses CT, a predominantly anatomic imaging modality, and through imaging processing creates functional images. CT ventilation imaging provides functional images that are higher resolution, faster and cheaper to perform than the clinical standard, SPECT. Indeed the number of CT ventilation abstracts presented at the AAPM meeting has been doubling every two years. With the world's‐first clinical trial of CT ventilation functional image‐guided radiation therapy now underway, the first dedicated scientific symposium will educate and stimulate AAPM members from both radiology and radiation oncology.

This symposium will compare the foundations of CT ventilation imaging with competing MRI, PET and SPECT ventilation imaging methods, and details the first clinical trial of CT ventilation imaging for functional avoidance in lung cancer radiation therapy. The spatial‐temporal nature of pulmonary ventilation, response maps to radiation and the design of predictive models will be presented. Validation efforts and challenges will also be discussed, from clinical outcome correlations in single time point and longitudinal studies, to cross‐modality image comparisons in the first multi‐institutional CT ventilation imaging challenge.

The panel will discuss the future role of CT ventilation imaging, and what level of physiologic validation is needed for applications in radiation oncology and beyond.

Learning Objectives:

Learn the principles of CT ventilation imaging and how ventilation images are acquired with MRI, PET and SPECT

Understand the methods used to benchmark CT ventilation and the correlations between CT ventilation imaging and clinical outcomes

Recognize the clinical applications of CT ventilation imaging in radiation oncology and beyond

Australian NHMRC Fellowship. Australian NSW Cancer Institute Fellowship.; Y. Vinogradskiy, The authors acknowledge NIH R01CA200817 grant and Stat of Colorado grant.; T. Yamamoto, This study was supported in part by the American Cancer Society and the Dean of the University of California Davis School of Medicine (ACS IRG‐95‐125‐13). Philips Radiation Oncology Systems loaned us a research version of the Pinnacle3 treatment planning system.; J. Bayouth, Funding support from NCI

R01 CA166703; J. Kipritidis, This work has been supported by a Cancer Institute NSW Early Career Fellowship and an NHMRC Australia Fellowship.

No commercial funding was received for this work.
TU‐H‐207A‐02: Relative Importance of the Various Factors Influencing the Accuracy of Monte Carlo Simulated CT Dose Index
Authors: Marous L , Morgan A , Dong F , Muryn J , Liptak C , Primak A , Li X
Published: July 2016

Purpose:

Monte Carlo simulation is a frequently used technique for assessing patient dose in CT. The accuracy of a Monte Carlo program is often validated using the standard CT dose index (CTDI) phantoms by comparing simulated and measured CTDI100. To achieve good agreement, many input parameters in the simulation (e.g., energy spectrum and effective beam width) need to be determined. However, not all the parameters have equal importance. Our aim was to assess the relative importance of the various factors that influence the accuracy of simulated CTDI100.

Methods:

A Monte Carlo program previously validated for a clinical CT system was used to simulate CTDI100. For the standard CTDI phantoms (32 and 16 cm in diameter), CTDI100 values from central and four peripheral locations at 70 and 120 kVp were first simulated using a set of reference input parameter values (treated as the truth). To emulate the situation in which the input parameter values used by the researcher may deviate from the truth, additional simulations were performed in which intentional errors were introduced into the input parameters, the effects of which on simulated CTDI100 were analyzed.

Results:

At 38.4‐mm collimation, errors in effective beam width up to 5.0 mm showed negligible effects on simulated CTDI100 (<1.0%). Likewise, errors in acrylic density of up to 0.01 g/cm3 resulted in small CTDI100 errors (<2.5%). In contrast, errors in spectral HVL produced more significant effects: slight deviations (±0.2 mm Al) produced errors up to 4.4%, whereas more extreme deviations (±1.4 mm Al) produced errors as high as 25.9%. Lastly, ignoring the CT table introduced errors up to 13.9%.

Conclusion:

Monte Carlo simulated CTDI100 is insensitive to errors in effective beam width and acrylic density. However, they are sensitive to errors in spectral HVL. To obtain accurate results, the CT table should not be ignored.

This work was supported by a Faculty Research and Development Award from Cleveland State University.
TU‐H‐206‐07: Assessment of Geometric Distortion in EPI with a SPAMM Tagged Acquisition
Authors: Hwang K , Meier J , Yung J , Stafford R
Published: July 2016

Purpose:

Echo planar imaging (EPI) is known to exhibit gross geometric distortion caused by multiple factors, including B0 inhomgeneity and transient eddy currents. However, diffusion weighted (DW) EPI has become indispensable for diagnosis and therapy assessment. We propose a methodology for quantifying distortion in EPI sequences that does not require the use of dedicated spatial accuracy phantoms, enabling flexibility in phantom design for QA of distortion effects in EPI protocols.

Methods:

The proposed methodology utilizes a saturation technique known as Spatial Modulation of Magnetization (SPAMM) that tags the imaging subject with saturated grid lines. Originally intended for tracking cardiac motion, these grids are applied to assess differences between diffusion weighting directions and b‐values, or against a more geometrically robust sequence such as fast spin echo (FSE). The saturation preparation sequence consists of binomially weighted (e.g. 1‐3‐3‐1) pulses interleaved with gradient blips along the frequency encode direction, followed by the same sequence with gradient blips in the phase encode direction. Three phantoms were assessed with these sequences: a spherical head‐sized phantom, a large shimming phantom, and a modified PET ACR phantom that included compartments of water, air, oil, and Teflon. Each phantom was acquired with three sequences using parameters from a clinically appropriate protocol (22 cm head or 46 cm abdomen): a conventional DW‐EPI sequence (3 DW directions), and both the DW‐EPI and FSE sequences with tagging. Differences in grid locations were visualized with minimum intensity projection between images, and measured using intersecting locations on the grids.

Results:

Grid lines were clearly visualized on tagged images and enabled quantification of distortions. Maximum eddy current induced errors of 10.8 to 14.8 mm were observed in areas away from isocenter with DW gradients applied in various directions.

Conclusion:

SPAMM tagging provides a promising mechanism for assessing spatial distribution of distortion in EPI sequences.
TU‐H‐209‐02: Quality Assurance and QMP for Brachytherapy Treatment Delivery and Treatment Planning System
Authors: Chilukuri M.
Published: July 2016

Learnings Objectives:

Although brachytherapy is the oldest form of radiation therapy, the rapid advancement of the methods of dose calculation, treatment planning and treatment delivery pushes us to keep updating our knowledge and experience to new procedures all the time. Our purpose is to present the newest applicators used in Accelerated Partial Breast Irradiation (APBI) and the techniques of using them for a maximum effective treatment. Our objective will be to get the user familiar with the Savi, Contura and ML Mammosite from the detailed description and measurements to cavity eval and choice or size, to acceptance tests and use of each.

At the end of the session the attendants will be able to assist at the scanning of the patient for the first treatment, decide on the proper localization and immobilization devices, import the scans in the treatment planning system, perform the structure segmentation, reconstruct the catheters and develop a treatment plan using inverse planning (IPSA) or volume optimization. The attendant should be able to evaluate the quality of a treatment plan according to the ABS protocols and B39 after this session.

Our goal is that all the attendants to gain knowledge of all the quality assurance procedures required to be performed prior to a treatment, at the beginning of a treatment day, weekly, monthly and annualy on the remote afterloader, the treatment planning system and the secondary check system. We will provide tips for a consistent treatment delivery of the 10 fractions in a BID (twice daily) regimen.
TU‐H‐209‐03: Planning and Treatment Delivery for APBI Using Savi, Contura and ML Mammosite
Authors: Pella S.
Published: July 2016

Learnings Objectives:

Although brachytherapy is the oldest form of radiation therapy, the rapid advancement of the methods of dose calculation, treatment planning and treatment delivery pushes us to keep updating our knowledge and experience to new procedures all the time. Our purpose is to present the newest applicators used in Accelerated Partial Breast Irradiation (APBI) and the techniques of using them for a maximum effective treatment. Our objective will be to get the user familiar with the Savi, Contura and ML Mammosite from the detailed description and measurements to cavity eval and choice or size, to acceptance tests and use of each.

At the end of the session the attendants will be able to assist at the scanning of the patient for the first treatment, decide on the proper localization and immobilization devices, import the scans in the treatment planning system, perform the structure segmentation, reconstruct the catheters and develop a treatment plan using inverse planning (IPSA) or volume optimization. The attendant should be able to evaluate the quality of a treatment plan according to the ABS protocols and B39 after this session.

Our goal is that all the attendants to gain knowledge of all the quality assurance procedures required to be performed prior to a treatment, at the beginning of a treatment day, weekly, monthly and annualy on the remote afterloader, the treatment planning system and the secondary check system. We will provide tips for a consistent treatment delivery of the 10 fractions in a BID (twice daily) regimen.
TU‐H‐207B‐02: Funding (NCI) for Radiomics
Authors: Jacobs P.
Published: July 2016

Research and development in radiomics for precision medicine have been advancing at a rapid pace, and can be extended to eventually be mature enough for integration into clinical practice. To facilitate advances in this field, investigators need updated information on research funding, regulatory matters, and clinical translation efforts. In this special radiomics symposium, the attendee will learn of various novel funding mechanisms – both past and present – that have been used to support a number of quantitative imaging and radiomics research and resource infrastructures. In addition, a regulatory presentation will be given to provide the attendee with an understanding of when a radiomics tool might require FDA clearance or approval, and with what supporting performance data. We will end with insights from a clinical radiologist who is greatly involved in quantitative imaging in order to enable the attendee to appreciate the needs and subtleties involved in moving radiomics into the clinical workflow.

J. Boone, This is a memorial and not a funded event.
TU‐H‐CAMPUS‐JeP1‐03: Results From a Multi Institution Study On Image Quality Impact in Deformable Image Registration
Authors: Loi G , Fusella M , Lanzi E , Fiandra C , Orlani G , Lucio F , Strolin S , Gino E , Mezzenga E , Roggio A , Cagni E , Vigorito S
Published: July 2016

Purpose:

Various commercial algorithms for deformable image registration (DIR) were tested to investigate their accuracy and robustness, against image noise and artifacts.

Methods:

Ten institutions with five available commercial solutions provided data to assess the agreement of DIR‐propagated ROIs with automatically drawn ROIs considered as ground‐truth for the comparison. The DIR algorithms were tested on real patient data (pelvis). A Deformation was applied to the reference data set (CTref) using the ImSimQA software, a (CTeval) and seven CBCT images with increasing level of noise and capping artifacts were simulated. Every center performed DIR between CTref, and the deformed datasets. The noise was defined as standard deviation normalized to signal in an homogeneous medium, artefacts as the difference of mean HU values between the central and peripheral region of an homogeneous medium. To investigate the relationship between image quality parameters and the DIR results a three way ANOVA was performed on logit function of DICE index.

Results:

Based on 480 DIR‐mapped ROIs the ANOVA test states that centers, ROIs and Image Quality are significant predictors of DIR performances. DIR conducted on CBCT simulated images is significant worst of the ones obtained on the original images. Increasing noise and artefacts didn't affect significantly DIR performances. Considering a limit for Dice Index of 0.75 one center underperform this level. DIR resulted significantly more accurate in rectal contours propagation.

Conclusion:

This work illustrates the effect of image noise to DIR performances in a ground truth provided scenario. Clinical issues like ART or Dose Accumulation need accurate and robust DIR software using CBCT images. For the range of artefacts and noise explored in this experiment the commercial software appeared to be robust. One centre didn't satisfy the minimum accuracy requirement showing that QA is mandatory to implement clinically DIR for ROI propagation.
TU‐H‐CAMPUS‐TeP1‐01: Variable‐Beam Fractionation for SAbR
Authors: Modiri A , Sawant A
Published: July 2016

Purpose:

In current conventionally‐fractionated as well as hypofractionated 3D conformal radiotherapy (CRT), the same beam arrangement is employed from fraction to fraction. We challenge this notion and postulate that by varying the beam arrangement between fractions we can achieve greater sparing of organs at risk (OARs) while maintaining PTV coverage. We use an inverse planning strategy using a swarm intelligence‐based global optimization algorithm to exploit the additional degree of freedom represented by inter‐fractional variation in beam angles.

Methods:

To evaluate our variable‐beam fractionation (VBF) method, a 10‐beam ITV‐based conformal stereotactic ablative radiotherapy (CRT‐SAbR) plan was optimized. In the clinical plan, 54 Gy was delivered to a 41cc lung tumor over 3 fractions. In VBF, each original clinically‐assigned beam was multiplied to a bundle of n α‐degree‐spaced beams, n being number of fractions. Selection of α was a compromise between retaining similar tumor irradiation and separating inline OAR sub‐regions. We optimized the beam fluence weights setting an upper limit for beam delivery duration (and implicitly, monitor units) along with clinical organ‐based dose‐volume constraints. Zero weights were allowed so that the optimization algorithm could remove unnecessary beams. All fractions in final plan had to deliver identical monitor units (MU) while satisfying a soft constraint on having no more than one beam from every n‐beam bundle in each fraction. α was 10 degrees and the dose rate was 600 MU/min.

Results:

The VBF plan achieved significantly superior OAR sparing compared to the clinical internal target volume (ITV)‐based plan. Setting maximum beam delivery duration to 13 seconds (well within breath‐hold range), Esophagus Dmax, Heart Dmax, Spinal cord Dmax and Lung V13 were improved by 25%, 81%, 0% and 27%, respectively.

Conclusion:

We investigated a simple approach to inter‐fractional VBF planning and demonstrated its potential in reducing dose to OARs.

This work was partially supported through research funding from National Institutes of Health (R01CA169102) and Varian Medical Systems, Palo Alto, CA, USA.
TU‐H‐CAMPUS‐JeP3‐01: Towards Robust Adaptive Radiation Therapy Strategies
Authors: Boeck M , Eriksson K , Forsgren A , Hardemark B
Published: July 2016

Purpose:

To set up a framework combining robust treatment planning with adaptive reoptimization in order to maintain high treatment quality, to respond to interfractional variations and to identify those patients who will benefit the most from an adaptive fractionation schedule.

Methods:

We propose adaptive strategies based on stochastic minimax optimization for a series of simulated treatments on a one‐dimensional patient phantom. The plan should be able to handle anticipated systematic and random errors and is applied during the first fractions. Information on the individual geometric variations is gathered at each fraction. At scheduled fractions, the impact of the measured errors on the delivered dose distribution is evaluated. For a patient that receives a dose that does not satisfy specified plan quality criteria, the plan is reoptimized based on these individual measurements using one of three different adaptive strategies. The reoptimized plan is then applied during future fractions until a new scheduled adaptation becomes necessary. In the first adaptive strategy the measured systematic and random error scenarios and their assigned probabilities are updated to guide the robust reoptimization. The focus of the second strategy lies on variation of the fraction of the worst scenarios taken into account during robust reoptimization. In the third strategy the uncertainty margins around the target are recalculated with the measured errors.

Results:

By studying the effect of the three adaptive strategies combined with various adaptation schedules on the same patient population, the group which benefits from adaptation is identified together with the most suitable strategy and schedule. Preliminary computational results indicate when and how best to adapt for the three different strategies.

Conclusion:

A workflow is presented that provides robust adaptation of the treatment plan throughout the course of treatment and useful measures to identify patients in need for an adaptive treatment strategy.
TU‐H‐CAMPUS‐JeP3‐02: Automated Dose Accumulation and Dose Accuracy Assessment for Online Or Offline Adaptive Replanning
Authors: Chen G , Ahunbay E , Li X
Published: July 2016

Purpose:

With introduction of high‐quality treatment imaging during radiation therapy (RT) delivery, e.g., MR‐Linac, adaptive replanning of either online or offline becomes appealing. Dose accumulation of delivered fractions, a prerequisite for the adaptive replanning, can be cumbersome and inaccurate. The purpose of this work is to develop an automated process to accumulate daily doses and to assess the dose accumulation accuracy voxel‐by‐voxel for adaptive replanning.

Methods:

The process includes the following main steps: 1) reconstructing daily dose for each delivered fraction with a treatment planning system (Monaco, Elekta) based on the daily images using machine delivery log file and considering patient repositioning if applicable, 2) overlaying the daily dose to the planning image based on deformable image registering (DIR) (ADMIRE, Elekta), 3) assessing voxel dose deformation accuracy based on deformation field using predetermined criteria, and 4) outputting accumulated dose and dose‐accuracy volume histograms and parameters. Daily CTs acquired using a CT‐on‐rails during routine CT‐guided RT for sample patients with head and neck and prostate cancers were used to test the process.

Results:

Daily and accumulated doses (dose‐volume histograms, etc) along with their accuracies (dose‐accuracy volume histogram) can be robustly generated using the proposed process. The test data for a head and neck cancer case shows that the gross tumor volume decreased by 20% towards the end of treatment course, and the parotid gland mean dose increased by 10%. Such information would trigger adaptive replanning for the subsequent fractions. The voxel‐based accuracy in the accumulated dose showed that errors in accumulated dose near rigid structures were small.

Conclusion:

A procedure as well as necessary tools to automatically accumulate daily dose and assess dose accumulation accuracy is developed and is useful for adaptive replanning.

Partially supported by Elekta, Inc.
TU‐H‐CAMPUS‐TeP3‐01: Gold Nanoparticle‐Enhanced Radiation Therapy in In Vitro A549 Lung Carcinoma: Studies in Both Traditional Monolayer and Three Dimensional Cell Culture Models
Authors: Oumano M , Ngwa W , Celli J , Arnoldussen M , Hanlon J , Hempstead J , Petrovic L
Published: July 2016

Purpose:

To measure the increase in in vitro radiosensitivity for A549 lung carcinoma cells due to gold nanoparticle (GNP) radiation dose enhancement in both traditional monolayer and three dimensional (3D) cell culture models.

Methods:

A γH2AX immunofluorescence assay is performed on monolayer A549 cell culture and quantitatively analyzed to measure the increase in double strand breaks (DSBs) resulting from GNP dose enhancement. A clonogenic survival assay (CSA) is then performed on monolayer A549 cell culture to assess true viability after treatment. And lastly, another γH2AX assay is performed on 3D A549 multicellular nodules overlaid on a bed of growth factor reduced matrigel to measure dose response in a model that better recapitulates treatment response to actual tumors in vivo.

Results:

The first γH2AX assay performed on the monolayer cell culture shows a significant increase in DSBs due to GNP dose enhancement. The maximum average observed increase in normalized fluorescent intensity for monolayer cell culture is 171% for the 6Gy‐treatment groups incubated in 0.556 mg Au/ml solution. The CSA performed on monolayer cell culture also shows considerable GNP dose enhancement. The maximum decrease in the normalized surviving fraction is 12% for the 4Gy‐treatment group incubated in 0.556 mg Au/ml. And lastly, the GNP dose enhancement is confirmed to be mitigated in three dimensional cell culture models as compared to the traditional monolayer model. The maximum average observed dose enhancement for 3D cell culture is 19% for the 6Gy‐treatment groups and incubated in 0.556 mg Au/ml.

Conclusion:

A marked increase in radiosensitivity is observed for A549 lung carcinoma cells when treated with GNPs plus radiation as opposed to radiation alone. Traditional monolayer cell culture also shows a much more pronounced radiation dose enhancement than 3D cell culture.
WE‐AB‐204‐08: Pathway to Developing D&I Program at AAPM
Authors: Higginbotham E.
Published: July 2016

Many efforts have been made to increase diversity in the science workforce. In order for us to be competitive in innovation and ingenuity we need to reach out to any source of intellectual talent. Having greater diversity can only increase the creativity in medical physics. In order for students to succeed academically they need role models and mentors with whom they can identify. Literature has shown that racial and ethnic diversity has both direct and indirect positive effects on the educational outcomes, career advancement and motivation of students. Diversity not only focuses on race, ethnicity and gender, but it can also include socioeconomic status, sexual orientation and more. Underrepresented populations have had low numbers over the years not only in medical physics but also in the sciences in general. With the rapidly changing face of our country we need to address how we attract and train the next generation of scientists to stay competitive. It is necessary to examine the role that diversity and inclusion play in the long term goals of institutions, workplaces and classrooms. To increase innovation we must engage people from all walks of life with different perspectives and life experiences to solve the problems that we will face. Diversity should be viewed as a strategy to achieve our goals instead of acts of good citizenship. Many of today's businesses and corporations have discovered that embracing diversity prepares future leaders in today's global market.

This lecture will provide insight to how differences within our society can drive innovation. We will provide an overview of the role diversity and inclusion plays in the clinic, education and research to develop the future workforce in medical physics.

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

The importance of developing education and research strategies for a global workforce.

How to develop a roadmap to diversity excellence within AAPM.
WE‐AB‐BRA‐07: Operating Room Quality Assurance (ORQA) for Spine Surgery Using Known‐Component 3D‐2D Image Registration
Authors: Uneri A , De Silva T , Goerres J , Jacobson M , Ketcha M , Reaungamornrat S , Kleinszig G , Vogt S , Khanna A , Wolinsky J , Siewerdsen J
Published: July 2016

Purpose:

Intraoperative x‐ray radiography/fluoroscopy is commonly used to qualitatively assess delivery of surgical devices (e.g., spine pedicle screws) but can fail to reliably detect suboptimal placement (e.g., breach of adjacent critical structures). We present a method wherein prior knowledge of the patient and surgical components is leveraged to match preoperative CT and intraoperative radiographs for quantitative assessment of 3D pose. The method presents a new means of operating room quantitative quality assurance (ORQA) that could improve quality and safety, and reduce the frequency of revision surgeries.

Methods:

The algorithm (known‐component registration, KC‐Reg) uses patient‐specific preoperative CT and parametrically defined surgical component models within a robust 3D‐2D registration method to iteratively optimize gradient similarity using the covariance matrix adaptation evolution strategy. Advances from previous work address key challenges to clinical translation: i) absolving the need for offline geometric calibration of the C‐arm; and ii) solving multiple component bodies simultaneously, thereby allowing QA in a single step (e.g., spinal construct with 4–20 screws), rather than sequential QA of each component. Performance was tested in a spine phantom with 10 pedicle screws, and first results from clinical studies are reported.

Results:

Phantom experiments demonstrated median target registration error (TRE) of (1.0±0.3) mm at the screw tip and (0.7°±0.4°) in angulation. The simultaneous multi‐body registration approach improved TRE from the previous (sequential) method by 42%, reduced outliers, and fits into the natural workflow. Initial application of KC‐Reg in clinical data shows TRE of (2.5±4.5) mm and (4.7°±0.5°).

Conclusion:

The KC‐Reg algorithm offers a potentially valuable method for quantitative QA of the surgical product, using radiographic systems that are already within the surgical arsenal. For spine surgery, the method offers a near‐real‐time independent check on the quality of surgical product, facilitating immediate revision if necessary and potentially avoiding postoperative morbidity and/or revision surgery.

Gerhard Kleinszig and Sebastian Vogt are employees of Siemens Healthcare.
WE‐AB‐202‐05: Validation of Lung Stress Maps for CT‐Ventilation Imaging
Authors: Cazoulat G , Kipritidis J , Siva S , Hofman M , Jolly S , Matuszak M , Balter J , Keall P , Brock K
Published: July 2016

Purpose:

To date, lung CT‐ventilation imaging has been based on quantification of local breathing‐induced changes in Hounsfield Units (HU) or volume. This work investigates the use of a stress map resulting from a biomechanical deformable image registration (DIR) algorithm as a metric of the ventilation function.

Method:

Eight lung cancer patients presenting different kinds of ventilation defects were retrospectively analyzed. Additionally, to the 4DCT acquired for radiotherapy planning, five of them had PET and three had SPECT imaging following inhalation of Ga‐68 and Tc‐99m, respectively. For each patient, the inhale phase of the 4DCT was registered to the exhale phase using Morfeus, a biomechanical DIR algorithm based on the determination of boundary conditions on the lung surfaces and vessel tree. To take into account the heterogeneity of the tissue stiffness in the stress map estimation, each tetrahedral element of the finite‐element model was assigned a Young's modulus ranging from 60kPa to 12MPa, as a function of the HU in the inhale CT. The node displacements and element stresses resulting from the numerical simulation were used to generate three CT‐ventilation maps based on: (i) volume changes (Jacobian determinant), (ii) changes in HU, (iii) the maximum principal stress. The voxel‐wise correlation between each CT‐ventilation map and the PET or SPECT V image was computed in a lung mask.

Results:

For patients with PET, the mean (min‐max) Spearman correlation coefficients r were: 0.33 (0.19–0.45), 0.36 (0.16–0.51) and 0.42 (0.21–0.59) considering the Jacobian, changes in HU and maximum principal stress, respectively. For patients with SPECT V, the mean r were: 0.12 (−0.12–0.43), 0.29 (0.22–0.45) and 0.33 (0.25–0.39).

Conclusion:

The maximum principal stress maps showed a stronger correlation with the ventilation images than the previously proposed Jacobian or change in HU maps. This metric thus appears promising for CT‐ventilation imaging.

This work was funded in part by NIH P01CA059827.
WE‐AB‐207A‐05: New Dosimetry Methods for CBCT
Authors: Lawless M , Anderson D , Culberson W , DeWerd L
Published: July 2016

Purpose:

To determine the absorbed dose to water in the moderately filtered (M‐series) x‐ray beams at the UWADCL and assess the feasibility of transferring this dose to water to a clinical CBCT environment.

Methods:

The dose was determined in the M‐series beams using three dosimetry

Methods:

the TG‐61 protocol, a 60Co absorbed dose to water calibration, and through the use of a Monte Carlo (MC) model of the x‐ray tube. The dose to water in the M‐series beams determined by the MC model was used to calibrate an ionization chamber. The calibrated chamber was used to measure the dose to water from a Varian CBCT system. The dose from the CBCT beams was also measured using the same methods as for the M‐series beams.

Results:

The measured surface doses in the M‐series beams determined by MC method and TG‐61 agreed within 3% for all beams. The dose to water a depth of 2 cm in the M‐series beams as determined by the TG‐61, 60Co, and MC methods, agreed within 2%. The dose in the CBCT beams was determined using the same methods as for the M‐series beams and using the newly determined x‐ray dose to water calibration coefficient. At the phantom surface, the dose values agreed within 1.5% and at a 2 cm depth the values agreed within 3%.

Conclusion:

New techniques to determine the absorbed dose to water in standard x‐ray beams were developed. The dose values were in good agreement with previous techniques, but with much lower uncertainties. The dose to water in the M‐series beams was used to calibrate an ionization chamber and the dose in the CBCT beams was measured using this calibration. The CBCT dose at a depth of 2 cm was measured in this manner and it agreed with other dose determination methods.
WE‐AB‐207A‐08: BEST IN PHYSICS (IMAGING): Advanced Scatter Correction and Iterative Reconstruction for Improved Cone‐Beam CT Imaging On the TrueBeam Radiotherapy Machine
Authors: Wang A , Paysan P , Brehm M , Maslowski A , Lehmann M , Messmer P , Munro P , Yoon S , Star‐Lack J , Seghers D
Published: July 2016

Purpose:

To improve CBCT image quality for image‐guided radiotherapy by applying advanced reconstruction algorithms to overcome scatter, noise, and artifact limitations

Methods:

CBCT is used extensively for patient setup in radiotherapy. However, image quality generally falls short of diagnostic CT, limiting soft‐tissue based positioning and potential applications such as adaptive radiotherapy. The conventional TrueBeam CBCT reconstructor uses a basic scatter correction and FDK reconstruction, resulting in residual scatter artifacts, suboptimal image noise characteristics, and other artifacts like cone‐beam artifacts. We have developed an advanced scatter correction that uses a finite‐element solver (AcurosCTS) to model the behavior of photons as they pass (and scatter) through the object. Furthermore, iterative reconstruction is applied to the scatter‐corrected projections, enforcing data consistency with statistical weighting and applying an edge‐preserving image regularizer to reduce image noise. The combined algorithms have been implemented on a GPU. CBCT projections from clinically operating TrueBeam systems have been used to compare image quality between the conventional and improved reconstruction methods. Planning CT images of the same patients have also been compared.

Results:

The advanced scatter correction removes shading and inhomogeneity artifacts, reducing the scatter artifact from 99.5 HU to 13.7 HU in a typical pelvis case. Iterative reconstruction provides further benefit by reducing image noise and eliminating streak artifacts, thereby improving soft‐tissue visualization. In a clinical head and pelvis CBCT, the noise was reduced by 43% and 48%, respectively, with no change in spatial resolution (assessed visually). Additional benefits include reduction of cone‐beam artifacts and reduction of metal artifacts due to intrinsic downweighting of corrupted rays.

Conclusion:

The combination of an advanced scatter correction with iterative reconstruction substantially improves CBCT image quality. It is anticipated that clinically acceptable reconstruction times will result from a multi‐GPU implementation (the algorithms are under active development and not yet commercially available).

All authors are employees of and (may) own stock of Varian Medical Systems.
WE‐AB‐207A‐10: Transmission Characteristics of a Two Dimensional Antiscatter Grid Prototype for CBCT
Authors: Altunbas C , Kavanagh B , Miften M
Published: July 2016

Purpose:

Scattered radiation remains to be a major contributor to image quality degradation in CBCT. To address the scatter problem, a focused, 2D antiscatter grid (2DASG) prototype was designed, and fabricated using additive manufacturing processes. Its scatter and primary transmission properties were characterized using a linac mounted CBCT system.

Methods:

The prototype 2DASG was composed of rectangular grid holes separated by tungsten septa, and has a grid pitch of 2.91 mm, grid ratio of 8, and a septal thickness of 0.1 mm. Each grid hole was aligned or focused towards the x‐ray source in half‐fan (i.e. offset detector) geometry of the Varian TrueBeam CBCT system. Scatter and primary transmission experiments were performed by using acrylic blocks and the beam‐stop method. Transmission properties of a radiographic ASG (1DASG) (grid ratio of 10) was also performed by using the identical setup.

Results:

At 30 cm phantom thickness, scatter to primary ratio (SPR) was 4.51 without any ASG device. SPR was reduced to 1.28 with 1DASG, and it was further reduced to 0.28 with 2DASG. Scatter transmission fraction (Ts) of 1DASG was 21%, and Ts was reduced to 5.8% with 2DASG. The average primary transmission fraction (Tp) of 1DASG was 70.6%, whereas Tp increased to 85.1% with 2DASG. Variation of Tp across 40 cm length (the long axis of flat panel detector) was 2.6%.

Conclusion:

When compared to conventional ASGs, the focused 2DASG can vastly improve scatter suppression and primary transmission performance. Due to precise alignment of 2DASG's grid holes with respect to beam divergence, high degree of primary transmission through the 2DASG was maintained across the full length of the prototype. We strongly believe that robust scatter rejection and primary transmission characteristics of our 2DASG can translate into both improved quantitative accuracy and soft tissue resolution in linac mounted CBCT systems.