bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 dosimetryMethods: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 limitationsMethods: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.