bluuebunny/crossref_metadata_2025_split huggingface dataset:
WE‐H‐BRA‐01: BEST IN PHYSICS (THERAPY): Nano‐Dosimetric Kinetic Model for Variable Relative Biological Effectiveness of Proton and Ion Beams
Authors: Abolfath R , Bronk L , Helo Y , Schuemann J , Titt U. , Grosshans D , Mohan R 
Published: July 2016

Purpose:Recent clonogenic cell survival and γH2AX studies suggest proton relative biological effectiveness (RBE) may be a non‐linear function of linear energy transfer (LET) in the distal edge of the Bragg peak and beyond. We sought to develop a multiscale model to account for non‐linear response phenomena to aid in the optimization of intensity‐modulated proton therapy.Methods:The model is based on first‐principle simulations of proton track structures, including secondary ions, and an analytical derivation of the dependence on particle LET of the linear‐quadratic (LQ) model parameters α and β. The derived formulas are an extension of the microdosimetric kinetic (MK) model that captures dissipative track structures and non‐Poissonian distribution of DNA damage at the distal edge of the Bragg peak and beyond. Monte Carlo simulations were performed to confirm the non‐linear dose‐response characteristics arising from the non‐Poisson distribution of initial DNA damage.Results:In contrast to low LET segments of the proton depth dose, from the beam entrance to the Bragg peak, strong deviations from non‐dissipative track structures and Poisson distribution in the ionization events in the Bragg peak distal edge govern the non‐linear cell response and result in the transformation α=(1+c_1 L) α_x+2(c_0 L+c_2 L^2)(1+c_1 L) β_x and β=(1+c_1 L)^2 β_x. Here L is the charged particle LET, and c_0,c_1, and c_2 are functions of microscopic parameters and can be served as fitting parameters to the cell‐survival data. In the low LET limit c_1, and c_2 are negligible hence the linear model proposed and used by Wilkins‐Oelfke for the proton treatment planning system can be retrieved. The present model fits well the recent clonogenic survival data measured recently in our group in MDACC.Conclusion:The present hybrid method provides higher accuracy in calculating the RBE‐weighted dose in the target and normal tissues.
WE‐H‐207B‐01: Commissioning and QC
Authors: Stanescu T. 
Published: July 2016

In recent years, steady progress has been made towards the implementation of MRI in external beam radiation therapy for processes ranging from treatment simulation to in‐room guidance. Novel procedures relying mostly on MR data are currently implemented in the clinic. This session will cover topics such as (a) commissioning and quality control of the MR in‐room imagers and simulators specific to RT, (b) treatment planning requirements, constraints and challenges when dealing with various MR data, (c) quantification of organ motion with an emphasis on treatment delivery guidance, and (d) MR‐driven strategies for adaptive RT workflows. The content of the session was chosen to address both educational and practical key aspects of MR guidance.

Learning Objectives:
Good understanding of MR testing recommended for in‐room MR imaging as well as image data validation for RT chain (e.g. image transfer, filtering for consistency, spatial accuracy, manipulation for task specific);
Familiarity with MR‐based planning procedures: motivation, core workflow requirements, current status, challenges;
Overview of the current methods for the quantification of organ motion;
Discussion on approaches for adaptive treatment planning and delivery.T. Stanescu ‐ License agreement with Modus Medical Devices to develop a phantom for the quantification of MR image system‐related distortions.; T. Stanescu, N/A
TH‐A‐204‐02: Part II ‐ Worldwide Radiation Metrology
Authors: McEwen M. 
Published: July 2016

The ICRU is currently finalizing a report on key data for radiation dosimetry. This multi‐year review has resulted in a number of recommendations regarding “fundamental” data that are used in dosimetry related to radiation therapy. This educational session will explain the background for the ICRU committee's work, the content and conclusions of the report and the impact on outputs, including NIST primary standards, ADCL calibration coefficients and clinical reference dosimetry. Parameters and beam modalities potentially affected by this report include:The mean excitation energy, I, for graphite, air, and water, The average energy required to create an ion pair in dry air (commonly referred to as W/e), The uncertainty in the determination of air kerma in kV x‐rays The absolute value of Co‐60 and Cs‐137 primary standards and the dissemination of calibration coefficients, The determination of air kerma strength for Ir‐192 HDR brachytherapy sources Ion chamber kQ factors for linac MV beams Ion chamber kQ factors for proton beams.The changes in reference dosimetry that would result from adoption of the ICRU recommendations are of the order of 0.5% to 1%, an effect that will not impact clinical dose delivery but will be detectable in the clinical setting.This session will also outline how worldwide metrology is coordinated through the Convention of the Meter and therefore how the international dosimetry community will proceed with adopting these recommendations so that uniformity from country to country in reference dosimetry is maintained. Timelines and communications methods will also be discussed to ensure that users, such as clinical medical physicists, are not surprised when their chamber's calibration coefficient apparently changes.

Learning Objectives:
Understand the background for the ICRU committee's work on key dosimetry data.
Understand the proposed changes to key data and the impacts on reference dosimetry.
Understand the methodology and timeline for adoption of the ICRU recommendations.
TH‐AB‐201‐07: Filmless Treatment Localization QA for the CyberKnife System
Authors: Gersh J , Noll M 
Published: July 2016

Purpose:Accuray recommends daily evaluation of the treatment localization and delivery systems (TLS/TDS) of the CyberKnife. The vendor‐provided solution is a Winston‐Lutz‐type test that evaluates film shadows from an orthogonal beam pair (known as AQA). Since film‐based techniques are inherently inefficient and potentially inconsistent and uncertain, this study explores a method which provides a comparable test with greater efficiency, consistency, and certainty. This test uses the QAStereoChecker (QASC, Standard Imaging, Inc., Middleton, WI), a high‐resolution flat‐panel detector with coupled fiducial markers for automated alignment. Fiducial tracking is used to achieve high translational and rotational position accuracy.Methods:A plan is generated delivering five circular beams, with varying orientation and angular incidence. Several numeric quantities are calculated for each beam: eccentricity, centroid location, area, major‐axis length, minor‐axis length, and orientation angle. Baseline values were acquired and repeatability of baselines analyzed. Next, errors were induced in the path calibration of the CK, and the test repeated. A correlative study was performed between the induced errors and quantities measured using the QASC. Based on vendor recommendations, this test should be able to detect a TLS/TDS offset of 0.5mm.Results:Centroid shifts correlated well with induced plane‐perpendicular offsets (p < 0.01). Induced vertical shifts correlated best with the absolute average deviation of eccentricities (p < 0.05). The values of these metrics which correlated with the threshold of 0.5mm induced deviation were used as individual pass/fail criteria. These were then used to evaluate induced offsets which shifted the CK in all axes (a clinically‐realistic offset), with a total offset of 0.5mm. This test provided high and specificity and sensitivity.Conclusion:From setup to analysis, this filmless TLS/TDS test requires 4 minutes, as opposed to 15–20 minutes for film‐based methods. The techniques introduced can potentially isolate errors in individual joints of the CK robot.Spectrum Medical Physics, LLC of Greenville, SC has a consulting contract with Standard Imaging of Middleton, WI
TH‐AB‐BRB‐05: Using a Research Real‐Time Control Interface to Go Beyond Dynamic MLC Tracking
Authors: Nill S. 
Published: July 2016

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities.

Learning Objectives:
Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites.
Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement.
Understand methods for testing and validating delivery system performance.
Identify tools available on current delivery systems for implementation and control for such treatments.
Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.
TH‐CD‐206‐04: Learning Relevance Criterion for Multi‐Atlas Based Image Segmentation
Authors: Zhao T , Ruan D 
Published: July 2016

Purpose:It is important to effectively identify the subset of relevant training atlases in learning based segmentation. Since segmentation based geometry relevance between atlases and the target is inaccessible due to the unknown target segmentation, image feature based relevance criteria have to be used instead. This study aims to learn an image based criterion that best reflects the underlying geometry agreement.Methods:We learn the image‐based relevance criterion in the form of a Mahalanobis distance on linearly transformed image feature, which is specialized to image intensity in this work, and optimize such linear transformation. Given a set of atlases, i.e., image/segmentation pairs, a linear transformation is optimized to make the Mahalanobis distance small between the geometrically relevant atlases and large between the irrelevant pairs. Performance assessment and comparison with the commonly‐used mean square distance (MSD), a special case of the Mahalanobis distance with a trivial linear transform, are performed based on clinical brain MR images.Results:The proposed surrogate learning approach was validated with multi‐atlas based corpus callosum segmentation. Compared to MSD, our learned surrogate demonstrated superiority in selecting the geometrically relevant atlases. The learned surrogate yielded an improvement on the average pairwise Dice similarity coefficient (DSC) of the selected atlases from .004 to .007, and a corresponding improvement on the ultimate segmentation accuracy from .003 to .005, over an atlas subset size from 1 to 20.Conclusion:This work provides a systematic methodology to learn task‐specific criterion to select atlases for image segmentation, and demonstrates effectiveness in identifying the most relevant atlases. We are working on investigating various image features and extending to nonlinear transformations for further improvement.
TH‐CD‐206‐07: Determination of Patient‐Specific Myocardial Mass at Risk Using Computed Tomography Angiography
Authors: Hubbard L , Ziemer B , Malkasian S , Lipinski J , Sadeghi B , Javan H , Dertli B , Groves E , Molloi S 
Published: July 2016

Purpose:To evaluate the accuracy of a patient‐specific coronary perfusion territory assignment algorithm that uses CT angiography (CTA) and a minimum‐cost‐path approach to assign coronary perfusion territories on a voxel‐by‐voxel basis for determination of myocardial mass at risk.Methods:Intravenous (IV) contrast (370 mg/mL iodine, 25 mL, 7 mL/s) was injected centrally into five swine (35–45 kg) and CTA was performed using a 320‐slice CT scanner at 100 kVp and 200 mA. Additionally, a 4F catheter was advanced into the left anterior descending (LAD), left circumflex (LCX), and right coronary artery (RCA) and contrast (30 mg/mL iodine, 10 mL, 1.5 mL/s) was directly injected into each coronary artery for isolation of reference coronary perfusion territories. Semiautomatic myocardial segmentation of the CTA data was then performed and the centerlines of the LAD, LCX, and RCA were digitally extracted through image processing. Individual coronary perfusion territories were then assigned using a minimum‐cost‐path approach, and were quantitatively compared to the reference coronary perfusion territories.Results:The results of the coronary perfusion territory assignment algorithm were in good agreement with the reference coronary perfusion territories. The average volumetric assignment error from mitral orifice to apex was 5.5 ± 1.1%, corresponding to 2.1 ± 0.7 grams of myocardial mass misassigned for each coronary perfusion territory.Conclusion:The results indicate that accurate coronary perfusion territory assignment is possible on a voxel‐by‐voxel basis using CTA data and an assignment algorithm based on a minimum‐cost‐path approach. Thus, the technique can potentially be used to accurately determine patient‐specific myocardial mass at risk distal to a coronary stenosis, improving coronary lesion assessment and treatment.Conflict of Interest (only if applicable): Grant funding from Toshiba America Medical Systems.
TH‐CD‐206‐08: An Anthropopathic Deformable Phantom for Geometric and Dose Accumulation Accuracy Validation of Deformable Image Registration
Authors: Liao Y , Chen H , Chen J , Gu X , Zhen X , Zhou L 
Published: July 2016

Purpose:To design and construct a three‐dimensional (3D) anthropopathic abdominal phantom for evaluating deformable image registration (DIR) accuracy on images and dose deformation in adaptive radiation therapy (ART).Method:Organ moulds, including liver, kidney, spleen, stomach, vertebra and two metastasis tumors, are 3D printed using the contours from an ovarian cancer patient. The organ moulds are molded with deformable gels that made of different mixtures of polyvinyl chloride (PVC) and the softener dioctyl terephthalate. Gels with different densities are obtained by a polynomial fitting curve which describes the relation between the CT number and PVC‐softener blending ratio. The rigid vertebras are constructed by moulding with white cement. The final abdominal phantom is assembled by arranging all the fabricated organs inside a hollow dummy according to their anatomies and sealed with deformable gel with averaged CT number of muscle and fat. Geometric and dosimetric landmarks are embedded inside the phantom for spatial accuracy and dose accumulation accuracy studies. Three DIR algorithms available in the open source DIR toolkit‐DIRART, including the Demons, the Horn‐Schunck and Lucas‐Kanade method and the Level‐Set Motion method, are tested using the constructed phantom.Results:Viscoelastic behavior is observed in the constructed deformable gel, which serves as an ideal material for the deformable phantom. The constructed abdominal phantom consists of highly realistic anatomy and the fabricated organs inside have close CT number to its reference patient. DIR accuracy studies conducted on the constructed phantom using three DIR approaches indicate that geometric accuracy of a DIR algorithm has achieved does not guarantee accuracy in dose accumulation.Conclusions:We have designed and constructed an anthropopathic abdominal deformable phantom with satisfactory elastic property, realistic organ density and anatomy. This physical phantom is recyclable and can be used for routine validations of DIR geometric accuracy and dose accumulation accuracy in ART.This work is supported in part by grant from VARIAN MEDICAL SYSTEMS INC, the National Natural Science Foundation of China (no 81428019 and no 81301940), the Guangdong Natural Science Foundation (2015A030313302) and the 2015 Pearl River S&T Nova Program of Guangzhou (201506010096).
TH‐CD‐206‐11: An Ellipsoid Convex Enhancement Filter Based Computer‐Aided Diagnostic Framework of Intracranial Aneurysms in MRA Images
Authors: Jin Z , Arimura H , Kakeda S , Yamashita F , Sasaki M , Korogi Y 
Published: July 2016

Purpose:For early detections of asymptomatic intracranial aneurysms, computer aided diagnostic (CAD) frameworks of intracranial aneurysms in magnetic resonance angiography (MRA) images were developed with various enhancement filters. However, discrimination between aneurysms and false positive structures, such as bending or branching portions of vessels could still be a challenging task for the enhancement filters. Therefore, we focused on developing an ellipsoid convex enhancement (ECE) filter based CAD framework, which is capable of enhancing aneurysms while reducing the effect on bending and branching portions of vessels, for detection of intracranial aneurysm candidate.Methods:The proposed ECE filter was designed for selectively enhancing aneurysms with certain ellipsoid convex shapes, whose ratios of the shortest to longest diameters correspond to the ratio of reciprocals of the square roots of the first and third eigenvalues of Hessian matrices. This filter was applied to artificial images with Gaussian ellipsoid models and clinical MRA images of 30 patients (Male: 10, Female: 20; age: 48 to 86 years, mean: 69.2) with 31 unruptured aneurysms (longest diameter: 2.0 to 5.5 mm, mean: 3.7 mm) based on a leave‐one‐out‐by‐patient test.Results:The proposed ECE filter reduced the average contrast for false positive Gaussian ellipsoid models by 51.4%. The number of false positives per patient decreased from 41.1 to 22.8 at a sensitivity of 87% by using the ECE filter.Conclusion:The ellipsoid convex enhancement filter based CAD framework of intracranial aneurysms in MRA images would be useful by providing a higher contrast between aneurysms and false positive structures such as bending or branching portions of vessels.
TH‐CD‐206‐12: Image‐Based Motion Estimation for Plaque Visualization in Coronary Computed Tomography Angiography
Authors: Zhang X , Sisniega A , Zbijewski W , Contijoch F , McVeigh E , Stayman J 
Published: July 2016

Purpose:Visualization and quantification of coronary artery calcification and atherosclerotic plaque benefits from coronary artery motion (CAM) artifact elimination. This work applies a rigid linear motion model to a Volume of Interest (VoI) for estimating motion estimation and compensation of image degradation in Coronary Computed Tomography Angiography (CCTA).Methods:In both simulation and testbench experiments, translational CAM was generated by displacement of the imaging object (i.e. simulated coronary artery and explanted human heart) by ∼8 mm, approximating the motion of a main coronary branch. Rotation was assumed to be negligible. A motion degraded region containing a calcification was selected as the VoI. Local residual motion was assumed to be rigid and linear over the acquisition window, simulating motion observed during diastasis. The (negative) magnitude of the image gradient of the reconstructed VoI was chosen as the motion estimation objective and was minimized with Covariance Matrix Adaptation Evolution Strategy (CMAES).Results:Reconstruction incorporated the estimated CAM yielded signification recovery of fine calcification structures as well as reduced motion artifacts within the selected local region. The compensated reconstruction was further evaluated using two image similarity metrics, the structural similarity index (SSIM) and Root Mean Square Error (RMSE). At the calcification site, the compensated data achieved a 3% increase in SSIM and a 91.2% decrease in RMSE in comparison with the uncompensated reconstruction.Conclusion:Results demonstrate the feasibility of our image‐based motion estimation method exploiting a local rigid linear model for CAM compensation. The method shows promising preliminary results for the application of such estimation in CCTA. Further work will involve motion estimation of complex motion corrupted patient data acquired from clinical CT scanner.
TH‐CD‐209‐06: LET‐Based Adjustment of IMPT Plans Using Prioritized Optimization
Authors: Unkelbach J , Botas P , Qin N , Jia X , Giantsoudi D , Paganetti H 
Published: July 2016

Purpose:In‐vitro experiments suggest an increase in proton relative biological effectiveness (RBE) towards the end of range. However, proton treatment planning and dose reporting for clinical outcome assessment has been based on physical dose and constant RBE. Therefore, treatment planning for intensity‐modulated proton therapy (IMPT) is unlikely to transition radically to pure RBE‐based planning. We suggest a hybrid approach where treatment plans are initially created based on physical dose constraints and prescriptions, and are subsequently altered to avoid high linear energy transfer (LET) in critical structures while limiting the degradation of the physical dose distribution.Methods:To allow fast optimization based on dose and LET we extended a GPU‐based Monte‐Carlo code towards providing dose‐averaged LET in addition to dose for all pencil beams. After optimizing an initial IMPT plan based on physical dose, a prioritized optimization scheme is used to modify the LET distribution while constraining the physical dose objectives to values close to the initial plan. The LET optimization step is performed based on objective functions evaluated for the product of physical dose and LET (LETxD). To first approximation, LETxD represents a measure of the additional biological dose that is caused by high LET. Regarding optimization techniques, LETxD has the advantage of being a linear function of the pencil beam intensities.Results:The method is applicable to treatments where serial critical structures with maximum dose constraint are located in or near the target. We studied intra‐cranial tumors (high‐grade meningiomas, base‐of‐skull chordomas) where the target (CTV) overlaps with the brainstem and optic structures. Often, high LETxD in critical structures can be avoided while minimally compromising physical dose planning objectives.Conclusion:LET‐based re‐optimization of IMPT plans represents a pragmatic approach to bridge the gap between purely physical dose‐based and RBE‐based planning. It can be realized with fast GPU‐based Monte‐Carlo dose calculation.The project was in part supported by NIH grants U19 CA 021239‐36 and C06 CA 059267.