bluuebunny/crossref_metadata_2025_split huggingface dataset:
WE‐H‐207A‐09: Theoretical Limits to Molecular Biomarker Detection Using Magnetic Nanoparticles
Authors: Weaver J 
Published: July 2016

Purpose:Estimate the limits of molecular biomarker detection using magnetic nanoparticle methods like in vivo ELISA.Methods:Magnetic nanoparticles in an alternating magnetic field produce a magnetization that can be detected at exceedingly low levels because the signal at the harmonic frequencies is uniquely produced by the nanoparticles. Because the magnetization can also be used to characterize the nanoparticle rotational freedom, the bound state can be found. If the nanoparticles are coated with molecules that bind the desired biomarker, the rotational freedom reflects the biomarker concentration. The irreducible noise limit is the thermal noise or Johnson noise of the tissue and the contrast that can be measured must be larger than that limit. The contrast produced is a function of the applied field and depends strongly on nanoparticle volume. We have estimated the contrast using a Langevin function of a single composite variable to approximate the full stochastic Langevin equation for nanoparticle dynamics.Results:The thermal noise for a bandwidth reasonable for spectroscopy suggests mid zeptomolar (10–21) to low attomolar (10–18) concentrations can be measured in a volume that is 10cm in scale. The suggested sensitivity is far below the physiologically concentrations of almost all critical biomarkers including cytokines (picomolar), hormones (nanomolar) and heat shock proteins.Conclusion:The sensitivity of in vivo ELISA concentration measurements should be sufficient to measure physiological concentrations of critical biomarkers like cytokines in vivo. Further the sensitivity should be sufficient to measure concentrations of other biomarkers that are six to eight orders of magnitude lower in concentration than immune signaling molecules like cytokines.NIH ‐ 1U54CA151662‐01Department of Radiology
WE‐H‐209‐01: Advances in Ultrasound Therapy
Authors: Hynynen K. 
Published: July 2016

Focused ultrasound has been shown to be the only method that allows noninvasive thermal coagulation of tissues and recently this potential has been explored for image‐guided drug delivery. In this presentation, the advances in ultrasound phased array technology for energy delivery, exposure monitoring and control will be discussed. Experimental results from novel multi‐frequency transmit/receive arrays will be presented. In addition, the feasibility of fully electronically focused and steered high power arrays with many thousands of transducer elements will be discussed. Finally, some of the recent clinical and preclinical results for the treatment of brain disease will be reviewed.

Learning Objectives:
Introduce FUS therapy principles and modern techniques
Discuss use of FUS for drug delivery
Cover the technology required to deliver FUS and monitor therapy
Present clinical examples of the uses of these techniquesThis research was supported by funding from The Canada Research Chair Program, Grants from CIHR and NIH (no. EB003268).; K. Hynynen, Canada Foundation for Innovation; Canadian Institutes of Health Research; Focused Ultrasound Surgery Foundation; Canada Research Chair Program; Natural Sciences and Engineering Research Council of Canada; Ontario Research Fund; National Institutes of Health; Canadian Cancer Society Research Institute; The Weston Brain Institute; Harmonic Medical; Focused Ultrasound Instruments
WE‐H‐207B‐02: MR‐Driven RT Planning
Authors: Cao M. 
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‐204‐01: Part I ‐ Key Data for Ionizing‐Radiation Dosimetry
Authors: Seltzer S. 
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‐201‐03: Characterization of Electron Beam Out‐Of‐Field Doses and Neutron Contamination from Modern Varian and Elekta Linear Accelerators
Authors: Cardenas C , Nitsch P , Kudchadker R , Howell R , Kry S 
Published: July 2016

Purpose:To investigate out‐of‐field electron doses and neutron production from electron beams from modern Varian and Elekta linear accelerators.Methods:Electron dose measurements were made using 10×10cm2 applicators on two Varian 21iXs, a Varian TrueBeam, and an Elekta Versa HD operating at energies from 6 to 20 MeV. Out‐of‐field dose profiles and PDD curves were measured in a Wellhofer water phantom using a Farmer chamber. Neutron measurements were made with a combination of moderator buckets and gold activation‐foils placed on the treatment couch at various locations in the patient plane on both the 21iX and Versa HD linear accelerators.Results:Electron doses were highest for the highest electron energies. Dose profile curves for the Varian units were found to be lower than those from the Versa HD unit, and were lower than photon beams. Elekta's dose profiles were higher and exhibited a second dose peak around 20–30 cm from central‐axis. Electron doses in this region (0.8–1.3% of dmax at central‐axis) were close to 5 times (2.5–4.8) greater than doses from photon beams with similar energies. Electron doses decreased sharply with depth before becoming nearly constant; the dose was found to decrease to a depth of approximately E(MeV)/4 in cm. Q‐values and neutron dose equivalent increased with energy and were typically higher on central‐axis. 18 MV photon beam neutron dose equivalents were greater than any electron beam, being approximately 40 times greater than for the 20 MeV electron beam (21iX).Conclusion:The Versa HD exhibited higher than expected out‐of‐field electron doses in comparison to typical radiotherapy photon beams. Fortunately, out‐of‐field electron doses can be substantially reduced by applying a water‐equivalent bolus with thickness of E(MeV)/4 in cm. Neutron contamination from clinical electron beams can be considered negligible in relation to photon beams but may need to be considered for special cases.This work was supported by Public Health Service Grant CA180803 awarded by the National Cancer Institute, United States Department of Health and Human Services.
TH‐AB‐201‐06: Examining the Influence of Humidity On Reference Ion Chamber Performance
Authors: Taank J , McEwen M 
Published: July 2016

Purpose:International dosimetry protocols require measurements made with a vented ionization chamber to be corrected for the influence of air density by using the standard temperature‐pressure correction factor. The effect of humidity, on the other hand, is generally ignored with the provision that the relative humidity is between certain limits (15% to 80%). However, there is little experimental data in the published literature as to the true effect of humidity on modern reference‐class ion chambers. This investigation used two different radiation beams – a Co‐60 irradiator and a Sr‐90 check source – to examine the effect of humidity on several versions of the standard Farmer‐type ion chamber.Methods:An environmental cabinet controlled the humidity. For the Co‐60 beam, the irradiation was external, whereas for the Sr‐90 measurements, the source itself was placed within the cabinet. Extensive measurements were carried out to ensure that the experimental setup provided reproducible readings. Four chamber types were investigated: IBA FC65‐G (×2), IBA FC65‐P, PTW30013 & Exradin A19. The different wall materials provided potentially different mechanical responses (i.e., in terms of expansion/contraction) to the water content in the air. The relative humidity was varied between 8 % and 97 % and measurements were made with increasing and decreasing humidity to investigate possible hysteresis effects.Results:Measurements in Co‐60 were consistent with the published data obtained with primary standard cavity chambers in ICRU Report 31. Ionization currents with Sr‐90 showed no dependence with the relative humidity, within the measurement uncertainties. Very good repeatability of the ionization current was obtained over successive wet/dry cycles, no hysteresis was observed, and there was no dependence on chamber type.Conclusion:This null result is very encouraging as it indicates that humidity has no significant effect on these particular types of ionization chambers, consistent with recommendations in current megavoltage dosimetry protocols.
TH‐AB‐BRB‐00: Research Opportunities with Digital Linear Accelerators
Authors: Sheng Ke 
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‐AB‐BRB‐03: 4n Radiotherapy
Authors: Sheng K. 
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‐AB‐BRA‐01: A Novel Doubly‐Focused Multileaf Collimator Design for MR‐Guided Radiation Therapy
Authors: Li H , Mutic S , Low D , Green O , Fought G , Kawrakow I , Sharma A , Shvartsman S , Dempsey J 
Published: July 2016

Purpose:To describe the physical and dosimetric properties of a novel double‐stack multileaf collimator (MLC).Methods:One of the compromises made in the MLC design has been to employ linear‐motion singly‐divergent shapes. Because the MLC leading edge moves linearly, it is rounded to provide a consistent, albeit compromised penumbra. The MLC employed in the new linac‐based MR‐IGRT unit is designed to be doubly focused in that each leaf moves in an arc centered at the source, and the sides of the leaves are machined such that they lie parallel to a line between the leaf edge and the source. The curvature of the MLC keeps motors and encoders in lower magnetic field. However, high spatial‐resolution leaves are difficult to manufacture to sufficiently tight tolerances and difficult to move due to restricted space on the gantry. Wider leaves alleviate this problem with less moving parts but the coarse resolution disallows treating very small lesions. This compromise has been overcome by splitting the MLC leaf bank into two sets, stacked one upon the other and offset half of a leaf width. The dosimetry has been simulated using Monte‐Carlo and a 6 MV linac in a 0.35 T magnetic field.Results:The combined MLC leaf set has a spatial resolution of effectively half of the leaf width, 4mm here. The dosimetry resolution and conformality are consistent with 4mm wide MLC assisted by inverse fluence modulation. Also, because each leaf junction is backed up by the stacked leaf that lies over the junction, the problem of tongue‐and‐groove dosimetry has been greatly reduced. The novel MLC design allows the use of more powerful leaf motors than would be otherwise possible if a single MLC bank is employed.Conclusions:The stacked MLC will provide highly conformal dose distributions suitable for stereotactic radiation therapy of small lesions.The research was funded by ViewRay, Inc.
TH‐AB‐BRA‐02: Automated Triplet Beam Orientation Optimization for MRI‐Guided Co‐60 Radiotherapy
Authors: Nguyen D , Thomas D , Cao M , O'Connor D , Lamb J , Sheng K 
Published: July 2016

Purpose:MRI guided Co‐60 provides daily and intrafractional MRI soft tissue imaging for improved target tracking and adaptive radiotherapy. To remedy the low output limitation, the system uses three Co‐60 sources at 120° apart, but using all three sources in planning is considerably unintuitive. We automate the beam orientation optimization using column generation, and then solve a novel fluence map optimization (FMO) problem while regularizing the number of MLC segments.Methods:Three patients—1 prostate (PRT), 1 lung (LNG), and 1 head‐and‐neck boost plan (H&NBoost)—were evaluated. The beamlet dose for 180 equally spaced coplanar beams under 0.35 T magnetic field was calculated using Monte Carlo. The 60 triplets were selected utilizing the column generation algorithm. The FMO problem was formulated using an L2‐norm minimization with anisotropic total variation (TV) regularization term, which allows for control over the number of MLC segments. Our Fluence Regularized and Optimized Selection of Triplets (FROST) plans were compared against the clinical treatment plans (CLN) produced by an experienced dosimetrist.Results:The mean PTV D95, D98, and D99 differ by −0.02%, +0.12%, and +0.44% of the prescription dose between planning methods, showing same PTV dose coverage. The mean PTV homogeneity (D95/D5) was at 0.9360 (FROST) and 0.9356 (CLN). R50 decreased by 0.07 with FROST. On average, FROST reduced Dmax and Dmean of OARs by 6.56% and 5.86% of the prescription dose. The manual CLN planning required iterative trial and error runs which is very time consuming, while FROST required minimal human intervention.Conclusions:MRI guided Co‐60 therapy needs the output of all sources yet suffers from unintuitive and laborious manual beam selection processes. Automated triplet orientation optimization is shown essential to overcome the difficulty and improves the dosimetry. A novel FMO with regularization provides additional controls over the number of MLC segments and treatment time.Varian Medical Systems; NIH grant R01CA188300; NIH grant R43CA183390.
TH‐CD‐206‐01: Expectation‐Maximization Algorithm‐Based Tissue Mixture Quantification for Perfusion MRI
Authors: Han H , Liang Z , Li L , Xing L 
Published: July 2016

Purpose:To investigate the feasibility of estimating the tissue mixture perfusions and quantifying cerebral blood flow change in arterial spin labeled (ASL) perfusion MR images.Methods:The proposed perfusion MR image analysis framework consists of 5 steps: (1) Inhomogeneity correction was performed on the T1‐ and T2‐weighted images, which are available for each studied perfusion MR dataset. (2) We used the publicly available FSL toolbox to strip off the non‐brain structures from the T1‐ and T2‐weighted MR images. (3) We applied a multi‐spectral tissue‐mixture segmentation algorithm on both T1‐ and T2‐structural MR images to roughly estimate the fraction of each tissue type ‐ white matter, grey matter and cerebral spinal fluid inside each image voxel. (4) The distributions of the three tissue types or tissue mixture across the structural image array are down‐sampled and mapped onto the ASL voxel array via a co‐registration operation. (5) The presented 4‐dimensional expectation‐maximization (4D‐EM) algorithm takes the down‐sampled three tissue type distributions on perfusion image data to generate the perfusion mean, variance and percentage images for each tissue type of interest.Results:Experimental results on three volunteer datasets demonstrated that the multi‐spectral tissue‐mixture segmentation algorithm was effective to initialize tissue mixtures from T1‐ and T2‐weighted MR images. Compared with the conventional ASL image processing toolbox, the proposed 4D‐EM algorithm not only generated comparable perfusion mean images, but also produced perfusion variance and percentage images, which the ASL toolbox cannot obtain. It is observed that the perfusion contribution percentages may not be the same as the corresponding tissue mixture volume fractions estimated in the structural images.Conclusion:A specific application to brain ASL images showed that the presented perfusion image analysis method is promising for detecting subtle changes in tissue perfusions, which is valuable for the early diagnosis of certain brain diseases, e.g. multiple sclerosis.