bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐A‐19A‐01: Image Registration I: Deformable Image Registration, Contour Propagation and Dose Mapping: 101 and 201
Authors: Kessler M
Published: July 2014

Deformable image registration, contour propagation and dose mapping have become common, possibly essential tools for modern image‐guided radiation therapy. Historically, these tools have been largely developed at academic medical centers and used in a rather limited and well controlled fashion. Today these tools are now available to the radiotherapy community at large, both as stand‐alone applications and as integrated components of both treatment planning and treatment delivery systems. Unfortunately, the details of how these tools work and their limitations are not generally documented or described by the vendors that provide them. Although “it looks right”, determining that unphysical deformations may have occurred is crucial. Because of this, understanding how and when to use, and not use these tools to support everyday clinical decisions is far from straight forward.

The goal of this session will be to present both the theory (basic and advanced) and practical clinical use of deformable image registration, contour propagation and dose mapping. To the extent possible, the “secret sauce” that different vendor use to produce reasonable/acceptable results will be described. A detailed explanation of the possible sources of errors and actual examples of these will be presented. Knowing the underlying principles of the process and understanding the confounding factors will help the practicing medical physicist be better able to make decisions (about making decisions) using these tools available.

Learning Objectives:

Understand the basic (101) and advanced (201) principles of deformable image registration, contour propagation and dose mapping data mapping.

Understand the sources and impact of errors in registration and data mapping and the methods for evaluating the performance of these tools.

Understand the clinical use and value of these tools, especially when used as a “black box”.
TU‐A‐18A‐01: Basic Principles of PET/CT, Calibration Methods and Contrast Recovery Across Multiple Cameras
Authors: Kappadath S , Nye J
Published: July 2014

This continuing education session will discuss the physical principles of PET/CT imaging and characterization of contrast recovery using accreditation phantoms.

A detailed overview will be given on the physical principles of PET including positron decay physics, 2D and 3D data acquisition, time‐of‐flight, scatter correction, CT attenuation correction, and image reconstruction. Instrument quality control and calibration procedures will be discussed. Technical challenges, common image artifacts and strategies to mitigate these issues will also be discussed.

Data will be presented on acquisition techniques and reconstruction parameters affecting contrast recovery. The discussion will emphasize the minimization of reconstruction differences in quantification metrics such as SUV and contrast recovery coefficients for the NEMA and ACR clinical trial phantoms. Data from new and older generation scanners will be shown including comparison of contrast recovery measurements to their analytical solutions.

The goal of this session is to update attendees on the quality control and calibration of PET/CT scanners, on methods to establish a common calibration for PET/CT scanners to control for instrument variance across multiple sites.

Learning Objectives:

Review the physical principles of PET/CT, quality control and calibration

Gain further understanding on how to apply techniques for improving quantitative agreement across multiple cameras

Describe the differences between measured and expected contrast recovery for the NEMA and ACR PET phantoms
TU‐A‐18C‐01: ACR Accreditation Updates in CT, Ultrasound, Mammography and MRI
Authors: Price R , Berns E , Hangiandreou N , McNitt‐Gray M
Published: July 2014

A goal of an imaging accreditation program is to ensure adequate image quality, verify appropriate staff qualifications, and to assure patient and personnel safety. Currently, more than 35,000 facilities in 10 modalities have been accredited by the American College of Radiology (ACR), making the ACR program one of the most prolific accreditation options in the U.S. In addition, the ACR is one of the accepted accreditations required by some state laws, CMS/MIPPA insurance and others. Familiarity with the ACR accreditation process is therefore essential to clinical diagnostic medical physicists. Maintaining sufficient knowledge of the ACR program must include keeping up‐to‐date as the various modality requirements are refined to better serve the goals of the program and to accommodate newer technologies and practices. This session consists of presentations from authorities in four ACR accreditation modality programs, including magnetic resonance imaging, mammography, ultrasound, and computed tomography. Each speaker will discuss the general components of the modality program and address any recent changes to the requirements.

Learning Objectives:

To understand the requirements of the ACR MR accreditation program. The discussion will include accreditation of whole‐body general purpose magnets, dedicated extremity systems well as breast MRI accreditation. Anticipated updates to the ACR MRI Quality Control Manual will also be reviewed.

To understand the current ACR MAP Accreditation requirement and present the concepts and structure of the forthcoming ACR Digital Mammography QC Manual and Program.

To understand the new requirements of the ACR ultrasound accreditation program, and roles the physicist can play in annual equipment surveys and setting up and supervising the routine QC program.

To understand the requirements of the ACR CT accreditation program, including updates to the QC manual as well as updates through the FAQ process.
TU‐A‐16A‐01: Medical Physics Meets the Press: How to Talk to the Public Media
Authors: Opila S
Published: July 2014

The session will introduce medical physicists to the basics of working with public media. The media landscape is constantly changing and medical physicists can serve an important role by offering their expertise on research, public health issues and more. This session is designed to provide participants with tips to work confidently with media in many different settings and effectively communicate key messages. Through this session, participants will gain an understanding of how the media works and news stories are developed, as well as how their role as medical physicists fits into the news cycle. Specific approaches to effectively communicating research to journalists will be covered, including the difference between interviews with trade reporters and interviews with general consumer news outlets. The art of working effectively with media starts with telling a good story and this session will provide participants with the tools to do that.

Learning Objectives:

Understand how the media works and how news stories are developed.

Learn approaches to effectively communicate research to journalists.

Learn how to present information as a story appropriate for media consumption.
TU‐A‐BRE‐01: The Relative Biological Effectiveness of Proton Beams Relative to Photon Beams
Authors: Paganetti H , Stewart R , Carabe‐Fernandez A
Published: July 2014

Proton therapy patients receive a 10% lower physical dose than the dose administered using photons, i.e. the proton relative biological effectiveness (RBE) is 1.1 in comparison to high‐energy photons. The use of a generic, spatially invariant RBE within tumor targets and normal tissue structures disregards a large body of evidence indicating that proton RBE tends to increase with increasing linear energy transfer (LET). Because the doseaveraged proton LET in the distal edge of a spread out Bragg peak (SOBP) is larger than the LET in the plateau region or proximal edge of a SOBP, the use of a spatially invariant RBE is not well justified from a mechanistic point of view. On the other hand, the available clinical data on local tumor control rates and early or late side effects do not provide strong evidence against the continued use of a constant and spatially invariant clinical RBE. The only potential downside to the ongoing use of a constant RBE of 1.1 seems to be that we are missing a potential opportunity to enhance the therapeutic ratio, i.e., design proton therapy treatments in ways that exploit, rather than mitigate, spatial variations in proton RBE. Speakers in this symposium will:

1‐review the laboratory and clinical evidence for and against the continued use of a spatially invariant RBE of 1.1,

2‐examine some of the putative mechanisms connecting spatial variations in particle LET to estimates of the proton RBE at the molecular, cellular and tissue levels

3‐assess the possible clinical significance of incorporating models for spatial variations in proton RBE into treatment planning systems.

4‐discuss treatment planning and delivery techniques that will exploit the spatial variations of RBE within proton beams.

Learning Objectives:

To review laboratory and clinical evidence for and against the continued use of a constant RBE of 1.1

To understand major mechanisms connecting proton LET to RBE at the molecular, cellular and tissue levels.

To quantify the potential opportunities and potential pitfalls of neglecting spatial variations in proton RBE in treatment plans

To understand the minimum requirements required to design proton treatment plans that benefit from a spatially changing RBE and discuss some of the technological challenges they may require.
TU‐A‐BRD‐01: Outcomes of Hypofractionated Treatments – Initial Results of the WGSBRT
Authors: Li X , Lee P , Ohri N , Joiner M , Kong F , Jackson A
Published: July 2014

Stereotactic Body Radiation Therapy (SBRT) has emerged in recent decades as a treatment paradigm that is becoming increasingly important in clinical practice. Clinical outcomes data are rapidly accumulating. Although published relations between outcomes and dose distributions are still sparse, the field has progressed to the point where evidence‐based normal tissue dose‐volume constraints, prescription strategies, and Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) models can be developed.

The Working Group on SBRT (WGSBRT), under the Biological Effects Subcommittee of AAPM, is a group of physicists and physicians working in the area of SBRT. It is currently performing critical literature reviews to extract and synthesize usable data and to develop guidelines and models to aid with safe and effective treatment. The group is investigating clinically relevant findings from SBRT in six anatomical regions: Cranial, Head and Neck, Thoracic, Abdominal, Pelvic, and Spinal.

In this session of AAPM 2014, interim results are presented on TCP for lung and liver, NTCP for thoracic organs, and radiobiological foundations:• Lung TCP: Detailed modeling of TCP data from 118 published studies on early stage lung SBRT investigates dose response and hypothesized mechanisms to explain the improved outcomes of SBRT. This is presented from the perspective of a physicist, a physician, and a radiobiologist.• Liver TCP: For primary and metastatic liver tumors, individual patient data were extracted from published reports to examine the effects of biologically effective dose on local control.• Thoracic NTCP: Clinically significant SBRT toxicity of lung, rib / chest wall and other structures are evaluated and compared among published clinical data, in terms of risk, risk factors, and safe practice.• Improving the clinical utility of published toxicity reports from SBRT and Hypofractionated treatments. What do we want, and how do we get it? Methods and problems of synthesizing data from published reports.

Learning Objectives:

Common SBRT fractionation schemes and current evidence for efficacy.

Evidence for normal tissue tolerances in hypofractionated treatments.

Clinically relevant radiobiological effects at large fraction sizes.
TU‐A‐17A‐01: Memorial to Benjamin M. Galkin – Memorial Lecture
Authors: Suntharalingam N
Published: July 2014

This past year Medical Physics lost one of its active members, Benjamin M. Galkin. Ben Galkin was a Past‐Treasurer of the AAPM. During his leadership role he played an important part in Securing membership, for the AAPM, in the American Institute of physics. As Treasurer he was also a prime mover in starting the journal, Medical Physics, and served as its business manager in the formative years.Ben Galkin received his Masters Degree at Columbia University in New York, under the mentorship of Dr. Edith Quimby, one of the pioneer Hospital Radiation Physicists in the country. He started his professional career at Jefferson Hospital in Philadelphia, joining Robert Gorson, and remained there until retirement. He served as the institution’s Radiation Safety Officer throughout his career. His research interest was Breast Imaging. He held joint faculty appointments in the Department of Radiology and the Department of Radiation Therapy and Nuclear Medicine, rising up to the rank of Full professor. He was a well respected teacher for the residents in Radiology.
TU‐A‐9A‐01: A Precise Deformable Image Registration System Using Feature‐Based Irregular Meshes
Authors: Cai Y , Zhong Z , Guo X , Gu X , Chiu T , Kearney V , Liu H , Jiang L , Chen S , Yordy J , Nedzi L , Mao W
Published: July 2014

Purpose:

To develop a deformable image registration system using irregular meshes generated based on image features. Finer meshes are generated at organ or tissue boundaries so that higher deformation resolution is achieved with limited number of control points.

Methods:

This deformable image registration system consists of two parts: a finite element modeling system and a GPU‐based registration system. The finite element modeling system is used to generate irregular meshes for the entire body or region of interest without segmentation. This system uses a Laplacian of Gaussion operator to extract features such as boundaries between organs and tissues. The placement of control points (vertices) of meshes is optimized based on feature intensities. The registration framework uses elastic energy as regularity and guarantees the final deformation vector field to be diffeomorphic. This system has been compared with registration algorithms based on regular meshes or voxels (Demons). The comparison is performed on XCAT digital phantom data and patient data.

Results:

Both XCAT male phantom and female phantom were used. Two respiratory phases were treated as floating and fix images for every phantom. Similarity measures were performed for image intensity and displacement vector field (DVF) for four sets of testing data with three types of deformation algorithms (irregular mesh, regular grid, and voxel). It clearly shows that the voxel‐based Demons algorithm leads to slightly better images. However, the DVF results show that mesh‐based algorithms behave much better. Compared with regular meshes, the irregular mesh we proposed leads to much faster convergence and converge to better results. The calculation is accelerated by GPU cards and a typical registration of patient data could be completed in about 1 minute.

Conclusion:

The feature‐based irregular meshing method provides a fast and accurate deformable image registration.

This research is supported by CPRIT individual investigator award RP110329 and Varian research grant.
TU‐A‐9A‐10: Verification of Photoacoustic Computed Tomography Perfusion Imaging Using DCE‐CT
Authors: Roth A , Krutulis M , Verleker A , Stantz K
Published: July 2014

Purpose:

We propose to verify quantifiable perfusion information generated by a Photoacoustic Computed Tomography (PCT) scanner using Dynamic Contrast‐Enhanced CT (DCE‐CT), and to investigate physicsbased models of acoustic properties of tissue and photon transport to improve quantification. These corrections first necessitate a skin identifying algorithms to reduce speed‐of‐sound blurring and empirical photon correction methods.

Methods:

Xenograft mice (n=5) of breast cancer was imaged using DCE‐CT which was followed by DCE‐PCT. To obtain CT perfusion data, each mouse was i.v. injected (0.2mL Isovue @0.5mL/min) and subsequent radio‐opaque time curves fit to a 2‐compartmental model on a voxel‐wise basis. For DCE‐PCT, different concentrations of ICG (250, 125, and 62.5 micro‐Molar) were injected at the same rate, but also acquired at different sampling rates (3, 6, and 12 seconds). The time intensity curves from PCT were fit to a 1‐compartmental model on a voxel by voxel basis. The images were coregistered (Oncentra) based on the structural similarities of the tumor vasculature after which we compared both the contrastenhanced dynamics and the vascular physiology.

Results:

Moderate to high doses of ICG impact the washin phase of the PCT contrast due to photon losses as a function of depth. A semi‐automatic algorithm has been developed to identify the skin margin, and subsequent MC and empirical models of photon transport and variations in speed‐of‐sound are being evaluated.

Conclusion:

From our results we find that there is a need to apply photon and speed‐of‐sound corrections to our PCT data to improve the quantifiable image data at depth in the tumor for PCT. The dose and injection rate may help in reducing large systematic effects.

Our project is partially funded by a NIH SBIR grant.
TU‐A‐9A‐11: Gold Nanoparticles Enhanced Diffuse Optical Tomography: A Proof of Concept Study
Authors: Yang Y , Dogan N
Published: July 2014

Purpose:

To investigate the feasibility and potential of gold nanoparticles (GNP) enhanced diffuse optical tomography (DOT) as a novel imaging strategy for tumor detection.

Methods:

Simulation was performed on a digital homogeneous cylindrical phantom of 30mm×30mm. Gold nanorods (GNR) with aspect ratio 3.9 and effective radius 21.86nm were used as contrast agent. The peak light absorption for these GNR occurs at 842nm within the near‐infrared region, with the absorption cross‐section of 1.97×10‐14m‐2 and scatter cross‐section of 1.07×10‐14m‐2. A 6mmdiameter sphere of GNR solution was positioned inside the tissue‐simulating phantom. Simulations were performed at the GNR concentration level of 1nM, 100pM and 10pM, respectively. The points representing laser sources and light detectors were around the phantom with 30o apart tangentially and 1mm apart axially for 9 rows. As one point being source, all the other points within the current row and nearby four rows become detectors. Hence there are 108 source points in total and 55 detector points corresponding to each source. Forward light transport at 842nm wavelength was run on a three‐dimensional mesh of 33186 nodes (∼0.5mm resolution) to acquire the light emission data. Reconstruction was performed on a coarse mesh of 19408 nodes (∼1mm resolution) with ∼20minutes on a 2.4GHz CPU and 8GB RAM computer.

Results:

The position of the GNR solution at 1nM, 100pM and 10pM concentration was reconstructed, respectively, with <1mm error. The GNR concentration was interpreted from the reconstructed absorption coefficient within the enhanced volume. The reconstructed maximum concentrations were 0.3nM, 120.0pM, and 5.3pM, respectively.

Conclusion:

To the best of our knowledge, this is the first time to apply GNP to enhance DOT. The simulation results showed the high sensitivity of GNP enhanced DOT, which is in pM concentration level, compared to the μM level for MRI agents and nM level for PET agents.
TU‐A‐12A‐01: Consistency of Lung Expansion and Contraction During Respiration: Implications for Quantitative Imaging
Authors: Patton T , Du K , Christensen G , Reinhardt J , Bayouth J
Published: July 2014

Purpose:

Four‐dimensional computed tomography (4DCT) can be used to evaluate longitudinal changes in pulmonary function. The sensitivity of such measurements to identify function change may be improved with reproducible breathing patterns. The purpose of this study was to determine if inhale was more consistent than exhale, i.e., lung expansion during inhalation compared to lung contraction during exhalation.

Methods:

Repeat 4DCT image data acquired within a short time interval from 8 patients. Using a tissue volume preserving deformable image registration algorithm, Jacobian ventilation maps in two scanning sessions were computed and compared on the same coordinate for reproducibility analysis. Equivalent lung volumes (ELV) were used for 5 subjects and equivalent title volumes (ETV) for the 3 subjects who experienced a baseline shift between scans. In addition, gamma pass rate was calculated from a modified gamma index evaluation between two ventilation maps, using acceptance criterions of 2mm distance‐to‐agreement and 5% ventilation difference. The gamma pass rates were then compared using paired t‐test to determine if there was a significant difference.

Results:

Inhalation was more reproducible than exhalation. In the 5 ELV subjects 78.5% of the lung voxels met the gamma criteria for expansion during inhalation when comparing the two scans, while significantly fewer (70.9% of the lung voxels) met the gamma criteria for contraction during exhalation (p = .027). In the 8 total subjects analyzed the average gamma pass rate for expansion during inhalation was 75.2% while for contraction during exhalation it was 70.3%; which trended towards significant (p = .064).

Conclusion:

This work implies inhalation is more reproducible than exhalation, when equivalent respiratory volumes are considered. The reason for this difference is unknown. Longitudinal investigation of pulmonary function change based on inhalation images appears appropriate for Jacobian‐based measure of lung tissue expansion.

NIH Grant: R01 CA166703
TU‐A‐12A‐03: Monitoring Changes in Tumor Texture Features On Weekly CT and CBCT Scans of NSCLC Patients
Authors: Fave X , Zhang L , Yang J , Fried D , Balter P , Court L
Published: July 2014

Purpose:

To (1) track changes in CT texture features through time and (2) identify correlations between CT and CBCT texture feature values for NSCLC patients.

Methods:

Texture features were extracted from weekly CT and CBCT images of 30 NSCLC patients. The physician‐drawn GTV contours on the planning CT, during end of expiration phase (T50), were deformed to weekly CT images. The deformed contours were copied to rigidly registered average‐CT and CBCT images. These contours were imported to our in‐house texture feature analysis program, which performs a Laplacian of Gaussian spatial band‐pass filter at different scales followed by a calculation of the tumor uniformity. Three filter sizes were used (coarse, medium, and fine). (1) The normalized change in uniformity as a function of time was evaluated from the T50 images. (2) The uniformity values from the average‐CT and CBCT images were used to assess correlation.

Results:

(1) Texture features measured in T50 scans were shown to change over time for individual patients. As filter size increased, the range of measured normalized changes decreased from 103.6% (SD=22.8) to 25.2% (SD=7.9). (2) Texture features extracted from CT were shown to correlate with values in CBCT with R2 values of 0.79(coarse), 0.84(medium), and 0.84(fine). Correlation values increased for more coarse filters and lower lung tissue thresholds. The correlation was also dependent on removal of patients with metal artifacts, severe truncation of anatomy in CBCT images, or those with tumors smaller than 4.3cc. Seven patients were removed.

Conclusions:

We showed texture features vary for patients during their course of treatment and these changes can be monitored with CBCT images. Various studies have indicated CT texture features may correlate with patient prognosis. Therefore, our results could be used to observe changes in a patients prognosis and potentially adapt their treatment without any additional imaging studies.
TU‐A‐12A‐07: CT‐Based Biomarkers to Characterize Lung Lesion: Effects of CT Dose, Slice Thickness and Reconstruction Algorithm Based Upon a Phantom Study
Authors: Zhao B , Tan Y , Tsai W , Lu L , Schwartz L , Lu Z , So J , Goldman J
Published: July 2014

Purpose:

Radiogenomics promises the ability to study cancer tumor genotype from the phenotype obtained through radiographic imaging. However, little attention has been paid to the sensitivity of image features, the image‐based biomarkers, to imaging acquisition techniques. This study explores the impact of CT dose, slice thickness and reconstruction algorithm on measuring image features using a thorax phantom.

Methods:

Twentyfour phantom lesions of known volume (1 and 2mm), shape (spherical, elliptical, lobular and spicular) and density (‐630, ‐10 and +100 HU) were scanned on a GE VCT at four doses (25, 50, 100, and 200 mAs). For each scan, six image series were reconstructed at three slice thicknesses of 5, 2.5 and 1.25mm with continuous intervals, using the lung and standard reconstruction algorithms. The lesions were segmented with an in‐house 3D algorithm. Fifty (50) image features representing lesion size, shape, edge, and density distribution/texture were computed. Regression method was employed to analyze the effect of CT dose, slice of thickness and reconstruction algorithm on these features adjusting 3 confounding factors (size, density and shape of phantom lesions).

Results:

The coefficients of CT dose, slice thickness and reconstruction algorithm are presented in Table 1 in the supplementary material. No significant difference was found between the image features calculated on low dose CT scans (25mAs and 50mAs). About 50% texture features were found statistically different between low doses and high doses (100 and 200mAs). Significant differences were found for almost all features when calculated on 1.25mm, 2.5mm, and 5mm slice thickness images. Reconstruction algorithms significantly affected all density‐based image features, but not morphological features.

Conclusions:

There is a great need to standardize the CT imaging protocols for radiogenomics study because CT dose, slice thickness and reconstruction algorithm impact quantitative image features to various degrees as our study has shown.
TU‐C‐16A‐01: Joint AAPM/SEFM/AMPR Educational Workshop On “Education of Radiotherapy Physicists”
Authors: Mahesh M , Borras C , Frey G , Ribas‐Morales M , Ballester F , Kazantsev P , Kostylev D
Published: July 2014

This workshop is jointly organized by the AAPM, the Spanish (SEFM) and the Russian (AMPR) Medical Physics Societies, as part of formal educational exchange agreements signed by the AAPM with each one of these two societies.With the rapid technological advances in radiation therapy both for treatment and imaging, it is challenging how physics is taught to medical physicists practicing in radiation therapy. The main Objectives: of this workshop is to bring forth current status, challenges and issues related to education of radiation therapy physicists here in the US, Spain and Russia. Medical physicists from each one of these countries will present educational requirements of international recommendations and directives and analyze their impact on national legislations. Current and future educational models and plans for harmonization will be described. The role of universities, professional societies and examination boards, such as the American Board of Radiology, will be discussed. Minimum standards will be agreed upon.

Learning Objectives:

Review medical physics educational models supported by AAPM, SEFM, and AMPR.

Discuss the role of governmental and non‐governmental organizations in elaborating and adopting medical physics syllabi.

Debate minimum educational standards for medical physics education based on country‐specific resources.
TU‐C‐19A‐01: “Leaning In” to Equal Opportunity for Women: The Responsibility of Individuals, Employers and Organizations
Authors: Ranger N , Travers E
Published: July 2014

The publication of the book “Lean In” by Sheryl Sandberg created a lively discussion around the question of whether women were doing all they could do to ensure their own career success and advancement. In this session we will focus on the different roles and responsibilities that individuals, employers, and organizations need to embrace to ensure equal access to opportunity for individual women at all stages of their career. Initiatives within the AAPM and other professional organizations, institutional leadership and mentoring programs and strategies that individual women can adapt to take charge of their own career success, will be addressed.

Learning Objectives:

Learn about the efforts within the AAPM and related organizations geared towards enhancing opportunities for women.

Learn about the types of programs that institutions can create to support career success.

Learn strategies to apply to your own career to enhance your professional success.
TU‐C‐BRE‐02: A Novel, Highly Efficient and Automated Quality Assurance Tool for Modern Linear Accelerators
Authors: Goddu S , Sun B , Yaddanapudi S , Kamal G , Baltes C , Rose S , Stinson K , Mutic S
Published: July 2014

Purpose:

Quality assurance (QA) of complex linear accelerators is critical and highly time consuming. Varian’s Machine Performance Check (MPC) uses IsoCal phantom to test geometric and dosimetric aspects of the TrueBeam systems in <5min. In this study we independently tested the accuracy and robustness of the MPC tools.

Methods:

MPC is automated for simultaneous image‐acquisition, using kV‐and‐MV onboard‐imagers (EPIDs), while delivering kV‐and‐MV beams in a set routine of varying gantry, collimator and couch angles. MPC software‐tools analyze the images to test: i) beam‐output and uniformity, ii) positional accuracy of isocenter, EPIDs, collimating jaws (CJs), MLC leaves and couch and iii) rotational accuracy of gantry, collimator and couch. 6MV‐beam dose‐output and uniformity were tested using ionization‐chamber (IC) and ICarray. Winston‐Lutz‐Tests (WLT) were performed to measure isocenter‐offsets caused by gantry, collimator and couch rotations. Positional accuracy of EPIDs was evaluated using radio‐opaque markers of the IsoCal phantom. Furthermore, to test the robustness of the MPC tools we purposefully miscalibrated a non‐clinical TrueBeam by introducing errors in beam‐output, energy, symmetry, gantry angle, couch translations, CJs and MLC leaves positions.

Results:

6MV‐output and uniformity were within ±0.6% for most measurements with a maximum deviation of ±1.0%. Average isocenter‐offset caused by gantry and collimator rotations was 0.316±0.011mm agreeing with IsoLock (0.274mm) and WLT (0.41mm). Average rotation‐induced couch‐shift from MPC was 0.378±0.032mm agreeing with WLT (0.35mm). MV‐and‐kV imager‐offsets measured by MPC were within ±0.15mm. MPC predicted all machine miscalibrations within acceptable clinical tolerance. MPC detected the output miscalibrations within ±0.61% while the MLC and couch positions were within ±0.06mm and ±0.14mm, respectively. Gantry angle miscalibrations were detected within ±0.1°.

Conclusions:

MPC is a useful tool for QA of TrueBeam systems and its automation makes it highly efficient for testing both geometric and dosimetric aspects of the machine. This is very important for hypo‐fractionated SBRT treatments.

Received support from Varian Medical Systems, Palo Alto, CA 94304‐1038.
TU‐C‐BRE‐03: Aggregation of Linac Measurement Data
Authors: Kerns J , Alvarez P , Followill D , Lowenstein J , Molineu A , Summers P , Kry S
Published: July 2014

Purpose:

Accurate data of linear accelerator radiation characteristics is important for treatment planning system commissioning as well as regular quality assurance of the machine. The RPC has performed site visits of numerous machines . Data gathered from Varian machines from the past 15 years are presented. The data collected can be used as a secondary check or when commissioning a new machine to verify that values are reasonable.

Methods:

Data from the past 15 years of RPC site visits was compiled and analyzed. Data was composed from measurements from approximately 400 Varian machines. Each dataset consists of several point measurements at various locations in a water phantom to measure percentage depth dose, output factors, including small MLC fields, off‐axis factors, and wedge factors if applicable. Common statistical values are presented for each machine type. Where applicable, data was compared to other reference data given by the vendor or a select number of previous researchers.

Results:

Data is separated by energy and parameter and then analyzed by machine class. Data distributions of the parameter data were normal except occasionally at the tails. Distributions of the data for each class and parameter are tabulated to give not simply a singular reference value, but metrics about the distribution: 5th and 95th percentile values and the standard deviation as well as the median.

Conclusion:

The RPC has collected numerous data on Varian linacs and presented the finding of the past 15 years. The data can be used as a reference data set for physicists to compare against. A linac that deviates from the values does not necessarily indicate there is a problem as long as the treatment planning system correlates to the machine. Comparison of linac and treatment planning system data to external reference data can prevent serious treatment errors.
TU‐C‐BRE‐04: 3D Gel Dosimetry Using ViewRay On‐Board MR Scanner: A Feasibility Study
Authors: Zhang L , Du D , Green O , Rodriguez V , Wooten H , Xiao Z , Yang D , Hu Y , Li H
Published: July 2014

Purpose:

MR based 3D gel has been proposed for radiation therapy dosimetry. However, access to MR scanner has been one of the limiting factors for its wide acceptance. Recent commercialization of an on‐board MR‐IGRT device (ViewRay) may render the availability issue less of a concern. This work reports our attempts to simulate MR based dose measurement accuracy on ViewRay using three different gels.

Methods:

A spherical BANG gel dosimeter was purchased from MGS Research. Cylindrical MAGIC gel and Fricke gel were fabricated in‐house according to published recipes. After irradiation, BANG and MAGIC were imaged using a dual‐echo spin echo sequence for T2 measurement on a Philips 1.5T MR scanner, while Fricke gel was imaged using multiple spin echo sequences. Difference between MR measured and TPS calculated dose was defined as noise. The noise power spectrum was calculated and then simulated for the 0.35 T magnetic field associated with ViewRay. The estimated noise was then added to TG‐119 test cases to simulate measured dose distributions. Simulated measurements were evaluated against TPS calculated doses using gamma analysis.

Results:

Given same gel, sequence and coil setup, with a FOV of 180×90×90 mm3, resolution of 3×3×3 mm3, and scanning time of 30 minutes, the simulated measured dose distribution using BANG would have a gamma passing rate greater than 90% (3%/3mm and absolute). With a FOV 180×90×90 mm3, resolution of 4×4×5 mm3, and scanning time of 45 minutes, the simulated measuremened dose distribution would have a gamma passing rate greater than 97%. MAGIC exhibited similar performance while Fricke gel was inferior due to much higher noise.

Conclusions:

The simulation results demonstrated that it may be feasible to use MAGIC and BANG gels for 3D dose verification using ViewRay low‐field on‐board MRI scanner.
TU‐C‐BRE‐05: Clinical Implications of AAA Commissioning Errors and Ability of Common Commissioning ' Credentialing Procedures to Detect Them
Authors: McVicker A , Oldham M , Yin F , Adamson J
Published: July 2014

Purpose:

To test the ability of the TG‐119 commissioning process and RPC credentialing to detect errors in the commissioning process for a commercial Treatment Planning System (TPS).

Methods:

We introduced commissioning errors into the commissioning process for the Anisotropic Analytical Algorithm (AAA) within the Eclipse TPS. We included errors in Dosimetric Leaf Gap (DLG), electron contamination, flattening filter material, and beam profile measurement with an inappropriately large farmer chamber (simulated using sliding window smoothing of profiles). We then evaluated the clinical impact of these errors on clinical intensity modulated radiation therapy (IMRT) plans (head and neck, low and intermediate risk prostate, mesothelioma, and scalp) by looking at PTV D99, and mean and max OAR dose. Finally, for errors with substantial clinical impact we determined sensitivity of the RPC IMRT film analysis at the midpoint between PTV and OAR using a 4mm distance to agreement metric, and of a 7% TLD dose comparison. We also determined sensitivity of the 3 dose planes of the TG‐119 C‐shape IMRT phantom using gamma criteria of 3% 3mm.

Results:

The largest clinical impact came from large changes in the DLG with a change of 1mm resulting in up to a 5% change in the primary PTV D99. This resulted in a discrepancy in the RPC TLDs in the PTVs and OARs of 7.1% and 13.6% respectively, which would have resulted in detection. While use of incorrect flattening filter caused only subtle errors (<1%) in clinical plans, the effect was most pronounced for the RPC TLDs in the OARs (>6%).

Conclusion:

The AAA commissioning process within the Eclipse TPS is surprisingly robust to user error. When errors do occur, the RPC and TG‐119 commissioning credentialing criteria are effective at detecting them; however OAR TLDs are the most sensitive despite the RPC currently excluding them from analysis.
TU‐C‐BRE‐07: Quantifying the Clinical Impact of VMAT Delivery Errors Relative to Prior Patients’ Plans and Adjusted for Anatomical Differences
Authors: Stanhope C , Wu Q , Yuan L , Liu J , Hood R , Yin F , Adamson J
Published: July 2014

Purpose:

There is increased interest in the Radiation Oncology Physics community regarding sensitivity of pre‐treatment IMRT/VMAT QA to delivery errors. Consequently, tools mapping pre‐treatment QA to the patient DVH have been developed. However, the quantity of plan degradation that is acceptable remains uncertain. Using DVHs adapted from prior patients’ plans, we developed a technique to determine the magnitude of various delivery errors required to degrade a treatment plan to outside the clinically accepted range.

Methods:

DVHs for relevant organs at risk were adapted from a population of prior patients’ plans using a machine learning algorithm to establish the clinically acceptable DVH range specific to the patient’s anatomy. We applied this technique to six low‐risk prostate cancer patients treated with single‐arc VMAT and compared error‐induced DVH changes to the adapted DVHs to determine the magnitude of error required to push the plan outside of the acceptable range. The procedure follows: (1) Errors (systematic ' random shift of MLCs, gantry‐MLC desynchronization, dose rate fluctuations, etc.) were simulated and degraded DVHs calculated using the Varian Eclipse TPS. (2) Adapted DVHs and acceptable ranges for DVHs were established. (3) Relevant dosimetric indices and corresponding acceptable ranges were calculated from the DVHs. Key indices included NTCP (Lyman‐Kutcher‐Burman Model) and QUANTEC’s dose‐volume Objectives: s of V75Gy≤0.15 for the rectum and V75Gy≤0.25 for the bladder.

Results:

Degradations to the clinical plan became “unacceptable” for 19±29mm and 1.9±2.0mm systematic outward shifts of a single leaf and leaf bank, respectively. All other simulated errors fell within the acceptable range.

Conclusion:

Utilizing machine learning and prior patients’ plans one can predict a clinically acceptable range of DVH degradation for a specific patient. Comparing error‐induced DVH degradations to this range, it is shown that single‐arc VMAT plans for low‐risk prostate are relatively insensitive to many potential delivery errors.
TU‐C‐BRE‐09: Performance Comparisons of Patient Specific IMRT QA Methodologies Using ROC Analysis
Authors: McKenzie E , Balter P , Stingo F , Followill D , Jones J , Kry S
Published: July 2014

Purpose:

To evaluate the ability of a selection of patient‐specific QA methods to accurately classify IMRT plans as acceptable or unacceptable based on a multiple ion chamber (MIC) phantom.

Methods:

Twenty‐four IMRT plans were selected (20 previously failed the institutional QA), and were measured on a MIC phantom to assess their dosimetric acceptability. These same plans were then measured using film (Kodak EDR2) and ion chamber (Wellhofer cc04), ArcCheck (Sun Nuclear), and MapCheck (Sun Nuclear) (delivered AP field‐by‐field, AP composite, and with original gantry angles). All gamma analyses were performed at 2%/2mm, 3%/3mm, and 5%/3mm. By using the MIC results as a gold standard, the sensitivity and specificity were calculated across a range of cut‐off thresholds (% pixels passing for gamma analysis, and % dose difference for ion chamber), and were used to form ROC curves. Area under the curve (AUC) was used as a metric to quantify the performance of the various QA methods.

Results:

Grouping device’s AUC’s revealed two statistically significant different groups: ion chamber (AUC of 0.94), AP composite MapCheck (AUC of 0.85), ArcCheck (AUC of 0.84), and film (AUC of 0.82) were in the better performing group, while original gantry angles and AP field‐by‐field MapCheck (AUC of 0.65 and 0.66, respectively) matched less well with the gold standard results. Optimal cut‐offs were also assessed using the ROC curves. We found that while often 90% of pixels passing is used as a criteria, the differing sensitivities of QA methods can lead to device and methodology‐based optimal cutoff thresholds.

Conclusion:

While many methods exist to perform the same task of patient‐specific IMRT QA, they utilize different strategies. This work has shown that there are inconsistencies in these methodologies in terms of their sensitivity and specificity to dosimetric acceptability.

This work was supported by Public Health Service grants CA010953, CA081647, and CA21661 awarded by the National Cancer Institute, United States Department of Health and Human Services.
TU‐C‐BRE‐10: A Streamlined Approach to EPID Transit Dosimetry
Authors: Morris B , Fontenot J
Published: July 2014

Purpose:

To investigate the feasibility of a simple and efficient transit dosimetry method using the electronic portal imaging device (EPID) for dose delivery error detection and prevention.

Methods:

In the proposed method, 2D reference transit images are generated for comparison with online images acquired during treatment. Reference transit images are generated by convolving through‐air EPID measurements of each field with pixel‐specific kernels selected from a library of pre‐calculated Monte Carlo pencil kernels of varying radiological thickness. The kernel used for each pixel is selected based on the calculated radiological thickness of the patient along a line joining the pixel and the virtual source. The accuracy of the technique was evaluated in flat homogeneous and heterogeneous plastic water phantoms, a heterogeneous cylindrical phantom, and an anthropomorphic head phantom. Gamma criteria of 3%/3 mm was used to quantify the accuracy of the technique for the various cases.

Results:

An average of 99.9% and 99.7% of the points in the comparison between the measured and predicted images passed a 3%/3mm gamma for the homogeneous and heterogeneous plastic water phantoms, respectively. 97.1% of the points passed for the analysis of the heterogeneous cylindrical phantom. For the anthropomorphic head phantom, an average of 97.8% of points passed the 3%/3mm gamma criteria for all field sizes. Failures were observed primarily in areas of drastic thickness or material changes and at the edges of the fields.

Conclusion:

The data suggest that the proposed transit dosimetry method is a feasible approach to in vivo dose monitoring. Future research efforts could include implementation for more complex fields and sensitivity testing of the method to setup errors and changes in anatomy.

Oncology Data Systems provided partial funding support but did not participate in the collection or analysis of data
TU‐C‐9A‐01: IROC Organization and Clinical Trial Credentialing
Authors: Followill D , Molineu A , Xiao Y
Published: July 2014

As a response to recommendations from a report from the Institute of Medicine, NCI is reorganizing it clinical trial groups into a National Clinical Trial Network (NCTN) that consists of four adult groups (Alliance, ECOGACRIN, NRG, and SWOG) and one children’s group (COG). NRG will house CIRO, a center to promote innovative radiation therapy research and intergroup collaboration in radiation. The quality assurance groups that support clinical trials have also been restructured. ITC, OSU Imaging corelab, Philadelphia Imaging core‐lab, QARC, RPC, and RTOGQA have joined together to create the Imaging and Radiation Oncology Core (IROC) Group. IROC’s mission is to provide integrated radiation oncology and diagnostic imaging quality control programs in support of the NCI’s NCTN thereby assuring high quality data for clinical trials designed to improve the clinical outcomes for cancer patients worldwide. This will be accomplished through five core services: site qualification, trial design support, credentialing, data management, case review. These changes are important for physicist participating in NCI clinical trials to understand. We will describe in detail the IROC’s activities and five core services so that as a user, the medical physicist can learn how to efficiently utilize this group. We will describe common pitfalls encountered in credentialing for current protocols and present methods to avoid them. These may include the which benchmarks are required for NSABP B‐51/RTOG 1304 and how to plan them as well as tips for phantom planning. We will explain how to submit patient and phantom cases in the TRIAD system used by IROC.

Learning Objectives:

To understand the basic organization of IROC, its mission and five core services

To learn how to use TRIAD for patient and phantom data submission

To learn how to avoid common pitfalls in credentialing for current trials
TU‐C‐12A‐05: Repeatability Study of Reduced Field‐Of‐View Diffusion‐Weighted MRI On Human Thyroid Gland
Authors: Shukla‐Dave A , Lu Y , Hatzoglou V , Banerjee S , Stambuk H , Shankaranarayanan A , Mazaheri Y , Deasy J
Published: July 2014

Purpose:

To investigate the repeatability of reduced field‐of‐view diffusion‐weighted imaging (rFOV DWI) in quantifying apparent diffusion coefficients (ADCs) for human thyroid glands in a clinical setting.

Methods:

Nine healthy human volunteers were enrolled and underwent 3T MRI exams. For each volunteer, 3 longitudinal exams (2 weeks apart) with 2 repetitive sessions within each exam, including rFOV and conventional full field‐of‐view (fFOV) DWI scans, were performed. In the acquired DWI images, a fixed‐size region of interest (ROI; diameter=8mm) was placed on thyroid glands to calculate ADC. ADC was calculated using a monoexponential function with a noise correction scheme. The repeatability of ADC was assessed by using coefficient variation (CV) across sessions or exams, which was defined to be: r = 1‐CV, 0 < r < 1, where CV=STD/m, STD is the standard deviation of ADC, and m is the average of ADC across sessions or exams. An experienced radiologist assessed and scored rFOV and fFOV DW images based on image characteristics (1, nondiagnostic; 2, poor; 3, satisfactory; 4, good; and 5, excellent).Analysis of variance (ANOVA) was performed to compare ADC values, CV of ADC, repeatability of ADC across sessions and exams, and radiologic scores between rFOV and fFOV DWI techniques.

Results:

There was no significant difference in ADC values across sessions and exams either in rFOV or fFOV DWI. The average CVs of both rFOV and fFOV DWI were less than 13%. The repeatability of ADC measurement between rFOV and fFOV DWI was not significantly different. The overall image quality was significantly higher with rFOV DWI than with fFOV DWI.

Conclusion:

This study suggested that ADCs from both rFOV and fFOV DWI were repeatable, but rFOV DWI had superior imaging quality for human thyroid glands in a clinical setting.