bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐AB‐204‐04: D&I in Physics
Authors: Hammer P.
Published: July 2016

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

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

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

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

How to develop a roadmap to diversity excellence within AAPM.
WE‐AB‐204‐05: D&I in NIH ‐ Funding/Research
Authors: Chew D.
Published: July 2016

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

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

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

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

How to develop a roadmap to diversity excellence within AAPM.
WE‐AB‐204‐06: D&I in Global Health
Authors: Ngoma T.
Published: July 2016

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

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

Learning Objectives:

Understanding the role diversity and inclusion plays in medical physics.

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

How to develop a roadmap to diversity excellence within AAPM.
WE‐AB‐BRB‐01: Memorial Introduction; Storage Phosphor Panels for Radiation Therapy Dosimetry
Authors: Li H.
Published: July 2016

Despite widespread IMRT treatments at modern radiation therapy clinics, precise dosimetric commissioning of an IMRT system remains a challenge. In the most recent report from the Radiological Physics Center (RPC), nearly 20% of institutions failed an end‐to‐end test with an anthropomorphic head and neck phantom, a test that has rather lenient dose difference and distance‐to‐agreement criteria of 7% and 4 mm. The RPC report provides strong evidence that IMRT implementation is prone to error and that improved quality assurance tools are required. At the heart of radiation therapy dosimetry is the multidimensional dosimeter. However, due to the limited availability of water‐equivalent dosimetry materials, research and development in this important field is challenging. In this session, we will review a few dosimeter developments that are either in the laboratory phase or in the pre‐commercialization phase. 1) Radiochromic plastic. Novel formulations exhibit light absorbing optical contrast with very little scatter, enabling faster, broad beam optical CT design. 2) Storage phosphor. After irradiation, the dosimetry panels will be read out using a dedicated 2D scanning apparatus in a non‐invasive, electro‐optic manner and immediately restored for further use. 3) Liquid scintillator. Scintillators convert the energy from x‐rays and proton beams into visible light, which can be recorded with a scientific camera (CCD or CMOS) from multiple angles. The 3D shape of the dose distribution can then be reconstructed. 4) Cherenkov emission imaging. Gated intensified imaging allows video‐rate passive detection of Cherenkov emission during radiation therapy with the room lights on.

Learning Objectives:

To understand the physics of a variety of dosimetry techniques based upon optical imaging

To investigate the strategies to overcome respective challenges and limitations

To explore novel ideas of dosimeter design

Supported in part by NIH Grants R01CA148853, R01CA182450, R01CA109558. Brian Pogue is founder and president of the company DoseOptics LLC, dedicated to developing and commercializing the first dedicated Cerenkov imaging camera and system for radiation dose imaging. Work reported in this talk does not involve the use of DoseOptics technology.; H. Li, this work was supported in part by NIH Grant No. R01CA148853; S. Beddar, NIH funding R01‐CA182450
WE‐AB‐BRB‐02: Methods and Applications of 3D Radiochromic Dosimetry
Authors: Oldham M.
Published: July 2016

Despite widespread IMRT treatments at modern radiation therapy clinics, precise dosimetric commissioning of an IMRT system remains a challenge. In the most recent report from the Radiological Physics Center (RPC), nearly 20% of institutions failed an end‐to‐end test with an anthropomorphic head and neck phantom, a test that has rather lenient dose difference and distance‐to‐agreement criteria of 7% and 4 mm. The RPC report provides strong evidence that IMRT implementation is prone to error and that improved quality assurance tools are required. At the heart of radiation therapy dosimetry is the multidimensional dosimeter. However, due to the limited availability of water‐equivalent dosimetry materials, research and development in this important field is challenging. In this session, we will review a few dosimeter developments that are either in the laboratory phase or in the pre‐commercialization phase. 1) Radiochromic plastic. Novel formulations exhibit light absorbing optical contrast with very little scatter, enabling faster, broad beam optical CT design. 2) Storage phosphor. After irradiation, the dosimetry panels will be read out using a dedicated 2D scanning apparatus in a non‐invasive, electro‐optic manner and immediately restored for further use. 3) Liquid scintillator. Scintillators convert the energy from x‐rays and proton beams into visible light, which can be recorded with a scientific camera (CCD or CMOS) from multiple angles. The 3D shape of the dose distribution can then be reconstructed. 4) Cherenkov emission imaging. Gated intensified imaging allows video‐rate passive detection of Cherenkov emission during radiation therapy with the room lights on.

Learning Objectives:

To understand the physics of a variety of dosimetry techniques based upon optical imaging

To investigate the strategies to overcome respective challenges and limitations

To explore novel ideas of dosimeter design

Supported in part by NIH Grants R01CA148853, R01CA182450, R01CA109558. Brian Pogue is founder and president of the company DoseOptics LLC, dedicated to developing and commercializing the first dedicated Cerenkov imaging camera and system for radiation dose imaging. Work reported in this talk does not involve the use of DoseOptics technology.; H. Li, this work was supported in part by NIH Grant No. R01CA148853; S. Beddar, NIH funding R01‐CA182450
WE‐AB‐BRA‐02: Study of the Therapeutic Effects of Pulsed Focused Ultrasound Combined with Encapsulated Chemotherapeutic Agents for Prostate Cancer in Vivo
Authors: Chen L , Cvetkovic D , Chen X , Wang B , Gupta R , Ma C
Published: July 2016

Purpose:

To investigate the improvement of prostate cancer inhibition by combining pulsed focused ultrasound (pFUS) exposures and chemotherapeutic agents encapsulated nanodroplets under MR guidance for prostate cancer therapy.

Methods:

Prostate cancer (LNCaP) cells were implanted orthotopically. First we developed nanodroplets encapsulated with chemotherapeutic agents for both paclitaxel (PTX) and docetaxel (DTX). Secondly, tumor‐bearing mice were randomly divided into 5 groups (n=5). Group 1 animals were treated with an i.v injection of DTX‐encapsulated nanodroplets (DTX‐ND) + pFUS. Group 2 were treated with pFUS alone. Group 3 were injected (i.v) with DTX‐ND alone, Group 4 received free DTX and Group 5 was used as control. Ultrasound treatment parameters were 1MHz, 25W acoustic power, 10% duty cycle and 60 seconds for each sonication. After treatment, animals were allowed to survive for 4 weeks. Tumor volumes were measured on MRI. Third, we repeated the experiment with PTX‐ND. Finally we performed study on biodistribution of PTX‐ND for prostate cancer and the treatment effects on tumor growth delay are being evaluated.

Results:

With DTX‐ND, significant tumor growth delay was observed in Group 1 with p=0.039. There was no significant tumor growth delay observed for Group 2 (p=0.477), Group 3 (p=0.209) and Group 4 (p=0.476). The results are consistent with earlier PTX‐ND studies in which significant tumor growth delay was observed in Group 1 with p=0.004. There was no significant tumor growth delay observed for Group 2 (p=0.285), Group 3 (p=0.452) and Group 4 (p=0.158). The peak of drug update in tumor appeared at 4h after injection in the biodistribution study.

Conclusion:

Our results showed a great potential of targeted nanodroplets for prostate cancer therapy, which could be activated by pFUS. Our study also suggested that the optimal timing for applying pFUS is 4h after i.v injection of PTX‐ND and the treatment effect is being evaluated.
WE‐AB‐BRA‐06: 4DCT‐Ventilation: A Novel Imaging Modality for Thoracic Surgical Evaluation
Authors: Vinogradskiy Y , Jackson M , Schubert L , Jones B , Castillo R , Castillo E , Guerrero T , Mitchell J , Kavanagh B , Miften M
Published: July 2016

Purpose:

The current standard‐of‐care imaging used to evaluate lung cancer patients for surgical resection is nuclear‐medicine ventilation. Surgeons use nuclear‐medicine images along with pulmonary function tests (PFT) to calculate percent predicted postoperative (%PPO) PFT values by estimating the amount of functioning lung that would be lost with surgery. 4DCT‐ventilation is an emerging imaging modality developed in radiation oncology that uses 4DCT data to calculate lung ventilation maps. We perform the first retrospective study to assess the use of 4DCT‐ventilation for pre‐operative surgical evaluation. The purpose of this work was to compare %PPO_PFT values calculated with 4DCT‐ventilation and nuclear‐medicine imaging.

Methods:

16 lung cancer patients retrospectively reviewed had undergone 4DCTs, nuclear‐medicine imaging, and had Forced Expiratory Volume in 1 second (FEV1) acquired as part of a standard PFT. For each patient, 4DCT data sets, spatial registration, and a density‐change based model were used to compute 4DCT‐ventilation maps. Both 4DCT and nuclear‐medicine images were used to calculate %PPO_FEV1 using %PPO_FEV1=pre‐operative FEV1*(1‐fraction of total ventilation of resected lung). Fraction of ventilation resected was calculated assuming lobectomy and pneumonectomy. The %PPO_FEV1 values were compared between the 4DCT‐ventilation‐based calculations and the nuclear‐medicine‐based calculations using correlation coefficients and average differences.

Results:

The correlation between %PPO_FEV1 values calculated with 4DCT‐ventilation and nuclear‐medicine were 0.81 (p<0.01) and 0.99 (p<0.01) for pneumonectomy and lobectomy respectively. The average difference between the 4DCT‐ventilation based and the nuclear‐medicine‐based %PPO_FEV1 values were small, 4.1±8.5% and 2.9±3.0% for pneumonectomy and lobectomy respectively.

Conclusion:

The high correlation results provide a strong rationale for a clinical trial translating 4DCT‐ventilation to the surgical domain. Compared to nuclear‐medicine, 4DCT‐ventilation is cheaper, does not require a radioactive contrast agent, provides a faster imaging procedure, and has improved spatial resolution. 4DCT‐ventilation can reduce the cost and imaging time for patients while providing improved spatial accuracy and quantitative results for surgeons.

YV discloses grant from State of Colorado
WE‐AB‐BRA‐12: Post‐Implant Dosimetry in Prostate Brachytherapy by X‐Ray and MRI Fusion
Authors: Park S , Le Y , Song D , Lee J
Published: July 2016

Purpose:

For post‐implant dosimetric assessment after prostate brachytherapy, CT‐MR fusion approach has been advocated due to the superior accuracy on both seeds localization and soft tissue delineation. However, CT deposits additional radiation to the patient, and seed identification in CT requires manual review and correction. In this study, we propose an accurate, low‐dose, and cost‐effective post‐implant dosimetry approach based on X‐ray and MRI.

Methods:

Implanted seeds are reconstructed using only three X‐ray fluoroscopy images by solving a combinatorial optimization problem. The reconstructed seeds are then registered to MR images using an intensity‐based points‐to‐volume registration. MR images are first pre‐processed by geometric and Gaussian filtering, yielding smooth candidate seed‐only images. To accommodate potential soft tissue deformation, our registration is performed in two steps, an initial affine followed by local deformable registrations. An evolutionary optimizer in conjunction with a points‐to‐volume similarity metric is used for the affine registration. Local prostate deformation and seed migration are then adjusted by the deformable registration step with external and internal force constraints.

Results:

We tested our algorithm on twenty patient data sets. For quantitative evaluation, we obtained ground truth seed positions by fusing the post‐implant CT‐MR images. Seeds were semi‐automatically extracted from CT and manually corrected and then registered to the MR images. Target registration error (TRE) was computed by measuring the Euclidean distances from the ground truth to the closest registered X‐ray seeds. The overall TREs (mean±standard deviation in mm) are 1.6±1.1 (affine) and 1.3±0.8 (affine+deformable). The overall computation takes less than 1 minute.

Conclusion:

It has been reported that the CT‐based seed localization error is ∼1.6mm and the seed localization uncertainty of 2mm results in less than 5% deviation of prostate D90. The average error of 1.3mm with our system outperforms the CT‐based approach and is considered well within the clinically acceptable limit.

Supported in part by NIH/NCI grant 5R01CA151395. The X‐ray‐based implant reconstruction method (US patent No. 8,233,686) was licensed to Acoustic MedSystems Inc.
WE‐AB‐202‐08: Feasibility of Single‐Inhalation/Single‐Energy Xenon CT for High‐Resolution Imaging of Regional Lung Ventilation in Humans
Authors: Pinkham D , Negahdar M , Schueler E , Yamamoto T , Diehn M , Mittra E , Loo B , Maxim P
Published: July 2016

Purpose:

To demonstrate the efficacy of a novel functional lung imaging method that utilizes single‐inhalation, single‐energy xenon CT (Xe‐CT) lung ventilation scans, and to compare it against the current clinical standard, ventilation single‐photon emission CT (V‐SPECT).

Methods:

In an IRB‐approved clinical study, 14 patients undergoing thoracic radiotherapy received two successive single inhalation, single energy (80keV) CT images of the entire lung using 100% oxygen and a 70%/30% xenon‐oxygen mixture. A subset of ten patients also received concurrent SPECT ventilation scans. Anatomic reproducibility between the two scans was achieved using a custom video biofeedback apparatus. The CT images were registered to each other by deformable registration, and a calculated difference image served as surrogate xenon ventilation map. Both lungs were partitioned into twelve sectors, and a sector‐wise correlation was performed between the xenon and V‐SPECT scans. A linear regression model was developed with forced expiratory volume (FEV) as a predictor and the coefficient of variation (CoV) as the outcome.

Results:

The ventilation comparison for five of the patients had either moderate to strong Pearson correlation coefficients (0.47 to 0.69, p<0.05). Of these, four also had moderate to strong Spearman correlation coefficients (0.46 to 0.80, p<0.03). The patients with the strongest correlation had clear regional ventilation deficits. The patient comparisons with the weakest correlations had more homogeneous ventilation distributions, and those patients also had diminished lung function as assessed by spirometry. Analysis of the relationship between CoV and FEV yielded a non‐significant trend toward negative correlation (Pearson coefficient −0.60, p<0.15).

Conclusion:

Significant correlations were found between the Xe‐CT and V‐SPECT ventilation imagery. The results from this small cohort of patients indicate that single inhalation, single energy Xe‐CT has the potential to quantify regional lung ventilation volumetrically with high resolution using widely accessible radiologic equipment.

Bill Loo and Peter Maxim are founders of TibaRay, Inc. Bill Loo is also a board member. Bill Loo and Peter Maxim have received research grants from Varian Medical Systems, Inc. and RaySearch Laboratory
WE‐AB‐202‐09: Feasibility and Quantitative Analysis of 4DCT‐Based High Precision Lung Elastography
Authors: Hasse K , Neylon J , Low D , Santhanam A
Published: July 2016

Purpose:

The purpose of this project is to derive high precision elastography measurements from 4DCT lung scans to facilitate the implementation of elastography in a radiotherapy context.

Methods:

4DCT scans of the lungs were acquired, and breathing stages were subsequently registered to each other using an optical flow DIR algorithm. The displacement of each voxel gleaned from the registration was taken to be the ground‐truth deformation. These vectors, along with the 4DCT source datasets, were used to generate a GPU‐based biomechanical simulation that acted as a forward model to solve the inverse elasticity problem. The lung surface displacements were applied as boundary constraints for the model‐guided lung tissue elastography, while the inner voxels were allowed to deform according to the linear elastic forces within the model. A biomechanically‐based anisotropic convergence magnification technique was applied to the inner voxels in order to amplify the subtleties of the interior deformation. Solving the inverse elasticity problem was accomplished by modifying the tissue elasticity and iteratively deforming the biomechanical model. Convergence occurred when each voxel was within 0.5 mm of the ground‐truth deformation and 1 kPa of the ground‐truth elasticity distribution. To analyze the feasibility of the model‐guided approach, we present the results for regions of low ventilation, specifically, the apex.

Results:

The maximum apical boundary expansion was observed to be between 2 and 6 mm. Simulating this expansion within an apical lung model, it was observed that 100% of voxels converged within 0.5 mm of ground‐truth deformation, while 91.8% converged within 1 kPa of the ground‐truth elasticity distribution. A mean elasticity error of 0.6 kPa illustrates the high precision of our technique.

Conclusion:

By utilizing 4DCT lung data coupled with a biomechanical model, high precision lung elastography can be accurately performed, even in low ventilation regions of the lungs.

This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE‐1144087.
WE‐AB‐207A‐03: A CBCT Head Scanner for Point‐Of‐Care Imaging of Intracranial Hemorrhage
Authors: Xu J , Sisniega A , Zbijewski W , Dang H , Stayman J , Wang X , Foos D , Aygun N , Koliatsos V , Siewerdsen J
Published: July 2016

Purpose:

This work reports the design, development, and first technical assessment of a cone‐beam CT (CBCT) scanner developed specifically for imaging of acute intracranial hemorrhage (ICH) at the point of care, with target applications in diagnosis and monitoring of traumatic brain injury, stroke, and postsurgical hemorrhage.

Methods:

System design employed a task‐based image quality model to quantify the influence of factors such as additive noise and high‐gain (HG) detector readout on ICH detectability. Three bowtie filters with varying bare‐beam attenuation strength and curvature were designed to enable HG readout without detector saturation, and a polyenergetic gain correction was developed to minimize artifacts from bowtie flood‐field calibration. Image reconstruction used an iterative penalized weighted least squares (PWLS) method with artifact correction including Monte Carlo scatter estimation, Joseph‐Spital beam hardening correction, and spatiotemporal deconvolution of detector glare and lag. Radiation dose was characterized for half‐scan and full‐scan protocols at various kV, and imaging performance was assessed in a head phantom presenting simulated ICH with diameter ranging 2–12 mm.

Results:

The image quality model guided system design and was validated by measurements on a CBCT imaging bench. Compared to low‐gain readout without a bowtie filter, the combination of HG readout and a modest bowtie improved the contrast‐to‐noise ratio (CNR per unit square‐root dose) by 20% in the center of the image but degraded noise performance near the periphery (20% reduction in CNR). Low‐frequency bowtie artifacts (∼100 HU magnitude) were corrected by the polyenergetic gain correction. Image reconstructions on the prototype scanner demonstrate clear visibility of the smallest ICH insert (2 mm diameter) in both HG readout (with a bowtie) and dual‐gain readout (without bowtie).

Conclusion:

Technical assessment of the prototype scanner suggests the capability for reliable visualization of small (2 mm), low‐contrast (50 HU) ICH at <20 mGy dose and motivates translation to clinical studies, now underway.

Xiaohui Wang and David Foos (co‐authors) are employees of Carestream Health. Research funding support from Carestream Health.
WE‐AB‐207A‐06: Progressive Dose Control for Cone Beam CT with Deformation Assisted Temporal Nonlocal Means Method
Authors: Chen L , Shen C , Wang J , Jiang S , Jia X
Published: July 2016

Purpose:

To reduce cone beam CT (CBCT) imaging dose, we previously proposed a progressive dose control (PDC) scheme to employ temporal correlation between CBCT images at different fractions for image quality enhancement. A temporal non‐local means (TNLM) method was developed to enhance quality of a new low‐dose CBCT using existing high‐quality CBCT. To enhance a voxel value, the TNLM method searches for similar voxels in a window. Due to patient deformation among the two CBCTs, a large searching window was required, reducing image quality and computational efficiency. This abstract proposes a deformation‐assisted TNLM (DA‐TNLM) method to solve this problem.

Methods:

For a low‐dose CBCT to be enhanced using a high‐quality CBCT, we first performed deformable image registration between the low‐dose CBCT and the high‐quality CBCT to approximately establish voxel correspondence between the two. A searching window for a voxel was then set based on the deformation vector field. Specifically, the search window for each voxel was shifted by the deformation vector. A TNLM step was then applied using only voxels within this determined window to correct image intensity at the low‐dose CBCT.

Results:

We have tested the proposed scheme on simulated CIRS phantom data and real patient data. The CITS phantom was scanned on Varian onboard imaging CBCT system with coach shifting and dose reducing for each time. The real patient data was acquired in four fractions with dose reduced from standard CBCT dose to 12.5% of standard dose. It was found that the DA‐TNLM method can reduce total dose by over 75% on average in the first four fractions.

Conclusion:

We have developed a PDC scheme which can enhance the quality of image scanned at low dose using a DA‐TNLM method. Tests in phantom and patient studies demonstrated promising results.
WE‐AB‐207A‐07: A Planning CT‐Guided Scatter Artifact Correction Method for CBCT Images
Authors: Yang X , Liu T , Dong X , Elder E , Curran W , Dhabaan A
Published: July 2016

Purpose:

Cone beam computed tomography (CBCT) imaging is on increasing demand for high‐performance image‐guided radiotherapy such as online tumor delineation and dose calculation. However, the current CBCT imaging has severe scatter artifacts and its current clinical application is therefore limited to patient setup based mainly on the bony structures. This study's purpose is to develop a CBCT artifact correction method.

Methods:

The proposed scatter correction method utilizes the planning CT to improve CBCT image quality. First, an image registration is used to match the planning CT with the CBCT to reduce the geometry difference between the two images. Then, the planning CT‐based prior information is entered into the Bayesian deconvolution framework to iteratively perform a scatter artifact correction for the CBCT mages. This technique was evaluated using Catphan phantoms with multiple inserts. Contrast‐to‐noise ratios (CNR) and signal‐to‐noise ratios (SNR), and the image spatial nonuniformity (ISN) in selected volume of interests (VOIs) were calculated to assess the proposed correction method.

Results:

Post scatter correction, the CNR increased by a factor of 1.96, 3.22, 3.20, 3.46, 3.44, 1.97 and 1.65, and the SNR increased by a factor 1.05, 2.09, 1.71, 3.95, 2.52, 1.54 and 1.84 for the Air, PMP, LDPE, Polystryrene, Acrylic, Delrin and Teflon inserts, respectively. The ISN decreased from 21.1% to 4.7% in the corrected images. All values of CNR, SNR and ISN in the corrected CBCT image were much closer to those in the planning CT images. The results demonstrated that the proposed method reduces the relevant artifacts and recovers CT numbers.

Conclusion:

We have developed a novel CBCT artifact correction method based on CT image, and demonstrated that the proposed CT‐guided correction method could significantly reduce scatter artifacts and improve the image quality. This method has great potential to correct CBCT images allowing its use in adaptive radiotherapy.
WE‐AB‐206‐02: ACR Ultrasound Accreditation: Requirements and Pitfalls
Authors: Walter J.
Published: July 2016

The involvement of medical physicists in diagnostic ultrasound imaging service is increasing due to QC and accreditation requirements. The goal of this ultrasound hands‐on workshop is to demonstrate quality control (QC) testing in diagnostic ultrasound and to provide updates in ACR ultrasound accreditation requirements. The first half of this workshop will include two presentations reviewing diagnostic ultrasound QA/QC and ACR ultrasound accreditation requirements. The second half of the workshop will include live demonstrations of basic QC tests. An array of ultrasound testing phantoms and ultrasound scanners will be available for attendees to learn diagnostic ultrasound QC in a hands‐on environment with live demonstrations and on‐site instructors. The targeted attendees are medical physicists in diagnostic imaging.

Learning Objectives:

Gain familiarity with common elements of a QA/QC program for diagnostic ultrasound imaging

dentify QC tools available for testing diagnostic ultrasound systems and learn how to use these tools

Learn ACR ultrasound accreditation requirements

Jennifer Walter is an employee of American College of Radiology on Ultrasound Accreditation.
WE‐AB‐209‐11: Prostate Cancer Treatment Planning: Sensitivity and Representative Objective Function Weights
Authors: Goli A. , Boutilier J.J. , Craig T. , Sharpe M.B. , Chan T.C.Y.
Published: July 2016

Purpose:

To develop an automated planning methodology that exploits patient sensitivity to objective function weights.

Methods:

Given a treatment plan, we first create an acceptable treatment region that encompasses a set of treatment plans with similar clinical performance (e.g., +/−1% at V70Gy). We use inverse optimization to map this region in criterion space to the weight space and find a corresponding region of acceptable weight vectors (W). The shape and size of W describes how sensitive a patient is to perturbations in objective function weights. To exploit the information encoded by these regions, we approximate W for each patient by a polyhedron and we cluster patients using a novel integer programming model with cluster sizes from k=1,2,…,10. Each cluster centroid is a representative objective function weight vector and we use these weight vectors to generate k treatment plans for each patient (AUTO plans). Using 315 prostate cancer plans, we determine the number of patients that would have received an improved treatment plan using our automated approach.

Results:

Clustering patients into five groups produced a global set of representative weights such that for 88% of patients there exists at least one AUTO plan that improves upon the clinical treatment plan in terms of organ‐at‐risk mean dose and clinical acceptability criteria satisfaction (i.e., V54Gy50% and V70Gy30%). The AUTO plans provided bladder or rectum mean dose improvement over the clinical treatment plans for 296 (94%) patients, bladder mean dose improvement for 185 (59%) patients, rectum mean dose improvement for 273 (87%) patients, and mean dose improvements for both bladder and rectum in 162 (51%) patients. The AUTO plans provided fewer violations for bladder/rectum V54Gy50% and slightly more for bladder/rectum V70Gy30% when compared to clinical plans.

Conclusion:

A method combining inverse optimization and clustering automatically produces prostate treatment plans for 88% of patients.
WE‐AB‐207B‐02: A Bayesian Network Approach for Joint Prediction of Tumor Control and Radiation Pneumonitis (RP) in Non‐Small‐Cell Lung Cancer (NSCLC)
Authors: Luo Y , McShan D , Matuszak M , Hobson S , Jolly S , Ten Haken R , El Naqa I
Published: July 2016

Purpose:

NSCLC radiotherapy treatment is a trade‐off between controlling the tumor while limiting radiation‐induced toxicities. Here we identify hierarchical biophysical relationships that could simultaneously influence both local control (LC) and RP by using an integrated Bayesian Networks (BN) approach.

Methods:

We studied 79 NSCLC patients treated on prospective protocol with 56 cases of LC and 21 events of RP. Beyond dosimetric information, each patient had 193 features including 12 clinical factors, 60 circulating blood cytokines before and during radiotherapy, 62 microRNAs, and 59 single‐nucleotide polymorphisms (SNPs). The most relevant biophysical predictors for both LC and RP were identified using a Markov blanket local discovery algorithm and the corresponding BN was constructed using a score‐learning algorithm. The area under the free‐response receiver operating characteristics (AU‐FROC) was used for performance evaluation. Cross‐validation was employed to guard against overfitting pitfalls.

Results:

A BN revealing the biophysical interrelationships jointly in terms of LC and RP was developed and evaluated. The integrated BN included two SNPs, one microRNA, one clinical factor, three pre‐treatment cytokines, relative changes of two cytokines between pre and during‐treatment, and gEUDs of the GTV (a=‐20) and lung (a=1). On cross‐validation, the AUC prediction of independent LC was 0.85 (95% CI: 0.75–0.95) and RP was 0.83 (0.73–0.92). The AU‐FROC of the integrated BN to predict both LC/RP was 0.81 (0.71–0.90) based on 2000 stratified bootstrap, indicating minimal loss in joint prediction power.

Conclusions:

We developed a new approach for multiple outcome utility application in radiotherapy based on integrated BN techniques. The BN developed from large‐scale retrospective data is able to simultaneously predict LC and RP in NSCLC treatments based on individual patient characteristics. The joint prediction is only slightly compromised compared to independent predictions. Our approach shows promise for use in clinical decision support system for personalized radiotherapy subject to multiple endpoints.

These studies were supported by a grant from the NCI/NIH P01‐CA59827.
WE‐AB‐207B‐04: A Preliminary Investigation of Indicators for Treatment Outcomes of CT Guided Cervical Cancer Brachytherapy
Authors: Meerschaert R , Paul A , Chen W , Miller S , Zhuang L
Published: July 2016

Purpose:

To identify indicators for recurrence in cervical cancer patients treated with high‐dose‐rate brachytherapy (HDR‐BT).

Methods:

A total of 37 biopsy proven uterine cervical cancer patients of stage IB‐IVA treated between 2011 and 2015 were included in this study. All patients were treated with 37.8–52.2Gy of external beam radiotherapy (EBRT) plus 5 × 5.0–6.5Gy of HDR‐BT. Patient age, standard deviation of high‐risk clinical tumor volume (HR‐CTVSD) collected throughout HDR‐BT, and D90 (EQD2, α/β=10Gy) of the HR‐CTV were investigated as potential indicators for local/distant recurrence using ROC analysis. The optimal cutoff value was identified through the Youden index and was subsequently used to obtain a group assignment for all patients. Another two comparing groups were defined per evidence of post‐EBRT tumor shrinkage based on the pre‐HDR MR scan. Kaplan‐Meier curves were generated for recurrence‐free proportions for comparing groups where time was measured from the final HDR treatment date to the date of the final follow‐up exam and compared through Cox regression.

Results:

Patients had a median follow‐up of 12 months, where 16% had local pelvic recurrence and 16% had distant recurrence. HR‐CTVSD was identified as a statistically significant indicator for recurrence (AUC=0.802, p=0.007) compared to D90 (AUC=0.655, p=0.167) and patient age (AUC=0.683, p=0.103). HR‐CTVSD of 6.26cc was chosen as the optimal cutoff value, which was used as the basis for patient group assignment. Patients with HR‐CTVSD>6.26cc had a hazard ratio of 3.92 (95% CI‐1.37, 11.24; p=0.011) for recurrence compared to HRCTVSD≤ 6.26cc. Patients without evidence of post‐EBRT tumor shrinkage compared to those with had a hazard ratio of 4.28 (95% CI‐1.14, 16.15; p=0.032) for recurrence.

Conclusion:

HR‐CTVSD was identified as an indicator for recurrence and an optimal value of 6.26cc was established in our study. In addition, patients without evidence of post‐EBRT tumor shrinkage demonstrated an increased recurrence rate.
WE‐B‐201‐02: Statistical Failings That Can Keep Us All in the Dark
Authors: Sloan J.
Published: July 2016

Evidence is growing to suggest that many published clinical results cannot be replicated. At the same time, the number of published clinical papers is steadily increasing and most if not all base their conclusions on evidence provided by formal statistical tests. Medical physicists have a critical need to understand and be able to interpret the methods and results of these studies in order to judge their scientific quality and relevance. However many medical physicists have minimal or no training in the sort of practical statistical methods commonly found in the literature. They may therefore have an inadequate ability to detect statistical errors and limitations that are an unfortunately too frequent occurrence in clinical papers.

In this session we will use published examples to demonstrate common statistical errors frequently encountered in peer‐reviewed literature, distinctive symptoms that can help detect these errors, and explanations for how they might have been corrected. In the process, we will explain some of the basic concepts of inferential statistics. Some specific case studies we will cover will include misunderstanding the meaning of p‐values and clinical significance, misinterpreting statistical power, not accounting for multiple‐hypothesis testing, ignoring missing data, and faulty survival analysis.

Learning Objectives:

Learn about the presence of statistical problems in published studies

Identify common signs and symptoms of potential problems in various types of statistical tests

Learn methods for correctly implementing statistical analyses of the type commonly found in clinical publications
WE‐B‐BRC‐01: Current Methodologies in Risk Assessment
Authors: Rath F.
Published: July 2016

Prospective quality management techniques, long used by engineering and industry, have become a growing aspect of efforts to improve quality management and safety in healthcare. These techniques are of particular interest to medical physics as scope and complexity of clinical practice continue to grow, thus making the prescriptive methods we have used harder to apply and potentially less effective for our interconnected and highly complex healthcare enterprise, especially in imaging and radiation oncology.

An essential part of most prospective methods is the need to assess the various risks associated with problems, failures, errors, and design flaws in our systems. We therefore begin with an overview of risk assessment methodologies used in healthcare and industry and discuss their strengths and weaknesses. The rationale for use of process mapping, failure modes and effects analysis (FMEA) and fault tree analysis (FTA) by TG‐100 will be described, as well as suggestions for the way forward. This is followed by discussion of radiation oncology specific risk assessment strategies and issues, including the TG‐100 effort to evaluate IMRT and other ways to think about risk in the context of radiotherapy. Incident learning systems, local as well as the ASTRO/AAPM ROILS system, can also be useful in the risk assessment process. Finally, risk in the context of medical imaging will be discussed. Radiation (and other) safety considerations, as well as lack of quality and certainty all contribute to the potential risks associated with suboptimal imaging.

The goal of this session is to summarize a wide variety of risk analysis methods and issues to give the medical physicist access to tools which can better define risks (and their importance) which we work to mitigate with both prescriptive and prospective risk‐based quality management methods.

Learning Objectives:

Description of risk assessment methodologies used in healthcare and industry

Discussion of radiation oncology‐specific risk assessment strategies and issues

Evaluation of risk in the context of medical imaging and image quality

E. Samei: Research grants from Siemens and GE
WE‐B‐BRC‐03: Risk in the Context of Medical Imaging
Authors: Samei E.
Published: July 2016

Prospective quality management techniques, long used by engineering and industry, have become a growing aspect of efforts to improve quality management and safety in healthcare. These techniques are of particular interest to medical physics as scope and complexity of clinical practice continue to grow, thus making the prescriptive methods we have used harder to apply and potentially less effective for our interconnected and highly complex healthcare enterprise, especially in imaging and radiation oncology.

An essential part of most prospective methods is the need to assess the various risks associated with problems, failures, errors, and design flaws in our systems. We therefore begin with an overview of risk assessment methodologies used in healthcare and industry and discuss their strengths and weaknesses. The rationale for use of process mapping, failure modes and effects analysis (FMEA) and fault tree analysis (FTA) by TG‐100 will be described, as well as suggestions for the way forward. This is followed by discussion of radiation oncology specific risk assessment strategies and issues, including the TG‐100 effort to evaluate IMRT and other ways to think about risk in the context of radiotherapy. Incident learning systems, local as well as the ASTRO/AAPM ROILS system, can also be useful in the risk assessment process. Finally, risk in the context of medical imaging will be discussed. Radiation (and other) safety considerations, as well as lack of quality and certainty all contribute to the potential risks associated with suboptimal imaging.

The goal of this session is to summarize a wide variety of risk analysis methods and issues to give the medical physicist access to tools which can better define risks (and their importance) which we work to mitigate with both prescriptive and prospective risk‐based quality management methods.

Learning Objectives:

Description of risk assessment methodologies used in healthcare and industry

Discussion of radiation oncology‐specific risk assessment strategies and issues

Evaluation of risk in the context of medical imaging and image quality

E. Samei: Research grants from Siemens and GE
WE‐DE‐201‐05: Evaluation of a Windowless Extrapolation Chamber Design and Monte Carlo Based Corrections for the Calibration of Ophthalmic Applicators
Authors: Hansen J , Culberson W , Soares C , DeWerd L
Published: July 2016

Purpose:

To test the validity of a windowless extrapolation chamber used to measure surface dose rate from planar ophthalmic applicators and to compare different Monte Carlo based codes for deriving correction factors.

Methods:

Dose rate measurements were performed using a windowless, planar extrapolation chamber with a 90Sr/90Y Tracerlab RA‐1 ophthalmic applicator previously calibrated at the National Institute of Standards and Technology (NIST). Capacitance measurements were performed to estimate the initial air gap width between the source face and collecting electrode. Current was measured as a function of air gap, and Bragg‐Gray cavity theory was used to calculate the absorbed dose rate to water. To determine correction factors for backscatter, divergence, and attenuation from the Mylar entrance window found in the NIST extrapolation chamber, both EGSnrc Monte Carlo user code and Monte Carlo N‐Particle Transport Code (MCNP) were utilized. Simulation results were compared with experimental current readings from the windowless extrapolation chamber as a function of air gap. Additionally, measured dose rate values were compared with the expected result from the NIST source calibration to test the validity of the windowless chamber design.

Results:

Better agreement was seen between EGSnrc simulated dose results and experimental current readings at very small air gaps (<100 µm) for the windowless extrapolation chamber, while MCNP results demonstrated divergence at these small gap widths. Three separate dose rate measurements were performed with the RA‐1 applicator. The average observed difference from the expected result based on the NIST calibration was −1.88% with a statistical standard deviation of 0.39% (k=1).

Conclusion:

EGSnrc user code will be used during future work to derive correction factors for extrapolation chamber measurements. Additionally, experiment results suggest that an entrance window is not needed in order for an extrapolation chamber to provide accurate dose rate measurements for a planar ophthalmic applicator.