bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐18C‐08: A Validation Study of a Commercially Available Software Package's Absorbed Dose Estimates in a Physical Phantom
Authors: Supanich M , Siegelman J
Published: July 2014

Purpose:

This study assesses the accuracy of the absorbed dose estimates from CT scans generated by Monte Carlo (MC) simulation using a commercially available radiation dose monitoring software program.

Methods:

Axial CT studies of an anthropomorphic abdomen phantom with dose bores at a central location and 4 peripheral locations were conducted using a fixed tube current at 120 kV. A 100 mm ion chamber and a 0.6 cc ion chamber calibrated at diagnostic energy levels were used to measure dose in the phantom at each of the 5 dose bore locations. Simulations using the software program's Monte Carlo engine were run using a mathematical model of the anthropomorphic phantom to determine conversion coefficients between the CTDIvol used for the study and the dose at the location of the dose bores. Simulations were conducted using both the software's generic CT beam model and a refined model generated using HVL and bow tie filter profile measurements made on the scanner used for the study.

Results:

Monte Carlo simulations completed using the generalized beam model differed from the measured conversion factors by an absolute value average of 13.0% and 13.8% for the 100 mm and 0.6 cc ion chamber studies, respectively. The MC simulations using the scanner specific beam model generated conversion coefficients that differed from the CTDIvol to measured dose conversion coefficients by an absolute value average of 7.3% and 7.8% for the 100 mm and 0.6 cc ion chamber cases, respectively.

Conclusion:

A scanner specific beam model used in MC simulations generates more accurate dose conversion coefficients in an anthropomorphic phantom than those generated with a generalized beam model. Agreement between measured conversion coefficients and simulated values were less than 20% for all positions using the universal beam model.
SU‐F‐18C‐09: Assessment of OSL Dosimeter Technology in the Validation of a Monte Carlo Radiation Transport Code for CT Dosimetry
Authors: Carver D , Kost S , Pickens D , Price R , Stabin M
Published: July 2014

Purpose:

To assess the utility of optically stimulated luminescent (OSL) dosimeter technology in calibrating and validating a Monte Carlo radiation transport code for computed tomography (CT).

Methods:

Exposure data were taken using both a standard CT 100‐mm pencil ionization chamber and a series of 150‐mm OSL CT dosimeters. Measurements were made at system isocenter in air as well as in standard 16‐cm (head) and 32‐cm (body) CTDI phantoms at isocenter and at the 12 o' clock positions. Scans were performed on a Philips Brilliance 64 CT scanner for 100 and 120 kVp at 300 mAs with a nominal beam width of 40 mm. A radiation transport code to simulate the CT scanner conditions was developed using the GEANT4 physics toolkit. The imaging geometry and associated parameters were simulated for each ionization chamber and phantom combination. Simulated absorbed doses were compared to both CTDI100 values determined from the ion chamber and to CTDI100 values reported from the OSLs. The dose profiles from each simulation were also compared to the physical OSL dose profiles.

Results:

CTDI100 values reported by the ion chamber and OSLs are generally in good agreement (average percent difference of 9%), and provide a suitable way to calibrate doses obtained from simulation to real absorbed doses. Simulated and real CTDI100 values agree to within 10% or less, and the simulated dose profiles also predict the physical profiles reported by the OSLs.

Conclusion:

Ionization chambers are generally considered the standard for absolute dose measurements. However, OSL dosimeters may also serve as a useful tool with the significant benefit of also assessing the radiation dose profile. This may offer an advantage to those developing simulations for assessing radiation dosimetry such as verification of spatial dose distribution and beam width.
SU‐F‐18C‐12: On the Relationship of the Weighted Dose to the Surface Dose In Abdominal CT – Patient Size Dependency
Authors: Zhou Y , Scott A , Allahverdian J
Published: July 2014

Purpose:

It is possible to measure the patient surface dose non‐invasively using radiolucent dosimeters. However, the patient size specific weighted dose remains unknown. We attempted to study the weighted dose to surface dose relationship as the patient size varies in abdominal CT.

Methods:

Seven abdomen phantoms (CIRS TE series) simulating patients from an infant to a large adult were used. Size specific doses were measured with a 100 mm CT chamber under axial scans using a Siemens Sensation 64 (mCT) and a GE 750 HD. The scanner settings were 120 kVp, 200 mAs with fully opened collimations. Additional kVps (80, 100, 140) were added depending on the phantom sizes. The ratios (r) of the weighted CT dose (Dw) to the surface dose (Ds) were related to the phantom size (L) defined as the diameter resulting the equivalent cross‐sectional area.

Results:

The Dw versus Ds ratio (r) was fitted to a linear relationship: r = 1.083 − 0.007L (R square = 0.995), and r = 1.064 − 0.007L (R square = 0.953), for Siemens Sensation 64 and GE 750 HD, respectively. The relationship appears to be independent of the scanner specifics.

Conclusion:

The surface dose to the weighted dose ratio decreases linearly as the patient size increases. The result is independent of the scanner specifics. The result can be used to obtain in vivo CT dosimetry in abdominal CT.
SU‐F‐18C‐13: Low‐Dose X‐Ray CT Reconstruction Using a Hybrid First‐Order Method
Authors: Liu L , Lin W , Jin M
Published: July 2014

Purpose:

To develop a novel reconstruction method for X‐ray CT that can lead to accurate reconstruction at significantly reduced dose levels combining low X‐ray incident intensity and few views of projection data.

Methods:

The noise nature of the projection data at low X‐ray incident intensity was modeled and accounted by the weighted least‐squares (WLS) criterion. The total variation (TV) penalty was used to mitigate artifacts caused by few views of data. The first order primal‐dual (FOPD) algorithm was used to minimize TV in image domain, which avoided the difficulty of the non‐smooth objective function. The TV penalized WLS reconstruction was achieved by alternated FOPD TV minimization and projection onto convex sets (POCS) for data fidelity constraints. The proposed FOPD‐POCS method was evaluated using the FORBILD jaw phantom and the real cadaver head CT data.

Results:

The quantitative measures, root mean square error (RMSE) and contrast‐to‐noise ratio (CNR), demonstrate the superior denoising capability of WLS over LS‐based TV iterative reconstruction. The improvement of RMSE (WLS vs. LS) is 15%∼21% and that of CNR is 17%∼72% when the incident counts per ray are ranged from 1×105 to 1×103. In addition, the TV regularization can accurately reconstruct images from about 50 views of the jaw phantom. The FOPD‐POCS reconstruction reveals more structural details and suffers fewer artifacts in both the phantom and real head images. The FOPD‐POCS method also shows fast convergence at low X‐ray incident intensity.

Conclusion:

The new hybrid FOPD‐POCS method, based on TV penalized WLS, yields excellent image quality when the incident X‐ray intensity is low and the projection views are limited. The reconstruction is computationally efficient since the FOPD minimization of TV is applied only in the image domain. The characteristics of FOPD‐POCS can be exploited to significantly reduce radiation dose of X‐ray CT without compromising accuracy for diagnosis or treatment planning.
SU‐F‐18C‐15: Model‐Based Multiscale Noise Reduction On Low Dose Cone Beam Projection
Authors: Yao W , Farr J
Published: July 2014

Purpose:

To improve image quality of low dose cone beam CT for patient positioning in radiation therapy.

Methods:

In low dose cone beam CT (CBCT) imaging systems, Poisson process governs the randomness of photon fluence at x‐ray source and the detector because of the independent binomial process of photon absorption in medium. On a CBCT projection, the variance of fluence consists of the variance of noiseless imaging structure and that of Poisson noise, which is proportional to the mean (noiseless) of the fluence at the detector. This requires multiscale filters to smoothen noise while keeping the structure information of the imaged object. We used a mathematical model of Poisson process to design multiscale filters and established the balance of noise correction and structure blurring. The algorithm was checked with low dose kilo‐voltage CBCT projections acquired from a Varian OBI system.

Results:

From the investigation of low dose CBCT of a Catphan phantom and patients, it showed that our model‐based multiscale technique could efficiently reduce noise and meanwhile keep the fine structure of the imaged object. After the image processing, the number of visible line pairs in Catphan phantom scanned with 4 ms pulse time was similar to that scanned with 32 ms, and soft tissue structure from simulated 4 ms patient head‐and‐neck images was also comparable with scanned 20 ms ones. Compared with fixed‐scale technique, the image quality from multiscale one was improved.

Conclusion:

Use of projection‐specific multiscale filters can reach better balance on noise reduction and structure information loss. The image quality of low dose CBCT can be improved by using multiscale filters.
MO‐B‐16A‐02: In Memoriam of Donald D. Tolbert: Surviving the Politics of Radiation Therapy
Authors: Bayouth J , Limmer J
Published: July 2014

Today's healthcare work environment is ever‐changing and without a doubt will continue to do so for the foreseeable future. How physicists are employed, evaluated, and valued are important aspects of our careers. With increasing demands and challenges being placed on the medical physics workforce, it is important to have the skills and knowledge to prepare for potential challenges to the status‐quo of our employment status. Surviving in a world of change, consolidation, increased workload, and financial constraints is not a given, and preparing for those changes and challenges will benefit individuals as well as the medical physics community at large.

Learning Objectives:

Understand the challenges of succeeding in different work environments.

Learn strategies to help define the role of a medical physicist to various administrators, physicians, and department staff and directors.

Learn how to successfully communicate and interact with University, Hospital, and Department administrators.
MO‐E‐18C‐02: Hands‐On Monte Carlo Project Assignment as a Method to Teach Radiation Physics
Authors: Pater P , Vallieres M , Seuntjens J
Published: July 2014

Purpose:

To present a hands‐on project on Monte Carlo methods (MC) recently added to the curriculum and to discuss the students' appreciation.

Methods:

Since 2012, a 1.5 hour lecture dedicated to MC fundamentals follows the detailed presentation of photon and electron interactions. Students also program all sampling steps (interaction length and type, scattering angle, energy deposit) of a MC photon transport code. A handout structured in a step‐by‐step fashion guides student in conducting consistency checks. For extra points, students can code a fully working MC simulation, that simulates a dose distribution for 50 keV photons. A kerma approximation to dose deposition is assumed. A survey was conducted to which 10 out of the 14 attending students responded. It compared MC knowledge prior to and after the project, questioned the usefulness of radiation physics teaching through MC and surveyed possible project improvements.

Results:

According to the survey, 76% of students had no or a basic knowledge of MC methods before the class and 65% estimate to have a good to very good understanding of MC methods after attending the class. 80% of students feel that the MC project helped them significantly to understand simulations of dose distributions. On average, students dedicated 12.5 hours to the project and appreciated the balance between hand‐holding and questions/implications.

Conclusion:

A lecture on MC methods with a hands‐on MC programming project requiring about 14 hours was added to the graduate study curriculum since 2012. MC methods produce “gold standard” dose distributions and slowly enter routine clinical work and a fundamental understanding of MC methods should be a requirement for future students. Overall, the lecture and project helped students relate crosssections to dose depositions and presented numerical sampling methods behind the simulation of these dose distributions.

Research funding from governments of Canada and Quebec. PP acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290)
MO‐E‐18C‐03: Incorporating Active Learning Into A Traditional Graduate Medical Physics Course
Authors: Burmeister J
Published: July 2014

Purpose:

To improve the ability of graduate students to learn medical physics concepts through the incorporation of active learning techniques.

Methods:

A traditional lecture‐based radiological physics course was modified such that: (1) traditional (two‐hour) lectures were provided online for students to watch prior to class, (2) a student was chosen randomly at the start of each class to give a two minute synopsis of the material and its relevance (two‐minute drill), (3) lectures were significantly abbreviated and remaining classroom time used for group problem solving, and (4) videos of the abbreviated lectures were made available online for review. In the transition year, students were surveyed about the perceived effects of these changes on learning. Student performance was evaluated for 3 years prior to and 4 years after modification.

Results:

The survey tool used a five point scale from 1=Not True to 5=Very True. While nearly all students reviewed written materials prior to class (4.3±0.9), a minority watched the lectures (2.1±1.5). A larger number watched the abbreviated lectures for further clarification (3.6±1.6) and found it helpful in learning the content (4.2±1.0). Most felt that the two‐minute drill helped them get more out of the lecture (3.9±0.8) and the problem solving contributed to their understanding of the content (4.1±0.8). However, no significant improvement in exam scores resulted from the modifications (mean scores well within 1 SD during study period).

Conclusion:

Students felt that active learning techniques improved their ability to learn the material in what is considered the most difficult course in the program. They valued the ability to review the abbreviated class lecture more than the opportunity to watch traditional lectures prior to class. While no significant changes in student performance were observed, aptitude variations across the student cohorts make it difficult to draw conclusions about the effectiveness of active learning.
MO‐E‐18C‐05: Global Health Catalyst: A Novel Platform for Enhancing Access to Medical Physics Education and Research Excellence (AMPERE)
Authors: Ngwa W , Moreau M , Asana L
Published: July 2014

Purpose:

To develop a platform for catalyzing collaborative global Cancer Care Education and Research (CaRE), with a prime focus on enhancing Access to Medical Physics Education and Research Excellence (AMPERE)

Methods:

An analysis of over 50 global health collaborations between partners in the U.S. and low and middle income countries (LMIC) in Africa was carried out to assess the models of collaborations in Education and Research and relative success. A survey was carried out with questions including: the nature of the collaboration, how it was initiated, impact of culture and other factors, and recommendations for catalyzing/enhancing such collaborations. An online platform called Global Health Catalyst was developed for enhancing AMPERE.

Results:

The analysis yielded three main models for global health collaborations with survey providing key recommendations on how to enhance such collaborations. Based on this, the platform was developed, and customized to allow Medical Physicists and other Radiation oncology (RadOnc) professionals interested in participating in Global health to readily do so e.g. teach an online course module, participate in training Medical Physicists or other RadOnc health professionals in LMIC, co‐mentor students, residents or postdocs, etc. The growing list of features on the platform also include: a feature to enable people to easily find each other, form teams, operate more effectively as partners from different disciplines, institutions, nations and cultural backgrounds, share tools and technologies, obtain seed funding to develop curricula and/or embark upon new areas of investigation, and participate in humanitarian outreach: remote treatment planning assistance, and participation in virtual Chart Rounds, etc.

Conclusion:

The developed Global Health Catalyst platform could enable any Medical Physicist or RadoOnc professional interested in global health to readily participate in the Education/training of next generation RadOnc professionals and global health leaders, and enhance AMPERE, especially for LMIC.
MO‐E‐18C‐06: Enriching Medical Physics Education By Visualizing The Invisible
Authors: Sprawls P
Published: July 2014

Purpose:

To enhance the understanding of medical physics concepts and develop higher levels of learning relating to invisible physics phenomena such as radiation. To provide medical physics educators in all countries of the world with understanding of knowledge structures in the human brain, the different levels of learning, and the types of knowledge required for higher level functions such as problem solving, creative innovations, and applied clinical applications. To provide medical physics educators with an open access resource (tool) that they can use in their teaching activities to enrich and elevate the level of learning for their students, residents, etc. with respect to the invisible realm of medical physics.

Methods:

An experienced clinical medical physicist and educator has created and provided with open access three complementary web‐based resources to achieve the purposes described above. One is a module focusing on the medical physics learning process with respect to mental knowledge structures, how they relate to outcomes and applications, and learning activities that are required to develop the required knowledge structures. The second is an extensive set of visuals that educators can use in their activities (classes, small group discussions, etc.) to visualize the invisible. The third is an interactive online simulation where learners can adjust factors and visually observe changes in x‐radiation. These resources are available online at www.BLINDEDFORREVIEW.

Results:

Medical physics education, especially for non‐physicists, is becoming much more interesting and useful especially with respect to invisible radiation. The global impact is that medical imaging professionals can be more effective in optimizing x‐ray imaging procedures and risk management when they have knowledge levels that enhance problem solving, innovation, and creativity.

Conclusion:

Medical physics educators in all institutions can be much more effective and efficient in the sharing of their knowledge and experience when enhanced with high‐quality visuals.
MO‐E‐9A‐01: Risk Based Quality Management: TG100 In Action
Authors: Huq M , Palta J , Dunscombe P , Thomadsen B
Published: July 2014

One of the goals of quality management in radiation therapy is to gain high confidence that patients will receive the prescribed treatment correctly. To accomplish these goals professional societies such as the American Association of Physicists in Medicine (AAPM) has published many quality assurance (QA), quality control (QC), and quality management (QM) guidance documents. In general, the recommendations provided in these documents have emphasized on performing device‐specific QA at the expense of process flow and protection of the patient against catastrophic errors. Analyses of radiation therapy incidents find that they are most often caused by flaws in the overall therapy process, from initial consult through final treatment, than by isolated hardware or computer failures detectable by traditional physics QA. This challenge is shared by many intrinsically hazardous industries. Risk assessment tools and analysis techniques have been developed to define, identify, and eliminate known and/or potential failures, problems, or errors, from a system, process and/or service before they reach the customer. These include, but are not limited to, process mapping, failure modes and effects analysis (FMEA), fault tree analysis (FTA), and establishment of a quality management program that best avoids the faults and risks that have been identified in the overall process. These tools can be easily adapted to radiation therapy practices because of their simplicity and effectiveness to provide efficient ways to enhance the safety and quality of treatment processes. Task group 100 (TG100) of AAPM has developed a risk‐based quality management program that uses these tools. This session will be devoted to a discussion of these tools and how these tools can be used in a given radiotherapy clinic to develop a risk based QM program.

Learning Objectives:

Learn how to design a process map for a radiotherapy process.

Learn how to perform a FMEA analysis for a given process.

Learn what Fault tree analysis is all about.

Learn how to design a quality management program based upon the information obtained from process mapping, FMEA and FTA.
MO‐E‐12A‐01: Quantitative Imaging: Techniques, Applications, and Challenges
Authors: Jackson E , McNitt‐Gray M , Jeraj R , Cao Y
Published: July 2014

The first symposium in the Quantitative Imaging Track focused on the introduction of quantitative imaging (QI) by illustrating the potential of QI in diagnostic and therapeutic applications in research and patient care, highlighting key challenges in implementation of such QI applications, and reviewing QI efforts of selected national and international agencies and organizations, including the FDA, NCI, NIST, and RSNA. This second QI symposium will focus more specifically on the techniques, applications, and challenges of QI. The first talk of the session will focus on modalityagnostic challenges of QI, beginning with challenges of the development and implementation of QI applications in single‐center, single‐vendor settings and progressing to the challenges encountered in the most general setting of multi‐center, multi‐vendor settings. The subsequent three talks will focus on specific QI challenges and opportunities in the modalityspecific settings of CT, PET/CT, and MR. Each talk will provide information on modality‐specific QI techniques, applications, and challenges, including current efforts focused on solutions to such challenges.

Learning Objectives:

Understand key general challenges of QI application development and implementation, regardless of modality.

Understand selected QI techniques and applications in CT, PET/CT, and MR.

Understand challenges, and potential solutions for such challenges, for the applications presented for each modality.
MO‐F‐16A‐01: Implementation of MPPG TPS Verification Tests On Various Accelerators
Authors: Smilowitz J , Bredfeldt J , Geurts M , Miller J
Published: July 2014

Purpose:

To demonstrate the implementation of the Medical Physics Practice Guideline (MPPG) for dose calculation and beam parameters verification of treatment planning systems (TPS).

Methods:

We implemented the draft TPS MPPG for three linacs: Varian Trilogy, TomoHDA and Elekta Infinity. Static and modulated test plans were created. The static fields are different than used in commissioning. Data was collected using ion chambers and diodes in a scanning water tank, Delta4 phantom and a custom phantom. MatLab and Microsoft Excel were used to create analysis tools to compare reference DICOM dose with scan data. This custom code allowed for the interpolation, registration and gamma analysis of arbitrary dose profiles. It will be provided as open source code. IMRT fields were validated with Delta4 registration and comparison tools. The time for each task was recorded.

Results:

The tests confirmed the strengths, and revealed some limitations, of our TPS. The agreement between calculated and measured dose was reported for all beams. For static fields, percent depth dose and profiles were analyzed with criteria in the draft MPPG. The results reveal areas of slight mismatch with the model (MLC leaf penumbra, buildup region.) For TomoTherapy, the IMRT plan 2%/2 mm gamma analysis revealed poorest agreement in the low dose regions. For one static test plan for all 10MV Trilogy photon beams, the plan generation, scan queue creation, data collection, data analysis and report took 2 hours, excluding tank setup.

Conclusions:

We have demonstrated the implementation feasibility of the TPS MPPG. This exercise generated an open source tool for dose comparisons between scan data and DICOM dose data. An easily reproducible and efficient infrastructure with streamlined data collection was created for repeatable robust testing of the TPS. The tests revealed minor discrepancies in our models and areas for improvement that are being investigated.
MO‐F‐16A‐06: Implementation of a Radiation Exposure Monitoring System for Surveillance of Multi‐Modality Radiation Dose Data
Authors: Stewart B , Kanal K , Dickinson R , Zamora D
Published: July 2014

Purpose:

We have implemented a commercially available Radiation Exposure Monitoring System (REMS) to enhance the processes of radiation dose data collection, analysis and alerting developed over the past decade at our sites of practice. REMS allows for consolidation of multiple radiation dose information sources and quicker alerting than previously developed processes.

Methods:

Thirty‐nine x‐ray producing imaging modalities were interfaced with the REMS: thirteen computed tomography scanners, sixteen angiography/interventional systems, nine digital radiography systems and one mammography system. A number of methodologies were used to provide dose data to the REMS: Modality Performed Procedure Step (MPPS) messages, DICOM Radiation Dose Structured Reports (RDSR), and DICOM header information. Once interfaced, the dosimetry information from each device underwent validation (first 15–20 exams) before release for viewing by end‐users: physicians, medical physicists, technologists and administrators.

Results:

Before REMS, our diagnostic physics group pulled dosimetry data from seven disparate databases throughout the radiology, radiation oncology, cardiology, electrophysiology, anesthesiology/pain management and vascular surgery departments at two major medical centers and four associated outpatient clinics. With the REMS implementation, we now have one authoritative source of dose information for alerting, longitudinal analysis, dashboard/graphics generation and benchmarking. REMS provides immediate automatic dose alerts utilizing thresholds calculated through daily statistical analysis. This has streamlined our Closing the Loop process for estimated skin exposures in excess of our institutional specific substantial radiation dose level which relied on technologist notification of the diagnostic physics group and daily report from the radiology information system (RIS). REMS also automatically calculates the CT size‐specific dose estimate (SSDE) as well as provides two‐dimensional angulation dose maps for angiography/interventional procedures.

Conclusion:

REMS implementation has streamlined and consolidated the dosimetry data collection and analysis process at our institutions while eliminating manual entry error and providing immediate alerting and access to dosimetry data to both physicists and physicians.

Brent Stewart has funded research through GE Healthcare.
MO‐G‐BRE‐07: Risk Assessment of Surface Image Guided Stereotactic Radiosurgery
Authors: Manger R , Paxton A , Pawlicki T , Kim G
Published: July 2014

Purpose:

To develop a process map detailing the steps in the clinical workflow for surface imaging guided stereotactic radiosurgery (SRS), conduct a failure mode and effects analysis (FMEA) based on the process map, and perform fault tree analysis (FTA) on the steps with the highest risk priority number (RPN).

Methods:

A multi‐disciplinary team was assembled to develop a comprehensive process map listing the steps from initial consult to final treatment of a patient receiving surface image guided SRS. This process map represents the ideal workflow that would lead to successful treatment. An FMEA was conducted to determine the failure modes for each of the surface imaging related steps in the workflow and their relative risks. The risk priority numbers were calculated as the product of the occurrence, severity, and lack of detectability. The failure modes were ranked by RPN to determine the relative risk of the various steps in the process, and FTA was used to identify the potential causal relationships

Results:

The SRS process map contained over 90 steps, resulting in an FMEA with over 150 failure modes – about 25% associated with surface imaging. Based on the FMEA, the steps with the highest RPN were related to image registration, target delineation, and image handling. Surface imaging processes had considerably lower RPNs on average due to the high detectability of failure.

Conclusion:

The process map and FMEA presented in this work has reinforced the importance of image registration and target delineation in SRS. Clinicians considering proactive quality management of their SRS and/or surface imaging programs should be able to use the process map and FMEA as a template for their analyses. Although the occurrence rate and detection efficiency are dependent on the policies and procedures of an institution, the steps with the greatest RPN should not vary greatly.
MO‐G‐BRE‐08: Taxonomy of Corrective Actions in Radiotherapy
Authors: Sutlief S , Brown D
Published: July 2014

Purpose:

Various causal taxonomies have been developed for healthcare incidents and for radiation therapy in particular. The causal analysis of incidents leads to corrective actions which can also be organized into a taxonomy. Such a corrective action classification system would provide information about the situational context, the action type, and the leverage of the action in order to detect patterns in the corrective actions frequently employed in radiation therapy. It would also provide practical guidance to the radiation therapy community for determining the appropriateness and potential effectiveness of proposed corrective actions.

Materials:

A review of causal analysis reports and corrective action plans was conducted using the following sources: US NRC medical event reports, IAEA reports, ROSIS submissions, US Veterans Health Administration reports, and singleincident report sources. The corrective actions presented in the published sources were then mapped onto four corrective action taxonomy prototypes: role‐based, safety‐context‐based, responsibility‐based, and hierarchy of hazard control. The resulting corrective action taxonomy was then validated through use of the published sources.

Results:

The responsibility‐based taxonomy and hierarchy of hazard taxonomy provided more intuitive and sensible categories than the role‐based taxonomy or the safety‐context taxonomy. The most frequent corrective actions were added safety barriers, training, process standardization, and development of a quality improvement program where one was lacking.

Conclusion:

Published corrective action statements in radiation therapy emphasize what to do more so than whom the recipient is or which process step is affected. The hierarchy of hazard taxonomy provides a suitable framework for radiation therapy and has the advantage of providing insight into the likelihood that a particular corrective action will mitigate the recurrence of the error it was meant to correct. This information would be useful to medical center administration, safety personnel, and regulators who must assess the projected efficacy of corrective actions.

Derek Brown is a director of TreatSafely, LLC.
MO‐G‐BRF‐01: BEST IN PHYSICS (JOINT IMAGING‐THERAPY) – Sensitivity of PET‐Based Texture Features to Respiratory Motion in Non‐Small Cell Lung Cancer (NSCLC)
Authors: Yip S , McCall K , Aristophanous M , Chen A , Aerts H , Berbeco R
Published: July 2014

Purpose:

PET‐based texture features are used to quantify tumor heterogeneity due to their predictive power in treatment outcome. We investigated the sensitivity of texture features to tumor motion by comparing whole body (3D) and respiratory‐gated (4D) PET imaging.

Methods:

Twenty‐six patients (34 lesions) received 3D and 4D [F‐18]FDG‐PET scans before chemo‐radiotherapy. The acquired 4D data were retrospectively binned into five breathing phases to create the 4D image sequence. Four texture features (Coarseness, Contrast, Busyness, and Complexity) were computed within the the physician‐defined tumor volume. The relative difference (δ) in each measure between the 3D‐ and 4D‐PET imaging was calculated. Wilcoxon signed‐rank test (p<0.01) was used to determine if δ was significantly different from zero. Coefficient of variation (CV) was used to determine the variability in the texture features between all 4D‐PET phases. Pearson correlation coefficient was used to investigate the impact of tumor size and motion amplitude on δ.

Results:

Significant differences (p<<0.01) between 3D and 4D imaging were found for Coarseness, Busyness, and Complexity. The difference for Contrast was not significant (p>0.24). 4D‐PET increased Busyness (∼20%) and Complexity (∼20%), and decreased Coarseness (∼10%) and Contrast (∼5%) compared to 3D‐PET. Nearly negligible variability (CV=3.9%) was found between the 4D phase bins for Coarseness and Complexity. Moderate variability was found for Contrast and Busyness (CV∼10%). Poor correlation was found between the tumor volume and δ for the texture features (R=−0.34−0.34). Motion amplitude had moderate impact on δ for Contrast and Busyness (R=−0.64− 0.54) and no impact for Coarseness and Complexity (R=−0.29−0.17).

Conclusion:

Substantial differences in textures were found between 3D and 4D‐PET imaging. Moreover, the variability between phase bins for Coarseness and Complexity was negligible, suggesting that similar quantification can be obtained from all phases. Texture features, blurred out by respiratory motion during 3D‐PET acquisition, can be better resolved by 4D‐PET imaging with any phase.
MO‐G‐BRF‐06: Radiotherapy and Prompt Oxygen Dynamics
Authors: Kissick M , Campos D , Adamson E , Niles D , Torres A , L Che Fru , Kimple R , Fain S , Jacques S , van der Kogel A
Published: July 2014

Purpose:

Adaptive radiotherapy requires a knowledge of the changing local tumor oxygen concentrations for times on the order of the treatment time, a time scale far shorter than cell death and proliferation. This knowledge will be needed to guide hypofractionated radiotherapy.

Methods:

A diffuse optical probe system was developed to spatially average over the whole interior of athymic Sprague Dawley nude mouse xenografts of human head and neck cancers. The blood volume and hemoglobin saturation was measured in real time. The quantities were measured with spectral fitting before and after 10 Gy of radiation is applied. An MRI BOLD scan is acquired before and after 10 Gy that measures regional changes in R2* which is inversely proportional to oxygen availability. Simulations were performed to fit the blood oxygen dynamics and infer changes in hypoxia within the tumor.

Results:

The optical probe measured nearly constant blood volume and a significant drop in hemoglobin saturation of about 30% after 10 Gy over the time scale of less than 30 minutes. The averaged R2* within the tumor volume increased by 15% after the 10 Gy dose, which is consistent with the optical results. The simulations and experiments support likely dynamic metabolic changes and/or fast vasoconstrictive signals are occurring that change the oxygen concentrations significantly, but not cell death or proliferation.

Conclusion:

Significant oxygen changes were observed to occur within 30 minutes, coinciding with the treatment time scale. This dynamic is very important for patient specific adaptive therapy. For hypofractionated therapy, the local instantaneous oxygen content is likely the most important variable to control. The invention of a bedside device for the purpose of measuring the instantaneous response to large radiation doses would be an important step to future improvements in outcome.
MO‐G‐BRF‐07: Anomalously Fast Diffusion of Carbon Nanotubes Carriers in 3D Tissue Model
Authors: Wang Y , Bahng J , Kotov N
Published: July 2014

Purpose:

We aim to investigate and understand diffusion process of carbon nanotubes (CNTs) and other nanoscale particles in tissue and organs.

Methods:

In this research, we utilized a 3D model tissue of hepatocellular carcinoma (HCC)cultured in inverted colloidal crystal (ICC) scaffolds to compare the diffusivity of CNTs with small molecules such as Rhodamine and FITC in vitro, and further investigated the transportation of CNTs with and without targeting ligand, TGFβ1. The real‐time permeation profiles of CNTs in HCC tissue model with high temporal and spatial resolution was demonstrated by using standard confocal microscopy. Quantitative analysis of the diffusion process in 3D was carried out using luminescence intensity in a series of Z‐stack images obtained for different time points of the diffusion process after initial addition of CNTs or small molecules to the cell culture and the image data was analyzed by software ImageJ and Mathematica.

Results:

CNTs display diffusion rate in model tissues substantially faster than small molecules of the similar charge such as FITC, and the diffusion rate of CNTs are significantly enhanced with targeting ligand, TGFβ1.

Conclusion:

In terms of the advantages of in‐vitro model, we were able to have access to measuring the rate of CNT penetration at designed conditions with variable parameters. And the findings by using this model, changed our understanding about advantages of CNTs as nanoscale drug carriers and provides design principles for making new drug carriers for both treatment and diagnostics. Additionally the fast diffusion opens the discussion of the best possible drug carriers to reach deep parts of cancerous tissues, which is often a prerequisite for successful cancer treatment.

This work was supported by the Center for Photonic and Multiscale Nanomaterials funded by National Science Foundation Materials Research Science and Engineering Center program DMR 1120923. The work was also partially supported by NSF grant ECS‐0601345; EFRI‐BSBA 0938019; CBET 0933384; CBET 0932823; CBET 1036672, AFOSR MURI 444286‐P061716 and NIH 1R21CA121841‐01A2.
MO‐G‐17A‐02: Computer Simulation Studies for On‐Board Functional and Molecular Imaging of the Prostate Using a Robotic Multi‐Pinhole SPECT System
Authors: Cheng L , Bowsher J , Yan S , Yin F
Published: July 2014

Purpose:

To investigate prostate imaging onboard radiation therapy machines using a novel robotic, 49‐pinhole Single Photon Emission Computed Tomography (SPECT) system.

Methods:

Computer‐simulation studies were performed for region‐of‐interest (ROI) imaging using a 49‐pinhole SPECT collimator and for broad cross‐section imaging using a parallel‐hole SPECT collimator. A male XCAT phantom was computersimulated in supine position with one 12mm‐diameter tumor added in the prostate. A treatment couch was added to the phantom. Four‐minute detector trajectories for imaging a 7cm‐diameter‐sphere ROI encompassing the tumor were investigated with different parameters, including pinhole focal length, pinhole diameter and trajectory starting angle. Pseudo‐random Poisson noise was included in the simulated projection data, and SPECT images were reconstructed by OSEM with 4 subsets and up to 10 iterations. Images were evaluated by visual inspection, profiles, and Root‐Mean‐ Square‐Error (RMSE).

Results:

The tumor was well visualized above background by the 49‐pinhole SPECT system with different pinhole parameters while it was not visible with parallel‐hole SPECT imaging. Minimum RMSEs were 0.30 for 49‐pinhole imaging and 0.41 for parallelhole imaging. For parallel‐hole imaging, the detector trajectory from rightto‐ left yielded slightly lower RMSEs than that from posterior to anterior. For 49‐pinhole imaging, near‐minimum RMSEs were maintained over a broader range of OSEM iterations with a 5mm pinhole diameter and 21cm focal length versus a 2mm diameter pinhole and 18cm focal length. The detector with 21cm pinhole focal length had the shortest rotation radius averaged over the trajectory.

Conclusion:

On‐board functional and molecular prostate imaging may be feasible in 4‐minute scan times by robotic SPECT. A 49‐pinhole SPECT system could improve such imaging as compared to broadcross‐section parallel‐hole collimated SPECT imaging. Multi‐pinhole imaging can be improved by considering pinhole focal length, pinhole diameter, and trajectory starting angle.

The project is supported by the NIH grant 5R21‐CA156390.
MO‐G‐17A‐04: Internal Dosimetric Calculations for Pediatric Nuclear Imaging Applications, Using Monte Carlo Simulations and High‐Resolution Pediatric Computational Models
Authors: Papadimitroulas P , Loudos G , Kagadis GC
Published: July 2014

Purpose:

Our purpose is to evaluate the administered absorbed dose in pediatric, nuclear imaging studies. Monte Carlo simulations with the incorporation of pediatric computational models can serve as reference for the accurate determination of absorbed dose. The procedure of the calculated dosimetric factors is described, while a dataset of reference doses is created.

Methods:

Realistic simulations were executed using the GATE toolkit and a series of pediatric computational models, developed by the “IT' IS Foundation”. The series of the phantoms used in our work includes 6 models in the range of 5–14 years old (3 boys and 3 girls). Pre‐processing techniques were applied to the images, to incorporate the phantoms in GATE simulations. The resolution of the phantoms was set to 2 mm3. The most important organ densities were simulated according to the GATE “Materials Database”. Several used radiopharmaceuticals in SPECT and PET applications are being tested, following the EANM pediatric dosage protocol. The biodistributions of the several isotopes used as activity maps in the simulations, were derived by the literature.

Results:

Initial results of absorbed dose per organ (mGy) are presented in a 5 years old girl from the whole body exposure to 99mTc – SestaMIBI, 30 minutes after administration. Heart, kidney, liver, ovary, pancreas and brain are the most critical organs, in which the S‐factors are calculated. The statistical uncertainty in the simulation procedure was kept lower than 5%. The Sfactors for each target organ are calculated in Gy/(MBq*sec) with highest dose being absorbed in kidneys and pancreas (9.29*1010 and 0.15*1010 respectively).

Conclusion:

An approach for the accurate dosimetry on pediatric models is presented, creating a reference dosage dataset for several radionuclides in children computational models with the advantages of MC techniques. Our study is ongoing, extending our investigation to other reference models and evaluating the results with clinical estimated doses.
MO‐G‐17A‐06: Kernel Based Dosimetry for 90Y Microsphere Liver Therapy Using 90Y Bremsstrahlung SPECT/CT
Authors: Mikell J , Siman W , Mahvash A , Mourtada F , Kappadath S
Published: July 2014

Purpose:

90Y microsphere therapy in liver presents a situation where beta transport is dominant and the tissue is relatively homogenous. We compare voxel‐based absorbed doses from a 90Y kernel to Monte Carlo (MC) using quantitative 90Y bremsstrahlung SPECT/CT as source distribution.

Methods:

Liver, normal liver, and tumors were delineated by an interventional radiologist using contrast‐enhanced CT registered with 90Y SPECT/CT scans for 14 therapies. Right lung was segmented via region growing. The kernel was generated with 1.04 g/cc soft tissue for 4.8 mm voxel matching the SPECT. MC simulation materials included air, lung, soft tissue, and bone with varying densities. We report percent difference between kernel and MC (%Δ(K,MC)) for mean absorbed dose, D70, and V20Gy in total liver, normal liver, tumors, and right lung. We also report %Δ(K,MC) for heterogeneity metrics: coefficient of variation (COV) and D10/D90. The impact of spatial resolution (0, 10, 20 mm FWHM) and lung shunt fraction (LSF) (1,5,10,20%) on the accuracy of MC and kernel doses near the liver‐lung interface was modeled in 1D. We report the distance from the interface where errors become <10% of unblurred MC as d10(side of interface, dose calculation, FWHM blurring, LSF).

Results:

The %Δ(K,MC) for mean, D70, and V20Gy in tumor and liver was <7% while right lung differences varied from 60–90%. The %Δ(K,MC) for COV was <4.8% for tumor and liver and <54% for the right lung. The %Δ(K,MC) for D10/D90 was <5% for 22/23 tumors. d10(liver,MC,10,1–20) awere <9mm and d10(liver,MC,20,1–20) awere <15mm; both agreed within 3mm to the kernel. d10(lung,MC,10,20), d10(lung,MC,10,1), d10(lung,MC,20,20), and d10(lung,MC,20,1) awere 6, 25, 15, and 34mm, respectively. Kernel calculations on blurred distributions in lung had errors > 10%.

Conclusions:

Liver and tumor voxel doses with 90Y kernel and MC agree within 7%. Large differences exist between the two methods in right lung.

Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA138986. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
MO‐G‐18C‐05: Real‐Time Prediction in Free‐Breathing Perfusion MRI
Authors: Song H , Liu W , Ruan D , Jung S , Gach M
Published: July 2014

Purpose:

The aim is to minimize frame‐wise difference errors caused by respiratory motion and eliminate the need for breath‐holds in magnetic resonance imaging (MRI) sequences with long acquisitions and repeat times (TRs). The technique is being applied to perfusion MRI using arterial spin labeling (ASL).

Methods:

Respiratory motion prediction (RMP) using navigator echoes was implemented in ASL. A least‐square method was used to extract the respiratory motion information from the 1D navigator. A generalized artificial neutral network (ANN) with three layers was developed to simultaneously predict 10 time points forward in time and correct for respiratory motion during MRI acquisition. During the training phase, the parameters of the ANN were optimized to minimize the aggregated prediction error based on acquired navigator data. During realtime prediction, the trained ANN was applied to the most recent estimated displacement trajectory to determine in real‐time the amount of spatial

Results:

The respiratory motion information extracted from the least‐square method can accurately represent the navigator profiles, with a normalized chi‐square value of 0.037±0.015 across the training phase. During the 60‐second training phase, the ANN successfully learned the respiratory motion pattern from the navigator training data. During real‐time prediction, the ANN received displacement estimates and predicted the motion in the continuum of a 1.0 s prediction window. The ANN prediction was able to provide corrections for different respiratory states (i.e., inhalation/exhalation) during real‐time scanning with a mean absolute error of < 1.8 mm.

Conclusion:

A new technique enabling free‐breathing acquisition during MRI is being developed. A generalized ANN development has demonstrated its efficacy in predicting a continuum of motion profile for volumetric imaging based on navigator inputs. Future work will enhance the robustness of ANN and verify its effectiveness with human subjects.

Research supported by National Institutes of Health National Cancer Institute Grant R01 CA159471‐01