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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-F-BRA-12: End-User Oriented Tools and Procedures for Testing Brachytherapy TPSs Employing MBDCAs

Purpose: To develop user-oriented tools for commissioning and dosimetry testing of {sup 192}Ir brachytherapy treatment planning systems (TPSs) employing model based dose calculation algorithms (MBDCAs). Methods: A software tool (BrachyGuide) has been developed for the automatic generation of MCNP6 input files from any CT based plan exported in DICOM RT format from Elekta and Varian TPSs. BrachyGuide also facilitates the evaluation of imported Monte Carlo (MC) and TPS dose distributions in terms of % dose differences and gamma index (CT overlaid colormaps or relative frequency plots) as well as DVHs and related indices. For users not equipped to perform MC, a set of computational models was prepared in DICOM format, accompanied by treatment plans and corresponding MCNP6 generated reference data. BrachyGuide can then be used to compare institutional and reference data as per TG186. The model set includes a water sphere with the MBDCA WG {sup 192}Ir source placed centrically and in two eccentric positions, a water sphere with cubic bone and lung inhomogeneities and a five source dwells plan, and a patient equivalent model with an Accelerated Partial Breast Irradiation (APBI) plan. Results: The tools developed were used for the dosimetry testing of the Acuros and ACE MBDCAs implemented in BrachyVision v.13 and Oncentra Brachy v.4.5, respectively. Findings were consistent with previous results in the literature. Besides points close to the source dwells, Acuros was found to agree within type A uncertainties with the reference MC results. Differences greater than MC type A uncertainty were observed for ACE at distances >5cm from the source dwells and in bone. Conclusion: The tools developed are efficient for brachytherapy MBDCA planning commissioning and testing. Since they are appropriate for distribution over the web, they will be put at the AAPM WG MBDCA’s disposal. Research co-financed by the ESF and Greek funds. NSRF operational Program: Education and Lifelong Learning Investing in Knowledge Society-Aristeia. Varian Medical Systems and Nucletron, an Elekta company provided access to TPSs for research purposes. Miss Peppa was supported by IKY-fellowships of excellence for postgraduate studies in Greece,Siemens Program.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Vacuum drying of spent fuel storage canisters/casks - 'just how much water could be left in there, anyway?' - 15233

The process of moving spent fuel assemblies from wet storage in the spent fuel pool to dry storage in an inert gas environment within a canister or cask typically involves two main stages. In the first stage, the bulk of the water is removed by a draining or siphoning operation, conducted with pressure inside the canister maintained at 1.3 to 2 atm. This process removes most of the water in the cask cavity, but residual water can be left behind, in three main regions. The largest region, typically, is the bottom of the cavity below the end of the siphon tube. A second general class of locations, also located at the bottom of the cask cavity, consists of the 'dashpots' at the ends of the various non-fuel tubular structures within the fuel assemblies. For PWR assemblies, these are the control rod guide sleeve tubes and instrumentation thimbles. For BWR assemblies, these are the water rods of various designs and control blade ends in some configurations. A third class of locations consists of porous material within the cavity that can absorb water, such as thin ceramic neutron poison plates, and ostensibly intact fuel rods that nevertheless might have pinholes or fine cracks in the cladding that could allow pool water to creep inside the fuel rod. To remove residual water from these locations, the second stage of drying operations utilizes vacuum drying, by reducing the pressure sufficiently to convert the water to vapor that can then be pumped out of the canister cavity. In this operation, the cask cavity pressure is slowly reduced from the nominal condition of (1.3-2.0 atm (1000-1520 torr), to a final target pressure below 3 torr (0.004 atm). This is typically accomplished in three to five stages, with prescribed 'hold' points defined in procedures or in the Technical Specifications, to preclude sudden pressure spikes due to flashing of water to steam, or development of large local temperature gradients in the fuel rods or other cask internal components. This paper discusses the various locations in the system where residual water may 'hang up' in the cask, and presents a discussion of the physical basis for the effectiveness of vacuum drying for removing it. Results and conclusions based on realistic qualitative and quantitative evaluations of the transient heat transfer behavior of the system are presented, based on detailed modeling of a range of spent fuel canister designs and decay heat loads, most notably the 24P Dry Shielded Canisters (DSCs) stored at the Rancho Seco Independent Spent Fuel Storage Installation (ISFSI), the NAC-MPC modules at Maine Yankee, the 24P DSCs stored at Calvert Cliffs, and the Holtec HI-STORM modules at Hope Creek. The evaluations presented here show that ice formation within a spent fuel canister is highly unlikely, due to the availability of a large thermal source term in the form of the decay heat load of the spent fuel. The formation of ice is an operational concern, since it mainly affects operation of equipment external to the canister (i.e., the hoses, valves, and fittings of the vacuum drying equipment.) Evaluations are presented for quantifying the amount of residual water that could remain in the cask cavity, even after successful drying operations, since vacuum drying is a limit process, and by definition, cannot remove all of the water from the cavity, no matter how long the operation goes on, even if all of it is in vapor form. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

FUSRAP Case Study - Benefits and Lessons Learned from Implementation of a Modern Data Solution at Maywood - 18399

This paper focuses on data production and management practices dating back to 1999 that continue to evolve to support the project today. In 2000, the FUSRAP Maywood Project began using a software environmental data management system and laboratory information management system, developed by a single database administrator (DA) and authored in Microsoft Access{sup TM} (MS Access). The original databases included basic functionality including sample number assignment and label generation, tracking of LIMS gamma spec QC and assignment of basic qualifiers and basic database queries. The DA continued over the next fifteen years to refine the EDMS/LIMS by integrating project-specific data evaluation guidance document processes and Quality Assurance/Quality Control (QA/QC) charting and excursion warning tools. With the retirement of the original DA, the U.S. Army Corps of Engineers (USACE)-Cabrera Team procured and implemented a commercial-leaning solution using modern database tools and an established EDMS vendor. For the database transition process, the project team established and configured the new EDMS/LIMS with basic architecture and accessibility; evaluated existing workflows; established/revised LIMS and EDMS-related documentation (manuals and procedures); and conducted dry runs and validation testing. The overall team coordinated closely to facilitate a seamless transition from initial assessment and authoring, to data migration, and finally to resumption of normal ongoing operations. Key features of the new EDMS Subcontractor's software included lookup tables, an import wizard, data checking options and unique indexes. Since the database systems became operational, the technical staff gathered useful feedback from end users (e.g., lab staff, field engineers, task managers, and the third-party data validator) to refine the EDMS/LIMS operation. This feedback triggered improvements in the performance of onsite laboratory qualification forms, promoted consistency in sample ID numbers between the database sample planning screens and field chain-of-custodies, corrected bugs in the LIMS Duplicate Evaluation Report, eliminated data import issues such as blank, inconsistent or missing data from key fields. One of the advantages of the commercial database solution was that it allowed the project to cut cost over time due to the lower cost of database maintenance provided by the commercial database vendor versus the cost of an on-staff DA. Cost savings are estimated at $40,000 per year. There were also indirect cost savings resulting from implementation of the new database since it allowed better integration of the LIMS and EDMS. While there will always be challenges associated with long term records/data management for any old remediation site, the Maywood Team's approach to an upgraded EDMS/LIMS implementation serves as one element of the overall effort to enhance the integrity and reproducibility of critical data that supports the remediation program while at the same time, more effectively using available resources. These lessons-learned will enhance implementation of cost-effective solutions for similar environmental remediation sites. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Dummy Run of Quality Assurance Program in a Phase 3 Randomized Trial Investigating the Role of Internal Mammary Lymph Node Irradiation in Breast Cancer Patients: Korean Radiation Oncology Group 08-06 Study

Purpose: The Korean Radiation Oncology Group (KROG) 08-06 study protocol allowed radiation therapy (RT) technique to include or exclude breast cancer patients from receiving radiation therapy to the internal mammary lymph node (IMN). The purpose of this study was to assess dosimetric differences between the 2 groups and potential influence on clinical outcome by a dummy run procedure. Methods and Materials: All participating institutions were asked to produce RT plans without irradiation (Arm 1) and with irradiation to the IMN (Arm 2) for 1 breast-conservation treatment case (breast-conserving surgery [BCS]) and 1 mastectomy case (modified radical mastectomy [MRM]) whose computed tomography images were provided. We assessed interinstitutional variations in IMN delineation and evaluated the dose-volume histograms of the IMN and normal organs. A reference IMN was delineated by an expert panel group based on the study guidelines. Also, we analyzed the potential influence of actual dose variation observed in this study on patient survival. Results: Although physicians intended to exclude the IMN within the RT field, the data showed almost 59.0% of the prescribed dose was delivered to the IMN in Arm 1. However, the mean doses covering the IMN in Arm 1 and Arm 2 were significantly different for both cases (P<.001). Due to the probability of overdose in Arm 1, the estimated gain in 7-year disease-free survival rate would be reduced from 10% to 7.9% for BCS cases and 7.1% for MRM cases. The radiation doses to the ipsilateral lung, heart, and coronary artery were lower in Arm 1 than in Arm 2. Conclusions: Although this dummy run study indicated that a substantial dose was delivered to the IMN, even in the nonirradiation group, the dose differences between the 2 groups were statistically significant. However, this dosimetric profile should be studied further with actual patient samples and be taken into consideration when analyzing clinical outcomes according to IMN irradiation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-J-34: Automatic Target-Based Patient Positioning Framework for Image-Guided Radiotherapy in Prostate Cancer Treatment

Purpose: Current image-guided radiotherapy (IGRT) procedure is bonebased patient positioning, followed by subjective manual correction using cone beam computed tomography (CBCT). This procedure might cause the misalignment of the patient positioning. Automatic target-based patient positioning systems achieve the better reproducibility of patient setup. Our aim of this study was to develop an automatic target-based patient positioning framework for IGRT with CBCT images in prostate cancer treatment. Methods: Seventy-three CBCT images of 10 patients and 24 planning CT images with digital imaging and communications in medicine for radiotherapy (DICOM-RT) structures were used for this study. Our proposed framework started from the generation of probabilistic atlases of bone and prostate from 24 planning CT images and prostate contours, which were made in the treatment planning. Next, the gray-scale histograms of CBCT values within CTV regions in the planning CT images were obtained as the occurrence probability of the CBCT values. Then, CBCT images were registered to the atlases using a rigid registration with mutual information. Finally, prostate regions were estimated by applying the Bayesian inference to CBCT images with the probabilistic atlases and CBCT value occurrence probability. The proposed framework was evaluated by calculating the Euclidean distance of errors between two centroids of prostate regions determined by our method and ground truths of manual delineations by a radiation oncologist and a medical physicist on CBCT images for 10 patients. Results: The average Euclidean distance between the centroids of extracted prostate regions determined by our proposed method and ground truths was 4.4 mm. The average errors for each direction were 1.8 mm in anteroposterior direction, 0.6 mm in lateral direction and 2.1 mm in craniocaudal direction. Conclusion: Our proposed framework based on probabilistic atlases and Bayesian inference might be feasible to automatically determine prostate regions on CBCT images.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Identification and Quantification of Beta-Emitters in Waste Packages by Segmented Gamma-Scanning - 20114

A commonly applied method for the non-destructive characterization of the radioactive inventory of waste packages (e.g. 200-l drums) is segmented gamma-scanning. The gamma-emitting inventory is identified via their characteristic lines in the measured spectra. The corresponding net peak areas allow for quantification applying appropriate models. The identification and quantification of beta-emitters present in the waste package require further evaluation. While some of them emit gamma-rays, too, which can be used for identification and quantification, pure beta-emitters contribute to the gamma-spectra only by their Bremsstrahlung-spectra. {sup 32}P, {sup 90}Sr and {sup 90}Y are typical representatives of these isotopes. A method is developed for identification and quantification of these pure beta-emitters in radioactive waste packages. Origin of the procedure is the evaluation of the measured gamma-spectrum. After the identification of all lines present in the spectrum (characteristic gamma-lines, single- and double-escape-lines, X-ray-lines, annihilation peak etc.) this information is used together with calibration data of the detection system and further a-priori information like matrix composition, cross-section data from databases etc. to simulate the spectra without the Bremsstrahlung-components by an appropriate method. This may be Monte Carlo simulations or, like in our case, a computer code taking into account mathematical descriptions of the physical effects like photo effect, (multiple) Compton scattering, backscattering etc. and the attenuation effects of the waste matrix. In any case, the resulting spectrum must simulate the real spectrum without its Bremsstrahlung-component as good as possible. Subtracting the simulated from the measured spectrum then results in the Bremsstrahlung-components caused by the beta-emitters. Prior to evaluation, a set of Bremsstrahlung-spectra is calculated and stored for different beta-emitters in different matrices using the Bethe-Heitler equation. This data set can be extended for new conditions, if necessary, and is allocated in a data base for future application. Applying a non-linear optimization using the generalized reduced gradient method for comparing the calculated with the derived Bremsstrahlung-spectra results in the identification of the beta-emitter and a factor, which is proportional to its activity. The proportionality is determined by previous calibration measurements. The application of the method is demonstrated by measurements on a 200-l mock-up drum and a real waste package. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2019

Informative Path Planning for Mapping Radiation

This project involves making measurements of contaminated areas using portable radiation detectors and small robots. Tasks involve operating detectors and small robots, combining data acquisition for the two systems, and automating the systems. The end result is a radiation map of contamination areas. Localization of radioactive sources and mapping of contamination distribution is essential when responding to emergencies, or when dealing with cleanup efforts. Radiation maps are used for situational awareness and for establishing a safe perimeter. However, it may be hazardous or impossible for humans to safely enter the site and survey the area. Informative Path Planning (IPP) is used to design a path for a robotic sensor platform to gather the most information about the radiation distribution while operating under the set of constraints given by the dynamics of the robot and other requirements such as minimizing the overall mission time. The key challenge for IPP is the tight coupling in multiple layers of decisions: Selection of locations to visit; Allocation of sensors to those locations; Processing of information gathered. Given a robot equipped with a basic gamma detector and Lidar sensor, how can we efficiently explore an unknown environment in such a way that we can satisfy the robot's constraints while simultaneously maximizing the accuracy of the map and minimizing the total runtime? This work presents a systematic procedure for IPP and environmental mapping that: Selects the best locations at which to sample; Finds the best path for robots; Estimates the measurement value at unknown locations using a Gaussian Process regression framework. Given a set of points where radiation measurements were taken, we are utilizing a Gaussian Process Regression with a Matern kernel to reconstruct the shape of the underlying ground truth. Mapping is done via the Robot Operating System's OpenSlam Gmapping package, which creates a 2D occupancy grid map. Simulated trials were run with a radiation source placed at random locations, and allowing the robot to select and move towards 20 samples at separate locations, as well as sampling along the path while moving. The simulated sensor model assumed an efficiency of 0.3, collection time of 1 second. Various weighting schemes were tested and compared. Quantitative evaluations often favored exploitation-heavy weighting schemes where μ was emphasized, with the Root Mean Squared Error (RMSE) quickly tending towards 2, whereas qualitative comparisons would favor exploration-biased schemes with greater weight on σ. The difference comes from operators often favoring knowing the general location of a source, rather than the exact properties of a source. Weighting of the path-length π often reduced the quality of the regression as less exploration occurred, however this may be deemed a worthwhile trade-off under certain circumstances, such as with sensitive robots. Successfully developed a methodology for informative path-planning for a robot to efficiently gather information and create a map of radiation. In the future, we would like to focus on: Hardware trials with integration of the robot platform and the IPP software; More refined sensor and environmental modeling; Multiple robot platforms.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Deformable Registration for Longitudinal Breast MRI Screening

MRI screening of high-risk patients for breast cancer provides very high sensitivity, but with a high recall rate and negative biopsies. Comparing the current exam to prior exams reduces the number of follow-up procedures requested by radiologists. Such comparison, however, can be challenging due to the highly deformable nature of breast tissues. Automated co-registration of multiple scans has the potential to aid diagnosis by providing 3D images for side-by-side comparison and also for use in CAD systems. Although many deformable registration techniques exist, they generally have a large number of parameters that need to be optimized and validated for each new application. Here, we propose a framework for such optimization and also identify the optimal input parameter set for registration of 3D T{sub 1}-weighted MRI of breast using Elastix, a widely used and freely available registration tool. A numerical simulation study was first conducted to model the breast tissue and its deformation through finite element (FE) modeling. This model generated the ground truth for evaluating the registration accuracy by providing the deformation of each voxel in the breast volume. An exhaustive search was performed over various values of 7 registration parameters (4050 different combinations of parameters were assessed) and the optimum parameter set was determined. This study showed that there was a large variation in the registration accuracy of different parameter sets ranging from 0.29 mm to 2.50 mm in median registration error and 3.71 mm to 8.90 mm in 95 percentile of the registration error. Mean registration errors of 0.32 mm, 0.29 mm, and 0.30 mm and 95 percentile errors of 3.71 mm, 5.02 mm, and 4.70 mm were obtained by the three best parameter sets. The optimal parameter set was applied to consecutive breast MRI scans of 13 patients. A radiologist identified 113 landmark pairs (~ 11 per patient) which were used to assess registration accuracy. The results demonstrated that using the optimal registration parameter set, a registration accuracy (in mm) of 3.4 [1.8 6.8] was achieved.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

SU-E-J-08: Comparison of Unintended Radiation Doses to Organs at Risk Resulting From the Out-Of-Field Therapeutic Beams and From Image-Guidance X-Ray Procedures

Purpose: The unintended radiation dose to organs at risk (OAR) can be contributed from imaging guidance procedures as well as from leakage and scatter of therapeutic beams. This study compares the imaging dose with the unintended out-of-field therapeutic dose to patient sensitive organs. Methods: The Monte Carlo EGSnrc user codes, BEAMnrc and DOSXYZnrc, were used to simulate kV X-ray sources from imaging devices as well as the therapeutic IMRT/VMAT beams and to calculate doses to target and OARs on patient treatment planning CT images. The accuracy of the Monte Carlo simulations was benchmarked against measurements in phantoms. The dose-volume histogram was utilized in analyzing the patient organ doses. Results: The dose resulting from Standard Head kV-CBCT scans to bone and soft tissues ranges from 0.7 to 1.1 cGy and from 0.03 to 0.3 cGy, respectively. The dose resulting from Thorax scans on the chest to bone and soft tissues ranges from 1.1 to 1.8 cGy and from 0.3 to 0.6 cGy, respectively. The dose resulting from Pelvis scans on the abdomen to bone and soft tissues range from 3.2 to 4.2 cGy and from 1.2 to 2.2 cGy, respectively. The out-of-field doses to OAR are sensitive to the distance between the treated target and the OAR. For a typical Head-and-Neck IMRT/VMAT treatment the out-of-field doses to eyes are 1–3% of the target dose, or 2–6 cGy per fraction. Conclusion: The imaging doses to OAR are predictable based on the imaging protocols used when OARs are within the imaged volume and can be estimated and accounted for by using tabulated values. The unintended out-of-field doses are proportional to the target dose, strongly depend on the distance between the treated target and OAR, and are generally higher comparing to the imaging dose. This work was partially supported by Varian research grant VUMC40590.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-J-07: IGRT Gently: Evaluating Imaging Dose in Phantoms of Different Sizes

Purpose: IGRT imaging procedures have emerged as a common method of patient position verification in radiotherapy, though imaging dose is generally neglected in the treatment plan. Consequently, evaluating and optimizing the dose from these procedures is worthwhile. This process is especially important for children, who are more radiosensitive than adults. The aim of this work was to gain some understanding of the relative doses involved with various XVI-preset parameters for an “adult” and “child” phantom set, with the hopes that imaging dose for a child can be reduced. Methods: 32 and 16cm CTDI-phantoms were used as surrogates for adult and child torsos, respectively. Dose was measured in the central and peripheral chamber positions of the phantoms. CBCT scans were made for both phantoms using Elekta’s Chest-preset to establish a dose baseline. The child-phantom was then scanned using the Elekta Head and Neck (HN) preset. A modified HN-preset (named Peds Abd-pelvis) was also created with a doubled mAs to maintain a reduction in dose to the child-phantom (relative to the baseline), while providing clinically-usable image quality. Results: The baseline dose to the child-phantom from the Chest-preset was 310% that of the adult-phantom for the center chamber position and 150% at the periphery. An average dose reduction of 97% was obtained in the childphantom by switching from the Chest-preset to the HN-preset, while the Peds Abd-pelvis-preset similarly reduced the dose by an average of 92%. Conclusion: XVI-preset parameters significantly affect dose, and should be optimized to reduce dose, while ensuring clinically-usable image quality. Using a modified imaging preset (Peds Abd-pelvis-preset) greatly reduced the dose to the child-phantom compared to the dose for the Chest-preset for both the child and adult-phantoms. This outcome provides support for the development of child-specific protocols for IGRT imaging in pediatric patients.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

MO-F-CAMPUS-J-01: A Novel and Efficient Daily QA Program for Both Modern Linear Accelerator and Optical Surface Motion Systems

Purpose: The camera-based optical surface monitoring system(OSMS) is a standard motion-tracking system for TrueBeam™ machine. Daily quality assurance(DQA) procedures for the TrueBeam and OSMS systems currently require multiple phantoms and test sequences. Machine Performance Check(MPC) uses the IsoCal™ phantom to test geometric and dosimetric aspects, and has been validated for routine TrueBeam DQA. This work examines the novel use of MPC to simultaneously conduct DQA of OSMS,utilizing one phantom and test sequence for QA of both the TrueBeam and OSMS systems. Methods: TrueBeam with 6 degree-of-freedom(6DOF) couch, MPC and OSMS were installed. The therapists routinely use MPC with the IsoCal phantom to verify geometric and dosimetric parameters with an automated sequence of varying gantry and collimator angles, MLC positions, and couch translations and rotations as the DQA for TrueBeam. A surface outline of the IsoCal phantom, generated from a CT dataset, was imported to OSMS and used to monitor the position of the phantom at isocenter and to track its movement up to 5cm/10°(yaw) and rotation in pitch and roll up to 3° in real time during the automated MPC sequence. Motion of the phantom throughout the MPC routine was compared to the couch position shown by the digital readout. Results: The coincidence of isocenter, as determined by OSMS, and TrueBeam radiation isocenter was within ±0.8mm/±0.8° in three axes. Between OSMS and TrueBeam 6DOF couch, the mean couch relative shifts/angles were within ±0.7mm/±0.8° for each axis. Reported pitch and roll values were within ±0.4mm/±0.4°. The total measurement time for each DQA session took approximately 5 minutes. Conclusion: Use of the IsoCal phantom and MPC for simultaneous DQA of TrueBeam and OSMS increases QA efficiency and reduces complexity. OSMS isocenter position and motion-tracking capability in 6DOF were verified in real-time and were found to be within 1mm of the expected value.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Combined iterative reconstruction and image-domain decomposition for dual energy CT using total-variation regularization

Purpose: Dual-energy CT (DECT) is being increasingly used for its capability of material decomposition and energy-selective imaging. A generic problem of DECT, however, is that the decomposition process is unstable in the sense that the relative magnitude of decomposed signals is reduced due to signal cancellation while the image noise is accumulating from the two CT images of independent scans. Direct image decomposition, therefore, leads to severe degradation of signal-to-noise ratio on the resultant images. Existing noise suppression techniques are typically implemented in DECT with the procedures of reconstruction and decomposition performed independently, which do not explore the statistical properties of decomposed images during the reconstruction for noise reduction. In this work, the authors propose an iterative approach that combines the reconstruction and the signal decomposition procedures to minimize the DECT image noise without noticeable loss of resolution. Methods: The proposed algorithm is formulated as an optimization problem, which balances the data fidelity and total variation of decomposed images in one framework, and the decomposition step is carried out iteratively together with reconstruction. The noise in the CT images from the proposed algorithm becomes well correlated even though the noise of the raw projections is independent on the two CT scans. Due to this feature, the proposed algorithm avoids noise accumulation during the decomposition process. The authors evaluate the method performance on noise suppression and spatial resolution using phantom studies and compare the algorithm with conventional denoising approaches as well as combined iterative reconstruction methods with different forms of regularization. Results: On the Catphan©600 phantom, the proposed method outperforms the existing denoising methods on preserving spatial resolution at the same level of noise suppression, i.e., a reduction of noise standard deviation by one order of magnitude. This improvement is mainly attributed to the high noise correlation in the CT images reconstructed by the proposed algorithm. Iterative reconstruction using different regularization, including quadratic orq-generalized Gaussian Markov random field regularization, achieves similar noise suppression from high noise correlation. However, the proposed TV regularization obtains a better edge preserving performance. Studies of electron density measurement also show that our method reduces the average estimation error from 9.5% to 7.1%. On the anthropomorphic head phantom, the proposed method suppresses the noise standard deviation of the decomposed images by a factor of ∼14 without blurring the fine structures in the sinus area. Conclusions: The authors propose a practical method for DECT imaging reconstruction, which combines the image reconstruction and material decomposition into one optimization framework. Compared to the existing approaches, our method achieves a superior performance on DECT imaging with respect to decomposition accuracy, noise reduction, and spatial resolution.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Robust electromagnetically guided endoscopic procedure using enhanced particle swarm optimization for multimodal information fusion

Purpose: Electromagnetically guided endoscopic procedure, which aims at accurately and robustly localizing the endoscope, involves multimodal sensory information during interventions. However, it still remains challenging in how to integrate these information for precise and stable endoscopic guidance. To tackle such a challenge, this paper proposes a new framework on the basis of an enhanced particle swarm optimization method to effectively fuse these information for accurate and continuous endoscope localization. Methods: The authors use the particle swarm optimization method, which is one of stochastic evolutionary computation algorithms, to effectively fuse the multimodal information including preoperative information (i.e., computed tomography images) as a frame of reference, endoscopic camera videos, and positional sensor measurements (i.e., electromagnetic sensor outputs). Since the evolutionary computation method usually limits its possible premature convergence and evolutionary factors, the authors introduce the current (endoscopic camera and electromagnetic sensor’s) observation to boost the particle swarm optimization and also adaptively update evolutionary parameters in accordance with spatial constraints and the current observation, resulting in advantageous performance in the enhanced algorithm. Results: The experimental results demonstrate that the authors’ proposed method provides a more accurate and robust endoscopic guidance framework than state-of-the-art methods. The average guidance accuracy of the authors’ framework was about 3.0 mm and 5.6° while the previous methods show at least 3.9 mm and 7.0°. The average position and orientation smoothness of their method was 1.0 mm and 1.6°, which is significantly better than the other methods at least with (2.0 mm and 2.6°). Additionally, the average visual quality of the endoscopic guidance was improved to 0.29. Conclusions: A robust electromagnetically guided endoscopy framework was proposed on the basis of an enhanced particle swarm optimization method with using the current observation information and adaptive evolutionary factors. The authors proposed framework greatly reduced the guidance errors from (4.3, 7.8) to (3.0 mm, 5.6°), compared to state-of-the-art methods.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

A 1.5 T transverse magnetic field in radiotherapy of rectal cancer: Impact on the dose distribution

Purpose: MRI guidance during radiotherapy has the potential to enable more accurate dose delivery, optimizing the balance between local control and treatment related toxicity. However, the presence of a permanent magnetic field influences the dose delivery, especially around air cavities. Here, electrons are able to return to the surface through which they entered the air cavity (electron return effect, ERE) locally resulting in dose hot- and cold-spots. Where RT of rectal cancer patients might benefit from MRI guidance for margin reduction, air cavities in and around the target volume are frequently present. The purpose of this research is to evaluate the impact of the presence of a 1.5 T transverse magnetic field on dose delivery in patients with rectal cancer. Methods: Ten patients treated with 5 × 5 Gy RT having large changes in pelvic air content were selected out of a cohort of 33 patients. On the planning CT, a 1.5 T, 6 MV, 7-field intensity modulated radiotherapy (IMRT) plan was created. This plan was subsequently recalculated on daily CT scans. For each daily CT, the CTV V{sub 95%} and V{sub 107%} and bowel area V{sub 5Gy}, V{sub 10Gy}, V{sub 15Gy}, V{sub 20Gy}, and V{sub 25Gy} were calculated to evaluate the changes in dose distribution from fraction to fraction. For comparison, the authors repeated this procedure for the 0 T situation. To study the effect of changing air cavities separate from other anatomical changes, the authors also generated artificial air cavities in the CTV of one patient (2 and 5 cm diameter), in the high dose gradient region (2 cm), and in the low dose area (2 cm). Treatment plans were optimized without and with each simulated air cavity. For appearing and disappearing air cavities, the CTV V{sub 95%} and V{sub 107%} were evaluated. The authors also evaluated the ERE separate from attenuation changes locally around appearing gas pockets. Results: For the ten patients, at 1.5 T, the V{sub 95%} was influenced by both appearing and disappearing air, and dropped to <98% in 2 out of 50 fractions due a disappearing air cavity of 150 cm{sup 3}. V{sub 95%} differences between 0 and 1.5 T were all within 2%. The V{sub 107%} was below 1% in 46 out of 50 fractions, and increased to 3% in the remaining fractions due to appearing air of around 120 cm{sup 3}. For comparison, V{sub 107%} was <1% at 0 T for all fractions. In the bowel area, the V{sub 15Gy} varied strongest from fraction to fraction, but differences between 1.5 and 0 T were minimal with an average difference of 2.3 cm{sup 3} (SD = 18.7 cm{sup 3}, p = 0.38). For the simulated air cavities, the ERE resulted in cold-spots maximally 5% lower than prescribed and hot-spots maximally 6% higher than prescribed. Conclusions: The presence of a 1.5 T magnetic field has an impact on the dose distribution when the air content changes of within a few percent in these selected rectal cancer patients. The authors consider this influence of the transverse magnetic field on the dose distribution in IMRT for rectal cancer patients clinically acceptable.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Modeling treatment couches in the Pinnacle treatment planning system: Especially important for arc therapy

This study is to demonstrate the importance and a method of properly modeling the treatment couch for dose calculation in patient treatment using arc therapy. The 2 treatment couch tops—Aktina AK550 and Elekta iBEAM evo—of Elekta LINACs were scanned using Philips Brilliance Big Bore CT Simulator. Various parts of the couch tops were contoured, and their densities were measured and recorded on the Pinnacle treatment planning system (TPS) using the established computed tomography density table. These contours were saved as organ models to be placed beneath the patient during planning. Relative attenuation measurements were performed following procedures outlined by TG-176 as well as absolute dose comparison of static fields of 10 × 10 cm{sup 2} that were delivered through the couch tops with that calculated in the TPS with the couch models. A total of 10 random arc therapy treatment plans (5 volumetric-modulated arc therapy [VMAT] and 5 stereotactic body radiation therapy [SBRT]), using 24 beams, were selected for this study. All selected plans were calculated with and without couch modeling. Each beam was evaluated using the Delta{sup 4} dosimetry system (Delta{sup 4}). The Student t-test was used to determine statistical significance. Independent reviews were exploited as per the Imaging and Radiation Oncology Core head and neck credentialing phantom. The selected plans were calculated on the actual patient anatomies with and without couch modeling to determine potential clinical effects. Large relative beam attenuations were noted dependent on which part of the couch top beams were passing through. Substantial improvements were also noted for static fields both calculated with the TPS and delivered physically when the couch models were included in the calculation. A statistically significant increase in agreement was noted for dose difference, distance to agreement, and γ-analysis with the Delta{sup 4} on VMAT and SBRT plans. A credentialing review showed improvement in treatment delivery after couch modeling with both thermoluminescent dosimeter doses and film analysis. Furthermore, analysis of treatment plans with and without using the couch model showed a statistically significant reduction in planning target volume coverage and increase in skin dose. In conclusion, ignoring the treatment couch, a common practice when generating a patient treatment plan, can overestimate the dose delivered especially for arc therapy. This work shows that explicitly modeling the couch during planning can meaningfully improve the agreement between calculated and measured dose distributions. Because of this project, we have implemented the couch models clinically across all treatment plans.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

A novel electron gun for inline MRI-linac configurations

Purpose: This work introduces a new electron gun geometry capable of robust functioning in the presence of a high strength external magnetic field for axisymmetric magnetic resonance imaging (MRI)-linac configurations. This allows an inline MRI-linac to operate without the need to isolate the linear accelerator (linac) using a magnetic shield. This MRI-linac integration approach not only leaves the magnet homogeneity unchanged but also provides the linac flexibility to move along the magnet axis of symmetry if the source to target distance needs to be adjusted. Methods: Simple electron gun geometry modifications of a Varian 600C electron gun are considered and solved in the presence of an external magnetic field in order to determine a set of design principles for the new geometry. Based on these results, a new gun geometry is proposed and optimized in the fringe field of a 0.5 T open bore MRI magnet (GE Signa SP). A computer model for the 6 MeV Varian 600C linac is used to determine the capture efficiency of the new electron gun-linac system in the presence of the fringe field of the same MRI scanner. The behavior of the new electron gun plus the linac system is also studied in the fringe fields of two other magnets, a 1.0 T prototype open bore magnet and a 1.5 T GE Conquest scanner. Results: Simple geometrical modifications of the original electron gun geometry do not provide feasible solutions. However, these tests show that a smaller transverse cathode diameter with a flat surface and a slightly larger anode diameter could alleviate the current loss due to beam interactions with the anode in the presence of magnetic fields. Based on these findings, an initial geometry resembling a parallel plate capacitor with a hole in the anode is proposed. The optimization procedure finds a cathode-anode distance of 5 mm, a focusing electrode angle of 5°, and an anode drift tube length of 17.1 mm. Also, the linac can be displaced with ±15 cm along the axis of the 0.5 T magnet without capture efficiency reduction below the experimental value in zero field. In this range of linac displacements, the electron beam generated by the new gun geometry is more effectively injected into the linac in the presence of an external magnetic field, resulting in approximately 20% increase of the target current compared to the original gun geometry behavior at zero field. The new gun geometry can generate and accelerate electron beams in external magnetic fields without current loss for fields higher than 0.11 T. The new electron-gun geometry is robust enough to function in the fringe fields of the other two magnets with a target current loss of no more than 16% with respect to the current obtained with no external magnetic fields. Conclusions: In this work, a specially designed electron gun was presented which can operate in the presence of axisymmetric strong magnetic fringe fields of MRI magnets. Computer simulations show that the electron gun can produce high quality beams which can be injected into a straight through linac such as Varian 600C and accelerated with more efficiency in the presence of the external magnetic fields. Also, the new configuration allows linac displacements along the magnet axis in a range equal to the diameter of the imaging spherical volume of the magnet under consideration. The new electron gun-linac system can function in the fringe field of a MRI magnet if the field strength at the cathode position is higher than 0.11 T. The capture efficiency of the linac depends on the magnetic field strength and the field gradient. The higher the gradient the better the capture efficiency. The capture efficiency does not degrade more than 16%.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Immobilization and image-guidance methods for radiation therapy of limb extremity soft tissue sarcomas: Results of a multi-institutional survey

Radiation therapy for limb-extremity soft tissue sarcoma (STS) requires accurate, reproducible dose delivery. However, patient positioning is challenging and there is a lack of existing guidelines to assist institutional standardization. Therefore, we conducted a multi-institutional international survey of STS immobilization, image guidance methods, and treatment protocols to investigate current practice. Seventy-three UK radiotherapy centers and 15 hospitals in 7 other countries completed a questionnaire on STS immobilization and image-guidance procedures. Specifically, the survey collated information on the current usage of immobilization equipment, including custom devices, patient setup tolerances, the use of written protocols, the modality and frequency of image guidance, the method of treatment, allocated treatment times, and the application of surgical clips. Multiple combinations of immobilization devices were reported. In the UK, 12%, 40%, 30%, 12%, and 5% use 1, 2, 3, 4, and 5 types of device for lower limb STS. Vacuum bag plus either foot or ankle support was most common (66%). Of 15 international centers, 27%, 60%, 7%, 0%, 7% use 1, 2, 3, 4, 5 devices, with vacuum bags (73%) and thermoplastic (47%) predominant, similar to UK values of 77% and 52%. For image guidance, in the UK, 37% use kV planar, 34% use MV planar, and 16% use cone-beam CT for the first 3 fractions and then weekly. Internationally, daily imaging was more prevalent with 33% using kV planar, 7% MV planar, and 40% cone-beam CT daily. Custom devices plus combinations of devices, along with 5- and 10-mm set-up tolerances, were most commonly reported. Less than half of centers have written treatment protocols. Conventional treatment is most common in the UK, with only 42% using conformal techniques. Treatment is allocated between 10 and 30 minutes. Twenty-six percent of UK centers and 53% of international centers use surgical clips. Across treatment centers, there is no consistent approach to STS immobilization, image-guidance methods, or treatment protocols assessed by this survey. A wide variety of immobilization devices and configurations are utilized, and the frequency and modality of imaging are similarly diverse. In the absence of guidelines, the creation of an online repository of example immobilization techniques could enable centers to compare a diversity of cases. The availability of a forum for viewing and discussing a range of cases could potentially lead to improved patient setup and reduce the time taken to devise an individual immobilization strategy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

TU-E-201-00: Eye Lens Dosimetry for Patients and Staff

Madan M. Rehani, Massachusetts General Hospital and Harvard Medical School, Boston Methods for Eye Lens Dosimetry and Studies On Lens Opacities with Interventionalists Radiation induced cataract is a major threat among staff working in interventional suites. Nearly 16 million interventional procedures are performed annually in USA. Recent studies by the principal investigator’s group, primarily among interventional cardiologists, on behalf of the International Atomic Energy Agency, show posterior subcapsular (PSC) changes in the eye lens in 38–53% of main operators and 21–45% of support staff. These changes have potential to lead to cataract in future years, as per information from A-Bomb survivors. The International Commission on Radiological Protection has reduced dose limit for staff by a factor of 7.5 (from 150 mSv/y to 20 mSv/y). With increasing emphasis on radiation induced cataracts and reduction in threshold dose for eye lens, there is a need to implement strategies for estimating eye lens dose. Unfortunately eye lens dosimetry is at infancy when it comes to routine application. Various approaches are being tried namely direct measurement using active or passive dosimeters kept close to eyes, retrospective estimations and lastly correlating patient dose in interventional procedures with staff eye dose. The talk will review all approaches available and ongoing active research in this area, as well as data from surveys done in Europe on status of eye dose monitoring in interventional radiology and nuclear medicine. The talk will provide update on how good is Hp(10) against Hp(3), estimations from CTDI values, Monte Carlo based simulations and current status of eye lens dosimetry in USA and Europe. The cataract risk among patients is in CT examinations of the head. Since radiation induced cataract predominantly occurs in posterior sub-capsular (PSC) region and is thus distinguishable from age or drug related cataracts and is also preventable, actions on awareness can lead to avoidance or even prevention. Learning Objectives: To understand recent changes in eye lens dose limits and thresholds for tissue reactions To understand different approaches to dose estimation for eye lens To learn about challenges in eye lens opacities among staff in interventional fluoroscopy Di Zhang, Toshiba America Medical Systems, Tustin, CA, USA Eye lens radiation dose from brain perfusion CT exams CT perfusion imaging requires repeatedly exposing one location of the head to monitor the uptake and washout of iodinated contrast. The accumulated radiation dose to the eye lens can be high, leading to concerns about potential radiation injury from these scans. CTDIvol assumes continuous z coverage and can overestimate eye lens dose in CT perfusion scans where the table do not increment. The radiation dose to the eye lens from clinical CT brain perfusion studies can be estimated using Monte Carlo simulation methods on voxelized patient models. MDCT scanners from four major manufacturers were simulated and the eye lens doses were estimated using the AAPM posted clinical protocols. They were also compared to CTDIvol values to evaluate the overestimation from CTDIvol. The efficacy of eye lens dose reduction techniques such as tilting the gantry and moving the scan location away from the eyelens were also investigated. Eye lens dose ranged from 81 mGy to 279 mGy, depending on the scanner and protocol used. It is between 59% and 63% of the CTDIvol values reported by the scanners. The eye lens dose is significantly reduced when the eye lenses were not directly irradiated. CTDIvol should not be interpreted as patient dose; this study has shown it to overestimate dose to the eye lens. These results may be used to provide more accurate estimates of actual dose to ensure that protocols are operated safely below thresholds. Tilting the gantry or moving the scanning region further away from the eyes are effective for reducing lens dose in clinical practice. These actions should be considered when they are consistent with the clinical task and patient anatomy. Learning Objectives: To become familiar with method of eye dose estimation for patient in specific situation of brain perfusion CT To become familiar with level of eye lens radiation doses in patients undergoing brain perfusion MDCT To understand methods for reducing eye lens dose to patient Jong Min Park, Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea Eye lens dosimetry in radiotherapy using contact lens-shaped applicator Dose calculation accuracy of commercial treatment planning systems is relatively low at shallow depths. Therefore, in-vivo measurements are often performed in the clinic to verify delivered doses to eye lens which are located at shallow depth. Current in-vivo dosimetry for eye lens during radiotherapy is generally performed with small in-vivo dosimeters on the surface of patient eyelid. Since this procedure potentially contains considerable uncertainty, a contact lens-shaped applicator made of acrylic (lens applicator) was developed for in-vivo measurements of eye lens dose during radiotherapy to reduce uncertainty. The lens applicator allows the insertion of commercially available metal oxide semiconductor field effect transistor (MOSFET) dosimeters. Computed tomography (CT) images of an anthropomorphic phantom with and without the lens applicator were acquired. A total of 20 VMAT plans were delivered to an anthropomorphic phantom and the doses with the lens applicator and the doses at the surface of the eyelid were measured using both micro and standard MOSFET dosimeters. The differences in measured dose at the surface of the eyelid from the calculated lens dose were acquired. The differences between the measured and the calculated doses at the lens applicator, as well as the differences between the measured and the calculated doses at the surface of the eyelid were acquired. The statistical significance of the differences was analyzed. The average difference between the measured and the calculated dose with the lens applicator was 16.8 % ± 10.4 % with a micro MOSFET dosimeter and 16.6 % ± 10.9% with a standard MOSFET dosimeter. The average difference without the lens applicator was 35.9% ± 41.5% with micro MOSFET dosimeter and 42.9% ± 52.2% with standard MOSFET dosimeter. The maximum difference with micro MOSFET dosimeter was 46% with the applicator and 188.4% without the applicator. For the standard MOSFET dosimeter, the maximum difference was 44.4% with the applicator and 246.4% without the applicator. The lens applicator allowed reduction of the differences between the calculated and the measured dose during in-vivo measurement for the eye lens as compared to in-vivo measurement at the surface of the eyelid. Learning Objectives: To understand limitations of dose calculation with commercial treatment planning system for eye lens during radiotherapy To learn about current in-vivo dosimetry methods for eye lens in the clinic To understand limitations of in-vivo dosimetry for eye lens during radiotherapy Di Zhang is an employee of Toshiba America Medical Systems.

60 APPLIED LIFE SCIENCES↗