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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

SU-E-J-29: Audiovisual Biofeedback Improves Tumor Motion Consistency for Lung Cancer Patients

Purpose: To investigate whether the breathing-guidance system: audiovisual (AV) biofeedback improves tumor motion consistency for lung cancer patients. This will minimize respiratory-induced tumor motion variations across cancer imaging and radiotherapy procedues. This is the first study to investigate the impact of respiratory guidance on tumor motion. Methods: Tumor motion consistency was investigated with five lung cancer patients (age: 55 to 64), who underwent a training session to get familiarized with AV biofeedback, followed by two MRI sessions across different dates (pre and mid treatment). During the training session in a CT room, two patient specific breathing patterns were obtained before (Breathing-Pattern-1) and after (Breathing-Pattern-2) training with AV biofeedback. In each MRI session, four MRI scans were performed to obtain 2D coronal and sagittal image datasets in free breathing (FB), and with AV biofeedback utilizing Breathing-Pattern-2. Image pixel values of 2D images after the normalization of 2D images per dataset and Gaussian filter per image were used to extract tumor motion using image pixel values. The tumor motion consistency of the superior-inferior (SI) direction was evaluated in terms of an average tumor motion range and period. Results: Audiovisual biofeedback improved tumor motion consistency by 60% (p value = 0.019) from 1.0±0.6 mm (FB) to 0.4±0.4 mm (AV) in SI motion range, and by 86% (p value < 0.001) from 0.7±0.6 s (FB) to 0.1±0.2 s (AV) in period. Conclusion: This study demonstrated that audiovisual biofeedback improves both breathing pattern and tumor motion consistency for lung cancer patients. These results suggest that AV biofeedback has the potential for facilitating reproducible tumor motion towards achieving more accurate medical imaging and radiation therapy procedures.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-J-94: Positioning Errors Resulting From Using Bony Anatomy Alignment for Treating SBRT Lung Tumor

Purpose: To quantify patient setups errors based on bony anatomy registration rather than 3D tumor alignment for SBRT lung treatments. Method: A retrospective study was performed for patients treated with lung SBRT and imaged with kV cone beam computed tomography (kV-CBCT) image-guidance. Daily CBCT images were registered to treatment planning CTs based on bony anatomy alignment and then inter-fraction tumor movement was evaluated by comparing shift in the tumor center in the medial-lateral, anterior-posterior, and superior-inferior directions. The PTV V100% was evaluated for each patient based on the average daily tumor displacement to assess the impact of the positioning error on the target coverage when the registrations were based on bony anatomy. Of the 35 patients studied, 15 were free-breathing treatments, 10 used abdominal compression with a stereotactic body frame, and the remaining 10 were performed with BodyFIX vacuum bags. Results: For free-breathing treatments, the range of tumor displacement error is between 1–6 mm in the medial-lateral, 1–13 mm in the anterior-posterior, and 1–7 mm in the superior-inferior directions. These positioning errors lead to 6–22% underdose coverage for PTV - V100% . Patients treated with abdominal compression immobilization showed positional errors of 0–4mm mediallaterally, 0–3mm anterior-posteriorly, and 0–2 mm inferior-superiorly with PTV - V100% underdose ranging between 6–17%. For patients immobilized with the vacuum bags, the positional errors were found to be 0–1 mm medial-laterally, 0–1mm anterior-posteriorly, and 0–2 mm inferior-superiorly with PTV - V100% under dose ranging between 5–6% only. Conclusion: It is necessary to align the tumor target by using 3D image guidance to ensure adequate tumor coverage before performing SBRT lung treatments. The BodyFIX vacuum bag immobilization method has the least positioning errors among the three methods studied when bony anatomy is used for registration.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-J-205: Monte Carlo Modeling of Ultrasound Probes for Real-Time Ultrasound Image-Guided Radiotherapy

Purpose: To quantify the effect of ultrasound (US) probe beam attenuation for radiation therapy delivered under real-time US image guidance by means of Monte Carlo (MC) simulations. Methods: MC models of two Philips US probes, an X6-1 matrix-array transducer and a C5-2 curved-array transducer, were built based on their CT images in the EGSnrc BEAMnrc and DOSXYZnrc codes. Due to the metal parts, the probes were scanned in a Tomotherapy machine with a 3.5 MV beam. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2–8.0 g/cm{sup 3}. Beam attenuation due to the probes was measured in a solid water phantom for a 6 MV and 15 MV 15x15 cm{sup 2} beam delivered on a Varian Trilogy linear accelerator. The dose was measured with the PTW-729 ionization chamber array at two depths and compared to MC simulations. The extreme case beam attenuation expected in robotic US image guided radiotherapy for probes in upright position was quantified by means of MC simulations. Results: The 3.5 MV CT number to mass density calibration curve was found to be linear with R{sup 2} > 0.99. The maximum mass densities were 4.6 and 4.2 g/cm{sup 3} in the C5-2 and X6-1 probe, respectively. Gamma analysis of the simulated and measured doses revealed that over 98% of measurement points passed the 3%/3mm criteria for both probes and measurement depths. The extreme attenuation for probes in upright position was found to be 25% and 31% for the C5-2 and X6-1 probe, respectively, for both 6 and 15 MV beams at 10 cm depth. Conclusion: MC models of two US probes used for real-time image guidance during radiotherapy have been built. As a Result, radiotherapy treatment planning with the imaging probes in place can now be performed. J Schlosser is an employee of SoniTrack Systems, Inc. D Hristov has financial interest in SoniTrack Systems, Inc.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

SU-E-T-268: Proton Radiosurgery End-To-End Testing Using Lucy 3D QA Phantom

Purpose: To check the overall accuracy of proton radiosurgery treatment delivery using ready-made circular collimator inserts and fixed thickness compensating boluses. Methods: Lucy 3D QA phantom (Standard Imaging Inc. WI, USA) inserted with GaFchromicTM film was irradiated with laterally scattered and longitudinally spread-out 126.8 MeV proton beams. The tests followed every step in the proton radiosurgery treatment delivery process: CT scan (GE Lightspeed VCT), target contouring, treatment planning (Odyssey 5.0, Optivus, CA), portal calibration, target localization using robotic couch with image guidance and dose delivery at planned gantry angles. A 2 cm diameter collimator insert in a 4 cm diameter radiosurgery cone and a 1.2 cm thick compensating flat bolus were used for all beams. Film dosimetry (RIT114 v5.0, Radiological Imaging Technology, CO, USA) was used to evaluate the accuracy of target localization and relative dose distributions compared to those calculated by the treatment planning system. Results: The localization accuracy was estimated by analyzing the GaFchromic films irradiated at gantry 0, 90 and 270 degrees. We observed 0.5 mm shift in lateral direction (patient left), ±0.9 mm shift in AP direction and ±1.0 mm shift in vertical direction (gantry dependent). The isodose overlays showed good agreement (<2mm, 50% isodose lines) between measured and calculated doses. Conclusion: Localization accuracy depends on gantry sag, CT resolution and distortion, DRRs from treatment planning computer, localization accuracy of image guidance system, fabrication of ready-made aperture and cone housing. The total deviation from the isocenter was 1.4 mm. Dose distribution uncertainty comes from distal end error due to bolus and CT density, in addition to localization error. The planned dose distribution was well matched (>90%) to the measured values 2%/2mm criteria. Our test showed the robustness of our proton radiosurgery treatment delivery system using ready-made collimator inserts and fixed thickness compensating boluses.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-E-T-433: Calibration Accuracy in Mailed High-Resolution 3D Dosimetry Service for SRS/SBRT QA

Purpose: SRS/SBRT combines hypofractionation with excellent dose distributions. However, extremely steep gradients across the target along with dose escalation, if not administered accurately, may lead to serious complications, recurrences, or even fatalities. Existing commercial QA products either lack adequate spatial resolution or the 3D aspect. By contrast, the new CrystalBall™ mailed high-resolution 3D dosimetry service removes the above limitations while reducing the overall workload on medical physics staff. The exposed dosimeters, which change optical density in proportion to local dose, are sent back to the manufacturer (MGS Research Inc., Madison, CT) for sub-millimeter-resolution laser-CT scanning and QA data analysis. QA report is returned electronically within 24 hours. The purpose of this study was to evaluate the dose calibration accuracy in this system. Methods: Two spherical CrystalBall™ polymer gel dosimeters from the same batch, 166 mm diameter, with embedded 3D image registration markers, were mounted in a special phantom designed for reproducible positioning. For full end to end testing, the optical guidance array was mounted onto the phantom and a CT was taken. Two separate Rapid Arc SRS plans were designed. Varian Medical Systems optical guidance system was used to position the phantom and the SRS treatment plans were delivered to the two spheres on Varian's Trilogy Accelerator. Exposed dosimeters were mailed back to the manufacturer for laser CT scanning and analysis. Results: For each plan, 3D gamma passing rate was 100% for 2%/2mm distance-to-agreement criteria above 50% isodose level. The two calibration curves, generated using volumetric dose and optical density data, showed excellent mutual agreement (max difference 2.2%, median difference 0.75%). Conclusion: The clinical utility of new CrystalBall™ mailed QA service for SRS/SBRT and high accuracy of dose calibration have been validated. The workflow associated with the use of the CrystalBall™ in clinical setting was found to be minimal. The presenting author is the founder of and has an ownership in MGS Research Inc which manufactures the CrystalBall system for 3D dosimetry.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

SU-E-T-494: A MOSFET-Based In-Vivo Dosimetry System for MR Image-Guided Radiation Therapy (MR-IGRT)

Purpose: To determine if a MOSFET based in-vivo dosimetry system can be used for patients undergoing MR-IGRT. Methods: Standard and high sensitivity MOSFET detectors were used for in-field and out-of-field measurements respectively. The systems were benchmarked and calibrated against a calibrated ionization chamber on a standard 6 MV linear accelerator, and then on the MR-IGRT system. Known doses were delivered to a water phantom with the MOSFETs placed between the top of the phantom and underneath a layer of bolus and water equivalent plastic, using a 6 MV beam and a {sup 6} {sup 0}Co MR-IGRT beam. The latter was performed with and without real-time MRI-guidance during the beam delivery (MRIGRT). Results: The in-field dosimeter response was linear from 50-500 cGy with little evidence of energy dependence or change in response due to the permanent static magnetic field of the MR-IGRT system. The detector response varied by < 2% between 6 MV and {sup 6} {sup 0}Co without image guided delivery. The out-of-field dosimeter response was linear from 1-50 cGy; however the detectors did display dose rate and energy dependence as the response varied by > 20% depending on distance from isocenter used during calibration. Therefore, to use the dosimeters for out-of-field measurements they must be calibrated out-of-field. Regardless of the detector orientation in the coronal plan, the response of the MOSFETs during MRI-guided delivery increased by 5% due to induced currents from the dynamic magnetic field present with image guidance. During the MRI-guided delivery, some loss in image quality was seen when the MOSFETs were present in the imaging plane. This was mitigated by using a handheld reader without a transmitting wireless receiver. Conclusion: A MOSFET-based in-vivo dosimetry system can be used for patients receiving MR-IGRT; however the change in detector response due to the dynamic magnetic field requires a special calibration.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

MO-C-BRD-01: SBRT I: Overview of Simulation, Planning, and Delivery

SBRT is having a dramatic impact on radiation therapy of early-stage, locally advanced cancers. Treatment planning of SBRT is characterized by precise target volume delineation, highly conformal dose distribution, sharp dose gradient outside the target volume, and meticulous tumor motion management. Stringent dose volume constraints of SBRT require the treatment planning to be highly personalized. Not only the complete patient's medical information (anatomy, tumor size/shape/location/motion, breathing pattern, health status) should be taken into consideration during planning, but also a wide range of factors including imaging techniques (imaging modality, breathing control, immobilization, patient position, etc.), treatment planning techniques (3D-conformal, dynamic conformal arcs, IMRT, VMAT, etc.), image guidance techniques (CBCT, orthogonal X-Ray, fiducial marker tracking, fluoroscopy, etc.), and delivery techniques (FFF, gating, tracking, etc.). In addition, potential pitfalls may exist in SBRT techniques and processes, such as target volume error in 4DCT and image registration error in image guidance. How to manage these affecting factors to achieve optimal, personalized SBRT treatment plans remains a great challenge. In this proposal, we will review technologies, share experiences, and discuss strategies concerning SBRT simulation, planning, and delivery. Learning Objectives: Understand requirements and challenges of SBRT treatment planning Discuss information-driven strategies of developing optimal SBRT plans Discuss practical considerations and potential pitfalls of SBRT treatment planning.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

MO-C-BRF-01: Pediatric Treatment Planning I: Overview of Planning Strategies

Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year-old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. This fact has important implications for the choice of delivery techniques, especially when considering IMRT. For bilateral retinoblastoma for example, an irradiated child has a 50% chance of developing a second cancer by age 50. In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ-at-risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. In the second presentation, specific focus will be on radiation therapy simulation, treatment planning guidelines, image guidance for delivery, and proton therapy for children. We will discuss uniqueness of pediatric simulation with different imaging modalities (CT, MRI, and PET). Some related issues are sedation for younger patients, radiation exposure reduction for CT, distortion and artifacts on pediatric MRI, and measuring pediatric organ motion. We will discuss the tradeoff of tumor coverage and normal tissue sparing in treatment planning using example organ data. Image guidance approaches for pediatric radiation therapy and methods for dose reduction will be reviewed. Finally, we will describe technical advances and trends in proton therapy for children. Advantages, caveats, and opportunities will be presented. Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status of state-of-the-art treatment techniques for pediatric radiation therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

TU-A-BRF-01: MR Guided Radiation Therapy

In recent years, there has been an increasing interest in the development of new technologies focused on the deeper integration of MR in radiotherapy. The innovations span from image data acquisition and post-processing to clinical implementation of MR-guided RT systems and workflow development. The session is intended to provide a review of the key and most recent advancements. Targeted discussions will cover topics which currently define the concept of MR-guided radiotherapy including a) system commissioning, quality control and safety, b) MR data manipulation for dose computations and treatment simulation, c) quantification/management of organ motion and treatment delivery guidance. Learning Objectives: Understand the concept and specifics of MR-guided radiotherapy; Understand the requirements for system integration in clinical workflow; Become familiar with the proposed strategies for system commissioning, RT planning and delivery guidance.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

TU-B-16A-01: To Which Journal Should I Submit My Paper

Research papers authored by Medical Physicists address a large spectrum of oncologic, imaging, or basic research problems; exploit a wide range of physical and engineering methodologies; and often describe the efforts of a multidisciplinary research team. Given the large number (about 100) competing journals accepting medical physics articles, it may not be clear to an individual author which journal is the best venue for disseminating their work to the scientific community. Relevant factors usually include the Journal’s audience and scientific impact, but also such factors as perceived acceptance rate, interest in their topic, and quality of service. The purpose of this symposium is to provide the medical physics community with an overview of scope, review processes, and article guidelines for the following journals: Medical Physics, International Journal of Radiation Biology and Physics, Journal of Applied Clinical Medical Physics, and Practical Radiation Oncology. The senior editors for each journal will provide details as to the journals review process, for example: single blind versus double blind reviews; the hierarchy of the review process in terms of editorial board structure; the reality of acceptance, in terms of acceptance rate; and the types of research the journal prefers to publish. The goal is to provide for authors guidance before they begin to write their papers, not only for proper formatting, but also that the readership is appropriate for the particular paper, hopefully increasing the likelihood of publication. Learning Objectives: To review each Journal’s submission and review process Guidance as to how to increase chances of acceptance To help decipher which journal is appropriate for a given work.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

WE-A-BRD-01: Innovation in Radiation Therapy Planning I: Knowledge Guided Treatment Planning

Intensity modulated radiation therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) offer the capability of normal tissues and organs sparing. However, the exact amount of sparing is often unknown until the plan is complete. This lack of prior guidance has led to the iterative, trial and-error approach in current planning practice. Even with this effort the search for patient-specific optimal organ sparing is still strongly influenced by planner's experience. While experience generally helps in maximizing the dosimetric advantages of IMRT/VMAT, there have been several reports showing unnecessarily high degree of plan quality variability at individual institutions and amongst different institutions, even with a large amount of experience and the best available tools. Further, when physician and physicist evaluate a plan, the dosimetric quality of the plan is often compared with a standard protocol that ignores individual patient anatomy and tumor characteristic variations. In recent years, developments of knowledge models for clinical IMRT/VMAT planning guidance have shown promising clinical potentials. These knowledge models extract past expert clinical experience into mathematical models that predict dose sparing references at patient-specific level. For physicians and planners, these references provide objective values that reflect best achievable dosimetric constraints. For quality assurance, applying patient-specific dosimetry requirements will enable more quantitative and objective assessment of protocol compliance for complex IMRT planning. Learning Objectives: Modeling and representation of knowledge for knowledge-guided treatment planning. Demonstrations of knowledge-guided treatment planning with a few clinical caanatomical sites. Validation and evaluation of knowledge models for cost and quality effective standardization of plan optimization.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

WE-D-BRD-01: Innovation in Radiation Therapy Delivery: Advanced Digital Linac Features

Last few years has witnessed significant advances in linac technology and therapeutic dose delivery method. Digital linacs equipped with high dose rate FFF beams have been clinically implemented in a number of hospitals. Gated VMAT is becoming increasingly popular in treating tumors affected by respiratory motion. This session is devoted to update the audience with these technical advances and to present our experience in clinically implementing the new linacs and dose delivery methods. Topics to be covered include, technical features of new generation of linacs from different vendors, dosimetric characteristics and clinical need for FFF-beam based IMRT and VMAT, respiration-gated VMAT, the concept and implementation of station parameter optimized radiation therapy (SPORT), beam level imaging and onboard image guidance tools. Emphasis will be on providing fundamental understanding of the new treatment delivery and image guidance strategies, control systems, and the associated dosimetric characteristics. Commissioning and acceptance experience on these new treatment delivery technologies will be reported. Clinical experience and challenges encountered during the process of implementation of the new treatment techniques and future applications of the systems will also be highlighted. Learning Objectives: Present background knowledge of emerging digital linacs and summarize their key geometric and dosimetric features. SPORT as an emerging radiation therapy modality specifically designed to take advantage of digital linacs. Discuss issues related to the acceptance and commissioning of the digital linacs and FFF beams. Describe clinical utility of the new generation of digital linacs and their future applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

WE-G-BRF-04: Robust Real-Time Volumetric Imaging Based On One Single Projection

Purpose: Real-time volumetric imaging is highly desirable to provide instantaneous image guidance for lung radiation therapy. This study proposes a scheme to achieve this goal using one single projection by utilizing sparse learning and a principal component analysis (PCA) based lung motion model. Methods: A patient-specific PCA-based lung motion model is first constructed by analyzing deformable vector fields (DVFs) between a reference image and 4DCT images at each phase. At the training stage, we “learn” the relationship between the DVFs and the projection using sparse learning. Specifically, we first partition the projections into patches, and then apply sparse learning to automatically identify patches that best correlate with the principal components of the DVFs. Once the relationship is established, at the application stage, we first employ a patchbased intensity correction method to overcome the problem of different intensity scale between the calculated projection in the training stage and the measured projection in the application stage. The corrected projection image is then fed to the trained model to derive a DVF, which is applied to the reference image, yielding a volumetric image corresponding to the projection. We have validated our method through a NCAT phantom simulation case and one experiment case. Results: Sparse learning can automatically select those patches containing motion information, such as those around diaphragm. For the simulation case, over 98% of the lung region pass the generalized gamma test (10HU/1mm), indicating combined accuracy in both intensity and spatial domain. For the experimental case, the average tumor localization errors projected to the imager are 0.68 mm and 0.4 mm on the axial and tangential direction, respectively. Conclusion: The proposed method is capable of accurately generating a volumetric image using one single projection. It will potentially offer real-time volumetric image guidance to facilitate lung radiotherapy. This study is supported in part by NIH (1R01CA154747-01), The Core Technology Research in Strategic Emerging Industry, Guangdong, China(2011A081402003)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

TH-A-18C-10: Dynamic Intensity Weighted Region of Interest Imaging

Purpose: For image guidance tasks full image quality is not required throughout the entire image. With dynamic filtration of the kV imaging beam the noise properties of the CT image can be locally controlled, providing a high quality image around the target volume with a lower quality surrounding region while providing substantial dose sparing to the patient as well as reduced scatter fluence on the detector. Methods: A dynamic collimation device with 3mm copper blades has been designed to mount in place of the bowtie filter on the On-Board Imager (Varian Medical Systems). The beam intensity is reduced by 95% behind the copper filters and the aperture is controlled dynamically to conformally illuminate a given ROI during a standard cone-beam CT scan. A data correction framework to account for the physical effects of the collimator prior to reconstruction was developed. Furthermore, to determine the dose savings and scatter reduction a monte carlo model was built in BEAMnrc with specifics from the Varian Monte Carlo Data Package. The MC model was validated with Gafchromic film. Results: The reconstructed image shows image quality comparable to a standard scan in the specified ROI, with higher noise and streaks in the outer region but still sufficient information for alignment to high contrast structures. The monte carlo modeling showed that the scatter-to-primary ratio was reduced from 1.26 for an unfiltered scan to 0.45 for an intensity weighted scan, suggesting that image quality may be improved in the inner ROI. Dose in the inner region was reduced 10–15% due to reduced scatter and by as much as 75% in the outer region. Conclusion: Dynamic intensity-weighted ROI imaging allows reduction of imaging dose to sensitive organs away from the target region while providing images that retain their utility for patient setup and procedure guidance. Funding was provided in part by Varian Medical Systems and NIH Grants 1RO1CA120540, T32EB002103, S10 RR021039 and P30 CA14599. The contents of this work are solely the responsibility of the authors and do not necessarily represent the official views of any of the supporting organizations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

TH-C-17A-12: Integrated CBCT and Optical Tomography System On-Board a Small Animal Radiation Research Platform (SARRP)

Purpose: We present a newly developed on-board optical tomography system for SARRP. Innovative features include the compact design and fast acquisition optical method to perform 3D soft tissue radiation guidance. Because of the on-board feature and the combination of the CBCT, diffusive optical tomography (DOT), bioluminescence and fluorescence tomography (BLT and FT), this integrated system is expected to provide more accurate soft tissue guidance than an off-line system as well as highly sensitive functional imaging in preclinical research. Methods: Images are acquired in the order of CBCT, DOT and then BLT/FT, where the SARRP CBCT and DOT are used to provide the anatomical and optical properties information to enhance the subsequent BLT/FT optical reconstruction. The SARRP stage is redesigned to include 9 imbedded optical fibers in contact with the animal's skin. These fibers, connected to a white light lamp or laser, serve as the light sources for the DOT or FT, respectively. A CCD camera with f/1.4 lens and multi-spectral filter set is used as the optical detector and is mounted on a portable cart ready to dock into the SARRP. No radiation is delivered during optical image acquisition. A 3-way mirror system capable of 180 degree rotation around the animal reflects the optical signal to the camera at multiple projection angles. A special black-painted dome covers the stage and provides the light shielding. Results: Spontaneous metastatic bioluminescent liver and lung tumor models will be used to validate the 3D BLT reconstruction. To demonstrate the capability of our FT system, GastroSense750 fluorescence agent will be used to imaging the mouse stomach and intestinal region in 3D. Conclusion: We expect that this integrated CBCT and optical tomography on-board a SARRP will present new research opportunities for pre-clinical radiation research. Supported by NCI RO1-CA 158100.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Prostate CT segmentation method based on nonrigid registration in ultrasound-guided CT-based HDR prostate brachytherapy

Purpose: The technological advances in real-time ultrasound image guidance for high-dose-rate (HDR) prostate brachytherapy have placed this treatment modality at the forefront of innovation in cancer radiotherapy. Prostate HDR treatment often involves placing the HDR catheters (needles) into the prostate gland under the transrectal ultrasound (TRUS) guidance, then generating a radiation treatment plan based on CT prostate images, and subsequently delivering high dose of radiation through these catheters. The main challenge for this HDR procedure is to accurately segment the prostate volume in the CT images for the radiation treatment planning. In this study, the authors propose a novel approach that integrates the prostate volume from 3D TRUS images into the treatment planning CT images to provide an accurate prostate delineation for prostate HDR treatment. Methods: The authors’ approach requires acquisition of 3D TRUS prostate images in the operating room right after the HDR catheters are inserted, which takes 1–3 min. These TRUS images are used to create prostate contours. The HDR catheters are reconstructed from the intraoperative TRUS and postoperative CT images, and subsequently used as landmarks for the TRUS–CT image fusion. After TRUS–CT fusion, the TRUS-based prostate volume is deformed to the CT images for treatment planning. This method was first validated with a prostate-phantom study. In addition, a pilot study of ten patients undergoing HDR prostate brachytherapy was conducted to test its clinical feasibility. The accuracy of their approach was assessed through the locations of three implanted fiducial (gold) markers, as well as T2-weighted MR prostate images of patients. Results: For the phantom study, the target registration error (TRE) of gold-markers was 0.41 ± 0.11 mm. For the ten patients, the TRE of gold markers was 1.18 ± 0.26 mm; the prostate volume difference between the authors’ approach and the MRI-based volume was 7.28% ± 0.86%, and the prostate volume Dice overlap coefficient was 91.89% ± 1.19%. Conclusions: The authors have developed a novel approach to improve prostate contour utilizing intraoperative TRUS-based prostate volume in the CT-based prostate HDR treatment planning, demonstrated its clinical feasibility, and validated its accuracy with MRIs. The proposed segmentation method would improve prostate delineations, enable accurate dose planning and treatment delivery, and potentially enhance the treatment outcome of prostate HDR brachytherapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

A method of surface marker location optimization for tumor motion estimation in lung stereotactic body radiation therapy

Purpose: Accurately localizing lung tumor localization is essential for high-precision radiation therapy techniques such as stereotactic body radiation therapy (SBRT). Since direct monitoring of tumor motion is not always achievable due to the limitation of imaging modalities for treatment guidance, placement of fiducial markers on the patient’s body surface to act as a surrogate for tumor position prediction is a practical alternative for tracking lung tumor motion during SBRT treatments. In this work, the authors propose an innovative and robust model to solve the multimarker position optimization problem. The model is able to overcome the major drawbacks of the sparse optimization approach (SOA) model. Methods: The principle-component-analysis (PCA) method was employed as the framework to build the authors’ statistical prediction model. The method can be divided into two stages. The first stage is to build the surrogate tumor matrix and calculate its eigenvalues and associated eigenvectors. The second stage is to determine the “best represented” columns of the eigenvector matrix obtained from stage one and subsequently acquire the optimal marker positions as well as numbers. Using 4-dimensional CT (4DCT) and breath hold CT imaging data, the PCA method was compared to the SOA method with respect to calculation time, average prediction accuracy, prediction stability, noise resistance, marker position consistency, and marker distribution. Results: The PCA and SOA methods which were both tested were on all 11 patients for a total of 130 cases including 4DCT and breath-hold CT scenarios. The maximum calculation time for the PCA method was less than 1 s with 64 752 surface points, whereas the average calculation time for the SOA method was over 12 min with 400 surface points. Overall, the tumor center position prediction errors were comparable between the two methods, and all were less than 1.5 mm. However, for the extreme scenarios (breath hold), the prediction errors for the PCA method were not only smaller, but were also more stable than for the SOA method. Results obtained by imposing a series of random noises to the surrogates indicated that the PCA method was much more noise resistant than the SOA method. The marker position consistency tests using various combinations of 4DCT phases to construct the surrogates suggested that the marker position predictions of the PCA method were more consistent than those of the SOA method, in spite of surrogate construction. Marker distribution tests indicated that greater than 80% of the calculated marker positions fell into the high cross correlation and high motion magnitude regions for both of the algorithms. Conclusions: The PCA model is an accurate, efficient, robust, and practical model for solving the multimarker position optimization problem to predict lung tumor motion during SBRT treatments. Due to its generality, PCA model can also be applied to other imaging guidance system whichever using surface motion as the surrogates.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Investigating the accuracy of microstereotactic-body-radiotherapy utilizing anatomically accurate 3D printed rodent-morphic dosimeters

Purpose: Sophisticated small animal irradiators, incorporating cone-beam-CT image-guidance, have recently been developed which enable exploration of the efficacy of advanced radiation treatments in the preclinical setting. Microstereotactic-body-radiation-therapy (microSBRT) is one technique of interest, utilizing field sizes in the range of 1–15 mm. Verification of the accuracy of microSBRT treatment delivery is challenging due to the lack of available methods to comprehensively measure dose distributions in representative phantoms with sufficiently high spatial resolution and in 3 dimensions (3D). This work introduces a potential solution in the form of anatomically accurate rodent-morphic 3D dosimeters compatible with ultrahigh resolution (0.3 mm{sup 3}) optical computed tomography (optical-CT) dose read-out. Methods: Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from contours defined on x-ray CT data sets of rats and mice, and using these molds to create tissue-equivalent radiochromic 3D dosimeters from Presage. Anatomically accurate spines were incorporated into some dosimeters, by first 3D printing the spine mold, then forming a high-Z bone equivalent spine insert. This spine insert was then set inside the tissue equivalent body mold. The high-Z spinal insert enabled representative cone-beam CT IGRT targeting. On irradiation, a linear radiochromic change in optical-density occurs in the dosimeter, which is proportional to absorbed dose, and was read out using optical-CT in high-resolution (0.5 mm isotropic voxels). Optical-CT data were converted to absolute dose in two ways: (i) using a calibration curve derived from other Presage dosimeters from the same batch, and (ii) by independent measurement of calibrated dose at a point using a novel detector comprised of a yttrium oxide based nanocrystalline scintillator, with a submillimeter active length. A microSBRT spinal treatment was delivered consisting of a 180° continuous arc at 225 kVp with a 20 × 10 mm field size. Dose response was evaluated using both the Presage/optical-CT 3D dosimetry system described above, and independent verification in select planes using EBT2 radiochromic film placed inside rodent-morphic dosimeters that had been sectioned in half. Results: Rodent-morphic 3D dosimeters were successfully produced from Presage radiochromic material by utilizing 3D printed molds of rat CT contours. The dosimeters were found to be compatible with optical-CT dose readout in high-resolution 3D (0.5 mm isotropic voxels) with minimal artifacts or noise. Cone-beam CT image guidance was possible with these dosimeters due to sufficient contrast between high-Z spinal inserts and tissue equivalent Presage material (CNR ∼10 on CBCT images). Dose at isocenter measured with optical-CT was found to agree with nanoscintillator measurement to within 2.8%. Maximum dose in line profiles taken through Presage and film dose slices agreed within 3%, with FWHM measurements through each profile found to agree within 2%. Conclusions: This work demonstrates the feasibility of using 3D printing technology to make anatomically accurate Presage rodent-morphic dosimeters incorporating spinal-mimicking inserts. High quality optical-CT 3D dosimetry is feasible on these dosimeters, despite the irregular surfaces and implanted inserts. The ability to measure dose distributions in anatomically accurate phantoms represents a powerful useful additional verification tool for preclinical microSBRT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗