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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

SU-E-J-109: Testing the KV Imaging Center Congruence with Radiation Isocenter of Small MLC and SRS Cone Field On Two Machines

Purpose: Orthogonal kV image pairs are used for target localization when fiducial markers are implanted. CBCT is used to verify cone SRS setup. Therefore it is necessary to evaluate the isocenter congruence between radiation fields and kV imaging center. This study used a simple method to evaluate the isocenter congruence, and compared the results for MLC and cone fields on two different Linacs. Methods: Varian OBI block was attached on the couch. It has a central 1mm BB with markers on three surfaces to align with laser. KV and MV images were taken at four cardinal angles. A 3x3cm2 MLC field and a 20mm cone field were irradiated respectively. On each kV image, the distance from BB center to the kV graticule center were measured. On the MV image of MLC field, the center of radiation field was determined manually, while for cone field, the Varian AM maintenance software was used to analyze the distance between BB and radiation field. The subtraction of the two distances gives the discrepancy between kV and radiation centers. Each procedure was repeated on five days at Trilogy and TrueBeam respectively. Results: The maximum discrepancy was found in the longitudinal direction at 180° gantry angel. It was 1.5±0.1mm for Trilogy and 0.6±0.1mm for TrueBeam. For Trilogy, although radiation center wobbled only 0.7mm and image center wobbled 0.8mm, they wobbled to the opposite direction. KV Pair using gantry 180° should be avoided in this case. Cone vs. kV isocenter has less discrepancy than MLC for Trilogy. Conclusion: Radiation isocenter of MLC and cone field is different, so is between Trilogy and TrueBeam. The method is simple and reproducible to check kV and radiation isocenter congruence.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Photonic Doppler velocimetry probe used to measure grain boundaries of dynamic shocked materials

Material scientists have developed computational modeling to predict the dynamic response of materials undergoing stress, but there is still a need to make precision measurements of surfaces undergoing shock compression. Miniature photonic Doppler velocimetry (PDV) probes have been developed to measure the velocity distribution from a moving surface traveling tens of kilometers per second. These probes use hundreds of optical fibers imaged by optical relays onto different regions of this moving surface. While previous work examined large surface areas, we have now developed a PDV microscope that can interrogate 37 different spots within a field of view of <1 mm, with a standoff distance of 17 mm, to analyze the motion differences across grain boundaries of the material undergoing dynamic stress. Each PDV fiber interrogates a 10 μm spot size on the moving surface. A separate imaging system using a coherent bundle records the location of the PDV spots relative to the grain boundaries prior to the dynamic event. Designing the mounting structures for the lenses, fibers, and coherent bundle was a challenge. To minimize back reflections, the fibers are index matched onto the first relay lens, which is made of fused silica. The PDV fibers are aligned normal to the moving surface. The imaging probe views the surface at an 18° angle. The coherent bundle is tilted 11° to its optical relay. All components are assembled into a single probe head assembly. The coherent bundle is removed from the probe head to be used for the next dynamic event. Alignment issues will also be discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

WE-D-17A-02: Evaluation of a Two-Dimensional Optical Dosimeter On Measuring Lateral Profiles of Proton Pencil Beams

Purpose: To evaluate the accuracy of a two-dimensional optical dosimeter on measuring lateral profiles for spots and scanned fields of proton pencil beams. Methods: A digital camera with a color image senor was utilized to image proton-induced scintillations on Gadolinium-oxysulfide phosphor reflected by a stainless-steel mirror. Intensities of three colors were summed for each pixel with proper spatial-resolution calibration. To benchmark this dosimeter, the field size and penumbra for 100mm square fields of singleenergy pencil-scan protons were measured and compared between this optical dosimeter and an ionization-chamber profiler. Sigma widths of proton spots in air were measured and compared between this dosimeter and a commercial optical dosimeter. Clinical proton beams with ranges between 80 mm and 300 mm at CDH proton center were used for this benchmark. Results: Pixel resolutions vary 1.5% between two perpendicular axes. For a pencil-scan field with 302 mm range, measured field sizes and penumbras between two detection systems agreed to 0.5 mm and 0.3 mm, respectively. Sigma widths agree to 0.3 mm between two optical dosimeters for a proton spot with 158 mm range; having widths of 5.76 mm and 5.92 mm for X and Y axes, respectively. Similar agreements were obtained for others beam ranges. This dosimeter was successfully utilizing on mapping the shapes and sizes of proton spots at the technical acceptance of McLaren proton therapy system. Snow-flake spots seen on images indicated the image sensor having pixels damaged by radiations. Minor variations in intensity between different colors were observed. Conclusions: The accuracy of our dosimeter was in good agreement with other established devices in measuring lateral profiles of pencil-scan fields and proton spots. A precise docking mechanism for camera was designed to keep aligned optical path while replacing damaged image senor. Causes for minor variations between emitted color lights will be investigated.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1973

Investigation of the dielectric waveguide modes in homostructure GaAs laser.

The investigation of the propagation modes in a homostructure GaAs laser and particularly of the spatial displacement of the TE and TM mode is reported. For this investigation, a homostructure GaAs laser was operated in an external optical cavity and experiments were performed where the resonator alignment was varied to displace the image of the p-n junction, formed in the optical cavity, from the p-n junction of the laser diode. The peak power of the laser radiation (which is in the TEM (sub 00) mode), the delay, the optical waveform, and the polarization were measured at room temperature for different cavity alignments. For the evaluation of the propagation modes the experimental results are correlated with the computed field distributions of the modes in a three-layer dielectric waveguide.

Philipp-Rutz, E. M.↗
NASA NTRS1984

Simulation of electronic registration of multispectral remote sensing images to 0.1 pixel accuracy

Band-to-band coregistration of multispectral remote sensing images can be achieved by electronic signal processing techniques rather than by costly and difficult mechanical alignment. This paper describes the results of a study of the end-to-end performance of electronic registration. The software simulation includes steps which model the performance of the geometric calibration process, the instrument image quality, detector performance and the effects of achieving coregistration through image resampling. The image resampling step emulates the Pipelined Resampling Processor, a real-time image resampler. The study demonstrates that the electronic alignment technique produces multispectral images which are superior to those produced by an imager whose pixel geometry is accurate to 0.1 pixel rms. The implications of this approach for future earth observation programs are discussed.

Reitsema, H. J.↗
DOE OSTI2023

A coded aperture with sub-mean-free-path thickness for implosion geometry imaging on ICF and IFE experiments

Inertial confinement fusion and inertial fusion energy experiments diagnose the geometry of the fusion region through imaging of the neutrons released through fusion reactions. Pinhole arrays typically used for such imaging require thick substrates to obtain high contrast along with a small pinhole diameter to obtain high resolution capability, resulting in pinholes that have large aspect ratios. This leads to expensive pinhole arrays that have small solid angles and are difficult to align. Here, we propose a coded aperture with scatter and partial attenuation (CASPA) for fusion neutron imaging that relaxes the thick substrate requirement for good image contrast. These coded apertures are expected to scale to larger solid angles and are easier to align without sacrificing imaging resolution or throughput. We use Monte Carlo simulations (Geant4) to explore a coded aperture design to measure neutron implosion asymmetries on fusion experiments at the National Ignition Facility (NIF) and discuss the viability of this technique, matching the current nominal resolution of 10 µm. The results show that a 10 mm thick tungsten CASPA can image NIF implosions with neutron yields above 10 14 with quality comparable to unprocessed data from a current NIF neutron imaging aperture. Furthermore, this CASPA substrate is 20 times thinner than the current aperture arrays for fusion neutron imaging and less than one mean free-path of 14.1 MeV neutrons through the substrate. Since the resolution, solid angle, and throughput are decoupled in coded aperture imaging, the resolution and solid angle achievable with future designs will be limited primarily by manufacturing capability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

SU-E-J-256: Dual Energy Planar Image Based Localization in the Absence of On-Board CT Images

Purpose: To develop a tool enabling soft tissue based image guidance using dual energy radiographs for cases when on-board CT is not available. Method: Dual energy planar radiographs can be applied to image guidance for targeting lung lesions because the bone based alignment only may not be sufficient as the lesions move. We acquired images of an anthropomorphic thorax phantom at 120 and 60 KVp respectively. Using a weighted logarithmic subtraction of these dual energy images, a soft tissue enhanced and a bone enhanced image were generated and they could be used for the image guidance purpose. Similar processing was also applied to a dual energy image set acquired for a patient undergoing a proton therapy. Results: The soft tissue enhanced images suppressed bones (ribs and scapula) overlying on lung, thus enabling a better visualization of soft tissue and lesion, while the bone enhanced image suppressed the soft tissue. These enhanced effects were visually apparent without further processing for display enhancements, such as using histogram or edge enhancement technique. Conclusions: The phantom image processing was encouraging. The initial test on the patient image set showed that other post processing might still be able to add value in visualizing soft tissues in addition to the dual energy soft tissue enhancement. More evaluations are needed to determine the potential benefit of this technique in the clinic.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2012

Real-Time X-ray Radiography Diagnostics of Components in Solid Rocket Motors

Solid rocket motors (SRMs) typically use nozzle materials which are required to maintain their shape as well as insulate the underlying support structure during the motor operation. In addition, SRMs need internal insulation materials to protect the motor case from the harsh environment resulting from the combustion of solid propellant. In the nozzle, typical materials consist of high density graphite, carbon-carbon composites and carbon phenolic composites. Internal insulation of the motor cases is typically a composite material with carbon, asbestos, Kevlar, or silica fibers in an ablative matrix such as EPDM or NBR. For both nozzle and internal insulation materials, the charring process occurs when the hot combustion products heat the material intensely. The pyrolysis of the matrix material takes away a portion of the thermal energy near the wall surface and leaves behind a char layer. The fiber reinforcement retains the porous char layer which provides continued thermal protection from the hot combustion products. It is of great interest to characterize both the total erosion rates of the material and the char layer thickness. By better understanding of the erosion process for a particular ablative material in a specific flow environment, the required insulation material thickness can be properly selected. The recession rates of internal insulation and nozzle materials of SRMs are typically determined by testing in some sort of simulated environment; either arc-jet testing, flame torch testing, or subscale SRMs of different size. Material recession rates are deduced by comparison of pre- and post-test measurements and then averaging over the duration of the test. However, these averaging techniques cannot be used to determine the instantaneous recession rates of the material. Knowledge of the variation in recession rates in response to the instantaneous flow conditions during the motor operation is of great importance. For example, in many SRM configurations the recession of the solid propellant grain can drastically alter the flow-field and effect the recession of internal insulation and nozzle materials. Simultaneous measurement of the overall erosion rate, the development of the char layer, and the recession of the char-virgin interface during the motor operation can be rather difficult. While invasive techniques have been used with limited success, they have serious drawbacks. Break wires or make wire sensors can be installed into a sufficient number of locations in the charring material from which a time history of the charring surface can be deduced. These sensors fundamentally alter the local structure of the material in which they are imbedded. Also, the location of these sensors within the material is not known precisely without the use of an X-ray. To determine instantaneous recession rates, real-time X-ray radiography (X-ray RTR) has been utilized in several SRM experiments at PSU. The X-ray RTR system discussed in this paper consists of an X-ray source, X-ray image intensifier, and CCD camera connected to a capture computer. The system has been used to examine the ablation process of internal insulation as well as nozzle material erosion in a subscale SRM. The X-ray source is rated to 320 kV at 10 mA and has both a large (5.5 mm) and small (3.0 mm) focal spot. The lead-lined cesium iodide X-ray image intensifier produces an image which is captured by a CCD camera with a 1,000 x 1,000 pixel resolution. To produce accurate imagery of the object of interest, the alignment of the X-ray source to the X-ray image intensifier is crucial. The image sequences captured during the operation of an SRM are then processed to enhance the quality of the images. This procedure allows for computer software to extract data on the total erosion rate and the char layer thickness. Figure 1 Error! Reference source not found.shows a sequence of images captured during the operation the subscale SRM with the X-ray RTR system. The X-rayTR system, alignment procedure, uncertainty determination, and image analysis process will be discussed in detail in the full manuscript.

Cortopassi, A. C.↗
DOE OSTI2015

SU-E-J-33: Comparison Between Soft Tissue Alignment and Bony Alignment for Pancreatic Cancer Radiotherapy

Purpose An IGRT modality for pancreatic cancer treatment with dose escalation at our institution is in-room daily CT imaging. The purpose of this study is to assess the difference between soft tissue alignment and bony alignment for pancreatic tumor localization. Methods Eighteen patients with pancreatic tumors who underwent IMRT treatment with an inspiration breath-hold technique between July 2012 and February 2015 are included in this study. Prior to each treatment, a CT scan was acquired. The CT image guidance started with auto-alignment to either the bony anatomy (vertebral bodies) or fiducials (for the six patients with the stent in/near the tumor) and then, when necessary, manual adjustments were made based on soft tissue alignment using clinical software (CT-Assisted Targeting system). The difference between soft tissue alignment and bony/fiducial alignment was evaluated. Results Of all 380 treatments, manual adjustment was made in 225 treatments, ranging from 11% (3 treatments out of 28) to 96% (27 treatments out of 28) per patient. The mean of the difference between soft tissue alignment and bony/fiducial alignment per patient ranged from −3.6 to 0.3 mm, −1.5 to 2.8 mm, and −3.3 to 3.4 mm in the AP, SI, and RL directions, respectively. The maximum difference over all treatments was −9.5, −14.6, and −14.6 mm in the AP, SI, and RL directions, respectively. Conclusion About 60% of the time, manual adjustment based on soft tissue alignment was required. The extent of manual adjustment was usually small but varied significantly from patient to patient. The ultimate goal of the IGRT modality using daily CT imaging is not to fully cover the target but to spare organs-at-risk as much as possible to avoid them moving into higher dose gradients than accepted in the treatment plan. To this end, manual adjustment based on soft tissue alignment is critically important.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-361: Energy Dependent Radiation/light-Field Misalignment On Truebeam Linear Accelerator

Purpose: Verifying the co-incidence of the radiation and light field is recommended by TG-142 for monthly and annual checks. On a digital accelerator, it is simple to verify that beam steering settings are consistent with accepted and commissioned values. This fact should allow for physicists to verify radiation-light-field co-incidence for a single energy and accept that Result for all energies. We present a case where the radiation isocenter deviated for a single energy without any apparent modification to the beam steering parameters. Methods: The radiation isocenter was determined using multiple Methods: Gafchromic film, a BB test, and radiation profiles measured with a diode. Light-field borders were marked on Gafchromic film and then irradiated for all photon energies. Images of acceptance films were compared with films taken four months later. A phantom with a radio-opaque BB was aligned to isocenter using the light-field and imaged using the EPID for all photon energies. An unshielded diode was aligned using the crosshairs and then beam profiles of multiple field sizes were obtained. Field centers were determined using Omni-Pro v7.4 software, and compared to similar scans taken during commissioning. Beam steering parameter files were checked against backups to determine that the steering parameters were unchanged. Results: There were no differences between the configuration files from acceptance. All three tests demonstrated that a single energy had deviated from accepted values by 0.8 mm in the inline direction. The other two energies remained consistent with previous measurements. The deviated energy was re-steered to be within our clinical tolerance. Conclusions: Our study demonstrates that radiation-light-field coincidence is an energy dependent effect for modern linacs. We recommend that radiation-light-field coincidence be verified for all energies on a monthly basis, particularly for modes used to treat small fields, as these may drift without influencing results from other tests.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2010

Method for nanoscale spatial registration of scanning probes with substrates and surfaces

Embodiments in accordance with the present invention relate to methods and apparatuses for aligning a scanning probe used to pattern a substrate, by comparing the position of the probe to a reference location or spot on the substrate. A first light beam is focused on a surface of the substrate as a spatial reference point. A second light beam then illuminates the scanning probe being used for patterning. An optical microscope images both the focused light beam, and a diffraction pattern, shadow, or light backscattered by the illuminated scanning probe tip of a scanning probe microscope (SPM), which is typically the tip of the scanning probe on an atomic force microscope (AFM). Alignment of the scanning probe tip relative to the mark is then determined by visual observation of the microscope image. This alignment process may be repeated to allow for modification or changing of the scanning probe microscope tip.

Wade, Lawrence A.↗
NASA NTRS1995

Sub-pixel localization of highways in AVIRIS images

Roads and highways show up clearly in many bands of AVIRIS images. A typical lane in the U.S. is 12 feet wide, and the total width of a four lane highway, including 18 feet of paved shoulders, is 19.8 m. Such a highway will cover only a portion of any 20x20 m AVIRIS pixel that it traverses. The other portion of these pixels wil be usually covered by vegetation. An interesting problem is to precisely determine the location of a highway within the AVIRIS pixels that it traverses. This information may be used for alignment and spatial calibration of AVIRIS images. Also, since the reflection properties of highway surfaces do not change with time, and they can be determined once and for all, such information can be of help in calculating and filtering out the atmospheric noise that contaminates AVIRIS measurements. The purpose of this report is to describe a method for sub-pixel localization of highways.

Salu, Yehuda↗
DOE OSTI2016

Observation and analysis of emergent coherent structures in a high-energy-density shock-driven planar mixing layer experiment

Coherent emergent structures have been observed in a high-energy-density supersonic mixing layer experiment. A millimeter-scale shock tube uses lasers to drive Mbar shocks into the tube volume. The shocks are driven into initially solid foam (60 mg/cm 3 ) hemicylinders separated by an Al or Ti metal tracer strip; the components are vaporized by the drive. Before the experiment disassembles, the shocks cross at the tube center, creating a very fast (ΔU > 200 km/s) shear-unstable zone. After several nanoseconds, an expanding mixing layer is measured, and after 10+ ns we observe the appearance of streamwise-periodic, spanwise-aligned rollers associated with the primary Kelvin-Helmholtz instability of mixing layers. We additionally image roller pairing and spanwise-periodic streamwise-aligned filaments associated with secondary instabilities. New closures are derived to connect length scales of these structures to estimates of fluctuating velocity data otherwise unobtainable in the high-energy-density environment. Finally, this analysis indicates shear-induced specific turbulent energies 10 3 – 10 4 times higher than the nearest conventional experiments. Because of difficulties in continuously driving systems under these conditions and the harshness of the experimental environment limiting the usable diagnostics, clear evidence of these developing structures has never before been observed in this regime.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

SU-E-T-48: Automated Quality Assurance for XML Controlled Linacs

Purpose: To automate routine imaging QA procedures so that complying with TG 142 and TG 179 can be efficient and reliable. Methods: Two QA tests for a True Beam Linac were automatized. A Winston Lutz test as described by Lutz et al{sup 1} using the Winston Lutz test kit from BrainLab, Germany and a CBCT Image Quality test as described in TG 179 using the EMMA phantom, Siemens Medical Physics, Germany were performed in our True Beam. For each QA procedure tested, a 3 step paradigm was used. First, the data was automatically acquired using True Beam Developer Mode and XML scripting. Second, the data acquired in the first step was automatically processed using in-home grown Matlab GUIs. Third, Machine Learning algorithms were used to automatically classify the processed data and reports generated. Results: The Winston Luzt test could be performed by an experienced medical physicist in 29.0 ± 8.0 min. The same test, if automated using our paradigm, could be performed in 3.0 ± 0.1 min. In the same lieu, time could be substantially saved for image quality tests. In this case, the amount of time saved will depend on the phantoms used and the initial localization method. Additionally, machine learning algorithms could automatically identify the roots of the problems if any and possibly help reduce machine down time. Conclusion: Modern linear accelerators are equipped with advanced 2D and 3D imaging that are used for patient alignment substantially improving IGRT protocols. However, this extra complexity exponentially increases the number of QA tests needed. Using the new paradigm described above, not only bare minimum but best practice QA programs could be implemented with the same manpower. This work is supported by Varian, Palo Alto, CA.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Scanning transmission election microscopy observations of twisted epitaxial gold nanodiscs in twisted molybdenum disulfide bilayers

Atomic scale, scanning transmission electron microscopy (STEM) analysis of the moiré structures in twisted epitaxial gold nanodiscs encapsulated in twisted bilayer molybdenum disulfide is presented. High angle annular dark field STEM imaging reveals that the period of the moiré patterns between gold and molybdenum disulfide varies with different twist angles of the bilayer molybdenum disulfide, ranging from 1.80 nm (epitaxial alignment of gold) to 1.53 nm (twisted epitaxial alignment of gold). Additionally, bright field STEM imaging reveals a faint, larger "moiré of moiré" structure in cases where the bilayer molybdenum disulfide twist angle is small (~6°), arising from the overlapping three-layers, which is not visible in conventional transmission electron microscopy images. In conclusion, our experiments indicate that scanning transmission electron microscopy as a suitable tool for moiré analysis of twisted multilayer planar heterostructures, complementary to information provided by conventional transmission electron microscopy and diffraction.

Au↗
DOE OSTI2023

Regiospecific Cellulose Orientation and Anisotropic Mechanical Property in Plant Cell Walls

Cellulose microfibrils (CMFs) are a major load-bearing component in plant cell walls. Thus, their structures have been studied extensively with spectroscopic and microscopic characterization methods; but the findings from these two approaches were inconsistent, which hampers mechanistic understanding of cell wall mechanics. Here, we report the regiospecific assembly of CMFs in the periclinal wall of plant epidermal cells. Using sum frequency generation spectroscopic imaging, we found that CMFs are highly aligned in the cell edge region where two cells form a junction, whereas they are mostly isotropic on average throughout the wall thickness in the flat face region of the epidermal cell. This subcellular-level heterogeneity in CMF alignment provided insights into tissue-level anisotropy in tensile modulus of cell wall materials. Furthermore, this finding also has resolved a previous contradiction between the spectroscopic and microscopic imaging studies, which paves a foundation for better understanding of cell wall artichecture, especially structure-geometry relationships.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1994

Near-infrared continuum and 3.3 micrometer(s) polycyclic aromatic hydrocarbon imaging of the starburst ring in the type 1 Seyfert galaxy NGC 7469

High resolution near-infrared images of the type 1 Seyfert galaxy NGC 7469 have been obtained to probe its dusty nuclear environment. Direct J, H, and K images are relatively featureless, but residual images created by subtracting a smooth model based on best-fitting elliptical isophotes reveal a tight inner spiral whose high surface-brightness portions correspond to a previously detected 3 sec (1 kpc) diameter ring of radio continuum emission. The inner infrared spiral arms extended approximately equal to 4 sec NW and SE from the nucleus, and the NW arm joins up with large-scale spiral structure visible in the R band. The residual images also show a bar-like structure aligned with the brightest infrared/radio hotspots at PA approximately equal to 50 deg. Three infrared hotspots are detected which align remarkably well with 6 cm radio continuum sources. The near-infrared ring and the hotspots are visible in the residual images, and in a high-resolution direct K-band image restored to an effective resolution of 0.65 sec (FWHM) using the Richardson-Lucy algorithm. The infrared hotspots have luminosities of nuL(sub nu) (2.2 micrometer(s)) approximately equal to 10(exp 8) solar luminosity (M(sub k) approximately equal to -16 mag), suggesting they are either giant H II regions or individual supernovae. The two brightest regions may be associated with enhanced star formation triggered by orbit crowding of gas where spiral arms emerge from an inner bar. Narrowband (delta lambda/lambda approximately 1.5%) imaging in the 3.28 micrometer(s) dust emission feature and surrounding continuum confirms the 3 sec diameter 3.28 micrometer(s) emission region detected previously using multiaperture photometry. The extended polycyclic aromatic hydrocarbon (PAH) emission is slightly elongated and aligned with published 1O III1 line emission and 12.5 micrometer(s) continuum emission, apparently tracing the starburst. The presence of approximately equal to 25% of the total 3.28 micrometer(s) PAH emission within R less than 1 sec demonstrates that a starburst within the central few hundred parsecs must supply a significant fraction of the infrared continuum from the nucleus, and there is apparently sufficient shielding material between the starburst and the active galactic nucleus (AGN) to preserve the PAHs along our line of sight to the nucleus.

Mazzarella, J. M.↗
DOE OSTI2014

Sci—Fri AM: Mountain — 06: Optimizing planning target volume in lung radiotherapy using deformable registration

A four dimensional computed tomography (4DCT) image is acquired for all radically treated, lung cancer patients to define the internal target volume (ITV), which encompasses tumour motion due to breathing and subclinical disease. Patient set-up error and anatomical motion that is not due to breathing is addressed through an additional 1 cm margin around the ITV to obtain the planning target volume (PTV). The objective of this retrospective study is to find the minimum PTV margin that provides an acceptable probability of delivering the prescribed dose to the ITV. Acquisition of a kV cone beam computed tomography (CBCT) image at each fraction was used to shift the treatment couch to accurately align the spinal cord and carina. Our method utilized deformable image registration to automatically position the planning ITV on each CBCT. We evaluated the percentage of the ITV surface that fell within various PTVs for 79 fractions across 18 patients. Treatment success was defined as a situation where at least 99% of the ITV is covered by the PTV. Overall, this is to be achieved in at least 90% of the treatment fractions. The current approach with a 1cm PTV margin was successful ∼96% of the time. This analysis revealed that the current margin can be reduced to 0.8cm isotropic or 0.6×0.6×1 cm{sup 3} non-isotropic, which were successful 92 and 91 percent of the time respectively. Moreover, we have shown that these margins maintain accuracy, despite intrafractional variation, and maximize CBCT image guidance capabilities.

60 APPLIED LIFE SCIENCES↗