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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Dynamic assembly of polymer nanotube networks via kinesin powered microtubule filaments

In this study, we describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4–5 h for corresponding lipid networks). The transport of materials in and on the polymer membranes differs substantially from the transport on analogous lipid networks. Specifically, our data suggest that polymer mobility in nanotubular structures is considerably different from planar or 3D structures, and is stunted by 1D confinement of the polymer subunits. Moreover, quantum dots adsorbed onto polymer nanotubes are completely immobile, which is related to this 1D confinement effect and is in stark contrast to the highly fluid transport observed on lipid tubules.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Enzymatically triggered rupture of polymersomes

Polymersomes are robust vesicles made from di-block co-polymers. We have engineered a two step enzymatic cascade to trigger the release of contents from polymersomes, in which extravesicular glucose oxidase makes hydrogen peroxide, when then penetrates the membrane and is converted by entrapped catalase to oxygen, leading to vesicle failure.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

The structural fate of lipid nanoparticles in the extracellular matrix

Drug-loaded liposomes are the most successful nanomedicine to date, with multiple FDA-approved systems for a myriad of diseases. While liposome circulation time in blood and retention in tissues have been studied in detail, the structural fate of liposomes—and nanoparticles in general—in the body has not been extensively investigated. In this work, we explore the interactions of liposomes with synthetic and natural hydrogel materials to understand how the natural extracellular matrix influences liposome structural characteristics. Small angle X-ray scattering, confocal microscopy, and cryogenic transmission electron microscopy data demonstrate that poly(ethylene glycol) (PEG), gelatin, alginate, and Matrigel ® hydrogels cause 200 nm liposomes of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to transform into micrometer-sized aggregates. These aggregates are composed of multilamellar vesicles around 100 nm in diameter with a mean interlamellar separation of 5.5 nm. Protecting the liposomes with a corona of PEG damps this restructuring effect, making the multilamellar vesicles less stable. We attribute this unilamellar to multilamellar transition to an osmotic driving force from the hydrogel environment. This lipid restructuring has broad ramifications in the design and use of nanomedicines, and in understanding the fate and function of natural lipid-based materials within the tissue microenvironment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Transverse lipid organization dictates bending fluctuations in model plasma membranes

Membrane undulations play a vital role in many biological processes, including the regulation of membrane protein activity. The asymmetric lipid composition of most biological membranes complicates theoretical description of these bending fluctuations, yet experimental data that would inform any such a theory is scarce. In this work, we used neutron spin-echo (NSE) spectroscopy to measure the bending fluctuations of large unilamellar vesicles (LUV) having an asymmetric transbilayer distribution of high- and lowmelting lipids. The asymmetric vesicles were prepared using cyclodextrin-mediated lipid exchange, and were composed of an outer leaflet enriched in egg sphingomyelin (ESM) and an inner leaflet enriched in 1-palmitoyl-2-oleoyl-phosphoethanolamine (POPE), which have main transition temperatures of 37 °C and 25 °C, respectively. The overall membrane bending rigidity was measured at three temperatures: 15 °C, where both lipids are in a gel state; 45 °C, where both lipids are in a fluid state; and 30 °C, where there is gel-fluid co-existence. Remarkably, the dynamics for the fluid asymmetric LUVs (aLUVs) at 30 °C and 45 °C do not follow trends predicted by their symmetric counterparts. At 30 °C, compositional asymmetry suppressed the bending fluctuations, with the asymmetric bilayer exhibiting a larger bending modulus than that of symmetric bilayers corresponding to either the outer or inner leaflet. We conclude that the compositional asymmetry and leaflet coupling influence the internal dissipation within the bilayer and result in membrane properties that cannot be directly predicted from corresponding symmetric bilayers.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Structure of supported DPPC/cholesterol bilayers studied via X-ray reflectivity

The electron density profile of bilayers of DPPC/cholesterol mixtures supported on semiconductor grade silicon substrates were studied with the objective of determining how the proximity of a solid interface modifies the phase diagram of mixed bilayers. The bilayers were studiedin situimmersed in waterviasynchrotron X-ray reflectivity (XRR). Measurements were performed as a function of temperature through the main phase transition and cholesterol mole fractions up to 40%. Analysis of XRR yields the bilayer thickness, roughness and leaflet asymmetry. We find that the structure of the pure DPPC bilayers in the gel phase is in agreement with previous X-ray measurements of supported bilayers depositedviavesicle fusion and multilamellar vesicles but show more clearly defined features than measurements made on films formed using Langmuir-Blodget Langmuir-Shaffer (LB) deposition. Examination of bilayer thicknessvs.temperature shows that the melting temperature for supported bilayers is shifted upwards by approximately 4 degrees C relative to multilamellar vesicles and that the melting temperature decreases with increasing cholesterol content up to 20%. For pure DPPC bilayers the leaflets melt in two stages with the distal leaflet melting first. For cholesterol concentrations of 10% and 20% there is no clear indication of separate melting. Finally. for 33% and 40% cholesterol content no clear transition is seen in the bilayer thickness, but an abrupt change in roughness indicates possible microdomain formation in the 40% cholesterol sample.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Conjugated polyelectrolyte-based ternary exciton funnels via liposome scaffolds

There is great interest in developing inexpensive, molecular light-harvesting systems capable of efficiently converting photon energy to chemical potential energy. It is highly desirable to do so using self-assembly and in a manner that supports environmentally benign processing. A critical consideration in any such assembly is the ability to absorb a substantial fraction of the solar emission spectrum and to be able to efficiently move excited states through the space to a functional interface. We have previously shown that aqueous inter-conjugated polyelectrolyte (CPE) complexes can act as ultrafast and efficient energy-transfer antennae. Here we demonstrate formation of a hierarchically assembled, aqueous system based on an inter-CPE exciton donor/acceptor network and a lipid vesicle scaffold. Using a model small-molecule organic semiconductor embedded in the vesicle membrane, we form a ternary exciton funnel that is oriented towards the membrane interior. We show that, although energy transfer is efficient, the assembly morphology depends sensitively on preparation conditions and relative ionic stoichiometry. We propose several approaches towards stabilizing such aqueous assemblies. Furthermore, this work highlights a path to formation of an aqueous, panchromatic light-harvesting system, whose functional complexity can be systematically increased with modularity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Engineering endosomolytic nanocarriers of diverse morphologies using confined impingement jet mixing

The clinical translation of many biomolecular therapeutics has been hindered by undesirable pharmacokinetic (PK) properties, inadequate membrane permeability, poor endosomal escape and cytosolic delivery, and/or susceptibility to degradation. Overcoming these challenges merits the development of nanoscale drug carriers (nanocarriers) to improve the delivery of therapeutic cargo. Herein, we implement a flash nanoprecipitation (FNP) approach to produce nanocarriers of diverse vesicular morphologies by using various molecular weight PEG-bl-DEAEMA-co-BMA (PEG-DB) polymers. We demonstrated that FNP can produce uniform (PDI < 0.1) particles after 5 impingements, and that by varying the copolymer hydrophilic mass fraction, FNP enables access to a diverse variety of nanoarchitectures including micelles, unilamellar vesicles (polymersomes), and multi-compartment vesicles (MCVs). We synthesized a library of 2 kDa PEG block copolymers, with DEAEMA-co-BMA second block molecular weights of 3, 6, 12, 15, 20, and 30 kDa. All formulations were both pH responsive, endosomolytic, and capable of loading and cytosolically delivering small negatively charged molecules – albeit to different degrees. Using a B16.F10 melanoma model, we showcased the therapeutic potential of a lead FNP formulated PEG-DB nanocarrier, encapsulating the cyclic dinucleotide (CDN) cGAMP to activate the stimulator of interferon genes (STING) pathway in a therapeutically relevant context. Collectively, these data demonstrate that an FNP process can be used to formulate pH-responsive nanocarriers of diverse morphologies using a PEG-DB polymer system. As FNP is an industrially scalable process, these data address the critical translational challenge of producing PEG-DB nanoparticles at scale. Furthermore, the diverse morphologies produced may specialize in the delivery of distinct biomolecular cargos for other therapeutic applications, implicating the therapeutic potential of this platform in an array of disease applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Perturbation of nanoplastics on biomembranes: molecular insights from neutron scattering

Plastic waste is now pervasive in the environment, breaking down into microplastics and nanoplastics under many environmental conditions. These particles have been found in various ecosystems and even in human tissues, raising significant environmental and health concerns. In this study, we investigated the interaction of polystyrene nanoplastics, with and without surface modifications, on biomembrane structures using contrast-matching small-angle neutron scattering and neutron spin echo spectroscopy. The neutron contrast matching enabled the selective study of biomembranes in the presence of nanoplastics. Two model membranes were employed: a simple zwitterionic bilayer (i.e., dimyristoylphosphatidylcholine [DMPC]) and an Escherichia coli lipid extract as a bacterial membrane model. The results show profound membrane disruptions, including possible thinning, vesicle fragmentation, lipid monolayer formation, and inter-vesicle aggregation, with the more severe effects observed in DMPC membranes. Notably, E. coli membranes exhibited greater resilience, suggesting that natural membranes with diverse lipid compositions may reduce susceptibility to perturbation by extracellular nanoplastics. Here, these findings highlight potential risks posed by environmental nanoplastic particles to biological membranes, with insights into molecular-level interactions and the environmental toxicity of nanoplastics. This work provides a foundation for future studies into nanoplastic–biomembrane interactions and their broader implications for health and environment using neutrons.

Qian, Shuo [Oak Ridge National Laboratory (ORNL), ↗
DOE OSTI2014

Shewanella oneidensis MR-1 Nanowires are Outer Membrane and Periplasmic Extensions of the Extracellular Electron Transport Components

Bacterial nanowires offer an extracellular electron transport (EET) pathway for linking the respiratory chain of bacteria to external surfaces, including oxidized metals in the environment and engineered electrodes in renewable energy devices. Despite the global, environmental, and technological consequences of this biotic-abiotic interaction, the composition, physiological relevance, and electron transport mechanisms of bacterial nanowires remain unclear. We report the first in vivo observations of the formation and respiratory impact of nanowires in the model metal-reducing microbe Shewanella neidensis MR-1. Using live fluorescence measurements, immunolabeling, and quantitative gene expression analysis, we report that S. oneidensis MR-1 nanowires are extensions of the outer membrane and periplasm that include the multiheme cytochromes responsible for EET, rather than pilin-based structures, as previously thought. These bacterial nanowires were also associated with outer membrane vesicles and vesicle chains, structures ubiquitous in gram-negative bacteria. Redoxfunctionalized membrane and vesicular extensions may represent a general microbial strategy for electron transport and energy distribution.

membranes↗
DOE OSTI2016

Calcium transport into the cells of the sea urchin larva in relation to spicule formation

We investigated the manner in which the sea urchin larva takes up calcium from its body cavity into the primary mesenchymal cells (PMCs) that are responsible for spicule formation. We used the membrane-impermeable fluorescent dye calcein and alexa-dextran, with or without a calcium channel inhibitor, and imaged the larvae in vivo with selective-plane illumination microscopy. Both fluorescent molecules are taken up from the body cavity into the PMCs and ectoderm cells, where the two labels are predominantly colocalized in particles, whereas the calcium-binding calcein label is mainly excluded from the endoderm and is concentrated in the spicules. The presence of vesicles and vacuoles inside the PMCs that have openings through the plasma membrane directly to the body cavity was documented using high-resolution cryo-focused ion beam-SEM serial imaging. Some of the vesicles and vacuoles are interconnected to form large networks. We suggest that these vacuolar networks are involved in direct sea water uptake. We conclude that the calcium pathway from the body cavity into cells involves nonspecific endocytosis of sea water with its calcium.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Lipid sponge droplets as programmable synthetic organelles

Living cells segregate molecules and reactions in various subcellular compartments known as organelles. Spatial organization is likely essential for expanding the biochemical functions of synthetic reaction systems, including artificial cells. Many studies have attempted to mimic organelle functions using lamellar membrane-bound vesicles. However, vesicles typically suffer from highly limited transport across the membranes and an inability to mimic the dense membrane networks typically found in organelles such as the endoplasmic reticulum. Here, we describe programmable synthetic organelles based on highly stable nonlamellar sponge phase droplets that spontaneously assemble from a single-chain galactolipid and nonionic detergents. Due to their nanoporous structure, lipid sponge droplets readily exchange materials with the surrounding environment. In addition, the sponge phase contains a dense network of lipid bilayers and nanometric aqueous channels, which allows different classes of molecules to partition based on their size, polarity, and specific binding motifs. The sequestration of biologically relevant macromolecules can be programmed by the addition of suitably functionalized amphiphiles to the droplets. We demonstrate that droplets can harbor functional soluble and transmembrane proteins, allowing for the colocalization and concentration of enzymes and substrates to enhance reaction rates. Droplets protect bound proteins from proteases, and these interactions can be engineered to be reversible and optically controlled. Our results show that lipid sponge droplets permit the facile integration of membrane-rich environments and self-assembling spatial organization with biochemical reaction systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Subdomain cryo-EM structure of nodaviral replication protein A crown complex provides mechanistic insights into RNA genome replication

For positive-strand RNA [(+)RNA] viruses, the major target for antiviral therapies is genomic RNA replication, which occurs at poorly understood membrane-bound viral RNA replication complexes. Recent cryoelectron microscopy (cryo-EM) of nodavirus RNA replication complexes revealed that the viral double-stranded RNA replication template is coiled inside a 30- to 90-nm invagination of the outer mitochondrial membrane, whose necked aperture to the cytoplasm is gated by a 12-fold symmetric, 35-nm diameter “crown” complex that contains multifunctional viral RNA replication protein A. Here we report optimizing cryo-EM tomography and image processing to improve crown resolution from 33 to 8.5 Å. This resolves the crown into 12 distinct vertical segments, each with 3 major subdomains: A membrane-connected basal lobe and an apical lobe that together comprise the ~19-nm-diameter central turret, and a leg emerging from the basal lobe that connects to the membrane at ~35-nm diameter. Despite widely varying replication vesicle diameters, the resulting two rings of membrane interaction sites constrain the vesicle neck to a highly uniform shape. Labeling protein A with a His-tag that binds 5-nm Ni-nanogold allowed cryo-EM tomography mapping of the C terminus of protein A to the apical lobe, which correlates well with the predicted structure of the C-proximal polymerase domain of protein A. These and other results indicate that the crown contains 12 copies of protein A arranged basally to apically in an N-to-C orientation. Moreover, the apical polymerase localization has significant mechanistic implications for template RNA recruitment and (-) and (+)RNA synthesis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Cytosolic Acetyl-CoA Generated by ATP-Citrate Lyase Is Essential for Acetylation of Cell Wall Polysaccharides

Abstract Plant cell wall polysaccharides, including xylan, glucomannan, xyloglucan and pectin, are often acetylated. Although a number of acetyltransferases responsible for the acetylation of some of these polysaccharides have been biochemically characterized, little is known about the source of acetyl donors and how acetyl donors are translocated into the Golgi, where these polysaccharides are synthesized. In this report, we investigated roles of ATP-citrate lyase (ACL) that generates cytosolic acetyl-CoA in cell wall polysaccharide acetylation and effects of simultaneous mutations of four Reduced Wall Acetylation (RWA) genes on acetyl-CoA transport into the Golgi in Arabidopsis thaliana. Expression analyses of genes involved in the generation of acetyl-CoA in different subcellular compartments showed that the expression of several ACL genes responsible for cytosolic acetyl-CoA synthesis was elevated in interfascicular fiber cells and induced by secondary wall-associated transcriptional activators. Simultaneous downregulation of the expression of ACL genes was demonstrated to result in a substantial decrease in the degree of xylan acetylation and a severe alteration in secondary wall structure in xylem vessels. In addition, the degree of acetylation of other cell wall polysaccharides, including glucomannan, xyloglucan and pectin, was also reduced. Moreover, Golgi-enriched membrane vesicles isolated from the rwa1/2/3/4 quadruple mutant were found to exhibit a drastic reduction in acetyl-CoA transport activity compared with the wild type. These findings indicate that cytosolic acetyl-CoA generated by ACL is essential for cell wall polysaccharide acetylation and RWAs are required for its transport from the cytosol into the Golgi.

Cell Biology↗
DOE OSTI2014

SU-E-J-53: Dosimetric Evaluation at Volumetric Modulated Arc Therapy for Treatment of Prostate Cancer Using Single Or Double Arcs

Purpose: Evaluate and compare retrospective prostate treatment plan using Volumetric Modulated Arc Therapy (RapidArc™ - Varian) technique with single or double arcs at COI Group. Methods: Ten patients with present prostate and seminal vesicle neoplasia were replanned as a target treatment volume and a prescribed dose of 78 Gy. A baseline planning, using single arc, was developed for each case reaching for the best result on PTV, in order to minimize the dose on organs at risk (OAR). Maintaining the same optimization objectives used on baseline plan, two copies for optimizing single and double arcs, have been developed. The plans were performed with 10 MV photon beam energy on Eclipse software, version 11.0, making use of Trilogy linear accelerator with Millenium HD120 multileaf collimator. Comparisons on PTV have been performed, such as: maximum, minimum and mean dose, gradient dose, as well as the quantity of monitor units, treatment time and homogeneity and conformity index. OARs constrains dose have been evaluated, comparing both optimizations. Results: Regarding PTV coverage, the difference of the minimum, maximum and mean dose were 1.28%, 0.7% and 0.2% respectively higher for single arc. When analyzed the index of homogeneity found a difference of 0.99% higher when compared with double arcs. However homogeneity index was 0.97% lower on average by using single arc. The doses on the OARs, in both cases, were in compliance to the recommended limits RTOG 0415. With the use of single arc, the quantity of monitor units was 10,1% lower, as well as the Beam-On time, 41,78%, when comparing double arcs, respectively. Conclusion: Concerning the optimization of patients with present prostate and seminal vesicle neoplasia, the use of single arc reaches similar objectives, when compared to double arcs, in order to decrease the treatment time and the quantity of monitor units.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

A novel approach for evaluation of prostate deformation and associated dosimetric implications in IGRT of the prostate

Purpose: Prostate deformation is assumed to be a secondary correction and is typically ignored in the planning target volume (PTV) margin calculations. This assumption needs to be tested, especially when planning margins are reduced with daily image-guidance. In this study, deformation characteristics of the prostate and seminal vesicles were determined, and the dosimetric impact on treatment plans with different PTV margins was investigated. Methods: Ten prostate cancer patients were retrospectively selected for the study, each with three fiducial markers implanted in the prostate. Two hundred CBCT images were registered to respective planning CT images using a B-spline-based deformable image registration (DIR) software. A manual bony anatomy-based match was first applied based on the alignment of the pelvic bones and fiducial landmarks. DIR was then performed. For each registration, deformation vector fields (DVFs) of the prostate and seminal vesicles (SVs) were quantified using deformation-volume histograms. In addition, prostate rotation was evaluated and compared with prostate deformation. For a patient demonstrating small and large prostate deformations, target coverage degradation was analyzed in each of three treatment plans with PTV margins of 10 mm (6 mm at the prostate/rectum interface), as well as 5, and 3 mm uniformly. Results: Deformation of the prostate was most significant in the anterior direction. Maximum prostate deformation of greater than 10, 5, and 3 mm occurred in 1%, 17%, and 76% of the cases, respectively. Based on DVF-histograms, DVF magnitudes greater than 5 and 3 mm occurred in 2% and 27% of the cases, respectively. Deformation of the SVs was most significant in the posterior direction, and it was greater than 5 and 3 mm in 7.5% and 44.9% of the cases, respectively. Prostate deformation was found to be poorly correlated with rotation. Fifty percent of the cases showed rotation with negligible deformation and 7% of the cases showed significant deformation with minimal rotation (<3°). Average differences in the D{sub 95} dose to the prostate + SVs between the planning CT and CBCT images was 0.4% ± 0.5%, 3.0% ± 2.8%, and 6.6% ± 6.1%, respectively, for the plans with 10/6, 5, and 3 mm margins. For the case with both a large degree of prostate deformation (≈10% of the prostate volume) and rotation (≈8°), D{sub 95} was reduced by 0.5% ± 0.1%, 6.8% ± 0.6%, and 20.9% ± 1.6% for 10/6, 5, and 3 mm margin plans, respectively. For the case with large prostate deformation but negligible rotation (<1°), D{sub 95} was reduced by 0.4 ± 0.3, 3.9 ± 1.0, and 11.5 ± 2.5 for 10/6, 5, and 3 mm margin plans, respectively. Conclusions: Prostate deformation over a course of fractionated prostate radiotherapy may not be insignificant and may need to be accounted for in the planning margin design. A consequence of these results is that use of highly reduced planning margins must be viewed with caution.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-P-12: Pinnacle-Based Tool to Evaluate the Effect of Prostate Rotation as Determined by Calypso

Purpose: When the Calypso reports a large prostate rotation and one does not have the means to make corrections, it is helpful to quantify its dosimetric effects. We have devised a simple scheme to achieve this in Pinnacle TPS. If it is determined that the PTV margin is inadequate, an alternate larger-margin plan may be adapted for the day. Methods: A three-step process using the Pinnacle Image fusion module was formulated to analyze the clinical effect of prostate rotation. The process includes (1) translating the image set such that the rotational axis is about the isocenter, (2) performing 3D rotations of the structures of interest, and (3) restoring the coordinates associated with the plan. The rotated structures are imported and overlayed on the original plan for evaluation. The tool was applied to three prostate cancer patients with relatively large rotations (95 fractions total). Prostate rotations are primarily due to variations in bladder and rectal filling, which may also affect the seminal vesicles. It is difficult to estimate the perturbation of seminal vesicles for a given prostate rotation. Therefore, the Calypso-derived rotation matrix was applied only to CTV and PTV (CTV+5mm). Results: The rotations were predominantly in the pitch direction with an absolute value ranging from 0–29 degrees (Median = 10°, Average = 14.5°). For various magnitudes of rotation, the CTV V100 decreased from the original 100% to 99.6%/99%/95% for 10°/15°/29° rotations, respectively. Likewise, the PTV V100 diminished from 95% to 92%/89%/82%. Conclusion: A tool, consisting only of features within a TPS, was used to evaluate the dosimetric effect of prostate rotation. Our study shows that under large uncorrected rotations, the tumor coverage is degraded and may require intervention in the form of plan adaptation. To this end, alternate plans with variable margins can be generated in advance for daily adaption.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-J-177: A Computational Approach for Determination of Anisotropic PTV Margins Based On Statistical Shape Analysis for Prostate Cancer Radiotherapy

Purpose: Our aim of this study was to propose a computational approach for determination of anisotropic planning target volume (PTV) margins based on statistical shape analysis with taking into account time variations of clinical target volume (CTV) shapes for the prostate cancer radiation treatment planning (RTP). Methods: Systematic and random setup errors were measured using orthogonal projection and cone beam computed tomography (CBCT) images for data of 20 patients, who underwent the intensity modulated radiation therapy for prostate cancer. The low-risk, intermediate-risk, and high-risk CTVs were defined as only a prostate, a prostate plus proximal 1-cm seminal vesicles, and a prostate plus proximal 2-cm seminal vesicles, respectively. All CTV regions were registered with a reference CTV region with a median volume to remove the effect of the setup errors, and converted to a point distribution models. The systematic and random errors for translations of CTV regions were automatically evaluated by analyzing the movements of centroids of CTV regions. The random and systematic errors for shape variations of CTV regions were obtained from covariance matrices based on point distributions for the CTV contours on CBCT images of 72 fractions of 10 patients. Anisotropic PTV margins for 6 directions (right, left, anterior, posterior, superior and inferior) were derived by using Yoda’s PTV margin model. Results: PTV margins with and without shape variations were 5.75 to 8.03 mm and 5.23 to 7.67 mm for low-risk group, 5.87 to 8.33 mm and 5.23 to 7.67 mm for intermediate-risk group, and 5.88 to 8.25 mm and 5.29 to 7.82 mm for highrisk group, respectively. Conclusion: The proposed computational approach could be feasible for determination of the anisotropic PTV margins with taking into account CTV shape variations for the RTP.

60 APPLIED LIFE SCIENCES↗