TH-AB-BRA-01: A Novel Doubly-Focused Multileaf Collimator Design for MR-Guided Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, H; Mutic, S; Green, O

2016-06-15

Purpose: To describe the physical and dosimetric properties of a novel double-stack multileaf collimator (MLC). Methods: One of the compromises made in the MLC design has been to employ linear-motion singly-divergent shapes. Because the MLC leading edge moves linearly, it is rounded to provide a consistent, albeit compromised penumbra. The MLC employed in the new linac-based MR-IGRT unit is designed to be doubly focused in that each leaf moves in an arc centered at the source, and the sides of the leaves are machined such that they lie parallel to a line between the leaf edge and the source. Themore » curvature of the MLC keeps motors and encoders in lower magnetic field. However, high spatial-resolution leaves are difficult to manufacture to sufficiently tight tolerances and difficult to move due to restricted space on the gantry. Wider leaves alleviate this problem with less moving parts but the coarse resolution disallows treating very small lesions. This compromise has been overcome by splitting the MLC leaf bank into two sets, stacked one upon the other and offset half of a leaf width. The dosimetry has been simulated using Monte-Carlo and a 6 MV linac in a 0.35 T magnetic field. Results: The combined MLC leaf set has a spatial resolution of effectively half of the leaf width, 4mm here. The dosimetry resolution and conformality are consistent with 4mm wide MLC assisted by inverse fluence modulation. Also, because each leaf junction is backed up by the stacked leaf that lies over the junction, the problem of tongue-and-groove dosimetry has been greatly reduced. The novel MLC design allows the use of more powerful leaf motors than would be otherwise possible if a single MLC bank is employed. Conclusions: The stacked MLC will provide highly conformal dose distributions suitable for stereotactic radiation therapy of small lesions. The research was funded by ViewRay, Inc.« less

Progress and prospects for an FI relevant point design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Key, M; Amendt, P; Bellei, C

The physics issues involved in scaling from sub ignition to high gain fast ignition are discussed. Successful point designs must collimate the electrons and minimize the stand off distance to avoid multi mega-joule ignition energies. Collimating B field configurations are identified and some initial designs are explored.

SU-F-T-366: Dosimetric Parameters Enhancement of 120-Leaf Millennium MLC Using EGSnrc and IAEA Phase-Space Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haddad, K; Alopoor, H

Purpose: Recently, the multileaf collimators (MLC) have become an important part of any LINAC collimation systems because they reduce the treatment planning time and improves the conformity. Important factors that affects the MLCs collimation performance are leaves material composition and their thickness. In this study, we investigate the main dosimetric parameters of 120-leaf Millennium MLC including dose in the buildup point, physical penumbra as well as average and end leaf leakages. Effects of the leaves geometry and density on these parameters are evaluated Methods: From EGSnrc Monte Carlo code, BEAMnrc and DOSXYZnrc modules are used to evaluate the dosimetric parametersmore » of a water phantom exposed to a Varian xi for 100cm SSD. Using IAEA phasespace data just above MLC (Z=46cm) and BEAMnrc, for the modified 120-leaf Millennium MLC a new phase space data at Z=52cm is produces. The MLC is modified both in leaf thickness and material composition. EGSgui code generates 521ICRU library for tungsten alloys. DOSXYZnrc with the new phase space evaluates the dose distribution in a water phantom of 60×60×20 cm3 with voxel size of 4×4×2 mm3. Using DOSXYZnrc dose distributions for open beam and closed beam as well as the leakages definition, end leakage, average leakage and physical penumbra are evaluated. Results: A new MLC with improved dosimetric parameters is proposed. The physical penumbra for proposed MLC is 4.7mm compared to 5.16 mm for Millennium. Average leakage in our design is reduced to 1.16% compared to 1.73% for Millennium, the end leaf leakage suggested design is also reduced to 4.86% compared to 7.26% of Millennium. Conclusion: The results show that the proposed MLC with enhanced dosimetric parameters could improve the conformity of treatment planning.« less

Matching of electron beams for conformal therapy of target volumes at moderate depths.

PubMed

Zackrisson, B; Karlsson, M

1996-06-01

The basic requirements for conformal electron therapy are an accelerator with a wide range of energies and field shapes. The beams should be well characterised in a full 3-D dose planning system which has been verified for the geometries of the current application. Differences in the basic design of treatment units have been shown to have a large influence on beam quality and dosimetry. Modern equipment can deliver electron beams of good quality with a high degree of accuracy. A race-track microtron with minimised electron scattering and a multi-leaf collimator (MLC) for electron collimating will facilitate the isocentric technique as a general treatment technique for electrons. This will improve the possibility of performing combined electron field techniques in order to conform the dose distribution with no or minimal use of a bolus. Furthermore, the isocentric technique will facilitate multiple field arrangements that decrease the problems with distortion of the dose distribution due to inhomogeneities, etc. These situations are demonstrated by clinical examples where isocentric, matched electron fields for treatment of the nose, thyroid and thoracic wall have been used.

SU-E-T-515: Field-In-Field Compensation Technique Using Multi-Leaf Collimator to Deliver Total Body Irradiation (TBI) Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakeman, T; Wang, IZ; Roswell Park Cancer Institute, Buffalo, NY

Purpose: Total body irradiation (TBI) uses large parallel-opposed radiation fields to suppress the patient's immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has been used conventionally to compensate for the varying thickness through the entire body in large-field TBI. The goal of this study is to pursue utilizing the modern field-in-field (FIF) technique with the multi-leaf collimator (MLC) to more accurately and efficiently deliver dose to patients in need of TBI. Method: Treatment plans utilizing the FIF technique to deliver a total body dose were createdmore » retrospectively for patients for whom CT data had been previously acquired. Treatment fields include one pair of opposed open large fields (collimator=45°) with a specific weighting and a succession of smaller fields (collimator=90°) each with their own weighting. The smaller fields are shaped by moving MLC to block the sections of the patient which have already received close to 100% of the prescribed dose. The weighting factors for each of these fields were calculated using the attenuation coefficient of the initial lead compensators and the separation of the patient in different positions in the axial plane. Results: Dose-volume histograms (DVH) were calculated for evaluating the FIF compensation technique. The maximum body doses calculated from the DVH were reduced from the non-compensated 179.3% to 148.2% in the FIF plans, indicating a more uniform dose with the FIF compensation. All calculated monitor units were well within clinically acceptable limits and exceeded those of the original lead compensation plan by less than 50 MU (only ~1.1% increase). Conclusion: MLC FIF technique for TBI will not significantly increase the beam on time while it can substantially reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.« less

WE-AB-BRB-10: Filmless QA of CyberKnife MLC-Collimated and Iris-Collimated Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gersh, J; Spectrum Medical Physics, LLC, Greenville, SC

Purpose: Current methods of CK field shape QA is based on the use of radiochromic film. Though accurate results can be attained, these methods are prone to error, time consuming, and expensive. The techniques described herein perform similar QA using the FOIL Detector (Field, Output, and Image Localization). A key feature of this in-house QA solution, and central to this study, is an aSi flat-panel detector which provides the user with the means to perform accurate, immediate, and quantitative field analysis. Methods: The FOIL detector is automatically aligned in the CK beam using fiducial markers implanted within the detector case.more » Once the system is aligned, a treatment plan is delivered which irradiates the flat-panel imager using the field being tested. The current study tests each of the clinically-used fields shaped using the Iris variable-aperture collimation system using a plan which takes 6 minutes to deliver. The user is immediately provided with field diameter and beam profile, as well as a comparison to baseline values. Additionally, the detector is used to acquire and analyze leaf positions of the InCise multi-leaf collimation system. Results: Using a 6-minute plan consisting of 11 beams of 25MU-per-beam, the FOIL detector provided the user with a quantitative analysis of all clinically-used field shapes. The FOIL detector was also able to clearly resolve field edge junctions in a picket fence test, including slight over-travel of individual leaves as well as inter-leaf leakage. Conclusion: The FOIL system provided comparable field diameter and profile data when compared to methods using film; providing results much faster and with 5% of the MU used for film. When used with the MLC system, the FOIL detector provided the means for immediate quantification of the performance of the system through analysis of leaf positions in a picket fence test field. Author is the President/Owner of Spectrum Medical Physics, LLC, a company which maintains contracts with Siemens Healthcare and Standard Imaging, Inc.« less

Method for selecting minimum width of leaf in multileaf adjustable collimator while inhibiting passage of particle beams of radiation through sawtooth joints between collimator leaves

DOEpatents

Ludewigt, Bernhard; Bercovitz, John; Nyman, Mark; Chu, William

1995-01-01

A method is disclosed for selecting the minimum width of individual leaves of a multileaf adjustable collimator having sawtooth top and bottom surfaces between adjacent leaves of a first stack of leaves and sawtooth end edges which are capable of intermeshing with the corresponding sawtooth end edges of leaves in a second stack of leaves of the collimator. The minimum width of individual leaves in the collimator, each having a sawtooth configuration in the surface facing another leaf in the same stack and a sawtooth end edge, is selected to comprise the sum of the penetration depth or range of the particular type of radiation comprising the beam in the particular material used for forming the leaf; plus the total path length across all the air gaps in the area of the joint at the edges between two leaves defined between lines drawn across the peaks of adjacent sawtooth edges; plus at least one half of the length or period of a single sawtooth. To accomplish this, in accordance with the method of the invention, the penetration depth of the particular type of radiation in the particular material to be used for the collimator leaf is first measured. Then the distance or gap between adjoining or abutting leaves is selected, and the ratio of this distance to the height of the sawteeth is selected. Finally the number of air gaps through which the radiation will pass between sawteeth is determined by selecting the number of sawteeth to be formed in the joint. The measurement and/or selection of these parameters will permit one to determine the minimum width of the leaf which is required to prevent passage of the beam through the sawtooth joint.

SU-E-T-467: Implementation of Monte Carlo Dose Calculation for a Multileaf Collimator Equipped Robotic Radiotherapy System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, JS; Fan, J; Ma, C-M

Purpose: To improve the treatment efficiency and capabilities for full-body treatment, a robotic radiosurgery system has equipped with a multileaf collimator (MLC) to extend its accuracy and precision to radiation therapy. To model the MLC and include it in the Monte Carlo patient dose calculation is the goal of this work. Methods: The radiation source and the MLC were carefully modeled to consider the effects of the source size, collimator scattering, leaf transmission and leaf end shape. A source model was built based on the output factors, percentage depth dose curves and lateral dose profiles measured in a water phantom.more » MLC leaf shape, leaf end design and leaf tilt for minimizing the interleaf leakage and their effects on beam fluence and energy spectrum were all considered in the calculation. Transmission/leakage was added to the fluence based on the transmission factors of the leaf and the leaf end. The transmitted photon energy was tuned to consider the beam hardening effects. The calculated results with the Monte Carlo implementation was compared with measurements in homogeneous water phantom and inhomogeneous phantoms with slab lung or bone material for 4 square fields and 9 irregularly shaped fields. Results: The calculated output factors are compared with the measured ones and the difference is within 1% for different field sizes. The calculated dose distributions in the phantoms show good agreement with measurements using diode detector and films. The dose difference is within 2% inside the field and the distance to agreement is within 2mm in the penumbra region. The gamma passing rate is more than 95% with 2%/2mm criteria for all the test cases. Conclusion: Implementation of Monte Carlo dose calculation for a MLC equipped robotic radiosurgery system is completed successfully. The accuracy of Monte Carlo dose calculation with MLC is clinically acceptable. This work was supported by Accuray Inc.« less

Design of a fast multileaf collimator for radiobiological optimized IMRT with scanned beams of photons, electrons, and light ions.

PubMed

Svensson, Roger; Larsson, Susanne; Gudowska, Irena; Holmberg, Rickard; Brahme, Anders

2007-03-01

Intensity modulated radiation therapy is rapidly becoming the treatment of choice for most tumors with respect to minimizing damage to the normal tissues and maximizing tumor control. Today, intensity modulated beams are most commonly delivered using segmental multileaf collimation, although an increasing number of radiation therapy departments are employing dynamic multileaf collimation. The irradiation time using dynamic multileaf collimation depends strongly on the nature of the desired dose distribution, and it is difficult to reduce this time to less than the sum of the irradiation times for all individual peak heights using dynamic leaf collimation [Svensson et al., Phys. Med. Biol. 39, 37-61 (1994)]. Therefore, the intensity modulation will considerably increase the total treatment time. A more cost-effective procedure for rapid intensity modulation is using narrow scanned photon, electron, and light ion beams in combination with fast multileaf collimator penumbra trimming. With this approach, the irradiation time is largely independent of the complexity of the desired intensity distribution and, in the case of photon beams, may even be shorter than with uniform beams. The intensity modulation is achieved primarily by scanning of a narrow elementary photon pencil beam generated by directing a narrow well focused high energy electron beam onto a thin bremsstrahlung target. In the present study, the design of a fast low-weight multileaf collimator that is capable of further sharpening the penumbra at the edge of the elementary scanned beam has been simulated, in order to minimize the dose or radiation response of healthy tissues. In the case of photon beams, such a multileaf collimator can be placed relatively close to the bremsstrahlung target to minimize its size. It can also be flat and thin, i.e., only 15-25 mm thick in the direction of the beam with edges made of tungsten or preferably osmium to optimize the sharpening of the penumbra. The low height of the collimator will minimize edge scatter from glancing incidence. The major portions of the collimator leafs can then be made of steel or even aluminum, so that the total weight of the multileaf collimator will be as low as 10 kg, which may even allow high-speed collimation in real time in synchrony with organ movements. To demonstrate the efficiency of this collimator design in combination with pencil beam scanning, optimal radiobiological treatments of an advanced cervix cancer were simulated. Different geometrical collimator designs were tested for bremsstrahlung, electron, and light ion beams. With a 10 mm half-width elementary scanned photon beam and a steel collimator with tungsten edges, it was possible to make as effective treatments as obtained with intensity modulated beams of full resolution, i.e., here 5 mm resolution in the fluence map. In combination with narrow pencil beam scanning, such a collimator may provide ideal delivery of photons, electrons, or light ions for radiation therapy synchronized to breathing and other organ motions. These high-energy photon and light ion beams may allow three-dimensional in vivo verification of delivery and thereby clinical implementation of the BioArt approach using Biologically Optimized three-dimensional in vivo predictive Assay based adaptive Radiation Therapy [Brahme, Acta Oncol. 42, 123-126 (2003)].

Enhanced PET resolution by combining pinhole collimation and coincidence detection

NASA Astrophysics Data System (ADS)

DiFilippo, Frank P.

2015-10-01

Spatial resolution of clinical PET scanners is limited by detector design and photon non-colinearity. Although dedicated small animal PET scanners using specialized high-resolution detectors have been developed, enhancing the spatial resolution of clinical PET scanners is of interest as a more available alternative. Multi-pinhole 511 keV SPECT is capable of high spatial resolution but requires heavily shielded collimators to avoid significant background counts. A practical approach with clinical PET detectors is to combine multi-pinhole collimation with coincidence detection. In this new hybrid modality, there are three locations associated with each event, namely those of the two detected photons and the pinhole aperture. These three locations over-determine the line of response and provide redundant information that is superior to coincidence detection or pinhole collimation alone. Multi-pinhole collimation provides high resolution and avoids non-colinearity error but is subject to collimator penetration and artifacts from overlapping projections. However the coincidence information, though at lower resolution, is valuable for determining whether the photon passed near a pinhole within the cone acceptance angle and for identifying through which pinhole the photon passed. This information allows most photons penetrating through the collimator to be rejected and avoids overlapping projections. With much improved event rejection, a collimator with minimal shielding may be used, and a lightweight add-on collimator for high resolution imaging is feasible for use with a clinical PET scanner. Monte Carlo simulations were performed of a 18F hot rods phantom and a 54-pinhole unfocused whole-body mouse collimator with a clinical PET scanner. Based on coincidence information and pinhole geometry, events were accepted or rejected, and pinhole-specific crystal-map projections were generated. Tomographic images then were reconstructed using a conventional pinhole SPECT algorithm. Hot rods of 1.4 mm diameter were resolved easily in a simulated phantom. System sensitivity was 0.09% for a simulated 70-mm line source corresponding to the NEMA NU-4 mouse phantom. Higher resolution is expected with further optimization of pinhole design, and higher sensitivity is expected with a focused and denser pinhole configuration. The simulations demonstrate high spatial resolution and feasibility of small animal imaging with an add-on multi-pinhole collimator for a clinical PET scanner. Further work is needed to develop geometric calibration and quantitative data corrections and, eventually, to construct a prototype device and produce images with physical phantoms.

SU-E-T-347: Effect of MLC Leaf Position Inaccuracy On Dose Distribution for Spinal SBRT with Different Energies and Dose Rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

You, T; Dang, J; Dai, C

2015-06-15

Purpose: To evaluate dosimetric impact of spinal SBRT when MLC leaf positions deviate from planning positions for different energies and doserates. Methods and Materials: 18 localized spinal metastases patients were selected for SBRT using IMRT planning with 9 posterior beams delivered at gantry angles ranging between 100°–260°. A modern linear accelerator(Varian Turebeam STX with HDMLC 2.5 mm thick leaf at isocenter) IMRT plans were generated using both 6X and 6X-FFF(Flattening filter free) beams with a nominal prescription dose of 6 Gy/fraction to PTV. Doserates ranging from 200–600 MU/min for 6X and 400–1400 MU/min for 6X-FFF, with 200 increments were examined.more » A fixed amount(0.3, 0.5, 1, and 2 mm) of MLC-leaf position deviation was simulated to each plan under following conditions: 1)only along X1 collimator; 2)with increments at both X1 and X2 collimator directions;3)with reductions at both X1 and X2 collimator directions. Dose was recalculated for each modified plans. Both original and modified plans were delivered using Turebeam STX machine and measured using both portal dosimetry and a 3D dosimeter(Delta4 of ScandiDos). Each field’s Result were compared using following three parameters: the 95% iso-dose level Conformal Index(95%CI), the spinal cord maximum dose(SCDmax), and the planned target volume(PTV) mean dose. Results: Dosimetric impacts on the 95%CI, SCDmax and the PTV mean dose are: 1)negligible if MLC-leaf position deviation only along a single collimator direction ≥1.0 mm,2)substantial if MLC-leaf position increment along both collimator directions ≥0.3 mm(95% CI decreases while SCDmax and PTV mean-dose increase), 3)substantial if MLC-leaf position reduction along both collimator directions ≥0.3 mm(95% CI first increases and then decreases while SCDmax and PTV mean-dose decrease). Different energies and doserates demonstrated comparable dosimetric impacts. Conclusion: Substantial dose deviations could happen for spinal SBRT using IMRT plan with HD-MLC if leaf position deviation ≥0.3 mm. The effects of different energy and doserate are negligible.« less

TU-H-BRC-09: Validation of a Novel Therapeutic X-Ray Array Source and Collimation System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trovati, S; King, GJ; Loo, BW

2016-06-15

Purpose: We have experimentally characterized and simulated the dosimetric properties and spatial fidelity of a novel X-ray array source and collimation system called SPHINX that has the potential to generate complex intensity modulated X-ray beams by varying the electron beam intensity only, and without any moving parts like in multi-leaf collimators. Methods: We investigated the spatial fidelity and the X-ray performances of a SPHINX prototype in tungsten, using a Cyber Knife and the experimental high-energy electron beam line at XTA at SLAC National Laboratory. Dose distributions were recorded with gafchromic films, placed at the distal end of SPHINX and atmore » several depths in a solid water phantom. The geometry of SPHINX and of the experimental set-ups was also modeled in Monte Carlo (MC) simulations with the FLUKA code, used to reproduce the experimental results and, after validation, to predict and optimize the performance and design of the SPHINX. Results: The results indicate significant particle leakage through the channels during a single-channel irradiation for high incident energies, followed by a rapid decrease for energies of clinical interest. When the collimator channels are used as target, the photon production increases, however at expense of the beam size that is also enlarged. The illumination of all channels simultaneously shows a fairly even transmission of the beam. Conclusion: With the measurements we have verified the MC models and the uniformity of beam transmission through SPHINX, and we have evaluated the importance of particle leakage through adjacent channels. These results can be used to optimize SPHINX design through the validated MC simulations. Funding: Weston Havens Foundation, Office of the Dean of Medical School and Office of the Provost (Stanford University). Loo, Maxim, Borchard, Tantawi are co-founders of TibaRay Inc. Loo and Tantawi are TibaRay Inc. board members. Loo and Maxim received grants from Varian Medical Systems and RaySearch Laboratory.« less

Simultaneous delivery time and aperture shape optimization for the volumetric-modulated arc therapy (VMAT) treatment planning problem

NASA Astrophysics Data System (ADS)

Mahnam, Mehdi; Gendreau, Michel; Lahrichi, Nadia; Rousseau, Louis-Martin

2017-07-01

In this paper, we propose a novel heuristic algorithm for the volumetric-modulated arc therapy treatment planning problem, optimizing the trade-off between delivery time and treatment quality. We present a new mixed integer programming model in which the multi-leaf collimator leaf positions, gantry speed, and dose rate are determined simultaneously. Our heuristic is based on column generation; the aperture configuration is modeled in the columns and the dose distribution and time restriction in the rows. To reduce the number of voxels and increase the efficiency of the master model, we aggregate similar voxels using a clustering technique. The efficiency of the algorithm and the treatment quality are evaluated on a benchmark clinical prostate cancer case. The computational results show that a high-quality treatment is achievable using a four-thread CPU. Finally, we analyze the effects of the various parameters and two leaf-motion strategies.

Design of a Multi-Pinhole Collimator for I-123 DaTscan Imaging on Dual-Headed SPECT Systems in Combination with a Fan-Beam Collimator.

PubMed

King, Michael A; Mukherjee, Joyeeta M; Könik, Arda; Zubal, I George; Dey, Joyoni; Licho, Robert

2016-02-01

For the 2011 FDA approved Parkinson's Disease (PD) SPECT imaging agent I-123 labeled DaTscan, the volume of interest (VOI) is the interior portion of the brain. However imaging of the occipital lobe is also required with PD for calculation of the striatal binding ratio (SBR), a parameter of significance in early diagnosis, differentiation of PD from other disorders with similar clinical presentations, and monitoring progression. Thus we propose the usage of a combination of a multi-pinhole (MPH) collimator on one head of the SPECT system and a fan-beam on the other. The MPH would be designed to provide high resolution and sensitivity for imaging of the interior portion of the brain. The fan-beam collimator would provide lower resolution but complete sampling of the brain addressing data sufficiency and allowing a volume-of-interest to be defined over the occipital lobe for calculation of SBR's. Herein we focus on the design of the MPH component of the combined system. Combined reconstruction will be addressed in a subsequent publication. An analysis of 46 clinical DaTscan studies was performed to provide information to define the VOI, and design of a MPH collimator to image this VOI. The system spatial resolution for the MPH was set to 4.7 mm, which is comparable to that of clinical PET systems, and significantly smaller than that of fan-beam collimators employed in SPECT. With this set, we compared system sensitivities for three aperture array designs, and selected the 3 × 3 array due to it being the highest of the three. The combined sensitivity of the apertures for it was similar to that of an ultra-high resolution fan-beam (LEUHRF) collimator, but smaller than that of a high-resolution fan-beam collimator (LEHRF). On the basis of these results we propose the further exploration of this design through simulations, and the development of combined MPH and fan-beam reconstruction.

Development and validation of a BEAMnrc component module for a miniature multileaf collimator.

PubMed

Doerner, E; Hartmann, G H

2012-05-21

A new component module (CM) named mini multileaf collimator (mMLC) was developed for the Monte Carlo code BEAMnrc. It models the geometry of the add-on miniature multileaf collimator ModuLeaf (MRC Systems GmbH, Heidelberg, Germany, now part of Siemens, Erlangen, Germany). The new CM is partly based on the existing CM called DYNVMLC. The development was performed using a modified EGSnrc platform which enables us to work in the Microsoft Visual Studio environment. In order to validate the new CM, the PRIMUS linac with 6 MV x-rays (Siemens OCS, Concord, CA, USA) equipped with the ModuLeaf mMLC was modelled. Validation was performed by two methods: (a) a ray-tracing method to check the correct geometry of the multileaf collimator (MLC) and (b) a comparison of calculated and measured results of the following dosimetrical parameters: output factors, dose profiles, field edge position penumbra, MLC interleaf leakage and transmission values. Excellent agreement was found for all parameters. It was, in particular, found that the relationship between leaf position and field edge depending on the shape of the leaf ends can be investigated with a higher accuracy by this new CM than by measurements demonstrating the usefulness of the new CM.

Development and validation of a BEAMnrc component module for a miniature multileaf collimator

NASA Astrophysics Data System (ADS)

Doerner, E.; Hartmann, G. H.

2012-05-01

A new component module (CM) named mini multileaf collimator (mMLC) was developed for the Monte Carlo code BEAMnrc. It models the geometry of the add-on miniature multileaf collimator ModuLeaf (MRC Systems GmbH, Heidelberg, Germany, now part of Siemens, Erlangen, Germany). The new CM is partly based on the existing CM called DYNVMLC. The development was performed using a modified EGSnrc platform which enables us to work in the Microsoft Visual Studio environment. In order to validate the new CM, the PRIMUS linac with 6 MV x-rays (Siemens OCS, Concord, CA, USA) equipped with the ModuLeaf mMLC was modelled. Validation was performed by two methods: (a) a ray-tracing method to check the correct geometry of the multileaf collimator (MLC) and (b) a comparison of calculated and measured results of the following dosimetrical parameters: output factors, dose profiles, field edge position penumbra, MLC interleaf leakage and transmission values. Excellent agreement was found for all parameters. It was, in particular, found that the relationship between leaf position and field edge depending on the shape of the leaf ends can be investigated with a higher accuracy by this new CM than by measurements demonstrating the usefulness of the new CM.

Missouri University Multi-Plane Imager (MUMPI): A high sensitivity rapid dynamic ECT brain imager

DOE Office of Scientific and Technical Information (OSTI.GOV)

Logan, K.W.; Holmes, R.A.

1984-01-01

The authors have designed a unique ECT imaging device that can record rapid dynamic images of brain perfusion. The Missouri University Multi-Plane Imager (MUMPI) uses a single crystal detector that produces four orthogonal two-dimensional images simultaneously. Multiple slice images are reconstructed from counts recorded from stepwise or continuous collimator rotation. Four simultaneous 2-d image fields may also be recorded and reviewed. The cylindrical sodium iodide crystal and the rotating collimator concentrically surround the source volume being imaged with the collimator the only moving part. The design and function parameters of MUMPI have been compared to other competitive tomographic head imagingmore » devices. MUMPI's principal advantages are: 1) simultaneous direct acquisition of four two-dimensional images; 2) extremely rapid project set acquisition for ECT reconstruction; and 3) instrument practicality and economy due to single detector design and the absence of heavy mechanical moving components (only collimator rotation is required). MUMPI should be ideal for imaging neutral lipophilic chelates such as Tc-99m-PnAO which passively diffuses across the intact blood-brain-barrier and rapidly clears from brain tissue.« less

Analysis and design of fiber-coupled high-power laser diode array

NASA Astrophysics Data System (ADS)

Zhou, Chongxi; Liu, Yinhui; Xie, Weimin; Du, Chunlei

2003-11-01

A conclusion that a single conventional optical system could not realize fiber coupled high-power laser diode array is drawn based on the BPP of laser beam. According to the parameters of coupled fiber, a method to couple LDA beams into a single multi-mode fiber including beams collimating, shaping, focusing and coupling is present. The divergence angles after collimating are calculated and analyzed; the shape equation of the collimating micro-lenses array is deprived. The focusing lens is designed. A fiber coupled LDA result with the core diameter of 800 um and numeric aperture of 0.37 is gotten.

Collimation system design for beam loss localization with slipstacking injection in the Fermilab Main Injector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drozhdin, A.I.; Brown, B.C.; Johnson, D.E.

2007-06-01

Results of modeling with the 3-D STRUCT and MARS15 codes of beam loss localization and related radiation effects are presented for the slipstacking injection to the Fermilab Main Injector. Simulations of proton beam loss are done using multi-turn tracking with realistic accelerator apertures, nonlinear fields in the accelerator magnets and time function of the RF manipulations to explain the results of beam loss measurements. The collimation system consists of one primary and four secondary collimators. It intercepts a beam power of 1.6 kW at a scraping rate of 5% of 5.5E+13 ppp, with a beam loss rate in the ringmore » outside the collimation region of 1 W/m or less. Based on thorough energy deposition and radiation modeling, a corresponding collimator design was developed that satisfies all the radiation and engineering constraints.« less

Development, physical properties and clinical applicability of a mechanical Multileaf Collimator for the use in Cobalt-60 radiotherapy

NASA Astrophysics Data System (ADS)

Langhans, Marco; Echner, Gernot; Runz, Armin; Baumann, Martin; Xu, Mark; Ueltzhöffer, Stefan; Häring, Peter; Schlegel, Wolfgang

2015-04-01

According to the Directory of Radiotherapy Centres (DIRAC) there are 2348 Cobalt-60 (Co-60) teletherapy units worldwide, most of them in low and middle income countries, compared to 11046 clinical accelerators. To improve teletherapy with Co-60, a mechanical Multi-Leaf Collimator (MLC) was developed, working with pneumatic pressure and thus independent of electricity supply. Instead of tungsten, brass was used as leaf material to make the mechanical MLC more affordable. The physical properties and clinical applicability of this mechanical MLC are presented here. The leakage strongly depends on the fieldsize of the therapy unit due to scatter effects. The maximum transmission through the leaves measured 2.5 cm from the end-to-end gap, within a field size of 20 cm × 30 cm defined by jaws of the therapy unit at 80 cm SAD, amounts 4.2%, normalized to an open 10 cm × 10 cm field, created by the mechanical MLC. Within a precollimated field size of 12.5 cm × 12.5 cm, the end-to-end leakage is 6.5% normalized to an open 10 cm × 10 cm field as well. This characteristic is clinically acceptable considering the criteria for non-IMRT MLCs of the International Electrotechnical Commission (IEC 60601-2-1). The penumbra for a 10 cm × 10 cm field was measured to be 9.14 mm in plane and 8.38 mm cross plane. The clinical applicability of the designed mechanical MLC was affirmed by measurements relating to all relevant clinical properties such as penumbra, leakage, output factors and field widths. Hence this novel device presents an apt way forward to make radiotherapy with conformal fields possible in low-infrastructure environments, using gantry based Co-60 therapy units.

A new dual-collimation batch reactor for determination of ultraviolet inactivation rate constants for microorganisms in aqueous suspensions

PubMed Central

Martin, Stephen B.; Schauer, Elizabeth S.; Blum, David H.; Kremer, Paul A.; Bahnfleth, William P.; Freihaut, James D.

2017-01-01

We developed, characterized, and tested a new dual-collimation aqueous UV reactor to improve the accuracy and consistency of aqueous k-value determinations. This new system is unique because it collimates UV energy from a single lamp in two opposite directions. The design provides two distinct advantages over traditional single-collimation systems: 1) real-time UV dose (fluence) determination; and 2) simple actinometric determination of a reactor factor that relates measured irradiance levels to actual irradiance levels experienced by the microbial suspension. This reactor factor replaces three of the four typical correction factors required for single-collimation reactors. Using this dual-collimation reactor, Bacillus subtilis spores demonstrated inactivation following the classic multi-hit model with k = 0.1471 cm2/mJ (with 95% confidence bounds of 0.1426 to 0.1516). PMID:27498232

SU-E-T-214: Intensity Modulated Proton Therapy (IMPT) Based On Passively Scattered Protons and Multi-Leaf Collimation: Prototype TPS and Dosimetry Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez-Parcerisa, D; Carabe-Fernandez, A

2014-06-01

Purpose. Intensity-modulated proton therapy is usually implemented with multi-field optimization of pencil-beam scanning (PBS) proton fields. However, at the view of the experience with photon-IMRT, proton facilities equipped with double-scattering (DS) delivery and multi-leaf collimation (MLC) could produce highly conformal dose distributions (and possibly eliminate the need for patient-specific compensators) with a clever use of their MLC field shaping, provided that an optimal inverse TPS is developed. Methods. A prototype TPS was developed in MATLAB. The dose calculation process was based on a fluence-dose algorithm on an adaptive divergent grid. A database of dose kernels was precalculated in order tomore » allow for fast variations of the field range and modulation during optimization. The inverse planning process was based on the adaptive simulated annealing approach, with direct aperture optimization of the MLC leaves. A dosimetry study was performed on a phantom formed by three concentrical semicylinders separated by 5 mm, of which the inner-most and outer-most were regarded as organs at risk (OARs), and the middle one as the PTV. We chose a concave target (which is not treatable with conventional DS fields) to show the potential of our technique. The optimizer was configured to minimize the mean dose to the OARs while keeping a good coverage of the target. Results. The plan produced by the prototype TPS achieved a conformity index of 1.34, with the mean doses to the OARs below 78% of the prescribed dose. This Result is hardly achievable with traditional conformal DS technique with compensators, and it compares to what can be obtained with PBS. Conclusion. It is certainly feasible to produce IMPT fields with MLC passive scattering fields. With a fully developed treatment planning system, the produced plans can be superior to traditional DS plans in terms of plan conformity and dose to organs at risk.« less

Characterization of a commercial multileaf collimator used for intensity modulated radiation therapy.

PubMed

Low, D A; Sohn, J W; Klein, E E; Markman, J; Mutic, S; Dempsey, J F

2001-05-01

The characteristics of a commercial multileaf collimator (MLC) to deliver static and dynamic multileaf collimation (SMLC and DMLC, respectively) were investigated to determine their influence on intensity modulated radiation therapy (IMRT) treatment planning and quality assurance. The influence of MLC leaf positioning accuracy on sequentially abutted SMLC fields was measured by creating abutting fields with selected gaps and overlaps. These data were also used to measure static leaf positioning precision. The characteristics of high leaf-velocity DMLC delivery were measured with constant velocity leaf sequences starting with an open field and closing a single leaf bank. A range of 1-72 monitor units (MU) was used providing a range of leaf velocities. The field abutment measurements yielded dose errors (as a percentage of the open field max dose) of 16.7+/-0.7% mm(-1) and 12.8+/-0.7% mm(-1) for 6 MV and 18 MV photon beams, respectively. The MLC leaf positioning precision was 0.080+/-0.018 mm (single standard deviation) highlighting the excellent delivery hardware tolerances for the tested beam delivery geometry. The high leaf-velocity DMLC measurements showed delivery artifacts when the leaf sequence and selected monitor units caused the linear accelerator to move the leaves at their maximum velocity while modulating the accelerator dose rate to deliver the desired leaf and MU sequence (termed leaf-velocity limited delivery). According to the vendor, a unique feature to their linear accelerator and MLC is that the dose rate is reduced to provide the correct cm MU(-1) leaf velocity when the delivery is leaf-velocity limited. However, it was found that the system delivered roughly 1 MU per pulse when the delivery was leaf-velocity limited causing dose profiles to exhibit discrete steps rather than a smooth dose gradient. The root mean square difference between the steps and desired linear gradient was less than 3% when more than 4 MU were used. The average dose per MU was greater and less than desired for closing and opening leaf patterns, respectively, when the delivery was leaf-velocity limited. The results indicated that the dose delivery artifacts should be minor for most clinical cases, but limit the assumption of dose linearity when significantly reducing the delivered dose for dosimeter characterization studies or QA measurements.

System geometry optimization for molecular breast tomosynthesis with focusing multi-pinhole collimators

NASA Astrophysics Data System (ADS)

van Roosmalen, Jarno; Beekman, Freek J.; Goorden, Marlies C.

2018-01-01

Imaging of 99mTc-labelled tracers is gaining popularity for detecting breast tumours. Recently, we proposed a novel design for molecular breast tomosynthesis (MBT) based on two sliding focusing multi-pinhole collimators that scan a modestly compressed breast. Simulation studies indicate that MBT has the potential to improve the tumour-to-background contrast-to-noise ratio significantly over state-of-the-art planar molecular breast imaging. The aim of the present paper is to optimize the collimator-detector geometry of MBT. Using analytical models, we first optimized sensitivity at different fixed system resolutions (ranging from 5 to 12 mm) by tuning the pinhole diameters and the distance between breast and detector for a whole series of automatically generated multi-pinhole designs. We evaluated both MBT with a conventional continuous crystal detector with 3.2 mm intrinsic resolution and with a pixelated detector with 1.6 mm pixels. Subsequently, full system simulations of a breast phantom containing several lesions were performed for the optimized geometry at each system resolution for both types of detector. From these simulations, we found that tumour-to-background contrast-to-noise ratio was highest for systems in the 7 mm-10 mm system resolution range over which it hardly varied. No significant differences between the two detector types were found.

Synchronized moving aperture radiation therapy (SMART): superimposing tumor motion on IMRT MLC leaf sequences under realistic delivery conditions

NASA Astrophysics Data System (ADS)

Xu, Jun; Papanikolaou, Nikos; Shi, Chengyu; Jiang, Steve B.

2009-08-01

Synchronized moving aperture radiation therapy (SMART) has been proposed to account for tumor motions during radiotherapy in prior work. The basic idea of SMART is to synchronize the moving radiation beam aperture formed by a dynamic multileaf collimator (DMLC) with the tumor motion induced by respiration. In this paper, a two-dimensional (2D) superimposing leaf sequencing method is presented for SMART. A leaf sequence optimization strategy was generated to assure the SMART delivery under realistic delivery conditions. The study of delivery performance using the Varian LINAC and the Millennium DMLC showed that clinical factors such as collimator angle, dose rate, initial phase and machine tolerance affect the delivery accuracy and efficiency. An in-house leaf sequencing software was developed to implement the 2D superimposing leaf sequencing method and optimize the motion-corrected leaf sequence under realistic clinical conditions. The analysis of dynamic log (Dynalog) files showed that optimization of the leaf sequence for various clinical factors can avoid beam hold-offs which break the synchronization of SMART and fail the SMART dose delivery. Through comparison between the simulated delivered fluence map and the planed fluence map, it was shown that the motion-corrected leaf sequence can greatly reduce the dose error.

Synchronized moving aperture radiation therapy (SMART): superimposing tumor motion on IMRT MLC leaf sequences under realistic delivery conditions.

PubMed

Xu, Jun; Papanikolaou, Nikos; Shi, Chengyu; Jiang, Steve B

2009-08-21

Synchronized moving aperture radiation therapy (SMART) has been proposed to account for tumor motions during radiotherapy in prior work. The basic idea of SMART is to synchronize the moving radiation beam aperture formed by a dynamic multileaf collimator (DMLC) with the tumor motion induced by respiration. In this paper, a two-dimensional (2D) superimposing leaf sequencing method is presented for SMART. A leaf sequence optimization strategy was generated to assure the SMART delivery under realistic delivery conditions. The study of delivery performance using the Varian LINAC and the Millennium DMLC showed that clinical factors such as collimator angle, dose rate, initial phase and machine tolerance affect the delivery accuracy and efficiency. An in-house leaf sequencing software was developed to implement the 2D superimposing leaf sequencing method and optimize the motion-corrected leaf sequence under realistic clinical conditions. The analysis of dynamic log (Dynalog) files showed that optimization of the leaf sequence for various clinical factors can avoid beam hold-offs which break the synchronization of SMART and fail the SMART dose delivery. Through comparison between the simulated delivered fluence map and the planed fluence map, it was shown that the motion-corrected leaf sequence can greatly reduce the dose error.

SU-G-JeP1-12: Head-To-Head Performance Characterization of Two Multileaf Collimator Tracking Algorithms for Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caillet, V; Colvill, E; Royal North Shore Hospital, St Leonards, Sydney

2016-06-15

Purpose: Multi-leaf collimator (MLC) tracking is being clinically pioneered to continuously compensate for thoracic and abdominal motion during radiotherapy. The purpose of this work is to characterize the performance of two MLC tracking algorithms for cancer radiotherapy, based on a direct optimization and a piecewise leaf fitting approach respectively. Methods: To test the algorithms, both physical and in silico experiments were performed. Previously published high and low modulation VMAT plans for lung and prostate cancer cases were used along with eight patient-measured organ-specific trajectories. For both MLC tracking algorithm, the plans were run with their corresponding patient trajectories. The physicalmore » experiments were performed on a Trilogy Varian linac and a programmable phantom (HexaMotion platform). For each MLC tracking algorithm, plan and patient trajectory, the tracking accuracy was quantified as the difference in aperture area between ideal and fitted MLC. To compare algorithms, the average cumulative tracking error area for each experiment was calculated. The two-sample Kolmogorov-Smirnov (KS) test was used to evaluate the cumulative tracking errors between algorithms. Results: Comparison of tracking errors for the physical and in silico experiments showed minor differences between the two algorithms. The KS D-statistics for the physical experiments were below 0.05 denoting no significant differences between the two distributions pattern and the average error area (direct optimization/piecewise leaf-fitting) were comparable (66.64 cm2/65.65 cm2). For the in silico experiments, the KS D-statistics were below 0.05 and the average errors area were also equivalent (49.38 cm2/48.98 cm2). Conclusion: The comparison between the two leaf fittings algorithms demonstrated no significant differences in tracking errors, neither in a clinically realistic environment nor in silico. The similarities in the two independent algorithms give confidence in the use of either algorithm for clinical implementation.« less

Assessment of human exposure doses received by activation of medical linear accelerator components

NASA Astrophysics Data System (ADS)

Lee, D.-Y.; Kim, J.-H.; Park, E.-T.

2017-08-01

This study analyzes the radiation exposure dose that an operator can receive from radioactive components during maintenance or repair of a linear accelerator. This study further aims to evaluate radiological safety. Simulations are performed on 10 MV and 15 MV photon beams, which are the most frequently used high-energy beams in clinics. The simulation analyzes components in order of activity and the human exposure dose based on the amount of neutrons received. As a result, the neutron dose, radiation dose, and human exposure dose are ranked in order of target, primary collimator, flattening filter, multi-leaf collimator, and secondary collimator, where the minimum dose is 9.34E-07 mSv/h and the maximum is 1.71E-02 mSv/h. When applying the general dose limit (radiation worker 20 mSv/year, pubic 1 mSv/year) in accordance with the Nuclear Safety Act, all components of a linear accelerator are evaluated as below the threshold value. Therefore, the results suggest that there is no serious safety issue for operators in maintaining and repairing a linear accelerator. Nevertheless, if an operator recognizes an exposure from the components of a linear accelerator during operation and considers the operating time and shielding against external exposure, exposure of the operator is expected to be minimized.

Poster — Thur Eve — 19: Performance assessment of a 160-leaf beam collimation system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, E. S. M.; La Russa, D. J.; Vandervoort, E.

2014-08-15

In this study, the performance of the new beam collimation system with 160 leaves, each with a 5 mm leaf width projected at isocenter, is evaluated in terms of positional accuracy and plan/delivery quality. Positional accuracy was evaluated using a set of static and dynamic MLC/jaw delivery patterns at different gantry angles, dose rates, and MLC/jaw speeds. The impact on IMRT plan quality was assessed by comparing against a previous generation collimation system using the same optimization parameters, while delivery quality was quantified using a combination of patient-specific QA measurements with ion chambers, film, and a bi-planar diode array. Positionalmore » accuracy for four separate units was comparable. The field size accuracy, junction width, and total displacement over 16 cm leaf travel are 0.3 ± 0.2 mm, 0.4 ± 0.3 mm, and 0.5 ± 0.2 mm, respectively. The typical leaf minor offset is 0.05 ± 0.04 mm, and MLC hysteresis effects are 0.2 ± 0.1 mm over 16 cm travel. The dynamic output is linear with MU and MLC/jaw speed, and is within 0.7 ± 0.3 % of the planning system value. Plan quality is significantly improved both in terms of target coverage and OAR sparing due, in part, to the larger allowable MLC and jaw speeds. γ-index pass rates for the patient-specific QA measurements exceeded 97% using criteria of 2%/2 mm. In conclusion, the performance of the Agility system is consistent among four separate installations, and is superior to its previous generations of collimation systems.« less

Markerless EPID image guided dynamic multi-leaf collimator tracking for lung tumors

NASA Astrophysics Data System (ADS)

Rottmann, J.; Keall, P.; Berbeco, R.

2013-06-01

Compensation of target motion during the delivery of radiotherapy has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. We implement an online image guided therapy system based on soft tissue localization (STiL) of the target from electronic portal images and treatment aperture adaptation with a dynamic multi-leaf collimator (DMLC). The treatment aperture is moved synchronously and in real time with the tumor during the entire breathing cycle. The system is implemented and tested on a Varian TX clinical linear accelerator featuring an AS-1000 electronic portal imaging device (EPID) acquiring images at a frame rate of 12.86 Hz throughout the treatment. A position update cycle for the treatment aperture consists of four steps: in the first step at time t = t0 a frame is grabbed, in the second step the frame is processed with the STiL algorithm to get the tumor position at t = t0, in a third step the tumor position at t = ti + δt is predicted to overcome system latencies and in the fourth step, the DMLC control software calculates the required leaf motions and applies them at time t = ti + δt. The prediction model is trained before the start of the treatment with data representing the tumor motion. We analyze the system latency with a dynamic chest phantom (4D motion phantom, Washington University). We estimate the average planar position deviation between target and treatment aperture in a clinical setting by driving the phantom with several lung tumor trajectories (recorded from fiducial tracking during radiotherapy delivery to the lung). DMLC tracking for lung stereotactic body radiation therapy without fiducial markers was successfully demonstrated. The inherent system latency is found to be δt = (230 ± 11) ms for a MV portal image acquisition frame rate of 12.86 Hz. The root mean square deviation between tumor and aperture position is smaller than 1 mm. We demonstrate the feasibility of real-time markerless DMLC tracking with a standard LINAC-mounted (EPID).

Beam feasibility study of a collimator with in-jaw beam position monitors

NASA Astrophysics Data System (ADS)

Wollmann, Daniel; Nosych, Andriy A.; Valentino, Gianluca; Aberle, Oliver; Aßmann, Ralph W.; Bertarelli, Alessandro; Boccard, Christian; Bruce, Roderik; Burkart, Florian; Calvo, Eva; Cauchi, Marija; Dallocchio, Alessandro; Deboy, Daniel; Gasior, Marek; Jones, Rhodri; Kain, Verena; Lari, Luisella; Redaelli, Stefano; Rossi, Adriana

2014-12-01

At present, the beam-based alignment of the LHC collimators is performed by touching the beam halo with both jaws of each collimator. This method requires dedicated fills at low intensities that are done infrequently and makes this procedure time consuming. This limits the operational flexibility, in particular in the case of changes of optics and orbit configuration in the experimental regions. The performance of the LHC collimation system relies on the machine reproducibility and regular loss maps to validate the settings of the collimator jaws. To overcome these limitations and to allow a continuous monitoring of the beam position at the collimators, a design with jaw-integrated Beam Position Monitors (BPMs) was proposed and successfully tested with a prototype (mock-up) collimator in the CERN SPS. Extensive beam experiments allowed to determine the achievable accuracy of the jaw alignment for single and multi-turn operation. In this paper, the results of these experiments are discussed. The non-linear response of the BPMs is compared to the predictions from electromagnetic simulations. Finally, the measured alignment accuracy is compared to the one achieved with the present collimators in the LHC.

SU-E-T-312: Dosimetric Consideration for the Agility MLC When Planning Rotational SRT/SBRT Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kong, X; Harris, J; Spitznagel, D

2015-06-15

Purpose: To analyze the radiation transmission of the Agility MLC and make recommendation based on the MLC dosimetric characteristics for SRT, SBRT and VMAT planning Method and Materials: Agility MLC is the newest model from Elekta and has no back up diaphragm behind leaves for this generation. Leaves are single focused with rounded end; composed of leafs each 0.5cm wide, 9cm thick, constructed from tungsten alloy and provide low transmission <0.5%. Total radiation transmission from leaves and diaphragm is <0.13%. A 360degree arc was generated using iCom tools; leaves were programmed closed while keeping the diaphragm fully open to maximizemore » the MLC transmission effect. Gafchromic EBT films were sandwiched between 4cm of solid water and situated at midplane to take dose measurement. 5000MU was delivered using 6MV VersaHD, various collimator angles, and a 5cm central axis offset was tested also. Films were scanned with Epson 10000XL scanner and analyzed using DoseLab Pro. Results: Due to the rounded leaf end and nature of rotation therapy, dose accumulation through the leaf gap is significant. By offsetting the leaf gap from central axis, this accumulation can be greatly reduced. There are dark bands showing accumulation of interleaf transmission which is improved by increasing collimator angle from 0 to 45dgree. However for 45 degree, in most cases, there are larger volumes sweeping under MLC alone, which needs considered planning. Conclusions: While inter-leaf leakage is minimized by using collimator angles greater than 0 degrees, the location of the leaf gap must also be managed. The leaf gap position becomes critically important when the treatment area is off axis such is the case when more than one PTV is being treated. With VMAT for SRT, SBRT becoming a more popular planning technique, special attention needs to be paid when initially setting up the field geometry.« less

A flexible Monte Carlo tool for patient or phantom specific calculations: comparison with preliminary validation measurements

NASA Astrophysics Data System (ADS)

Davidson, S.; Cui, J.; Followill, D.; Ibbott, G.; Deasy, J.

2008-02-01

The Dose Planning Method (DPM) is one of several 'fast' Monte Carlo (MC) computer codes designed to produce an accurate dose calculation for advanced clinical applications. We have developed a flexible machine modeling process and validation tests for open-field and IMRT calculations. To complement the DPM code, a practical and versatile source model has been developed, whose parameters are derived from a standard set of planning system commissioning measurements. The primary photon spectrum and the spectrum resulting from the flattening filter are modeled by a Fatigue function, cut-off by a multiplying Fermi function, which effectively regularizes the difficult energy spectrum determination process. Commonly-used functions are applied to represent the off-axis softening, increasing primary fluence with increasing angle ('the horn effect'), and electron contamination. The patient dependent aspect of the MC dose calculation utilizes the multi-leaf collimator (MLC) leaf sequence file exported from the treatment planning system DICOM output, coupled with the source model, to derive the particle transport. This model has been commissioned for Varian 2100C 6 MV and 18 MV photon beams using percent depth dose, dose profiles, and output factors. A 3-D conformal plan and an IMRT plan delivered to an anthropomorphic thorax phantom were used to benchmark the model. The calculated results were compared to Pinnacle v7.6c results and measurements made using radiochromic film and thermoluminescent detectors (TLD).

Experimental Comparison of Knife-Edge and Multi-Parallel Slit Collimators for Prompt Gamma Imaging of Proton Pencil Beams.

PubMed

Smeets, Julien; Roellinghoff, Frauke; Janssens, Guillaume; Perali, Irene; Celani, Andrea; Fiorini, Carlo; Freud, Nicolas; Testa, Etienne; Prieels, Damien

2016-01-01

More and more camera concepts are being investigated to try and seize the opportunity of instantaneous range verification of proton therapy treatments offered by prompt gammas emitted along the proton tracks. Focusing on one-dimensional imaging with a passive collimator, the present study experimentally compared in combination with the first, clinically compatible, dedicated camera device the performances of instances of the two main options: a knife-edge slit (KES) and a multi-parallel slit (MPS) design. These two options were experimentally assessed in this specific context as they were previously demonstrated through analytical and numerical studies to allow similar performances in terms of Bragg peak retrieval precision and spatial resolution in a general context. Both collimators were prototyped according to the conclusions of Monte Carlo optimization studies under constraints of equal weight (40 mm tungsten alloy equivalent thickness) and of the specificities of the camera device under consideration (in particular 4 mm segmentation along beam axis and no time-of-flight discrimination, both of which less favorable to the MPS performance than to the KES one). Acquisitions of proton pencil beams of 100, 160, and 230 MeV in a PMMA target revealed that, in order to reach a given level of statistical precision on Bragg peak depth retrieval, the KES collimator requires only half the dose the present MPS collimator needs, making the KES collimator a preferred option for a compact camera device aimed at imaging only the Bragg peak position. On the other hand, the present MPS collimator proves more effective at retrieving the entrance of the beam in the target in the context of an extended camera device aimed at imaging the whole proton track within the patient.

Electron intensity modulation for mixed-beam radiation therapy with an x-ray multi-leaf collimator

NASA Astrophysics Data System (ADS)

Weinberg, Rebecca

The current standard treatment for head and neck cancer at our institution uses intensity-modulated x-ray therapy (IMRT), which improves target coverage and sparing of critical structures by delivering complex fluence patterns from a variety of beam directions to conform dose distributions to the shape of the target volume. The standard treatment for breast patients is field-in-field forward-planned IMRT, with initial tangential fields and additional reduced-weight tangents with blocking to minimize hot spots. For these treatment sites, the addition of electrons has the potential of improving target coverage and sparing of critical structures due to rapid dose falloff with depth and reduced exit dose. In this work, the use of mixed-beam therapy (MBT), i.e., combined intensity-modulated electron and x-ray beams using the x-ray multi-leaf collimator (MLC), was explored. The hypothesis of this study was that addition of intensity-modulated electron beams to existing clinical IMRT plans would produce MBT plans that were superior to the original IMRT plans for at least 50% of selected head and neck and 50% of breast cases. Dose calculations for electron beams collimated by the MLC were performed with Monte Carlo methods. An automation system was created to facilitate communication between the dose calculation engine and the treatment planning system. Energy and intensity modulation of the electron beams was accomplished by dividing the electron beams into 2x2-cm2 beamlets, which were then beam-weight optimized along with intensity-modulated x-ray beams. Treatment plans were optimized to obtain equivalent target dose coverage, and then compared with the original treatment plans. MBT treatment plans were evaluated by participating physicians with respect to target coverage, normal structure dose, and overall plan quality in comparison with original clinical plans. The physician evaluations did not support the hypothesis for either site, with MBT selected as superior in 1 out of the 15 head and neck cases (p=1) and 6 out of 18 breast cases (p=0.95). While MBT was not shown to be superior to IMRT, reductions were observed in doses to critical structures distal to the target along the electron beam direction and to non-target tissues, at the expense of target coverage and dose homogeneity.

The Process of Developing a Multi-Cell KEMS Instrument

NASA Technical Reports Server (NTRS)

Copland, E. H.; Auping, J. V.; Jacobson, N. S.

2012-01-01

Multi-cell KEMS offers many advantages over single cell instruments in regard to in-situ temperature calibration and studies on high temperature alloys and oxides of interest to NASA. The instrument at NASA Glenn is a 90 deg magnetic sector instrument originally designed for single cell operation. The conversion of this instrument to a multi-cell instrument with restricted collimation is discussed. For restricted collimation, the 'field aperture' is in the copper plate separating the Knudsen Cell region and the ionizer and the 'source aperture' is adjacent to the ionizer box. A computer controlled x-y table allows positioning of one of the three cells into the sampling region. Heating is accomplished via a Ta sheet element and temperature is measured via an automatic pyrometer from the bottom of the cells. The computer control and data system have been custom developed for this instrument and are discussed. Future improvements are also discussed.

A comparison of two prompt gamma imaging techniques with collimator-based cameras for range verification in proton therapy

NASA Astrophysics Data System (ADS)

Lin, Hsin-Hon; Chang, Hao-Ting; Chao, Tsi-Chian; Chuang, Keh-Shih

2017-08-01

In vivo range verification plays an important role in proton therapy to fully utilize the benefits of the Bragg peak (BP) for delivering high radiation dose to tumor, while sparing the normal tissue. For accurately locating the position of BP, camera equipped with collimators (multi-slit and knife-edge collimator) to image prompt gamma (PG) emitted along the proton tracks in the patient have been proposed for range verification. The aim of the work is to compare the performance of multi-slit collimator and knife-edge collimator for non-invasive proton beam range verification. PG imaging was simulated by a validated GATE/GEANT4 Monte Carlo code to model the spot-scanning proton therapy and cylindrical PMMA phantom in detail. For each spot, 108 protons were simulated. To investigate the correlation between the acquired PG profile and the proton range, the falloff regions of PG profiles were fitted with a 3-line-segment curve function as the range estimate. Factors including the energy window setting, proton energy, phantom size, and phantom shift that may influence the accuracy of detecting range were studied. Results indicated that both collimator systems achieve reasonable accuracy and good response to the phantom shift. The accuracy of range predicted by multi-slit collimator system is less affected by the proton energy, while knife-edge collimator system can achieve higher detection efficiency that lead to a smaller deviation in predicting range. We conclude that both collimator systems have potentials for accurately range monitoring in proton therapy. It is noted that neutron contamination has a marked impact on range prediction of the two systems, especially in multi-slit system. Therefore, a neutron reduction technique for improving the accuracy of range verification of proton therapy is needed.

Maximizing the potential of direct aperture optimization through collimator rotation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milette, Marie-Pierre; Otto, Karl; Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia

Intensity-modulated radiation therapy (IMRT) treatment plans are conventionally produced by the optimization of fluence maps followed by a leaf sequencing step. An alternative to fluence based inverse planning is to optimize directly the leaf positions and field weights of multileaf collimator (MLC) apertures. This approach is typically referred to as direct aperture optimization (DAO). It has been shown that equivalent dose distributions may be generated that have substantially fewer monitor units (MU) and number of apertures compared to fluence based optimization techniques. Here we introduce a DAO technique with rotated apertures that we call rotating aperture optimization (RAO). The advantagesmore » of collimator rotation in IMRT have been shown previously and include higher fluence spatial resolution, increased flexibility in the generation of aperture shapes and less interleaf effects. We have tested our RAO algorithm on a complex C-shaped target, seven nasopharynx cancer recurrences, and one multitarget nasopharynx carcinoma patient. A study was performed in order to assess the capabilities of RAO as compared to fixed collimator angle DAO. The accuracy of fixed and rotated collimator aperture delivery was also verified. An analysis of the optimized treatment plans indicates that plans generated with RAO are as good as or better than DAO while maintaining a smaller number of apertures and MU than fluence based IMRT. Delivery verification results show that RAO is less sensitive to tongue and groove effects than DAO. Delivery time is currently increased due to the collimator rotation speed although this is a mechanical limitation that can be eliminated in the future.« less

SU-E-T-178: Clinical Feasibility of Multi-Leaf Collimator Based Dynamic Wedge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, C; Kwak, J; Ahn, S

2015-06-15

Purpose: A multi-leaf collimator (MLC) based dynamic wedge (MDW), which provide similar dose profile of physical wedge (PW) along x-jaw direction while significant monitor unit (MU) reduction, was developed and investigated for clinical use. Methods: A novel technique was used to create the wedge profile using MLC. A modification was applied to the DICOM-RT format file of the plan made with the PW to replace PW with MDW. The Varian enhanced dynamic wedge profile was used to produce MLC sequence, while the MU of the wedged field was recalculated using PW factor and fluence map. The profiles for all possiblemore » MDWs to substitute PWs were verified in 6/15 MV x-ray irradiations. New plans with MDWs were compared with the original plans in 5 rectal, 5 RT breast and 5 liver cases. Results: The wedge profile of the MDW fields were well matched with those of PWs inside the fields while less scatter than PW out of the fields. For plan comparisons of the clinical cases no significant dose discrepancy was observed between MDW plan and PW’s with the dose volume histograms. The maximum and mean doses in PTVs are agreed within 1.0%. The Result of OARs of MDW plans are slightly improved in the maximum doses (3.22 ∼ 150.4 cGy) and the mean doses (17.18 ∼ 85.52 cGy) on average for all cases while the prescribed doses are 45 Gy for rectal cases, 40 or 45 Gy for liver cases and 50 Gy for breast cases. The MUs of the fields which replace PW with MDW are reduced to 68% of those of PW. Conclusion: We developed a novel dynamic wedge technique with MLC that shows clinical advantage compared to PW.« less

SU-F-T-540: Comprehensive Fluence Delivery Optimization with Multileaf Collimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weppler, S; Villarreal-Barajas, J; Department of Medical Physics, Tom Baker Cancer Center, Calgary, Alberta

2016-06-15

Purpose: Multileaf collimator (MLC) leaf sequencing is performed via commercial black-box implementations, on which a user has limited to no access. We have developed an explicit, generic MLC sequencing model to serve as a tool for future investigations of fluence map optimization, fluence delivery optimization, and rotational collimator delivery methods. Methods: We have developed a novel, comprehensive model to effectively account for a variety of transmission and penumbra effects previously treated on an ad hoc basis in the literature. As the model is capable of quantifying a variety of effects, we utilize the asymmetric leakage intensity across each leaf tomore » deliver fluence maps with pixel size smaller than the narrowest leaf width. Developed using linear programming and mixed integer programming formulations, the model is implemented using state of the art open-source solvers. To demonstrate the versatility of the algorithm, a graphical user interface (GUI) was developed in MATLAB capable of accepting custom leaf specifications and transmission parameters. As a preliminary proof-ofconcept, we have sequenced the leaves of a Varian 120 Leaf Millennium MLC for five prostate cancer patient fields and one head and neck field. Predetermined fluence maps have been processed by data smoothing methods to obtain pixel sizes of 2.5 cm{sup 2}. The quality of output was analyzed using computer simulations. Results: For the prostate fields, an average root mean squared error (RMSE) of 0.82 and gamma (0.5mm/0.5%) of 91.4% were observed compared to RMSE and gamma (0.5mm/0.5%) values of 7.04 and 34.0% when the leakage considerations were omitted. Similar results were observed for the head and neck case. Conclusion: A model to sequence MLC leaves to optimality has been proposed. Future work will involve extensive testing and evaluation of the method on clinical MLCs and comparison with black-box leaf sequencing algorithms currently used by commercial treatment planning systems.« less

Design and evaluation of two multi-pinhole collimators for brain SPECT.

PubMed

Chen, Ling; Tsui, Benjamin M W; Mok, Greta S P

2017-10-01

SPECT is a powerful tool for diagnosing or staging brain diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) but is limited by its inferior resolution and sensitivity. At the same time, pinhole SPECT provides superior resolution and detection efficiency trade-off as compared to the conventional parallel-hole collimator for imaging small field-of-view (FOV), which fits for the case of brain imaging. In this study, we propose to develop and evaluate two multi-pinhole (MPH) collimator designs to improve the imaging of cerebral blood flow and striatum. We set the target resolutions to be 12 and 8 mm, respectively, and the FOV at 200 mm which is large enough to cover the whole brain. The constraints for system optimization include maximum and minimum detector-to-center-of-FOV (CFOV) distances of 344 and 294 mm, respectively, and minimal radius-of-rotation (ROR) of 135 mm to accommodate patients' shoulder. According to the targeted FOV, resolutions, and constraints, we determined the pinhole number, ROR, focal length, aperture acceptance angle, and aperture diameter which maximized the system sensitivity. We then assessed the imaging performance of the proposed MPH and standard low-energy high-resolution (LEHR) collimators using analytical simulations of a digital NCAT brain phantom with 99m Tc-HMPAO/ 99m Tc-TRODAT-1 distributions; Monte Carlo simulations of a hot-rod phantom; and a Defrise phantom using GATE v6.1. Projections were generated over 360° and reconstructed using the 3D MPH/LEHR OS-EM methods with up to 720 updates. The normalized mean square error (NMSE) was calculated over the cerebral and striatal regions extracted from the reconstructed images for 99m Tc-HMPAO and 99m Tc-TRODAT-1 simulations, respectively, and average normalized standard deviation (NSD) based on 20 noise realizations was assessed on selected uniform 3D regions as the noise index. Visual assessment and image profiles were applied to the results of Monte Carlo simulations. The optimized design parameters of the MPH collimators were 9 pinholes with 4.7 and 2.8 mm pinhole diameter, 73° acceptance angle, 127 mm focal length, 167 mm ROR for 12 mm and 8 mm target resolution, respectively. According to the optimization results, the detection efficiencies of the proposed collimators were 270 and 40% more as compared to LEHR. The Monte Carlo simulations showed that 7.9 and 6.4 mm rods can be discriminated for the MPH collimators with target resolutions of 12 and 8 mm, respectively. The eight 12 mm-thick discs of the Defrise phantom can also be resolved clearly in the axial plane as demonstrated by the image profiles generated with the MPH collimators. The two collimator designs provide superior image quality as compared to the conventional LEHR, and shows potential to improve current brain SPECT imaging based on a conventional SPECT scanner.

High intensity multi beam design of SANS instrument for Dhruva reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, Sohrab, E-mail: abbas@barc.gov.in; Aswal, V. K.; Désert, S.

A new and versatile design of Small Angle Neutron Scattering (SANS) instrument based on utilization of multi-beam is presented. The multi-pinholes and multi-slits as SANS collimator for medium flux Dhruva rearctor have been proposed and their designs have been validated using McStas simulations. Various instrument configurations to achieve different minimum wave vector transfers in scattering experiments are envisioned. These options enable smooth access to minimum wave vector transfers as low as ~ 6×10{sup −4} Å{sup −1} with a significant improvement in neutron intensity, allowing faster measurements. Such angularly well defined and intense neutron beam will allow faster SANS studies ofmore » agglomerates larger than few tens of nm.« less

Continuous intensity map optimization (CIMO): A novel approach to leaf sequencing in step and shoot IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao Daliang; Earl, Matthew A.; Luan, Shuang

2006-04-15

A new leaf-sequencing approach has been developed that is designed to reduce the number of required beam segments for step-and-shoot intensity modulated radiation therapy (IMRT). This approach to leaf sequencing is called continuous-intensity-map-optimization (CIMO). Using a simulated annealing algorithm, CIMO seeks to minimize differences between the optimized and sequenced intensity maps. Two distinguishing features of the CIMO algorithm are (1) CIMO does not require that each optimized intensity map be clustered into discrete levels and (2) CIMO is not rule-based but rather simultaneously optimizes both the aperture shapes and weights. To test the CIMO algorithm, ten IMRT patient cases weremore » selected (four head-and-neck, two pancreas, two prostate, one brain, and one pelvis). For each case, the optimized intensity maps were extracted from the Pinnacle{sup 3} treatment planning system. The CIMO algorithm was applied, and the optimized aperture shapes and weights were loaded back into Pinnacle. A final dose calculation was performed using Pinnacle's convolution/superposition based dose calculation. On average, the CIMO algorithm provided a 54% reduction in the number of beam segments as compared with Pinnacle's leaf sequencer. The plans sequenced using the CIMO algorithm also provided improved target dose uniformity and a reduced discrepancy between the optimized and sequenced intensity maps. For ten clinical intensity maps, comparisons were performed between the CIMO algorithm and the power-of-two reduction algorithm of Xia and Verhey [Med. Phys. 25(8), 1424-1434 (1998)]. When the constraints of a Varian Millennium multileaf collimator were applied, the CIMO algorithm resulted in a 26% reduction in the number of segments. For an Elekta multileaf collimator, the CIMO algorithm resulted in a 67% reduction in the number of segments. An average leaf sequencing time of less than one minute per beam was observed.« less

Design and performance of a multi-pinhole collimation device for small animal imaging with clinical SPECT and SPECT-CT scanners

PubMed Central

DiFilippo, Frank P.

2008-01-01

A multi-pinhole collimation device is developed that uses the gamma camera detectors of a clinical SPECT or SPECT-CT scanner to produce high resolution SPECT images. The device consists of a rotating cylindrical collimator having 22 tungsten pinholes with 0.9 mm diameter apertures and an animal bed inside the collimator that moves linearly to provide helical or ordered-subsets axial sampling. CT images also may be acquired on a SPECT-CT scanner for purposes of image co-registration and SPECT attenuation correction. The device is placed on the patient table of the scanner without attaching to the detectors or scanner gantry. The system geometry is calibrated in-place from point source data and is then used during image reconstruction. The SPECT imaging performance of the device is evaluated with test phantom scans. Spatial resolution from reconstructed point source images is measured to be 0.6 mm full width at half maximum or better. Micro-Derenzo phantom images demonstrate the ability to resolve 0.7 mm diameter rod patterns. The axial slabs of a Micro-Defrise phantom are visualized well. Collimator efficiency exceeds 0.05% at the center of the field of view, and images of a uniform phantom show acceptable uniformity and minimal artifact. The overall simplicity and relatively good imaging performance of the device make it an interesting low-cost alternative to dedicated small animal scanners. PMID:18635899

Design and performance of a multi-pinhole collimation device for small animal imaging with clinical SPECT and SPECT CT scanners

NASA Astrophysics Data System (ADS)

Di Filippo, Frank P.

2008-08-01

A multi-pinhole collimation device is developed that uses the gamma camera detectors of a clinical SPECT or SPECT-CT scanner to produce high-resolution SPECT images. The device consists of a rotating cylindrical collimator having 22 tungsten pinholes with 0.9 mm diameter apertures and an animal bed inside the collimator that moves linearly to provide helical or ordered-subsets axial sampling. CT images also may be acquired on a SPECT-CT scanner for purposes of image co-registration and SPECT attenuation correction. The device is placed on the patient table of the scanner without attaching to the detectors or scanner gantry. The system geometry is calibrated in-place from point source data and is then used during image reconstruction. The SPECT imaging performance of the device is evaluated with test phantom scans. Spatial resolution from reconstructed point source images is measured to be 0.6 mm full width at half maximum or better. Micro-Derenzo phantom images demonstrate the ability to resolve 0.7 mm diameter rod patterns. The axial slabs of a Micro-Defrise phantom are visualized well. Collimator efficiency exceeds 0.05% at the center of the field of view, and images of a uniform phantom show acceptable uniformity and minimal artifact. The overall simplicity and relatively good imaging performance of the device make it an interesting low-cost alternative to dedicated small animal scanners.

Poster - Thur Eve - 10: Long term stability of VMAT quality assurance parameters using an EPID.

PubMed

Pekar, J; Diamond, K R

2012-07-01

The rapidly growing use of volumetric modulated arc therapy (VMAT) treatments in radiation therapy calls for a quantitative, automated, and reliable quality assurance (QA) procedure that can be used routinely in the clinical setting. In this work, we present a series VMAT QA procedures used to assess dynamic multi-leaf collimator (MLC) positional accuracy, variable dose-rate accuracy, and MLC leaf speed accuracy. The QA procedures were performed using amorphous silicon electronic portal imaging devices (EPID) to determine the long term stability of the measured parameters on two Varian linear accelerators. The measurements were repeated weekly on both linear accelerators for a period of three months and the EPID images were analyzed using custom Matlab software. The results of the picket fence tests indicate that MLC leaf positions can be identified to within 0.11 mm and 0.15 mm for static gantry delivery and VMAT delivery respectively. In addition, the dose-rate, gantry speed and MLC leaf speed tests both show very good stability over the measurement period. The measurements thus far, suggest that a number of the dosimetry tests may be suitable for quarterly QA for Varian iX and Trilogy linacs. However, additional measurements are required to confirm the frequency with which each test is required for safe and reliable VMAT delivery at our centre. © 2012 American Association of Physicists in Medicine.

WE-DE-BRA-10: Development of a Novel Scanning Beam Low-Energy Intraoperative Radiation Therapy (SBIORT) System for Pancreatic Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wears, B; Mohiuddin, I; Flynn, R

2016-06-15

Purpose: Developing a compact collimator system and validating a 3D surface imaging module for a scanning beam low-energy x-ray radiation therapy (SBIORT) system that enables delivery of non-uniform radiation dose to targets with irregular shapes intraoperatively. Methods: SBIORT consists of a low energy x-ray source, a custom compact collimator module, a robotic arm, and a 3D surface imaging module. The 3D surface imaging system (structure sensor) is utilized for treatment planning and motion monitoring of the surgical cavity. SBIORT can deliver non-uniform dose distributions by dynamically moving the x-ray source assembly along optimal paths with various collimator apertures. The compactmore » collimator utilizes a dynamic shutter mechanism to form a variable square aperture. The accuracy and reproducibility of the collimator were evaluated using a high accuracy encoder and a high resolution camera platform. The dosimetrical characteristics of the collimator prototype were evaluated using EBT3 films with a Pantak Therapax unit. The accuracy and clinical feasibility of the 3D imaging system were evaluated using a phantom and a cadaver cavity. Results: The SBIORT collimator has a compact size: 66 mm diameter and 10 mm thickness with the maximum aperture of 20 mm. The mechanical experiment indicated the average accuracy of leaf position was 0.08 mm with a reproducibility of 0.25 mm at 95% confidence level. The dosimetry study indicated the collimator had a penumbra of 0.35 mm with a leaf transmission of 0.5%. 3D surface scans can be acquired in 5 seconds. The average difference between the acquired 3D surface and the ground truth is 1 mm with a standard deviation of 0.6 mm. Conclusion: This work demonstrates the feasibility of the compact collimator and 3D scanning system for the SBIORT. SBIORT is a way of delivering IORT with a compact system that requires minimum shielding of the procedure room. This research is supported by the University of Iowa Internal Funding Initiatives.« less

TU-FG-201-04: Computer Vision in Autonomous Quality Assurance of Linear Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, H; Jenkins, C; Yu, S

Purpose: Routine quality assurance (QA) of linear accelerators represents a critical and costly element of a radiation oncology center. Recently, a system was developed to autonomously perform routine quality assurance on linear accelerators. The purpose of this work is to extend this system and contribute computer vision techniques for obtaining quantitative measurements for a monthly multi-leaf collimator (MLC) QA test specified by TG-142, namely leaf position accuracy, and demonstrate extensibility for additional routines. Methods: Grayscale images of a picket fence delivery on a radioluminescent phosphor coated phantom are captured using a CMOS camera. Collected images are processed to correct formore » camera distortions, rotation and alignment, reduce noise, and enhance contrast. The location of each MLC leaf is determined through logistic fitting and a priori modeling based on knowledge of the delivered beams. Using the data collected and the criteria from TG-142, a decision is made on whether or not the leaf position accuracy of the MLC passes or fails. Results: The locations of all MLC leaf edges are found for three different picket fence images in a picket fence routine to 0.1mm/1pixel precision. The program to correct for image alignment and determination of leaf positions requires a runtime of 21– 25 seconds for a single picket, and 44 – 46 seconds for a group of three pickets on a standard workstation CPU, 2.2 GHz Intel Core i7. Conclusion: MLC leaf edges were successfully found using techniques in computer vision. With the addition of computer vision techniques to the previously described autonomous QA system, the system is able to quickly perform complete QA routines with minimal human contribution.« less

Design and dosimetry of a few leaf electron collimator for energy modulated electron therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Yahya, Khalid; Verhaegen, Frank; Seuntjens, Jan

2007-12-15

Despite the capability of energy modulated electron therapy (EMET) to achieve highly conformal dose distributions in superficial targets it has not been widely implemented due to problems inherent in electron beam radiotherapy such as planning dosimetry accuracy, and verification as well as a lack of systems for automated delivery. In previous work we proposed a novel technique to deliver EMET using an automated 'few leaf electron collimator' (FLEC) that consists of four motor-driven leaves fit in a standard clinical electron beam applicator. Integrated with a Monte Carlo based optimization algorithm that utilizes patient-specific dose kernels, a treatment delivery was incorporatedmore » within the linear accelerator operation. The FLEC was envisioned to work as an accessory tool added to the clinical accelerator. In this article the design and construction of the FLEC prototype that match our compact design goals are presented. It is controlled using an in-house developed EMET controller. The structure of the software and the hardware characteristics of the EMET controller are demonstrated. Using a parallel plate ionization chamber, output measurements were obtained to validate the Monte Carlo calculations for a range of fields with different energies and sizes. Further verifications were also performed for comparing 1-D and 2-D dose distributions using energy independent radiochromic films. Comparisons between Monte Carlo calculations and measurements of complex intensity map deliveries show an overall agreement to within {+-}3%. This work confirms our design objectives of the FLEC that allow for automated delivery of EMET. Furthermore, the Monte Carlo dose calculation engine required for EMET planning was validated. The result supports the potential of the prototype FLEC for the planning and delivery of EMET.« less

Multileaf collimator characteristics and reliability requirements for IMRT Elekta system.

PubMed

Liu, Chihray; Simon, Thomas A; Fox, Christopher; Li, Jonathan; Palta, Jatinder R

2008-01-01

Understanding the characteristics of a multileaf collimator (MLC) system, modeling MLC in a treatment planning system, and maintaining the mechanical accuracy of the linear accelerator gantry head system are important factors in the safe implementation of an intensity-modulated radiotherapy program. We review the characteristics of an Elekta MLC system, discuss the necessary MLC modeling parameters for a treatment planning system, and provide a novel method to establish an MLC leaf position quality assurance program. To perform quality assurance on 40 pairs of individual MLC leaves is a time-consuming and difficult task. In this report, an effective routine MLC quality assurance method based on the field edge of a backup jaw as referenced in conjunction with a diode array as a radiation detector system is discussed. The sensitivity of this test for determining the relative leaf positions was observed to be better than 0.1 mm. The Elekta MLC leaf position accuracy measured with this system has been better than 0.3 mm.

SU-F-T-527: A Novel Dynamic Multileaf Collimator Leaf-Sequencing Algorithm in Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, J; Lin, H; Chow, J

Purpose: A novel leaf-sequencing algorithm is developed for generating arbitrary beam intensity profiles in discrete levels using dynamic multileaf collimator (MLC). The efficiency of this dynamic MLC leaf-sequencing method was evaluated using external beam treatment plans delivered by intensity modulated radiation therapy technique. Methods: To qualify and validate this algorithm, integral test for the beam segment of MLC generated by the CORVUS treatment planning system was performed with clinical intensity map experiments. The treatment plans were optimized and the fluence maps for all photon beams were determined. This algorithm started with the algebraic expression for the area under the beammore » profile. The coefficients in the expression can be transformed into the specifications for the leaf-setting sequence. The leaf optimization procedure was then applied and analyzed for clinical relevant intensity profiles in cancer treatment. Results: The macrophysical effect of this method can be described by volumetric plan evaluation tools such as dose-volume histograms (DVHs). The DVH results are in good agreement compared to those from the CORVUS treatment planning system. Conclusion: We developed a dynamic MLC method to examine the stability of leaf speed including effects of acceleration and deceleration of leaf motion in order to make sure the stability of leaf speed did not affect the intensity profile generated. It was found that the mechanical requirements were better satisfied using this method. The Project is sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.« less

Monte Carlo design and simulation of a grid-type multi-layer pixel collimator for radiotherapy: Feasibility study

NASA Astrophysics Data System (ADS)

Yoon, Do-Kun; Jung, Joo-Young; Suh, Tae Suk

2014-05-01

In order to confirm the possibility of field application of a different type collimator with a multileaf collimator (MLC), we constructed a grid-type multi-layer pixel collimator (GTPC) by using a Monte Carlo n-particle simulation (MCNPX). In this research, a number of factors related to the performance of the GPTC were evaluated using simulated output data of a basic MLC model. A layer was comprised of a 1024-pixel collimator (5.0 × 5.0 mm2) which could operate individually as a grid-type collimator (32 × 32). A 30-layer collimator was constructed for a specific portal form to pass radiation through the opening and closing of each pixel cover. The radiation attenuation level and the leakage were compared between the GTPC modality simulation and MLC modeling (tungsten, 17.50 g/cm3, 5.0 × 70.0 × 160.0 mm3) currently used for a radiation field. Comparisons of the portal imaging, the lateral dose profile from a virtual water phantom, the dependence of the performance on the increase in the number of layers, the radiation intensity modulation verification, and the geometric error between the GTPC and the MLC were done using the MCNPX simulation data. From the simulation data, the intensity modulation of the GTPC showed a faster response than the MLC's (29.6%). In addition, the agreement between the doses that should be delivered to the target region was measured as 97.0%, and the GTPC system had an error below 0.01%, which is identical to that of MLC. A Monte Carlo simulation of the GTPC could be useful for verification of application possibilities. Because the line artifact is caused by the grid frame and the folded cover, a lineal dose transfer type is chosen for the operation of this system. However, the result of GTPC's performance showed that the methods of effective intensity modulation and the specific geometric beam shaping differed with the MLC modality.

Radiation Transport Calculation of the UGXR Collimators for the Jules Horowitz Reactor (JHR)

NASA Astrophysics Data System (ADS)

Chento, Yelko; Hueso, César; Zamora, Imanol; Fabbri, Marco; Fuente, Cristina De La; Larringan, Asier

2017-09-01

Jules Horowitz Reactor (JHR), a major infrastructure of European interest in the fission domain, will be built and operated in the framework of an international cooperation, including the development and qualification of materials and nuclear fuel used in nuclear industry. For this purpose UGXR Collimators, two multi slit gamma and X-ray collimation mechatronic systems, will be installed at the JHR pool and at the Irradiated Components Storage pool. Expected amounts of radiation produced by the spent fuel and X-ray accelerator implies diverse aspects need to be verified to ensure adequate radiological zoning and personnel radiation protection. A computational methodology was devised to validate the Collimators design by means of coupling different engineering codes. In summary, several assessments were performed by means of MCNP5v1.60 to fulfil all the radiological requirements in Nominal scenario (TEDE < 25µSv/h) and in Maintenance scenario (TEDE < 2mSv/h) among others, detailing the methodology, hypotheses and assumptions employed.

Development of an iterative reconstruction method to overcome 2D detector low resolution limitations in MLC leaf position error detection for 3D dose verification in IMRT.

PubMed

Visser, R; Godart, J; Wauben, D J L; Langendijk, J A; Van't Veld, A A; Korevaar, E W

2016-05-21

The objective of this study was to introduce a new iterative method to reconstruct multi leaf collimator (MLC) positions based on low resolution ionization detector array measurements and to evaluate its error detection performance. The iterative reconstruction method consists of a fluence model, a detector model and an optimizer. Expected detector response was calculated using a radiotherapy treatment plan in combination with the fluence model and detector model. MLC leaf positions were reconstructed by minimizing differences between expected and measured detector response. The iterative reconstruction method was evaluated for an Elekta SLi with 10.0 mm MLC leafs in combination with the COMPASS system and the MatriXX Evolution (IBA Dosimetry) detector with a spacing of 7.62 mm. The detector was positioned in such a way that each leaf pair of the MLC was aligned with one row of ionization chambers. Known leaf displacements were introduced in various field geometries ranging from  -10.0 mm to 10.0 mm. Error detection performance was tested for MLC leaf position dependency relative to the detector position, gantry angle dependency, monitor unit dependency, and for ten clinical intensity modulated radiotherapy (IMRT) treatment beams. For one clinical head and neck IMRT treatment beam, influence of the iterative reconstruction method on existing 3D dose reconstruction artifacts was evaluated. The described iterative reconstruction method was capable of individual MLC leaf position reconstruction with millimeter accuracy, independent of the relative detector position within the range of clinically applied MU's for IMRT. Dose reconstruction artifacts in a clinical IMRT treatment beam were considerably reduced as compared to the current dose verification procedure. The iterative reconstruction method allows high accuracy 3D dose verification by including actual MLC leaf positions reconstructed from low resolution 2D measurements.

Validation of Dosimetric Leaf Gap (DLG) prior to its implementation in Treatment Planning System (TPS): TrueBeam™ millennium 120 leaf MLC.

PubMed

Shende, Ravindra; Patel, Ganesh

2017-01-01

Objective of present study is to determine optimum value of DLG and its validation prior to being incorporated in TPS for Varian TrueBeam™ millennium 120 leaves MLC. Partial transmission through the rounded leaf ends of the Multi Leaf Collimator (MLC) causes a conflict between the edges of the light field and radiation field. Parameter account for this partial transmission is called Dosimetric Leaf Gap (DLG). The complex high precession technique, such as Intensity Modulated Radiation Therapy (IMRT), entails the modeling of optimum value of DLG inside Eclipse Treatment Planning System (TPS) for precise dose calculation. Distinct synchronized uniformed extension of sweeping dynamic MLC leaf gap fields created by Varian MLC shaper software were use to determine DLG. DLG measurements performed with both 0.13 cc semi-flex ionization chamber and 2D-Array I-Matrix were used to validate the DLG; similarly, values of DLG from TPS were estimated from predicted dose. Similar mathematical approaches were employed to determine DLG from delivered and TPS predicted dose. DLG determined from delivered dose measured with both ionization chamber (DLG Ion ) and I-Matrix (DLG I-Matrix ) compared with DLG estimate from TPS predicted dose (DLG TPS ). Measurements were carried out for all available 6MV, 10MV, 15MV, 6MVFFF and 10MVFFF beam energies. Maximum and minimum DLG deviation between measured and TPS calculated DLG was found to be 0.2 mm and 0.1 mm, respectively. Both of the measured DLGs (DLG Ion and DLG I-Matrix ) were found to be in a very good agreement with estimated DLG from TPS (DLG TPS ). Proposed method proved to be helpful in verifying and validating the DLG value prior to its clinical implementation in TPS.

Characteristics and performance of the first commercial multileaf collimator for a robotic radiosurgery system.

PubMed

Fürweger, Christoph; Prins, Paulette; Coskan, Harun; Heijmen, Ben J M

2016-05-01

The "InCise™ multileaf-collimator (MLC)" is the first commercial MLC to be mounted on a robotic SRS/SBRT platform (CyberKnife). The authors assessed characteristics and performance of this novel device in a preclinical five months test period. Commissioning beam data were acquired with unshielded diodes. EBT3 radiochromic films were employed for measurement of transmission, leaf/bank position accuracy (garden fence) before and after exercising the MLC, for end-to-end testing and further characterization of the beam. The robot workspace with MLC was assessed analytically by transformation to an Euler geometry ("plane," "gantry," and "collimator" angles) and by measuring pointing accuracy at each node. Stability over time was evaluated in picket fence and adapted Winston-Lutz tests (AQA). Beam penumbrae (80%-20%, with 100% = 2 × dose at inflection point for field sizes ≥ 50 × 50 mm(2)) were 2.2-3.7 mm for square fields in reference condition (source-axis-distance 800 mm, depth 15 mm) and depended on field size and off-axis position. Transmission and leakage did not exceed 0.5%. Accessible clinical workspace with MLC covered non-coplanar gantry angles of [-113°; +112°] and collimator angles of [-100°; +107°], with an average robot pointing accuracy of 0.12 ± 0.09 mm. For vertical beams, garden fence tests exhibited an average leaf positioning error of ≤0.2 mm, which increased by 0.25 and 0.30 mm (banks X1 and X2) with leaves traveling parallel to gravity. After execution of a leaf motion stress routine, garden fence tests showed slightly increased jaggedness and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.38 ± 0.05 mm in nine end-to-end tests. Picket fence and AQA tests displayed stable results over the test period. The InCise™ MLC for CyberKnife showed high accuracy and adequate characteristics for SRS/SBRT applications. MLC performance after exercise demands specific quality assurance measures.

Toward the development of intrafraction tumor deformation tracking using a dynamic multi-leaf collimator

PubMed Central

Ge, Yuanyuan; O’Brien, Ricky T.; Shieh, Chun-Chien; Booth, Jeremy T.; Keall, Paul J.

2014-01-01

Purpose: Intrafraction deformation limits targeting accuracy in radiotherapy. Studies show tumor deformation of over 10 mm for both single tumor deformation and system deformation (due to differential motion between primary tumors and involved lymph nodes). Such deformation cannot be adapted to with current radiotherapy methods. The objective of this study was to develop and experimentally investigate the ability of a dynamic multi-leaf collimator (DMLC) tracking system to account for tumor deformation. Methods: To compensate for tumor deformation, the DMLC tracking strategy is to warp the planned beam aperture directly to conform to the new tumor shape based on real time tumor deformation input. Two deformable phantoms that correspond to a single tumor and a tumor system were developed. The planar deformations derived from the phantom images in beam's eye view were used to guide the aperture warping. An in-house deformable image registration software was developed to automatically trigger the registration once new target image was acquired and send the computed deformation to the DMLC tracking software. Because the registration speed is not fast enough to implement the experiment in real-time manner, the phantom deformation only proceeded to the next position until registration of the current deformation position was completed. The deformation tracking accuracy was evaluated by a geometric target coverage metric defined as the sum of the area incorrectly outside and inside the ideal aperture. The individual contributions from the deformable registration algorithm and the finite leaf width to the tracking uncertainty were analyzed. Clinical proof-of-principle experiment of deformation tracking using previously acquired MR images of a lung cancer patient was implemented to represent the MRI-Linac environment. Intensity-modulated radiation therapy (IMRT) treatment delivered with enabled deformation tracking was simulated and demonstrated. Results: The first experimental investigation of adapting to tumor deformation has been performed using simple deformable phantoms. For the single tumor deformation, the Au+Ao was reduced over 56% when deformation was larger than 2 mm. Overall, the total improvement was 82%. For the tumor system deformation, the Au+Ao reductions were all above 75% and the total Au+Ao improvement was 86%. Similar coverage improvement was also found in simulating deformation tracking during IMRT delivery. The deformable image registration algorithm was identified as the dominant contributor to the tracking error rather than the finite leaf width. The discrepancy between the warped beam shape and the ideal beam shape due to the deformable registration was observed to be partially compensated during leaf fitting due to the finite leaf width. The clinical proof-of-principle experiment demonstrated the feasibility of intrafraction deformable tracking for clinical scenarios. Conclusions: For the first time, we developed and demonstrated an experimental system that is capable of adapting the MLC aperture to account for tumor deformation. This work provides a potentially widely available management method to effectively account for intrafractional tumor deformation. This proof-of-principle study is the first experimental step toward the development of an image-guided radiotherapy system to treat deforming tumors in real-time. PMID:24877798

Toward the development of intrafraction tumor deformation tracking using a dynamic multi-leaf collimator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Yuanyuan; O’Brien, Ricky T.; Shieh, Chun-Chien

Purpose: Intrafraction deformation limits targeting accuracy in radiotherapy. Studies show tumor deformation of over 10 mm for both single tumor deformation and system deformation (due to differential motion between primary tumors and involved lymph nodes). Such deformation cannot be adapted to with current radiotherapy methods. The objective of this study was to develop and experimentally investigate the ability of a dynamic multi-leaf collimator (DMLC) tracking system to account for tumor deformation. Methods: To compensate for tumor deformation, the DMLC tracking strategy is to warp the planned beam aperture directly to conform to the new tumor shape based on real timemore » tumor deformation input. Two deformable phantoms that correspond to a single tumor and a tumor system were developed. The planar deformations derived from the phantom images in beam's eye view were used to guide the aperture warping. An in-house deformable image registration software was developed to automatically trigger the registration once new target image was acquired and send the computed deformation to the DMLC tracking software. Because the registration speed is not fast enough to implement the experiment in real-time manner, the phantom deformation only proceeded to the next position until registration of the current deformation position was completed. The deformation tracking accuracy was evaluated by a geometric target coverage metric defined as the sum of the area incorrectly outside and inside the ideal aperture. The individual contributions from the deformable registration algorithm and the finite leaf width to the tracking uncertainty were analyzed. Clinical proof-of-principle experiment of deformation tracking using previously acquired MR images of a lung cancer patient was implemented to represent the MRI-Linac environment. Intensity-modulated radiation therapy (IMRT) treatment delivered with enabled deformation tracking was simulated and demonstrated. Results: The first experimental investigation of adapting to tumor deformation has been performed using simple deformable phantoms. For the single tumor deformation, the A{sub u}+A{sub o} was reduced over 56% when deformation was larger than 2 mm. Overall, the total improvement was 82%. For the tumor system deformation, the A{sub u}+A{sub o} reductions were all above 75% and the total A{sub u}+A{sub o} improvement was 86%. Similar coverage improvement was also found in simulating deformation tracking during IMRT delivery. The deformable image registration algorithm was identified as the dominant contributor to the tracking error rather than the finite leaf width. The discrepancy between the warped beam shape and the ideal beam shape due to the deformable registration was observed to be partially compensated during leaf fitting due to the finite leaf width. The clinical proof-of-principle experiment demonstrated the feasibility of intrafraction deformable tracking for clinical scenarios. Conclusions: For the first time, we developed and demonstrated an experimental system that is capable of adapting the MLC aperture to account for tumor deformation. This work provides a potentially widely available management method to effectively account for intrafractional tumor deformation. This proof-of-principle study is the first experimental step toward the development of an image-guided radiotherapy system to treat deforming tumors in real-time.« less

Leaf position optimization for step-and-shoot IMRT.

PubMed

De Gersem, W; Claus, F; De Wagter, C; Van Duyse, B; De Neve, W

2001-12-01

To describe the theoretical basis, the algorithm, and implementation of a tool that optimizes segment shapes and weights for step-and-shoot intensity-modulated radiation therapy delivered by multileaf collimators. The tool, called SOWAT (Segment Outline and Weight Adapting Tool) is applied to a set of segments, segment weights, and corresponding dose distribution, computed by an external dose computation engine. SOWAT evaluates the effects of changing the position of each collimating leaf of each segment on an objective function, as follows. Changing a leaf position causes a change in the segment-specific dose matrix, which is calculated by a fast dose computation algorithm. A weighted sum of all segment-specific dose matrices provides the dose distribution and allows computation of the value of the objective function. Only leaf position changes that comply with the multileaf collimator constraints are evaluated. Leaf position changes that tend to decrease the value of the objective function are retained. After several possible positions have been evaluated for all collimating leaves of all segments, an external dose engine recomputes the dose distribution, based on the adapted leaf positions and weights. The plan is evaluated. If the plan is accepted, a segment sequencer is used to make the prescription files for the treatment machine. Otherwise, the user can restart SOWAT using the new set of segments, segment weights, and corresponding dose distribution. The implementation was illustrated using two example cases. The first example is a T1N0M0 supraglottic cancer case that was distributed as a multicenter planning exercise by investigators from Rotterdam, The Netherlands. The exercise involved a two-phase plan. Phase 1 involved the delivery of 46 Gy to a concave-shaped planning target volume (PTV) consisting of the primary tumor volume and the elective lymph nodal regions II-IV on both sides of the neck. Phase 2 involved a boost of 24 Gy to the primary tumor region only. SOWAT was applied to the Phase 1 plan. Parotid sparing was a planning goal. The second implementation example is an ethmoid sinus cancer case, planned with the intent of bilateral visus sparing. The median PTV prescription dose was 70 Gy with a maximum dose constraint to the optic pathway structures of 60 Gy. The initial set of segments, segment weights, and corresponding dose distribution were obtained, respectively, by an anatomy-based segmentation tool, a segment weight optimization tool, and a differential scatter-air ratio dose computation algorithm as external dose engine. For the supraglottic case, this resulted in a plan that proved to be comparable to the plans obtained at the other institutes by forward or inverse planning techniques. After using SOWAT, the minimum PTV dose and PTV dose homogeneity increased; the maximum dose to the spinal cord decreased from 38 Gy to 32 Gy. The left parotid mean dose decreased from 22 Gy to 19 Gy and the right parotid mean dose from 20 to 18 Gy. For the ethmoid sinus case, the target homogeneity increased by leaf position optimization, together with a better sparing of the optical tracts. By using SOWAT, the plans improved with respect to all plan evaluation end points. Compliance with the multileaf collimator constraints is guaranteed. The treatment delivery time remains almost unchanged, because no additional segments are created.

Development and Validation of a Monte Carlo Simulation Tool for Multi-Pinhole SPECT

PubMed Central

Mok, Greta S. P.; Du, Yong; Wang, Yuchuan; Frey, Eric C.; Tsui, Benjamin M. W.

2011-01-01

Purpose In this work, we developed and validated a Monte Carlo simulation (MCS) tool for investigation and evaluation of multi-pinhole (MPH) SPECT imaging. Procedures This tool was based on a combination of the SimSET and MCNP codes. Photon attenuation and scatter in the object, as well as penetration and scatter through the collimator detector, are modeled in this tool. It allows accurate and efficient simulation of MPH SPECT with focused pinhole apertures and user-specified photon energy, aperture material, and imaging geometry. The MCS method was validated by comparing the point response function (PRF), detection efficiency (DE), and image profiles obtained from point sources and phantom experiments. A prototype single-pinhole collimator and focused four- and five-pinhole collimators fitted on a small animal imager were used for the experimental validations. We have also compared computational speed among various simulation tools for MPH SPECT, including SimSET-MCNP, MCNP, SimSET-GATE, and GATE for simulating projections of a hot sphere phantom. Results We found good agreement between the MCS and experimental results for PRF, DE, and image profiles, indicating the validity of the simulation method. The relative computational speeds for SimSET-MCNP, MCNP, SimSET-GATE, and GATE are 1: 2.73: 3.54: 7.34, respectively, for 120-view simulations. We also demonstrated the application of this MCS tool in small animal imaging by generating a set of low-noise MPH projection data of a 3D digital mouse whole body phantom. Conclusions The new method is useful for studying MPH collimator designs, data acquisition protocols, image reconstructions, and compensation techniques. It also has great potential to be applied for modeling the collimator-detector response with penetration and scatter effects for MPH in the quantitative reconstruction method. PMID:19779896

MO-F-CAMPUS-T-01: Radiosurgery of Multiple Brain Metastases with Single-Isocenter VMAT: Optimizing Treatment Geometry to Reduce Normal Brain Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Q; Snyder, K; Liu, C

Purpose: To develop an optimization algorithm to reduce normal brain dose by optimizing couch and collimator angles for single isocenter multiple targets treatment of stereotactic radiosurgery. Methods: Three metastatic brain lesions were retrospectively planned using single-isocenter volumetric modulated arc therapy (VMAT). Three matrices were developed to calculate the projection of each lesion on Beam’s Eye View (BEV) by the rotating couch, collimator and gantry respectively. The island blocking problem was addressed by computing the total area of open space between any two lesions with shared MLC leaf pairs. The couch and collimator angles resulting in the smallest open areas weremore » the optimized angles for each treatment arc. Two treatment plans with and without couch and collimator angle optimization were developed using the same objective functions and to achieve 99% of each target volume receiving full prescription dose of 18Gy. Plan quality was evaluated by calculating each target’s Conformity Index (CI), Gradient Index (GI), and Homogeneity index (HI), and absolute volume of normal brain V8Gy, V10Gy, V12Gy, and V14Gy. Results: Using the new couch/collimator optimization strategy, dose to normal brain tissue was reduced substantially. V8, V10, V12, and V14 decreased by 2.3%, 3.6%, 3.5%, and 6%, respectively. There were no significant differences in the conformity index, gradient index, and homogeneity index between two treatment plans with and without the new optimization algorithm. Conclusion: We have developed a solution to the island blocking problem in delivering radiation to multiple brain metastases with shared isocenter. Significant reduction in dose to normal brain was achieved by using optimal couch and collimator angles that minimize total area of open space between any of the two lesions with shared MLC leaf pairs. This technique has been integrated into Eclipse treatment system using scripting API.« less

Controllability in Multi-Stage Laser Ion Acceleration

NASA Astrophysics Data System (ADS)

Kawata, S.; Kamiyama, D.; Ohtake, Y.; Barada, D.; Ma, Y. Y.; Kong, Q.; Wang, P. X.; Gu, Y. J.; Li, X. F.; Yu, Q.

2015-11-01

The present paper shows a concept for a future laser ion accelerator, which should have an ion source, ion collimators, ion beam bunchers and ion post acceleration devices. Based on the laser ion accelerator components, the ion particle energy and the ion energy spectrum are controlled, and a future compact laser ion accelerator would be designed for ion cancer therapy or for ion material treatment. In this study each component is designed to control the ion beam quality. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching are successfully realized by a multi-stage laser-target interaction. A combination of each component provides a high controllability of the ion beam quality to meet variable requirements in various purposes in the laser ion accelerator. The work was partly supported by MEXT, JSPS, ASHULA project/ ILE, Osaka University, CORE (Center for Optical Research and Education, Utsunomiya University, Japan), Fudan University and CDI (Creative Dept. for Innovation) in CCRD, Utsunomiya University.

A study on dosimetric properties of electronic portal imaging device and its use as a quality assurance tool in Volumetric Modulated Arc Therapy

PubMed Central

Sukumar, Prabakar; Padmanaban, Sriram; Jeevanandam, Prakash; Syam Kumar, S.A.; Nagarajan, Vivekanandan

2011-01-01

Aim In this study, the dosimetric properties of the electronic portal imaging device were examined and the quality assurance testing of Volumetric Modulated Arc Therapy was performed. Background RapidArc involves the variable dose rate, leaf speed and the gantry rotation. The imager was studied for the effects like dose, dose rate, field size, leaf speed and sag during gantry rotation. Materials and methods A Varian RapidArc machine equipped with 120 multileaf collimator and amorphous silicon detector was used for the study. The characteristics that are variable in RapidArc treatment were studied for the portal imager. The accuracy of a dynamic multileaf collimator position at different gantry angles and during gantry rotation was examined using the picket fence test. The control of the dose rate and gantry speed was verified using a test field irradiating seven strips of the same dose with different dose rate and gantry speeds. The control over leaf speed during arc was verified by irradiating four strips of different leaf speeds with the same dose in each strip. To verify the results, the RapidArc test procedure was compared with the X-Omat film and verified for a period of 6 weeks using EPID. Results The effect of gantry rotation on leaf accuracy was minimal. The dose in segments showed good agreement with mean deviation of 0.8% for dose rate control and 1.09% for leaf speed control over different gantry speeds. Conclusion The results provided a precise control of gantry speed, dose rate and leaf speeds during RapidArc delivery and were consistent over 6 weeks. PMID:24376989

A clinically observed discrepancy between image-based and log-based MLC positions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neal, Brian, E-mail: bpn2p@virginia.edu; Ahmed, Mahmoud; Kathuria, Kunal

2016-06-15

Purpose: To present a clinical case in which real-time intratreatment imaging identified an multileaf collimator (MLC) leaf to be consistently deviating from its programmed and logged position by >1 mm. Methods: An EPID-based exit-fluence dosimetry system designed to prevent gross delivery errors was used to capture cine during treatment images. The author serendipitously visually identified a suspected MLC leaf displacement that was not otherwise detected. The leaf position as recorded on the EPID images was measured and log-files were analyzed for the treatment in question, the prior day’s treatment, and for daily MLC test patterns acquired on those treatment days.more » Additional standard test patterns were used to quantify the leaf position. Results: Whereas the log-file reported no difference between planned and recorded positions, image-based measurements showed the leaf to be 1.3 ± 0.1 mm medial from the planned position. This offset was confirmed with the test pattern irradiations. Conclusions: It has been clinically observed that log-file derived leaf positions can differ from their actual position by >1 mm, and therefore cannot be considered to be the actual leaf positions. This cautions the use of log-based methods for MLC or patient quality assurance without independent confirmation of log integrity. Frequent verification of MLC positions through independent means is a necessary precondition to trust log-file records. Intratreatment EPID imaging provides a method to capture departures from MLC planned positions.« less

Multi-detector row CT colonography: effect of collimation, pitch, and orientation on polyp detection in a human colectomy specimen.

PubMed

Taylor, Stuart A; Halligan, Steve; Bartram, Clive I; Morgan, Paul R; Talbot, Ian C; Fry, Nicola; Saunders, Brian P; Khosraviani, Kirosh; Atkin, Wendy

2003-10-01

To investigate the effects of orientation, collimation, pitch, and tube current setting on polyp detection at multi-detector row computed tomographic (CT) colonography and to determine the optimal combination of scanning parameters for screening. A colectomy specimen containing 117 polyps of different sizes was insufflated and imaged with a multi-detector row CT scanner at various collimation (1.25 and 2.5 mm), pitch (3 and 6), and tube current (50, 100, and 150 mA) settings. Two-dimensional multiplanar reformatted images and three-dimensional endoluminal surface renderings from the 12 resultant data sets were examined by one observer for the presence and conspicuity of polyps. The results were analyzed with Poisson regression and logistic regression to determine the effects of scanning parameters and of specimen orientation on polyp detection. The percentage of polyps that were detected significantly increased when collimation (P =.008) and table feed (P =.03) were decreased. Increased tube current resulted in improved detection only of polyps with a diameter of less than 5 mm. Polyps of less than 5 mm were optimally depicted with a collimation of 1.25 mm, a pitch of 3, and a tube current setting of 150 mA; polyps with a diameter greater than 5 mm were adequately depicted with 1.25-mm collimation and with either pitch setting and any of the three tube current settings. Small polyps in the transverse segment (positioned at a 90 degrees angle to the z axis of scanning) were significantly less visible than those in parallel or oblique orientations (P <.001). The effective radiation dose, calculated with a Monte Carlo simulation, was 1.4-10.0 mSv. Detection of small polyps (<5 mm) with multi-detector row CT is highly dependent on collimation, pitch, and, to a lesser extent, tube current. Collimation of 1.25 mm, combined with pitch of 6 and tube current of 50 mA, provides for reliable detection of polyps 5 mm or larger while limiting the effective radiation dose. Polyps smaller than 5 mm, however, may be poorly depicted with use of these settings in the transverse colon. Copyright RSNA, 2003

Feasibility study of the neutron dose for real-time image-guided proton therapy: A Monte Carlo study

NASA Astrophysics Data System (ADS)

Kim, Jin Sung; Shin, Jung Suk; Kim, Daehyun; Shin, Eunhyuk; Chung, Kwangzoo; Cho, Sungkoo; Ahn, Sung Hwan; Ju, Sanggyu; Chung, Yoonsun; Jung, Sang Hoon; Han, Youngyih

2015-07-01

Two full rotating gantries with different nozzles (multipurpose nozzle with MLC, scanning dedicated nozzle) for a conventional cyclotron system are installed and being commissioned for various proton treatment options at Samsung Medical Center in Korea. The purpose of this study is to use Monte Carlo simulation to investigate the neutron dose equivalent per therapeutic dose, H/D, for X-ray imaging equipment under various treatment conditions. At first, we investigated the H/D for various modifications of the beamline devices (scattering, scanning, multi-leaf collimator, aperture, compensator) at the isocenter and at 20, 40 and 60 cm distances from the isocenter, and we compared our results with those of other research groups. Next, we investigated the neutron dose at the X-ray equipment used for real-time imaging under various treatment conditions. Our investigation showed doses of 0.07 ~ 0.19 mSv/Gy at the X-ray imaging equipment, depending on the treatment option and interestingly, the 50% neutron dose reduction was observed due to multileaf collimator during proton scanning treatment with the multipurpose nozzle. In future studies, we plan to measure the neutron dose experimentally and to validate the simulation data for X-ray imaging equipment for use as an additional neutron dose reduction method.

SU-G-TeP4-03: A Multileaf Collimator Calibration and Quality Assurance Technique Using An Electronic Portal Imaging Device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lebron, S; Yan, G; Li, J

2016-06-15

Purpose: To develop an accurate and quick multileaf collimator (MLC) calibration and quality assurance technique using an electronic portal imaging device (EPID) Methods: The MLC models used include the MLCi and Agility (Elekta Ltd). This technique consists of two 22(L)x10(W) cm{sup 2} fields with 0{sup 0} and 180{sup 0} collimator angles centered to an offset EPID. The MLC opening is estimated by calculating the profile at the image’s center in the image’s horizontal direction. Scans in the image’s vertical direction were calculated every 20 pixels in the inner 70% of estimated MLC opening. The profiles’ edges were fitted with linearmore » equations to determine the image’s rotation angle. Then, crossline profiles were scanned at the center of each leaf taking into account the leaf’s width at isocenter and the rotation angle. The profiles’ edges determine the location of the leaves’ edges and these were subtracted from the reference leaf’s position in order to determine the relative leaf offsets. The edge location of all profiles was determined by using the parameterized gradient of the penumbra region. The technique was tested against an established diode array-based method, and for different MLC systems, patterns, gantry angles, days, energies, beam modalities and MLC openings. Results: The differences between the proposed and established methods were 0.26±0.19mm. The leaf offsets’ deviation was <0.3mm (5 months period). For pattern fields, the differences between predetermined and calculated offsets were 0.18±0.18mm. The leaf offset deviation of measurements with different energies and MLC openings were <0.1mm and <0.3mm, respectively. The differences between offsets of FF and FFF beams were 0.01±0.02mm (<0.07mm). The differences between the offsets at different gantry angles were 0.08±0.15mm. Conclusion: The proposed method proved to be accurate and efficient in calculating the relative leaf offsets. Parameterized field edge is essential to obtain accurate result by eliminating the noise from EPID.« less

SU-F-T-629: Effect of Multi-Leaf Collimator (MLC) Width On Plan Quality of Single-Isocenter VMAT Intracranial Stereotactic Radiosurgery for Multiple Metastases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, J; Thomas, E; Wu, X

2016-06-15

Purpose: Single-isocenter VMAT has been shown able to create high quality plans for complex intracranial multiple metastasis SRS cases. Linacs capable of the technique are typically outfitted with an MLC that consists of a combination of 5 mm and 10 mm leaves (standard) or 2.5 mm and 5 mm leaves (high-definition). In this study, we test the hypothesis that thinner collimator leaves are associated with improved plan quality. Methods: Ten multiple metastasis cases were identified and planned for VMAT SRS using a 10 MV flattening filter free beam. Plans were created for a standard (std) and a high-definition (HD) MLC.more » Published values for leaf transmission factor and dosimetric leaf gap were utilized. All other parameters were invariant. Conformity (plan and individual target), moderate isodose spill (V50%), and low isodose spill (mean brain dose) were selected for analysis. Results: Compared to standard MLC, HD-MLC improved overall plan conformity (median: Paddick CI-HD = 0.83, Paddick CI-std = 0.79; p = 0.004 and median: RTOG CI-HD =1.18, RTOG CI-std =1.24; p = 0.01 ), improved individual lesion conformity (median: Paddick CI-HD,i =0.77, Paddick CI-std,i =0.72; p < 0.001 and median: RTOG CI-HD,i = 1.28, RTOG CI-std,i =1.35; p < 0.001), improved moderate isodose spill (median: V50%-HD = 37.0 cc, V50%-std = 45.7 cc; p = 0.002), and improved low dose spill (median: dmean-HD = 2.90 Gy, dmean-std = 3.19 Gy; p = 0.002). Conclusion: For the single-isocenter VMAT SRS of multiple metastasis plans examined, use of HD-MLC modestly improved conformity, moderate isodose, and low isodose spill compared to standard MLC. However, in all cases we were able to generate clinically acceptable plans with the standard MLC. More work is need to further quantify the difference in cases with higher numbers of small targets and to better understand any potential clinical significance. This research was supported in part by Varian Medical Systems.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hussain, A

Purpose: Novel linac machines, TrueBeam (TB) and Elekta Versa have updated head designing and software control system, include flattening-filter-free (FFF) photon and electron beams. Later on FFF beams were also introduced on C-Series machines. In this work FFF beams for same energy 6MV but from different machine versions were studied with reference to beam data parameters. Methods: The 6MV-FFF percent depth doses, profile symmetry and flatness, dose rate tables, and multi-leaf collimator (MLC) transmission factors were measured during commissioning process of both C-series and Truebeam machines. The scanning and dosimetric data for 6MV-FFF beam from Truebeam and C-Series linacs wasmore » compared. A correlation of 6MV-FFF beam from Elekta Versa with that of Varian linacs was also found. Results: The scanning files were plotted for both qualitative and quantitative analysis. The dosimetric leaf gap (DLG) for C-Series 6MV-FFF beam is 1.1 mm. Published values for Truebeam dosimetric leaf gap is 1.16 mm. 6MV MLC transmission factor varies between 1.3 % and 1.4 % in two separate measurements and measured DLG values vary between 1.32 mm and 1.33 mm on C-Series machine. MLC transmission factor from C-Series machine varies between 1.5 % and 1.6 %. Some of the measured data values from C-Series FFF beam are compared with Truebeam representative data. 6MV-FFF beam parameter values like dmax, OP factors, beam symmetry and flatness and additional parameters for C-Series and Truebeam liancs will be presented and compared in graphical form and tabular data form if selected. Conclusion: The 6MV flattening filter (FF) beam data from C-Series & Truebeam and 6MV-FFF beam data from Truebeam has already presented. This particular analysis to compare 6MV-FFF beam from C-Series and Truebeam provides opportunity to better elaborate FFF mode on novel machines. It was found that C-Series and Truebeam 6MV-FFF dosimetric and beam data was quite similar.« less

Dynamic tumor tracking using the Elekta Agility MLC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fast, Martin F., E-mail: martin.fast@icr.ac.uk; Nill, Simeon, E-mail: simeon.nill@icr.ac.uk; Bedford, James L.

2014-11-01

Purpose: To evaluate the performance of the Elekta Agility multileaf collimator (MLC) for dynamic real-time tumor tracking. Methods: The authors have developed a new control software which interfaces to the Agility MLC to dynamically program the movement of individual leaves, the dynamic leaf guides (DLGs), and the Y collimators (“jaws”) based on the actual target trajectory. A motion platform was used to perform dynamic tracking experiments with sinusoidal trajectories. The actual target positions reported by the motion platform at 20, 30, or 40 Hz were used as shift vectors for the MLC in beams-eye-view. The system latency of the MLCmore » (i.e., the average latency comprising target device reporting latencies and MLC adjustment latency) and the geometric tracking accuracy were extracted from a sequence of MV portal images acquired during irradiation for the following treatment scenarios: leaf-only motion, jaw + leaf motion, and DLG + leaf motion. Results: The portal imager measurements indicated a clear dependence of the system latency on the target position reporting frequency. Deducting the effect of the target frequency, the leaf adjustment latency was measured to be 38 ± 3 ms for a maximum target speed v of 13 mm/s. The jaw + leaf adjustment latency was 53 ± 3 at a similar speed. The system latency at a target position frequency of 30 Hz was in the range of 56–61 ms for the leaves (v ≤ 31 mm/s), 71–78 ms for the jaw + leaf motion (v ≤ 25 mm/s), and 58–72 ms for the DLG + leaf motion (v ≤ 59 mm/s). The tracking accuracy showed a similar dependency on the target position frequency and the maximum target speed. For the leaves, the root-mean-squared error (RMSE) was between 0.6–1.5 mm depending on the maximum target speed. For the jaw + leaf (DLG + leaf) motion, the RMSE was between 0.7–1.5 mm (1.9–3.4 mm). Conclusions: The authors have measured the latency and geometric accuracy of the Agility MLC, facilitating its future use for clinical tracking applications.« less

Design and development of MR-compatible SPECT systems for simultaneous SPECT-MR imaging of small animals

NASA Astrophysics Data System (ADS)

Tsui, Benjamin M. W.; Hugg, James W.; Xu, Jingyan; Chen, Si; Meier, Dirk; Edelstein, William; El-Sharkawy, Abdel; Wagenaar, Douglas J.; Patt, Bradley E.

2011-03-01

We describe a continuing design and development of MR-compatible SPECT systems for simultaneous SPECT-MR imaging of small animals. A first generation prototype SPECT system was designed and constructed to fit inside a MRI system with a gradient bore inner diameter of 12 cm. It consists of 3 angularly offset rings of 8 detectors (1"x1", 16x16 pixels MR-compatible solid-state CZT). A matching 24-pinhole collimator sleeve, made of a tungsten-compound, provides projections from a common FOV of ~25 mm. A birdcage RF coil for MRI data acquisition surrounds the collimator. The SPECT system was tested inside a clinical 3T MRI system. Minimal interference was observed on the simultaneously acquired SPECT and MR images. We developed a sparse-view image reconstruction method based on accurate modeling of the point response function (PRF) of each of the 24 pinholes to provide artifact-free SPECT images. The stationary SPECT system provides relatively low resolution of 3-5 mm but high geometric efficiency of 0.5- 1.2% for fast dynamic acquisition, demonstrated in a SPECT renal kinetics study using Tc-99m DTPA. Based on these results, a second generation prototype MR-compatible SPECT system with an outer diameter of 20 cm that fits inside a mid-sized preclinical MRI system is being developed. It consists of 5 rings of 19 CZT detectors. The larger ring diameter allows the use of optimized multi-pinhole collimator designs, such as high system resolution up to ~1 mm, high geometric efficiency, or lower system resolution without collimator rotation. The anticipated performance of the new system is supported by simulation data.

SU-E-T-627: Precision Modelling of the Leaf-Bank Rotation in Elekta’s Agility MLC: Is It Necessary?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vujicic, M; Belec, J; Heath, E

Purpose: To demonstrate the method used to determine the leaf bank rotation angle (LBROT) as a parameter for modeling the Elekta Agility multi-leaf collimator (MLC) for Monte Carlo simulations and to evaluate the clinical impact of LBROT. Methods: A detailed model of an Elekta Infinity linac including an Agility MLC was built using the EGSnrc/BEAMnrc Monte Carlo code. The Agility 160-leaf MLC is modelled using the MLCE component module which allows for leaf bank rotation using the parameter LBROT. A precise value of LBROT is obtained by comparing measured and simulated profiles of a specific field, which has leaves arrangedmore » in a repeated pattern such that one leaf is opened and the adjacent one is closed. Profile measurements from an Agility linac are taken with gafchromic film, and an ion chamber is used to set the absolute dose. The measurements are compared to Monte Carlo (MC) simulations and the LBROT is adjusted until a match is found. The clinical impact of LBROT is evaluated by observing how an MC dose calculation changes with LBROT. A clinical Stereotactic Body Radiation Treatment (SBRT) plan is calculated using BEAMnrc/DOSXYZnrc simulations with different input values for LBROT. Results: Using the method outlined above, the LBROT is determined to be 9±1 mrad. Differences as high as 4% are observed in a clinical SBRT plan between the extreme case (LBROT not modeled) and the nominal case. Conclusion: In small-field radiation therapy treatment planning, it is important to properly account for LBROT as an input parameter for MC dose calculations with the Agility MLC. More work is ongoing to elucidate the observed differences by determining the contributions from transmission dose, change in field size, and source occlusion, which are all dependent on LBROT. This work was supported by OCAIRO (Ontario Consortium of Adaptive Interventions in Radiation Oncology), funded by the Ontario Research Fund.« less

Design and optimization of an energy degrader with a multi-wedge scheme based on Geant4

NASA Astrophysics Data System (ADS)

Liang, Zhikai; Liu, Kaifeng; Qin, Bin; Chen, Wei; Liu, Xu; Li, Dong; Xiong, Yongqian

2018-05-01

A proton therapy facility based on an isochronous superconducting cyclotron is under construction in Huazhong University of Science and Technology (HUST). To meet the clinical requirements, an energy degrader is essential in the beamline to modulate the fixed beam energy extracted from the cyclotron. Because of the multiple Coulomb scattering in the degrader, the beam emittance and the energy spread will be considerably increased during the energy degradation process. Therefore, a set of collimators is designed to restrict the increase in beam emittance after the energy degradation. The energy spread will be reduced in the following beam line which is not discussed in this paper. In this paper, the design considerations of an energy degrader and collimators are introduced, and the properties of the degrader material, degrader structure and the initial beam parameters are discussed using the Geant4 Monte-Carlo toolkit, with the main purpose of improving the overall performance of the degrader by multiple parameter optimization.

Complexity metric based on fraction of penumbra dose - initial study

NASA Astrophysics Data System (ADS)

Bäck, A.; Nordström, F.; Gustafsson, M.; Götstedt, J.; Karlsson Hauer, A.

2017-05-01

Volumetric modulated arc therapy improve radiotherapy outcome for many patients compared to conventional three dimensional conformal radiotherapy but require a more extensive, most often measurement based, quality assurance. Multi leaf collimator (MLC) aperture-based complexity metrics have been suggested to be used to distinguish complex treatment plans unsuitable for treatment without time consuming measurements. This study introduce a spatially resolved complexity score that correlate to the fraction of penumbra dose and will give information on the spatial distribution and the clinical relevance of the calculated complexity. The complexity metric is described and an initial study on the correlation between the complexity score and the difference between measured and calculated dose for 30 MLC openings is presented. The result of an analysis of the complexity scores were found to correlate to differences between measurements and calculations with a Pearson’s r-value of 0.97.

Planning and delivery of four-dimensional radiation therapy with multileaf collimators

NASA Astrophysics Data System (ADS)

McMahon, Ryan L.

This study is an investigation of the application of multileaf collimators (MLCs) to the treatment of moving anatomy with external beam radiation therapy. First, a method for delivering intensity modulated radiation therapy (IMRT) to moving tumors is presented. This method uses an MLC control algorithm that calculates appropriate MLC leaf speeds in response to feedback from real-time imaging. The algorithm does not require a priori knowledge of a tumor's motion, and is based on the concept of self-correcting DMLC leaf trajectories . This gives the algorithm the distinct advantage of allowing for correction of DMLC delivery errors without interrupting delivery. The algorithm is first tested for the case of one-dimensional (1D) rigid tumor motion in the beam's eye view (BEV). For this type of motion, it is shown that the real-time tracking algorithm results in more accurate deliveries, with respect to delivered intensity, than those which ignore motion altogether. This is followed by an appropriate extension of the algorithm to two-dimensional (2D) rigid motion in the BEV. For this type of motion, it is shown that the 2D real-time tracking algorithm results in improved accuracy (in the delivered intensity) in comparison to deliveries which ignore tumor motion or only account for tumor motion which is aligned with MLC leaf travel. Finally, a method is presented for designing DMLC leaf trajectories which deliver a specified intensity over a moving tumor without overexposing critical structures which exhibit motion patterns that differ from that of the tumor. In addition to avoiding overexposure of critical organs, the method can, in the case shown, produce deliveries that are superior to anything achievable using stationary anatomy. In this regard, the method represents a systematic way to include anatomical motion as a degree of freedom in the optimization of IMRT while producing treatment plans that are deliverable with currently available technology. These results, combined with those related to the real-time MLC tracking algorithm, show that an MLC is a promising tool to investigate for the delivery of four-dimensional radiation therapy.

Real-time dose computation: GPU-accelerated source modeling and superposition/convolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacques, Robert; Wong, John; Taylor, Russell

Purpose: To accelerate dose calculation to interactive rates using highly parallel graphics processing units (GPUs). Methods: The authors have extended their prior work in GPU-accelerated superposition/convolution with a modern dual-source model and have enhanced performance. The primary source algorithm supports both focused leaf ends and asymmetric rounded leaf ends. The extra-focal algorithm uses a discretized, isotropic area source and models multileaf collimator leaf height effects. The spectral and attenuation effects of static beam modifiers were integrated into each source's spectral function. The authors introduce the concepts of arc superposition and delta superposition. Arc superposition utilizes separate angular sampling for themore » total energy released per unit mass (TERMA) and superposition computations to increase accuracy and performance. Delta superposition allows single beamlet changes to be computed efficiently. The authors extended their concept of multi-resolution superposition to include kernel tilting. Multi-resolution superposition approximates solid angle ray-tracing, improving performance and scalability with a minor loss in accuracy. Superposition/convolution was implemented using the inverse cumulative-cumulative kernel and exact radiological path ray-tracing. The accuracy analyses were performed using multiple kernel ray samplings, both with and without kernel tilting and multi-resolution superposition. Results: Source model performance was <9 ms (data dependent) for a high resolution (400{sup 2}) field using an NVIDIA (Santa Clara, CA) GeForce GTX 280. Computation of the physically correct multispectral TERMA attenuation was improved by a material centric approach, which increased performance by over 80%. Superposition performance was improved by {approx}24% to 0.058 and 0.94 s for 64{sup 3} and 128{sup 3} water phantoms; a speed-up of 101-144x over the highly optimized Pinnacle{sup 3} (Philips, Madison, WI) implementation. Pinnacle{sup 3} times were 8.3 and 94 s, respectively, on an AMD (Sunnyvale, CA) Opteron 254 (two cores, 2.8 GHz). Conclusions: The authors have completed a comprehensive, GPU-accelerated dose engine in order to provide a substantial performance gain over CPU based implementations. Real-time dose computation is feasible with the accuracy levels of the superposition/convolution algorithm.« less

Heavy-ion conformal irradiation in the shallow-seated tumor therapy terminal at HIRFL.

PubMed

Li, Qiang; Dai, Zhongying; Yan, Zheng; Jin, Xiaodong; Liu, Xinguo; Xiao, Guoqing

2007-11-01

Basic research related to heavy-ion cancer therapy has been done at the Institute of Modern Physics (IMP), Chinese Academy of Sciences since 1995. Now a plan of clinical trial with heavy ions has been launched at IMP. First, superficially placed tumor treatment with heavy ions is expected in the therapy terminal at the Heavy Ion Research Facility in Lanzhou (HIRFL), where carbon ion beams with energy up to 100 MeV/u can be supplied. The shallow-seated tumor therapy terminal at HIRFL is equipped with a passive beam delivery system including two orthogonal dipole magnets, which continuously scan pencil beams laterally and generate a broad and uniform irradiation field, a motor-driven energy degrader and a multi-leaf collimator. Two different types of range modulator, ripple filter and ridge filter with which Guassian-shaped physical dose and uniform biological effective dose Bragg peaks can be shaped for therapeutic ion beams respectively, have been designed and manufactured. Therefore, two-dimensional and three-dimensional conformal irradiations to tumors can be performed with the passive beam delivery system at the earlier therapy terminal. Both the conformal irradiation methods have been verified experimentally and carbon-ion conformal irradiations to patients with superficially placed tumors have been carried out at HIRFL since November 2006.

Wireless Synchronization of a Multi-Pinhole Small Animal SPECT Collimation Device With a Clinical Scanner

NASA Astrophysics Data System (ADS)

DiFilippo, Frank P.; Patel, Sagar

2009-06-01

A multi-pinhole collimation device for small animal single photon emission computed tomography (SPECT) uses the gamma camera detectors of a standard clinical SPECT scanner. The collimator and animal bed move independently of the detectors, and therefore their motions must be synchronized. One approach is manual triggering of the SPECT acquisition simultaneously with a programmed motion sequence for the device. However, some data blurring and loss of image quality result, and true electronic synchronization is preferred. An off-the-shelf digital gyroscope with integrated Bluetooth interface provides a wireless solution to device synchronization. The sensor attaches to the SPECT gantry and reports its rotational speed to a notebook computer controlling the device. Software processes the rotation data in real-time, averaging the signal and issuing triggers while compensating for baseline drift. Motion commands are sent to the collimation device with minimal delay, within approximately 0.5 second of the start of SPECT gantry rotation. Test scans of a point source demonstrate an increase in true counts and a reduction in background counts compared to manual synchronization. The wireless rotation sensor provides robust synchronization of the collimation device with the clinical SPECT scanner and enhances image quality.

Two normal incidence collimators designed for the calibration of the extreme ultraviolet explorer

NASA Technical Reports Server (NTRS)

Jelinsky, Sharon R.; Welsh, Barry; Jelinsky, Patrick; Spiller, Eberhard

1988-01-01

Two Dall-Kirkham, normal incidence collimators have been designed to calibrate the imaging properties of the Extreme Ultraviolet Explorer over the wavelength region from 114 to 2000 A. The mirrors of the short-wavelength, 25-cm diameter collimator are superpolished Zerodur which have been multilayer coated for optimal reflectivity at 114 A. The mirrors of the long-wavelength, 41.25-cm diameter collimator are gold coated Zerodur for high reflectance above 300 A. The design, performance, and future use of these collimators in the extreme ultra-violet is discussed.

Brushed permanent magnet DC MLC motor operation in an external magnetic field.

PubMed

Yun, J; St Aubin, J; Rathee, S; Fallone, B G

2010-05-01

Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450 +/- 10 G. The carriage motor tolerated up to 2000 +/- 10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600 +/- 10 G. The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required.

[Evaluation of Dose Reduction of the Active Collimator in Multi Detector Row CT].

PubMed

Ueno, Hiroyuki; Matsubara, Kosuke

The purpose of this study was to evaluate the performance of active collimator by changing acquisition parameters and obtaining dose profiles in z-axis direction. Dose profiles along z-axis were obtained using XRQA2 Gafchromic film. As a result, the active collimator reduced overranging about 55% compared to that without the active collimator. In addition, by changing the combination of X-ray beam width (32 mm, 40 mm), pitch factor (1.4, 0.6), and the X-ray tube rotation time (0.5 s/rot, 1.0 s/rot), the overranging changed from 19.4 to 34.9 mm. Although the active collimator is effective for reducing overranging, it is necessary to adjust acquisition parameters by taking the properties of the active collimator for acquisition parameters, especially setting beam width, into consideration.

Monte Carlo design of optimal wire mesh collimator for breast tumor imaging process

NASA Astrophysics Data System (ADS)

Saad, W. H. M.; Roslan, R. E.; Mahdi, M. A.; Choong, W.-S.; Saion, E.; Saripan, M. I.

2011-08-01

This paper presents the modeling of breast tumor imaging process using wire mesh collimator gamma camera. Previous studies showed that the wire mesh collimator has a potential to improve the sensitivity of the tumor detection. In this paper, we extend our research significantly, to find an optimal configuration of the wire mesh collimator specifically for semi-compressed breast tumor detection, by looking into four major factors: weight, sensitivity, spatial resolution and tumor contrast. The numbers of layers in the wire mesh collimator is varied to optimize the collimator design. The statistical variations of the results are studied by simulating multiple realizations for each experiment using different starting random numbers. All the simulation environments are modeled using Monte Carlo N-Particle Code (MCNP). The quality of the detection is measured directly by comparing the sensitivity, spatial resolution and tumor contrast of the images produced by the wire mesh collimator and benchmarked that with a standard multihole collimator. The proposed optimal configuration of the wire mesh collimator is optimized by selecting the number of layers in wire mesh collimator, where the tumor contrast shows a relatively comparable value to the multihole collimator, when it is tested with uniformly semi-compressed breast phantom. The wire mesh collimator showed higher number of sensitivity because of its loose arrangement while the spatial resolution of wire mesh collimator does not shows much different compared to the multihole collimator. With a relatively good tumor contrast and spatial resolution, and increased in sensitivity, a new proposed wire mesh collimator gives a significant improvement in the wire mesh collimator design for breast cancer imaging process. The proposed collimator configuration is reduced to 44.09% from the total multihole collimator weight.

Randomized algorithms for high quality treatment planning in volumetric modulated arc therapy

NASA Astrophysics Data System (ADS)

Yang, Yu; Dong, Bin; Wen, Zaiwen

2017-02-01

In recent years, volumetric modulated arc therapy (VMAT) has been becoming a more and more important radiation technique widely used in clinical application for cancer treatment. One of the key problems in VMAT is treatment plan optimization, which is complicated due to the constraints imposed by the involved equipments. In this paper, we consider a model with four major constraints: the bound on the beam intensity, an upper bound on the rate of the change of the beam intensity, the moving speed of leaves of the multi-leaf collimator (MLC) and its directional-convexity. We solve the model by a two-stage algorithm: performing minimization with respect to the shapes of the aperture and the beam intensities alternatively. Specifically, the shapes of the aperture are obtained by a greedy algorithm whose performance is enhanced by random sampling in the leaf pairs with a decremental rate. The beam intensity is optimized using a gradient projection method with non-monotonic line search. We further improve the proposed algorithm by an incremental random importance sampling of the voxels to reduce the computational cost of the energy functional. Numerical simulations on two clinical cancer date sets demonstrate that our method is highly competitive to the state-of-the-art algorithms in terms of both computational time and quality of treatment planning.

Characteristics and performance of the first commercial multileaf collimator for a robotic radiosurgery system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fürweger, Christoph, E-mail: christoph.fuerweger@cyber-knife.net; Prins, Paulette; Coskan, Harun

Purpose: The “InCise™ multileaf-collimator (MLC)” is the first commercial MLC to be mounted on a robotic SRS/SBRT platform (CyberKnife). The authors assessed characteristics and performance of this novel device in a preclinical five months test period. Methods: Commissioning beam data were acquired with unshielded diodes. EBT3 radiochromic films were employed for measurement of transmission, leaf/bank position accuracy (garden fence) before and after exercising the MLC, for end-to-end testing and further characterization of the beam. The robot workspace with MLC was assessed analytically by transformation to an Euler geometry (“plane,” “gantry,” and “collimator” angles) and by measuring pointing accuracy at eachmore » node. Stability over time was evaluated in picket fence and adapted Winston–Lutz tests (AQA). Results: Beam penumbrae (80%–20%, with 100% = 2 × dose at inflection point for field sizes ≥ 50 × 50 mm{sup 2}) were 2.2–3.7 mm for square fields in reference condition (source-axis-distance 800 mm, depth 15 mm) and depended on field size and off-axis position. Transmission and leakage did not exceed 0.5%. Accessible clinical workspace with MLC covered non-coplanar gantry angles of [−113°; +112°] and collimator angles of [−100°; +107°], with an average robot pointing accuracy of 0.12 ± 0.09 mm. For vertical beams, garden fence tests exhibited an average leaf positioning error of ≤0.2 mm, which increased by 0.25 and 0.30 mm (banks X1 and X2) with leaves traveling parallel to gravity. After execution of a leaf motion stress routine, garden fence tests showed slightly increased jaggedness and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.38 ± 0.05 mm in nine end-to-end tests. Picket fence and AQA tests displayed stable results over the test period. Conclusions: The InCise™ MLC for CyberKnife showed high accuracy and adequate characteristics for SRS/SBRT applications. MLC performance after exercise demands specific quality assurance measures.« less

Methodology Plan for Minimum Resolvable Temperature Difference (MRTD) Testing of Aircraft Installed Sensors

DTIC Science & Technology

2011-03-23

sensors (e.g., sensor fusion) or use different detector materials to increase spectral bands into the Near IR (NIR). 3. Holst2provides an...a. Detector type: Multi-element MCT SPRITE b. Wavelength: Long wave, 8-12 um c. Cooling system: Integrated Sterling cooler d. Cooldown...A-1 B. COLLIMATOR SYSTEM DESIGN AND EO/ IR TOPICS ................ B-1 C. ATTC FACILITIES AND INSTRUMENTATION

Micro-Slit Collimators for X-Ray/Gamma-Ray Imaging

NASA Technical Reports Server (NTRS)

Appleby, Michael; Fraser, Iain; Klinger, Jill

2011-01-01

A hybrid photochemical-machining process is coupled with precision stack lamination to allow for the fabrication of multiple ultra-high-resolution grids on a single array substrate. In addition, special fixturing and etching techniques have been developed that allow higher-resolution multi-grid collimators to be fabricated. Building on past work of developing a manufacturing technique for fabricating multi-grid, high-resolution coating modulation collimators for arcsecond and subarcsecond x-ray and gamma-ray imaging, the current work reduces the grid pitch by almost a factor of two, down to 22 microns. Additionally, a process was developed for reducing thin, high-Z (tungsten or molybdenum) from the thinnest commercially available foil (25 microns thick) down to approximately equal to 10 microns thick using precisely controlled chemical etching

Generating Long Scale-Length Plasma Jets Embedded in a Uniform, Multi-Tesla Magnetic-Field

NASA Astrophysics Data System (ADS)

Manuel, Mario; Kuranz, Carolyn; Rasmus, Alex; Klein, Sallee; Fein, Jeff; Belancourt, Patrick; Drake, R. P.; Pollock, Brad; Hazi, Andrew; Park, Jaebum; Williams, Jackson; Chen, Hui

2013-10-01

Collimated plasma jets emerge in many classes of astrophysical objects and are of great interest to explore in the laboratory. In many cases, these astrophysical jets exist within a background magnetic field where the magnetic pressure approaches the plasma pressure. Recent experiments performed at the Jupiter Laser Facility utilized a custom-designed solenoid to generate the multi-tesla fields necessary to achieve proper magnetization of the plasma. Time-gated interferometry, Schlieren imaging, and proton radiography were used to characterize jet evolution and collimation under varying degrees of magnetization. Experimental results will be presented and discussed. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, by the National Laser User Facility Program, grant number DE-NA0000850, by the Predictive Sciences Academic Alliances Program in NNSA-ASC, grant number DEFC52-08NA28616, and by NASA through Einstein Postdoctoral Fellowship grant number PF3-140111 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060.

Impact of Multileaf Collimator Configuration Parameters on the Dosimetric Accuracy of 6-MV Intensity-Modulated Radiation Therapy Treatment Plans.

PubMed

Petersen, Nick; Perrin, David; Newhauser, Wayne; Zhang, Rui

2017-01-01

The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle 3 , Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being -0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.

Thermal analysis and cooling structure design of the primary collimator in CSNS/RCS

NASA Astrophysics Data System (ADS)

Zou, Yi-Qing; Wang, Na; Kang, Ling; Qu, Hua-Min; He, Zhe-Xi; Yu, Jie-Bing

2013-05-01

The rapid cycling synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is a high intensity proton ring with beam power of 100 kW. In order to control the residual activation to meet the requirements of hands-on maintenance, a two-stage collimation system has been designed for the RCS. The collimation system consists of one primary collimator made of thin metal to scatter the beam and four secondary collimators as absorbers. Thermal analysis is an important aspect in evaluating the reliability of the collimation system. The calculation of the temperature distribution and thermal stress of the primary collimator with different materials is carried out by using ANSYS code. In order to control the temperature rise and thermal stress of the primary collimator to a reasonable level, an air cooling structure is intended to be used. The mechanical design of the cooling structure is presented, and the cooling efficiency with different chin numbers and wind velocity is also analyzed. Finally, the fatigue lifetime of the collimator under thermal shocks is estimated.

Design consideration of a multipinhole collimator with septa for ultra high-resolution silicon drift detector modules

NASA Astrophysics Data System (ADS)

Min, Byung Jun; Choi, Yong; Lee, Nam-Yong; Lee, Kisung; Ahn, Young Bok; Joung, Jinhun

2009-07-01

The aim of this study was to design a multipinhole (MP) collimator with lead vertical septa coupled to a high-resolution detector module containing silicon drift detectors (SDDs) with an intrinsic resolution approaching the sub-millimeter level. Monte Carlo simulations were performed to determine pinhole parameters such as pinhole diameter, focal length, and number of pinholes. Effects of parallax error and collimator penetration were investigated for the new MP collimator design. The MP detector module was evaluated using reconstructed images of resolution and mathematical cardiac torso (MCAT) phantoms. In addition, the reduced angular sampling effect was investigated over 180°. The images were reconstructed using dedicated maximum likelihood expectation maximization (MLEM) algorithm. An MP collimator with 81-pinhole was designed with a 2-mm-diameter pinhole and a focal length of 40 mm . Planar sensitivity and resolution obtained using the devised MP collimator were 3.9 cps/μCi and 6 mm full-width at half-maximum (FWHM) at a 10 cm distance. The parallax error and penetration ratio were significantly improved using the proposed MP collimation design. The simulation results demonstrated that the proposed MP detector provided enlarged imaging field of view (FOV) and improved the angular sampling effect in resolution and MCAT phantom studies. Moreover, the novel design enables tomography images by simultaneously obtaining eight projections with eight-detector modules located along the 180° orbit surrounding a patient, which allows designing of a stationary cardiac SPECT. In conclusion, the MP collimator with lead vertical septa was designed to have comparable system resolution and sensitivity to those of the low-energy high-resolution (LEHR) collimator per detector. The system sensitivity with an eight-detector configuration would be four times higher than that with a standard dual-detector cardiac SPECT.

MuSICa at GRIS: a prototype image slicer for EST at GREGOR

NASA Astrophysics Data System (ADS)

Calcines, A.; Collados, M.; López, R. L.

2013-05-01

This communication presents a prototype image slicer for the 4-m European Solar Telescope (EST) designed for the spectrograph of the 1.5-m GREGOR solar telescope (GRIS). The design of this integral field unit has been called MuSICa (Multi-Slit Image slicer based on collimator-Camera). It is a telecentric system developed specifically for the integral field, high resolution spectrograph of EST and presents multi-slit capability, reorganizing a bidimensional field of view of 80 arcsec^{2} into 8 slits, each one of them with 200 arcsec length × 0.05 arcsec width. It minimizes the number of optical components needed to fulfil this multi-slit capability, three arrays of mirrors: slicer, collimator and camera mirror arrays (the first one flat and the other two spherical). The symmetry of the layout makes it possible to overlap the pupil images associated to each part of the sliced entrance field of view. A mask with only one circular aperture is placed at the pupil position. This symmetric characteristic offers some advantages: facilitates the manufacturing process, the alignment and reduces the costs. In addition, it is compatible with two modes of operation: spectroscopic and spectro-polarimetric, offering a great versatility. The optical quality of the system is diffraction-limited. The prototype will improve the performances of GRIS at GREGOR and is part of the feasibility study of the integral field unit for the spectrographs of EST. Although MuSICa has been designed as a solar image slicer, its concept can also be applied to night-time astronomical instruments (Collados et al. 2010, Proc. SPIE, Vol. 7733, 77330H; Collados et al. 2012, AN, 333, 901; Calcines et al. 2010, Proc. SPIE, Vol. 7735, 77351X)

Design and Performance of a Triple Source Air Mass Zero Solar Simulator

NASA Technical Reports Server (NTRS)

Jenkins, Phillip; Scheiman, David; Snyder, David

2005-01-01

Simulating the sun in a laboratory for the purpose of measuring solar cells has long been a challenge for engineers and scientists. Multi-junction cells demand higher fidelity of a solar simulator than do single junction cells, due to a need for close spectral matching as well as AM0 intensity. A GaInP/GaAs/Ge solar cell for example, requires spectral matching in three distinct spectral bands (figure 1). A commercial single source high-pressure xenon arc solar simulator such as the Spectrolab X-25 at NASA Glenn Research Center, can match the top two junctions of a GaInP/GaAs/Ge cell to within 1.3% mismatch, with the GaAs cell receiving slightly more current than required. The Ge bottom cell however, is mismatched +8.8%. Multi source simulators are designed to match the current for all junctions but typically have small illuminated areas, less uniformity and less beam collimation compared to an X-25 simulator. It was our intent when designing a multi source simulator to preserve as many aspects of the X-25 while adding multi-source capability.

Neutron collimator design of neutron radiography based on the BNCT facility

NASA Astrophysics Data System (ADS)

Yang, Xiao-Peng; Yu, Bo-Xiang; Li, Yi-Guo; Peng, Dan; Lu, Jin; Zhang, Gao-Long; Zhao, Hang; Zhang, Ai-Wu; Li, Chun-Yang; Liu, Wan-Jin; Hu, Tao; Lü, Jun-Guang

2014-02-01

For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0×106 n/cm2/s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.

SU-F-T-481: Physics Evaluation of a Newly Released InCise™ Multileaf Collimator for CyberKnife M6™ System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, L; Chin, E; Lo, A

2016-06-15

Purpose: This work reports the results of the physics evaluation of a newly released InCise™2 Multileaf Collimator (MLC) installed in our institution. Methods: Beam property data was measured with unshielded diode and EBT2 films. The measurements included MLC leaf transmission, beam profiles, output factors and tissue-phantom ratios. MLC performance was evaluated for one month after commissioning. Weekly Garden Fence tests were performed for leaf / bank positioning in standard (A/P) and clinically relevant non-standard positions, before and after MLC driving exercises of 10+ minutes. Daily Picket Fence test and AQA test, End-to-End tests and dosimetric quality assurance were performed tomore » evaluate the overall system performance. Results: All measurements including beam energy, flatness and symmetry, were within manufacture specifications. Leaf transmission was 0.4% <0.5% specification. The values of output factors ranged from 0.825 (7.6 mm × 7.5 mm) to 1.026 (115.0 mm × 100.1 mm). Average beam penumbra at 10 cm depth ranged from 2.7mm/2.7mm(7.6 mm × 7.5 mm) to 6.0 mm/6.2mm(84.6 mm × 84.7 mm). Slight penumbra difference (<10% from average penumbra for fields >20 mm) was observed in the direction perpendicular to leaf motion due to the tilting of the leaf housing. Mean leaf position offsets was −0.08±0.07mm and −0.13 ± 0.08 for X1 and X2 leaf banks in 13 Garden Fence tests. No significant difference on average leaf positioning offsets was observed between different leaf orientations and before/after MLC driving exercises. Six End-to-End tests showed 0.43±0.23mm overall targeting accuracy. Picket-Fence and AQA showed stable performance of MLC during the test period. Dosimetric point dose measurements for test cases agreed with calculation within 3%. All film measurements on relative dose had Gamma (2%, 2mm) passing rate of >95%. Conclusion: The Incise™2 MLC for CyberKnife M6™ was proven to be accurate and reliable, and it is currently in clinical use. Stanford was one of the physics evaluation sites for the newly released InCise 2 MLC for Accuray Inc.« less

Design of optimal collimation for dedicated molecular breast imaging systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weinmann, Amanda L.; Hruska, Carrie B.; O'Connor, Michael K.

2009-03-15

Molecular breast imaging (MBI) is a functional imaging technique that uses specialized small field-of-view gamma cameras to detect the preferential uptake of a radiotracer in breast lesions. MBI has potential to be a useful adjunct method to screening mammography for the detection of occult breast cancer. However, a current limitation of MBI is the high radiation dose (a factor of 7-10 times that of screening mammography) associated with current technology. The purpose of this study was to optimize the gamma camera collimation with the aim of improving sensitivity while retaining adequate resolution for the detection of sub-10-mm lesions. Square-hole collimatorsmore » with holes matched to the pixilated cadmium zinc telluride detector elements of the MBI system were designed. Data from MBI patient studies and parameters of existing dual-head MBI systems were used to guide the range of desired collimator resolutions, source-to-collimator distances, pixel sizes, and collimator materials that were examined. General equations describing collimator performance for a conventional gamma camera were used in the design process along with several important adjustments to account for the specialized imaging geometry of the MBI system. Both theoretical calculations and a Monte Carlo model were used to measure the geometric efficiency (or sensitivity) and resolution of each designed collimator. Results showed that through optimal collimation, collimator sensitivity could be improved by factors of 1.5-3.2, while maintaining a collimator resolution of either {<=}5 or {<=}7.5 mm at a distance of 3 cm from the collimator face. These gains in collimator sensitivity permit an inversely proportional drop in the required dose to perform MBI.« less

A novel software and conceptual design of the hardware platform for intensity modulated radiation therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Dan; Ruan, Dan; O’Connor, Daniel

Purpose: To deliver high quality intensity modulated radiotherapy (IMRT) using a novel generalized sparse orthogonal collimators (SOCs), the authors introduce a novel direct aperture optimization (DAO) approach based on discrete rectangular representation. Methods: A total of seven patients—two glioblastoma multiforme, three head & neck (including one with three prescription doses), and two lung—were included. 20 noncoplanar beams were selected using a column generation and pricing optimization method. The SOC is a generalized conventional orthogonal collimators with N leaves in each collimator bank, where N = 1, 2, or 4. SOC degenerates to conventional jaws when N = 1. For SOC-basedmore » IMRT, rectangular aperture optimization (RAO) was performed to optimize the fluence maps using rectangular representation, producing fluence maps that can be directly converted into a set of deliverable rectangular apertures. In order to optimize the dose distribution and minimize the number of apertures used, the overall objective was formulated to incorporate an L2 penalty reflecting the difference between the prescription and the projected doses, and an L1 sparsity regularization term to encourage a low number of nonzero rectangular basis coefficients. The optimization problem was solved using the Chambolle–Pock algorithm, a first-order primal–dual algorithm. Performance of RAO was compared to conventional two-step IMRT optimization including fluence map optimization and direct stratification for multileaf collimator (MLC) segmentation (DMS) using the same number of segments. For the RAO plans, segment travel time for SOC delivery was evaluated for the N = 1, N = 2, and N = 4 SOC designs to characterize the improvement in delivery efficiency as a function of N. Results: Comparable PTV dose homogeneity and coverage were observed between the RAO and the DMS plans. The RAO plans were slightly superior to the DMS plans in sparing critical structures. On average, the maximum and mean critical organ doses were reduced by 1.94% and 1.44% of the prescription dose. The average number of delivery segments was 12.68 segments per beam for both the RAO and DMS plans. The N = 2 and N = 4 SOC designs were, on average, 1.56 and 1.80 times more efficient than the N = 1 SOC design to deliver. The mean aperture size produced by the RAO plans was 3.9 times larger than that of the DMS plans. Conclusions: The DAO and dose domain optimization approach enabled high quality IMRT plans using a low-complexity collimator setup. The dosimetric quality is comparable or slightly superior to conventional MLC-based IMRT plans using the same number of delivery segments. The SOC IMRT delivery efficiency can be significantly improved by increasing the leaf numbers, but the number is still significantly lower than the number of leaves in a typical MLC.« less

A novel software and conceptual design of the hardware platform for intensity modulated radiation therapy.

PubMed

Nguyen, Dan; Ruan, Dan; O'Connor, Daniel; Woods, Kaley; Low, Daniel A; Boucher, Salime; Sheng, Ke

2016-02-01

To deliver high quality intensity modulated radiotherapy (IMRT) using a novel generalized sparse orthogonal collimators (SOCs), the authors introduce a novel direct aperture optimization (DAO) approach based on discrete rectangular representation. A total of seven patients-two glioblastoma multiforme, three head & neck (including one with three prescription doses), and two lung-were included. 20 noncoplanar beams were selected using a column generation and pricing optimization method. The SOC is a generalized conventional orthogonal collimators with N leaves in each collimator bank, where N = 1, 2, or 4. SOC degenerates to conventional jaws when N = 1. For SOC-based IMRT, rectangular aperture optimization (RAO) was performed to optimize the fluence maps using rectangular representation, producing fluence maps that can be directly converted into a set of deliverable rectangular apertures. In order to optimize the dose distribution and minimize the number of apertures used, the overall objective was formulated to incorporate an L2 penalty reflecting the difference between the prescription and the projected doses, and an L1 sparsity regularization term to encourage a low number of nonzero rectangular basis coefficients. The optimization problem was solved using the Chambolle-Pock algorithm, a first-order primal-dual algorithm. Performance of RAO was compared to conventional two-step IMRT optimization including fluence map optimization and direct stratification for multileaf collimator (MLC) segmentation (DMS) using the same number of segments. For the RAO plans, segment travel time for SOC delivery was evaluated for the N = 1, N = 2, and N = 4 SOC designs to characterize the improvement in delivery efficiency as a function of N. Comparable PTV dose homogeneity and coverage were observed between the RAO and the DMS plans. The RAO plans were slightly superior to the DMS plans in sparing critical structures. On average, the maximum and mean critical organ doses were reduced by 1.94% and 1.44% of the prescription dose. The average number of delivery segments was 12.68 segments per beam for both the RAO and DMS plans. The N = 2 and N = 4 SOC designs were, on average, 1.56 and 1.80 times more efficient than the N = 1 SOC design to deliver. The mean aperture size produced by the RAO plans was 3.9 times larger than that of the DMS plans. The DAO and dose domain optimization approach enabled high quality IMRT plans using a low-complexity collimator setup. The dosimetric quality is comparable or slightly superior to conventional MLC-based IMRT plans using the same number of delivery segments. The SOC IMRT delivery efficiency can be significantly improved by increasing the leaf numbers, but the number is still significantly lower than the number of leaves in a typical MLC.

A four mirror anastigmat collimator design for optical payload calibration

NASA Astrophysics Data System (ADS)

Rolt, Stephen; Calcines, Ariadna; Lomanowski, Bart A.; Bramall, David G.

2016-07-01

We present here a four mirror anastigmatic optical collimator design intended for the calibration of an earth observation satellite instrument. Specifically, the collimator is to be applied to the ground based calibration of the Sentinel-4/UVN instrument. This imaging spectrometer instrument itself is expected to be deployed in 2019 in a geostationary orbit and will make spatially resolved spectroscopic measurements of atmospheric contaminants. The collimator is to be deployed during the ground based calibration only and does not form part of the instrument itself. The purpose of the collimator is to provide collimated light within the two instrument passbands in the UV-VIS (305 - 500 nm) and the NIR (750 - 775 nm). Moreover, that collimated light will be derived from a variety of slit like objects located at the input focal (object) plane of the collimator which is uniformly illuminated by a number of light sources. The collimator must relay these objects with exceptionally high fidelity. To this end, the wavefront error of the collimator should be less than 30 nm rms across the collimator field of view. This field is determined by the largest object which is a large rectangular slit, 4.4° x 0.25°. Other important considerations affecting the optical design are the requirements for input telecentricity and the size (85 mm) and location (2500 mm `back focal distance') of the exit pupil. The design of the instrument against these basic requirements is discussed in detail. In addition an analysis of the straylight and tolerancing is presented in detail.

Multi-channel automotive night vision system

NASA Astrophysics Data System (ADS)

Lu, Gang; Wang, Li-jun; Zhang, Yi

2013-09-01

A four-channel automotive night vision system is designed and developed .It is consist of the four active near-infrared cameras and an Mulit-channel image processing display unit,cameras were placed in the automobile front, left, right and rear of the system .The system uses near-infrared laser light source，the laser light beam is collimated, the light source contains a thermoelectric cooler (TEC),It can be synchronized with the camera focusing, also has an automatic light intensity adjustment, and thus can ensure the image quality. The principle of composition of the system is description in detail,on this basis, beam collimation,the LD driving and LD temperature control of near-infrared laser light source,four-channel image processing display are discussed.The system can be used in driver assistance, car BLIS, car parking assist system and car alarm system in day and night.

The first private-hospital based proton therapy center in Korea; status of the Proton Therapy Center at Samsung Medical Center.

PubMed

Chung, Kwangzoo; Han, Youngyih; Kim, Jinsung; Ahn, Sung Hwan; Ju, Sang Gyu; Jung, Sang Hoon; Chung, Yoonsun; Cho, Sungkoo; Jo, Kwanghyun; Shin, Eun Hyuk; Hong, Chae-Seon; Shin, Jung Suk; Park, Seyjoon; Kim, Dae-Hyun; Kim, Hye Young; Lee, Boram; Shibagaki, Gantaro; Nonaka, Hideki; Sasai, Kenzo; Koyabu, Yukio; Choi, Changhoon; Huh, Seung Jae; Ahn, Yong Chan; Pyo, Hong Ryull; Lim, Do Hoon; Park, Hee Chul; Park, Won; Oh, Dong Ryul; Noh, Jae Myung; Yu, Jeong Il; Song, Sanghyuk; Lee, Ji Eun; Lee, Bomi; Choi, Doo Ho

2015-12-01

The purpose of this report is to describe the proton therapy system at Samsung Medical Center (SMC-PTS) including the proton beam generator, irradiation system, patient positioning system, patient position verification system, respiratory gating system, and operating and safety control system, and review the current status of the SMC-PTS. The SMC-PTS has a cyclotron (230 MeV) and two treatment rooms: one treatment room is equipped with a multi-purpose nozzle and the other treatment room is equipped with a dedicated pencil beam scanning nozzle. The proton beam generator including the cyclotron and the energy selection system can lower the energy of protons down to 70 MeV from the maximum 230 MeV. The multi-purpose nozzle can deliver both wobbling proton beam and active scanning proton beam, and a multi-leaf collimator has been installed in the downstream of the nozzle. The dedicated scanning nozzle can deliver active scanning proton beam with a helium gas filled pipe minimizing unnecessary interactions with the air in the beam path. The equipment was provided by Sumitomo Heavy Industries Ltd., RayStation from RaySearch Laboratories AB is the selected treatment planning system, and data management will be handled by the MOSAIQ system from Elekta AB. The SMC-PTS located in Seoul, Korea, is scheduled to begin treating cancer patients in 2015.

SU-G-IeP4-04: DD-Neutron Source Collimation for Neutron Stimulated Emission Computed Tomography: A Monte Carlo Simulation Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fong, G; Kapadia, A

Purpose: To optimize collimation and shielding for a deuterium-deuterium (DD) neutron generator for an inexpensive and compact clinical neutron imaging system. The envisioned application is cancer diagnosis through Neutron Stimulated Emission Computed Tomography (NSECT). Methods: Collimator designs were tested with an isotropic 2.5 MeV neutron source through GEANT4 simulations. The collimator is a 52×52×52 cm{sup 3} polyethylene block coupled with a 1 cm lead sheet in sequence. Composite opening was modeled into the collimator to permit passage of neutrons. The opening varied in shape (cylindrical vs. tapered), size (1–5 cm source-side and target-side openings) and aperture placements (13–39 cm frommore » source-side). Spatial and energy distribution of neutrons and gammas were tracked from each collimator design. Parameters analyzed were primary beam width (FWHM), divergence, and efficiency (percent transmission) for different configurations of the collimator. Select resultant outputs were then used for simulated NSECT imaging of a virtual breast phantom containing a 2.5 cm diameter tumor to assess the effect of the collimator on spatial resolution, noise, and scan time. Finally, composite shielding enclosure made of polyethylene and lead was designed and evaluated to block 99.99% of neutron and gamma radiation generated in the system. Results: Analysis of primary beam indicated the beam-width is linear to the aperture size. Increasing source-side opening allowed at least 20% more neutron throughput for all designs relative to the cylindrical openings. Maximum throughput for all designs was 364% relative to cylindrical openings. Conclusion: The work indicates potential for collimating and shielding a DD neutron generator for use in a clinical NSECT system. The proposed collimator designs produced a well-defined collimated neutron beam that can be used to image samples of interest with millimeter resolution. Balance in output efficiency, noise reduction, and scan time should be considered to determine the optimal design for specific NSECT applications.« less

3D-printed focused collimator for intra-operative gamma-ray detection

NASA Astrophysics Data System (ADS)

Holdsworth, David W.; Nikolov, Hristo N.; Pollmann, Steven I.

2017-03-01

Recent developments in targeted radiopharmaceutical labels have increased the need for sensitive, real-time gamma detection during cancer surgery and biopsy. Additive manufacturing (3D printing) in metal has now made it possible to design and fabricate complex metal collimators for compact gamma probes. We describe the design and implementation of a 3D-printed focused collimator that allows for real-time detection of gamma radiation from within a small volume of interest, using a single-crystal large-area detector. The collimator was fabricated using laser melting of powdered stainless steel (316L), using a commercial 3D metal printer (AM125, Renishaw plc). The prototype collimator is 20 mm thick, with hexagonal close-packed holes designed to focus to a point 35 mm below the surface of the collimator face. Tests were carried out with a low-activity (<1 μCi) 241 Am source, using a conventional gamma-ray detector probe, incorporating a 2.5 cm diameter, 2.5 cm thick NaI crystal coupled to a photomultiplier. The measured full-width half maximum (FWHM) was less than 5.6 mm, and collimator detection efficiency was 44%. The ability to fabricate fine features in solid metal makes it possible to develop optimized designs for high-efficiency, focused gamma collimators for real-time intraoperative imaging applications.

Using the Wiener estimator to determine optimal imaging parameters in a synthetic-collimator SPECT system used for small animal imaging

NASA Astrophysics Data System (ADS)

Lin, Alexander; Johnson, Lindsay C.; Shokouhi, Sepideh; Peterson, Todd E.; Kupinski, Matthew A.

2015-03-01

In synthetic-collimator SPECT imaging, two detectors are placed at different distances behind a multi-pinhole aperture. This configuration allows for image detection at different magnifications and photon energies, resulting in higher overall sensitivity while maintaining high resolution. Image multiplexing the undesired overlapping between images due to photon origin uncertainty may occur in both detector planes and is often present in the second detector plane due to greater magnification. However, artifact-free image reconstruction is possible by combining data from both the front detector (little to no multiplexing) and the back detector (noticeable multiplexing). When the two detectors are used in tandem, spatial resolution is increased, allowing for a higher sensitivity-to-detector-area ratio. Due to variability in detector distances and pinhole spacings found in synthetic-collimator SPECT systems, a large parameter space must be examined to determine optimal imaging configurations. We chose to assess image quality based on the task of estimating activity in various regions of a mouse brain. Phantom objects were simulated using mouse brain data from the Magnetic Resonance Microimaging Neurological Atlas (MRM NeAt) and projected at different angles through models of a synthetic-collimator SPECT system, which was developed by collaborators at Vanderbilt University. Uptake in the different brain regions was modeled as being normally distributed about predetermined means and variances. We computed the performance of the Wiener estimator for the task of estimating activity in different regions of the mouse brain. Our results demonstrate the utility of the method for optimizing synthetic-collimator system design.

Collimated prompt gamma TOF measurements with multi-slit multi-detector configurations

NASA Astrophysics Data System (ADS)

Krimmer, J.; Chevallier, M.; Constanzo, J.; Dauvergne, D.; De Rydt, M.; Dedes, G.; Freud, N.; Henriquet, P.; La Tessa, C.; Létang, J. M.; Pleskač, R.; Pinto, M.; Ray, C.; Reithinger, V.; Richard, M. H.; Rinaldi, I.; Roellinghoff, F.; Schuy, C.; Testa, E.; Testa, M.

2015-01-01

Longitudinal prompt-gamma ray profiles have been measured with a multi-slit multi-detector configuration at a 75 MeV/u 13C beam and with a PMMA target. Selections in time-of-flight and energy have been applied in order to discriminate prompt-gamma rays produced in the target from background events. The ion ranges which have been extracted from each individual detector module agree amongst each other and are consistent with theoretical expectations. In a separate dedicated experiment with 200 MeV/u 12C ions the fraction of inter-detector scattering has been determined to be on the 10%-level via a combination of experimental results and simulations. At the same experiment different collimator configurations have been tested and the shielding properties of tungsten and lead for prompt-gamma rays have been measured.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y; Liu, B; Liang, B

Purpose: Current CyberKnife treatment planning system (TPS) provided two dose calculation algorithms: Ray-tracing and Monte Carlo. Ray-tracing algorithm is fast, but less accurate, and also can’t handle irregular fields since a multi-leaf collimator system was recently introduced to CyberKnife M6 system. Monte Carlo method has well-known accuracy, but the current version still takes a long time to finish dose calculations. The purpose of this paper is to develop a GPU-based fast C/S dose engine for CyberKnife system to achieve both accuracy and efficiency. Methods: The TERMA distribution from a poly-energetic source was calculated based on beam’s eye view coordinate system,more » which is GPU friendly and has linear complexity. The dose distribution was then computed by inversely collecting the energy depositions from all TERMA points along 192 collapsed-cone directions. EGSnrc user code was used to pre-calculate energy deposition kernels (EDKs) for a series of mono-energy photons The energy spectrum was reconstructed based on measured tissue maximum ratio (TMR) curve, the TERMA averaged cumulative kernels was then calculated. Beam hardening parameters and intensity profiles were optimized based on measurement data from CyberKnife system. Results: The difference between measured and calculated TMR are less than 1% for all collimators except in the build-up regions. The calculated profiles also showed good agreements with the measured doses within 1% except in the penumbra regions. The developed C/S dose engine was also used to evaluate four clinical CyberKnife treatment plans, the results showed a better dose calculation accuracy than Ray-tracing algorithm compared with Monte Carlo method for heterogeneous cases. For the dose calculation time, it takes about several seconds for one beam depends on collimator size and dose calculation grids. Conclusion: A GPU-based C/S dose engine has been developed for CyberKnife system, which was proven to be efficient and accurate for clinical purpose, and can be easily implemented in TPS.« less

SU-E-T-444: Gravity Effect On Maximum Leaf Speed in Dynamic IMRT Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olasolo, J; Pellejero, S; Gracia, M

Purpose: A leaf sequencing algorithm has been recently developed in our department. Our purpose is to utilize this algorithm to reduce treatment time by studying the feasibility of using several maximum leaf speeds depending on gantry angle and leaf thickness (0.5 or 1 cm at isocenter). To do so, the gravity effect on MLC performance has been examined by means of analysing the dynalog files. Methods: Leaf position errors has been ascertained according to gantry angle and leaf speed in MLC Millenium120 (Varian). In order to do this, the following test has been designed: all leaves move in synchrony, withmore » same speed and 1 cm gap between opposite leaves. This test is implemented for 18 different speeds: 0.25-0.5-0.75-1-1.25-1.5-1.75-2-2.1-2.2-2.3-2.4-2.5-2.6-2.7-2.8-2.9-3.0 cm/s and 8 gantry angles: 0-45-90-135-180-225-270-315. Collimator angle is 2 degrees in all cases since it is the most usual one in IMRT treatments in our department. Dynamic tolerance is 2 mm. Dynalogs files of 10 repetitions of the test are analysed with a Mathlab in-house developed software and RMS error and 95th percentiles are calculated. Varian recommends 2.5 cm/s as the maximum leaf speed for its segmentation algorithm. In our case, we accept this speed in the most restrictive situation: gantry angle 270 and 1 cm leaf thickness. Maximum speeds for the rest of the cases are calculated by keeping the difference between 95th percentile and dynamic tolerance. In this way, beam hold-off probability does not increase. Results: Maximum speeds every 45 degrees of gantry rotation have been calculated for both leaf thickness. These results are 2.9-2.9-2.9-2.9-2.7-2.6-2.6-2.7 cm/s for 0.5 cm leaf thickness and 2.7-2.7-2.7-2.7-2.6-2.5-2.5-2.6 cm/s for 1 cm leaf thickness. Conclusion: Gravity effect on MLC positioning has been studied. Maximum leaf speed according to leaf thickness and gantry angle have been calculated which reduces treatment time.« less

Modulation indices for volumetric modulated arc therapy.

PubMed

Park, Jong Min; Park, So-Yeon; Kim, Hyoungnyoun; Kim, Jin Ho; Carlson, Joel; Ye, Sung-Joon

2014-12-07

The aim of this study is to present a modulation index (MI) for volumetric modulated arc therapy (VMAT) based on the speed and acceleration analysis of modulating-parameters such as multi-leaf collimator (MLC) movements, gantry rotation and dose-rate, comprehensively. The performance of the presented MI (MIt) was evaluated with correlation analyses to the pre-treatment quality assurance (QA) results, differences in modulating-parameters between VMAT plans versus dynamic log files, and differences in dose-volumetric parameters between VMAT plans versus reconstructed plans using dynamic log files. For comparison, the same correlation analyses were performed for the previously suggested modulation complexity score (MCS(v)), leaf travel modulation complexity score (LTMCS) and MI by Li and Xing (MI Li&Xing). In the two-tailed unpaired parameter condition, p values were acquired. The Spearman's rho (r(s)) values of MIt, MCSv, LTMCS and MI Li&Xing to the local gamma passing rate with 2%/2 mm criterion were -0.658 (p < 0.001), 0.186 (p = 0.251), 0.312 (p = 0.05) and -0.455 (p = 0.003), respectively. The values of rs to the modulating-parameter (MLC positions) differences were 0.917, -0.635, -0.857 and 0.795, respectively (p < 0.001). For dose-volumetric parameters, MIt showed higher statistically significant correlations than the conventional MIs. The MIt showed good performance for the evaluation of the modulation-degree of VMAT plans.

Design and tolerance analysis of two null corrector designs for the Space Telescope fine guidance aspheric collimating mirror

NASA Technical Reports Server (NTRS)

Friedman, I.; Casas, R. E.

1982-01-01

The collimating mirror within the Fine Guidance Subsystem of the Space Telescope's Pointing Control System is aspherized in order to correct the pupil aberration. A null corrector is needed to test the collimating mirror in autocollimation. Triplet and doublet null corrector designs are subjected to tolerance sensitivity analyses, and the doublet design is chosen despite its more restricted tolerances because of its compactness and simplicity.

SU-E-T-195: Gantry Angle Dependency of MLC Leaf Position Error

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ju, S; Hong, C; Kim, M

Purpose: The aim of this study was to investigate the gantry angle dependency of the multileaf collimator (MLC) leaf position error. Methods: An automatic MLC quality assurance system (AutoMLCQA) was developed to evaluate the gantry angle dependency of the MLC leaf position error using an electronic portal imaging device (EPID). To eliminate the EPID position error due to gantry rotation, we designed a reference maker (RM) that could be inserted into the wedge mount. After setting up the EPID, a reference image was taken of the RM using an open field. Next, an EPID-based picket-fence test (PFT) was performed withoutmore » the RM. These procedures were repeated at every 45° intervals of the gantry angle. A total of eight reference images and PFT image sets were analyzed using in-house software. The average MLC leaf position error was calculated at five pickets (-10, -5, 0, 5, and 10 cm) in accordance with general PFT guidelines using in-house software. This test was carried out for four linear accelerators. Results: The average MLC leaf position errors were within the set criterion of <1 mm (actual errors ranged from -0.7 to 0.8 mm) for all gantry angles, but significant gantry angle dependency was observed in all machines. The error was smaller at a gantry angle of 0° but increased toward the positive direction with gantry angle increments in the clockwise direction. The error reached a maximum value at a gantry angle of 90° and then gradually decreased until 180°. In the counter-clockwise rotation of the gantry, the same pattern of error was observed but the error increased in the negative direction. Conclusion: The AutoMLCQA system was useful to evaluate the MLC leaf position error for various gantry angles without the EPID position error. The Gantry angle dependency should be considered during MLC leaf position error analysis.« less

SU-F-T-618: Evaluation of a Mono-Isocentric Treatment Planning Software for Stereotactic Radiosurgery of Multiple Brain Metastases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sham, E; Sattarivand, M; Mulroy, L

Purpose: To evaluate planning performance of an automated treatment planning software (BrainLAB; Elements) for stereotactic radiosurgery (SRS) of multiple brain metastases. Methods: Brainlab’s Multiple Metastases Elements (MME) uses single isocentric technique to treat up to 10 cranial planning target volumes (PTVs). The planning algorithm of the MME accounts for multiple PTVs overlapping with one another on the beam eyes view (BEV) and automatically selects a subset of all overlapping PTVs on each arc for sparing normal tissues in the brain. The algorithm also optimizes collimator angles, margins between multi-leaf collimators (MLCs) and PTVs, as well as monitor units (MUs) usingmore » minimization of conformity index (CI) for all targets. Planning performance was evaluated by comparing the MME-calculated treatment plan parameters with the same parameters calculated with the Volumetric Modulated Arc Therapy (VMAT) optimization on Varian’s Eclipse platform. Results: Figures 1 to 3 compare several treatment plan outcomes calculated between the MME and VMAT for 5 clinical multi-targets SRS patient plans. Prescribed target dose was volume-dependent and defined based on the RTOG recommendation. For a total number of 18 PTV’s, mean values for the CI, PITV, and GI were comparable between the MME and VMAT within one standard deviation (σ). However, MME-calculated MDPD was larger than the same VMAT-calculated parameter. While both techniques delivered similar maximum point doses to the critical cranial structures and total MU’s for the 5 patient plans, the MME required less treatment planning time by an order of magnitude compared to VMAT. Conclusion: The MME and VMAT produce similar plan qualities in terms of MUs, target dose conformation, and OAR dose sparing. While the selective use of PTVs for arc-optimization with the MME reduces significantly the total planning time in comparison to VMAT, the target dose homogeneity was also compromised due to its simplified inverse planning algorithm used.« less

Feasibility of using Geant4 Monte Carlo simulation for IMRT dose calculations for the Novalis Tx with a HD-120 multi-leaf collimator

NASA Astrophysics Data System (ADS)

Jung, Hyunuk; Shin, Jungsuk; Chung, Kwangzoo; Han, Youngyih; Kim, Jinsung; Choi, Doo Ho

2015-05-01

The aim of this study was to develop an independent dose verification system by using a Monte Carlo (MC) calculation method for intensity modulated radiation therapy (IMRT) conducted by using a Varian Novalis Tx (Varian Medical Systems, Palo Alto, CA, USA) equipped with a highdefinition multi-leaf collimator (HD-120 MLC). The Geant4 framework was used to implement a dose calculation system that accurately predicted the delivered dose. For this purpose, the Novalis Tx Linac head was modeled according to the specifications acquired from the manufacturer. Subsequently, MC simulations were performed by varying the mean energy, energy spread, and electron spot radius to determine optimum values of irradiation with 6-MV X-ray beams by using the Novalis Tx system. Computed percentage depth dose curves (PDDs) and lateral profiles were compared to the measurements obtained by using an ionization chamber (CC13). To validate the IMRT simulation by using the MC model we developed, we calculated a simple IMRT field and compared the result with the EBT3 film measurements in a water-equivalent solid phantom. Clinical cases, such as prostate cancer treatment plans, were then selected, and MC simulations were performed. The accuracy of the simulation was assessed against the EBT3 film measurements by using a gamma-index criterion. The optimal MC model parameters to specify the beam characteristics were a 6.8-MeV mean energy, a 0.5-MeV energy spread, and a 3-mm electron radius. The accuracy of these parameters was determined by comparison of MC simulations with measurements. The PDDs and the lateral profiles of the MC simulation deviated from the measurements by 1% and 2%, respectively, on average. The computed simple MLC fields agreed with the EBT3 measurements with a 95% passing rate with 3%/3-mm gamma-index criterion. Additionally, in applying our model to clinical IMRT plans, we found that the MC calculations and the EBT3 measurements agreed well with a passing rate of greater than 95% on average with a 3%/3-mm gamma-index criterion. In summary, the Novalis Tx Linac head equipped with a HD-120 MLC was successfully modeled by using a Geant4 platform, and the accuracy of the Geant4 platform was successfully validated by comparisons with measurements. The MC model we have developed can be a useful tool for pretreatment quality assurance of IMRT plans and for commissioning of radiotherapy treatment planning.

Normal values and standardization of parameters in nuclear cardiology: Japanese Society of Nuclear Medicine working group database.

PubMed

Nakajima, Kenichi; Matsumoto, Naoya; Kasai, Tokuo; Matsuo, Shinro; Kiso, Keisuke; Okuda, Koichi

2016-04-01

As a 2-year project of the Japanese Society of Nuclear Medicine working group activity, normal myocardial imaging databases were accumulated and summarized. Stress-rest with gated and non-gated image sets were accumulated for myocardial perfusion imaging and could be used for perfusion defect scoring and normal left ventricular (LV) function analysis. For single-photon emission computed tomography (SPECT) with multi-focal collimator design, databases of supine and prone positions and computed tomography (CT)-based attenuation correction were created. The CT-based correction provided similar perfusion patterns between genders. In phase analysis of gated myocardial perfusion SPECT, a new approach for analyzing dyssynchrony, normal ranges of parameters for phase bandwidth, standard deviation and entropy were determined in four software programs. Although the results were not interchangeable, dependency on gender, ejection fraction and volumes were common characteristics of these parameters. Standardization of (123)I-MIBG sympathetic imaging was performed regarding heart-to-mediastinum ratio (HMR) using a calibration phantom method. The HMRs from any collimator types could be converted to the value with medium-energy comparable collimators. Appropriate quantification based on common normal databases and standard technology could play a pivotal role for clinical practice and researches.

Beam Loss Simulation and Collimator System Configurations for the Advanced Photon Source Upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, A.; Borland, M.

The proposed multi-bend achromat lattice for the Advanced Photon Source upgrade (APS-U) has a design emittance of less than 70 pm. The Touschek loss rate is high: compared with the current APS ring, which has an average beam lifetime ~ 10 h, the simulated beam lifetime for APS-U is only ~2 h when operated in the high flux mode (I=200 mA in 48 bunches). An additional consequence of the short lifetime is that injection must be more frequent, which provides another potential source of particle loss. In order to provide information for the radiation shielding system evaluation and to avoidmore » particle loss in sensitive locations around the ring (for example, insertion device straight sections), simulations of the detailed beam loss distribution have been performed. Several possible collimation configurations have been simulated and compared.« less

Research Advances on Radiation Transfer Modeling and Inversion for Multi-Scale Land Surface Remote Sensing

NASA Astrophysics Data System (ADS)

Liu, Q.

2011-09-01

At first, research advances on radiation transfer modeling on multi-scale remote sensing data are presented: after a general overview of remote sensing radiation transfer modeling, several recent research advances are presented, including leaf spectrum model (dPROS-PECT), vegetation canopy BRDF models, directional thermal infrared emission models(TRGM, SLEC), rugged mountains area radiation models, and kernel driven models etc. Then, new methodologies on land surface parameters inversion based on multi-source remote sensing data are proposed. The land surface Albedo, leaf area index, temperature/emissivity, and surface net radiation etc. are taken as examples. A new synthetic land surface parameter quantitative remote sensing product generation system is designed and the software system prototype will be demonstrated. At last, multi-scale field experiment campaigns, such as the field campaigns in Gansu and Beijing, China will be introduced briefly. The ground based, tower based, and airborne multi-angular measurement system have been built to measure the directional reflectance, emission and scattering characteristics from visible, near infrared, thermal infrared and microwave bands for model validation and calibration. The remote sensing pixel scale "true value" measurement strategy have been designed to gain the ground "true value" of LST, ALBEDO, LAI, soil moisture and ET etc. at 1-km2 for remote sensing product validation.

Design Studies of a CZT-based Detector Combined with a Pixel-Geometry-Matching Collimator for SPECT Imaging.

PubMed

Weng, Fenghua; Bagchi, Srijeeta; Huang, Qiu; Seo, Youngho

2013-10-01

Single Photon Emission Computed Tomography (SPECT) suffers limited efficiency due to the need for collimators. Collimator properties largely decide the data statistics and image quality. Various materials and configurations of collimators have been investigated in many years. The main thrust of our study is to evaluate the design of pixel-geometry-matching collimators to investigate their potential performances using Geant4 Monte Carlo simulations. Here, a pixel-geometry-matching collimator is defined as a collimator which is divided into the same number of pixels as the detector's and the center of each pixel in the collimator is a one-to-one correspondence to that in the detector. The detector is made of Cadmium Zinc Telluride (CZT), which is one of the most promising materials for applications to detect hard X-rays and γ -rays due to its ability to obtain good energy resolution and high light output at room temperature. For our current project, we have designed a large-area, CZT-based gamma camera (20.192 cm×20.192 cm) with a small pixel pitch (1.60 mm). The detector is pixelated and hence the intrinsic resolution can be as small as the size of the pixel. Materials of collimator, collimator hole geometry, detection efficiency, and spatial resolution of the CZT detector combined with the pixel-matching collimator were calculated and analyzed under different conditions. From the simulation studies, we found that such a camera using rectangular holes has promising imaging characteristics in terms of spatial resolution, detection efficiency, and energy resolution.

Performance characterization of a new CZT-based preclinical SPECT system: a comparative study of different collimators

NASA Astrophysics Data System (ADS)

Yu, A. R.; Park, S.-J.; Choi, Y. Y.; Kim, K. M.; Kim, H.-J.

2015-09-01

Triumph X-SPECT is a newly released CZT-based preclinical small-animal SPECT system with interchangeable collimators. The purpose of this work was to evaluate and systematically compare the imaging performances of three different collimators in the CZT-based preclinical small-animal system: a single-pinhole collimator (SPH), a multi-pinhole collimator (MPH) and a parallel-hole collimator. We measured the spatial resolutions and sensitivities of the three collimators with 99mTc sources, considering three distinct energy window widths (5, 10, and 20%), and used the NEMA NU4-2008 Image Quality phantom to test the imaging performance of the three collimators in terms of uniformity and spill-over ratio (SOR) for each energy window. With a 10% energy window width at a radius of rotation (ROR) of 30 mm, the system resolution of the SPH, MPH and parallel-hole collimators was 0.715, 0.855 and 3.270 mm FWHM, respectively. For the same energy window, the sensitivity of the system with SPH, MPH and parallel-hole collimators was 32.860, 152.514 and 49.205 counts/sec/MBq at a 100 mm source-to-detector distance and 6.790, 33.376 and 49.038 counts/sec/MBq at a 130 mm source-to-detector distance, respectively. The image noise and SORair for the three collimators were 20.137, 12.278 and 11.232 (%STDunif) and 0.106, 0.140 and 0.161, respectively. Overall, the results show that the SPH had better spatial resolution than the other collimators. The MPH had the highest sensitivity at 100 mm source-to-collimator distance, and the parallel-hole collimator had the highest sensitivity at 130 mm-source-to-detector distance. Therefore, the proper collimator for Triumph X-SPECT system must be determined by the task. These results provide valuable reference data and insight into the imaging performance of various collimators in CZT-based preclinical small-animal SPECT.

Thermal Lens Measurement in Diode-Pumped Nd:YAG Zig-Zag Slab

NASA Technical Reports Server (NTRS)

Smoak, M. C.; Kay, R. B.; Coyle, D. B.; Hopf, D.

1998-01-01

A major advantage that solid state zig-zag slab lasers have over conventional rod-based designs is that a much weaker thermal lens is produced in the slab when side-pumped with Quasi-CW laser diode arrays, particularly if the pump radiation is kept well away from the Brewster-cut ends. This paper reports on a rather strong thermal lens produced when diode pump radiation is collimated into a narrow portion of the zig-zag slab. The collimation of multi-bar pump packages to increase brightness and improve overlap is a direct consequence of designs which seek to maximize performance and efficiency. Our slab design employed a 8.1 cm x 2.5 mm x 5 mm slab with opposing Brewster end faces. It was pumped through the 2.5 mm direction by seven laser diode array packages, each housing four 6OW diode bars, 1 cm in width. The pump face, anti-reflection (AR) coated at 809 nm, was 6.8 cm in width and the 8.1 cm opposing side, high-reflection (HR) coated at 809 nm, reflected the unabsorbed pump beam for a second pass through the slab.

Design a freeform microlens array module for any arbitrary-shape collimated beam shaping and color mixing

NASA Astrophysics Data System (ADS)

Chen, Enguo; Wu, Rengmao; Guo, Tailiang

2014-06-01

Collimated beam shaping with freeform surface usually employs a predefined mapping to tailor one or multiple freeform surfaces. Limitation on those designs is that the source, the freeform optics and the target are in fixed one-to-one correspondence with each other. To overcome this drawback, this paper presents a kind of freeform microlens array module integrated with an ultra-thin freeform microlens array and a condenser lens to reshape any arbitrary-shape collimated beam into a prescribed uniform rectangular illumination and achieve color mixing. The design theory is explicitly given, and some key issues are addressed. Several different application examples are given, and the target is obtained with high uniformity and energy efficiency. This freeform microlens array module, which shows better flexibility and practicality than the regular designs, can be used not only to reshape any arbitrary-shape collimated beam (or a collimated beam integrated with several sub-collimated beams), but also most importantly to achieve color mixing. With excellent optical performance and ultra-compact volume, this optical module together with the design theory can be further introduced into other applications and will have a huge market potential in the near future.

Quantitative measurement of MLC leaf displacements using an electronic portal image device

NASA Astrophysics Data System (ADS)

Yang, Yong; Xing, Lei

2004-04-01

The success of an IMRT treatment relies on the positioning accuracy of the MLC (multileaf collimator) leaves for both step-and-shoot and dynamic deliveries. In practice, however, there exists no effective and quantitative means for routine MLC QA and this has become one of the bottleneck problems in IMRT implementation. In this work we present an electronic portal image device (EPID) based method for fast and accurate measurement of MLC leaf positions at arbitrary locations within the 40 cm × 40 cm radiation field. The new technique utilizes the fact that the integral signal in a small region of interest (ROI) is a sensitive and reliable indicator of the leaf displacement. In this approach, the integral signal at a ROI was expressed as a weighted sum of the contributions from the displacements of the leaf above the point and the adjacent leaves. The weighting factors or linear coefficients of the system equations were determined by fitting the integral signal data for a group of pre-designed MLC leaf sequences to the known leaf displacements that were intentionally introduced during the creation of the leaf sequences. Once the calibration is done, the system can be used for routine MLC leaf positioning QA to detect possible leaf errors. A series of tests was carried out to examine the functionality and accuracy of the technique. Our results show that the proposed technique is potentially superior to the conventional edge-detecting approach in two aspects: (i) it deals with the problem in a systematic approach and allows us to take into account the influence of the adjacent MLC leaves effectively; and (ii) it may improve the signal-to-noise ratio and is thus capable of quantitatively measuring extremely small leaf positional displacements. Our results indicate that the technique can detect a leaf positional error as small as 0.1 mm at an arbitrary point within the field in the absence of EPID set-up error and 0.3 mm when the uncertainty is considered. Given its simplicity, efficiency and accuracy, we believe that the technique is ideally suitable for routine MLC leaf positioning QA. This work was presented at the 45th Annual Meeting of American Society of Therapeutic Radiology and Oncology (ASTRO), Salt Lake City, UT, 2003. A US Patent is pending (application no. 10/197,232).

SU-E-T-261: Plan Quality Assurance of VMAT Using Fluence Images Reconstituted From Log-Files

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsuta, Y; Shimizu, E; Matsunaga, K

2014-06-01

Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi-leaf collimator (MLC) shapes. One of the main problem in the plan quality assurance is dosimetric errors associated with leaf-positional errors are difficult to analyze because they vary with MU delivered and leaf number. In this study, we calculated integrated fluence error image (IFEI) from log-files and evaluated plan quality in the area of all and individual MLC leaves scanned. Methods: The log-file reported the expected and actual position for inner 20 MLC leaves and the dose fraction every 0.25 seconds during prostate VMAT onmore » Elekta Synergy. These data were imported to in-house software that developed to calculate expected and actual fluence images from the difference of opposing leaf trajectories and dose fraction at each time. The IFEI was obtained by adding all of the absolute value of the difference between expected and actual fluence images corresponding. Results: In the area all MLC leaves scanned in the IFEI, the average and root mean square (rms) were 2.5 and 3.6 MU, the area of errors below 10, 5 and 3 MU were 98.5, 86.7 and 68.1 %, the 95 % of area was covered with less than error of 7.1 MU. In the area individual MLC leaves scanned in the IFEI, the average and rms value were 2.1 – 3.0 and 3.1 – 4.0 MU, the area of errors below 10, 5 and 3 MU were 97.6 – 99.5, 81.7 – 89.5 and 51.2 – 72.8 %, the 95 % of area was covered with less than error of 6.6 – 8.2 MU. Conclusion: The analysis of the IFEI reconstituted from log-file was provided detailed information about the delivery in the area of all and individual MLC leaves scanned.« less

SU-F-T-402: The Effect of Extremely Narrow MLC Leaf Width On the Plan Quality of VMAT for Prostate Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J; Park, S; Kim, J

2016-06-15

Purpose: To investigate the effect of multi-leaf collimators (MLCs) with leaf width of 1.25 mm on the plan quality of volumetric modulated arc therapy (VMAT) for prostate cancer. Methods: A total of 20 patients with prostate cancer were retrospectively selected. Using a high definition MLC (HD MLC), primary and boost VMAT plans with two full arcs were generated for each patient (original plan). After that, by shifting patient CT images by 1.25 mm in the cranio-caudal direction between the 1st and the 2nd arc, we simulated fluences made with MLCs with leaf width of 1.25 mm. After shifting, primary andmore » boost plans were generated for each patient (shifted plan). A sum plan was generated by summation of the primary and boost plan for each patient. Dose-volumetric parameters were calculated and compared. Results: Both homogeneity index (HI) and conformity index (CI) of the shifted plans were better than those of the original plans in primary plans (HI = 0.044 vs. 0.040 with p < 0.001 and CI = 1.056 vs. 1.044 with p = 0.006). Similarly, the shifted plans for boost target volume showed better homogeneity and conformity than did the original plans (HI = 0.042 vs. 0.037 with p = 0.006 and CI = 1.015 vs. 1.009 with p < 0.001). The total body volumes of the original plans irradiated by the prescription dose were larger than those of the shifted plans in sum plans (60.9 cc vs. 49.0 cc with p = 0.007). Conclusion: Use of extremely narrow MLCs could increase dose homogeneity and conformity of the target volume for prostate VMAT. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1C1A1A02036331).« less

Improvement of VMAT plan quality for head and neck cancer with high resolution fluences generated by couch shift between arcs.

PubMed

Park, Jong Min; Park, So-Yeon; Wu, Hong-Gyun; Kim, Jung-In

2018-02-01

To investigate the changes in quality of the volumetric modulated arc therapy (VMAT) plans with couch-shift between arcs by half of a multi-leaf collimator (MLC) leaf width. A total of 22 patients with head-and-neck cancer were retrospectively selected. Since the smallest MLC leaf width was 5 mm in this study, the couch was shifted by 2.5 mm in the longitudinal-direction between arcs to increase the resolution of fluence map. A total of three types of VMAT plans were generated for each patient; the three types of plans were a two-full-arc plan without couch-shift (NS plan), a two-half-arc-pair plan with couch-shift (HAS plan), and a two-full-arc pair plan with couch-shift (FAS plan). Changes in the dose-volumetric parameters were investigated. The FAS plan showed the best plan quality for the target volumes and organs at risk compared to the NS and HAS plans. However, the magnitudes of differences among the three types of plans were minimal, and every plan was clinically acceptable. The average integral doses of the NS, HAS, and FAS plans were 160,549 ± 37,600 Gy-cc, 147,828 ± 33,343 Gy-cc, and 156,030 ± 36,263 Gy-cc, respectively. The average monitor unit of the NS, HAS, and FAS plans were 717 ± 120 MU, 648 ± 100 MU, and 763 ± 158 MU, respectively. The HAS plan was better than the others in terms of normal tissue sparing and plan efficiency. By shifting the couch by half of the MLC leaf width in the longitudinal direction between arcs, the VMAT plan quality could be improved. Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

SU-F-T-463: Light-Field Based Dynalog Verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atwal, P; Ramaseshan, R

2016-06-15

Purpose: To independently verify leaf positions in so-called dynalog files for a Varian iX linac with a Millennium 120 MLC. This verification provides a measure of confidence that the files can be used directly as part of a more extensive intensity modulated radiation therapy / volumetric modulated arc therapy QA program. Methods: Initial testing used white paper placed at the collimator plane and a standard hand-held digital camera to image the light and shadow of a static MLC field through the paper. Known markings on the paper allow for image calibration. Noise reduction was attempted with removal of ‘inherent noise’more » from an open-field light image through the paper, but the method was found to be inconsequential. This is likely because the environment could not be controlled to the precision required for the sort of reproducible characterization of the quantum noise needed in order to meaningfully characterize and account for it. A multi-scale iterative edge detection algorithm was used for localizing the leaf ends. These were compared with the planned locations from the treatment console. Results: With a very basic setup, the image of the central bank A leaves 15–45, which are arguably the most important for beam modulation, differed from the planned location by [0.38±0.28] mm. Similarly, for bank B leaves 15–45 had a difference of [0.42±0.28] mm Conclusion: It should be possible to determine leaf position accurately with not much more than a modern hand-held camera and some software. This means we can have a periodic and independent verification of the dynalog file information. This is indicated by the precision already achieved using a basic setup and analysis methodology. Currently, work is being done to reduce imaging and setup errors, which will bring the leaf position error down further, and allow meaningful analysis over the full range of leaves.« less

Design optimisation of a TOF-based collimated camera prototype for online hadrontherapy monitoring

NASA Astrophysics Data System (ADS)

Pinto, M.; Dauvergne, D.; Freud, N.; Krimmer, J.; Letang, J. M.; Ray, C.; Roellinghoff, F.; Testa, E.

2014-12-01

Hadrontherapy is an innovative radiation therapy modality for which one of the main key advantages is the target conformality allowed by the physical properties of ion species. However, in order to maximise the exploitation of its potentialities, online monitoring is required in order to assert the treatment quality, namely monitoring devices relying on the detection of secondary radiations. Herein is presented a method based on Monte Carlo simulations to optimise a multi-slit collimated camera employing time-of-flight selection of prompt-gamma rays to be used in a clinical scenario. In addition, an analytical tool is developed based on the Monte Carlo data to predict the expected precision for a given geometrical configuration. Such a method follows the clinical workflow requirements to simultaneously have a solution that is relatively accurate and fast. Two different camera designs are proposed, considering different endpoints based on the trade-off between camera detection efficiency and spatial resolution to be used in a proton therapy treatment with active dose delivery and assuming a homogeneous target.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stathakis, S; Defoor, D; Linden, P

Purpose: To study the frequency of Multi-Leaf Collimator (MLC) leaf failures, investigate methods to predict them and reduce linac downtime. Methods: A Varian HD120 MLC was used in our study. The hyperterminal MLC errors logged from 06/2012 to 12/2014 were collected. Along with the hyperterminal errors, the MLC motor changes and all other MLC interventions by the linear accelerator engineer were recorded. The MLC dynalog files were also recorded on a daily basis for each treatment and during linac QA. The dynalog files were analyzed to calculate root mean square errors (RMS) and cumulative MLC travel distance per motor. Anmore » in-house MatLab code was used to analyze all dynalog files, record RMS errors and calculate the distance each MLC traveled per day. Results: A total of 269 interventions were recorded over a period of 18 months. Of these, 146 included MLC motor leaf change, 39 T-nut replacements, and 84 MLC cleaning sessions. Leaves close to the middle of each side required the most maintenance. In the A bank, leaves A27 to A40 recorded 73% of all interventions, while the same leaves in the B bank counted for 52% of the interventions. On average, leaves in the middle of the bank had their motors changed approximately every 1500m of travel. Finally, it was found that the number of RMS errors increased prior to an MLC motor change. Conclusion: An MLC dynalog file analysis software was developed that can be used to log daily MLC usage. Our eighteen-month data analysis showed that there is a correlation between the distance an MLC travels, the RMS and the life of the MLC motor. We plan to use this tool to predict MLC motor failures and with proper and timely intervention, reduce the downtime of the linac during clinical hours.« less

Incorrect dosimetric leaf separation in IMRT and VMAT treatment planning: Clinical impact and correlation with pretreatment quality assurance.

PubMed

Sjölin, Maria; Edmund, Jens Morgenthaler

2016-07-01

Dynamic treatment planning algorithms use a dosimetric leaf separation (DLS) parameter to model the multi-leaf collimator (MLC) characteristics. Here, we quantify the dosimetric impact of an incorrect DLS parameter and investigate whether common pretreatment quality assurance (QA) methods can detect this effect. 16 treatment plans with intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) technique for multiple treatment sites were calculated with a correct and incorrect setting of the DLS, corresponding to a MLC gap difference of 0.5mm. Pretreatment verification QA was performed with a bi-planar diode array phantom and the electronic portal imaging device (EPID). Measurements were compared to the correct and incorrect planned doses using gamma evaluation with both global (G) and local (L) normalization. Correlation, specificity and sensitivity between the dose volume histogram (DVH) points for the planning target volume (PTV) and the gamma passing rates were calculated. The change in PTV and organs at risk DVH parameters were 0.4-4.1%. Good correlation (>0.83) between the PTVmean dose deviation and measured gamma passing rates was observed. Optimal gamma settings with 3%L/3mm (per beam and composite plan) and 3%G/2mm (composite plan) for the diode array phantom and 2%G/2mm (composite plan) for the EPID system were found. Global normalization and per beam ROC analysis of the diode array phantom showed an area under the curve <0.6. A DLS error can worsen pretreatment QA using gamma analysis with reasonable credibility for the composite plan. A low detectability was demonstrated for a 3%G/3mm per beam gamma setting. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

MuSICa: the Multi-Slit Image Slicer for the est Spectrograph

NASA Astrophysics Data System (ADS)

Calcines, A.; López, R. L.; Collados, M.

2013-09-01

Integral field spectroscopy (IFS) is a technique that allows one to obtain the spectra of all the points of a bidimensional field of view simultaneously. It is being applied to the new generation of the largest night-time telescopes but it is also an innovative technique for solar physics. This paper presents the design of a new image slicer, MuSICa (Multi-Slit Image slicer based on collimator-Camera), for the integral field spectrograph of the 4-m aperture European Solar Telescope (EST). MuSICa is a multi-slit image slicer that decomposes an 80 arcsec2 field of view into slices of 50 μm and reorganizes it into eight slits of 0.05 arcsec width × 200 arcsec length. It is a telecentric system with an optical quality at diffraction limit compatible with the two modes of operation of the spectrograph: spectroscopic and spectro-polarimetric. This paper shows the requirements, technical characteristics and layout of MuSICa, as well as other studied design options.

Implementation of GPU accelerated SPECT reconstruction with Monte Carlo-based scatter correction.

PubMed

Bexelius, Tobias; Sohlberg, Antti

2018-06-01

Statistical SPECT reconstruction can be very time-consuming especially when compensations for collimator and detector response, attenuation, and scatter are included in the reconstruction. This work proposes an accelerated SPECT reconstruction algorithm based on graphics processing unit (GPU) processing. Ordered subset expectation maximization (OSEM) algorithm with CT-based attenuation modelling, depth-dependent Gaussian convolution-based collimator-detector response modelling, and Monte Carlo-based scatter compensation was implemented using OpenCL. The OpenCL implementation was compared against the existing multi-threaded OSEM implementation running on a central processing unit (CPU) in terms of scatter-to-primary ratios, standardized uptake values (SUVs), and processing speed using mathematical phantoms and clinical multi-bed bone SPECT/CT studies. The difference in scatter-to-primary ratios, visual appearance, and SUVs between GPU and CPU implementations was minor. On the other hand, at its best, the GPU implementation was noticed to be 24 times faster than the multi-threaded CPU version on a normal 128 × 128 matrix size 3 bed bone SPECT/CT data set when compensations for collimator and detector response, attenuation, and scatter were included. GPU SPECT reconstructions show great promise as an every day clinical reconstruction tool.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weinmann, Amanda L.; Hruska, Carrie B.; Conners, Amy L.

Purpose: Molecular breast imaging (MBI) is a dedicated nuclear medicine breast imaging modality that employs dual-head cadmium zinc telluride (CZT) gamma cameras to functionally detect breast cancer. MBI has been shown to detect breast cancers otherwise occult on mammography and ultrasound. Currently, a MBI-guided biopsy system does not exist to biopsy such lesions. Our objective was to consider the utility of a novel conical slant-hole (CSH) collimator for rapid (<1 min) and accurate monitoring of lesion position to serve as part of a MBI-guided biopsy system. Methods: An initial CSH collimator design was derived from the dimensions of a parallel-holemore » collimator optimized for MBI performed with dual-head CZT gamma cameras. The parameters of the CSH collimator included the collimator height, cone slant angle, thickness of septa and cones of the collimator, and the annular areas exposed at the base of the cones. These parameters were varied within the geometric constraints of the MBI system to create several potential CSH collimator designs. The CSH collimator designs were evaluated using Monte Carlo simulations. The model included a breast compressed to a thickness of 6 cm with a 1-cm diameter lesion located 3 cm from the collimator face. The number of particles simulated was chosen to represent the count density of a low-dose, screening MBI study acquired with the parallel-hole collimator for 10 min after a {approx}150 MBq (4 mCi) injection of Tc-99m sestamibi. The same number of particles was used for the CSH collimator simulations. In the resulting simulated images, the count sensitivity, spatial resolution, and accuracy of the lesion depth determined from the lesion profile width were evaluated. Results: The CSH collimator design with default parameters derived from the optimal parallel-hole collimator provided 1-min images with error in the lesion depth estimation of 1.1 {+-} 0.7 mm and over 21 times the lesion count sensitivity relative to 1-min images acquired with the current parallel-hole collimator. Sensitivity was increased via more vertical cone slant angles, larger annular areas, thinner cone walls, shorter cone heights, and thinner radiating septa. Full width at half maximum trended in the opposite direction as sensitivity for all parameters. There was less error in the depth estimates for less vertical slant angles, smaller annular areas, thinner cone walls, cone heights near 1 cm, and generally thinner radiating septa. Conclusions: A Monte Carlo model was used to demonstrate the feasibility of a CSH collimator design for rapid biopsy application in molecular breast imaging. Specifically, lesion depth of a 1-cm diameter lesion positioned in the center of a typical breast can be estimated with error of less than 2 mm using circumferential count profiles of images acquired in 1 min.« less

WE-EF-BRA-06: Feasibility of Spatially Modulated Proton Beams for Small Animal Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, E; Meyer, J

Purpose: To investigate the feasibility of proton minibeam radiotherapy (pMBRT) for small animal research. The motivation is to explore with protons the extraordinary normal tissue sparing effects to spatially modulated beams as observed on high flux synchrotron beam lines. We hypothesized that we can design a multi-slit collimator for our proton beam line to produce planar-parallel dose profiles with high modulation in the entrance region and homogenous dose coverage in the overlap of the Bragg peaks. Methods: The high dose rate 50 MeV research proton beamline at the University of Washington was modeled using the TOol for PArticle Simulation (TOPAS)more » Monte Carlo package. A brass collimator was implemented to generate proton minibeams. The collimator consists of an array of 2 cm long slits to cover an area of 2×2 cm{sup 2}. The slit widths (0.1–1 mm), center-to-center (ctc) distances (1–3 mm) and collimator thickness (1–7 cm) were varied to evaluate the effect on dose rate, the peak-to-valley dose ratios (PVDR) and the change of penumbra and peak width (FWHM) with depth. Results: The Bragg peak was at a depth of ∼21 mm. The penumbra and FWHM remained relatively constant to a depth of about 10–15 mm. The PVDR ranged from 1.6 to 26 and the dose rate dropped exponentially with collimator thickness. A uniform dose can be achieved at depth with slightly compromised PVDRs and dose rate. Conclusion: The technical realization of pMBRT is feasible. The simulations have shown that it is possible to obtain uniform dose at depth while modulation is maintained on the entrance side. While the simulated beam widths are larger than on synchrotron generated microbeams the dosimetric advantage could avoid having to interlace two microbeams to achieve uniform dose in the target. The next steps are to build a collimator and verify the simulations experimentally.« less

TH-AB-202-03: A Novel Tool for Computing Deliverable Doses in Dynamic MLC Tracking Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fast, M; Kamerling, C; Menten, M

2016-06-15

Purpose: In tracked dynamic multi-leaf collimator (MLC) treatments, segments are continuously adapted to the target centroid motion in beams-eye-view. On-the-fly segment adaptation, however, potentially induces dosimetric errors due to the finite MLC leaf width and non-rigid target motion. In this study, we outline a novel tool for computing the 4d dose of lung SBRT plans delivered with MLC tracking. Methods: The following automated workflow was developed: A) centroid tracking, where the initial segments are morphed to each 4dCT phase based on the beams-eye-view GTV shift (followed by a dose calculation on each phase); B) re-optimized tracking, in which all morphedmore » initial plans from (A) are further optimised (“warm-started”) in each 4dCT phase using the initial optimisation parameters but phase-specific volume definitions. Finally, both dose sets are accumulated to the reference phase using deformable image registration. Initial plans were generated according to the RTOG-1021 guideline (54Gy, 3-Fx, equidistant 9-beam IMRT) on the peak-exhale (reference) phase of a phase-binned 4dCT. Treatment planning and delivery simulations were performed in RayStation (research v4.6) using our in-house segment-morphing algorithm, which directly links to RayStation through a native C++ interface. Results: Computing the tracking plans and 4d dose distributions via the in-house interface takes 5 and 8 minutes respectively for centroid and re-optimized tracking. For a sample lung SBRT patient with 14mm peak-to-peak motion in sup-inf direction, mainly perpendicular leaf motion (0-collimator) resulted in small dose changes for PTV-D95 (−13cGy) and GTV-D98 (+18cGy) for the centroid tracking case compared to the initial plan. Modest reductions of OAR doses (e.g. spinal cord D2: −11cGy) were achieved in the idealized tracking case. Conclusion: This study presents an automated “1-click” workflow for computing deliverable MLC tracking doses in RayStation. Adding a non-deliverable re-optimized tracking scenario is expected to help quantify plan robustness for more challenging patients with anatomy deformations. We acknowledge support of the MLC tracking research from Elekta AB. MFF is supported by Cancer Research UK under Programme C33589/A19908. Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR.« less

LOR-interleaving image reconstruction for PET imaging with fractional-crystal collimation

NASA Astrophysics Data System (ADS)

Li, Yusheng; Matej, Samuel; Karp, Joel S.; Metzler, Scott D.

2015-01-01

Positron emission tomography (PET) has become an important modality in medical and molecular imaging. However, in most PET applications, the resolution is still mainly limited by the physical crystal sizes or the detector’s intrinsic spatial resolution. To achieve images with better spatial resolution in a central region of interest (ROI), we have previously proposed using collimation in PET scanners. The collimator is designed to partially mask detector crystals to detect lines of response (LORs) within fractional crystals. A sequence of collimator-encoded LORs is measured with different collimation configurations. This novel collimated scanner geometry makes the reconstruction problem challenging, as both detector and collimator effects need to be modeled to reconstruct high-resolution images from collimated LORs. In this paper, we present a LOR-interleaving (LORI) algorithm, which incorporates these effects and has the advantage of reusing existing reconstruction software, to reconstruct high-resolution images for PET with fractional-crystal collimation. We also develop a 3D ray-tracing model incorporating both the collimator and crystal penetration for simulations and reconstructions of the collimated PET. By registering the collimator-encoded LORs with the collimator configurations, high-resolution LORs are restored based on the modeled transfer matrices using the non-negative least-squares method and EM algorithm. The resolution-enhanced images are then reconstructed from the high-resolution LORs using the MLEM or OSEM algorithm. For validation, we applied the LORI method to a small-animal PET scanner, A-PET, with a specially designed collimator. We demonstrate through simulated reconstructions with a hot-rod phantom and MOBY phantom that the LORI reconstructions can substantially improve spatial resolution and quantification compared to the uncollimated reconstructions. The LORI algorithm is crucial to improve overall image quality of collimated PET, which can have significant implications in preclinical and clinical ROI imaging applications.

Multi-angle nuclear imaging apparatus and method

DOEpatents

Anger, Hal O. [Berkeley, CA

1980-04-08

Nuclear imaging apparatus for obtaining multi-plane readouts of radioactive material in a human or animal subject. A probe disposed in the vicinity of the subject is provided for receiving radiation from radiating sources in the subject and for forming a probe radiation image. The probe has a collimator with different portions thereof having holes disposed at different angles. A single scintillation crystal overlies the collimator for receiving radiation passing through the collimator and producing scintillations to provide the probe image. An array of photomultiplier tubes overlie the single crystal for observing the probe image and providing electrical outputs. Conversion apparatus is provided for converting the electrical outputs representing the probe image into optical images displayed on the screen of a cathode ray tube. Divider apparatus is provided for dividing the probe radiation image into a plurality of areas with the areas corresponding to different portions of the collimator having holes disposed at different angles. A light sensitive medium is provided for receiving optical images. Apparatus is provided for causing relative movement between the probe and the subject. Apparatus is also provided for causing relative movement between the optical image on the screen and the light sensitive medium which corresponds to the relative movement between the probe and the subject whereby there is produced on the light sensitive medium a plurality of images that portray the subject as seen from different angles corresponding to the portions of the collimator having holes at different angles.

Multi-angle nuclear imaging apparatus and method

DOEpatents

Anger, H.O.

1980-04-08

A nuclear imaging apparatus is described for obtaining multi-plane readouts of radioactive material in a human or animal subject. A probe disposed in the vicinity of the subject is provided for receiving radiation from radiating sources in the subject and for forming a probe radiation image. The probe has a collimator with different portions having holes disposed at different angles. A single scintillation crystal overlies the collimator for receiving radiation passing through the collimator and producing scintillations to provide the probe image. An array of photomultiplier tubes overlie the single crystal for observing the probe image and providing electrical outputs. Conversion apparatus is provided for converting the electrical outputs representing the probe image into optical images displayed on the screen of a cathode ray tube. Divider apparatus is provided for dividing the probe radiation image into a plurality of areas with the areas corresponding to different portions of the collimator having holes disposed at different angles. A light sensitive medium is provided for receiving optical images. Apparatus is provided for causing relative movement between the probe and the subject. Apparatus is also provided for causing relative movement between the optical image on the screen and the light sensitive medium which corresponds to the relative movement between the probe and the subject whereby there is produced on the light sensitive medium a plurality of images that portray the subject as seen from different angles corresponding to the portions of the collimator having holes at different angles. 11 figs.

The first private-hospital based proton therapy center in Korea; status of the Proton Therapy Center at Samsung Medical Center

PubMed Central

Chung, Kwangzoo; Kim, Jinsung; Ahn, Sung Hwan; Ju, Sang Gyu; Jung, Sang Hoon; Chung, Yoonsun; Cho, Sungkoo; Jo, Kwanghyun; Shin, Eun Hyuk; Hong, Chae-Seon; Shin, Jung Suk; Park, Seyjoon; Kim, Dae-Hyun; Kim, Hye Young; Lee, Boram; Shibagaki, Gantaro; Nonaka, Hideki; Sasai, Kenzo; Koyabu, Yukio; Choi, Changhoon; Huh, Seung Jae; Ahn, Yong Chan; Pyo, Hong Ryull; Lim, Do Hoon; Park, Hee Chul; Park, Won; Oh, Dong Ryul; Noh, Jae Myung; Yu, Jeong Il; Song, Sanghyuk; Lee, Ji Eun; Lee, Bomi; Choi, Doo Ho

2015-01-01

Purpose The purpose of this report is to describe the proton therapy system at Samsung Medical Center (SMC-PTS) including the proton beam generator, irradiation system, patient positioning system, patient position verification system, respiratory gating system, and operating and safety control system, and review the current status of the SMC-PTS. Materials and Methods The SMC-PTS has a cyclotron (230 MeV) and two treatment rooms: one treatment room is equipped with a multi-purpose nozzle and the other treatment room is equipped with a dedicated pencil beam scanning nozzle. The proton beam generator including the cyclotron and the energy selection system can lower the energy of protons down to 70 MeV from the maximum 230 MeV. Results The multi-purpose nozzle can deliver both wobbling proton beam and active scanning proton beam, and a multi-leaf collimator has been installed in the downstream of the nozzle. The dedicated scanning nozzle can deliver active scanning proton beam with a helium gas filled pipe minimizing unnecessary interactions with the air in the beam path. The equipment was provided by Sumitomo Heavy Industries Ltd., RayStation from RaySearch Laboratories AB is the selected treatment planning system, and data management will be handled by the MOSAIQ system from Elekta AB. Conclusion The SMC-PTS located in Seoul, Korea, is scheduled to begin treating cancer patients in 2015. PMID:26756034

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jungho; Shi, Xianbo; Casa, Diego

Advances in resonant inelastic X-ray scattering (RIXS) have come in lockstep with improvements in energy resolution. Currently, the best energy resolution at the IrL 3-edge stands at ~25 meV, which is achieved using a diced Si(844) spherical crystal analyzer. However, spherical analyzers are limited by their intrinsic reflection width. A novel analyzer system using multiple flat crystals provides a promising way to overcome this limitation. For the present design, an energy resolution at or below 10 meV was selected. Recognizing that the angular acceptance of flat crystals is severely limited, a collimating element is essential to achieve the necessary solid-anglemore » acceptance. For this purpose, a laterally graded, parabolic, multilayer Montel mirror was designed for use at the IrL 3-absorption edge. It provides an acceptance larger than 10 mrad, collimating the reflected X-ray beam to smaller than 100 µrad, in both vertical and horizontal directions. The performance of this mirror was studied at beamline 27-ID at the Advanced Photon Source. X-rays from a diamond (111) monochromator illuminated a scattering source of diameter 5 µm, generating an incident beam on the mirror with a well determined divergence of 40 mrad. A flat Si(111) crystal after the mirror served as the divergence analyzer. From X-ray measurements, ray-tracing simulations and optical metrology results, it was established that the Montel mirror satisfied the specifications of angular acceptance and collimation quality necessary for a high-resolution RIXS multi-crystal analyzer system.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, S; Ji, Y; Kim, K

Purpose: A diagnostics Multileaf Collimator (MLC) was designed for diagnostic radiography dose reduction. Monte Carlo simulation was used to evaluate efficiency of shielding material for producing leaves of Multileaf collimator. Material & Methods: The general radiography unit (Rex-650R, Listem, Korea) was modeling with Monte Carlo simulation (MCNPX, LANL, USA) and we used SRS-78 program to calculate the energy spectrum of tube voltage (80, 100, 120 kVp). The shielding materials was SKD 11 alloy tool steel that is composed of 1.6% carbon(C), 0.4% silicon (Si), 0.6% manganese (Mn), 5% chromium (Cr), 1% molybdenum (Mo), and vanadium (V). The density of itmore » was 7.89 g/m3. We simulated leafs diagnostic MLC using SKD 11 with general radiography unit. We calculated efficiency of diagnostic MLC using tally6 card of MCNPX depending on energy. Results: The diagnostic MLC consisted of 25 individual metal shielding leaves on both sides, with dimensions of 10 × 0.5 × 0.5 cm3. The leaves of MLC were controlled by motors positioned on both sides of the MLC. According to energy (tube voltage), the shielding efficiency of MLC in Monte Carlo simulation was 99% (80 kVp), 96% (100 kVp) and 93% (120 kVp). Conclusion: We certified efficiency of diagnostic MLC fabricated from SKD11 alloy tool steel. Based on the results, the diagnostic MLC was designed. We will make the diagnostic MLC for dose reduction of diagnostic radiography.« less

Fabricating High-Resolution X-Ray Collimators

NASA Technical Reports Server (NTRS)

Appleby, Michael; Atkinson, James E.; Fraser, Iain; Klinger, Jill

2008-01-01

A process and method for fabricating multi-grid, high-resolution rotating modulation collimators for arcsecond and sub-arcsecond x-ray and gamma-ray imaging involves photochemical machining and precision stack lamination. The special fixturing and etching techniques that have been developed are used for the fabrication of multiple high-resolution grids on a single array substrate. This technology has application in solar and astrophysics and in a number of medical imaging applications including mammography, computed tomography (CT), single photon emission computed tomography (SPECT), and gamma cameras used in nuclear medicine. This collimator improvement can also be used in non-destructive testing, hydrodynamic weapons testing, and microbeam radiation therapy.

Simulation, design, and testing of a high power collimator for the RDS-112 cyclotron.

PubMed

Peeples, Johanna L; Stokely, Matthew H; Poorman, Michael C; Bida, Gerald T; Wieland, Bruce W

2015-03-01

A high power [F-18] fluoride target package for the RDS-112 cyclotron has been designed, tested, and commercially deployed. The upgrade includes the CF-1000 target, a 1.3kW water target with an established commercial history on RDS-111/Eclipse cyclotrons, and a redesigned collimator with improved heat rejection capabilities. Conjugate heat transfer analyses were employed to both evaluate the existing collimator capabilities and design a suitable high current replacement. Copyright © 2014 Elsevier Ltd. All rights reserved.

Lotus-on-chip: computer-aided design and 3D direct laser writing of bioinspired surfaces for controlling the wettability of materials and devices.

PubMed

Lantada, Andrés Díaz; Hengsbach, Stefan; Bade, Klaus

2017-10-16

In this study we present the combination of a math-based design strategy with direct laser writing as high-precision technology for promoting solid free-form fabrication of multi-scale biomimetic surfaces. Results show a remarkable control of surface topography and wettability properties. Different examples of surfaces inspired on the lotus leaf, which to our knowledge are obtained for the first time following a computer-aided design with this degree of precision, are presented. Design and manufacturing strategies towards microfluidic systems whose fluid driving capabilities are obtained just by promoting a design-controlled wettability of their surfaces, are also discussed and illustrated by means of conceptual proofs. According to our experience, the synergies between the presented computer-aided design strategy and the capabilities of direct laser writing, supported by innovative writing strategies to promote final size while maintaining high precision, constitute a relevant step forward towards materials and devices with design-controlled multi-scale and micro-structured surfaces for advanced functionalities. To our knowledge, the surface geometry of the lotus leaf, which has relevant industrial applications thanks to its hydrophobic and self-cleaning behavior, has not yet been adequately modeled and manufactured in an additive way with the degree of precision that we present here.

Optomechanical and thermal design of the Multi-Application Solar Telescope for USO

NASA Astrophysics Data System (ADS)

Denis, Stefan; Coucke, Pierre; Gabriel, Eric; Delrez, Christophe; Venkatakrishnan, Parameshwaran

2008-07-01

The Multi-Application Solar Telescope (MAST) is a 50 cm diameter class telescope to be installed on the Udaipur Solar Observatory's Island on the Lake Fatehsagar in Udaipur, India. It is dedicated to solar observation. The telescope is designed, manufactured, assembled and installed on-site by the belgian company AMOS SA for the Udaipur Solar Observatory (USO), an academic division of the Physical Research Laboratory (PRL) in India. Despite its limited size, the telescope is expected to be competitive with respect to worldwide large and costly projects thanks to its versatility regarding science goals and also thanks to its demanding optomechanical and thermal specification. This paper describes the optomechanical and thermal design of this telescope and presents solutions adopted by AMOS to meet the specific requirements. The optical configuration of the telescope is based on an afocal off-axis gregorian combination integrated on an Alt.-Az. mechanical mount, with a suite of flat folding mirrors to provide the required stationary collimated beam.

Compact collimators designed with a modified point approximation for light-emitting diodes

NASA Astrophysics Data System (ADS)

Luo, Tao; Wang, Gang

2017-09-01

We present a novel freeform lens design method for an application to LED collimating illumination. The method is derived from a basic geometric-optics analysis and construction approach. By using this method, a compact collimated lenses with Aspect Ratio = 0.219 is presented. Moreover, the utility efficiency (UE) inside the angle defined by ideal concentrator hypothesis with different lens-to-LED size ratios for both this lens and TIR lens are presented. A prototype of the collimator lens is also made to verify the practical performance of the lens, which has light distribution very compatible with the simulation results.

Freeform lens design for LED collimating illumination.

PubMed

Chen, Jin-Jia; Wang, Te-Yuan; Huang, Kuang-Lung; Liu, Te-Shu; Tsai, Ming-Da; Lin, Chin-Tang

2012-05-07

We present a simple freeform lens design method for an application to LED collimating illumination. The method is derived from a basic geometric-optics analysis and construction approach. By using this method, a highly collimating lens with LED chip size of 1.0 mm × 1.0 mm and optical simulation efficiency of 86.5% under a view angle of ± 5 deg is constructed. To verify the practical performance of the lens, a prototype of the collimator lens is also made, and an optical efficiency of 90.3% with a beam angle of 4.75 deg is measured.

Simulated Design Strategies for SPECT Collimators to Reduce the Eddy Currents Induced by MRI Gradient Fields

NASA Astrophysics Data System (ADS)

Samoudi, Amine M.; Van Audenhaege, Karen; Vermeeren, Günter; Verhoyen, Gregory; Martens, Luc; Van Holen, Roel; Joseph, Wout

2015-10-01

Combining single photon emission computed tomography (SPECT) with magnetic resonance imaging (MRI) requires the insertion of highly conductive SPECT collimators inside the MRI scanner, resulting in an induced eddy current disturbing the combined system. We reduced the eddy currents due to the insert of a novel tungsten collimator inside transverse and longitudinal gradient coils. The collimator was produced with metal additive manufacturing, that is part of a microSPECT insert for a preclinical SPECT/MRI scanner. We characterized the induced magnetic field due to the gradient field and adapted the collimators to reduce the induced eddy currents. We modeled the x-, y-, and z-gradient coil and the different collimator designs and simulated them with FEKO, a three-dimensional method of moments / finite element methods (MoM/FEM) full-wave simulation tool. We used a time analysis approach to generate the pulsed magnetic field gradient. Simulation results show that the maximum induced field can be reduced by 50.82% in the final design bringing the maximum induced magnetic field to less than 2% of the applied gradient for all the gradient coils. The numerical model was validated with measurements and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.

Automatic detection of MLC relative position errors for VMAT using the EPID-based picket fence test

NASA Astrophysics Data System (ADS)

Christophides, Damianos; Davies, Alex; Fleckney, Mark

2016-12-01

Multi-leaf collimators (MLCs) ensure the accurate delivery of treatments requiring complex beam fluences like intensity modulated radiotherapy and volumetric modulated arc therapy. The purpose of this work is to automate the detection of MLC relative position errors  ⩾0.5 mm using electronic portal imaging device-based picket fence tests and compare the results to the qualitative assessment currently in use. Picket fence tests with and without intentional MLC errors were measured weekly on three Varian linacs. The picket fence images analysed covered a time period ranging between 14-20 months depending on the linac. An algorithm was developed that calculated the MLC error for each leaf-pair present in the picket fence images. The baseline error distributions of each linac were characterised for an initial period of 6 months and compared with the intentional MLC errors using statistical metrics. The distributions of median and one-sample Kolmogorov-Smirnov test p-value exhibited no overlap between baseline and intentional errors and were used retrospectively to automatically detect MLC errors in routine clinical practice. Agreement was found between the MLC errors detected by the automatic method and the fault reports during clinical use, as well as interventions for MLC repair and calibration. In conclusion the method presented provides for full automation of MLC quality assurance, based on individual linac performance characteristics. The use of the automatic method has been shown to provide early warning for MLC errors that resulted in clinical downtime.

A study of reconstruction accuracy for a cardiac SPECT system with multi-segmental collimation

NASA Astrophysics Data System (ADS)

Yu, D.-C.; Chang, W.; Pan, T.-S.

1997-06-01

To improve the geometric efficiency of cardiac SPECT imaging, the authors previously proposed to use a multi-segmental collimation with a cylindrical geometry. The proposed collimator consists of multiple parallel-hole collimators with most of the segments directed toward a small central region, where the patient's heart should be positioned. This technique provides a significantly increased detection efficiency for the central region, but at the expense of reduced efficiency for the surrounding region. The authors have used computer simulations to evaluate the implication of this technique on the accuracy of the reconstructed cardiac images. Two imaging situations were simulated: 1) the heart well placed inside the central region, and 2) the heart shifted and partially outside the central region. A neighboring high-uptake liver was simulated for both imaging situations. The images were reconstructed and corrected for attenuation with ML-EM and OS-FM methods using a complete attenuation map. The results indicate that errors caused by projection truncation are not significant and are not strongly dependent on the activity of the liver when the heart is well positioned within the central region. When the heart is partially outside the central region, hybrid emission data (a combination of high-count projections from the central region and low-count projections from the background region) can be used to restore the activity of the truncated section of the myocardium. However, the variance of the image in the section of the myocardium outside the central region is increased by 2-3 times when 10% of the collimator segments are used to image the background region.

Diffraction effects on angular response of X-ray collimators

NASA Technical Reports Server (NTRS)

Blake, R. L.; Barrus, D. M.; Fenimore, E.

1976-01-01

Angular responses have been measured for X-ray collimators with half-widths ranging from minutes of arc down to 10 arcsec. In the seconds-of-arc range, diffraction peaks at off-axis angles can masquerade as side lobes of the collimator angular response. Measurements and qualitative physical arguments lead to a rule of thumb for collimator design; namely, the angle of first minimum in the Fraunhofer single-slit diffraction pattern should be less than one-fourth of the collimator geometrical full-width at half-maximum intensity.

Investigation of the feasibility of a simple method for verifying the motion of a binary multileaf collimator synchronized with the rotation of the gantry for helical tomotherapy

PubMed Central

Uematsu, Masahiro; Ito, Makiko; Hama, Yukihiro; Inomata, Takayuki; Fujii, Masahiro; Nishio, Teiji; Nakamura, Naoki; Nakagawa, Keiichi

2012-01-01

In this paper, we suggest a new method for verifying the motion of a binary multileaf collimator (MLC) in helical tomotherapy. For this we used a combination of a cylindrical scintillator and a general‐purpose camcorder. The camcorder records the light from the scintillator following photon irradiation, which we use to track the motion of the binary MLC. The purpose of this study is to demonstrate the feasibility of this method as a binary MLC quality assurance (QA) tool. First, the verification was performed using a simple binary MLC pattern with a constant leaf open time; secondly, verification using the binary MLC pattern used in a clinical setting was also performed. Sinograms of simple binary MLC patterns, in which leaves that were open were detected as “open” from the measured light, define the sensitivity which, in this case, was 1.000. On the other hand, the specificity, which gives the fraction of closed leaves detected as “closed”, was 0.919. The leaf open error identified by our method was −1.3±7.5%. The 68.6% of observed leaves were performed within ± 3% relative error. The leaf open error was expressed by the relative errors calculated on the sinogram. In the clinical binary MLC pattern, the sensitivity and specificity were 0.994 and 0.997, respectively. The measurement could be performed with −3.4±8.0% leaf open error. The 77.5% of observed leaves were performed within ± 3% relative error. With this method, we can easily verify the motion of the binary MLC, and the measurement unit developed was found to be an effective QA tool. PACS numbers: 87.56.Fc, 87.56.nk PMID:22231222

SU-E-T-610: Comparison of Treatment Times Between the MLCi and Agility Multileaf Collimators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramsey, C; Bowling, J

2014-06-01

Purpose: The Agility is a new 160-leaf MLC developed by Elekta for use in their Infinity and Versa HD linacs. As compared to the MLCi, the Agility increased the maximum leaf speed from 2 cm/s to 3.5 cm/s, and the maximum primary collimator speed from 1.5 cm/s to 9.0 cm/s. The purpose of this study was to determine if the Agility MLC resulted in improved plan quality and/or shorter treatment times. Methods: An Elekta Infinity that was originally equipped with a 80 leaf MLCi was upgraded to an 160 leaf Agility. Treatment plan quality was evaluated using the Pinnacle planningmore » system with SmartArc. Optimization was performed once for the MLCi and once for the Agility beam models using the same optimization parameters and the same number of iterations. Patient treatment times were measured for all IMRT, VMAT, and SBRT patients treated on the Infinity with the MLCi and Agility MLCs. Treatment times were extracted from the EMR and measured from when the patient first walked into the treatment room until exiting the treatment room. Results: 11,380 delivery times were measured for patients treated with the MLCi, and 1,827 measurements have been made for the Agility MLC. The average treatment times were 19.1 minutes for the MLCi and 20.8 minutes for the Agility. Using a t-test analysis, there was no difference between the two groups (t = 0.22). The dose differences between patients planned with the MLCi and the Agility MLC were minimal. For example, the dose difference for the PTV, GTV, and cord for a head and neck patient planned using Pinnacle were effectively equivalent. However, the dose to the parotid glands was slightly worse with the Agility MLC. Conclusion: There was no statistical difference in treatment time, or any significant dosimetric difference between the Agility MLC and the MLCi.« less

A prototype optical-CT system for PRESAGE 3D dosimeter readout

NASA Astrophysics Data System (ADS)

Miles, Devin; Yoon, Paul; Kodra, Jacob; Adamovics, John; Oldham, Mark

2017-05-01

This work introduces the Duke Integrated-lens Optical Scanner (DIOS), a prototype optical-CT system designed for convenient and low-cost readout of PRESAGE 3D dosimeters. A key novelty of the DIOS is the incorporation of a multi-purpose light-collimating tank (the LC-tank). The LC-tank collimates light from a point source, maintains parallel ray geometry through a dosimeter mounted inside the tank, and refocuses emergent light onto a CCD detector. A second purpose is to dramatically reduce the amount of refractive matched fluid required in prior optical-CT scanners. This is achieved by substituting large quantities of refractive-matched fluid with solid RI-matched polyurethane. The advantages of DIOS include eliminating the need for expensive telecentric lenses, and eliminating the impracticality of large volumes of RI matched fluid. The DIOS is potentially more susceptible to stray-light artifacts. Preliminary phantom testing shows promising agreement between PRESAGE/DIOS readout and prior commissioned optical-CT scanners, as well as with Eclipse dose calculations.

Introduction of a novel ultrahigh sensitivity collimator for brain SPECT imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Mi-Ae, E-mail: miaepark@bwh.harvard.edu; Kij

Purpose: Noise levels of brain SPECT images are highest in central regions, due to preferential attenuation of photons emitted from deep structures. To address this problem, the authors have designed a novel collimator for brain SPECT imaging that yields greatly increased sensitivity near the center of the brain without loss of resolution. This hybrid collimator consisted of ultrashort cone-beam holes in the central regions and slant-holes in the periphery (USCB). We evaluated this collimator for quantitative brain imaging tasks. Methods: Owing to the uniqueness of the USCB collimation, the hole pattern required substantial variations in collimator parameters. To utilize themore » lead-casting technique, the authors designed two supporting plates to position about 37 000 hexagonal, slightly tapered pins. The holes in the supporting plates were modeled to yield the desired focal length, hole length, and septal thickness. To determine the properties of the manufactured collimator and to compute the system matrix, the authors prepared an array of point sources that covered the entire detector area. Each point source contained 32 μCi of Tc-99m at the first scan time. The array was imaged for 5 min at each of the 64 shifted locations to yield a 2-mm sampling distance, and hole parameters were calculated. The sensitivity was also measured using a point source placed along the central ray at several distances from the collimator face. High-count projection data from a five-compartment brain phantom were acquired with the three collimators on a dual-head SPECT/CT system. The authors calculated Cramer-Rao bounds on the precision of estimates of striatal and background activity concentration. In order to assess the new collimation system to detect changes in striatal activity, the authors evaluated the precision of measuring a 5% decrease in right putamen activity. The authors also reconstructed images of projection data obtained by summing data from the individual phantom compartments. Results: The sensitivity of the novel cone-beam collimator varied with distance from the detector face; it was higher than that of the fan-beam collimator by factors ranging from 2.7 to 162. Examination of the projections of the point sources revealed that only a few holes were distorted or partially blocked, indicating that the intensive manual fabrication process was very successful. Better reconstructed phantom images were obtained from the USCB+FAN collimator pair than from either LEHR or FAN collimation. For the left caudate, located near the center of the brain, the detected counts were 9.8 (8.3) times higher for UCSB compared with LEHR (FAN), averaged over 60 views. The task-specific SNR for detecting a 5% decrease in putamen uptake was 7.4 for USCB and 3.2 for LEHR. Conclusions: The authors have designed and manufactured a novel collimator for brain SPECT imaging. The sensitivity is much higher than that of a fan-beam collimator. Because of differences between the manufactured collimator and its design, reconstruction of the data requires a measured system matrix. The authors have demonstrated the potential of USCB collimation for improved precision in estimating striatal uptake. The novel collimator may be useful for early detection of Parkinson’s disease, and for monitoring therapy response and disease progression.« less

SU-F-T-604: Dosimetric Evaluation of Intracranial Stereotactic Radiotherapy Plans On a LINAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheth, N; Tabibian, A; Rose, J

2016-06-15

Purpose: To evaluate the dosimetry of cranial stereotactic radiotherapy (SRT) plans of varying techniques on linac that meets appropriate TG-142 tolerances using 1 cm leaf width multileaf collimator (MLC). Methods: Seventeen spherical targets were generated in the center of a head phantom with diameters ranging 8 mm to 40 mm. SRT plans used 100° non-coplanar arcs and 5 couch angles with 35° spacing. The field size was target plus 1 mm margin. Four plans were created for each target: symmetrical jaws blocking for 5 arcs with 0° collimator (J1C), symmetrical jaws blocking with 5 clockwise arcs with 0° collimator andmore » 5 counter-clockwise arcs with 45° collimator (J2C), MLC blocking for 5 dynamic conformal arcs with 0° collimator (M1C), and MLC blocking for 5 clockwise dynamic conformal arcs with 0° collimators and 5 counter-clockwise dynamic conformal arcs with 45° collimator (M2C).Conformity was evaluated using a ratio of Rx to target volume (PITV). Heterogeneity was determined using a ratio of maximum dose to Rx dose. Falloff was scored using CGIg: difference of effective radii of spheres equal to half and full Rx volumes. Results: All plans met RTOG SRS criteria for conformity and heterogeneity. The mean PITV was 1.52±0.07, 1.49±0.08, 1.39±0.05, and 1.37±0.04 for J1C, J2C, M1C, and M2C plans respectively. The mean CGIg was 75.35±15.79, 74.19±16.66, 77.14±15.12, and 76.28±15.78 for J1C, J2C, M1C, and M2C plans respectively. The mean MDPD was 1.25±0.00 for all techniques. Conclusion: Clinically acceptable SRT plans for spherical targets were created on a linac with 1 cm MLC. Adding two collimator angles and MLC to arcs each improved conformity. The MLC improved the dose falloff while two collimator angles degraded it. This technique can expand the availability of SRT to patients especially to those who cannot travel to a facility with a dedicated stereotactic radiosurgery machine.« less

Nondestructive Evaluation of Aircraft Composites Using Terahertz Time Domain Spectroscopy

DTIC Science & Technology

2008-12-10

substrate lenses : collimating and aplanatic. In a collimating lens , the rays emitted near the optic axis emerge as a collimated beam, while the rays...emitted at larger angles emerge at substantial angles or are internally reflected and lost. The aplanatic hyperhemispherical lens design, which...propagates out of the lens before it spreads. Many of the hemispherical designs result in the spreading of the THz beam at a given angle , which can then be

Technology assessment of multileaf collimation: a North American users survey.

PubMed

Klein, E E; Tepper, J; Sontag, M; Franklin, M; Ling, C; Kubo, D

1999-06-01

The American Association of Physicists in Medicine (AAPM) initiated an Assessment of Technology Subcommittee (ATS) to help the radiotherapy community evaluate emerging technologies. The ATS decided to first address multileaf collimation (MLC) by means of a North American users survey. The survey attempted to address issues such as MLC utility, efficacy, cost-effectiveness, and customer satisfaction. The survey was designed with 38 questions, with cross-tabulation set up to decipher a particular clinic's perception of MLC. The surveys were coded according to MLC types, which were narrowed to four: Elekta, Siemens, Varian 52-leaf, and Varian 80-leaf. A 40% return rate was desired. A 44% (108 of 250) return was achieved. On an MLC machine, 76.5% of photon patients are being treated with MLC. The main reasons for not using MLC were stair stepping, field size limitation, and physician objection. The most common sites in which MLC is being used are lung, pelvis, and prostate. The least used sites are head & neck and mantle fields. Of the facilities, 31% claimed an increase in number of patients being treated since MLC was installed, and 44% claimed an increase in the number of fields. Though the staffing for block cutting has decreased, therapist staffing has not. However, 91% of the facilities claimed a decreased workload for the therapists, despite the increase in daily treated patients and fields. Of the facilities that justified MLC purchase for more daily patients, 63% are actually treating more patients. Only 26% of the facilities that justified an MLC purchase for intensity-modulated radiotherapy (IMRT) are currently using it for that purpose. The satisfaction rating (1 = low to 5 = high) for department groups averaged 4.0. Therapists ranked MLC as 4.6. Our survey shows that most users have successfully introduced MLC into the clinic as a block replacement. Most have found MLC to be cost-effective and efficient. The use of MLC for IMRT has progressed slower, but users anticipate escalated use.

Optimization of planar self-collimating photonic crystals.

PubMed

Rumpf, Raymond C; Pazos, Javier J

2013-07-01

Self-collimation in photonic crystals has received a lot of attention in the literature, partly due to recent interest in silicon photonics, yet no performance metrics have been proposed. This paper proposes a figure of merit (FOM) for self-collimation and outlines a methodical approach for calculating it. Performance metrics include bandwidth, angular acceptance, strength, and an overall FOM. Two key contributions of this work include the performance metrics and identifying that the optimum frequency for self-collimation is not at the inflection point. The FOM is used to optimize a planar photonic crystal composed of a square array of cylinders. Conclusions are drawn about how the refractive indices and fill fraction of the lattice impact each of the performance metrics. The optimization is demonstrated by simulating two spatially variant self-collimating photonic crystals, where one has a high FOM and the other has a low FOM. This work gives optical designers tremendous insight into how to design and optimize robust self-collimating photonic crystals, which promises many applications in silicon photonics and integrated optics.

Collimated autostereoscopic displays for cockpit applications

NASA Astrophysics Data System (ADS)

Eichenlaub, Jesse B.

1995-06-01

The use of an autostereoscopic display (a display that produces stereoscopic images that the user can see without wearing special glasses) for cockpit applications is now under investigation at Wright Patterson Air Force Base. DTI reported on this display, built for testing in a simulator, at last year's conference. It is believed, based on testing performed at NASA's Langley Research Center, that collimating this type of display will accrue benefits to the user including a grater useful imaging volume and more accurate stereo perception. DTI has therefore investigated the feasibility of collimating an autostereoscopic display, and has experimentally demonstrated a proof of concept model of such a display. As in the case of conventional displays, a collimated autostereoscopic display utilizes an optical element located one focal length from the surface of the image forming device. The presence of this element must be taken into account when designing the optics used to create the autostereoscopic images. The major design issues associated with collimated 2D displays are also associated with collimated autostereoscopic displays.

BPM Design and Impedance Considerations for a Rotatable Collimator for the LHC Collimation Upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Jeffrey Claiborne; /SLAC; Keller, Lewis

2010-08-26

The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. This paper reports on BPM and impedance considerations and measurements of the integrated BPMs in the prototype rotatable collimator to be installed in the Super Proton Synchrotron (SPS) at CERN. The BPMs are necessary to align the jaws with the beam. Without careful design the beam impedance can result in unacceptable heating of the chamber wall or beam instabilities. The impedance measurements involve utilizing both a single displaced wire and two wiresmore » excited in opposite phase to disentangle the driving and detuning transverse impedances. Trapped mode resonances and longitudinal impedance are to also be measured and compared with simulations. These measurements, when completed, will demonstrate the device is fully operational and has the impedance characteristics and BPM performance acceptable for installation in the SPS.« less

Dose calculation of dynamic trajectory radiotherapy using Monte Carlo.

PubMed

Manser, P; Frauchiger, D; Frei, D; Volken, W; Terribilini, D; Fix, M K

2018-04-06

Using volumetric modulated arc therapy (VMAT) delivery technique gantry position, multi-leaf collimator (MLC) as well as dose rate change dynamically during the application. However, additional components can be dynamically altered throughout the dose delivery such as the collimator or the couch. Thus, the degrees of freedom increase allowing almost arbitrary dynamic trajectories for the beam. While the dose delivery of such dynamic trajectories for linear accelerators is technically possible, there is currently no dose calculation and validation tool available. Thus, the aim of this work is to develop a dose calculation and verification tool for dynamic trajectories using Monte Carlo (MC) methods. The dose calculation for dynamic trajectories is implemented in the previously developed Swiss Monte Carlo Plan (SMCP). SMCP interfaces the treatment planning system Eclipse with a MC dose calculation algorithm and is already able to handle dynamic MLC and gantry rotations. Hence, the additional dynamic components, namely the collimator and the couch, are described similarly to the dynamic MLC by defining data pairs of positions of the dynamic component and the corresponding MU-fractions. For validation purposes, measurements are performed with the Delta4 phantom and film measurements using the developer mode on a TrueBeam linear accelerator. These measured dose distributions are then compared with the corresponding calculations using SMCP. First, simple academic cases applying one-dimensional movements are investigated and second, more complex dynamic trajectories with several simultaneously moving components are compared considering academic cases as well as a clinically motivated prostate case. The dose calculation for dynamic trajectories is successfully implemented into SMCP. The comparisons between the measured and calculated dose distributions for the simple as well as for the more complex situations show an agreement which is generally within 3% of the maximum dose or 3mm. The required computation time for the dose calculation remains the same when the additional dynamic moving components are included. The results obtained for the dose comparisons for simple and complex situations suggest that the extended SMCP is an accurate dose calculation and efficient verification tool for dynamic trajectory radiotherapy. This work was supported by Varian Medical Systems. Copyright © 2018. Published by Elsevier GmbH.

Ultra-high spatial resolution multi-energy CT using photon counting detector technology

NASA Astrophysics Data System (ADS)

Leng, S.; Gutjahr, R.; Ferrero, A.; Kappler, S.; Henning, A.; Halaweish, A.; Zhou, W.; Montoya, J.; McCollough, C.

2017-03-01

Two ultra-high-resolution (UHR) imaging modes, each with two energy thresholds, were implemented on a research, whole-body photon-counting-detector (PCD) CT scanner, referred to as sharp and UHR, respectively. The UHR mode has a pixel size of 0.25 mm at iso-center for both energy thresholds, with a collimation of 32 × 0.25 mm. The sharp mode has a 0.25 mm pixel for the low-energy threshold and 0.5 mm for the high-energy threshold, with a collimation of 48 × 0.25 mm. Kidney stones with mixed mineral composition and lung nodules with different shapes were scanned using both modes, and with the standard imaging mode, referred to as macro mode (0.5 mm pixel and 32 × 0.5 mm collimation). Evaluation and comparison of the three modes focused on the ability to accurately delineate anatomic structures using the high-spatial resolution capability and the ability to quantify stone composition using the multi-energy capability. The low-energy threshold images of the sharp and UHR modes showed better shape and texture information due to the achieved higher spatial resolution, although noise was also higher. No noticeable benefit was shown in multi-energy analysis using UHR compared to standard resolution (macro mode) when standard doses were used. This was due to excessive noise in the higher resolution images. However, UHR scans at higher dose showed improvement in multi-energy analysis over macro mode with regular dose. To fully take advantage of the higher spatial resolution in multi-energy analysis, either increased radiation dose, or application of noise reduction techniques, is needed.

MEGARA spectrograph optics

NASA Astrophysics Data System (ADS)

Carrasco, E.; Sánchez-Blanco, E.; García-Vargas, M. L.; Gil de Paz, A.; Páez, G.; Gallego, J.; Sánchez, F. M.; Vílchez, J. M.

2012-09-01

MEGARA is the next optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) for Gran Telescopio Canarias. The instrument offers two IFUs plus a Multi-Object Spectroscopy (MOS) mode: a large compact bundle covering 12.5 arcsec x 11.3 arcsec on sky with 100 μm fiber-core; a small compact bundle, of 8.5 arcsec x 6.7 arcsec with 70 μm fiber-core and a fiber MOS positioner that allows to place up to 100 mini-bundles, 7 fibers each, with 100 μm fiber-core, within a 3.5 arcmin x 3.5 arcmin field of view, around the two IFUs. The fibers, organized in bundles, end in the pseudo-slit plate, which will be placed at the entrance focal plane of the MEGARA spectrograph. The large IFU and MOS modes will provide intermediate to high spectral resolutions, R=6800-17000. The small IFU mode will provide R=8000-20000. All these resolutions are possible thanks to a spectrograph design based in the used of volume phase holographic gratings in combination with prisms to keep fixed the collimator and camera angle. The MEGARA optics is composed by a total of 53 large optical elements per spectrograph: the field lens, the collimator and the camera lenses plus the complete set of pupil elements including holograms, windows and prisms. INAOE, a partner of the GTC and a partner of MEGARA consortium, is responsible of the optics manufacturing and tests. INAOE will carry out this project working in an alliance with CIO. This paper summarizes the status of MEGARA spectrograph optics at the Preliminary Design Review, held on March 2012.

Design and implementation of a crystal collimation test stand at the Large Hadron Collider

NASA Astrophysics Data System (ADS)

Mirarchi, D.; Hall, G.; Redaelli, S.; Scandale, W.

2017-06-01

Future upgrades of the CERN Large Hadron Collider (LHC) demand improved cleaning performance of its collimation system. Very efficient collimation is required during regular operations at high intensities, because even a small amount of energy deposited on superconducting magnets can cause an abrupt loss of superconducting conditions (quench). The possibility to use a crystal-based collimation system represents an option for improving both cleaning performance and impedance compared to the present system. Before relying on crystal collimation for the LHC, a demonstration under LHC conditions (energy, beam parameters, etc.) and a comparison against the present system is considered mandatory. Thus, a prototype crystal collimation system has been designed and installed in the LHC during the Long Shutdown 1 (LS1), to perform feasibility tests during the Run 2 at energies up to 6.5 TeV. The layout is suitable for operation with proton as well as heavy ion beams. In this paper, the design constraints and the solutions proposed for this test stand for feasibility demonstration of crystal collimation at the LHC are presented. The expected cleaning performance achievable with this test stand, as assessed in simulations, is presented and compared to that of the present LHC collimation system. The first experimental observation of crystal channeling in the LHC at the record beam energy of 6.5 TeV has been obtained in 2015 using the layout presented (Scandale et al., Phys Lett B 758:129, 2016). First tests to measure the cleaning performance of this test stand have been carried out in 2016 and the detailed data analysis is still on-going.

Analysis of Neutron Production in Passively Scattered Ion-Beam Therapy.

PubMed

Heo, Seunguk; Yoo, Seunghoon; Song, Yongkeun; Kim, Eunho; Shin, Jaeik; Han, Soorim; Jung, Wongyun; Nam, Sanghee; Lee, Rena; Lee, Kitae; Cho, Sungho

2017-07-01

A new treatment facility for heavy ion therapy since 2010 was constructed. In the broad beam, a range shifter, ridge filter and multi leaf collimator (MLC) for the generation of the spread-out Bragg peak is used. In this case, secondary neutrons produced by the interactions of the ion field with beam-modifying devices (e.g. double-scattering system, beam shaping collimators and range compensators) are very important for patient safety. Therefore, these components must be carefully examined in the context of secondary neutron yield and associated secondary cancer risk. In this article, Monte Carlo simulation has been carried out with the FLUktuierende KAskade particle transport code, the fluence and distribution of neutron generation and the neutron dose equivalent from the broad beam components are compared using carbon and proton beams. As a result, it is confirmed that the yield of neutron production using a carbon beam from all components of the broad beam was higher than using a proton beam. The ambient dose by neutrons per heavy ion and proton ion from the MLC surface was 0.12-0.18 and 0.0067-0.0087 pSv, respectively, which shows that heavy ions generate more neutrons than protons. However, ambient dose per treatment 2 Gy, which means physical dose during treatment by ion beam, is higher than carbon beam because proton therapy needs more beam flux to make 2-Gy prescription dose. Therefore, the neutron production from the MLC, which is closed to the patient, is a very important parameter for patient safety. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

SPECT data acquisition and image reconstruction in a stationary small animal SPECT/MRI system

NASA Astrophysics Data System (ADS)

Xu, Jingyan; Chen, Si; Yu, Jianhua; Meier, Dirk; Wagenaar, Douglas J.; Patt, Bradley E.; Tsui, Benjamin M. W.

2010-04-01

The goal of the study was to investigate data acquisition strategies and image reconstruction methods for a stationary SPECT insert that can operate inside an MRI scanner with a 12 cm bore diameter for simultaneous SPECT/MRI imaging of small animals. The SPECT insert consists of 3 octagonal rings of 8 MR-compatible CZT detectors per ring surrounding a multi-pinhole (MPH) collimator sleeve. Each pinhole is constructed to project the field-of-view (FOV) to one CZT detector. All 24 pinholes are focused to a cylindrical FOV of 25 mm in diameter and 34 mm in length. The data acquisition strategies we evaluated were optional collimator rotations to improve tomographic sampling; and the image reconstruction methods were iterative ML-EM with and without compensation for the geometric response function (GRF) of the MPH collimator. For this purpose, we developed an analytic simulator that calculates the system matrix with the GRF models of the MPH collimator. The simulator was used to generate projection data of a digital rod phantom with pinhole aperture sizes of 1 mm and 2 mm and with different collimator rotation patterns. Iterative ML-EM reconstruction with and without GRF compensation were used to reconstruct the projection data from the central ring of 8 detectors only, and from all 24 detectors. Our results indicated that without GRF compensation and at the default design of 24 projection views, the reconstructed images had significant artifacts. Accurate GRF compensation substantially improved the reconstructed image resolution and reduced image artifacts. With accurate GRF compensation, useful reconstructed images can be obtained using 24 projection views only. This last finding potentially enables dynamic SPECT (and/or MRI) studies in small animals, one of many possible application areas of the SPECT/MRI system. Further research efforts are warranted including experimentally measuring the system matrix for improved geometrical accuracy, incorporating the co-registered MRI image in SPECT reconstruction, and exploring potential applications of the simultaneous SPECT/MRI SA system including dynamic SPECT studies.

Influence of detector collimation on SNR in four different MDCT scanners using a reconstructed slice thickness of 5 mm.

PubMed

Verdun, F R; Noel, A; Meuli, R; Pachoud, M; Monnin, P; Valley, J-F; Schnyder, P; Denys, A

2004-10-01

The purpose of this paper is to compare the influence of detector collimation on the signal-to-noise ratio (SNR) for a 5.0 mm reconstructed slice thickness for four multi-detector row CT (MDCT) units. SNRs were measured on Catphan test phantom images from four MDCT units: a GE LightSpeed QX/I, a Marconi MX 8000, a Toshiba Aquilion and a Siemens Volume Zoom. Five-millimetre-thick reconstructed slices were obtained from acquisitions performed using detector collimations of 2.0-2.5 mm and 5.0 mm, 120 kV, a 360 degrees tube rotation time of 0.5 s, a wide range of mA and pitch values in the range of 0.75-0.85 and 1.25-1.5. For each set of acquisition parameters, a Wiener spectrum was also calculated. Statistical differences in SNR for the different acquisition parameters were evaluated using a Student's t-test (P<0.05). The influence of detector collimation on the SNR for a 5.0-mm reconstructed slice thickness is different for different MDCT scanners. At pitch values lower than unity, the use of a small detector collimation to produce 5.0-mm thick slices is beneficial for one unit and detrimental for another. At pitch values higher than unity, using a small detector collimation is beneficial for two units. One manufacturer uses different reconstruction filters when switching from a 2.5- to a 5.0-mm detector collimation. For a comparable reconstructed slice thickness, using a smaller detector collimation does not always reduce image noise. Thus, the impact of the detector collimation on image noise should be determined by standard deviation calculations, and also by assessing the power spectra of the noise. Copyright 2004 Springer-Verlag

Compact, high-resolution, gamma ray imaging for scintimammography and other medical diagostic applications

DOEpatents

Majewski, Stanislaw; Weisenberger, Andrew G.; Wojcik, Randolph F.; Steinbach, Daniela

1999-01-01

A high resolution gamma ray imaging device includes an aluminum housing, a lead screen collimator at an opened end of the housing, a crystal scintillator array mounted behind the lead screen collimator, a foam layer between the lead screen collimator and the crystal scintillator array, a photomultiplier window coupled to the crystal with optical coupling grease, a photomultiplier having a dynode chain body and a base voltage divider with anodes, anode wire amplifiers each connected to four anodes and a multi pin connector having pin connections to each anode wire amplifier. In one embodiment the crystal scintillator array includes a yttrium aluminum perovskite (YAP) crystal array. In an alternate embodiment, the crystal scintillator array includes a gadolinium oxyorthosilicate (GSO) crystal array.

A micro-scale plasma spectrometer for space and plasma edge applications (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scime, E. E., E-mail: escime@wvu.edu; Keesee, A. M.; Elliott, D.

2016-11-15

A plasma spectrometer design based on advances in lithography and microchip stacking technologies is described. A series of curved plate energy analyzers, with an integrated collimator, is etched into a silicon wafer. Tests of spectrometer elements, the energy analyzer and collimator, were performed with a 5 keV electron beam. The measured collimator transmission and energy selectivity were in good agreement with design targets. A single wafer element could be used as a plasma processing or fusion first wall diagnostic.

Patient handling system for carbon ion beam scanning therapy

PubMed Central

Shirai, Toshiyuki; Takei, Yuka; Furukawa, Takuji; Inaniwa, Taku; Matsuzaki, Yuka; Kumagai, Motoki; Murakami, Takeshi; Noda, Koji

2012-01-01

Our institution established a new treatment facility for carbon ion beam scanning therapy in 2010. The major advantages of scanning beam treatment compared to the passive beam treatment are the following: high dose conformation with less excessive dose to the normal tissues, no bolus compensator and patient collimator/ multi‐leaf collimator, better dose efficiency by reducing the number of scatters. The new facility was designed to solve several problems encountered in the existing facility, at which several thousand patients were treated over more than 15 years. Here, we introduce the patient handling system in the new treatment facility. The new facility incorporates three main systems, a scanning irradiation system (S‐IR), treatment planning system (TPS), and patient handling system (PTH). The PTH covers a wide range of functions including imaging, geometrical/position accuracy including motion management (immobilization, robotic arm treatment bed), layout of the treatment room, treatment workflow, software, and others. The first clinical trials without respiratory gating have been successfully started. The PTH allows a reduction in patient stay in the treatment room to as few as 7 min. The PTH plays an important role in carbon ion beam scanning therapy at the new institution, particularly in the management of patient handling, application of image‐guided therapy, and improvement of treatment workflow, and thereby allows substantially better treatment at minimum cost. PACS numbers: 87.56.‐v; 87.57.‐s; 87.55.‐x PMID:23149784

Computerized optimization of multiple isocentres in stereotactic convergent beam irradiation

NASA Astrophysics Data System (ADS)

Treuer, U.; Treuer, H.; Hoevels, M.; Müller, R. P.; Sturm, V.

1998-01-01

A method for the fully computerized determination and optimization of positions of target points and collimator sizes in convergent beam irradiation is presented. In conventional interactive trial and error methods, which are very time consuming, the treatment parameters are chosen according to the operator's experience and improved successively. This time is reduced significantly by the use of a computerized procedure. After the definition of target volume and organs at risk in the CT or MR scans, an initial configuration is created automatically. In the next step the target point positions and collimator diameters are optimized by the program. The aim of the optimization is to find a configuration for which a prescribed dose at the target surface is approximated as close as possible. At the same time dose peaks inside the target volume are minimized and organs at risk and tissue surrounding the target are spared. To enhance the speed of the optimization a fast method for approximate dose calculation in convergent beam irradiation is used. A possible application of the method for calculating the leaf positions when irradiating with a micromultileaf collimator is briefly discussed. The success of the procedure has been demonstrated for several clinical cases with up to six target points.

SU-G-BRC-04: Collimator Angle Optimization in Volumetric Modulated Arc Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersen, A; Johnson, C; Bartlett, G

2016-06-15

Purpose: Volumetric modulated arc therapy (VMAT) has revolutionized radiation treatment by decreasing treatment time and monitor units, thus reducing scattered and whole body radiation dose. As the collimator angle changes the apparent leaf gap becomes larger which can impact plan quality, organ at risk (OAR) sparing as well as IMRT QA passing rate which is investigated. Methods: Two sites (prostate and head and neck) that have maximum utilization of VMAT were investigated. Two previously treated VMAT patients were chosen. For each patient 10 plans were created by maintaining constant optimization constraints while varying collimator angles from 0-90 deg at anmore » interval of 10 degrees for the first arc and the appropriate complimentary angle for the second arc. Plans were created with AAA algorithm using 6 MV beam on a Varian IX machine with Millennium 120 MLC. The dose-volume histogram (DVH) for each plan was exported and dosimetric parameters (D98, D95, D50, D2) as well homogeneity index (HI) and conformity index (CI) were computed. Each plan was validated for QA using ArcCheck with gamma index passing criteria of 2%/2 mm and 3%/3 mm. Additionally, normal tissue complication probability (NTCP) for each OAR was computed using Uzan-Nahum software. Results: The CI values for both sites had no impact as target volume coverage in every collimator angle were the same since it was optimized for adequate coverage. The HI which is representative of DVH gradient or dose uniformity in PTV showed a clear trend in both sites. The NTCP for OAR (brain and cochlea) in H&N plan and (bladder and rectum) in prostate plan showed a distinct superiority for collimator angles between 15-30 deg. The gamma passing rates were not correlated with angle. Conclusion: Based on CI, HI, NTCP and gamma passing index, it can be concluded that collimator angles should be maintained within 15–30 deg.« less

Model-Based Normalization of a Fractional-Crystal Collimator for Small-Animal PET Imaging

PubMed Central

Li, Yusheng; Matej, Samuel; Karp, Joel S.; Metzler, Scott D.

2017-01-01

Previously, we proposed to use a coincidence collimator to achieve fractional-crystal resolution in PET imaging. We have designed and fabricated a collimator prototype for a small-animal PET scanner, A-PET. To compensate for imperfections in the fabricated collimator prototype, collimator normalization, as well as scanner normalization, is required to reconstruct quantitative and artifact-free images. In this study, we develop a normalization method for the collimator prototype based on the A-PET normalization using a uniform cylinder phantom. We performed data acquisition without the collimator for scanner normalization first, and then with the collimator from eight different rotation views for collimator normalization. After a reconstruction without correction, we extracted the cylinder parameters from which we generated expected emission sinograms. Single scatter simulation was used to generate the scattered sinograms. We used the least-squares method to generate the normalization coefficient for each LOR based on measured, expected and scattered sinograms. The scanner and collimator normalization coefficients were factorized by performing two normalizations separately. The normalization methods were also verified using experimental data acquired from A-PET with and without the collimator. In summary, we developed a model-base collimator normalization that can significantly reduce variance and produce collimator normalization with adequate statistical quality within feasible scan time. PMID:29270539

Model-Based Normalization of a Fractional-Crystal Collimator for Small-Animal PET Imaging.

PubMed

Li, Yusheng; Matej, Samuel; Karp, Joel S; Metzler, Scott D

2017-05-01

Previously, we proposed to use a coincidence collimator to achieve fractional-crystal resolution in PET imaging. We have designed and fabricated a collimator prototype for a small-animal PET scanner, A-PET. To compensate for imperfections in the fabricated collimator prototype, collimator normalization, as well as scanner normalization, is required to reconstruct quantitative and artifact-free images. In this study, we develop a normalization method for the collimator prototype based on the A-PET normalization using a uniform cylinder phantom. We performed data acquisition without the collimator for scanner normalization first, and then with the collimator from eight different rotation views for collimator normalization. After a reconstruction without correction, we extracted the cylinder parameters from which we generated expected emission sinograms. Single scatter simulation was used to generate the scattered sinograms. We used the least-squares method to generate the normalization coefficient for each LOR based on measured, expected and scattered sinograms. The scanner and collimator normalization coefficients were factorized by performing two normalizations separately. The normalization methods were also verified using experimental data acquired from A-PET with and without the collimator. In summary, we developed a model-base collimator normalization that can significantly reduce variance and produce collimator normalization with adequate statistical quality within feasible scan time.

Use of Herbal Supplements in Chronic Kidney Disease

MedlinePlus

... build up in your body. The herbal supplement market is a multi-million dollar business. You may ... Ginseng Bai Zhi (root) Bitter Melon (fruit, leaf) Black Mustard (leaf) Blessed Thistle Chervit (leaf) Chicory (leaf) ...

A Silicon SPECT System for Molecular Imaging of the Mouse Brain.

PubMed

Shokouhi, Sepideh; Fritz, Mark A; McDonald, Benjamin S; Durko, Heather L; Furenlid, Lars R; Wilson, Donald W; Peterson, Todd E

2007-01-01

We previously demonstrated the feasibility of using silicon double-sided strip detectors (DSSDs) for SPECT imaging of the activity distribution of iodine-125 using a 300-micrometer thick detector. Based on this experience, we now have developed fully customized silicon DSSDs and associated readout electronics with the intent of developing a multi-pinhole SPECT system. Each DSSD has a 60.4 mm × 60.4 mm active area and is 1 mm thick. The strip pitch is 59 micrometers, and the readout of the 1024 strips on each side gives rise to a detector with over one million pixels. Combining four high-resolution DSSDs into a SPECT system offers an unprecedented space-bandwidth product for the imaging of single-photon emitters. The system consists of two camera heads with two silicon detectors stacked one behind the other in each head. The collimator has a focused pinhole system with cylindrical-shaped pinholes that are laser-drilled in a 250 μm tungsten plate. The unique ability to collect projection data at two magnifications simultaneously allows for multiplexed data at high resolution to be combined with lower magnification data with little or no multiplexing. With the current multi-pinhole collimator design, our SPECT system will be capable of offering high spatial resolution, sensitivity and angular sampling for small field-of-view applications, such as molecular imaging of the mouse brain.

Direct design of achromatic lens for Lambertian sources in collimating illumination

NASA Astrophysics Data System (ADS)

Yin, Peng; Xu, Xiping; Jiang, Zhaoguo; Wang, Hongshu

2017-10-01

Illumination design used to redistribute the spatial energy distribution of light source is a key technique in lighting applications. However, there is still no effective illumination design method for the removing of the chromatic dispersion. What we present here is an achromatic lens design to enhance the efficiency and uniform illumination of white light-emitting diode (LED) with diffractive optical element (DOE). We employ the chromatic aberration value (deg) to measure the degree of chromatic dispersion in illumination systems. Monte Carlo ray tracing simulation results indicate that the chromatic dispersion of the modified achromatic collimator significantly decreases from 0.5 to 0.1 with LED chip size of 1.0mm×1.0mm and simulation efficiency of 90.73%, compared with the traditional collimator. Moreover, with different corrected wavelengths we compared different chromatic aberration values that followed with the changing pupil percent. The achromatic collimator provided an effective way to achieve white LED with low chromatic dispersion at high efficiency and uniform illumination.

Applications of Elpasolites as a Multimode Radiation Sensor

NASA Astrophysics Data System (ADS)

Guckes, Amber

This study consists of both computational and experimental investigations. The computational results enabled detector design selections and confirmed experimental results. The experimental results determined that the CLYC scintillation detector can be applied as a functional and field-deployable multimode radiation sensor. The computational study utilized MCNP6 code to investigate the response of CLYC to various incident radiations and to determine the feasibility of its application as a handheld multimode sensor and as a single-scintillator collimated directional detection system. These simulations include: • Characterization of the response of the CLYC scintillator to gamma-rays and neutrons; • Study of the isotopic enrichment of 7Li versus 6Li in the CLYC for optimal detection of both thermal neutrons and fast neutrons; • Analysis of collimator designs to determine the optimal collimator for the single CLYC sensor directional detection system to assay gamma rays and neutrons; Simulations of a handheld CLYC multimode sensor and a single CLYC scintillator collimated directional detection system with the optimized collimator to determine the feasibility of detecting nuclear materials that could be encountered during field operations. These nuclear materials include depleted uranium, natural uranium, low-enriched uranium, highly-enriched uranium, reactor-grade plutonium, and weapons-grade plutonium. The experimental study includes the design, construction, and testing of both a handheld CLYC multimode sensor and a single CLYC scintillator collimated directional detection system. Both were designed in the Inventor CAD software and based on results of the computational study to optimize its performance. The handheld CLYC multimode sensor is modular, scalable, low?power, and optimized for high count rates. Commercial?off?the?shelf components were used where possible in order to optimize size, increase robustness, and minimize cost. The handheld CLYC multimode sensor was successfully tested to confirm its ability for gamma-ray and neutron detection, and gamma?ray and neutron spectroscopy. The sensor utilizes wireless data transfer for possible radiation mapping and network?centric deployment. The handheld multimode sensor was tested by performing laboratory measurements with various gamma-ray sources and neutron sources. The single CLYC scintillator collimated directional detection system is portable, robust, and capable of source localization and identification. The collimator was designed based on the results of the computational study and is constructed with high density polyethylene (HDPE) and lead (Pb). The collimator design and construction allows for the directional detection of gamma rays and fast neutrons utilizing only one scintillator which is interchangeable. For this study, a CLYC-7 scintillator was used. The collimated directional detection system was tested by performing laboratory directional measurements with various gamma-ray sources, 252Cf and a 239PuBe source.

SU-E-T-563: Multi-Fraction Stereotactic Radiosurgery with Extend System of Gamma Knife: Treatment Verification Using Indigenously Designed Patient Simulating Multipurpose Phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisht, R; Kale, S; Gopishankar, N

2015-06-15

Purpose: Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom. Methods: A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum headmore » cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X-Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi-fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner. Results: The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of > 95%. Conclusion: Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife. The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247)« less

Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source

DOE PAGES

Tamalonis, A.; Weber, J. K. R.; Neuefeind, J. C.; ...

2015-09-09

We constructed and tested five neutron collimator designs using the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. Moreover, in the Q-range 10-20 Å -1, signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 Å -1, the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q similar to 9.5 Å -1 was significantly decreased when themore » collimators were installed.« less

Modulation transfer function assessment in parallel beam and fan beam collimators with square and cylindrical holes.

PubMed

Khorshidi, Abdollah; Ashoor, Mansour

2014-05-01

This study investigates modulation transfer function (MTF) in parallel beam (PB) and fan beam (FB) collimators using the Monte Carlo method with full width at half maximum (FWHM), square and circular-shaped holes, and scatter and penetration (S + P) components. A regulation similar to the lead-to-air ratio was used for both collimators to estimate output data. The hole pattern was designed to compare FB by PB parameters. The radioactive source in air and in a water phantom placed in front of the collimators was simulated using MCNP5 code. The test results indicated that the square holes in PB (PBs) had better FWHM than did the cylindrical (PBc) holes. In contrast, the cylindrical holes in the FB (FBc) had better FWHM than the square holes. In general, the resolution of FBc was better than that of the PBc in air and scatter mediums. The S + P decreased for all collimators as the distance from the source to the collimator surface (z) increased. The FBc had a lower S + P than FBs, but PBc had a higher S + P than PBs. Of the FB and PB collimators with the identical hole shapes, PBs had a smaller S + P than FBs, and FBc had a smaller S + P than PBc. The MTF value for the FB was greater than for the PB and had increased spatial frequency; the FBc had higher MTF than the FBs and PB collimators. Estimating the FB using PB parameters and diverse hole shapes may be useful in collimator design to improve the resolution and efficiency of SPECT images.

Application of Gaussian beam ray-equivalent model and back-propagation artificial neural network in laser diode fast axis collimator assembly.

PubMed

Yu, Hao; Rossi, Giammarco; Braglia, Andrea; Perrone, Guido

2016-08-10

The paper presents the development of a tool based on a back-propagation artificial neural network to assist in the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodes along the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network is capable of indicating the tilt, decenter, and defocus of such lenses from the measured field distribution, so the operator can determine the errors with respect to the actual lens position and optimize the diode assembly procedure. An experimental validation using a typical configuration exploited in multi-emitter diode module assembly and fast axis collimating lenses with different focal lengths and numerical apertures is reported.

Review of SPECT collimator selection, optimization, and fabrication for clinical and preclinical imaging

PubMed Central

Van Audenhaege, Karen; Van Holen, Roel; Vandenberghe, Stefaan; Vanhove, Christian; Metzler, Scott D.; Moore, Stephen C.

2015-01-01

In single photon emission computed tomography, the choice of the collimator has a major impact on the sensitivity and resolution of the system. Traditional parallel-hole and fan-beam collimators used in clinical practice, for example, have a relatively poor sensitivity and subcentimeter spatial resolution, while in small-animal imaging, pinhole collimators are used to obtain submillimeter resolution and multiple pinholes are often combined to increase sensitivity. This paper reviews methods for production, sensitivity maximization, and task-based optimization of collimation for both clinical and preclinical imaging applications. New opportunities for improved collimation are now arising primarily because of (i) new collimator-production techniques and (ii) detectors with improved intrinsic spatial resolution that have recently become available. These new technologies are expected to impact the design of collimators in the future. The authors also discuss concepts like septal penetration, high-resolution applications, multiplexing, sampling completeness, and adaptive systems, and the authors conclude with an example of an optimization study for a parallel-hole, fan-beam, cone-beam, and multiple-pinhole collimator for different applications. PMID:26233207

Improved estimation of leaf area index and leaf chlorophyll content of a potato crop using multi-angle spectral data - potential of unmanned aerial vehicle imagery

NASA Astrophysics Data System (ADS)

Roosjen, Peter P. J.; Brede, Benjamin; Suomalainen, Juha M.; Bartholomeus, Harm M.; Kooistra, Lammert; Clevers, Jan G. P. W.

2018-04-01

In addition to single-angle reflectance data, multi-angular observations can be used as an additional information source for the retrieval of properties of an observed target surface. In this paper, we studied the potential of multi-angular reflectance data for the improvement of leaf area index (LAI) and leaf chlorophyll content (LCC) estimation by numerical inversion of the PROSAIL model. The potential for improvement of LAI and LCC was evaluated for both measured data and simulated data. The measured data was collected on 19 July 2016 by a frame-camera mounted on an unmanned aerial vehicle (UAV) over a potato field, where eight experimental plots of 30 × 30 m were designed with different fertilization levels. Dozens of viewing angles, covering the hemisphere up to around 30° from nadir, were obtained by a large forward and sideways overlap of collected images. Simultaneously to the UAV flight, in situ measurements of LAI and LCC were performed. Inversion of the PROSAIL model was done based on nadir data and based on multi-angular data collected by the UAV. Inversion based on the multi-angular data performed slightly better than inversion based on nadir data, indicated by the decrease in RMSE from 0.70 to 0.65 m2/m2 for the estimation of LAI, and from 17.35 to 17.29 μg/cm2 for the estimation of LCC, when nadir data were used and when multi-angular data were used, respectively. In addition to inversions based on measured data, we simulated several datasets at different multi-angular configurations and compared the accuracy of the inversions of these datasets with the inversion based on data simulated at nadir position. In general, the results based on simulated (synthetic) data indicated that when more viewing angles, more well distributed viewing angles, and viewing angles up to larger zenith angles were available for inversion, the most accurate estimations were obtained. Interestingly, when using spectra simulated at multi-angular sampling configurations as were captured by the UAV platform (view zenith angles up to 30°), already a huge improvement could be obtained when compared to solely using spectra simulated at nadir position. The results of this study show that the estimation of LAI and LCC by numerical inversion of the PROSAIL model can be improved when multi-angular observations are introduced. However, for the potato crop, PROSAIL inversion for measured data only showed moderate accuracy and slight improvements.

Machine-related backgrounds in the SiD detector at ILC

NASA Astrophysics Data System (ADS)

Denisov, D. S.; Mokhov, N. V.; Striganov, S. I.; Kostin, M. A.; Tropin, I. S.

2006-12-01

With a multi-stage collimation system and magnetic iron spoilers in the tunnel, the background particle fluxes on the ILC detector can be substantially reduced. At the same time, beam-halo interactions with collimators and protective masks in the beam delivery system create fluxes of muons and other secondary particles which can still exceed the tolerable levels for some of the ILC sub-detectors. Results of modeling of such backgrounds in comparison to those from the e+e- interactions are presented in this paper for the SiD detector.

Laser diode stack beam shaping for efficient and compact long-range laser illuminator design

NASA Astrophysics Data System (ADS)

Lutz, Y.; Poyet, J. M.

2014-04-01

Laser diode stacks are interesting laser sources for active imaging illuminators. They allow the accumulation of large amounts of energy in multi-pulse mode, which is best suited for long-range image recording. Even when the laser diode stacks are equipped with fast-axis collimation (FAC) and slow-axis collimation (SAC) micro-lenses, their beam parameter products BPP are not compatible with direct use in highly efficient and compact illuminators. This is particularly true when narrow divergences are required such as for long-range applications. A solution to overcome these difficulties is to enhance the poor slow-axis BPP by virtually restacking the laser diode stack. We present a beam shaping and homogenization method that is low-cost and efficient and has low alignment sensitivity. After conducting simulations, we have realized and characterized the illuminator. A compact long-range laser illuminator has been set up with a divergence of 3.5×2.6 mrad and a global efficiency of 81%. Here, a projection lens with a clear aperture of 62 mm and a focal length of 571 mm was used.

SU-E-T-331: Dosimetric Impact of Multileaf Collimator Leaf Width On Stereotactic Radiosurgery (SRS) RapidArc Treatment Plans for Single and Multiple Brain Metastases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hossain, S; Keeling, V; Ahmad, S

Purpose: To determine the effects of multileaf collimator (MLC) leaf width on normal-brain-tissue doses and dose conformity of SRS RapidArc treatment plans for brain tumors. Methods: Ten patients with 24 intracranial tumors (seven with 1–2 and three with 4–6 lesions) were planned using RapidArc for both Varian Millennium 120 MLC (5 mm leaf width) and high definition (HD) MLC (2.5 mm leaf width). Between 2 and 8 arcs were used with two full coplanar arcs and the rest non-coplanar half arcs. 6 MV beams were used and plans were optimized with a high priority to the Normal Tissue Objective (tomore » achieve dose conformity and sharp dose fall-off) and normal brain tissue. Calculation was done using AAA on a 1 mm grid size. The prescription dose ranged from 14–22 Gy. Plans were normalized such that 99% of the target received the prescription dose. Identical beam geometries, optimizations, calculations, and normalizations were used for both plans. Paddick Conformity Index (PCI), V4, V8 and V12 Gy for normal brain tissue and Integral Dose were used for analysis. Results: In all cases, HD MLC plans performed better in sparing normal brain tissue, achieving a higher PCI with a lower Integral Dose. The average PCI for all 24 targets was 0.75±0.23 and 0.70±0.23 (p ≤0.0015) for HD MLC and Millennium MLC plans, respectively. The average ratio of normal brain doses for Millennium MLC to HD MLC plans was 1.30±0.16, 1.27±0.15, and 1.31±0.18 for the V4, V8, and V12, respectively. The differences in normal brain dose for all criteria were statistically significant with p-value < 0.02. On average Millennium MLC plans had a 16% higher integral dose than HD MLC plans. Conclusion: Significantly better dose conformity with reduced volume of normal brain tissue and integral dose was achieved with HD MLC plans compared to Millennium MLC plans.« less

Characterization of plastic and boron carbide additive manufactured neutron collimators

NASA Astrophysics Data System (ADS)

Stone, M. B.; Siddel, D. H.; Elliott, A. M.; Anderson, D.; Abernathy, D. L.

2017-12-01

Additive manufacturing techniques allow for the production of materials with complicated geometries with reduced costs and production time over traditional methods. We have applied this technique to the production of neutron collimators for use in thermal and cold neutron scattering instrumentation directly out of boron carbide. We discuss the design and generation of these collimators. We also provide measurements at neutron scattering beamlines which serve to characterize the performance of these collimators. Additive manufacturing of parts using neutron absorbing material may also find applications in radiography and neutron moderation.

Chalcogenide molded freeform optics for mid-infrared lasers

NASA Astrophysics Data System (ADS)

Chenard, Francois; Alvarez, Oseas; Yi, Allen

2017-05-01

High-precision chalcogenide molded micro-lenses were produced to collimate mid-infrared Quantum Cascade Lasers (QCLs). Molded cylindrical micro-lens prototypes with aspheric contour (acylindrical), high numerical aperture (NA 0.8) and small focal length (f<2 mm) were fabricated to collimate the QCL fast-axis beam. Another innovative freeform micro-lens has an input acylindrical surface to collimate the fast axis and an orthogonal output acylindrical surface to collimate the slow axis. The thickness of the freeform lens is such that the output fast- and slow-axis beams are circular. This paper presents results on the chalcogenide molded freeform micro-lens designed to collimate and circularize QCL at 4.6 microns.

Optimal design of a high accuracy photoelectric auto-collimator based on position sensitive detector

NASA Astrophysics Data System (ADS)

Yan, Pei-pei; Yang, Yong-qing; She, Wen-ji; Liu, Kai; Jiang, Kai; Duan, Jing; Shan, Qiusha

2018-02-01

A kind of high accuracy Photo-electric auto-collimator based on PSD was designed. The integral structure composed of light source, optical lens group, Position Sensitive Detector (PSD) sensor, and its hardware and software processing system constituted. Telephoto objective optical type is chosen during the designing process, which effectively reduces the length, weight and volume of the optical system, as well as develops simulation-based design and analysis of the auto-collimator optical system. The technical indicators of auto-collimator presented by this paper are: measuring resolution less than 0.05″; a field of view is 2ω=0.4° × 0.4° measuring range is +/-5' error of whole range measurement is less than 0.2″. Measuring distance is 10m, which are applicable to minor-angle precise measuring environment. Aberration analysis indicates that the MTF close to the diffraction limit, the spot in the spot diagram is much smaller than the Airy disk. The total length of the telephoto lens is only 450mm by the design of the optical machine structure optimization. The autocollimator's dimension get compact obviously under the condition of the image quality is guaranteed.

Optical design of MEMS-based infrared multi-object spectrograph concept for the Gemini South Telescope

NASA Astrophysics Data System (ADS)

Chen, Shaojie; Sivanandam, Suresh; Moon, Dae-Sik

2016-08-01

We discuss the optical design of an infrared multi-object spectrograph (MOS) concept that is designed to take advantage of the multi-conjugate adaptive optics (MCAO) corrected field at the Gemini South telescope. This design employs a unique, cryogenic MEMS-based focal plane mask to select target objects for spectroscopy by utilizing the Micro-Shutter Array (MSA) technology originally developed for the Near Infrared Spectrometer (NIRSpec) of the James Webb Space Telescope (JWST). The optical design is based on all spherical refractive optics, which serves both imaging and spectroscopic modes across the wavelength range of 0.9-2.5 μm. The optical system consists of a reimaging system, MSA, collimator, volume phase holographic (VPH) grisms, and spectrograph camera optics. The VPH grisms, which are VPH gratings sandwiched between two prisms, provide high dispersing efficiencies, and a set of several VPH grisms provide the broad spectral coverage at high throughputs. The imaging mode is implemented by removing the MSA and the dispersing unit out of the beam. We optimize both the imaging and spectrographic modes simultaneously, while paying special attention to the performance of the pupil imaging at the cold stop. Our current design provides a 1' ♢ 1' and a 0.5' ♢ 1' field of views for imaging and spectroscopic modes, respectively, on a 2048 × 2048 pixel HAWAII-2RG detector array. The spectrograph's slit width and spectral resolving power are 0.18'' and 3,000, respectively, and spectra of up to 100 objects can be obtained simultaneously. We present the overall results of simulated performance using optical model we designed.

Mini-beam collimator applications at the Advanced Photon Source

NASA Astrophysics Data System (ADS)

Xu, Shenglan; Keefe, Lisa J.; Mulichak, Anne; Yan, Lifen; Alp, Ercan E.; Zhao, Jiyong; Fischetti, Robert F.

2011-09-01

In 2007, the General Medicine and Cancer Institutes Collaborative Access Team (GM/CA CAT, Sector 23, Advanced Photon Source) began providing mini-beam collimators to its users. These collimators contained individual, 5- or 10-μm pinholes and were rapidly exchangeable, thereby allowing users to tailor the beam size to their experimental needs. The use of these collimators provided a reduction in background noise, and thus improved the signal-to-noise ratio [1,2]. Recent improvements in the collimator design include construction of the device from a monolithic piece of molybdenum with multiple pinholes mounted inside [3]. This allows users to select from various size options from within the beamline control software without the realignment that was previously necessary. In addition, a new, 20-μm pinhole has been added to create a "quad-collimator", resulting in greater flexibility for the users. The mini-beam collimator is now available at multiple crystallographic beamlines and also is a part of the first Mössbauer Microscopic system at sector 3-ID.

Final implementation, commissioning, and performance of embedded collimator beam position monitors in the Large Hadron Collider

NASA Astrophysics Data System (ADS)

Valentino, Gianluca; Baud, Guillaume; Bruce, Roderik; Gasior, Marek; Mereghetti, Alessio; Mirarchi, Daniele; Olexa, Jakub; Redaelli, Stefano; Salvachua, Belen; Valloni, Alessandra; Wenninger, Jorg

2017-08-01

During Long Shutdown 1, 18 Large Hadron Collider (LHC) collimators were replaced with a new design, in which beam position monitor (BPM) pick-up buttons are embedded in the collimator jaws. The BPMs provide a direct measurement of the beam orbit at the collimators, and therefore can be used to align the collimators more quickly than using the standard technique which relies on feedback from beam losses. Online orbit measurements also allow for reducing operational margins in the collimation hierarchy placed specifically to cater for unknown orbit drifts, therefore decreasing the β* and increasing the luminosity reach of the LHC. In this paper, the results from the commissioning of the embedded BPMs in the LHC are presented. The data acquisition and control software architectures are reviewed. A comparison with the standard alignment technique is provided, together with a fill-to-fill analysis of the measured orbit in different machine modes, which will also be used to determine suitable beam interlocks for a tighter collimation hierarchy.

Hybrid Parallel-Slant Hole Collimators for SPECT Imaging

NASA Astrophysics Data System (ADS)

Bai, Chuanyong; Shao, Ling; Ye, Jinghan; Durbin, M.; Petrillo, M.

2004-06-01

We propose a new collimator geometry, the hybrid parallel-slant (HPS) hole geometry, to improve sensitivity for SPECT imaging with large field of view (LFOV) gamma cameras. A HPS collimator has one segment with parallel holes and one or more segments with slant holes. The collimator can be mounted on a conventional SPECT LFOV system that uses parallel-beam collimators, and no additional detector or collimator motion is required for data acquisition. The parallel segment of the collimator allows for the acquisition of a complete data set of the organs-of-interest and the slant segments provide additional data. In this work, simulation studies of an MCAT phantom were performed with a HPS collimator with one slant segment. The slant direction points from patient head to patient feet with a slant angle of 30/spl deg/. We simulated 64 projection views over 180/spl deg/ with the modeling of nonuniform attenuation effect, and then reconstructed images using an MLEM algorithm that incorporated the hybrid geometry. It was shown that sensitivity to the cardiac region of the phantom was increased by approximately 50% when using the HPS collimator compared with a parallel-hole collimator. No visible artifacts were observed in the myocardium and the signal-to-noise ratio (SNR) of the myocardium walls was improved. Compared with collimators with other geometries, using a HPS collimator has the following advantages: (a) significant sensitivity increase; (b) a complete data set obtained from the parallel segment that allows for artifact-free image reconstruction; and (c) no additional collimator or detector motion. This work demonstrates the potential value of hybrid geometry in collimator design for LFOV SPECT imaging.

Investigation on the reflector/moderator geometry and its effect on the neutron beam design in BNCT.

PubMed

Kasesaz, Y; Rahmani, F; Khalafi, H

2015-12-01

In order to provide an appropriate neutron beam for Boron Neutron Capture Therapy (BNCT), a special Beam Shaping Assembly (BSA) must be designed based on the neutron source specifications. A typical BSA includes moderator, reflector, collimator, thermal neutron filter, and gamma filter. In common BSA, the reflector is considered as a layer which covers the sides of the moderator materials. In this paper, new reflector/moderator geometries including multi-layer and hexagonal lattice have been suggested and the effect of them has been investigated by MCNP4C Monte Carlo code. It was found that the proposed configurations have a significant effect to improve the thermal to epithermal neutron flux ratio which is an important neutron beam parameter. Copyright © 2015 Elsevier Ltd. All rights reserved.

Recent technologic advances in multi-detector row cardiac CT.

PubMed

Halliburton, Sandra Simon

2009-11-01

Recent technical advances in multi-detector row CT have resulted in lower radiation dose, improved temporal and spatial resolution, decreased scan time, and improved tissue differentiation. Lower radiation doses have resulted from the use of pre-patient z collimators, the availability of thin-slice axial data acquisition, the increased efficiency of ECG-based tube current modulation, and the implementation of iterative reconstruction algorithms. Faster gantry rotation and the simultaneous use of two x-ray sources have led to improvements in temporal resolution, and gains in spatial resolution have been achieved through application of the flying x-ray focal-spot technique in the z-direction. Shorter scan times have resulted from the design of detector arrays with increasing numbers of detector rows and through the simultaneous use of two x-ray sources to allow higher helical pitch. Some improvement in tissue differentiation has been achieved with dual energy CT. This article discusses these recent technical advances in detail.

Note: Detector collimators for the nanoscale ordered materials diffractometer instrument at the Spallation Neutron Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamalonis, A.; Weber, J. K. R.; Neuefeind, J. C.

2015-09-01

Five neutron collimator designs were constructed and tested at the nanoscale ordered materials diffractometer (NOMAD) instrument. Collimators were made from High Density PolyEthylene (HDPE) or 5% borated HDPE. In all cases, collimators improved the signal to background ratio and reduced detection of secondary scattering. In the Q-range 10-20 (angstrom) -1, signal to background ratio improved by factors of approximately 1.6 and 2.0 for 50 and 100 mm deep collimators, respectively. In the Q-range 40-50 angstrom -1, the improvement factors were 1.8 and 2.7. Secondary scattering as measured at Q similar to 9.5 angstrom -1 was significantly decreased when the collimatorsmore » were installed.« less

Crystals and collimators for X-ray spectrometry. [Bragg reflection properties and design for astronomical applications

NASA Technical Reports Server (NTRS)

Mckenzie, D. L.; Landecker, P. B.; Underwood, J. H.

1976-01-01

Results of the measurement of Bragg reflection properties of crystals suitable for use in X-ray astronomy are presented. Measurements with a double crystal spectrometer were performed on rubidium acid phthalate and thallium acid phthalate to yield values of the integrated reflectivity and diffraction width in the range 8-18 A, and measurements of integrated reflectivity were also performed on ammonium dihydrogen phosphate. The theory and design of an arc-minute range multigrid collimator to be flown on a rocket for solar X-ray studies are also described, along with a method for determining the collimator's X-ray axis.

Intensity-modulated radiation therapy (IMRT) with different combinations of treatment-planning systems and linacs: issues and how to detect them.

PubMed

Dobler, Barbara; Lorenz, Friedlieb; Wertz, Hansjörg; Polednik, Martin; Wolff, Dirk; Steil, Volker; Lohr, Frank; Wenz, Frederik

2006-08-01

To compare different combinations of intensity-modulated radiation therapy (IMRT) system components with regard to quality assurance (QA), especially robustness against malfunctions and dosimetry. Three different treatment-planning systems (TPS), two types of linacs and three multileaf collimator (MLC) types were compared: commissioning procedures were performed for the combination of the TPS Corvus 5.0 (Nomos) and KonRad v2.1.3 (Siemens OCS) with the linacs KD2 (Siemens) and Synergy (Elekta). For PrecisePLAN 2.03 (Elekta) measurements were performed for Elekta Synergy only. As record and verify (R&V) system Multi-Access v7 (IMPAC) was used. The use of the serial tomotherapy system Peacock (Nomos) was investigated in combination with the Siemens KD2 linac. In the comparison of calculated to measured dose, problems were encountered for the combination of KonRad and Elekta MLC as well as for the Peacock system. Multi-Access failed to assign the collimator angle correctly for plans with multiple collimator angles per beam. Communication problems of Multi-Access with both linacs were observed, resulting in incorrect recording of the treatment. All reported issues were addressed by the manufacturers. For the commissioning of IMRT systems, the whole chain from the TPS to the linac has to be investigated. Components that passed the commissioning in another clinical environment can have severe malfunctions when used in a new environment. Therefore, not only single components but the whole chain from planning to delivery has to be evaluated in commissioning and checked regularly for QA.

A high-speed scintillation-based electronic portal imaging device to quantitatively characterize IMRT delivery.

PubMed

Ranade, Manisha K; Lynch, Bart D; Li, Jonathan G; Dempsey, James F

2006-01-01

We have developed an electronic portal imaging device (EPID) employing a fast scintillator and a high-speed camera. The device is designed to accurately and independently characterize the fluence delivered by a linear accelerator during intensity modulated radiation therapy (IMRT) with either step-and-shoot or dynamic multileaf collimator (MLC) delivery. Our aim is to accurately obtain the beam shape and fluence of all segments delivered during IMRT, in order to study the nature of discrepancies between the plan and the delivered doses. A commercial high-speed camera was combined with a terbium-doped gadolinium-oxy-sulfide (Gd2O2S:Tb) scintillator to form an EPID for the unaliased capture of two-dimensional fluence distributions of each beam in an IMRT delivery. The high speed EPID was synchronized to the accelerator pulse-forming network and gated to capture every possible pulse emitted from the accelerator, with an approximate frame rate of 360 frames-per-second (fps). A 62-segment beam from a head-and-neck IMRT treatment plan requiring 68 s to deliver was recorded with our high speed EPID producing approximately 6 Gbytes of imaging data. The EPID data were compared with the MLC instruction files and the MLC controller log files. The frames were binned to provide a frame rate of 72 fps with a signal-to-noise ratio that was sufficient to resolve leaf positions and segment fluence. The fractional fluence from the log files and EPID data agreed well. An ambiguity in the motion of the MLC during beam on was resolved. The log files reported leaf motions at the end of 33 of the 42 segments, while the EPID observed leaf motions in only 7 of the 42 segments. The static IMRT segment shapes observed by the high speed EPID were in good agreement with the shapes reported in the log files. The leaf motions observed during beam-on for step-and-shoot delivery were not temporally resolved by the log files.

Joint Multi-Leaf Segmentation, Alignment, and Tracking for Fluorescence Plant Videos.

PubMed

Yin, Xi; Liu, Xiaoming; Chen, Jin; Kramer, David M

2018-06-01

This paper proposes a novel framework for fluorescence plant video processing. The plant research community is interested in the leaf-level photosynthetic analysis within a plant. A prerequisite for such analysis is to segment all leaves, estimate their structures, and track them over time. We identify this as a joint multi-leaf segmentation, alignment, and tracking problem. First, leaf segmentation and alignment are applied on the last frame of a plant video to find a number of well-aligned leaf candidates. Second, leaf tracking is applied on the remaining frames with leaf candidate transformation from the previous frame. We form two optimization problems with shared terms in their objective functions for leaf alignment and tracking respectively. A quantitative evaluation framework is formulated to evaluate the performance of our algorithm with four metrics. Two models are learned to predict the alignment accuracy and detect tracking failure respectively in order to provide guidance for subsequent plant biology analysis. The limitation of our algorithm is also studied. Experimental results show the effectiveness, efficiency, and robustness of the proposed method.

Research Advances on Radiation Transfer Modeling and Inversion for Multi-scale Land Surface Remote Sensing

NASA Astrophysics Data System (ADS)

Liu, Q.; Li, J.; Du, Y.; Wen, J.; Zhong, B.; Wang, K.

2011-12-01

As the remote sensing data accumulating, it is a challenge and significant issue how to generate high accurate and consistent land surface parameter product from the multi source remote observation and the radiation transfer modeling and inversion methodology are the theoretical bases. In this paper, recent research advances and unresolved issues are presented. At first, after a general overview, recent research advances on multi-scale remote sensing radiation transfer modeling are presented, including leaf spectrum model, vegetation canopy BRDF models, directional thermal infrared emission models, rugged mountains area radiation models, and kernel driven models etc. Then, new methodologies on land surface parameters inversion based on multi-source remote sensing data are proposed, taking the land surface Albedo, leaf area index, temperature/emissivity, and surface net radiation as examples. A new synthetic land surface parameter quantitative remote sensing product generation system is suggested and the software system prototype will be demonstrated. At last, multi-scale field experiment campaigns, such as the field campaigns in Gansu and Beijing, China are introduced briefly. The ground based, tower based, and airborne multi-angular measurement system have been built to measure the directional reflectance, emission and scattering characteristics from visible, near infrared, thermal infrared and microwave bands for model validation and calibration. The remote sensing pixel scale "true value" measurement strategy have been designed to gain the ground "true value" of LST, ALBEDO, LAI, soil moisture and ET etc. at 1-km2 for remote sensing product validation.

A novel method for dose distribution registration using fiducial marks made by a megavoltage beam in film dosimetry for intensity-modulated radiation therapy quality assurance.

PubMed

Nakayama, Shinichi; Monzen, Hajime; Oonishi, Yuuichi; Mizote, Rika; Iramina, Hiraku; Kaneshige, Souichirou; Mizowaki, Takashi

2015-06-01

Photographic film is widely used for the dose distribution verification of intensity-modulated radiation therapy (IMRT). However, analysis for verification of the results is subjective. We present a novel method for marking the isocenter using irradiation from a megavoltage (MV) beam transmitted through slits in a multi-leaf collimator (MLC). We evaluated the effect of the marking irradiation at 500 monitor units (MU) on the total transmission through the MLC using an ionization chamber and Radiochromic Film. Film dosimetry was performed for quality assurance (QA) of IMRT plans. Three methods of registration were used for each film: marking by irradiating with an MV beam through slits in the MLC (MLC-IC); marking with a fabricated phantom (Phantom-IC); and a subjective method based on isodose lines (Manual). Each method was subjected to local γ-analysis. The effect of the marking irradiation on the total transmission was 0.16%, as measured by a ionization chamber at a 10-cm depth in a solid phantom, while the inter-leaf transmission was 0.3%, determined from the film. The mean pass rates for each registration method agreed within ± 1% when the criteria used were a distance-to-agreement (DTA) of 3 mm and a dose difference (DD) of 3%. For DTA/DD criteria of 2mm/3%, the pass rates in the sagittal plane were 96.09 ± 0.631% (MLC-IC), 96.27 ± 0.399% (Phantom-IC), and 95.62 ± 0.988% (Manual). The present method is a versatile and useful method of improving the objectivity of film dosimetry for IMRT QA. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

ARGOS laser system mechanical design

NASA Astrophysics Data System (ADS)

Deysenroth, M.; Honsberg, M.; Gemperlein, H.; Ziegleder, J.; Raab, W.; Rabien, S.; Barl, L.; Gässler, W.; Borelli, J. L.

2014-07-01

ARGOS, a multi-star adaptive optics system is designed for the wide-field imager and multi-object spectrograph LUCI on the LBT (Large Binocular Telescope). Based on Rayleigh scattering the laser constellation images 3 artificial stars (at 532 nm) per each of the 2 eyes of the LBT, focused at a height of 12 km (Ground Layer Adaptive Optics). The stars are nominally positioned on a circle 2' in radius, but each star can be moved by up to 0.5' in any direction. For all of these needs are following main subsystems necessary: 1. A laser system with its 3 Lasers (Nd:YAG ~18W each) for delivering strong collimated light as for LGS indispensable. 2. The Launch system to project 3 beams per main mirror as a 40 cm telescope to the sky. 3. The Wave Front Sensor with a dichroic mirror. 4. The dichroic mirror unit to grab and interpret the data. 5. A Calibration Unit to adjust the system independently also during day time. 6. Racks + platforms for the WFS units. 7. Platforms and ladders for a secure access. This paper should mainly demonstrate how the ARGOS Laser System is configured and designed to support all other systems.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): theoretical and technological aspects

PubMed Central

Yartsev, S; Kron, T; Van Dyk, J

2007-01-01

Helical tomotherapy (HT) is a novel treatment approach that combines Intensity-Modulate Radiation Therapy (IMRT) delivery with in-built image guidance using megavoltage (MV) CT scanning. The technique utilises a 6 MV linear accelerator mounted on a CT type ring gantry. The beam is collimated to a fan beam, which is intensity modulated using a binary multileaf collimator (MLC). As the patient advances slowly through the ring gantry, the linac rotates around the patient with a leaf-opening pattern optimised to deliver a highly conformal dose distribution to the target in the helical beam trajectory. The unit also allows the acquisition of MVCT images using the same radiation source detuned to reduce its effective energy to 3.5 MV, making the dose required for imaging less than 3 cGy. This paper discusses the major features of HT and describes the advantages and disadvantages of this approach in the context of the commercial Hi-ART system. PMID:21614257

Light distribution in plant canopies: A comparison between 1-D multi-layer modeling approach and 3-D ray tracing

NASA Astrophysics Data System (ADS)

Srinivasan, V.; Yiwen, X.; Ellis, A.; Christensen, A.; Borkiewic, K.; Cox, D.; Hart, J.; Long, S.; Marshall-Colon, A.

2016-12-01

The distribution of absorbed solar radiation in the photosynthetically active region wavelength (PAR) within plant canopies plays a critical role in determining photosynthetic carbon uptake and its associated transpiration. The vertical distribution of leaf area, leaf angles, leaf absorptivity and reflectivity within the canopy, affect the distribution of PAR absorbed throughout the canopy. While the upper canopy sunlit leaves absorb most of the incoming PAR and hence contribute most towards total canopy carbon uptake, the lower canopy shaded leaves which receive mostly lower intensity diffuse PAR make significant contributions towards plant carbon uptake. Most detailed vegetation models use a 1-D vertical multi-layer approach to model the sunlight and shaded canopy leaf fractions, and quantify the direct and diffuse radiation absorbed by the respective leaf fractions. However, this approach is only applicable under canopy closure conditions, and furthermore it fails to accurately capture the effects of diurnally varying leaf angle distributions in some plant canopies. Here, we show by using a 3-D ray tracing model which uses an explicit 3-D canopy structure that enforces no conditions about canopy closure, that the effects of diurnal variation of canopy leaf angle distributions better match with observed data. Our comparative analysis performed on soybean crop canopies between 3-D ray tracing model and the multi-layer model shows that the distribution of absorbed direct PAR is not exponential while, the distribution of absorbed diffuse PAR radiation within plant canopies is exponential. These results show the multi-layer model to significantly over-predict canopy PAR absorbed, and in turn significantly overestimate photosynthetic carbon uptake by up to 13% and canopy transpiration by 7% under mid-day sun conditions as verified through our canopy chamber experiments. Our results indicate that current detailed 1-D multi-layer canopy radiation attenuation models significantly over predict canopy radiation absorption and its associated canopy photosynthetic and transpiration fluxes, and use of a 3-D ray tracing model provides more realistic predictions of leaf canopy integrated fluxes of carbon and water.

Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications.

PubMed

Bowen, Jason D; Huang, Qiu; Ellin, Justin R; Lee, Tzu-Cheng; Shrestha, Uttam; Gullberg, Grant T; Seo, Youngho

2013-10-21

Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1.94-2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.

Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications

NASA Astrophysics Data System (ADS)

Bowen, Jason D.; Huang, Qiu; Ellin, Justin R.; Lee, Tzu-Cheng; Shrestha, Uttam; Gullberg, Grant T.; Seo, Youngho

2013-10-01

Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1.94-2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.

Effect of Fiberoptic Collimation Technique on 808 nm Wavelength Laser Stimulation of Cochlear Neurons.

PubMed

Wang, Jingxuan; Lu, Jianren; Tian, Lan

2016-06-01

The purpose of this study was to evaluate the effects of fiberoptic collimation technique on auditory neural stimulation in the cochlea with 808 nm wavelength lasers. Recently, the pulsed near-infrared lasers in the 800-1000 nm wavelength range have been investigated as an emerging technique to trigger auditory neural response in the cochlea. A laser beam divergence in the optical stimulation pathway exists, which may affect stimulation efficiency and spatial selectivity. The fiberoptic collimation technique was proposed for cochlear neuron stimulation, and the C-lens element was designed as the collimation structure. The spiral ganglion cells in deafened guinea pigs' cochlea were irradiated with collimated and uncollimated near-infrared lasers. Optically evoked auditory brainstem response (OABR) under the two laser output modes were recorded. Laser with the collimation technique evoked an average 58% higher OABR amplitude than the uncollimated laser output. In addition, the collimated laser setup consumed on average 35.2% of laser energy compared with the uncollimated laser when evoking the same OABR amplitude. The fiberoptic collimation technique improved stimulation efficiency and reduced stimulating energy consumption in near-infrared neural stimulation in cochlea. The positive effects of laser collimation technique could benefit further research in optically based cochlear implants.

Multi-isotope SPECT imaging of the 225Ac decay chain: feasibility studies

NASA Astrophysics Data System (ADS)

Robertson, A. K. H.; Ramogida, C. F.; Rodríguez-Rodríguez, C.; Blinder, Stephan; Kunz, Peter; Sossi, Vesna; Schaffer, Paul

2017-06-01

Effective use of the {}225Ac decay chain in targeted internal radioimmunotherapy requires the retention of both {}225Ac and progeny isotopes at the target site. Imaging-based pharmacokinetic tests of these pharmaceuticals must therefore separately yet simultaneously image multiple isotopes that may not be colocalized despite being part of the same decay chain. This work presents feasibility studies demonstrating the ability of a microSPECT/CT scanner equipped with a high energy collimator to simultaneously image two components of the {}225Ac decay chain: {}221Fr (218 keV) and {}213Bi (440 keV). Image quality phantoms were used to assess the performance of two collimators for simultaneous {}221Fr and {}213Bi imaging in terms of contrast and noise. A hotrod resolution phantom containing clusters of thin rods with diameters ranging between 0.85 and 1.70 mm was used to assess resolution. To demonstrate ability to simultaneously image dynamic {}221Fr and {}213Bi activity distributions, a phantom containing a {}213Bi generator from {}225Ac was imaged. These tests were performed with two collimators, a high-energy ultra-high resolution (HEUHR) collimator and an ultra-high sensitivity (UHS) collimator. Values consistent with activity concentrations determined independently via gamma spectroscopy were observed in high activity regions of the images. In hotrod phantom images, the HEUHR collimator resolved all rods for both {}221Fr and {}213Bi images. With the UHS collimator, no rods were resolvable in {}213Bi images and only rods  ⩾1.3 mm were resolved in {}221Fr images. After eluting the {}213Bi generator, images accurately visualized the reestablishment of transient equilibrium of the {}225Ac decay chain. The feasibility of evaluating the pharmacokinetics of the {}225Ac decay chain in vivo has been demonstrated. This presented method requires the use of a high-performance high-energy collimator.

The design of the new LHC connection cryostats

NASA Astrophysics Data System (ADS)

Vande Craen, A.; Barlow, G.; Eymin, C.; Moretti, M.; Parma, V.; Ramos, D.

2017-12-01

In the frame of the High Luminosity upgrade of the LHC, improved collimation schemes are needed to cope with the superconducting magnet quench limitations due to the increasing beam intensities and particle debris produced in the collision points. Two new TCLD collimators have to be installed on either side of the ALICE experiment to intercept heavy-ion particle debris. Beam optics solutions were found to place these collimators in the continuous cryostat of the machine, in the locations where connection cryostats, bridging a gap of about 13 m between adjacent magnets, are already present. It is therefore planned to replace these connection cryostats with two new shorter ones separated by a bypass cryostat allowing the collimators to be placed close to the beam pipes. The connection cryostats, of a new design when compared to the existing ones, will still have to ensure the continuity of the technical systems of the machine cryostat (i.e. beam lines, cryogenic and electrical circuits, insulation vacuum). This paper describes the functionalities and the design solutions implemented, as well as the plans for their construction.

Dosimetric effect of multileaf collimator leaf width on volumetric modulated arc stereotactic radiotherapy for spine tumors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amoush, Ahmad, E-mail: aamoush@augusta.edu; Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195; Long, Huang

This work aimed to study the dosimetric effect of multileaf collimator (MLC) leaf widths in treatment plans for patients receiving volumetric modulated arc therapy (VMAT) for spine stereotactic body radiation therapy (SBRT). Thirteen patients treated with spine SBRT were retrospectively selected for this study. The patients were treated following the protocol of the Radiation Therapy Oncology Group 0631 (RTOG 0631) for spine metastasis. The prescription dose was 16 Gy in 1 fraction to 90% of the target volume (V16 > 90%). The maximum spinal cord dose of 14 Gy and 10% of the spinal cord receiving < 10 Gy (V10) were the acceptable tolerance doses. For themore » purpose of this study, 2 dual-arc VMAT plans were created for each patient using 3 different MLC leaf widths: 2.5 mm, 4 mm, and 5 mm. The compliance with the RTOG 0631 protocol, conformity index (CI), dose gradient index (DGI), and number of monitor units (MUs) were compared. The average V16Gy of the targets was 91.8 ± 1.2%, 92.2 ± 2.1%, and 91.7 ± 2.3% for 2.5-mm, 4-mm, and 5-mm leaf widths, respectively (p = 0.78). Accordingly, the average CI was 1.45 ± 0.4, 1.47 ± 0.29, and 1.47 ± 0.31 (p = 0.98), respectively. The average DGI was 0.22 ± 0.04, 0.20 ± 0.06, and 0.22 ± 0.05, respectively (p = 0.77). The average maximum dose to the spinal cord was 12.45 ± 1.0 Gy, 12.80 ± 1.0 Gy, and 12.48 ± 1.1 (p = 0.62) and V10% of the spinal cord was 3.6 ± 2.1%, 5.6 ± 2.8%, and 5.5 ± 3.0% (p = 0.11) for 2.5-mm, 4-mm, and 5-mm leaf widths, respectively. Accordingly, the average number of MUs was 4341 ± 500 MU, 5019 ± 834 MU, and 4606 ± 691 MU, respectively (p = 0.053). The use of 2.5-mm, 4-mm, and 5-mm MLCs achieved similar VMAT plan quality as recommended by the RTOG 0631. The dosimetric parameters were also comparable for the 3 MLCs. In general, any of these leaf widths can be used for spine SBRT using VMAT.« less

Monte Carlo simulation of a compact microbeam radiotherapy system based on carbon nanotube field emission technology.

PubMed

Schreiber, Eric C; Chang, Sha X

2012-08-01

Microbeam radiation therapy (MRT) is an experimental radiotherapy technique that has shown potent antitumor effects with minimal damage to normal tissue in animal studies. This unique form of radiation is currently only produced in a few large synchrotron accelerator research facilities in the world. To promote widespread translational research on this promising treatment technology we have proposed and are in the initial development stages of a compact MRT system that is based on carbon nanotube field emission x-ray technology. We report on a Monte Carlo based feasibility study of the compact MRT system design. Monte Carlo calculations were performed using EGSnrc-based codes. The proposed small animal research MRT device design includes carbon nanotube cathodes shaped to match the corresponding MRT collimator apertures, a common reflection anode with filter, and a MRT collimator. Each collimator aperture is sized to deliver a beam width ranging from 30 to 200 μm at 18.6 cm source-to-axis distance. Design parameters studied with Monte Carlo include electron energy, cathode design, anode angle, filtration, and collimator design. Calculations were performed for single and multibeam configurations. Increasing the energy from 100 kVp to 160 kVp increased the photon fluence through the collimator by a factor of 1.7. Both energies produced a largely uniform fluence along the long dimension of the microbeam, with 5% decreases in intensity near the edges. The isocentric dose rate for 160 kVp was calculated to be 700 Gy∕min∕A in the center of a 3 cm diameter target. Scatter contributions resulting from collimator size were found to produce only small (<7%) changes in the dose rate for field widths greater than 50 μm. Dose vs depth was weakly dependent on filtration material. The peak-to-valley ratio varied from 10 to 100 as the separation between adjacent microbeams varies from 150 to 1000 μm. Monte Carlo simulations demonstrate that the proposed compact MRT system design is capable of delivering a sufficient dose rate and peak-to-valley ratio for small animal MRT studies.

Fast leaf-fitting with generalized underdose/overdose constraints for real-time MLC tracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, Douglas, E-mail: douglas.moore@utsouthwestern.edu; Sawant, Amit; Ruan, Dan

2016-01-15

Purpose: Real-time multileaf collimator (MLC) tracking is a promising approach to the management of intrafractional tumor motion during thoracic and abdominal radiotherapy. MLC tracking is typically performed in two steps: transforming a planned MLC aperture in response to patient motion and refitting the leaves to the newly generated aperture. One of the challenges of this approach is the inability to faithfully reproduce the desired motion-adapted aperture. This work presents an optimization-based framework with which to solve this leaf-fitting problem in real-time. Methods: This optimization framework is designed to facilitate the determination of leaf positions in real-time while accounting for themore » trade-off between coverage of the PTV and avoidance of organs at risk (OARs). Derived within this framework, an algorithm is presented that can account for general linear transformations of the planned MLC aperture, particularly 3D translations and in-plane rotations. This algorithm, together with algorithms presented in Sawant et al. [“Management of three-dimensional intrafraction motion through real-time DMLC tracking,” Med. Phys. 35, 2050–2061 (2008)] and Ruan and Keall [Presented at the 2011 IEEE Power Engineering and Automation Conference (PEAM) (2011) (unpublished)], was applied to apertures derived from eight lung intensity modulated radiotherapy plans subjected to six-degree-of-freedom motion traces acquired from lung cancer patients using the kilovoltage intrafraction monitoring system developed at the University of Sydney. A quality-of-fit metric was defined, and each algorithm was evaluated in terms of quality-of-fit and computation time. Results: This algorithm is shown to perform leaf-fittings of apertures, each with 80 leaf pairs, in 0.226 ms on average as compared to 0.082 and 64.2 ms for the algorithms of Sawant et al., Ruan, and Keall, respectively. The algorithm shows approximately 12% improvement in quality-of-fit over the Sawant et al. approach, while performing comparably to Ruan and Keall. Conclusions: This work improves upon the quality of the Sawant et al. approach, but does so without sacrificing run-time performance. In addition, using this framework allows for complex leaf-fitting strategies that can be used to account for PTV/OAR trade-off during real-time MLC tracking.« less

Design and development of new collimator cones for fractionated stereotactic radiation therapy in Samsung Medical Center.

PubMed

Ahn, Y C; Ju, S G; Kim, D Y; Choi, D R; Huh, S J; Park, Y H; Lim, D H; Kim, M K

1999-05-01

In stereotactic radiotherapy using X-Knife system, the commercially supplied collimator cone system had a few mechanical limitations. The authors have developed new collimator cones to overcome these limitations and named them "SMC type" collimator cones. We made use of cadmium-free cerrobend alloy within the stainless steel cylinder housing. We made nine cones of relatively larger sizes (3.0 cm to 7.0 cm in diameter) and of shorter length with bigger clearance from the isocenter than the commercial cones. The cone housing and the collimator cones were designed to insert into the wedge mount of the gantry head to enable double-exposure linac-gram taking. The mechanical accuracy of pointing to the isocenter was tested by ball test and cone rotation test, and the dosimetric measurements were performed, all of which were with satisfactory results. A new innovative quality assurance procedure using linac-grams on the patients at the actual treatment setup was attempted after taking 10 sets of AP and lateral linac-grams and the overall mechanical isocenter accuracy was excellent (average error = 0.4 +/- 0.2 mm). We have developed the SMC type collimator cone system mainly for fractionated stereotactic radiation therapy use with our innovative ideas. The new cones' mechanical accuracy and physical properties were satisfactory for clinical use, and the verification of the isocenter accuracy on the actual treatment setup has become possible.

Energy modulated electron therapy: Design, implementation, and evaluation of a novel method of treatment planning and delivery

NASA Astrophysics Data System (ADS)

Al-Yahya, Khalid

Energy modulated electron therapy (EMET) is a promising treatment modality that has the fundamental capabilities to enhance the treatment planning and delivery of superficially located targets. Although it offers advantages over x-ray intensity modulated radiation therapy (IMRT), EMET has not been widely implemented to the same level of accuracy, automation, and clinical routine as its x-ray counterpart. This lack of implementation is attributed to the absence of a remotely automated beam shaping system as well as the deficiency in dosimetric accuracy of clinical electron pencil beam algorithms in the presence of beam modifiers and tissue heterogeneities. In this study, we present a novel technique for treatment planning and delivery of EMET. The delivery is achieved using a prototype of an automated "few leaf electron collimator" (FLEC). It consists of four copper leaves driven by stepper motors which are synchronized with the x-ray jaws in order to form a series of collimated rectangular openings or "fieldlets". Based on Monte Carlo studies, the FLEC has been designed to serve as an accessory tool to the current accelerator equipment. The FLEC was constructed and its operation was fully automated and integrated with the accelerator through an in-house assembled control unit. The control unit is a portable computer system accompanied with customized software that delivers EMET plans after acquiring them from the optimization station. EMET plans are produced based on dose volume constraints that employ Monte Carlo pre-generated and patient-specific kernels which are utilized by an in-house developed optimization algorithm. The structure of the optimization software is demonstrated. Using Monte Carlo techniques to calculate dose allows for accurate modeling of the collimation system as well as the patient heterogeneous geometry and take into account their impact on optimization. The Monte Carlo calculations were validated by comparing them against output measurements with an ionization chamber. Comparisons with measurements using nearly energy-independent radiochromic films were performed to confirm the Monte Carlo calculation accuracy for 1-D and 2-D dose distributions. We investigated the clinical significance of EMET on cancer sites that are inherently difficult to plan with IMRT. Several parameters were used to analyze treatment plans where they show that EMET provides significant overall improvements over IMRT.

Sci—Thur PM: Planning and Delivery — 03: Automated delivery and quality assurance of a modulated electron radiation therapy plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connell, T; Papaconstadopoulos, P; Alexander, A

2014-08-15

Modulated electron radiation therapy (MERT) offers the potential to improve healthy tissue sparing through increased dose conformity. Challenges remain, however, in accurate beamlet dose calculation, plan optimization, collimation method and delivery accuracy. In this work, we investigate the accuracy and efficiency of an end-to-end MERT plan and automated-delivery workflow for the electron boost portion of a previously treated whole breast irradiation case. Dose calculations were performed using Monte Carlo methods and beam weights were determined using a research-based treatment planning system capable of inverse optimization. The plan was delivered to radiochromic film placed in a water equivalent phantom for verification,more » using an automated motorized tertiary collimator. The automated delivery, which covered 4 electron energies, 196 subfields and 6183 total MU was completed in 25.8 minutes, including 6.2 minutes of beam-on time with the remainder of the delivery time spent on collimator leaf motion and the automated interfacing with the accelerator in service mode. The delivery time could be reduced by 5.3 minutes with minor electron collimator modifications and the beam-on time could be reduced by and estimated factor of 2–3 through redesign of the scattering foils. Comparison of the planned and delivered film dose gave 3%/3 mm gamma pass rates of 62.1, 99.8, 97.8, 98.3, and 98.7 percent for the 9, 12, 16, 20 MeV, and combined energy deliveries respectively. Good results were also seen in the delivery verification performed with a MapCHECK 2 device. The results showed that accurate and efficient MERT delivery is possible with current technologies.« less

MCNP6 model of the University of Washington clinical neutron therapy system (CNTS).

PubMed

Moffitt, Gregory B; Stewart, Robert D; Sandison, George A; Goorley, John T; Argento, David C; Jevremovic, Tatjana

2016-01-21

A MCNP6 dosimetry model is presented for the Clinical Neutron Therapy System (CNTS) at the University of Washington. In the CNTS, fast neutrons are generated by a 50.5 MeV proton beam incident on a 10.5 mm thick Be target. The production, scattering and absorption of neutrons, photons, and other particles are explicitly tracked throughout the key components of the CNTS, including the target, primary collimator, flattening filter, monitor unit ionization chamber, and multi-leaf collimator. Simulations of the open field tissue maximum ratio (TMR), percentage depth dose profiles, and lateral dose profiles in a 40 cm × 40 cm × 40 cm water phantom are in good agreement with ionization chamber measurements. For a nominal 10 × 10 field, the measured and calculated TMR values for depths of 1.5 cm, 5 cm, 10 cm, and 20 cm (compared to the dose at 1.7 cm) are within 0.22%, 2.23%, 4.30%, and 6.27%, respectively. For the three field sizes studied, 2.8 cm × 2.8 cm, 10.4 cm × 10.3 cm, and 28.8 cm × 28.8 cm, a gamma test comparing the measured and simulated percent depth dose curves have pass rates of 96.4%, 100.0%, and 78.6% (depth from 1.5 to 15 cm), respectively, using a 3% or 3 mm agreement criterion. At a representative depth of 10 cm, simulated lateral dose profiles have in-field (⩾ 10% of central axis dose) pass rates of 89.7% (2.8 cm × 2.8 cm), 89.6% (10.4 cm × 10.3 cm), and 100.0% (28.8 cm × 28.8 cm) using a 3% and 3 mm criterion. The MCNP6 model of the CNTS meets the minimum requirements for use as a quality assurance tool for treatment planning and provides useful insights and information to aid in the advancement of fast neutron therapy.

TH-AB-BRA-12: Experimental Results From the First High-Field Inline MRI-Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keall, P; Dong, B; Zhang, K

Purpose: The pursuit of real-time image guided radiotherapy using optimal tissue contrast has seen the development of several hybrid MRI-treatment systems, high field and low field, and inline and perpendicular configurations. As part of a new MRI-Linac program, an MRI scanner was integrated with a linear accelerator to enable investigations of a coupled inline MRI-Linac system. This work describes our experimental results from the first high-field inline MRI-Linac. Methods: A 1.5 Tesla magnet (Sonata, Siemens) was located in a purpose built RF cage enabling shielding from and close proximity to a linear accelerator with inline orientation. A portable linear acceleratormore » (Linatron, Varian) was installed together with a multi-leaf collimator (Millennium, Varian) to provide dynamic field collimation and the whole assembly built onto a stainless-steel rail system. A series of MRI-Linac experiments was performed to investigate: (1) image quality with beam on measured using a macropodine (kangaroo) ex vivo phantom; (2) the noise as a function of beam state measured using a 6-channel surface coil array and; (3) electron focusing measured using GafChromic film. Results: (1) The macropodine phantom image quality with the beam on was almost identical to that with the beam off. (2) Noise measured with a surface RF coil produced a 25% elevation of background noise when the radiation beam was on. (3) Film measurements demonstrated electron focusing occurring at the center of the radiation field. Conclusion: The first high-field MRI-Linac has been built and experimentally characterized. This system has allowed us to establish the efficacy of a high field in-line MRI-Linac and study a number of the technical challenges and solutions. Supported by the Australian National Health and Medical Research Council, the Australian Research Council, the Australian Cancer Research Foundation and the Health and Hospitals Fund.« less

Anatomically shaped cranial collimation (ACC) for lateral cephalometric radiography: a technical report.

PubMed

Hoogeveen, R C; van der Stelt, P F; Berkhout, W E R

2014-01-01

Lateral cephalograms in orthodontic practice display an area cranial of the base of the skull that is not required for diagnostic evaluation. Attempts have been made to reduce the radiation dose to the patient using collimators combining the shielding of the areas above the base of the skull and below the mandible. These so-called "wedge-shaped" collimators have not become standard equipment in orthodontic offices, possibly because these collimators were not designed for today's combination panoramic-cephalometric imaging systems. It also may be that the anatomical variability of the area below the mandible makes this area unsuitable for standardized collimation. In addition, a wedge-shaped collimator shields the cervical vertebrae; therefore, assessment of skeletal maturation, which is based on the stage of development of the cervical vertebrae, cannot be performed. In this report, we describe our investigations into constructing a collimator to be attached to the cephalostat and shield the cranial area of the skull, while allowing the visualization of diagnostically relevant structures and markedly reducing the size of the irradiated area. The shape of the area shielded by this "anatomically shaped cranial collimator" (ACC) was based on mean measurements of cephalometric landmarks of 100 orthodontic patients. It appeared that this collimator reduced the area of irradiation by almost one-third without interfering with the imaging system or affecting the quality of the image. Further research is needed to validate the clinical efficacy of the collimator.

Spatial variation of dosimetric leaf gap and its impact on dose delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaraswamy, Lalith K., E-mail: Lalith.Kumaraswamy@roswellpark.org; Schmitt, Jonathan D.; Bailey, Daniel W.

Purpose: During dose calculation, the Eclipse treatment planning system (TPS) retracts the multileaf collimator (MLC) leaf positions by half of the dosimetric leaf gap (DLG) value (measured at central axis) for all leaf positions in a dynamic MLC plan to accurately model the rounded leaf ends. The aim of this study is to map the variation of DLG along the travel path of each MLC leaf pair and quantify how this variation impacts delivered dose. Methods: 6 MV DLG values were measured for all MLC leaf pairs in increments of 1.0 cm (from the line intersecting the CAX and perpendicularmore » to MLC motion) to 13.0 cm off axis distance at dmax. The measurements were performed on two Varian linear accelerators, both employing the Millennium 120-leaf MLCs. The measurements were performed at several locations in the beam with both a Sun Nuclear MapCHECK device and a PTW pinpoint ion chamber. Results: The measured DLGs for the middle 40 MLC leaf pairs (each 0.5 cm width) at positions along a line through the CAX and perpendicular to MLC leaf travel direction were very similar, varying maximally by only 0.2 mm. The outer 20 MLC leaf pairs (each 1.0 cm width) have much lower DLG values, about 0.3–0.5 mm lower than the central MLC leaf pair, at their respective central line position. Overall, the mean and the maximum variation between the 0.5 cm width leaves and the 1.0 cm width leaf pairs are 0.32 and 0.65 mm, respectively. Conclusions: The spatial variation in DLG is caused by the variation of intraleaf transmission through MLC leaves. Fluences centered on the CAX would not be affected since DLG does not vary; but any fluences residing significantly off axis with narrow sweeping leaves may exhibit significant dose differences. This is due to the fact that there are differences in DLG between the true DLG exhibited by the 1.0 cm width outer leaves and the constant DLG value utilized by the TPS for dose calculation. Since there are large differences in DLG between the 0.5 cm width leaf pairs and 1.0 cm width leaf pairs, there is a need to correct the TPS plans, especially those with high modulation (narrow dynamic MLC gap), with 2D variation of DLG.« less

WIYN bench upgrade: a revitalized spectrograph

NASA Astrophysics Data System (ADS)

Bershady, M.; Barden, S.; Blanche, P.-A.; Blanco, D.; Corson, C.; Crawford, S.; Glaspey, J.; Habraken, S.; Jacoby, G.; Keyes, J.; Knezek, P.; Lemaire, P.; Liang, M.; McDougall, E.; Poczulp, G.; Sawyer, D.; Westfall, K.; Willmarth, D.

2008-07-01

We describe the redesign and upgrade of the versatile fiber-fed Bench Spectrograph on the WIYN 3.5m telescope. The spectrograph is fed by either the Hydra multi-object positioner or integral-field units (IFUs) at two other ports, and can be configured with an adjustable camera-collimator angle to use low-order and echelle gratings. The upgrade, including a new collimator, charge-coupled device (CCD) and modern controller, and volume-phase holographic gratings (VPHG), has high performance-to-cost ratio by combining new technology with a system reconfiguration that optimizes throughput while utilizing as much of the existing instrument as possible. A faster, all-refractive collimator enhances throughput by 60%, nearly eliminates the slit-function due to vignetting, and improves image quality to maintain instrumental resolution. Two VPH gratings deliver twice the diffraction efficiency of existing surface-relief gratings: A 740 l/mm grating (float-glass and post-polished) used in 1st and 2nd-order, and a large 3300 l/mm grating (spectral resolution comparable to the R2 echelle). The combination of collimator, high-quantum efficiency (QE) CCD, and VPH gratings yields throughput gain-factors of up to 3.5.

SU-E-T-562: Motion Tracking Optimization for Conformal Arc Radiotherapy Plans: A QUASAR Phantom Based Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Z; Wang, I; Yao, R

Purpose: This study is to use plan parameters optimization (Dose rate, collimator angle, couch angle, initial starting phase) to improve the performance of conformal arc radiotherapy plans with motion tracking by increasing the plan performance score (PPS). Methods: Two types of 3D conformal arc plans were created based on QUASAR respiratory motion phantom with spherical and cylindrical targets. Sinusoidal model was applied to the MLC leaves to generate motion tracking plans. A MATLAB program was developed to calculate PPS of each plan (ranges from 0–1) and optimize plan parameters. We first selected the dose rate for motion tracking plans andmore » then used simulated annealing algorithm to search for the combination of the other parameters that resulted in the plan of the maximal PPS. The optimized motion tracking plan was delivered by Varian Truebeam Linac. In-room cameras and stopwatch were used for starting phase selection and synchronization between phantom motion and plan delivery. Gaf-EBT2 dosimetry films were used to measure the dose delivered to the target in QUASAR phantom. Dose profiles and Truebeam trajectory log files were used for plan delivery performance evaluation. Results: For spherical target, the maximal PPS (PPSsph) of the optimized plan was 0.79: (Dose rate: 500MU/min, Collimator: 90°, Couch: +10°, starting phase: 0.83π). For cylindrical target, the maximal PPScyl was 0.75 (Dose rate: 300MU/min, Collimator: 87°, starting phase: 0.97π) with couch at 0°. Differences of dose profiles between motion tracking plans (with the maximal and the minimal PPS) and 3D conformal plans were as follows: PPSsph=0.79: %ΔFWHM: 8.9%, %Dmax: 3.1%; PPSsph=0.52: %ΔFWHM: 10.4%, %Dmax: 6.1%. PPScyl=0.75: %ΔFWHM: 4.7%, %Dmax: 3.6%; PPScyl=0.42: %ΔFWHM: 12.5%, %Dmax: 9.6%. Conclusion: By achieving high plan performance score through parameters optimization, we can improve target dose conformity of motion tracking plan by decreasing total MLC leaf travel distance and leaf speed.« less

Multi-pinhole SPECT Imaging with Silicon Strip Detectors

PubMed Central

Peterson, Todd E.; Shokouhi, Sepideh; Furenlid, Lars R.; Wilson, Donald W.

2010-01-01

Silicon double-sided strip detectors offer outstanding instrinsic spatial resolution with reasonable detection efficiency for iodine-125 emissions. This spatial resolution allows for multiple-pinhole imaging at low magnification, minimizing the problem of multiplexing. We have conducted imaging studies using a prototype system that utilizes a detector of 300-micrometer thickness and 50-micrometer strip pitch together with a 23-pinhole collimator. These studies include an investigation of the synthetic-collimator imaging approach, which combines multiple-pinhole projections acquired at multiple magnifications to obtain tomographic reconstructions from limited-angle data using the ML-EM algorithm. Sub-millimeter spatial resolution was obtained, demonstrating the basic validity of this approach. PMID:20953300

Large area soft x-ray collimator to facilitate x-ray optics testing

NASA Technical Reports Server (NTRS)

Espy, Samuel L.

1994-01-01

The first objective of this program is to design a nested conical foil x-ray optic which will collimate x-rays diverging from a point source. The collimator could then be employed in a small, inexpensive x-ray test stand which would be used to test various x-ray optics and detector systems. The second objective is to demonstrate the fabrication of the x-ray reflectors for this optic using lacquer-smoothing and zero-stress electroforming techniques.

Commissioning of the tongue-and-groove modelling in treatment planning systems: from static fields to VMAT treatments

NASA Astrophysics Data System (ADS)

Hernandez, Victor; Vera-Sánchez, Juan Antonio; Vieillevigne, Laure; Saez, Jordi

2017-08-01

Adequate modelling of the multi-leaf collimator (MLC) by treatment planning systems (TPS) is essential for accurate dose calculations in intensity-modulated radiation-therapy. For this reason modern TPSs incorporate MLC characteristics such as the leaf end curvature, MLC transmission and the tongue-and-groove. However, the modelling of the tongue-and-groove is often neglected during TPS commissioning and it is not known how accurate it is. This study evaluates the dosimetric consequences of the tongue-and-groove effect for two different MLC models using both film dosimetry and ionisation chambers. A set of comprehensive tests are presented that evaluate the ability of TPSs to accurately model this effect in (a) static fields, (b) sliding window beams and (c) VMAT arcs. The tests proposed are useful for the commissioning of TPSs and for the validation of major upgrades. With the ECLIPSE TPS, relevant differences were found between calculations and measurements for beams with dynamic MLCs in the presence of the TG effect, especially for the High Definition MLC, small gap sizes and the 1 mm calculation grid. For this combination, dose differences as high as 10% and 7% were obtained for dynamic MLC gaps of 5 mm and 10 mm, respectively. These differences indicate inadequate modelling of the tongue-and-groove effect, which might not be identified without the proposed tests. In particular, the TPS tended to underestimate the calculated dose, which may require tuning of other configuration parameters in the TPS (such as the dosimetric leaf gap) in order to maximise the agreement between calculations and measurements in clinical plans. In conclusion, a need for better modelling of the MLC by TPSs is demonstrated, one of the relevant aspects being the tongue-and-groove effect. This would improve the accuracy of TPS calculations, especially for plans using small MLC gaps, such as plans with small target volumes or high complexities. Improved modelling of the MLC would also reduce the need for tuning parameters in the TPS, facilitating a more comprehensive configuration and commissioning of TPSs.

SU-E-J-57: First Development of Adapting to Intrafraction Relative Motion Between Prostate and Pelvic Lymph Nodes Targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Y; Colvill, E; O’Brien, R

2015-06-15

Purpose Large intrafraction relative motion of multiple targets is common in advanced head and neck, lung, abdominal, gynaecological and urological cancer, jeopardizing the treatment outcomes. The objective of this study is to develop a real-time adaptation strategy, for the first time, to accurately correct for the relative motion of multiple targets by reshaping the treatment field using the multi-leaf collimator (MLC). Methods The principle of tracking the simultaneously treated but differentially moving tumor targets is to determine the new aperture shape that conforms to the shifted targets. Three dimensional volumes representing the individual targets are projected to the beam’s eyemore » view. The leaf openings falling inside each 2D projection will be shifted according to the measured motion of each target to form the new aperture shape. Based on the updated beam shape, new leaf positions will be determined with optimized trade-off between the target underdose and healthy tissue overdose, and considerations of the physical constraints of the MLC. Taking a prostate cancer patient with pelvic lymph node involvement as an example, a preliminary dosimetric study was conducted to demonstrate the potential treatment improvement compared to the state-of- art adaptation technique which shifts the whole beam to track only one target. Results The world-first intrafraction adaptation system capable of reshaping the beam to correct for the relative motion of multiple targets has been developed. The dose in the static nodes and small bowel are closer to the planned distribution and the V45 of small bowel is decreased from 110cc to 75cc, corresponding to a 30% reduction by this technique compared to the state-of-art adaptation technique. Conclusion The developed adaptation system to correct for intrafraction relative motion of multiple targets will guarantee the tumour coverage and thus enable PTV margin reduction to minimize the high target dose to the adjacent organs-at-risk. The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.« less

[Design of longitudinal auto-tracking of the detector on X-ray in digital radiography].

PubMed

Yu, Xiaomin; Jiang, Tianhao; Liu, Zhihong; Zhao, Xu

2018-04-01

One algorithm is designed to implement longitudinal auto-tracking of the the detector on X-ray in the digital radiography system (DR) with manual collimator. In this study, when the longitudinal length of field of view (LFOV) on the detector is coincided with the longitudinal effective imaging size of the detector, the collimator half open angle ( Ψ ), the maximum centric distance ( e max ) between the center of X-ray field of view and the projection center of the focal spot, and the detector moving distance for auto-traking can be calculated automatically. When LFOV is smaller than the longitudinal effective imaging size of the detector by reducing Ψ , the e max can still be used to calculate the detector moving distance. Using this auto-tracking algorithm in DR with manual collimator, the tested results show that the X-ray projection is totally covered by the effective imaging area of the detector, although the center of the field of view is not aligned with the center of the effective imaging area of the detector. As a simple and low-cost design, the algorithm can be used for longitudinal auto-tracking of the detector on X-ray in the manual collimator DR.

Design and performance of a SWaP short-range fully fibered monostatic laser rangefinder

NASA Astrophysics Data System (ADS)

Pallier, G.; Portalis, A.; Canat, G.; Chiquet, F.; Auffray, P.; Le, S.-D.; Le Flohic, M.

2017-10-01

The development of a multisensor optronic device requires Size, Weight and Power (SWaP), cost-effective and modular rangefinders while keeping a good range performance. We report on a fully fibered monostatic laser rangerfinder based on a one lens collimator used as the aperture of both the emission and reception channels. This has been possible thanks to the use of a diplexer. This design makes the system compacter and achieves a 200g system weight. In addition to its low volume, the fully fibered architecture allows designing a building block rangefinder with the collimator sub-system on one side and the laser and electronics cards module on the other side. Both are linked up by only an optical fiber. This kit format enables the rangefinder to better fit in any available space in higher level systems such as gimbals and multi-function imagers. Besides, no alignment is needed, and no parallax error is possible: the alignment between channels is guaranteed by design over the whole range. The emission/reception channels of the first prototype has a 28mm diameter 80mm focal length lens, and a 1.55μm 100μJ pulsed laser firing in a burst mode. The rangefinder is set in a class 1 configuration, and measures at 1Hz. The achieved Extinction Ratio is 30dB, which is equivalent to a range on NATO targets of 7km. The achieved ER being class 1M at 5Hz is even 32dB, which is equivalent to a range of 8.5km on NATO targets. More configurations are reported in this article with their associated performance.

High contrast laser beam collimation testing using two proximately placed holographic optical elements

NASA Astrophysics Data System (ADS)

Rajkumar; Dubey, Rajiv; Debnath, Sanjit K.; Chhachhia, D. P.

2018-05-01

Accuracy in laser beam collimation is very important in systems used for precision measurements. The present work reports a technique for collimation testing of laser beams using two proximately placed holographic optical elements (HOEs). The required HOEs are designed and fabricated such that upon illumination with the test beam, they release two laterally sheared wavefronts, at desired angles from the directly transmitted beam, that superimpose each other to generate straight interference fringes. Deviation from the collimation of the test beam results in orientation of these otherwise horizontal fringes. The novelty of this setup comes from the fact that HOEs are lightweight, as well as easy to fabricate as compared to conventional wedge plates used for collimation testing, and generate high contrast fringes compared to other interferometry, holography, Talbot and Moiré based techniques in a compact manner. The proposed technique is experimentally validated by measuring the orientation of fringes by an angle of 16.4° when a collimating lens of focal length 200 mm is defocused by 600 μm. The accuracy in the setting of this collimation position is obtained to be 10 μm.

Computational Analysis Supporting the Design of a New Beamline for the Mines Neutron Radiography Facility

NASA Astrophysics Data System (ADS)

Wilson, C.; King, J.

The Colorado School of Mines installed a neutron radiography system at the United States Geological Survey TRIGA reactor in 2012. An upgraded beamline could dramatically improve the imaging capabilities of this system. This project performed computational analyses to support the design of a new beamline, with the major goals of minimizing beam divergence and maximizing beam intensity. The new beamline will consist of a square aluminum tube with an 11.43 cm (4.5 in) inner side length and 0.635 cm (0.25 in) thick walls. It is the same length as the original beam tube (8.53 m) and is composed of 1.22 m (4 ft) and 1.52 m (5 ft) flanged sections which bolt together. The bottom 1.22 m of the beamline is a cylindrical aluminum pre-collimator which is 0.635 cm (0.25 in) thick, with an inner diameter of 5.08 cm (2 in). Based on Monte Carlo model results, when a pre-collimator is present, the use of a neutron absorbing liner on the inside surface of the beam tube has almost no effect on the angular distribution of the neutron current at the collimator exit. The use of a pre-collimator may result in a non-uniform flux profile at the image plane; however, as long as the collimator is at least three times longer than the pre-collimator, the flux distortion is acceptably low.

Real-time tracking of tumor motions and deformations along the leaf travel direction with the aid of a synchronized dynamic MLC leaf sequencer.

PubMed

Tacke, Martin; Nill, Simeon; Oelfke, Uwe

2007-11-21

Advanced radiotherapeutical techniques like intensity-modulated radiation therapy (IMRT) are based on an accurate knowledge of the location of the radiation target. An accurate dose delivery, therefore, requires a method to account for the inter- and intrafractional target motion and the target deformation occurring during the course of treatment. A method to compensate in real time for changes in the position and shape of the target is the use of a dynamic multileaf collimator (MLC) technique which can be devised to automatically arrange the treatment field according to real-time image information. So far, various approaches proposed for leaf sequencers have had to rely on a priori known target motion data and have aimed to optimize the overall treatment time. Since for a real-time dose delivery the target motion is not known a priori, the velocity range of the leading leaves is restricted by a safety margin to c x v(max) while the following leaves can travel with an additional maximum speed to compensate for the respective target movements. Another aspect to be considered is the tongue and groove effect. A uniform radiation field can only be achieved if the leaf movements are synchronized. The method presented in this note is the first to combine a synchronizing sequencer and real-time tracking with a dynamic MLC. The newly developed algorithm is capable of online optimizing the leaf velocities by minimizing the overall treatment time while at the same time it synchronizes the leaf trajectories in order to avoid the tongue and groove effect. The simultaneous synchronization is performed with the help of an online-calculated mid-time leaf trajectory which is common for all leaf pairs and which takes into account the real-time target motion and deformation information.

Evaluation of collimation and imaging configuration in scintimammography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsui, B.M.W.; Frey, E.C.; Wessell, D.E.

1996-12-31

Conventional scintimammography (SM) with {sup 99m}Tc sestamibi has been limited to taking a single lateral view of the breast using a parallel-hole high resolution (LEHR) collimator. The collimator is placed close to the breast for best possible spatial resolution. However, the collimator geometry precludes imaging the breast from other views. We evaluated using a pinhole collimator instead of a LEHR collimator in SM for improved spatial resolution and detection efficiency, and to allow additional imaging views. Results from theoretical calculations indicated that pinhole collimators could be designed with higher spatial resolution and detection efficiency than LEHR when imaging small tomore » medium size breasts. The geometrical shape of the pinhole collimator allows imaging of the breasts from both the lateral and craniocaudal views. The dual-view images allow better determination of the location of the tumors within the breast and improved detection of tumors located in the medial region of the breast. A breast model that simulates the shape and composition of the breast and breast tumors with different sizes and locations was added to an existing 3D mathematical cardiac-torso (MCAT) phantom. A cylindrically shaped phantom with 10 cm diameter and spherical inserts with different sizes and {sup 99m}Tc sestamibi uptakes with respect to the background provide physical models of breast with tumors. Simulation studies using the breast and MCAT phantoms and experimental studies using the cylindrical phantom confirmed the utility of the pinhole collimator in SM for improved breast tumor detection.« less

Parametric study and optimization trends for the Von-Kármán-sodium dynamo experiment

NASA Astrophysics Data System (ADS)

Varela, J.

2018-05-01

We present magneto-hydrodynamic simulations of liquid sodium flow performed with the PLUTO compressible MHD code. We investigated the influence of the remanent magnetic field orientation and intensity, the impinging velocity field due to Ekman pumping as well as the impeller dimensions on the magnetic field collimation by helical flows in-between the impeller blades. For a simplified Cartesian geometry, we model the flow dynamics of a multi-blade impeller inspired by the Von-Kármán-Sodium experiment. This study shows that a remanent magnetic field oriented in the toroidal direction is the less efficient configuration to collimate the magnetic field, although if the radial or vertical components are not negligible, the collimation is significantly improved. As the intensity of the remanent magnetic field increases, the system magnetic energy becomes larger, but the magnetic field collimation efficiency remains the same, so the gain of magnetic energy is smaller as the remanent magnetic field intensity increases. The magnetic field collimation is modified if the impinging velocity field changes: the collimation is weaker if the impinging velocity increases from Γ = 0.8 to 0.9 and slightly larger if the impinging velocity decreases from Γ = 0.8 to 0.7. The analysis of the impeller dimensions points out that the most efficient configuration to collimate the magnetic field requires a ratio between the impeller blade height and the base longitude between 0.375 and 0.5. The largest enhancement of the hypothetical α2 dynamo loop, compared to the hypothetical Ω-α dynamo loop, is observed for the model that mimics the TM 73 impeller configuration rotating in the unscooping direction with a remanent magnetic field of 10-3 T orientated in the radial or vertical direction. The optimization trends obtained in the parametric analysis are also confirmed by simulations with a higher resolution and turbulence degree.

TH-C-BRC-02: A Review of Emerging Technologies in Robotic SRS/SBRT Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, L.

The delivery techniques for SRS/SBRT have been under rapid developments in recent years, which pose new challenges to medical physicists ranging from planning and quality assurance to imaging and motion management. This educational course will provide a general overview of the latest delivery techniques in SRS/SBRT, and discuss the clinical processes to address the challenges of each technique with special emphasis on dedicated gamma-ray based device, robotic x-band linac-based system and conventional C-arm s-band linac-based SRS systems. (1). Gamma-ray based SRS/SRT: This is the gold standard of intracranial SRS. With the advent of precision imaging guidance and frameless patient positioningmore » capabilities, novel stereoscopic CBCT and automatic dose adaption solution are introduced to the Gamma-ray based SRS for the first time. The first North American system has been approved by the US regulatory for patient treatments in the spring of 2016. (2). Robotic SRS/SBRT system: A number of technological milestones have been developed in the past few years, including variable aperture collimator, sequential optimization technique, and the time reduction technique. Recently, a new robotic model allows the option of a multi-leaf collimator. These technological advances have reduced the treatment time and improved dose conformity significantly and could potentially expand the application of radiosurgery for the treatment of targets not previously suitable for robotic SRS/SBRT or fractionated stereotactic radiotherapy. These technological advances have created new demanding mandates on hardware and patient quality assurance (QA) tasks, as well as the need for updating/educating the physicists in the community on these requirements. (3). Conventional Linac based treatments: Modulated arc therapy (MAT) has gained wide popularities in Linac-based treatments in recent years due to its high delivery efficiency and excellent dose conformities. Recently, MAT has been introduced to deliver highly conformal radiosurgery treatments to multiple targets simultaneously via a single isocenter to replace the conventional multi-iso multi-plan treatments. It becomes important to understand the advantages and limitations of this technique, and the pitfalls for implementing this technique in clinical practice. The planning process of single-iso multi-target MAT will be described, and its plan quality and delivery efficiency will be compared with multi-iso plans. The QA process for verifying such complex plans will be illustrated, and pitfalls in imaging and patient set up will be discussed. Overall, this session will focus on the following areas: 1) Update on the emerging technology in current SRS/SBRT delivery. 2) New developments in treatment planning and Quality Assurance program. 3) Imaging guidance and motion management. Learning Objectives: To understand the SRS/SBRT principles and its clinical applications, and gain knowledge on the emerging technologies in SRS/SBRT. To review planning concepts and useful tips in treatment planning. To learn about the imaging guidance procedures and the quality assurance program in SRS/SBRT. National Institutes of Health, Varian Medical System; L. Ren, The presenter is funded by National Institutes of Health and Varian Medical System.« less

TH-C-BRC-01: An Overview of Emerging Technologies in SRS/SBRT Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, L.

2016-06-15

The delivery techniques for SRS/SBRT have been under rapid developments in recent years, which pose new challenges to medical physicists ranging from planning and quality assurance to imaging and motion management. This educational course will provide a general overview of the latest delivery techniques in SRS/SBRT, and discuss the clinical processes to address the challenges of each technique with special emphasis on dedicated gamma-ray based device, robotic x-band linac-based system and conventional C-arm s-band linac-based SRS systems. (1). Gamma-ray based SRS/SRT: This is the gold standard of intracranial SRS. With the advent of precision imaging guidance and frameless patient positioningmore » capabilities, novel stereoscopic CBCT and automatic dose adaption solution are introduced to the Gamma-ray based SRS for the first time. The first North American system has been approved by the US regulatory for patient treatments in the spring of 2016. (2). Robotic SRS/SBRT system: A number of technological milestones have been developed in the past few years, including variable aperture collimator, sequential optimization technique, and the time reduction technique. Recently, a new robotic model allows the option of a multi-leaf collimator. These technological advances have reduced the treatment time and improved dose conformity significantly and could potentially expand the application of radiosurgery for the treatment of targets not previously suitable for robotic SRS/SBRT or fractionated stereotactic radiotherapy. These technological advances have created new demanding mandates on hardware and patient quality assurance (QA) tasks, as well as the need for updating/educating the physicists in the community on these requirements. (3). Conventional Linac based treatments: Modulated arc therapy (MAT) has gained wide popularities in Linac-based treatments in recent years due to its high delivery efficiency and excellent dose conformities. Recently, MAT has been introduced to deliver highly conformal radiosurgery treatments to multiple targets simultaneously via a single isocenter to replace the conventional multi-iso multi-plan treatments. It becomes important to understand the advantages and limitations of this technique, and the pitfalls for implementing this technique in clinical practice. The planning process of single-iso multi-target MAT will be described, and its plan quality and delivery efficiency will be compared with multi-iso plans. The QA process for verifying such complex plans will be illustrated, and pitfalls in imaging and patient set up will be discussed. Overall, this session will focus on the following areas: 1) Update on the emerging technology in current SRS/SBRT delivery. 2) New developments in treatment planning and Quality Assurance program. 3) Imaging guidance and motion management. Learning Objectives: To understand the SRS/SBRT principles and its clinical applications, and gain knowledge on the emerging technologies in SRS/SBRT. To review planning concepts and useful tips in treatment planning. To learn about the imaging guidance procedures and the quality assurance program in SRS/SBRT. National Institutes of Health, Varian Medical System; L. Ren, The presenter is funded by National Institutes of Health and Varian Medical System.« less

TH-C-BRC-00: Emerging Technologies in SRS/SBRT Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

2016-06-15

The delivery techniques for SRS/SBRT have been under rapid developments in recent years, which pose new challenges to medical physicists ranging from planning and quality assurance to imaging and motion management. This educational course will provide a general overview of the latest delivery techniques in SRS/SBRT, and discuss the clinical processes to address the challenges of each technique with special emphasis on dedicated gamma-ray based device, robotic x-band linac-based system and conventional C-arm s-band linac-based SRS systems. (1). Gamma-ray based SRS/SRT: This is the gold standard of intracranial SRS. With the advent of precision imaging guidance and frameless patient positioningmore » capabilities, novel stereoscopic CBCT and automatic dose adaption solution are introduced to the Gamma-ray based SRS for the first time. The first North American system has been approved by the US regulatory for patient treatments in the spring of 2016. (2). Robotic SRS/SBRT system: A number of technological milestones have been developed in the past few years, including variable aperture collimator, sequential optimization technique, and the time reduction technique. Recently, a new robotic model allows the option of a multi-leaf collimator. These technological advances have reduced the treatment time and improved dose conformity significantly and could potentially expand the application of radiosurgery for the treatment of targets not previously suitable for robotic SRS/SBRT or fractionated stereotactic radiotherapy. These technological advances have created new demanding mandates on hardware and patient quality assurance (QA) tasks, as well as the need for updating/educating the physicists in the community on these requirements. (3). Conventional Linac based treatments: Modulated arc therapy (MAT) has gained wide popularities in Linac-based treatments in recent years due to its high delivery efficiency and excellent dose conformities. Recently, MAT has been introduced to deliver highly conformal radiosurgery treatments to multiple targets simultaneously via a single isocenter to replace the conventional multi-iso multi-plan treatments. It becomes important to understand the advantages and limitations of this technique, and the pitfalls for implementing this technique in clinical practice. The planning process of single-iso multi-target MAT will be described, and its plan quality and delivery efficiency will be compared with multi-iso plans. The QA process for verifying such complex plans will be illustrated, and pitfalls in imaging and patient set up will be discussed. Overall, this session will focus on the following areas: 1) Update on the emerging technology in current SRS/SBRT delivery. 2) New developments in treatment planning and Quality Assurance program. 3) Imaging guidance and motion management. Learning Objectives: To understand the SRS/SBRT principles and its clinical applications, and gain knowledge on the emerging technologies in SRS/SBRT. To review planning concepts and useful tips in treatment planning. To learn about the imaging guidance procedures and the quality assurance program in SRS/SBRT. National Institutes of Health, Varian Medical System; L. Ren, The presenter is funded by National Institutes of Health and Varian Medical System.« less

TH-C-BRC-03: Emerging Linac Based SRS/SBRT Technologies with Modulated Arc Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, L.

2016-06-15

The delivery techniques for SRS/SBRT have been under rapid developments in recent years, which pose new challenges to medical physicists ranging from planning and quality assurance to imaging and motion management. This educational course will provide a general overview of the latest delivery techniques in SRS/SBRT, and discuss the clinical processes to address the challenges of each technique with special emphasis on dedicated gamma-ray based device, robotic x-band linac-based system and conventional C-arm s-band linac-based SRS systems. (1). Gamma-ray based SRS/SRT: This is the gold standard of intracranial SRS. With the advent of precision imaging guidance and frameless patient positioningmore » capabilities, novel stereoscopic CBCT and automatic dose adaption solution are introduced to the Gamma-ray based SRS for the first time. The first North American system has been approved by the US regulatory for patient treatments in the spring of 2016. (2). Robotic SRS/SBRT system: A number of technological milestones have been developed in the past few years, including variable aperture collimator, sequential optimization technique, and the time reduction technique. Recently, a new robotic model allows the option of a multi-leaf collimator. These technological advances have reduced the treatment time and improved dose conformity significantly and could potentially expand the application of radiosurgery for the treatment of targets not previously suitable for robotic SRS/SBRT or fractionated stereotactic radiotherapy. These technological advances have created new demanding mandates on hardware and patient quality assurance (QA) tasks, as well as the need for updating/educating the physicists in the community on these requirements. (3). Conventional Linac based treatments: Modulated arc therapy (MAT) has gained wide popularities in Linac-based treatments in recent years due to its high delivery efficiency and excellent dose conformities. Recently, MAT has been introduced to deliver highly conformal radiosurgery treatments to multiple targets simultaneously via a single isocenter to replace the conventional multi-iso multi-plan treatments. It becomes important to understand the advantages and limitations of this technique, and the pitfalls for implementing this technique in clinical practice. The planning process of single-iso multi-target MAT will be described, and its plan quality and delivery efficiency will be compared with multi-iso plans. The QA process for verifying such complex plans will be illustrated, and pitfalls in imaging and patient set up will be discussed. Overall, this session will focus on the following areas: 1) Update on the emerging technology in current SRS/SBRT delivery. 2) New developments in treatment planning and Quality Assurance program. 3) Imaging guidance and motion management. Learning Objectives: To understand the SRS/SBRT principles and its clinical applications, and gain knowledge on the emerging technologies in SRS/SBRT. To review planning concepts and useful tips in treatment planning. To learn about the imaging guidance procedures and the quality assurance program in SRS/SBRT. National Institutes of Health, Varian Medical System; L. Ren, The presenter is funded by National Institutes of Health and Varian Medical System.« less

Coherent beam combining of collimated fiber array based on target-in-the-loop technique

NASA Astrophysics Data System (ADS)

Li, Xinyang; Geng, Chao; Zhang, Xiaojun; Rao, Changhui

2011-11-01

Coherent beam combining (CBC) of fiber array is a promising way to generate high power and high quality laser beams. Target-in-the-loop (TIL) technique might be an effective way to ensure atmosphere propagation compensation without wavefront sensors. In this paper, we present very recent research work about CBC of collimated fiber array using TIL technique at the Key Lab on Adaptive Optics (KLAO), CAS. A novel Adaptive Fiber Optics Collimator (AFOC) composed of phase-locking module and tip/tilt control module was developed. CBC experimental setup of three-element fiber array was established. Feedback control is realized using stochastic parallel gradient descent (SPGD) algorithm. The CBC based on TIL with piston and tip/tilt correction simultaneously is demonstrated. And the beam pointing to locate or sweep position of combined spot on target was achieved through TIL technique too. The goal of our work is achieve multi-element CBC for long-distance transmission in atmosphere.

Aberration-free intraocular lenses - What does this really mean?

PubMed

Langenbucher, Achim; Schröder, Simon; Cayless, Alan; Eppig, Timo

2017-09-01

So-called aberration-free intraocular lenses (IOLs) are well established in modern cataract surgery. Usually, they are designed to perfectly refract a collimated light beam onto the focal point. We show how much aberration can be expected with such an IOL in a convergent light beam such as that found anterior to the human cornea. Additionally, the aberration in a collimated beam is estimated for an IOL that has no aberrations in the convergent beam. The convergent beam is modelled as the pencil of rays corresponding to the spherical wavefront resulting from a typical corneal power of 43m -1 . The IOLs are modelled as infinitely thin phase plates with 20m -1 optical power placed 5mm behind the cornea. Their aberrations are reported in terms of optical path length difference and longitudinal spherical aberration (LSA) of the marginal rays, as well as nominal spherical aberration (SA) calculated based on a Zernike representation of the wavefront-error at the corneal plane within a 6mm aperture. The IOL designed to have no aberrations in a collimated light beam has an optical path length difference of -1.8μm, and LSA of 0.15m -1 in the convergent beam of a typical eye. The corresponding nominal SA is 0.065μm. The IOL designed to have no aberrations in a convergent light beam has an optical path length difference of 1.8μm, and LSA of -0.15m -1 in the collimated beam. An IOL designed to have no aberrations in a collimated light beam will increase the SA of a patient's eye after implantation. Copyright © 2017. Published by Elsevier GmbH.

SU-E-I-42: Measurement of X-Ray Beam Width and Geometric Efficiency in MDCT Using Radiochromic Films.

PubMed

Liillau, T; Liebmann, M; von Boetticher, H; Poppe, B

2012-06-01

The purpose of this work was to measure the x-ray beam width and geometric efficiency (GE) of a multi detector computed tomography scanner (MDCT) for different beam collimations using radiochromic films. In MDCT, the primary beam width extends the nominal beam collimation to irradiate the active detector elements uniformly (called 'over-beaming') which contributes to increased radiation dose to the patient compared to single detector CT. Therefore, the precise determination of the primary beam width and GE is of value for any CT dose calculation using Monte Carlo or analytical methods. Single axial dose profiles free in air were measured for 6 different beam collimations nT for a Siemens SOMATOM Sensation 64 Scanner with Gafchromic XR-QA2 films. The films were calibrated relative to the measured charge of a PTW semiflex ionization chamber (type: 31010) for a single rotation in the CT scanner at the largest available beam collimation of 28.8 mm. The beam energy for all measurements in this work was set to 120 kVp. For every measured dose profile and beam collimation the GEin-air and the full-width-at-half- maximum value (FWHM) as a value for the x-ray beam width was determined. Over-beaming factors FWHM / nT were calculated accordingly. For MDCT beam collimations from 7.2 (12×0.6 mm) to 28.8 (24×1.2 mm) the geometric efficiency was between 58 and 85 %. The over- beaming factor ranged from 1.43 to 1.11. For beam collimations of 1×5 mm and 1×10 mm the GE was 77 % and 84 % respectively. The over-beaming factors were close to 1, as expected. This work has shown that radiochromic films can be used for accurate x-ray beam width and geometric efficiency measurements due to their high spatial resolution. The measured free-in-air geometric efficiency and the over-beaming factor depend strongly on beam collimation. © 2012 American Association of Physicists in Medicine.

Chloroplast avoidance movement as a sensitive indicator of relative water content during leaf desiccation in the dark.

PubMed

Nauš, Jan; Šmecko, Slavomír; Špundová, Martina

2016-08-01

In the context of global climate change, drought is one of the major stress factors with negative effect on photosynthesis and plant productivity. Currently, chlorophyll fluorescence parameters are widely used as indicators of plant stress, mainly owing to the rapid, non-destructive and simple measurements this technique allows. However, these parameters have been shown to have limited sensitivity for the monitoring of water deficit as leaf desiccation has relatively small effect on photosystem II photochemistry. In this study, we found that blue light-induced increase in leaf transmittance reflecting chloroplast avoidance movement was much more sensitive to a decrease in relative water content (RWC) than chlorophyll fluorescence parameters in dark-desiccating leaves of tobacco (Nicotiana tabacum L.) and barley (Hordeum vulgare L.). Whereas the inhibition of chloroplast avoidance movement was detectable in leaves even with a small RWC decrease, the chlorophyll fluorescence parameters (F V/F M, V J, Ф PSII, NPQ) changed markedly only when RWC dropped below 70 %. For this reason, we propose light-induced chloroplast avoidance movement as a sensitive indicator of the decrease in leaf RWC. As our measurement of chloroplast movement using collimated transmittance is simple and non-destructive, it may be more suitable in some cases for the detection of plant stresses including water deficit than the conventionally used chlorophyll fluorescence methods.

An experimental comparison of conventional two-bank and novel four-bank dynamic MLC tracking.

PubMed

Davies, G A; Clowes, P; McQuaid, D; Evans, P M; Webb, S; Poludniowski, G

2013-03-07

The AccuLeaf mMLC featuring four multileaf-collimator (MLC) banks has been used for the first time for an experimental comparison of conventional two-bank with novel four-bank dynamic MLC tracking of a two-dimensional sinusoidal respiratory motion. This comparison was performed for a square aperture, and for three conformal treatment apertures from clinical radiotherapy lung cancer patients. The system latency of this prototype tracking system was evaluated and found to be 1.0 s and the frequency at which MLC positions could be updated, 1 Hz, and therefore accurate MLC tracking of irregular patient motion would be difficult with the system in its current form. The MLC leaf velocity required for two-bank-MLC and four-bank-MLC tracking was evaluated for the apertures studied and a substantial decrease was found in the maximum MLC velocity required when four-banks were used for tracking rather than two. A dosimetric comparison of the two techniques was also performed and minimal difference was found between two-bank-MLC and four-bank-MLC tracking. The use of four MLC banks for dynamic MLC tracking is shown to be potentially advantageous for increasing the delivery efficiency compared with two-bank-MLC tracking where difficulties are encountered if large leaf shifts are required to track motion perpendicular to the direction of leaf travel.

Development of a multi-knife-edge slit collimator for prompt gamma ray imaging during proton beam cancer therapy

NASA Astrophysics Data System (ADS)

Ready, John Francis, III

Proton beam usage to treat cancer has recently experienced rapid growth, as it offers the ability to target dose delivery in a patient more precisely than traditional x-ray treatment methods. Protons stop within the patient, delivering the maximum dose at the end of their track--a phenomenon described as the Bragg peak. However, because a large dose is delivered to a small volume, proton therapy is very sensitive to errors in patient setup and treatment planning calculations. Additionally, because all primary beam particles stop in the patient, there is no direct information available to verify dose delivery. These factors contribute to the range uncertainty in proton therapy, which ultimately hinders its clinical usefulness. A reliable method of proton range verification would allow the clinician to fully utilize the precise dose delivery of the Bragg peak. Several methods to verify proton range detect secondary emissions, especially prompt gamma ray (PG) emissions. However, detection of PGs is challenging due to their high energy (2-10 MeV) and low attenuation coefficients, which limit PG interactions in materials. Therefore, detection and collimation methods must be specifically designed for prompt gamma ray imaging (PGI) applications. In addition, production of PGs relies on delivering a dose of radiation to the patient. Ideally, verification of the Bragg peak location exposes patients to a minimal dose, thus limiting the PG counts available to the imaging system. An additional challenge for PGI is the lack of accurate simulation models, which limit the study of PG production characteristics and the relationship between PG distribution and dose delivery. Specific limitations include incorrect modeling of the reaction cross sections, gamma emission yields, and angular distribution of emission for specific photon energies. While simulations can still be valuable assets in designing a system to detect and image PGs, until new models are developed and incorporated into Monte Carlo simulation packages, simulations cannot be used to study the production and location of PG emissions during proton therapy. This work presents a novel system to image PGs emitted during proton therapy to verify proton beam range. The imaging system consists of a multi-slit collimator paired with a position-sensitive LSO scintillation detector. This innovative design is the first collimated imaging system to implement two-dimensional (2-D) imaging for PG proton beam range verification, while also providing a larger field of view than compared to single-slit collimator systems. Other, uncollimated imaging systems have been explored for PGI applications, such as Compton cameras. However, Compton camera designs are severely limited by counting rate capabilities. A recent Compton camera study reported count rate capability of about 5 kHz. However, at a typical clinical beam current of 1.0 nA, the estimated PG emission rate would be 6 x 108 per second. After accounting for distance to the detector and interaction efficiencies, the detection system will still be overwhelmed with counts in the MHz range, causing false coincidences and hindering the operation of the imaging system. Initial measurements using 50 MeV protons demonstrated the ability of our system to reconstruct 2-D PG distributions at clinical beam currents. A Bragg peak localization precision of 1 mm (2sigma) was achieved with delivery of (1.7 +/- 0.8) x 108 protons into a PMMA target, suggesting the ability of the system to detect relative shifts in proton range while delivering fewer protons than used in a typical treatment fraction. This is key, as the ideal system allows the clinician to verify proton range when delivering only a small portion of the prescribed dose, preventing the mistreatment of the patient. Additionally, the absolute position of the Bragg peak was identified to within 1.6 mm (2sigma) with 5.6 x 1010 protons delivered. These promising results warrant further investigation and system optimization for clinical implementation. While further measurements at clinical beam energy levels will be required to verify system performance, these preliminary results provide evidence that 2-D image reconstruction, with 1-2 mm accuracy, is possible with this design. Implementing such a system in the clinical setting would greatly improve proton therapy cancer treatment outcomes.

Quantitative trait loci controlling leaf venation in Arabidopsis.

PubMed

Rishmawi, Louai; Bühler, Jonas; Jaegle, Benjamin; Hülskamp, Martin; Koornneef, Maarten

2017-08-01

Leaf veins provide the mechanical support and are responsible for the transport of nutrients and water to the plant. High vein density is a prerequisite for plants to have C4 photosynthesis. We investigated the genetic variation and genetic architecture of leaf venation traits within the species Arabidopsis thaliana using natural variation. Leaf venation traits, including leaf vein density (LVD) were analysed in 66 worldwide accessions and 399 lines of the multi-parent advanced generation intercross population. It was shown that there is no correlation between LVD and photosynthesis parameters within A. thaliana. Association mapping was performed for LVD and identified 16 and 17 putative quantitative trait loci (QTLs) in the multi-parent advanced generation intercross and worldwide sets, respectively. There was no overlap between the identified QTLs suggesting that many genes can affect the traits. In addition, linkage mapping was performed using two biparental recombinant inbred line populations. Combining linkage and association mapping revealed seven candidate genes. For one of the candidate genes, RCI2c, we demonstrated its function in leaf venation patterning. © 2017 John Wiley & Sons Ltd.

Single-Pulse Multi-Point Multi-Component Interferometric Rayleigh Scattering Velocimeter

NASA Technical Reports Server (NTRS)

Bivolaru, Daniel; Danehy, Paul M.; Lee, Joseph W.; Gaffney, Richard L., Jr.; Cutler, Andrew D.

2006-01-01

A simultaneous multi-point, multi-component velocimeter using interferometric detection of the Doppler shift of Rayleigh, Mie, and Rayleigh-Brillouin scattered light in supersonic flow is described. The system uses up to three sets of collection optics and one beam combiner for the reference laser light to form a single collimated beam. The planar Fabry-Perot interferometer used in the imaging mode for frequency detection preserves the spatial distribution of the signal reasonably well. Single-pulse multi-points measurements of up to two orthogonal and one non-orthogonal components of velocity in a Mach 2 free jet were performed to demonstrate the technique. The average velocity measurements show a close agreement with the CFD calculations using the VULCAN code.

Imaging characteristics of scintimammography using parallel-hole and pinhole collimators

NASA Astrophysics Data System (ADS)

Tsui, B. M. W.; Wessell, D. E.; Zhao, X. D.; Wang, W. T.; Lewis, D. P.; Frey, E. C.

1998-08-01

The purpose of the study is to investigate the imaging characteristics of scintimammography (SM) using parallel-hole (PR) and pinhole (PN) collimators in a clinical setting. Experimental data were acquired from a phantom that models the breast with small lesions using a low energy high resolution (LEHR) PR and a PN collimator. At close distances, the PN collimator provides better spatial resolution and higher detection efficiency than the PR collimator, at the expense of a smaller field-of-view (FOV). Detection of small breast lesions can be further enhanced by noise smoothing, field uniformity correction, scatter subtraction and resolution recovery filtering. Monte Carlo (MC) simulation data were generated from the 3D MCAT phantom that realistically models the Tc-99m sestamibi uptake and attenuation distributions in an average female patient. For both PR and PN collimation, the scatter to primary ratio (S/P) decreases from the base of the breast to the nipple and is higher in the left than right breast due to scatter of photons from the heart. Results from the study add to understanding of the imaging characteristics of SM using PR and PN collimators and assist in the design of data acquisition and image processing methods to enhance the detection of breast lesions using SM.

Geometric Characterization of Multi-Axis Multi-Pinhole SPECT

PubMed Central

DiFilippo, Frank P.

2008-01-01

A geometric model and calibration process are developed for SPECT imaging with multiple pinholes and multiple mechanical axes. Unlike the typical situation where pinhole collimators are mounted directly to rotating gamma ray detectors, this geometric model allows for independent rotation of the detectors and pinholes, for the case where the pinhole collimator is physically detached from the detectors. This geometric model is applied to a prototype small animal SPECT device with a total of 22 pinholes and which uses dual clinical SPECT detectors. All free parameters in the model are estimated from a calibration scan of point sources and without the need for a precision point source phantom. For a full calibration of this device, a scan of four point sources with 360° rotation is suitable for estimating all 95 free parameters of the geometric model. After a full calibration, a rapid calibration scan of two point sources with 180° rotation is suitable for estimating the subset of 22 parameters associated with repositioning the collimation device relative to the detectors. The high accuracy of the calibration process is validated experimentally. Residual differences between predicted and measured coordinates are normally distributed with 0.8 mm full width at half maximum and are estimated to contribute 0.12 mm root mean square to the reconstructed spatial resolution. Since this error is small compared to other contributions arising from the pinhole diameter and the detector, the accuracy of the calibration is sufficient for high resolution small animal SPECT imaging. PMID:18293574

Design and dosimetry of small animal radiation facilities

NASA Astrophysics Data System (ADS)

Rodriguez, Manuel R.

The aim of this work was to develop an irradiation system for radiobiology studies. We designed a novel image-guided micro-irradiator capable of partial-body zebrafish embryo irradiation. The radiation source is a 50 kV photon beam from a miniature x-ray source (Xoft Inc., CA). The source is inserted in a cylindrical brass collimator, 3 cm in diameter and 3 cm in length. The collimator has a 1 mm-diameter pinhole along the longitudinal axis, which provides a well-focused beam with a sharp penumbra. A photodiode is installed at one exit of the pinhole collimator to monitor the photon dose rate. The source with the collimator is attached under a movable table. A video camera, connected to the computer, is placed above the movable table to record position of the specimens in relation to the pinhole collimator. The captured images are analyzed, and the relative distances between the specimens and the pinhole are calculated. The coordinates are sent to the computer-controlled movable table to accurately position the specimens in the beam. Monte Carlo simulations were performed to characterize dosimetric properties of the system, to determine dosimetric sensitivity, and to help in the design. The image-guidance and high precision of the movable table enable very accurate specimen position. The beam monitoring system provides accurate, fast and easy dose determination. Portability and self-shielding make this system suitable for any radiobiology laboratory. This novel micro-irradiator is appropriate for partial irradiation of zebrafish embryos; however its potential use is much wider like irradiation of cell cultures or other small specimens.

Modified optical fiber daylighting system with sunlight transportation in free space.

PubMed

Vu, Ngoc-Hai; Pham, Thanh-Tuan; Shin, Seoyong

2016-12-26

We present the design, optical simulation, and experiment of a modified optical fiber daylighting system (M-OFDS) for indoor lighting. The M-OFDS is comprised of three sub-systems: concentration, collimation, and distribution. The concentration part is formed by coupling a Fresnel lens with a large-core plastic optical fiber. The sunlight collected by the concentration sub-system is propagated in a plastic optical fiber and then collimated by the collimator, which is a combination of a parabolic mirror and a convex lens. The collimated beam of sunlight travels in free space and is guided to the interior by directing flat mirrors, where it is diffused uniformly by a distributor. All parameters of the system are calculated theoretically. Based on the designed system, our simulation results demonstrated a maximum optical efficiency of 71%. The simulation results also showed that sunlight could be delivered to the illumination destination at distance of 30 m. A prototype of the M-OFDS was fabricated, and preliminary experiments were performed outdoors. The simulation results and experimental results confirmed that the M-OFDS was designed effectively. A large-scale system constructed by several M-OFDSs is also proposed. The results showed that the presented optical fiber daylighting system is a strong candidate for an inexpensive and highly efficient application of solar energy in buildings.

SU-C-BRB-04: Characteristics and Performance Evaluation of the First Commercial MLC for a Robotic Delivery System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fuerweger, C; European Cyberknife Center Munich, Munich, DE; Prins, P

Purpose: To assess characteristics and performance of the “Incise™” MLC (41 leaf pairs, 2.5mm width, FFF linac) mounted on the robotic SRS/SBRT platform “CyberKnife M6™” in a pre-clinical 5 months (11/2014–03/2015) test period. Methods: Beam properties were measured with unshielded diodes and EBT3 film. The CyberKnife workspace for MLC was analyzed by transforming robot node coordinates (cranial / body paths) into Euler geometry. Bayouth tests for leaf / bank position accuracy were performed in standard (A/P) and clinically relevant non-standard positions, before and after exercising the MLC for 10+ minutes. Total system and delivery accuracy were assessed in End-to-End testsmore » and dosimetric verification of exemplary plans. Stability over time was evaluated in Picket-Fence-and adapted Winston-Lutz-tests (AQA) for different collimator angles. Results: Penumbrae (80–20%, with 100%=2*dose at inflection point; SAD 80cm; 10cm depth) parallel / perpendicular to leaf motion were 2.87/2.64mm for the smallest (0×76×0.75cm{sup 2}) and 5.34/4.94mm for the largest (9.76×9.75cm{sup 2}) square field. MLC circular field penumbrae exceeded fixed cones by 10–20% (e.g. 60mm: 4.0 vs. 3.6mm; 20mm: 3.6 vs. 2.9mm). Interleaf leakage was <0.5%. Clinically accessible workspace with MLC covered (non-coplanar) gantry angles of [-113°;+112°] (cranial) and [-108°;+102°] (body), and collimator angles of [-100°;+107°] (cranial) and [-91°;+100°] (body). Average leaf position offsets were ≤0.2mm in 14 standard A/P Bayouth tests and ≤0.6mm in 8 non-standard direction tests. Pre-test MLC exercise increased jaggedness (range ±0.3mm vs. ±0.5mm) and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.39±0.06mm in 6 End-to-End tests. Picket-Fence and AQA showed no adverse trends during the test period. Conclusion: The Incise™ MLC for CyberKnife M6™ displayed high accuracy and mechanical stability over the test period. The specific CyberKnife geometry and performance after exercise demand dedicated QA measures. This work is in part funded by a research grant from Accuray Inc, Sunnyvale, USA. Erasmus MC Cancer Institute also has research collaborations with Elekta AB, Stockholm, Sweden. C Fuerweger has previously received speaker honoraria from Accuray Inc, Sunnyvale, USA.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senaratne, Ruwan, E-mail: rsenarat@physics.ucsb.edu; Rajagopal, Shankari V.; Geiger, Zachary A.

We present a simple and inexpensive design for a multichannel effusive oven nozzle which provides improved atomic beam collimation and thus extended oven lifetimes. Using this design, we demonstrate an atomic lithium source suitable for trapped-atom experiments. At a nozzle temperature of 525 °C, the collimated atomic beam flux directly after the nozzle is 1.2 × 10{sup 14} atoms/s with a peak beam intensity greater than 5.0 × 10{sup 16} atoms/s/sr. This suggests an oven lifetime of several decades of continuous operation.

Electron transport efficiency at opposite leaf sides: effect of vertical distribution of leaf angle, structure, chlorophyll content and species in a forest canopy.

PubMed

Mänd, Pille; Hallik, Lea; Peñuelas, Josep; Kull, Olevi

2013-02-01

We investigated changes in chlorophyll a fluorescence from alternate leaf surfaces to assess the intraleaf light acclimation patterns in combination with natural variations in radiation, leaf angles, leaf mass per area (LMA), chlorophyll content (Chl) and leaf optical parameters. Measurements were conducted on bottom- and top-layer leaves of Tilia cordata Mill. (a shade-tolerant sub-canopy species, sampled at heights of 11 and 16 m) and Populus tremula L. (a light-demanding upper canopy species, sampled at canopy heights of 19 and 26 m). The upper canopy species P. tremula had a six times higher PSII quantum yield (Φ(II)) and ratio of open reaction centres (qP), and a two times higher LMA than T. cordata. These species-specific differences were also present when the leaves of both species were in similar light conditions. Leaf adaxial/abaxial fluorescence ratio was significantly larger in the case of more horizontal leaves. Populus tremula (more vertical leaves), had smaller differences in fluorescence parameters between alternate leaf sides compared with T. cordata (more horizontal leaves). However, optical properties on alternate leaf sides showed a larger difference for P. tremula. Intraspecifically, the measured optical parameters were better correlated with LMA than with leaf Chl. Species-specific differences in leaf anatomy appear to enhance the photosynthetic potential of leaf biochemistry by decreasing the interception of excess light in P. tremula and increasing the light absorptance in T. cordata. Our results indicate that intraleaf light absorption gradient, described here as leaf adaxial/abaxial side ratio of chlorophyll a fluorescence, varies significantly with changes in leaf light environment in a multi-layer multi-species tree canopy. However, this variation cannot be described merely as a simple function of radiation, leaf angle, Chl or LMA, and species-specific differences in light acclimation strategies should also be considered.

Exploiting Auto-Collimation for Real-Time Onboard Monitoring of Space Optical Camera Geometric Parameters

NASA Astrophysics Data System (ADS)

Liu, W.; Wang, H.; Liu, D.; Miu, Y.

2018-05-01

Precise geometric parameters are essential to ensure the positioning accuracy for space optical cameras. However, state-of-the-art onorbit calibration method inevitably suffers from long update cycle and poor timeliness performance. To this end, in this paper we exploit the optical auto-collimation principle and propose a real-time onboard calibration scheme for monitoring key geometric parameters. Specifically, in the proposed scheme, auto-collimation devices are first designed by installing collimated light sources, area-array CCDs, and prisms inside the satellite payload system. Through utilizing those devices, the changes in the geometric parameters are elegantly converted into changes in the spot image positions. The variation of geometric parameters can be derived via extracting and processing the spot images. An experimental platform is then set up to verify the feasibility and analyze the precision index of the proposed scheme. The experiment results demonstrate that it is feasible to apply the optical auto-collimation principle for real-time onboard monitoring.

Thermomechanical assessment of the effects of a jaw-beam angle during beam impact on Large Hadron Collider collimators

NASA Astrophysics Data System (ADS)

Cauchi, Marija; Assmann, R. W.; Bertarelli, A.; Carra, F.; Lari, L.; Rossi, A.; Mollicone, P.; Sammut, N.

2015-02-01

The correct functioning of a collimation system is crucial to safely and successfully operate high-energy particle accelerators, such as the Large Hadron Collider (LHC). However, the requirements to handle high-intensity beams can be demanding, and accident scenarios must be well studied in order to assess if the collimator design is robust against possible error scenarios. One of the catastrophic, though not very probable, accident scenarios identified within the LHC is an asynchronous beam dump. In this case, one (or more) of the 15 precharged kicker circuits fires out of time with the abort gap, spraying beam pulses onto LHC machine elements before the machine protection system can fire the remaining kicker circuits and bring the beam to the dump. If a proton bunch directly hits a collimator during such an event, severe beam-induced damage such as magnet quenches and other equipment damage might result, with consequent downtime for the machine. This study investigates a number of newly defined jaw error cases, which include angular misalignment errors of the collimator jaw. A numerical finite element method approach is presented in order to precisely evaluate the thermomechanical response of tertiary collimators to beam impact. We identify the most critical and interesting cases, and show that a tilt of the jaw can actually mitigate the effect of an asynchronous dump on the collimators. Relevant collimator damage limits are taken into account, with the aim to identify optimal operational conditions for the LHC.

Titan Lifting Entry & Atmospheric Flight (T-LEAF) Science Mission

NASA Astrophysics Data System (ADS)

Lee, G.; Sen, B.; Ross, F.; Sokol, D.

2016-12-01

Northrop Grumman has been developing the Titan Lifting Entry & Atmospheric Flight (T-LEAF) sky rover to roam the lower atmosphere and observe at close quarters the lakes and plains of Saturn's ocean moon, Titan. T-LEAF also supports surface exploration and science by providing precision delivery of in-situ instruments to the surface of Titan. T-LEAF is a highly maneuverable sky rover and its aerodynamic shape (i.e., a flying wing) does not restrict it to following prevailing wind patterns on Titan, but allows mission operators to chart its course. This freedom of mobility allows T-LEAF to follow the shorelines of Titan's methane lakes, for example, or to target very specific surface locations. We will present a straw man concept of T-LEAF, including size, mass, power, on-board science payloads and measurement, and surface science dropsonde deployment CONOPS. We will discuss the various science instruments and their vehicle level impacts, such as meteorological and electric field sensors, acoustic sensors for measuring shallow depths, multi-spectral imagers, high definition cameras and surface science dropsondes. The stability of T-LEAF and its long residence time on Titan will provide for time to perform a large aerial survey of select prime surface targets deployment of dropsondes at selected locations surface measurements that are coordinated with on-board remote measurements communication relay capabilities to orbiter (or Earth). In this context, we will specifically focus upon key factors impacting the design and performance of T-LEAF science: science payload accommodation, constraints and opportunities characteristics of flight, payload deployment and measurement CONOPS in the Titan atmosphere. This presentation will show how these factors provide constraints as well as enable opportunities for novel long duration scientific studies of Titan's surface.

Comparison of Single and Multi-Scale Method for Leaf and Wood Points Classification from Terrestrial Laser Scanning Data

NASA Astrophysics Data System (ADS)

Wei, Hongqiang; Zhou, Guiyun; Zhou, Junjie

2018-04-01

The classification of leaf and wood points is an essential preprocessing step for extracting inventory measurements and canopy characterization of trees from the terrestrial laser scanning (TLS) data. The geometry-based approach is one of the widely used classification method. In the geometry-based method, it is common practice to extract salient features at one single scale before the features are used for classification. It remains unclear how different scale(s) used affect the classification accuracy and efficiency. To assess the scale effect on the classification accuracy and efficiency, we extracted the single-scale and multi-scale salient features from the point clouds of two oak trees of different sizes and conducted the classification on leaf and wood. Our experimental results show that the balanced accuracy of the multi-scale method is higher than the average balanced accuracy of the single-scale method by about 10 % for both trees. The average speed-up ratio of single scale classifiers over multi-scale classifier for each tree is higher than 30.

The HEAO-A Scanning Modulation Collimator instrument

NASA Technical Reports Server (NTRS)

Roy, A.; Ballas, J.; Jagoda, N.; Mckinnon, P.; Ramsey, A.; Wester, E.

1977-01-01

The Scanning Modulation Collimator X-ray instrument for the HEAO-A satellite was designed to measure celestial radiation in the range between 1 and 15 KeV and to resolve, and correlate, the position of X-ray sources with visible light sources on the celestial sphere to within 5 arc seconds. The positional accuracy is made possible by mechanical collimation of the X-ray sources viewed by the instrument. High sensitivity is provided from two systems each containing four gas filled proportional counters followed by preamplification, signal summing, pulse height analysis, pulse shape discrimination, X-ray event accumulators and telemetry processing electronics.

High collimated coherent illumination for reconstruction of digitally calculated holograms: design and experimental realization

NASA Astrophysics Data System (ADS)

Morozov, Alexander; Dubinin, German; Dubynin, Sergey; Yanusik, Igor; Kim, Sun Il; Choi, Chil-Sung; Song, Hoon; Lee, Hong-Seok; Putilin, Andrey; Kopenkin, Sergey; Borodin, Yuriy

2017-06-01

Future commercialization of glasses-free holographic real 3D displays requires not only appropriate image quality but also slim design of backlight unit and whole display device to match market needs. While a lot of research aimed to solve computational issues of forming Computer Generated Holograms for 3D Holographic displays, less focus on development of backlight units suitable for 3D holographic display applications with form-factor of conventional 2D display systems. Thereby, we report coherent backlight unit for 3D holographic display with thickness comparable to commercially available 2D displays (cell phones, tablets, laptops, etc.). Coherent backlight unit forms uniform, high-collimated and effective illumination of spatial light modulator. Realization of such backlight unit is possible due to holographic optical elements, based on volume gratings, constructing coherent collimated beam to illuminate display plane. Design, recording and measurement of 5.5 inch coherent backlight unit based on two holographic optical elements are presented in this paper.

Design requirements for a stand alone EUV interferometer

NASA Astrophysics Data System (ADS)

Michallon, Ph.; Constancias, C.; Lagrange, A.; Dalzotto, B.

2008-03-01

EUV lithography is expected to be inserted for the 32/22 nm nodes with possible extension below. EUV resist availability remains one of the main issues to be resolved. There is an urgent need to provide suitable tools to accelerate resist development and to achieve resolution, LER and sensitivity specifications simultaneously. An interferometer lithography tool offers advantages regarding conventional EUV exposure tool. It allows the evaluation of resists, free from the deficiencies of optics and mask which are limiting the achieved resolution. Traditionally, a dedicated beam line from a synchrotron, with limited access, is used as a light source in EUV interference lithography. This paper identifies the technology locks to develop a stand alone EUV interferometer using a compact EUV source. It will describe the theoretical solutions adopted and especially look at the feasibility according to available technologies. EUV sources available on the market have been evaluated in terms of power level, source size, spatial coherency, dose uniformity, accuracy, stability and reproducibility. According to the EUV source characteristics, several optic designs were studied (simple or double gratings). For each of these solutions, the source and collimation optic specifications have been determined. To reduce the exposure time, a new grating technology will also be presented allowing to significantly increasing the transmission system efficiency. The optical grating designs were studied to allow multi-pitch resolution print on the same exposure without any focus adjustment. Finally micro mechanical system supporting the gratings was studied integrating the issues due to vacuum environment, alignment capability, motion precision, automation and metrology to ensure the needed placement control between gratings and wafer. A similar study was carried out for the collimation-optics mechanical support which depends on the source characteristics.

Development of a 0.5m clear aperture Cassegrain type collimator telescope

NASA Astrophysics Data System (ADS)

Ekinci, Mustafa; Selimoǧlu, Özgür

2016-07-01

Collimator is an optical instrument used to evaluate performance of high precision instruments, especially space-born high resolution telescopes. Optical quality of the collimator telescope needs to be better than the instrument to be measured. This requirement leads collimator telescope to be a very precise instrument with high quality mirrors and a stable structure to keep it operational under specified conditions. In order to achieve precision requirements and to ensure repeatability of the mounts for polishing and metrology, opto-mechanical principles are applied to mirror mounts. Finite Element Method is utilized to simulate gravity effects, integration errors and temperature variations. Finite element analyses results of deformed optical surfaces are imported to optical domain by using Zernike polynomials to evaluate the design against specified WFE requirements. Both mirrors are aspheric and made from Zerodur for its stability and near zero CTE, M1 is further light-weighted. Optical quality measurements of the mirrors are achieved by using custom made CGHs on an interferometric test setup. Spider of the Cassegrain collimator telescope has a flexural adjustment mechanism driven by precise micrometers to overcome tilt errors originating from finite stiffness of the structure and integration errors. Collimator telescope is assembled and alignment methods are proposed.

Calibration techniques and results in the soft X-ray and extreme ultraviolet for components of the Extreme Ultraviolet Explorer Satellite

NASA Technical Reports Server (NTRS)

Malina, Roger F.; Jelinsky, Patrick; Bowyer, Stuart

1986-01-01

The calibration facilities and techniques for the Extreme Ultraviolet Explorer (EUVE) from 44 to 2500 A are described. Key elements include newly designed radiation sources and a collimated monochromatic EUV beam. Sample results for the calibration of the EUVE filters, detectors, gratings, collimators, and optics are summarized.

Automated Leaf Tracking using Multi-view Image Sequences of Maize Plants for Leaf-growth Monitoring

NASA Astrophysics Data System (ADS)

Das Choudhury, S.; Awada, T.; Samal, A.; Stoerger, V.; Bashyam, S.

2017-12-01

Extraction of phenotypes with botanical importance by analyzing plant image sequences has the desirable advantages of non-destructive temporal phenotypic measurements of a large number of plants with little or no manual intervention in a relatively short period of time. The health of a plant is best interpreted by the emergence timing and temporal growth of individual leaves. For automated leaf growth monitoring, it is essential to track each leaf throughout the life cycle of the plant. Plants are constantly changing organisms with increasing complexity in architecture due to variations in self-occlusions and phyllotaxy, i.e., arrangements of leaves around the stem. The leaf cross-overs pose challenges to accurately track each leaf using single view image sequence. Thus, we introduce a novel automated leaf tracking algorithm using a graph theoretic approach by multi-view image sequence analysis based on the determination of leaf-tips and leaf-junctions in the 3D space. The basis of the leaf tracking algorithm is: the leaves emerge using bottom-up approach in the case of a maize plant, and the direction of leaf emergence strictly alternates in terms of direction. The algorithm involves labeling of the individual parts of a plant, i.e., leaves and stem, following graphical representation of the plant skeleton, i.e., one-pixel wide connected line obtained from the binary image. The length of the leaf is measured by the number of pixels in the leaf skeleton. To evaluate the performance of the algorithm, a benchmark dataset is indispensable. Thus, we publicly release University of Nebraska-Lincoln Component Plant Phenotyping dataset-2 (UNL-CPPD-2) consisting of images of the 20 maize plants captured by visible light camera of the Lemnatec Scanalyzer 3D high throughout plant phenotyping facility once daily for 60 days from 10 different views. The dataset is aimed to facilitate the development and evaluation of leaf tracking algorithms and their uniform comparisons.

SU-E-J-56: Static Gantry Digital Tomosynthesis From the Beam’s-Eye-View

DOE Office of Scientific and Technical Information (OSTI.GOV)

Partain, L; Kwon, J; Boyd, D

Purpose We have designed a novel TumoTrak™ x-ray system that delivers 19 distinct kV views with the linac gantry stationary. It images MV treatment beam above and below the patient with a kV tomosysthesis slice image from the therapy beam’s-eye-view. Results will be high quality images without MLC shadowing for notable improvements relative to conventional fluoroscopic MV imaging and fluoroscopic kV imaging. Methods A complete design has a kV electron beam multisource X-ray tube that fits around the MV treatment beam path, with little interference with normal radiotherapy and unblocked by the multi-leaf-collimator. To simulate digital tomosynthesis, we used cone-beammore » CT projection data from a lung SBRT patient. These data were acquired at 125 kVp and 11 fps (0.4 mAs per projection). We chose 19 projections evenly spaced over 27° around one of the treatment angles (240°). Digital tomosynthesis reconstruction of a slice through the tumor was performed using iterative reconstruction. The visibility of the lesion was assessed for the reconstructed digital tomosynthesis (DTS), using fluoroscopy MV images acquired during radiation therapy, and a kV single projection image acquired at the same angle as the treatment field (240°). Results The fluoroscopic DTS images provide the best tumor contrast, surpassing the conventional radiographic and the in-treatment MV portal images. The electron beam multisource X-ray tube design has been completed and the tube is being fabricated. The estimated time to cycle through all 19 projections is 700 ms, enabling high frame-rate imaging. While the initial proposed use case is for image guided and gated treatment delivery, the enhanced imaging will also deliver superior radiographic images for patient setup. Conclusion The proposed device will deliver high quality planar images from the beam’s-eye-view without MLC obstruction. The prototype has been designed and is being assembled with first imaging scheduled for May 2015. L. Partain, J. Kwon, D. Boyd: NIH/SBIR R43CA192489-01. J. Rottmann, G. Zentai, R. Berbeco: NIH/NCI 1R01CA188446-01. R. Berbeco: E. Research Grant, Varian Medical Systems.« less

MULTI-COMPONENT ANALYSIS OF POSITION-VELOCITY CUBES OF THE HH 34 JET

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez-Gonzalez, A.; Esquivel, A.; Raga, A. C.

We present an analysis of H{alpha} spectra of the HH 34 jet with two-dimensional spectral resolution. We carry out multi-Gaussian fits to the spatially resolved line profiles and derive maps of the intensity, radial velocity, and velocity width of each of the components. We find that close to the outflow source we have three components: a high (negative) radial velocity component with a well-collimated, jet-like morphology; an intermediate velocity component with a broader morphology; and a positive radial velocity component with a non-collimated morphology and large linewidth. We suggest that this positive velocity component is associated with jet emission scatteredmore » in stationary dust present in the circumstellar environment. Farther away from the outflow source, we find only two components (a high, negative radial velocity component, which has a narrower spatial distribution than an intermediate velocity component). The fitting procedure was carried out with the new AGA-V1 code, which is available online and is described in detail in this paper.« less

Wavelength locking of single emitters and multi-emitter modules: simulation and experiments

NASA Astrophysics Data System (ADS)

Yanson, Dan; Rappaport, Noam; Peleg, Ophir; Berk, Yuri; Dahan, Nir; Klumel, Genady; Baskin, Ilya; Levy, Moshe

2016-03-01

Wavelength-stabilized high-brightness single emitters are commonly used in fiber-coupled laser diode modules for pumping Yb-doped lasers at 976 nm, and Nd-doped ones at 808 nm. We investigate the spectral behavior of single emitters under wavelength-selective feedback from a volume Bragg (or hologram) grating (VBG) in a multi-emitter module. By integrating a full VBG model as a multi-layer thin film structure with commercial raytracing software, we simulated wavelength locking conditions as a function of beam divergence and angular alignment tolerances. Good correlation between the simulated VBG feedback strength and experimentally measured locking ranges, in both VBG misalignment angle and laser temperature, is demonstrated. The challenges of assembling multi-emitter modules based on beam-stacked optical architectures are specifically addressed, where the wavelength locking conditions must be achieved simultaneously with high fiber coupling efficiency for each emitter in the module. It is shown that angular misorientation between fast and slow-axis collimating optics can have a dramatic effect on the spectral and power performance of the module. We report the development of our NEON-S wavelength-stabilized fiber laser pump module, which uses a VBG to provide wavelength-selective optical feedback in the collimated portion of the beam. Powered by our purpose-developed high-brightness single emitters, the module delivers 47 W output at 11 A from an 0.15 NA fiber and a 0.3 nm linewidth at 976 nm. Preliminary wavelength-locking results at 808 nm are also presented.

Development and deployment of the Collimated Directional Radiation Detection System

NASA Astrophysics Data System (ADS)

Guckes, Amber L.; Barzilov, Alexander

2017-09-01

The Collimated Directional Radiation Detection System (CDRDS) is capable of imaging radioactive sources in two dimensions (as a directional detector). The detection medium of the CDRDS is a single Cs2LiYCl6:Ce3+ scintillator cell enriched in 7Li (CLYC-7). The CLYC-7 is surrounded by a heterogeneous high-density polyethylene (HDPE) and lead (Pb) collimator. These materials make-up a coded aperture inlaid in the collimator. The collimator is rotated 360° by a stepper motor which enables time-encoded imaging of a radioactive source. The CDRDS is capable of spectroscopy and pulse shape discrimination (PSD) of photons and fast neutrons. The measurements of a radioactive source are carried out in discrete time steps that correlate to the angular rotation of the collimator. The measurement results are processed using a maximum likelihood expectation (MLEM) algorithm to create an image of the measured radiation. This collimator design allows for the directional detection of photons and fast neutrons simultaneously by utilizing only one CLYC-7 scintillator. Directional detection of thermal neutrons can also be performed by utilizing another suitable scintillator. Moreover, the CDRDS is portable, robust, and user friendly. This unit is capable of utilizing wireless data transfer for possible radiation mapping and network-centric applications. The CDRDS was tested by performing laboratory measurements with various gamma-ray and neutron sources.

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community

NASA Astrophysics Data System (ADS)

Zheng, S. X.; Ren, H. Y.; Lan, Z. C.; Li, W. H.; Wang, K. B.; Bai, Y. F.

2010-03-01

Understanding the mechanistic links between environmental drivers, human disturbance, plant functional traits, and ecosystem properties is a fundamental aspect of biodiversity-ecosystem functioning research. Recent studies have focused mostly on leaf-level traits or community-level weighted traits to predict species responses to grazing and the consequent change in ecosystem functioning. However, studies of leaf-level traits or community-level weighted traits seldom identify the mechanisms linking grazing impact on leaf traits to ecosystem functioning. Here, using a multi-organization-level approach, we examined the effects of grazing on leaf traits (i.e., leaf area, leaf dry mass and specific leaf area) and ecosystem functioning across six communities of three vegetation types along a soil moisture gradient in the Xilin River Basin of Inner Mongolia grassland, China. Our results showed that the effects of grazing on leaf traits differed substantially when scaling up from leaf-level to species, functional group (i.e., life forms and water ecotype types), and community levels; and they also varied with vegetation type or site conditions. The effects of grazing on leaf traits diminished progressively along the hierarchy of organizational levels in the meadow, whereas the impacts were predominantly negative and the magnitude of the effects increased considerably at higher organizational levels in the typical steppe. Soil water and nutrient availability, functional trade-offs between leaf size and number of leaves per individual, and differentiation in avoidance and tolerance strategies among coexisting species are likely to be responsible for the observed responses of leaf traits to grazing at different levels of organization and among vegetation types. Our findings also demonstrate that, at both the functional group and community levels, standing aboveground biomass increased with leaf area and specific leaf area. Compared with the large changes in leaf traits and standing aboveground biomass, the soil properties were relatively unaffected by grazing. Our study indicates that a multi-organization-level approach provides more robust and comprehensive predictions of the effects of grazing on leaf traits and ecosystem functioning.

Complete photonic band gaps and tunable self-collimation in the two-dimensional plasma photonic crystals with a new structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hai-Feng, E-mail: hanlor@163.com; Nanjing Artillery Academy, Nanjing 211132; Ding, Guo-Wen

2015-02-15

In this paper, the properties of complete photonic band gaps (CPBGs) and tunable self-collimation in two-dimensional plasma photonic crystals (2D PPCs) with a new structure in square lattices, whose dielectric fillers (GaAs) are inserted into homogeneous and nomagnetized plasma background are theoretically investigated by a modified plane wave expansion (PWE) method with a novel technique. The novel PWE method can be utilized to compute the dispersion curves of 2D PPCs with arbitrary-shaped cross section in any lattices. As a comparison, CPBGs of PPCs for four different configurations are numerically calculated. The computed results show that the proposed design has themore » advantages of achieving the larger CPBGs compared to the other three configurations. The influences of geometric parameters of filled unit cell and plasma frequency on the properties of CPBGs are studied in detail. The calculated results demonstrate that CPBGs of the proposed 2D PPCs can be easily engineered by changing those parameters, and the larger CPBGs also can be obtained by optimization. The self-collimation in such 2D PPCs also is discussed in theory under TM wave. The theoretical simulations reveal that the self-collimation phenomena can be found in the TM bands, and both the frequency range of self-collimation and the equifrequency surface contours can be tuned by the parameters as mentioned above. It means that the frequency range and direction of electromagnetic wave can be manipulated by designing, as it propagates in the proposed PPCs without diffraction. Those results can hold promise for designing the tunable applications based on the proposed PPCs.« less

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

NASA Astrophysics Data System (ADS)

Manuel, M. J.-E.; Kuranz, C. C.; Rasmus, A. M.; Klein, S. R.; MacDonald, M. J.; Trantham, M. R.; Fein, J. R.; Belancourt, P. X.; Young, R. P.; Keiter, P. A.; Drake, R. P.; Pollock, B. B.; Park, J.; Hazi, A. U.; Williams, G. J.; Chen, H.

2015-12-01

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysical systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. This result is a topic of ongoing investigation.

BEAM TRANSPORT LINES FOR THE BSNS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

WEI, J.

2006-06-26

This paper presents the design of two beam transport lines at the BSNS: one is the injection line from the Linac to the RCS and the other is the target line from the RCS to the target station. In the injection beam line, space charge effects, transverse halo collimation, momentum tail collimation and debunching are the main concerned topics. A new method of using triplet cells and stripping foils is used to collimate transverse halo. A long straight section is reserved for the future upgrading linac and debuncher. In the target beam line, large halo emittance, beam stability at themore » target due to kicker failures and beam jitters, shielding of back-scattering neutrons from the target are main concerned topics. Special bi-gap magnets will be used to reduce beam losses in the collimators in front of the target.« less

A method for photon beam Monte Carlo multileaf collimator particle transport

NASA Astrophysics Data System (ADS)

Siebers, Jeffrey V.; Keall, Paul J.; Kim, Jong Oh; Mohan, Radhe

2002-09-01

Monte Carlo (MC) algorithms are recognized as the most accurate methodology for patient dose assessment. For intensity-modulated radiation therapy (IMRT) delivered with dynamic multileaf collimators (DMLCs), accurate dose calculation, even with MC, is challenging. Accurate IMRT MC dose calculations require inclusion of the moving MLC in the MC simulation. Due to its complex geometry, full transport through the MLC can be time consuming. The aim of this work was to develop an MLC model for photon beam MC IMRT dose computations. The basis of the MC MLC model is that the complex MLC geometry can be separated into simple geometric regions, each of which readily lends itself to simplified radiation transport. For photons, only attenuation and first Compton scatter interactions are considered. The amount of attenuation material an individual particle encounters while traversing the entire MLC is determined by adding the individual amounts from each of the simplified geometric regions. Compton scatter is sampled based upon the total thickness traversed. Pair production and electron interactions (scattering and bremsstrahlung) within the MLC are ignored. The MLC model was tested for 6 MV and 18 MV photon beams by comparing it with measurements and MC simulations that incorporate the full physics and geometry for fields blocked by the MLC and with measurements for fields with the maximum possible tongue-and-groove and tongue-or-groove effects, for static test cases and for sliding windows of various widths. The MLC model predicts the field size dependence of the MLC leakage radiation within 0.1% of the open-field dose. The entrance dose and beam hardening behind a closed MLC are predicted within +/-1% or 1 mm. Dose undulations due to differences in inter- and intra-leaf leakage are also correctly predicted. The MC MLC model predicts leaf-edge tongue-and-groove dose effect within +/-1% or 1 mm for 95% of the points compared at 6 MV and 88% of the points compared at 18 MV. The dose through a static leaf tip is also predicted generally within +/-1% or 1 mm. Tests with sliding windows of various widths confirm the accuracy of the MLC model for dynamic delivery and indicate that accounting for a slight leaf position error (0.008 cm for our MLC) will improve the accuracy of the model. The MLC model developed is applicable to both dynamic MLC and segmental MLC IMRT beam delivery and will be useful for patient IMRT dose calculations, pre-treatment verification of IMRT delivery and IMRT portal dose transmission dosimetry.

The influence of plan modulation on the interplay effect in VMAT liver SBRT treatments.

PubMed

Hubley, Emily; Pierce, Greg

2017-08-01

Volumetric modulated arc therapy (VMAT) uses multileaf collimator (MLC) leaves, gantry speed, and dose rate to modulate beam fluence, producing the highly conformal doses required for liver radiotherapy. When targets that move with respiration are treated with a dynamic fluence, there exists the possibility for interplay between the target and leaf motions. This study employs a novel motion simulation technique to determine if VMAT liver SBRT plans with an increase in MLC leaf modulation are more susceptible to dosimetric differences in the GTV due to interplay effects. For ten liver SBRT patients, two VMAT plans with different amounts of MLC leaf modulation were created. Motion was simulated using a random starting point in the respiratory cycle for each fraction. To isolate the interplay effect, motion was also simulated using four specific starting points in the respiratory cycle. The dosimetric differences caused by different starting points were examined by subtracting resultant dose distributions from each other. When motion was simulated using random starting points for each fraction, or with specific starting points, there were significantly more dose differences in the GTV (maximum 100cGy) for more highly modulated plans, but the overall plan quality was not adversely affected. Plans with more MLC leaf modulation are more susceptible to interplay effects, but dose differences in the GTV are clinically negligible in magnitude. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Direct leaf wetness measurements and its numerical analysis using a multi-layer atmosphere-soil-vegetation model at a grassland site in pre-alpine region in Germany

NASA Astrophysics Data System (ADS)

Katata, Genki; Held, Andreas; Mauder, Matthias

2014-05-01

The wetness of plant leaf surfaces (leaf wetness) is important in meteorological, agricultural, and environmental studies including plant disease management and the deposition process of atmospheric trace gases and particles. Although many models have been developed to predict leaf wetness, wetness data directly measured at the leaf surface for model validations are still limited. In the present study, the leaf wetness was monitored using seven electrical sensors directly clipped to living leaf surfaces of thin and broad-leaved grasses. The measurements were carried out at the pre-alpine grassland site in TERestrial ENvironmental Observatories (TERENO) networks in Germany from September 20 to November 8, 2013. Numerical simulations of a multi-layer atmosphere-SOiL-VEGetation model (SOLVEG) developed by the authors were carried out for analyzing the data. For numerical simulations, the additional routine meteorological data of wind speed, air temperature and humidity, radiation, rainfall, long-wave radiative surface temperature, surface fluxes, ceilometer backscatter, and canopy or snow depth were used. The model reproduced well the observed leaf wetness, net radiation, momentum and heat, water vapor, and CO2 fluxes, surface temperature, and soil temperature and moisture. In rain-free days, a typical diurnal cycle as a decrease and increase during the day- and night-time, respectively, was observed in leaf wetness data. The high wetness level was always monitored under rain, fog, and snowcover conditions. Leaf wetness was also often high in the early morning due to thawing of leaf surface water frozen during a cold night. In general, leaf wetness was well correlated with relative humidity (RH) in condensation process, while it rather depended on wind speed in evaporation process. The comparisons in RH-wetness relations between leaf characteristics showed that broad-leaved grasses tended to be wetter than thin grasses.

Towards real-time VMAT verification using a prototype, high-speed CMOS active pixel sensor.

PubMed

Zin, Hafiz M; Harris, Emma J; Osmond, John P F; Allinson, Nigel M; Evans, Philip M

2013-05-21

This work investigates the feasibility of using a prototype complementary metal oxide semiconductor active pixel sensor (CMOS APS) for real-time verification of volumetric modulated arc therapy (VMAT) treatment. The prototype CMOS APS used region of interest read out on the chip to allow fast imaging of up to 403.6 frames per second (f/s). The sensor was made larger (5.4 cm × 5.4 cm) using recent advances in photolithographic technique but retains fast imaging speed with the sensor's regional read out. There is a paradigm shift in radiotherapy treatment verification with the advent of advanced treatment techniques such as VMAT. This work has demonstrated that the APS can track multi leaf collimator (MLC) leaves moving at 18 mm s(-1) with an automatic edge tracking algorithm at accuracy better than 1.0 mm even at the fastest imaging speed. Evaluation of the measured fluence distribution for an example VMAT delivery sampled at 50.4 f/s was shown to agree well with the planned fluence distribution, with an average gamma pass rate of 96% at 3%/3 mm. The MLC leaves motion and linac pulse rate variation delivered throughout the VMAT treatment can also be measured. The results demonstrate the potential of CMOS APS technology as a real-time radiotherapy dosimeter for delivery of complex treatments such as VMAT.

SU-E-T-67: A Quality Assurance Procedure for VMAT Delivery Technique with Multiple Verification Metric Using TG-119 Protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsuta, Y; Kadoya, N; Shimizu, E

2015-06-15

Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi-leaf collimator shapes. The purpose of this research is to construct routine QA protocol which focuses on VMAT delivery technique and to obtain a baseline including dose error, fluence distribution and mechanical accuracy during VMAT. Methods: The mock prostate, head and neck (HN) cases supplied from AAPM were used in this study. A VMAT plans were generated in Monaco TPS according to TG-119 protocol. Plans were created using 6 MV and 10 MV photon beams for each case. The phantom based measurement, fluence measurement andmore » log files analysis were performed. The dose measurement was performed using 0.6 cc ion chamber, which located at isocenter. The fluence distribution were acquired using the MapCHECK2 mounted in the MapPHAN. The trajectory log files recorded inner 20 leaf pairs and gantry angle positions at every 0.25 sec interval were exported to in-house software developed by MATLAB and determined those RMS values. Results: The dose difference is expressed as a ratio of the difference between measured and planned doses. The dose difference for 6 MV was 0.91%, for 10 MV was 0.67%. In turn, the fluence distribution using gamma criteria of 2%/2 mm with a 50% minimum dose threshold for 6 MV was 98.8%, for 10 MV was 97.5%, respectively. The RMS values of MLC for 6 MV and 10 MV were 0.32 mm and 0.37 mm, of gantry were 0.33 degree and 0.31 degree. Conclusion: In this study, QA protocol to assess VMAT delivery accuracy is constructed and results acquired in this study are used as a baseline of VMAT delivery performance verification.« less

SU-F-T-273: Using a Diode Array to Explore the Weakness of TPS DoseCalculation Algorithm for VMAT and Sliding Window Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Lu, B; Yan, G

Purpose: To identify the weakness of dose calculation algorithm in a treatment planning system for volumetric modulated arc therapy (VMAT) and sliding window (SW) techniques using a two-dimensional diode array. Methods: The VMAT quality assurance(QA) was implemented with a diode array using multiple partial arcs that divided from a VMAT plan; each partial arc has the same segments and the original monitor units. Arc angles were less than ± 30°. Multiple arcs delivered through consecutive and repetitive gantry operating clockwise and counterclockwise. The source-toaxis distance setup with the effective depths of 10 and 20 cm were used for a diodemore » array. To figure out dose errors caused in delivery of VMAT fields, the numerous fields having the same segments with the VMAT field irradiated using different delivery techniques of static and step-and-shoot. The dose distributions of the SW technique were evaluated by creating split fields having fine moving steps of multi-leaf collimator leaves. Calculated doses using the adaptive convolution algorithm were analyzed with measured ones with distance-to-agreement and dose difference of 3 mm and 3%.. Results: While the beam delivery through static and step-and-shoot techniques showed the passing rate of 97 ± 2%, partial arc delivery of the VMAT fields brought out passing rate of 85%. However, when leaf motion was restricted less than 4.6 mm/°, passing rate was improved up to 95 ± 2%. Similar passing rate were obtained for both 10 and 20 cm effective depth setup. The calculated doses using the SW technique showed the dose difference over 7% at the final arrival point of moving leaves. Conclusion: Error components in dynamic delivery of modulated beams were distinguished by using the suggested QA method. This partial arc method can be used for routine VMAT QA. Improved SW calculation algorithm is required to provide accurate estimated doses.« less

Microsystem enabled photovoltaic modules and systems

DOEpatents

Nielson, Gregory N; Sweatt, William C; Okandan, Murat

2015-05-12

A microsystem enabled photovoltaic (MEPV) module including: an absorber layer; a fixed optic layer coupled to the absorber layer; a translatable optic layer; a translation stage coupled between the fixed and translatable optic layers; and a motion processor electrically coupled to the translation stage to controls motion of the translatable optic layer relative to the fixed optic layer. The absorber layer includes an array of photovoltaic (PV) elements. The fixed optic layer includes an array of quasi-collimating (QC) micro-optical elements designed and arranged to couple incident radiation from an intermediate image formed by the translatable optic layer into one of the PV elements such that it is quasi-collimated. The translatable optic layer includes an array of focusing micro-optical elements corresponding to the QC micro-optical element array. Each focusing micro-optical element is designed to produce a quasi-telecentric intermediate image from substantially collimated radiation incident within a predetermined field of view.

Verification of dosimetric accuracy on the TrueBeam STx: rounded leaf effect of the high definition MLC.

PubMed

Kielar, Kayla N; Mok, Ed; Hsu, Annie; Wang, Lei; Luxton, Gary

2012-10-01

The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC). During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx. The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses. Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical leaf gap dimensions is more pronounced in the more recent versions of Eclipse for both the HDMLC and the Millennium MLC. Once properly commissioned and tested using a methodology based on treatment plan verification, Eclipse is able to accurately model radiation dose delivered for SBRT treatments using the TrueBeam STx.

Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter: a planning study

NASA Astrophysics Data System (ADS)

Fu, Weihua; Dai, Jianrong; Hu, Yimin; Han, Dongsheng; Song, Yixin

2004-04-01

The treatment delivery time of intensity-modulated radiation therapy (IMRT) with a multileaf collimator (MLC) is generally longer than that of conventional radiotherapy. In theory, removing the flattening filter from the treatment head may reduce the beam-on time by enhancing the output dose rate, and then reduce the treatment delivery time. And in practice, there is a possibility of delivering the required fluence distribution by modulating the unflattened non-uniform fluence distribution. However, the reduction of beam-on time may be discounted by the increase of leaf-travel time and (or) verification-and-recording (V&R) time. Here we investigate the overall effect of flattening filter on the treatment delivery time of IMRT with MLCs implemented in the step and shoot method, as well as with compensators on six hybrid machines. We compared the treatment delivery time with/without flattening filter for ten nasopharynx cases and ten prostate cases by observing the variations of the ratio of the beam-on time, segment number, leaf-travel time and the treatment delivery time with dose rate, leaf speed and V&R time. The results show that, without the flattening filter, the beam-on time reduces for both static MLC and compensator-based techniques; the number of segments and the leaf-travel time increase slightly for the static MLC technique; the relative IMRT treatment delivery time decreases more with lower dose rate, higher leaf speed and shorter V&R overhead time. The absolute treatment delivery time reduction depends on the fraction dose. It is not clinically significant at a fraction dose of 2 Gy for the technique of removing the flattening filter, but becomes significant when the fraction dose is as high as that for radiosurgery.

Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits.

PubMed

Kröber, W; Heklau, H; Bruelheide, H

2015-03-01

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity-Ecosystem Functioning experiment at Jiangxi (BEF-China). Information-theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi-layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi-predictor models for stomatal conductance (gs ) and xylem cavitation vulnerability. In addition, maximum gs was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum gs increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ50 ) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ50 values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

Sensitivity of 3D Dose Verification to Multileaf Collimator Misalignments in Stereotactic Body Radiation Therapy of Spinal Tumor.

PubMed

Xin-Ye, Ni; Ren, Lei; Yan, Hui; Yin, Fang-Fang

2016-12-01

This study aimed to detect the sensitivity of Delt 4 on ordinary field multileaf collimator misalignments, system misalignments, random misalignments, and misalignments caused by gravity of the multileaf collimator in stereotactic body radiation therapy. (1) Two field sizes, including 2.00 cm (X) × 6.00 cm (Y) and 7.00 cm (X) × 6.00 cm (Y), were set. The leaves of X1 and X2 in the multileaf collimator were simultaneously opened. (2) Three cases of stereotactic body radiation therapy of spinal tumor were used. The dose of the planning target volume was 1800 cGy with 3 fractions. The 4 types to be simulated included (1) the leaves of X1 and X2 in the multileaf collimator were simultaneously opened, (2) only X1 of the multileaf collimator and the unilateral leaf were opened, (3) the leaves of X1 and X2 in the multileaf collimator were randomly opened, and (4) gravity effect was simulated. The leaves of X1 and X2 in the multileaf collimator shifted to the same direction. The difference between the corresponding 3-dimensional dose distribution measured by Delt 4 and the dose distribution in the original plan made in the treatment planning system was analyzed with γ index criteria of 3.0 mm/3.0%, 2.5 mm/2.5%, 2.0 mm/2.0%, 2.5 mm/1.5%, and 1.0 mm/1.0%. (1) In the field size of 2.00 cm (X) × 6.00 cm (Y), the γ pass rate of the original was 100% with 2.5 mm/2.5% as the statistical standard. The pass rate decreased to 95.9% and 89.4% when the X1 and X2 directions of the multileaf collimator were opened within 0.3 and 0.5 mm, respectively. In the field size of 7.00 (X) cm × 6.00 (Y) cm with 1.5 mm/1.5% as the statistical standard, the pass rate of the original was 96.5%. After X1 and X2 of the multileaf collimator were opened within 0.3 mm, the pass rate decreased to lower than 95%. The pass rate was higher than 90% within the 3 mm opening. (2) For spinal tumor, the change in the planning target volume V 18 under various modes calculated using treatment planning system was within 1%. However, the maximum dose deviation of the spinal cord was high. In the spinal cord with a gravity of -0.25 mm, the maximum dose deviation minimally changed and increased by 6.8% than that of the original. In the largest opening of 1.00 mm, the deviation increased by 47.7% than that of the original. Moreover, the pass rate of the original determined through Delt 4 was 100% with 3 mm/3% as the statistical standard. The pass rate was 97.5% in the 0.25 mm opening and higher than 95% in the 0.5 mm opening A, 0.25 mm opening A, whole gravity series, and 0.20 mm random opening. Moreover, the pass rate was higher than 90% with 2.0 mm/2.0% as the statistical standard in the original and in the 0.25 mm gravity. The difference in the pass rates was not statistically significant among the -0.25 mm gravity, 0.25 mm opening A, 0.20 mm random opening, and original as calculated using SPSS 11.0 software with P > .05. Different analysis standards of Delt 4 were analyzed in different field sizes to improve the detection sensitivity of the multileaf collimator position on the basis of 90% throughout rate. In stereotactic body radiation therapy of spinal tumor, the 2.0 mm/2.0% standard can reveal the dosimetric differences caused by the minor multileaf collimator position compared with the 3.0 mm/3.0% statistical standard. However, some position derivations of the misalignments that caused high dose amount to the spinal cord cannot be detected. However, some misalignments were not detected when a large number of multileaf collimator were administered into the spinal cord. © The Author(s) 2015.

MEGARA: the new multi-object and integral field spectrograph for GTC

NASA Astrophysics Data System (ADS)

Carrasco, E.; Páez, G.; Izazaga-Pére, R.; Gil de Paz, A.; Gallego, J.; Iglesias-Páramo, J.

2017-07-01

MEGARA is an optical integral-field unit and multi-object spectrograph for the 10.4m Gran Telescopio Canarias. Both observational modes will provide identical spectral resolutions Rfwhm ˜ 6,000, 12,000 and 18,700. The spectrograph is a collimator-camera system. The unique characteristics of MEGARA in terms of throughput and versatility make this instrument the most efficient tool to date to analyze astrophysical objects at intermediate spectral resolutions. The instrument is currently at the telescope for on-sky commissioning. Here we describe the as-built main characteristics the instrument.

Gamma-Ray Burst Afterglows with ALMA

NASA Astrophysics Data System (ADS)

Urata, Y.; Huang, K.; Takahashi, S.

2015-12-01

We present multi-wavelength observations including sub-millimeter follow-ups for two GRB afterglows. The rapid SMA and multi-wavelength observations for GRB120326A revealed their complex emissions as the synchrotron self-inverse Compton radiation from reverse shock. The observations including ALMA for GRB131030A also showed the significant X-ray excess from the standard forward shock synchrotron model. Based on these results, we also discuss further observations for (A) constraining of the mass of progenitor with polarization, (B) the first confirmation of GRB jet collimation, and (C) revealing the origin of optically dark GRBs.

Microbial UV fluence-response assessment using a novel UV-LED collimated beam system.

PubMed

Bowker, Colleen; Sain, Amanda; Shatalov, Max; Ducoste, Joel

2011-02-01

A research study has been performed to determine the ultraviolet (UV) fluence-response of several target non-pathogenic microorganisms to UV light emitting diodes (UV-LEDs) by performing collimated beam tests. UV-LEDs do not contain toxic mercury, offer design flexibility due to their small size, and have a longer operational life than mercury lamps. Comsol Multiphysics was utilized to create an optimal UV-LED collimated beam design based on number and spacing of UV-LEDs and distance of the sample from the light source while minimizing the overall cost. The optimized UV-LED collimated beam apparatus and a low-pressure mercury lamp collimated beam apparatus were used to determine the UV fluence-response of three surrogate microorganisms (Escherichia coli, MS-2, T7) to 255 nm UV-LEDs, 275 nm UV-LEDs, and 254 nm low-pressure mercury lamps. Irradiation by low-pressure mercury lamps produced greater E. coli and MS-2 inactivation than 255 nm and 275 nm UV-LEDs and similar T7 inactivation to irradiation by 275 nm UV-LEDs. The 275 nm UV-LEDs produced more efficient T7 and E. coli inactivation than 255 nm UV-LEDs while both 255 nm and 275 nm UV-LEDs produced comparable microbial inactivation for MS-2. Differences may have been caused by a departure from the time-dose reciprocity law due to microbial repair mechanisms. Copyright © 2010 Elsevier Ltd. All rights reserved.

Reaching record-low β* at the CERN Large Hadron Collider using a novel scheme of collimator settings and optics

NASA Astrophysics Data System (ADS)

Bruce, R.; Bracco, C.; De Maria, R.; Giovannozzi, M.; Mereghetti, A.; Mirarchi, D.; Redaelli, S.; Quaranta, E.; Salvachua, B.

2017-03-01

The Large Hadron Collider (LHC) at CERN is built to collide intense proton beams with an unprecedented energy of 7 TeV. The design stored energy per beam of 362 MJ makes the LHC beams highly destructive, so that any beam losses risk to cause quenches of superconducting magnets or damage to accelerator components. Collimators are installed to protect the machine and they define a minimum normalized aperture, below which no other element is allowed. This imposes a limit on the achievable luminosity, since when squeezing β* (the β-function at the collision point) to smaller values for increased luminosity, the β-function in the final focusing system increases. This leads to a smaller normalized aperture that risks to go below the allowed collimation aperture. In the first run of the LHC, this was the main limitation on β*, which was constrained to values above the design specification. In this article, we show through theoretical and experimental studies how tighter collimator openings and a new optics with specific phase-advance constraints allows a β* as small as 40 cm, a factor 2 smaller than β*=80 cm used in 2015 and significantly below the design value β*=55 cm, in spite of a lower beam energy. The proposed configuration with β*=40 cm has been successfully put into operation and has been used throughout 2016 as the LHC baseline. The decrease in β* compared to 2015 has been an essential contribution to reaching and surpassing, in 2016, the LHC design luminosity for the first time, and to accumulating a record-high integrated luminosity of around 40 fb-1 in one year, in spite of using less bunches than in the design.

Optimization of Shielding- Collimator Parameters for ING-27 Neutron Generator Using MCNP5

NASA Astrophysics Data System (ADS)

Hegazy, Aya Hamdy; Skoy, V. R.; Hossny, K.

2018-04-01

Neutron generators are now used in various fields. They produce only fast neutrons; D-D neutron generator produces 2.45 MeV neutrons and D-T produces 14.1 MeV neutrons. In order to optimize shielding-collimator parameters to achieve higher neutron flux at the investigated sample (The signal) with lower neutron and gamma rays flux at the area of the detectors, design iterations are widely used. This work was applied to ROMASHA setup, TANGRA project, FLNP, Joint Institute for Nuclear Research. The studied parameters were; (1) shielding-collimator material, (2) Distance between the shielding-collimator assembly first plate and center of the neutron beam, and (3) thickness of collimator sheets. MCNP5 was used to simulate ROMASHA setup after it was validated on the experimental results of irradiation of Carbon-12 sample for one hour to detect its 4.44 MeV characteristic gamma line. The ratio between the signal and total neutron flux that enters each detector was calculated and plotted, concluding that the optimum shielding-collimator assembly is Tungsten of 5 cm thickness for each plate, and a distance of 2.3 cm. Also, the ratio between the signal and total gamma rays flux was calculated and plotted for each detector, leading to the previous conclusion but the distance was 1 cm.

Thermal Neutron Point Source Imaging using a Rotating Modulation Collimator (RMC)

DTIC Science & Technology

2010-03-01

Source Details.........................................................................................37 3.5 Simulation of RMC in MCNP ...passed through the masks at each rotation angle. ................................. 42 19. Figure 19: MCNP Generate Modulation Profile for Cadmium. The...Cadmium. The multi-energetic neutron source simulation from MCNP is used for this plot. The energy is values are shown per energy bin. The

Light beam shaping for collimated emission from white organic light-emitting diodes using customized lenticular microlens arrays structure

NASA Astrophysics Data System (ADS)

Zhou, Lei; Bai, Gui-Lin; Guo, Xin; Shen, Su; Ou, Qing-Dong; Fan, Yuan-Yuan

2018-05-01

We present a design approach to realizing a desired collimated planar incoherent light source (CPILS) by incorporating lenticular microlens arrays (LMLAs) onto the substrates of discrete white organic light-emitting diode (WOLED) light sources and demonstrate the effectiveness of this method in collimated light beam shaping and luminance enhancement simultaneously. The obtained collimated WOLED light source shows enhanced luminance by a factor of 2.7 compared with that of the flat conventional device at the normal polar angle and, more importantly, exhibits a narrowed angular emission with a full-width at half-maximum (FWHM) of ˜33.6°. We anticipate that the presented strategy could provide an alternative way for achieving the desired large scale CPILS, thereby opening the door to many potential applications, including LCD backlights, three-dimensional displays, car headlights, and so forth.

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

DOE PAGES

Manuel, M. J. -E.; Kuranz, C. C.; Rasmus, A. M.; ...

2014-08-20

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysicalmore » systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. Furthermore, this result is a topic of ongoing investigation.« less

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manuel, M. J. -E.; Kuranz, C. C.; Rasmus, A. M.

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysicalmore » systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. Furthermore, this result is a topic of ongoing investigation.« less

High energy beam impact tests on a LHC tertiary collimator at the CERN high-radiation to materials facility

NASA Astrophysics Data System (ADS)

Cauchi, Marija; Aberle, O.; Assmann, R. W.; Bertarelli, A.; Carra, F.; Cornelis, K.; Dallocchio, A.; Deboy, D.; Lari, L.; Redaelli, S.; Rossi, A.; Salvachua, B.; Mollicone, P.; Sammut, N.

2014-02-01

The correct functioning of a collimation system is crucial to safely operate highly energetic particle accelerators, such as the Large Hadron Collider (LHC). The requirements to handle high intensity beams can be demanding. In this respect, investigating the consequences of LHC particle beams hitting tertiary collimators (TCTs) in the experimental regions is a fundamental issue for machine protection. An experimental test was designed to investigate the robustness and effects of beam accidents on a fully assembled collimator, based on accident scenarios in the LHC. This experiment, carried out at the CERN High-Radiation to Materials (HiRadMat) facility, involved 440 GeV proton beam impacts of different intensities on the jaws of a horizontal TCT. This paper presents the experimental setup and the preliminary results obtained, together with some first outcomes from visual inspection and a comparison of such results with numerical simulations.

SU-F-T-637: Single-Isocenter Versus Multiple-Isocenter VMAT SRS for Unusual Multiple Metastasis Case with Two Widely Separated Lesions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, EM; Popple, RA; Fiveash, JB

Purpose: Single-isocenter (SI) volumetric modulated arc therapy has been shown to be an effective and efficient approach to multiple metastasis radiosurgery. However, certain extreme cases raise the question of whether multiple-isocenter (MI) approaches can still generate superior plans. In this study, we ask this question with respect to a clinical case with two very widely separated lesions. Methods: A patient with two widely separated (d = 12cm) tumors was treated with SI-VMAT SRS using 10MV flattening filter free (FFF) beam with high-definition multi-leaf collimator (HD-MLC, 2.5/5mm) in two non-coplanar arcs using concentric rings to enforce steep gradient. Because of lesionmore » positioning with respect to collimator angle selection, lesions were treated by 5mm leaves. We re-planned the case with a congruent arc arrangement but separate isocenter for each lesion. In this manner, lesions were treated by 2.5mm leaves. Conformity index (CI), V50%, and mean brain dose were compared. Results: Neither conformity (CI-SI = 1.12, CI-MI = 1.08) nor V50% (V50%-SI =8.82cc, V50%-MI =8.81cc) were improved by utilizing a separate isocenter for each lesion. Mean brain dose was slightly reduced (dmean-SI = 118.4 cGy, dmean-MI = 88.7 cGy) by using multiple isocenters. Conclusion: For this case with a lesion at the apex of the brain and another distantly located at the base of skull, employing a separate isocenter for each target did not meaningfully improve plan quality. Single-isocenter VMAT has been shown feasible and equivalent to multiple-isocenter VMAT for multiple metastasis cases in general. In this extreme case, single- and multiple- isocenter VMAT were also equivalent. If rotational setup errors are appropriately corrected, the increased delivery efficiency of the single-isocenter approach renders it preferable to the multiple isocenter approach. Dr’s Thomas, Popple, and Fiveash have all received honoraria from Varian Medical Systems for discussing their experiences with stereotactic radiosurgery.« less

SU-F-T-524: Investigation of the Dosimertric Benefits of Interchangeable Source Size of a Novel Rotating Gamma System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldib, A; Chibani, O; Chen, L

Purpose: Tremendous technological developments were made for conformal therapy techniques with linear accelerators, while less attention was paid to cobalt-60 units. The aim of the current study is to explore the dosimetric benefits of a novel rotating gamma ray system enhanced with interchangeable source sizes and multi-leaf collimator (MLC). Material and Methods: CybeRT is a novel rotating gamma ray machine with a ring gantry that ensures an iso-center accuracy of less than 0.3 mm. The new machine has a 70cm source axial distance allowing for improved penumbra compared to conventional machines. MCBEAM was used to simulate Cobalt-60 beams from themore » CybeRT head, while the MCPLAN code was used for modeling the MLC and for phantom/patient dose calculation. The CybeRT collimation will incorporate a system allowing for interchanging source sizes. In this work we have created phase space files for 1cm and 2cm source sizes. Evaluation of the system was done by comparing CybeRT beams with the 6MV beams in a water phantom and in patient geometry. Treatment plans were compared based on isodose distributions and dose volume histograms. Results: Profiles for the 1cm source were comparable to that from 6MV in the order of 6mm for 10×10 cm{sup 2} field size at the depth of maximum dose. This could ascribe to Cobalt-60 beams producing lowerenergy secondary electrons. Although, the 2cm source have a larger penumbra however it could be still used for large targets with proportionally increased dose rate. For large lung targets, the difference between cobalt and 6MV plans is clinically insignificant. Our preliminary results showed that interchanging source sizes will allow cobalt beams for volumetric arc therapy of both small lesions and large tumors. Conclusion: The CybeRT system will be a cost effective machine capable of performing advanced radiation therapy treatments of both small tumors and large target volumes.« less

Crop 3D-a LiDAR based platform for 3D high-throughput crop phenotyping.

PubMed

Guo, Qinghua; Wu, Fangfang; Pang, Shuxin; Zhao, Xiaoqian; Chen, Linhai; Liu, Jin; Xue, Baolin; Xu, Guangcai; Li, Le; Jing, Haichun; Chu, Chengcai

2018-03-01

With the growing population and the reducing arable land, breeding has been considered as an effective way to solve the food crisis. As an important part in breeding, high-throughput phenotyping can accelerate the breeding process effectively. Light detection and ranging (LiDAR) is an active remote sensing technology that is capable of acquiring three-dimensional (3D) data accurately, and has a great potential in crop phenotyping. Given that crop phenotyping based on LiDAR technology is not common in China, we developed a high-throughput crop phenotyping platform, named Crop 3D, which integrated LiDAR sensor, high-resolution camera, thermal camera and hyperspectral imager. Compared with traditional crop phenotyping techniques, Crop 3D can acquire multi-source phenotypic data in the whole crop growing period and extract plant height, plant width, leaf length, leaf width, leaf area, leaf inclination angle and other parameters for plant biology and genomics analysis. In this paper, we described the designs, functions and testing results of the Crop 3D platform, and briefly discussed the potential applications and future development of the platform in phenotyping. We concluded that platforms integrating LiDAR and traditional remote sensing techniques might be the future trend of crop high-throughput phenotyping.

Estimating 3D Leaf and Stem Shape of Nursery Paprika Plants by a Novel Multi-Camera Photography System

PubMed Central

Zhang, Yu; Teng, Poching; Shimizu, Yo; Hosoi, Fumiki; Omasa, Kenji

2016-01-01

For plant breeding and growth monitoring, accurate measurements of plant structure parameters are very crucial. We have, therefore, developed a high efficiency Multi-Camera Photography (MCP) system combining Multi-View Stereovision (MVS) with the Structure from Motion (SfM) algorithm. In this paper, we measured six variables of nursery paprika plants and investigated the accuracy of 3D models reconstructed from photos taken by four lens types at four different positions. The results demonstrated that error between the estimated and measured values was small, and the root-mean-square errors (RMSE) for leaf width/length and stem height/diameter were 1.65 mm (R2 = 0.98) and 0.57 mm (R2 = 0.99), respectively. The accuracies of the 3D model reconstruction of leaf and stem by a 28-mm lens at the first and third camera positions were the highest, and the number of reconstructed fine-scale 3D model shape surfaces of leaf and stem is the most. The results confirmed the practicability of our new method for the reconstruction of fine-scale plant model and accurate estimation of the plant parameters. They also displayed that our system is a good system for capturing high-resolution 3D images of nursery plants with high efficiency. PMID:27314348

Multi-modal sensor system for plant water stress assessment

USDA-ARS?s Scientific Manuscript database

Plant stress critically affects plant growth and causes significant loss of productivity and quality. When the plant is under water stress, it impedes photosynthesis and transpiration, resulting in changes in leaf color and temperature. Leaf discoloration in photosynthesis can be assessed by measu...

Biosorption kinetics of heavy metals by leaf biomass of Jatropha curcas in single and multi-metal system.

PubMed

Rawat, Anand Prabha; Giri, Krishna; Rai, J P N

2014-03-01

Biosorption of Cu(2+), Zn(2+), and Cr(6+) from aqueous solutions by leaf biomass of Jatropha curcas was investigated as a function of biomass concentration, initial metal ion concentration, contact time, and pH of the solution systematically. The aim of this study was to optimize biosorption process and find out a suitable kinetic model for the metal removal in single and multi-metal system. The experimental data were analyzed using two sorption kinetic models, viz., pseudo-first- and pseudo-second-order equations, to determine the best fit equation for the biosorption of metal ions Cu(2+), Zn(2+), and Cr(6+) onto the leaf biomass of J. curcas in different metal systems. The experimental data fitted well the pseudo-second-order equation and provided the best correlation for the biosorption process. The findings of the present investigation revealed that J. curcas leaf biomass was an eco-friendly and cost-effective biosorbent for the removal of heavy metal ions from wastewater.

Lens design of LED searchlight of high brightness and distant spot.

PubMed

Zhao, Shuang; Wang, Kai; Chen, Fei; Wu, Dan; Liu, Sheng

2011-05-01

The study related in this paper is the design of a ship-mounted LED of high brightness and distant spot. The freeform lens design obeying the edge ray principle and Snell's law is presented first. Then, to fit the illumination requirement of the searchlight, we designed a freeform lens to collimate all the light rays coming from the LED. However, theoretical analysis proves that there is a critical angle for incident rays beyond which the rays cannot be collimated, and 55% is the light-efficiency limit for polymethyl methacrylate freeform lens. We then designed a combination of a freeform lens-coupled parabolic reflector that improved light efficiency to 70%. In this paper, the design of the freeform lens-coupled parabolic reflector is given in detail. In addition, tolerance analysis and the effect of manufacturing defect are presented.

SU-E-T-433: Field-In-Field Irradiation for Breast Cancer with VERO-4DRT System: A Feasibility Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, N; Mizuno, T; Takada, Y

2015-06-15

Purpose: The Vero-4DRT system is a dedicated system for high precision radiation therapy. However, the field size is limited at 15 cm x 15 cm and shapes by using multi-leaf collimator (MLC) without X-Jaw and Y-Jaw. Therefore VERO-4DRT system is not available to simple wedged irradiation for breast cancer. In this study, we suppose FIF with ring and/or tilt/pan angles whole breast irradiation (FIFWBI). The purpose of this study is to verify the feasibility of FIFWBI with VERO-4DRT system. Methods: As fundamental evaluation, we performed commissioning test with phantom. The absorbed dose evaluation at several reference points and dose distributionmore » including split area were performed. We planned 10 demonstrative shapes in phantom for measuring these contents with i-plan workstation (BrainLAB). As clinical evaluation, the dose distribution and dose indexes were evaluated with actual patient data. Five patients with breast cancer were designed FIFWBI radiotherapy plan with split fields. Then, the dose distribution and dose indexes (including Dmax, Dmin, D95, D5 and Homogeneity index) were evaluated in these plans. Results: As the results of fundamental evaluation, all absorbed dose errors between calculated and measured doses were within 2%. The gamma passing rates with 2 mm/3% criteria in all cases were 96±2%. As the results of clinical evaluation, the values of Dmax, D95, D50, D5, and Homogeneity Index were 41.7±0.90 Gy, 49.4±0.34 Gy, 52.26±0.24 Gy, and 1.39±0.03, respectively. For Japanese breast cancer patients, this technique was feasible. However, the large split region was happened in FIFWBI in case of patient with large breast. Conclusion: We evaluated the FIFWBI technique with VERO-4DRT system. This technique is feasible for Japanese patients, but the patient with large breast should be disagreed with this technique.« less

1-D ELECTRO-OPTIC BEAM STEERING DEVICE

PubMed Central

Wang, Wei-Chih; Tsui, Chi Leung

2011-01-01

In this paper, we present the design and fabrication of a 1D beam steering device based on planar electro-optic thermal-plastic prisms and a collimator lens array. With the elimination of moving parts, the proposed device is able to overcome the mechanical limitations of present scanning devices, such as fatigue and low operating frequency, while maintaining a small system footprint (~0.5mm×0.5mm). From experimental data, our prototype device is able to achieve a maximum deflection angle of 5.6° for a single stage prism design and 29.2° for a cascaded three prisms stage design. The lens array shows a 4µm collimated beam diameter. PMID:22199458

Comparison of three methods reducing the beam parameter product of a laser diode stack for long range laser illumination applications

NASA Astrophysics Data System (ADS)

Lutz, Yves; Poyet, Jean-Michel; Metzger, Nicolas

2013-10-01

Laser diode stacks are interesting laser sources for active imaging illuminators. They allow the accumulation of large amounts of energy in multi-pulse mode, which is well suited for long-range image recording. Even when laser diode stacks are equipped with fast-axis collimation (FAC) and slow-axis collimation (SAC) microlenses, their beam parameter product (BPP) are not compatible with a direct use in highly efficient and compact illuminators. This is particularly true when narrow divergences are required such as for long range applications. To overcome these difficulties, we conducted investigations in three different ways. A first near infrared illuminator based on the use of conductively cooled mini-bars was designed, realized and successfully tested during outdoor experimentations. This custom specified stack was then replaced in a second step by an off-the-shelf FAC + SAC micro lensed stack where the brightness was increased by polarization overlapping. The third method still based on a commercial laser diode stack uses a non imaging optical shaping principle resulting in a virtually restacked laser source with enhanced beam parameters. This low cost, efficient and low alignment sensitivity beam shaping method allows obtaining a compact and high performance laser diode illuminator for long range active imaging applications. The three methods are presented and compared in this paper.

Design of a setup for 252Cf neutron source for storage and analysis purpose

NASA Astrophysics Data System (ADS)

Hei, Daqian; Zhuang, Haocheng; Jia, Wenbao; Cheng, Can; Jiang, Zhou; Wang, Hongtao; Chen, Da

2016-11-01

252Cf is a reliable isotopic neutron source and widely used in the prompt gamma ray neutron activation analysis (PGNAA) technique. A cylindrical barrel made by polymethyl methacrylate contained with the boric acid solution was designed for storage and application of a 5 μg 252Cf neutron source. The size of the setup was optimized with Monte Carlo code. The experiments were performed and the results showed the doses were reduced with the setup and less than the allowable limit. The intensity and collimating radius of the neutron beam could also be adjusted through different collimator.

Analysis of a color-matching backlight system using a blazed grating and a lenticular lens array.

PubMed

Son, Chang-Gyun; Gwag, Jin Seok; Lee, Jong Hoon; Kwon, Jin Hyuk

2012-12-20

A high efficiency LCD employing a color-matching backlight system that consists of a collimation lenticular lens sheet, a blazed grating, and a focusing lenticular lens array is proposed and analyzed. The RGB lights that are collimated and dispersed from the collimation lenticular lens sheet and the blazed grating are incident on the RGB color filters by the focusing lenticular lens array. The color-matched transmittance was increased 183% and 121% for divergence angles of 2° and 11°, respectively, compared to a conventional backlight that does not use a blazed grating. The design, simulation, and experimental results for the prototype color-matching backlight system are presented.

Decreasing radiation exposure on pediatric portable chest radiographs.

PubMed

Hawking, Nancy G; Sharp, Ted D

2013-01-01

To determine whether additional shielding designed for pediatric patients during portable chest exams that ascertain endotracheal tube placement would significantly decrease the amount of scatter radiation. Children aged 24 months or younger were intubated and received daily morning chest radiographs to determine endotracheal tube placement. For each measurement, the amount of scatter radiation decreased by more than 20% from a nonshielded exposure to a shielded exposure. There was a significant decrease in scatter radiation when using the lead shielding device along with appropriate collimation vs appropriate collimation alone. These results suggest that applying additional shielding to appropriately collimated chest radiographs could significantly reduce scatter radiation and therefore the overall dose to young children.

Use of thermal sieve to allow optical testing of cryogenic optical systems.

PubMed

Kim, Dae Wook; Cai, Wenrui; Burge, James H

2012-05-21

Full aperture testing of large cryogenic optical systems has been impractical due to the difficulty of operating a large collimator at cryogenic temperatures. The Thermal Sieve solves this problem by acting as a thermal barrier between an ambient temperature collimator and the cryogenic system under test. The Thermal Sieve uses a set of thermally controlled baffles with array of holes that are lined up to pass the light from the collimator without degrading the wavefront, while attenuating the thermal background by nearly 4 orders of magnitude. This paper provides the theory behind the Thermal Sieve system, evaluates the optimization for its optical and thermal performance, and presents the design and analysis for a specific system.

Molecular breast tomosynthesis with scanning focus multi-pinhole cameras

NASA Astrophysics Data System (ADS)

van Roosmalen, Jarno; Goorden, Marlies C.; Beekman, Freek J.

2016-08-01

Planar molecular breast imaging (MBI) is rapidly gaining in popularity in diagnostic oncology. To add 3D capabilities, we introduce a novel molecular breast tomosynthesis (MBT) scanner concept based on multi-pinhole collimation. In our design, the patient lies prone with the pendant breast lightly compressed between transparent plates. Integrated webcams view the breast through these plates and allow the operator to designate the scan volume (e.g. a whole breast or a suspected region). The breast is then scanned by translating focusing multi-pinhole plates and NaI(Tl) gamma detectors together in a sequence that optimizes count yield from the volume-of-interest. With simulations, we compared MBT with existing planar MBI. In a breast phantom containing different lesions, MBT improved tumour-to-background contrast-to-noise ratio (CNR) over planar MBI by 12% and 111% for 4.0 and 6.0 mm lesions respectively in case of whole breast scanning. For the same lesions, much larger CNR improvements of 92% and 241% over planar MBI were found in a scan that focused on a breast region containing several lesions. MBT resolved 3.0 mm rods in a Derenzo resolution phantom in the transverse plane compared to 2.5 mm rods distinguished by planar MBI. While planar MBI cannot provide depth information, MBT offered 4.0 mm depth resolution. Our simulations indicate that besides offering 3D localization of increased tracer uptake, multi-pinhole MBT can significantly increase tumour-to-background CNR compared to planar MBI. These properties could be promising for better estimating the position, extend and shape of lesions and distinguishing between single and multiple lesions.

Six-axis multi-anvil press for high-pressure, high-temperature neutron diffraction experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sano-Furukawa, A., E-mail: sano.asami@jaea.go.jp; Hattori, T.; J-PARC Center, Japan Atomic Energy Agency, Ibaraki 319-1195

2014-11-15

We developed a six-axis multi-anvil press, ATSUHIME, for high-pressure and high-temperature in situ time-of-flight neutron powder diffraction experiments. The press has six orthogonally oriented hydraulic rams that operate individually to compress a cubic sample assembly. Experiments indicate that the press can generate pressures up to 9.3 GPa and temperatures up to 2000 K using a 6-6-type cell assembly, with available sample volume of about 50 mm{sup 3}. Using a 6-8-type cell assembly, the available conditions expand to 16 GPa and 1273 K. Because the six-axis press has no guide blocks, there is sufficient space around the sample to use themore » aperture for diffraction and place an incident slit, radial collimators, and a neutron imaging camera close to the sample. Combination of the six-axis press and the collimation devices realized high-quality diffraction pattern with no contamination from the heater or the sample container surrounding the sample. This press constitutes a new tool for using neutron diffraction to study the structures of crystals and liquids under high pressures and temperatures.« less

Experimental study and numerical simulation on the structural and mechanical properties of Typha leaves through multimodal microscopy approaches.

PubMed

Liu, Jingjing; Zhang, Zhihui; Yu, Zhenglei; Liang, Yunhong; Li, Xiujuan; Ren, Luquan

2018-01-01

The Typha leaf, with special multi-level structure, low density and excellent mechanical properties, is an ideal bionic prototype utilized for lightweight design. In order to further study the relationship between the structure and mechanical properties, the three-dimensional macroscopic morphology of Typha leaves was characterized by micro computed tomography (Micro-CT) and its internal microstructure was observed by scanning electron microscopy (SEM). The combination of experimental and computational research was carried out in this paper, to reveal and verify the effect of multi-level structure on the mechanical properties. A universal testing machine and a self-developed mechanical testing apparatus with high precision and low load were used to measure the mechanical properties of the axial compression and lateral bending of the leaves, respectively. Three models with different internal structures were established based on the above-mentioned three-dimensional morphologies. The result demonstrated that the structure of partitions and diaphragms within the Typha leaf could form a reinforcement ribs structure which could provide multiple load paths and make the process of compression and bending difficult. The further nonlinear finite element analysis through LS-DYNA proved that internal structure could improve the ability of the models to resist compression and deformation. The investigation can be the reference for lightweight thin-walled structure design and inspire the application of the bionic structural materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

TomoTherapy MLC verification using exit detector data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Quan; Westerly, David; Fang Zhenyu

2012-01-15

Purpose: Treatment delivery verification (DV) is important in the field of intensity modulated radiation therapy (IMRT). While IMRT and image guided radiation therapy (IGRT), allow us to create more conformal plans and enables the use of tighter margins, an erroneously executed plan can have detrimental effects on the treatment outcome. The purpose of this study is to develop a DV technique to verify TomoTherapy's multileaf collimator (MLC) using the onboard mega-voltage CT detectors. Methods: The proposed DV method uses temporal changes in the MVCT detector signal to predict actual leaf open times delivered on the treatment machine. Penumbra and scatteredmore » radiation effects may produce confounding results when determining leaf open times from the raw detector data. To reduce the impact of the effects, an iterative, Richardson-Lucy (R-L) deconvolution algorithm is applied. Optical sensors installed on each MLC leaf are used to verify the accuracy of the DV technique. The robustness of the DV technique is examined by introducing different attenuation materials in the beam. Additionally, the DV technique has been used to investigate several clinical plans which failed to pass delivery quality assurance (DQA) and was successful in identifying MLC timing discrepancies as the root cause. Results: The leaf open time extracted from the exit detector showed good agreement with the optical sensors under a variety of conditions. Detector-measured leaf open times agreed with optical sensor data to within 0.2 ms, and 99% of the results agreed within 8.5 ms. These results changed little when attenuation was added in the beam. For the clinical plans failing DQA, the dose calculated from reconstructed leaf open times played an instrumental role in discovering the root-cause of the problem. Throughout the retrospective study, it is found that the reconstructed dose always agrees with measured doses to within 1%. Conclusions: The exit detectors in the TomoTherapy treatment systems can provide valuable information about MLC behavior during delivery. A technique to estimate the TomoTherapy binary MLC leaf open time from exit detector signals is described. This technique is shown to be both robust and accurate for delivery verification.« less

Rounded leaf end modeling in Pinnacle VMAT treatment planning for fixed jaw linacs

PubMed Central

Yang, Fei; Cao, Ning; Meyer, Juergen

2016-01-01

During volume‐modulated arc therapies (VMAT), dosimetric errors are introduced by multiple open dynamic leaf gaps that are present in fixed diaphragm linear accelerators. The purpose of this work was to develop a methodology for adjusting the rounded leaf end modeling parameters to improve out‐of‐field dose agreement in SmartArc VMAT treatment plans delivered by fixed jaw linacs where leaf gap dose is not negligible. Leaf gap doses were measured for an Elekta beam modulator linac with 0.4 cm micro‐multileaf collimators (MLC) using an A16 micro‐ionization chamber, a MatriXX ion chamber detector array, and Kodak EDR2 film dosimetry in a solid water phantom. The MLC offset and rounded end tip radius were adjusted in the Pinnacle treatment planning system (TPS) to iteratively arrive at the optimal configuration for 6 MV and 10 MV photon energies. Improvements in gamma index with a 3%/3 mm acceptance criteria and an inclusion threshold of 5% of maximum dose were measured, analyzed, and validated using an ArcCHECK diode detector array for field sizes ranging from 1.6 to 14 cm square field arcs and Task Group (TG) 119 VMAT test cases. The best results were achieved for a rounded leaf tip radius of 13 cm with a 0.1 cm MLC offset. With the optimized MLC model, measured gamma indices ranged between 99.9% and 91.7% for square field arcs with sizes between 3.6 cm and 1.6 cm, with a maximum improvement of 42.7% for the 1.6 cm square field size. Gamma indices improved up to 2.8% in TG‐119 VMAT treatment plans. Imaging and Radiation Oncology Core (IROC) credentialing of a VMAT plan with the head and neck phantom passed with a gamma index of 100%. Fine‐tune adjustments to MLC rounded leaf ends may improve patient‐specific QA pass rates and provide more accurate predictions of dose deposition to avoidance structures. PACS number(s): 87.55.D‐, 87.55.kd, 87.55.kh PMID:27929490

Dynamic-MLC leaf control utilizing on-flight intensity calculations: a robust method for real-time IMRT delivery over moving rigid targets.

PubMed

McMahon, Ryan; Papiez, Lech; Rangaraj, Dharanipathy

2007-08-01

An algorithm is presented that allows for the control of multileaf collimation (MLC) leaves based entirely on real-time calculations of the intensity delivered over the target. The algorithm is capable of efficiently correcting generalized delivery errors without requiring the interruption of delivery (self-correcting trajectories), where a generalized delivery error represents anything that causes a discrepancy between the delivered and intended intensity profiles. The intensity actually delivered over the target is continually compared to its intended value. For each pair of leaves, these comparisons are used to guide the control of the following leaf and keep this discrepancy below a user-specified value. To demonstrate the basic principles of the algorithm, results of corrected delivery are shown for a leading leaf positional error during dynamic-MLC (DMLC) IMRT delivery over a rigid moving target. It is then shown that, with slight modifications, the algorithm can be used to track moving targets in real time. The primary results of this article indicate that the algorithm is capable of accurately delivering DMLC IMRT over a rigid moving target whose motion is (1) completely unknown prior to delivery and (2) not faster than the maximum MLC leaf velocity over extended periods of time. These capabilities are demonstrated for clinically derived intensity profiles and actual tumor motion data, including situations when the target moves in some instances faster than the maximum admissible MLC leaf velocity. The results show that using the algorithm while calculating the delivered intensity every 50 ms will provide a good level of accuracy when delivering IMRT over a rigid moving target translating along the direction of MLC leaf travel. When the maximum velocities of the MLC leaves and target were 4 and 4.2 cm/s, respectively, the resulting error in the two intensity profiles used was 0.1 +/- 3.1% and -0.5 +/- 2.8% relative to the maximum of the intensity profiles. For the same target motion, the error was shown to increase rapidly as (1) the maximum MLC leaf velocity was reduced below 75% of the maximum target velocity and (2) the system response time was increased.

SU-D-201-04: Evaluation of Elekta Agility MLC Performance Using Statistical Process Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyers, SM; Balderson, MJ; Letourneau, D

2016-06-15

Purpose: to evaluate the performance and stability of the Elekta Agility MLC model using an automated quality control (QC) test in combination with statistical process control tools. Methods: Leaf positions were collected daily for 11 Elekta units over 5–19 months using the automated QC test, which analyzes 23 MV images to determine the location of MLC leaves relative to the radiation isocenter. The leaf positions are measured at 5 nominal positions, and images are acquired at collimator 0° and 180° to capture all MLC leaves in the field-of-view. Leaf positioning accuracy was assessed using individual and moving range control charts.more » Control limits were recomputed following MLC recalibration (occurred 1–2 times for 4 units). Specification levels of ±0.5, ±1 and ±1.5mm were tested. The mean and range of duration between out-of-control and out-of-specification events were determined. Results: Leaf position varied little over time, as confirmed by very tight individual control limits (mean ±0.19mm, range 0.09–0.44). Mean leaf position error was −0.03mm (range −0.89–0.83). Due to sporadic out-of-control events, the mean in-control duration was 3.3 days (range 1–23). Data stayed within ±1mm specification for 205 days on average (range 3–372) and within ±1.5mm for the entire date range. Measurements stayed within ±0.5mm for 1 day on average (range 0–17); however, our MLC leaves were not calibrated to this level of accuracy. Conclusion: The Elekta Agility MLC model was found to perform with high stability, as evidenced by the tight control limits. The in-specification durations support the current recommendation of monthly MLC QC tests with a ±1mm tolerance. Future work is on-going to determine if Agility performance can be optimized further using high-frequency QC test results to drive recalibration frequency. Factors that can affect leaf positioning accuracy, including beam spot motion, leaf gain calibration, drifting leaves, and image artifacts, are under investigation.« less

Hybrid algorithm for simulating the collimated transmittance of homogeneous stratified turbid media

PubMed Central

Cruzado, Beatriz Morales; Atencio, José Alberto Delgado; Vázquez y Montiel, Sergio; Gómez, Erick Sarmiento

2015-01-01

In this work we describe the development of a program that simulates the propagation of photons through refractive and reflecting optical components such as lenses, mirrors and stops that includes a biological tissue sample as the main issue to be investigated in order to get a simulated value of light distribution, in particular, of the unscattered light. The analysis of the photons that travel through the sample is based on the program Monte Carlo Multi-Layered with some modifications that consider a Gaussian beam as initial source of light. Position, directional cosines and weight of photons exiting the turbid media are used to propagate them through an optical system. As a mean of validation of the program, we selected a typical optical system for measurement of collimated transmittance. Therefore, several tests were carried out to find the optical system that gives the theoretical collimated transmittance at different values of the optical properties of the turbid media. Along this validation, the optimal experimental configuration is found. Using this results, a comparison between the simulated optimal configuration and the experimental set-up was done, by using a colloidal suspension as a turbid media. PMID:26137375

Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

DOE PAGES

Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

2017-02-06

We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam- pro les in water from the radial modes con rm the profile to be a Bessel beam.more » Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam- profile measurements in water with both free and clamped piezoelectric transducer are presented. The collimated beam generation using the present technique of using the laterally clamped radial modes finds significant applications in low-frequency imaging through highly attenuating materials.« less

Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam- pro les in water from the radial modes con rm the profile to be a Bessel beam.more » Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam- profile measurements in water with both free and clamped piezoelectric transducer are presented. The collimated beam generation using the present technique of using the laterally clamped radial modes finds significant applications in low-frequency imaging through highly attenuating materials.« less

Hierarchical Learning of Tree Classifiers for Large-Scale Plant Species Identification.

PubMed

Fan, Jianping; Zhou, Ning; Peng, Jinye; Gao, Ling

2015-11-01

In this paper, a hierarchical multi-task structural learning algorithm is developed to support large-scale plant species identification, where a visual tree is constructed for organizing large numbers of plant species in a coarse-to-fine fashion and determining the inter-related learning tasks automatically. For a given parent node on the visual tree, it contains a set of sibling coarse-grained categories of plant species or sibling fine-grained plant species, and a multi-task structural learning algorithm is developed to train their inter-related classifiers jointly for enhancing their discrimination power. The inter-level relationship constraint, e.g., a plant image must first be assigned to a parent node (high-level non-leaf node) correctly if it can further be assigned to the most relevant child node (low-level non-leaf node or leaf node) on the visual tree, is formally defined and leveraged to learn more discriminative tree classifiers over the visual tree. Our experimental results have demonstrated the effectiveness of our hierarchical multi-task structural learning algorithm on training more discriminative tree classifiers for large-scale plant species identification.

A novel method for routine quality assurance of volumetric-modulated arc therapy.

PubMed

Wang, Qingxin; Dai, Jianrong; Zhang, Ke

2013-10-01

Volumetric-modulated arc therapy (VMAT) is delivered through synchronized variation of gantry angle, dose rate, and multileaf collimator (MLC) leaf positions. The delivery dynamic nature challenges the parameter setting accuracy of linac control system. The purpose of this study was to develop a novel method for routine quality assurance (QA) of VMAT linacs. ArcCheck is a detector array with diodes distributing in spiral pattern on cylindrical surface. Utilizing its features, a QA plan was designed to strictly test all varying parameters during VMAT delivery on an Elekta Synergy linac. In this plan, there are 24 control points. The gantry rotates clockwise from 181° to 179°. The dose rate, gantry speed, and MLC positions cover their ranges commonly used in clinic. The two borders of MLC-shaped field seat over two columns of diodes of ArcCheck when the gantry rotates to the angle specified by each control point. The ratio of dose rate between each of these diodes and the diode closest to the field center is a certain value and sensitive to the MLC positioning error of the leaf crossing the diode. Consequently, the positioning error can be determined by the ratio with the help of a relationship curve. The time when the gantry reaches the angle specified by each control point can be acquired from the virtual inclinometer that is a feature of ArcCheck. The gantry speed between two consecutive control points is then calculated. The aforementioned dose rate is calculated from an acm file that is generated during ArcCheck measurements. This file stores the data measured by each detector in 50 ms updates with each update in a separate row. A computer program was written in MATLAB language to process the data. The program output included MLC positioning errors and the dose rate at each control point as well as the gantry speed between control points. To evaluate this method, this plan was delivered for four consecutive weeks. The actual dose rate and gantry speed were compared with the QA plan specified. Additionally, leaf positioning errors were intentionally introduced to investigate the sensitivity of this method. The relationship curves were established for detecting MLC positioning errors during VMAT delivery. For four consecutive weeks measured, 98.4%, 94.9%, 89.2%, and 91.0% of the leaf positioning errors were within ± 0.5 mm, respectively. For the intentionally introduced leaf positioning systematic errors of -0.5 and +1 mm, the detected leaf positioning errors of 20 Y1 leaf were -0.48 ± 0.14 and 1.02 ± 0.26 mm, respectively. The actual gantry speed and dose rate closely followed the values specified in the VMAT QA plan. This method can assess the accuracy of MLC positions and the dose rate at each control point as well as the gantry speed between control points at the same time. It is efficient and suitable for routine quality assurance of VMAT.

KiwiSpec - an advanced spectrograph for high resolution spectroscopy: optical design and variations

NASA Astrophysics Data System (ADS)

Barnes, Stuart I.; Gibson, Steve; Nield, Kathryn; Cochrane, Dave

2012-09-01

The KiwiSpec R4-100 is an advanced high resolution spectrograph developed by KiwiStar Optics, Industrial Research Ltd, New Zealand. The instrument is based around an R4 echelle grating and a 100mm collimated beam diameter. The optical design employs a highly asymmetric white pupil design, whereby the transfer collimator has a focal length only 1/3 that of the primary collimator. This allows the cross-dispersers (VPH gratings) and camera optics to be small and low cost while also ensuring a very compact instrument. The KiwiSpec instrument will be bre-fed and is designed to be contained in both thermal and/or vacuum enclosures. The instrument concept is highly exible in order to ensure that the same basic design can be used for a wide variety of science cases. Options include the possibility of splitting the wavelength coverage into 2 to 4 separate channels allowing each channel to be highly optimized for maximum eciency. CCDs ranging from smaller than 2K2K to larger than 4K4K can be accommodated. This allows good (3-4 pixel) sampling of resolving powers ranging from below 50,000 to greater than 100,000. Among the specic design options presented here will be a two-channel concept optimized for precision radial velocities, and a four-channel concept developed for the Gemini High- Resolution Optical Spectrograph (GHOST). The design and performance of a single-channel prototype will be presented elsewhere in these proceedings.

New stereotactic X-ray knife

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barish, R.J.; Barish, S.V.

1988-06-01

For many years, the irradiation of small volumes of tissue in the brain to necrotizing doses has been investigated as a non-invasive alternative to neurosurgery. We propose a new system in which a precisely machined helmet serves as a multi-port focussed X-ray collimator when it is itself irradiated by a conventional medical linear accelerator run in the electron mode. When the collimator is attached to a stereotactic frame, the geometric accuracy of delivering small radiation fields to the brain is limited primarily by the accuracy of the stereotactic localization, and is relatively independent of the positional stability of the accelerator.more » Field sizes as small as two millimeters are readily achievable. The problem of low dose rate associated with these small fields is overcome by the use of high electron beam currents.« less

Parallel detecting, spectroscopic ellipsometers/polarimeters

DOEpatents

Furtak, Thomas E.

2002-01-01

The parallel detecting spectroscopic ellipsometer/polarimeter sensor has no moving parts and operates in real-time for in-situ monitoring of the thin film surface properties of a sample within a processing chamber. It includes a multi-spectral source of radiation for producing a collimated beam of radiation directed towards the surface of the sample through a polarizer. The thus polarized collimated beam of radiation impacts and is reflected from the surface of the sample, thereby changing its polarization state due to the intrinsic material properties of the sample. The light reflected from the sample is separated into four separate polarized filtered beams, each having individual spectral intensities. Data about said four individual spectral intensities is collected within the processing chamber, and is transmitted into one or more spectrometers. The data of all four individual spectral intensities is then analyzed using transformation algorithms, in real-time.

Numerical simulations of a proposed hollow electron beam collimator for the LHC upgrade at CERN.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Previtali, V.; Stancari, G.; Valishev, A.

2013-07-12

In the last years the LHC collimation system has been performing over the expectations, providing the machine with a nearly perfect e cient cleaning system[1]. Nonetheless, when trying to push the existing accelerators to - and over - their design limits, all the accelerator components are required to boost their performances. In particular, in view of the high luminosity frontier for the LHC, the increased intensity would ask for a more e cient cleaning system. In this framework innovative collimation solutions are under evaluation[2]: one option is the usage of an hollow electron lens for beam halo cleaning. This workmore » intends to study the applicability of an the hollow electron lens for the LHC collimation, by evaluating the case of the existing Tevatron e-lens applied to the nominal LHC 7 TeV beam. New e-lens operation modes are here proposed to standard enhance the electron lens halo removal e ect.« less

The effects of intra-fraction organ motion on the delivery of intensity-modulated field with a multileaf collimator.

PubMed

Chui, Chen-Shou; Yorke, Ellen; Hong, Linda

2003-07-01

Intensity-modulated radiation therapy can be conveniently delivered with a multileaf collimator. With this method, the entire field is not delivered at once, but rather it is composed of many subfields defined by the leaf positions as a function of beam on time. At any given instant, only these subfields are delivered. During treatment, if the organ moves, part of the volume may move in or out of these subfields. Due to this interplay between organ motion and leaf motion the delivered dose may be different from what was planned. In this work, we present a method that calculates the effects of organ motion on delivered dose. The direction of organ motion may be parallel or perpendicular to the leaf motion, and the effect can be calculated for a single fraction or for multiple fractions. Three breast patients and four lung patients were included in this study,with the amplitude of the organ motion varying from +/- 3.5 mm to +/- 10 mm, and the period varying from 4 to 8 seconds. Calculations were made for these patients with and without organ motion, and results were examined in terms of isodose distribution and dose volume histograms. Each calculation was repeated ten times in order to estimate the statistical uncertainties. For selected patients, calculations were also made with conventional treatment technique. The effects of organ motion on conventional techniques were compared relative to that on IMRT techniques. For breast treatment, the effect of organ motion primarily broadened the penumbra at the posterior field edge. The dose in the rest of the treatment volume was not significantly affected. For lung treatment, the effect also broadened the penumbra and degraded the coverage of the planning target volume (PTV). However, the coverage of the clinical target volume (CTV) was not much affected, provided the PTV margin was adequate. The same effects were observed for both IMRT and conventional treatment techniques. For the IMRT technique, the standard deviations of ten samples of a 30-fraction calculation were very small for all patients, implying that over a typical treatment course of 30 fractions, the delivered dose was very close to the expected value. Hence, under typical clinical conditions, the effect of organ motion on delivered dose can be calculated without considering the interplay between the organ motion and the leaf motion. It can be calculated as the weighted average of the dose distribution without organ motion with the distribution of organ motion. Since the effects of organ motion on dose were comparable for both IMRT and conventional techniques, the PTV margin should remain the same for both techniques.

Design of a radiation facility for very small specimens used in radiobiology studies

NASA Astrophysics Data System (ADS)

Rodriguez, Manuel; Jeraj, Robert

2008-06-01

A design of a radiation facility for very small specimens used in radiobiology is presented. This micro-irradiator has been primarily designed to irradiate partial bodies in zebrafish embryos 3-4 mm in length. A miniature x-ray, 50 kV photon beam, is used as a radiation source. The source is inserted in a cylindrical brass collimator that has a pinhole of 1.0 mm in diameter along the central axis to produce a pencil photon beam. The collimator with the source is attached underneath a computer-controlled movable table which holds the specimens. Using a 45° tilted mirror, a digital camera, connected to the computer, takes pictures of the specimen and the pinhole collimator. From the image provided by the camera, the relative distance from the specimen to the pinhole axis is calculated and coordinates are sent to the movable table to properly position the samples in the beam path. Due to its monitoring system, characteristic of the radiation beam, accuracy and precision of specimen positioning, and automatic image-based specimen recognition, this radiation facility is a suitable tool to irradiate partial bodies in zebrafish embryos, cell cultures or any other small specimen used in radiobiology research.

The design, physical properties and clinical utility of an iris collimator for robotic radiosurgery

NASA Astrophysics Data System (ADS)

Echner, G. G.; Kilby, W.; Lee, M.; Earnst, E.; Sayeh, S.; Schlaefer, A.; Rhein, B.; Dooley, J. R.; Lang, C.; Blanck, O.; Lessard, E.; Maurer, C. R., Jr.; Schlegel, W.

2009-09-01

Robotic radiosurgery using more than one circular collimator can improve treatment plan quality and reduce total monitor units (MU). The rationale for an iris collimator that allows the field size to be varied during treatment delivery is to enable the benefits of multiple-field-size treatments to be realized with no increase in treatment time due to collimator exchange or multiple traversals of the robotic manipulator by allowing each beam to be delivered with any desired field size during a single traversal. This paper describes the Iris™ variable aperture collimator (Accuray Incorporated, Sunnyvale, CA, USA), which incorporates 12 tungsten-copper alloy segments in two banks of six. The banks are rotated by 30° with respect to each other, which limits the radiation leakage between the collimator segments and produces a 12-sided polygonal treatment beam. The beam is approximately circular, with a root-mean-square (rms) deviation in the 50% dose radius of <0.8% (corresponding to <0.25 mm at the 60 mm field size) and an rms variation in the 20-80% penumbra width of about 0.1 mm at the 5 mm field size increasing to about 0.5 mm at 60 mm. The maximum measured collimator leakage dose rate was 0.07%. A commissioning method is described by which the average dose profile can be obtained from four profile measurements at each depth based on the periodicity of the isodose line variations with azimuthal angle. The penumbra of averaged profiles increased with field size and was typically 0.2-0.6 mm larger than that of an equivalent fixed circular collimator. The aperture reproducibility is <=0.1 mm at the lower bank, diverging to <=0.2 mm at a nominal treatment distance of 800 mm from the beam focus. Output factors (OFs) and tissue-phantom-ratio data are identical to those used for fixed collimators, except the OFs for the two smallest field sizes (5 and 7.5 mm) are considerably lower for the Iris Collimator. If average collimator profiles are used, the assumption of circular symmetry results in dose calculation errors that are <1 mm or <1% for single beams across the full range of field sizes; errors for multiple non-coplanar beam treatment plans are expected to be smaller. Treatment plans were generated for 19 cases using the Iris Collimator (12 field sizes) and also using one and three fixed collimators. The results of the treatment planning study demonstrate that the use of multiple field sizes achieves multiple plan quality improvements, including reduction of total MU, increase of target volume coverage and improvements in conformality and homogeneity compared with using a single field size for a large proportion of the cases studied. The Iris Collimator offers the potential to greatly increase the clinical application of multiple field sizes for robotic radiosurgery.

Monte Carlo study for designing a dedicated “D”-shaped collimator used in the external beam radiotherapy of retinoblastoma patients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayorga, P. A.; Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada; Brualla, L.

2014-01-15

Purpose: Retinoblastoma is the most common intraocular malignancy in the early childhood. Patients treated with external beam radiotherapy respond very well to the treatment. However, owing to the genotype of children suffering hereditary retinoblastoma, the risk of secondary radio-induced malignancies is high. The University Hospital of Essen has successfully treated these patients on a daily basis during nearly 30 years using a dedicated “D”-shaped collimator. The use of this collimator that delivers a highly conformed small radiation field, gives very good results in the control of the primary tumor as well as in preserving visual function, while it avoids themore » devastating side effects of deformation of midface bones. The purpose of the present paper is to propose a modified version of the “D”-shaped collimator that reduces even further the irradiation field with the scope to reduce as well the risk of radio-induced secondary malignancies. Concurrently, the new dedicated “D”-shaped collimator must be easier to build and at the same time produces dose distributions that only differ on the field size with respect to the dose distributions obtained by the current collimator in use. The scope of the former requirement is to facilitate the employment of the authors' irradiation technique both at the authors' and at other hospitals. The fulfillment of the latter allows the authors to continue using the clinical experience gained in more than 30 years. Methods: The Monte Carlo codePENELOPE was used to study the effect that the different structural elements of the dedicated “D”-shaped collimator have on the absorbed dose distribution. To perform this study, the radiation transport through a Varian Clinac 2100 C/D operating at 6 MV was simulated in order to tally phase-space files which were then used as radiation sources to simulate the considered collimators and the subsequent dose distributions. With the knowledge gained in that study, a new, simpler, “D”-shaped collimator is proposed. Results: The proposed collimator delivers a dose distribution which is 2.4 cm wide along the inferior-superior direction of the eyeball. This width is 0.3 cm narrower than that of the dose distribution obtained with the collimator currently in clinical use. The other relevant characteristics of the dose distribution obtained with the new collimator, namely, depth doses at clinically relevant positions, penumbrae width, and shape of the lateral profiles, are statistically compatible with the results obtained for the collimator currently in use. Conclusions: The smaller field size delivered by the proposed collimator still fully covers the planning target volume with at least 95% of the maximum dose at a depth of 2 cm and provides a safety margin of 0.2 cm, so ensuring an adequate treatment while reducing the irradiated volume.« less

Water-cooled hard-soldered kilowatt laser diode arrays operating at high duty cycle

NASA Astrophysics Data System (ADS)

Klumel, Genady; Karni, Yoram; Oppenhaim, Jacob; Berk, Yuri; Shamay, Moshe; Tessler, Renana; Cohen, Shalom; Risemberg, Shlomo

2010-04-01

High brightness laser diode arrays are increasingly found in defense applications either as efficient optical pumps or as direct energy sources. In many instances, duty cycles of 10- 20 % are required, together with precise optical collimation. System requirements are not always compatible with the use of microchannel based cooling, notwithstanding their remarkable efficiency. Simpler but effective solutions, which will not involve high fluid pressure drops as well as deionized water, are needed. The designer is faced with a number of challenges: effective heat removal, minimization of the built- in and operational stresses as well as precise and accurate fast axis collimation. In this article, we report on a novel laser diode array which includes an integral tap water cooling system. Robustness is achieved by all around hard solder bonding of passivated 940nm laser bars. Far field mapping of the beam, after accurate fast axis collimation will be presented. It will be shown that the design of water cooling channels , proper selection of package materials, careful design of fatigue sensitive parts and active collimation technique allow for long life time and reliability, while not compromising the laser diode array efficiency, optical power density ,brightness and compactness. Main performance characteristics are 150W/bar peak optical power, 10% duty cycle and more than 50% wall plug efficiency with less than 1° fast axis divergence. Lifetime of 0.5 Gshots with less than 10% power degradation has been proved. Additionally, the devices have successfully survived harsh environmental conditions such as thermal cycling of the coolant temperature and mechanical shocks.

Optomechanical design concept for GMACS: a wide-field multi-object moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT)

NASA Astrophysics Data System (ADS)

Smee, Stephen A.; Prochaska, Travis; Shectman, Stephen A.; Hammond, Randolph P.; Barkhouser, Robert H.; DePoy, D. L.; Marshall, J. L.

2012-09-01

We describe the conceptual optomechanical design for GMACS, a wide-field, multi-object, moderate-resolution optical spectrograph for the Giant Magellan Telescope (GMT). GMACS is a candidate first-light instrument for the GMT and will be one of several instruments housed in the Gregorian Instrument Rotator (GIR) located at the Gregorian focus. The instrument samples a 9 arcminute x 18 arcminute field of view providing two resolution modes (i.e, low resolution, R ~ 2000, and moderate resolution, R ~ 4000) over a 3700 Å to 10200 Å wavelength range. To minimize the size of the optics, four fold mirrors at the GMT focal plane redirect the full field into four individual "arms", that each comprises a double spectrograph with a red and blue channel. Hence, each arm samples a 4.5 arcminute x 9 arcminute field of view. The optical layout naturally leads to three separate optomechanical assemblies: a focal plane assembly, and two identical optics modules. The focal plane assembly contains the last element of the telescope's wide-field corrector, slit-mask, tent-mirror assembly, and slit-mask magazine. Each of the two optics modules supports two of the four instrument arms and houses the aft-optics (i.e. collimators, dichroics, gratings, and cameras). A grating exchange mechanism, and articulated gratings and cameras facilitate multiple resolution modes. In this paper we describe the details of the GMACS optomechanical design, including the requirements and considerations leading to the design, mechanism details, optics mounts, and predicted flexure performance.

The 11 T dipole for HL-LHC: Status and plan

DOE PAGES

Savary, F.; Barzi, E.; Bordini, B.; ...

2016-06-01

The upgrade of the Large Hadron Collider (LHC) collimation system includes additional collimators in the LHC lattice. The longitudinal space for these collimators will be created by replacing some of the LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and main systems. The project plan comprises the construction of two cryoassemblies containing each of the two 11-T dipoles of 5.5-m length for possible installation on either side of interaction point 2 of LHC in the years 2018-2019 for ion operation, and the installation of two cryoassemblies on either side of interaction point 7 of LHCmore » in the years 2023-2024 for proton operation. The development program conducted in conjunction between the Fermilab and CERN magnet groups is progressing well. The development activities carried out on the side of Fermilab were concluded in the middle of 2015 with the fabrication and test of a 1-m-long two-in-one model and those on the CERN side are ramping up with the construction of 2-m-long models and the preparation of the tooling for the fabrication of the first full-length prototype. The engineering design of the cryomagnet is well advanced, including the definition of the various interfaces, e.g., with the collimator, powering, protection, and vacuum systems. Several practice coils of 5.5-m length have been already fabricated. This paper describes the overall progress of the project, the final design of the cryomagnet, and the performance of the most recent models. Furthermore, the overall plan toward the fabrication of the series magnets for the two phases of the upgrade of the LHC collimation system is also presented.« less

High duty cycle hard soldered kilowatt laser diode arrays

NASA Astrophysics Data System (ADS)

Klumel, Genady; Karni, Yoram; Oppenheim, Jacob; Berk, Yuri; Shamay, Moshe; Tessler, Renana; Cohen, Shalom

2010-02-01

High-brightness laser diode arrays operating at a duty cycle of 10% - 20% are in ever-increasing demand for the optical pumping of solid state lasers and directed energy applications. Under high duty-cycle operation at 10% - 20%, passive (conductive) cooling is of limited use, while micro-coolers using de-ionized cooling water can considerably degrade device reliability. When designing and developing actively-cooled collimated laser diode arrays for high duty cycle operation, three main problems should be carefully addressed: an effective local and total heat removal, a minimization of packaging-induced and operational stresses, and high-precision fast axis collimation. In this paper, we present a novel laser diode array incorporating a built-in tap water cooling system, all-hard-solder bonded assembly, facet-passivated high-power 940 nm laser bars and tight fast axis collimation. By employing an appropriate layout of water cooling channels, careful choice of packaging materials, proper design of critical parts, and active optics alignment, we have demonstrated actively-cooled collimated laser diode arrays with extended lifetime and reliability, without compromising their efficiency, optical power density, brightness or compactness. Among the key performance benchmarks achieved are: 150 W/bar optical peak power at 10% duty cycle, >50% wallplug efficiency and <1° collimated fast axis divergence. A lifetime of >0.5 Ghots with <2% degradation has been experimentally proven. The laser diode arrays have also been successfully tested under harsh environmental conditions, including thermal cycling between -20°C and 40°C and mechanical shocks at 500g acceleration. The results of both performance and reliability testing bear out the effectiveness and robustness of the manufacturing technology for high duty-cycle laser arrays.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakaguchi, Yuji, E-mail: nkgc2003@yahoo.co.jp; Ono, Takeshi; Onitsuka, Ryota

COMPASS system (IBA Dosimetry, Schwarzenbruck, Germany) and ArcCHECK with 3DVH software (Sun Nuclear Corp., Melbourne, FL) are commercial quasi-3-dimensional (3D) dosimetry arrays. Cross-validation to compare them under the same conditions, such as a treatment plan, allows for clear evaluation of such measurement devices. In this study, we evaluated the accuracy of reconstructed dose distributions from the COMPASS system and ArcCHECK with 3DVH software using Monte Carlo simulation (MC) for multi-leaf collimator (MLC) test patterns and clinical VMAT plans. In a phantom study, ArcCHECK 3DVH showed clear differences from COMPASS, measurement and MC due to the detector resolution and the dosemore » reconstruction method. Especially, ArcCHECK 3DVH showed 7% difference from MC for the heterogeneous phantom. ArcCHECK 3DVH only corrects the 3D dose distribution of treatment planning system (TPS) using ArcCHECK measurement, and therefore the accuracy of ArcCHECK 3DVH depends on TPS. In contrast, COMPASS showed good agreement with MC for all cases. However, the COMPASS system requires many complicated installation procedures such as beam modeling, and appropriate commissioning is needed. In terms of clinical cases, there were no large differences for each QA device. The accuracy of the compass and ArcCHECK 3DVH systems for phantoms and clinical cases was compared. Both systems have advantages and disadvantages for clinical use, and consideration of the operating environment is important. The QA system selection is depending on the purpose and workflow in each hospital.« less

Response analysis of TLD-300 dosimeters in heavy-particle beams.

PubMed

Loncol, T; Hamal, M; Denis, J M; Vynckier, S; Wambersie, A; Scalliet, P

1996-09-01

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65) + Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (150 degrees C) and peak 5 (250 degrees C) response of CaF2:Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental 12C heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to 60Co, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the 60Co reference radiation to the 12C heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

Textural feature calculated from segmental fluences as a modulation index for VMAT.

PubMed

Park, So-Yeon; Park, Jong Min; Kim, Jung-In; Kim, Hyoungnyoun; Kim, Il Han; Ye, Sung-Joon

2015-12-01

Textural features calculated from various segmental fluences of volumetric modulated arc therapy (VMAT) plans were optimized to enhance its performance to predict plan delivery accuracy. Twenty prostate and twenty head and neck VMAT plans were selected retrospectively. Fluences were generated for each VMAT plan by summations of segments at sequential groups of control points. The numbers of summed segments were 5, 10, 20, 45, 90, 178 and 356. For each fluence, we investigated 6 textural features: angular second moment, inverse difference moment, contrast, variance, correlation and entropy (particular displacement distances, d = 1, 5 and 10). Spearman's rank correlation coefficients (rs) were calculated between each textural feature and several different measures of VMAT delivery accuracy. The values of rs of contrast (d = 10) with 10 segments to both global and local gamma passing rates with 2%/2 mm were 0.666 (p <0.001) and 0.573 (p <0.001), respectively. It showed rs values of -0.895 (p <0.001) and 0.727 (p <0.001) to multi-leaf collimator positional errors and gantry angle errors during delivery, respectively. The number of statistically significant rs values (p <0.05) to the changes in dose-volumetric parameters during delivery was 14 among a total of 35 tested parameters. Contrast (d = 10) with 10 segments showed higher correlations to the VMAT delivery accuracy than did the conventional modulation indices. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Radiation Safety Considerations Near Collimators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, A. J.

1997-04-15

The primary collimators are clearly a concern as regards radiation safety since they are intended to be the place where "lost" beam particles interact. These collimators and the beam dumps, therefore, are expected to be the "hot spots" in the machine. Unfortunately, the amount of beam which will end up on the collimators is not really known. For the purposes of this note, the assumption will be made that, averaged over a year, 20% of the beam in each ring will interact in the limiting aperture collimator for that ring, and at most 10% of stored beam in in amore » single hour. Faults will also be considered, but the annual assumed beam loss will be shown to be the limiting factor. The annual beam per ring from the Beam Loss Scenario (BLS) is the equivalent of 5.5 x 10 14 au ions at 100 GeV/u. It should be noted that this number assumes operation at 4 times the design intensity for 38 weeks a year at 100% efficiency. The 20% loss assumption is somewhat higher than given by Ref. [1] because the internal dump aperture is larger than was assumed when the BLS was written and will therefore "catch" less lost particles than assumed at that time. For the purposes of the estimates made here, therefore, the loss assumption per primary collimator in normal operation are assumed to be 1.1 x 10 14 Au ions per year and 2.85 x 10 10 Au ions per hour. The last number is 10% of the maximum beam per ring per hour in the BLS which corresponds to 1.25 fill per hour. The assumption will also be made that both primary collimators are located downstream of the crossing point at 8 o'clock. In subsequent sections of this note the following potential problems are considered: (1) prompt radiation occupied regions nearest to the collimators, (2) skyshine, and (3) soil activation. Section VII recommends actions to address these problems.« less

The "collimator monitoring fill factor" of a two-dimensional detector array, a measure of its ability to detect collimation errors.

PubMed

Stelljes, Tenzin Sonam; Looe, Hui Khee; Harder, Dietrich; Poppe, Björn

2017-03-01

Two-dimensional detector arrays are routinely used for constancy checks and treatment plan verification in photon-beam radiotherapy. In addition to the spatial resolution of the dose profiles, the "coverage" of the radiation field with respect to the detection of any beam collimation deficiency appears as the second characteristic feature of a detector array. The here proposed "collimator monitoring fill factor" (CM fill factor) has been conceived to serve as a quantitative characteristic of this "coverage". The CM fill factor is defined as the probability of a 2D array to detect any collimator position error. Therefore, it is represented by the ratio of the "sensitive area" of a single detector, in which collimator position errors are detectable, and the geometrical "cell area" associated with this detector within the array. Numerical values of the CM fill factor have been Monte Carlo simulated for 2D detector arrays equipped with air-vented ionization chambers, liquid-filled ionization chambers and diode detectors and were compared with the "FWHM fill factor" defined by Gago-Arias et al. (2012). For arrays with vented ionization chambers, the differences between the CM fill factor and the FWHM fill factor are moderate, but occasionally the latter exceeds unity. For narrower detectors such as liquid-filled ionization chambers and Si diodes and for small sampling distances, large differences between the FWHM fill factor and the CM fill factor have been observed. These differences can be explained by the shapes of the fluence response functions of these narrow detectors. A new parameter "collimator monitoring fill factor" (CM fill factor), applicable to quantitate the collimator position error detection probability of a 2D detector array, has been proposed. It is designed as a help in classifying the clinical performance of two-dimensional detector arrays in photon-beam radiotherapy. © 2017 American Association of Physicists in Medicine.

Benchmarking the MCNP code for Monte Carlo modelling of an in vivo neutron activation analysis system.

PubMed

Natto, S A; Lewis, D G; Ryde, S J

1998-01-01

The Monte Carlo computer code MCNP (version 4A) has been used to develop a personal computer-based model of the Swansea in vivo neutron activation analysis (IVNAA) system. The model included specification of the neutron source (252Cf), collimators, reflectors and shielding. The MCNP model was 'benchmarked' against fast neutron and thermal neutron fluence data obtained experimentally from the IVNAA system. The Swansea system allows two irradiation geometries using 'short' and 'long' collimators, which provide alternative dose rates for IVNAA. The data presented here relate to the short collimator, although results of similar accuracy were obtained using the long collimator. The fast neutron fluence was measured in air at a series of depths inside the collimator. The measurements agreed with the MCNP simulation within the statistical uncertainty (5-10%) of the calculations. The thermal neutron fluence was measured and calculated inside the cuboidal water phantom. The depth of maximum thermal fluence was 3.2 cm (measured) and 3.0 cm (calculated). The width of the 50% thermal fluence level across the phantom at its mid-depth was found to be the same by both MCNP and experiment. This benchmarking exercise has given us a high degree of confidence in MCNP as a tool for the design of IVNAA systems.

Geometric beam coupling impedance of LHC secondary collimators

NASA Astrophysics Data System (ADS)

Frasciello, Oscar; Tomassini, Sandro; Zobov, Mikhail; Salvant, Benoit; Grudiev, Alexej; Mounet, Nicolas

2016-02-01

The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep beam instabilities under control and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are among the major impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were higher by about a factor of 2 with respect to the theoretical predictions based on the LHC impedance model up to 2012. In that model the resistive wall impedance has been considered as the dominating impedance contribution for collimators. By carefully simulating also their geometric impedance we have contributed to the update of the LHC impedance model, reaching also a better agreement between the measured and simulated betatron tune shifts. During the just ended LHC Long Shutdown I (LSI), TCS/TCT collimators were replaced by new devices embedding BPMs and TT2-111R ferrite blocks. We present here preliminary estimations of their broad-band impedance, showing that an increase of about 20% is expected in the kick factors with respect to previous collimators without BPMs.

Cryostat and CCD for MEGARA at GTC

NASA Astrophysics Data System (ADS)

Castillo-Domínguez, E.; Ferrusca, D.; Tulloch, S.; Velázquez, M.; Carrasco, E.; Gallego, J.; Gil de Paz, A.; Sánchez, F. M.; Vílchez Medina, J. M.

2012-09-01

MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the new integral field unit (IFU) and multi-object spectrograph (MOS) instrument for the GTC. The spectrograph subsystems include the pseudo-slit, the shutter, the collimator with a focusing mechanism, pupil elements on a volume phase holographic grating (VPH) wheel and the camera joined to the cryostat through the last lens, with a CCD detector inside. In this paper we describe the full preliminary design of the cryostat which will harbor the CCD detector for the spectrograph. The selected cryogenic device is an LN2 open-cycle cryostat which has been designed by the "Astronomical Instrumentation Lab for Millimeter Wavelengths" at INAOE. A complete description of the cryostat main body and CCD head is presented as well as all the vacuum and temperature sub-systems to operate it. The CCD is surrounded by a radiation shield to improve its performance and is placed in a custom made mechanical mounting which will allow physical adjustments for alignment with the spectrograph camera. The 4k x 4k pixel CCD231 is our selection for the cryogenically cooled detector of MEGARA. The characteristics of this CCD, the internal cryostat cabling and CCD controller hardware are discussed. Finally, static structural finite element modeling and thermal analysis results are shown to validate the cryostat model.

Research on starlight hardware-in-the-loop simulator

NASA Astrophysics Data System (ADS)

Zhang, Ying; Gao, Yang; Qu, Huiyang; Liu, Dongfang; Du, Huijie; Lei, Jie

2016-10-01

The starlight navigation is considered to be one of the most important methods for spacecraft navigation. Starlight simulation system is a high-precision system with large fields of view, designed to test the starlight navigation sensor performance on the ground. A complete hardware-in-the-loop simulation of the system has been built. The starlight simulator is made up of light source, light source controller, light filter, LCD, collimator and control computer. LCD is the key display component of the system, and is installed at the focal point of the collimator. For the LCD cannot emit light itself, so light source and light source power controller is specially designed for the brightness demanded by the LCD. Light filter is designed for the dark background which is also needed in the simulation.

SU-E-T-425: Spherical Dose Distributions for Radiosurgery Using a Standardized MLC Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popple, R; Brezovich, I; Wu, X

2014-06-01

Purpose: To investigate a standardized MLC treatment plan to generate small spherical dose distributions. Methods: The static virtual cone plan comprised six table positions with clockwise and counterclockwise arcs having collimator angles 45 and 135 degrees, respectively, at each position. The central two leaves of a 2.5 mm leaf width MLC were set to a constant gap. Control points were weighted proportional to the sine of the gantry angle. Plans were created for the 10 MV flattening-filter-free beam of a TrueBeam STx (Varian Medical Systems) with gaps of 1, 1.5, 2, and 3 mm and were delivered to a phantommore » containing radiochromic film. Dose was calculated using the Eclipse AAA (Varian Medical Systems). A dynamic plan in which the table and gantry moved simultaneously with 1.5 mm gap was also created and delivered using the TrueBeam developer mode. Results: The full-width-half-max (FWHM) varied with leaf gap, ranging from 5.2 to 6.2 mm. Calculated FWHM was smaller than measured by 0.7 mm for the 1 mm gap and ≤ 0.4 mm for the larger gaps. The measured-to-calculated dose ratio was 0.93, 0.96, 1.01, and 0.99 for 1 mm, 1.5 mm, 2 mm, and 3 mm gaps, respectively. The dynamic results were the same as the static. The position deviations between the phantom target position and the center of the dose distribution were < 0.4 mm. Conclusion: The virtual cone can deliver spherical dose distributions suitable for radio surgery of small targets such as the trigeminal nerve. The Eclipse AAA accurately calculates the expected dose, particularly for leaf gap ≥ 1.5 mm. The measured dose distribution is slightly larger than the calculation, which is likely due to systematic leaf position error, isocenter variation due to gantry sag and table eccentricity, and inaccuracy in MLC leaf end modeling.« less

Development of online NIR urine analyzing system based on AOTF

NASA Astrophysics Data System (ADS)

Wan, Feng; Sun, Zhendong; Li, Xiaoxia

2006-09-01

In this paper, some key techniques on development of on-line MR urine analyzing system based on AOTF (Acousto - Optics Tunable Filter) are introduced. Problems about designing the optical system including collimation of incident light and working distance (the shortest distance for separating incident light and diffracted light) are analyzed and researched. DDS (Direct Digital Synthesizer) controlled by microprocessor is used to realize the wavelength scan. The experiment results show that this MR urine analyzing system based on. AOTF has 10000 - 4000cm -1 wavelength range and O.3ms wavelength transfer rate. Compare with the conventional Fourier Transform NIP. spectrophotometer for analyzing multi-components in urine, this system features low cost, small volume and on-line measurement function. Unscrambler software (multivariate statistical software by CAMO Inc. Norway) is selected as the software for processing the data. This system can realize on line quantitative analysis of protein, urea and creatinine in urine.

Analysis of the hot-cavity mode composition of an X-band overmoded relativistic backward wave oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Yuzhang; Zhang, Jun; Zhong, Huihuang

Overmoded RBWO (Relativistic Backward Wave Oscillators) is utilized more and more often for its high power capacity. However, both sides of SWS (Slow Wave Structure) of overmoded RBWO consist multi TM{sub 0n} modes; in order to achieve the design of reflector, it is essential to make clear of the mode composition of TM{sub 0n}. NUDT (National University of Defence Technology) had done research of the output mode composition in overmoded O-type Cerenkov HPM (High Power Microwave) Oscillators in detail, but in the area where the electron beam exists, the influence of electron beam must be taken into account. Hot-cavity dispersionmore » equation is figured out in this article first, and then analyzes the hot-cavity mode composition of an X-band overmoded RBWO tentatively. The results show that in collimating hole, the hot-cavity mode analysis is more accurate.« less

Salt gland distribution in limonium bicolor at the individual level

NASA Astrophysics Data System (ADS)

Leng, B. Y.; Yuan, F.; Dong, X. X.; Wang, B. S.

2018-02-01

Limonium bicolor is a typical exo-recretohalophyte with multi-cellular salt glands. A differential interference contrast (DIC) microscope were applied to investigate the pattern of salt gland distribution in L. bicolor at the individual level. For a single mature leaf, more salt glands are distributed in the leaf central and apical regions than leaf base. For the leaves in different developmental stages, firstly, the density of salt glands linearly decreased at the beginning of leaf expansion and kept a relatively constant value in the later periods, which was mainly due to the rapid expansion of epidermal cells. Secondly, the total number of glands per leaf showed a reversed trend compared to the density of salt glands. These results suggested that the salt gland density was adapted to the leaf age and area as more and more salt accumulated in the saline soils.

Planetary X ray experiment

NASA Technical Reports Server (NTRS)

Anderson, K. A.

1972-01-01

Design studies for an X-ray experiment using solid state detectors and for an experiment using a proportional counter for investigating Jovian and Saturnian magnetospheres are reported. Background counting rates through the forward aperture and leakage fluxes are discussed for each design. It is concluded that the best choice of instrument appears to have following the characteristics: (1) two separate multiwire proportional counters for redundancy; (2) passive collimation to restrict the field to about 5 deg, wiregrid modulation collimation to about 0.1 deg angular resolution; (3) no active shielding system around the counter body; and (4) light passive shielding around any portion of the counter body exposed to space to absorb most of the cosmic X-ray background.

Allometric constraints to inversion of canopy structure from remote sensing

NASA Astrophysics Data System (ADS)

Wolf, A.; Berry, J. A.; Asner, G. P.

2008-12-01

Canopy radiative transfer models employ a large number of vegetation architectural and leaf biochemical attributes. Studies of leaf biochemistry show a wide array of chemical and spectral diversity that suggests that several leaf biochemical constituents can be independently retrieved from multi-spectral remotely sensed imagery. In contrast, attempts to exploit multi-angle imagery to retrieve canopy structure only succeed in finding two or three of the many unknown canopy arhitectural attributes. We examine a database of over 5000 destructive tree harvests from Eurasia to show that allometry - the covariation of plant form across a broad range of plant size and canopy density - restricts the architectural diversity of plant canopies into a single composite variable ranging from young canopies with many short trees with small crowns to older canopies with fewer trees and larger crowns. Moreover, these architectural attributes are closely linked to biomass via allometric constraints such as the "self-thinning law". We use the measured variance and covariance of plant canopy architecture in these stands to drive the radiative transfer model DISORD, which employs the Li-Strahler geometric optics model. This correlations introduced in the Monte Carlo study are used to determine which attributes of canopy architecture lead to important variation that can be observed by multi-angle or multi-spectral satellite observations, using the sun-view geometry characteristic of MODIS observations in different biomes located at different latitude bands. We conclude that although multi-angle/multi-spectral remote sensing is only sensitive to some of the many unknown canopy attributes that ecologists would wish to know, the strong allometric covariation between these attributes and others permits a large number of inferrences, such as forest biomass, that will be meaningful next-generation vegetation products useful for data assimilation.

Development of a hemispherical rotational modulation collimator system for imaging spatial distribution of radiation sources

NASA Astrophysics Data System (ADS)

Na, M.; Lee, S.; Kim, G.; Kim, H. S.; Rho, J.; Ok, J. G.

2017-12-01

Detecting and mapping the spatial distribution of radioactive materials is of great importance for environmental and security issues. We design and present a novel hemispherical rotational modulation collimator (H-RMC) system which can visualize the location of the radiation source by collecting signals from incident rays that go through collimator masks. The H-RMC system comprises a servo motor-controlled rotating module and a hollow heavy-metallic hemisphere with slits/slats equally spaced with the same angle subtended from the main axis. In addition, we also designed an auxiliary instrument to test the imaging performance of the H-RMC system, comprising a high-precision x- and y-axis staging station on which one can mount radiation sources of various shapes. We fabricated the H-RMC system which can be operated in a fully-automated fashion through the computer-based controller, and verify the accuracy and reproducibility of the system by measuring the rotational and linear positions with respect to the programmed values. Our H-RMC system may provide a pivotal tool for spatial radiation imaging with high reliability and accuracy.

Experimental investigation of multi-scale non-equilibrium plasma dynamics

NASA Astrophysics Data System (ADS)

Bellan, Paul

2013-10-01

Lab experiments at Caltech resolve complex, detailed MHD dynamics spatially and temporally. Unbalanced forces drive fast plasma flows which tend to self-collimate via self-pinching. Collimation results from flow stagnation compressing embedded magnetic flux and so amplifying the magnetic field responsible for pinching. Measurements show that the collimated flow is essentially a dense plasma jet with embedded axial and azimuthal magnetic fields, i.e., a magnetic flux tube (flux rope). The measured jet velocity is in good agreement with an MHD acceleration model. Depending on how flux tube radius varies with axial position, jets flow into a flux tube from both ends or from just one end. Jets kink when the flux tube in which they are embedded breaches the Kruskal-Shafranov stability limit. The lateral acceleration of a sufficiently strong kink can produce an enormous effective gravity which provides the environment for an observed fine-scale, extremely fast Rayleigh-Taylor (RT) instability. The RT can erode the jet current channel to be smaller than the ion skin depth so there is a cascade from the ideal MHD scale of the kink to the non-MHD ion skin depth scale. This process can result in a magnetic reconnection whereby the jet and its embedded flux tube break. Supported by USDOE.

The optical design of solar spectrograph

NASA Astrophysics Data System (ADS)

Zhang, Yang; Pan, Wen-Qiang; Meng, Xiang-Yue; Lv, Xian-Kui; Feng, Jie; Zhu, Jia-Wei; Zhang, Xiao-Xiao; Li, Lei; Yang, Wei-Ping

2017-08-01

At the beginning of this paper, we simply describe the theories of spectrograph and the operating principle of grating. Based on the Spectrometer theory and optical theory we design a solar spectrograph by analyzing and calculating. And the working waveband of this solar spectrograph is between 510nm and 540nm. Besides, according to the design data, we ensure the blaze level of grating and the focal length of collimate. Due to the presence of the collimate in the optical structure, astigmatism exists in the system. For this reason, we add a cylindrical lens to the structure to correct. The optical system is characterized by using white-pupil design and folding light path to make the whole system simple. In the end, according to the calculated design parameters, we use the Zemax software for simulation, then the result is RMS only has 4μm at the 520nm. It's worth nothing that the resolution merely near the reference wavelength (520nm)meets the design requirements.

The journey from proton to gamma knife.

PubMed

Ganz, Jeremy C

2014-01-01

It was generally accepted by the early 1960s that proton beam radiosurgery was too complex and impractical. The need was seen for a new machine. The beam design had to be as good as a proton beam. It was also decided that a static design was preferable even if the evolution of that notion is no longer clear. Complex collimators were designed that using sources of cobalt-60 could produce beams with characteristics adequately close to those of proton beams. The geometry of the machine was determined including the distance of the sources from the patient the optimal distance between the sources. The first gamma unit was built with private money with no contribution from the Swedish state, which nonetheless required detailed design information in order to ensure radiation safety. This original machine was built with rectangular collimators to produce lesions for thalamotomy for functional work. However, with the introduction of dopamine analogs, this indication virtually disappeared overnight.

Large beam deflection using cascaded prism array

NASA Astrophysics Data System (ADS)

Wang, Wei-Chih; Tsui, Chi-Leung

2012-04-01

Endoscopes have been utilize in the medical field to observe the internals of the human body to assist the diagnosis of diseases, such as breathing disorders, internal bleeding, stomach ulcers, and urinary tract infections. Endoscopy is also utilized in the procedure of biopsy for the diagnosis of cancer. Conventional endoscopes suffer from the compromise between overall size and image quality due to the required size of the sensor for acceptable image quality. To overcome the size constraint while maintaining the capture image quality, we propose an electro-optic beam steering device based on thermal-plastic polymer, which has a small foot-print (~5mmx5mm), and can be easily fabricated using conventional hot-embossing and micro-fabrication techniques. The proposed device can be implemented as an imaging device inside endoscopes to allow reduction in the overall system size. In our previous work, a single prism design has been used to amplify the deflection generated by the index change of the thermal-plastic polymer when a voltage is applied; it yields a result of 5.6° deflection. To further amplify the deflection, a new design utilizing a cascading three-prism array has been implemented and a deflection angle to 29.2° is observed. The new design amplifies the beam deflection, while keeping the advantage of simple fabrication made possible by thermal-plastic polymer. Also, a photo-resist based collimator lens array has been added to reduce and provide collimation of the beam for high quality imaging purposes. The collimator is able to collimate the exiting beam at 4 μm diameter for up to 25mm, which potentially allows high resolution image capturing.

Physical properties of new collimator cone system for stereotactic radiation therapy developed in samsung medical center.

PubMed

Kim, D Y; Ahn, Y C; Oh, D G; Choi, D R; Ju, S G; Yeo, I H; Huh, S J

2000-09-01

A new collimator cone system has been developed at the Samsung Medical Center that overcomes some of the limitations of present commercially supplied collimator cones. The physical properties of the newly developed cone system are described in this report. The new cones have relatively larger aperture sizes (3.0-7.0 cm in diameter) and are 16 cm in length. Each new cone is fabricated with cerrobend alloy melted and poured into a stainless steel housing that is permanently fixed to a mounting plate. The mounting plate of the new cone is designed to insert into the wedge mount slot of the gantry head. The mechanical accuracy of the central axis of the cone pointing to the isocenter was tested using film, a steel ball positioned at the isocenter by the mechanical isocenter device. For the evaluation of beam flatness and penumbra, off-axis ratios at 5 cm depth were measured by film dosimetry using polystyrene phantom. The average error of the mechanical isocenter was 0.27 mm (+/- 0.16 mm). The beam flatness was excellent in the central region of the beam, and the average penumbra width was 3.35 mm (+/- 0.25 mm). The new cone design has more clearance between the patient's head and the gantry, and can more easily be removed from the gantry head because it slides in and out of the wedge slot. This facilitates changing cone sizes during one treatment session, and makes the process of double exposure port films easier. A new collimator cone system for stereotactic radiation therapy has been developed. The mechanical accuracy and physical properties are satisfactory for clinical use, and the new design permits a wider range of clinical applications for stereotactic radiation therapy.

Field precision machining technology of target chamber in ICF lasers

NASA Astrophysics Data System (ADS)

Xu, Yuanli; Wu, Wenkai; Shi, Sucun; Duan, Lin; Chen, Gang; Wang, Baoxu; Song, Yugang; Liu, Huilin; Zhu, Mingzhi

2016-10-01

In ICF lasers, many independent laser beams are required to be positioned on target with a very high degree of accuracy during a shot. The target chamber provides a precision platform and datum reference for final optics assembly and target collimation and location system. The target chamber consists of shell with welded flanges, reinforced concrete pedestal, and lateral support structure. The field precision machining technology of target chamber in ICF lasers have been developed based on ShenGuangIII (SGIII). The same center of the target chamber is adopted in the process of design, fabrication, and alignment. The technologies of beam collimation and datum reference transformation are developed for the fabrication, positioning and adjustment of target chamber. A supporting and rotating mechanism and a special drilling machine are developed to bore the holes of ports. An adjustment mechanism is designed to accurately position the target chamber. In order to ensure the collimation requirements of the beam leading and focusing and the target positioning, custom-machined spacers are used to accurately correct the alignment error of the ports. Finally, this paper describes the chamber center, orientation, and centering alignment error measurements of SGIII. The measurements show the field precision machining of SGIII target chamber meet its design requirement. These information can be used on similar systems.

Simulation of gamma-ray spectra for a variety of user-specified detector designs

NASA Technical Reports Server (NTRS)

Rester, A. C., Jr.

1994-01-01

The gamma-ray spectrum simulation program BSIMUL was designed to allow the operator to follow the path of a gamma-ray through a detector, shield and collimator whose dimensions are entered by the operator. It can also be used to simulate spectra that would be generated by a detector. Several improvements have been made to the program within the last few months. The detector, shield and collimator dimensions can now be entered through an interactive menu whose options are discussed below. In addition, spectra containing more than one gamma-ray energy can now be generated with the menu - for isotopes listed in the program. Adding isotopes to the main routine is also quite easy. Subroutines have been added to enable the operator to specify the material and dimensions of a collimator. This report details the progress made in simulating gamma-ray spectra for a variety of user-specified detector designs. In addition, a short discussion of work done in the related areas of pulse shape analysis and the spectral analysis is included. The pulse shape analysis and spectral analysis work is being performed pursuant to the requirements of contract F-94-C-0006, for the Advanced Research Projects Agency and the U.S. Air Force.

Detecting leaf phenology of seasonally moist tropical forests in South America with multi-temporal MODIS images.

Treesearch

Xiangming Xiao; Stephen Hagen; Qingyuan Zhang; Michael Keller; Berrien Moore III

2006-01-01

Leaf phenology of tropical evergreen forests affects carbon and water fluxes. In an earlier study of a seasonally moist evergreen tropical forest site in the Amazon basin, time series data of Enhanced Vegetation Index (EVI) from the VEGETATION and Moderate Resolution Imaging Spectroradiometer (MODIS) sensors showed an unexpected seasonal pattern, with higher EVI in the...

Opto-mechanical design of an image slicer for the GRIS spectrograph at GREGOR

NASA Astrophysics Data System (ADS)

Vega Reyes, N.; Esteves, M. A.; Sánchez-Capuchino, J.; Salaun, Y.; López, R. L.; Gracia, F.; Estrada Herrera, P.; Grivel, C.; Vaz Cedillo, J. J.; Collados, M.

2016-07-01

An image slicer has been proposed for the Integral Field Spectrograph [1] of the 4-m European Solar Telescope (EST) [2] The image slicer for EST is called MuSICa (Multi-Slit Image slicer based on collimator-Camera) [3] and it is a telecentric system with diffraction limited optical quality offering the possibility to obtain high resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by coupling a polarimeter after the generated slit (or slits). Considering the technical complexity of the proposed Integral Field Unit (IFU), a prototype has been designed for the GRIS spectrograph at GREGOR telescope at Teide Observatory (Tenerife), composed by the optical elements of the image slicer itself, a scanning system (to cover a larger field of view with sequential adjacent measurements) and an appropriate re-imaging system. All these subsystems are placed in a bench, specially designed to facilitate their alignment, integration and verification, and their easy installation in front of the spectrograph. This communication describes the opto-mechanical solution adopted to upgrade GRIS while ensuring repeatability between the observational modes, IFU and long-slit. Results from several tests which have been performed to validate the opto-mechanical prototypes are also presented.

The Diagnostics of the External Plasma for the Plasma Rocket

NASA Technical Reports Server (NTRS)

Karr, Gerald R.

1997-01-01

Three regions of plasma temperature/energy are being investigated to understand fully the behavior of the plasma created by the propulsion device and the operation of the RPA. Each type of plasma has a RPA associated with it; i.e. a thermal RPA, a collimated RPA, and a high temperature RPA. Through the process of developing the thermal and collimated RPAs, the proper knowledge and experience has been gained to not only design a high temperature RPA for the plasma rocket, but to understand its operation, results, and uncertainty. After completing a literature search for, reading published papers on, and discussing the operation of the RPA with electric propulsion researchers, I applied the knowledge gained to the development of a RPA for thermal plasma. A design of a thermal RPA was made which compensates for a large Debye length and low ionized plasma. From this design a thermal RPA was constructed. It consists of an outer stainless steel casing, a phenolic insulator (outgases slightly), and stainless steel mesh for the voltage screens. From the experience and knowledge gained in the development of the thermal RPA, a RPA for collimated plasma was developed. A collimated RPA has been designed and constructed. It compensate for a smaller Debye length and much higher ionization than that existing in the thermal plasma. It is 17% of the size of the thermal RPA. A stainless steel casing shields the detector from impinging electrons and ions. An insulating material, epoxy resin, was utilized which has a negligible outgassing. This material can be molded in styrofoam and machined quite nicely. It is capable of withstanding moderately high temperatures. Attached to this resin insulator are inconel screens attached by silver plated copper wire to a voltage supply. All the work on the RPAs and thermal ion source, I performed in the University of Alabama in Huntsville's (UAH) engineering machine shop.

Monte Carlo-based QA for IMRT of head and neck cancers

NASA Astrophysics Data System (ADS)

Tang, F.; Sham, J.; Ma, C.-M.; Li, J.-S.

2007-06-01

It is well-known that the presence of large air cavity in a dense medium (or patient) introduces significant electronic disequilibrium when irradiated with megavoltage X-ray field. This condition may worsen by the possible use of tiny beamlets in intensity-modulated radiation therapy (IMRT). Commercial treatment planning systems (TPSs), in particular those based on the pencil-beam method, do not provide accurate dose computation for the lungs and other cavity-laden body sites such as the head and neck. In this paper we present the use of Monte Carlo (MC) technique for dose re-calculation of IMRT of head and neck cancers. In our clinic, a turn-key software system is set up for MC calculation and comparison with TPS-calculated treatment plans as part of the quality assurance (QA) programme for IMRT delivery. A set of 10 off-the-self PCs is employed as the MC calculation engine with treatment plan parameters imported from the TPS via a graphical user interface (GUI) which also provides a platform for launching remote MC simulation and subsequent dose comparison with the TPS. The TPS-segmented intensity maps are used as input for the simulation hence skipping the time-consuming simulation of the multi-leaf collimator (MLC). The primary objective of this approach is to assess the accuracy of the TPS calculations in the presence of air cavities in the head and neck whereas the accuracy of leaf segmentation is verified by fluence measurement using a fluoroscopic camera-based imaging device. This measurement can also validate the correct transfer of intensity maps to the record and verify system. Comparisons between TPS and MC calculations of 6 MV IMRT for typical head and neck treatments review regional consistency in dose distribution except at and around the sinuses where our pencil-beam-based TPS sometimes over-predicts the dose by up to 10%, depending on the size of the cavities. In addition, dose re-buildup of up to 4% is observed at the posterior nasopharyngeal mucosa for some treatments with heavily-weighted anterior fields.

Dynamic simulation of motion effects in IMAT lung SBRT.

PubMed

Zou, Wei; Yin, Lingshu; Shen, Jiajian; Corradetti, Michael N; Kirk, Maura; Munbodh, Reshma; Fang, Penny; Jabbour, Salma K; Simone, Charles B; Yue, Ning J; Rengan, Ramesh; Teo, Boon-Keng Kevin

2014-11-01

Intensity modulated arc therapy (IMAT) has been widely adopted for Stereotactic Body Radiotherapy (SBRT) for lung cancer. While treatment dose is optimized and calculated on a static Computed Tomography (CT) image, the effect of the interplay between the target and linac multi-leaf collimator (MLC) motion is not well described and may result in deviations between delivered and planned dose. In this study, we investigated the dosimetric consequences of the inter-play effect on target and organs at risk (OAR) by simulating dynamic dose delivery using dynamic CT datasets. Fifteen stage I non-small cell lung cancer (NSCLC) patients with greater than 10 mm tumor motion treated with SBRT in 4 fractions to a dose of 50 Gy were retrospectively analyzed for this study. Each IMAT plan was initially optimized using two arcs. Simulated dynamic delivery was performed by associating the MLC leaf position, gantry angle and delivered beam monitor units (MUs) for each control point with different respiratory phases of the 4D-CT using machine delivery log files containing time stamps of the control points. Dose maps associated with each phase of the 4D-CT dose were calculated in the treatment planning system and accumulated using deformable image registration onto the exhale phase of the 4D-CT. The original IMAT plans were recalculated on the exhale phase of the CT for comparison with the dynamic simulation. The dose coverage of the PTV showed negligible variation between the static and dynamic simulation. There was less than 1.5% difference in PTV V95% and V90%. The average inter-fraction and cumulative dosimetric effects among all the patients were less than 0.5% for PTV V95% and V90% coverage and 0.8 Gy for the OARs. However, in patients where target is close to the organs, large variations were observed on great vessels and bronchus for as much as 4.9 Gy and 7.8 Gy. Limited variation in target dose coverage and OAR constraints were seen for each SBRT fraction as well as over all four fractions. Large dose variations were observed on critical organs in patients where these organs were closer to the target.

A small-angle x-ray scattering system with a vertical layout.

PubMed

Wang, Zhen; Chen, Xiaowei; Meng, Lingpu; Cui, Kunpeng; Wu, Lihui; Li, Liangbin

2014-12-01

A small-angle x-ray scattering (SAXS) system with a vertical layout (V-SAXS) has been designed and constructed for in situ detection on nanostructures, which is well suitable for in situ study on self-assembly of nanoparticles at liquid interface and polymer processing. A steel-tower frame on a reinforced basement is built as the supporting skeleton for scattering beam path and detector platform, ensuring the system a high working stability and a high operating accuracy. A micro-focus x-ray source combining parabolic three-dimensional multi-layer mirror and scatteringless collimation system provides a highly parallel beam, which allows us to detect the very small angle range. With a sample-to-detector distance of 7 m, the largest measurable length scale is 420 nm in real space. With a large sample zone, it is possible to install different experimental setups such as film stretching machine, which makes the system perfect to follow the microstructures evolution of materials during processing. The capability of the V-SAXS on in situ study is tested with a drying experiment of a free latex droplet, which confirms our initial design.

Transparent silicon strip sensors for the optical alignment of particle detector systems

NASA Astrophysics Data System (ADS)

Blum, W.; Kroha, H.; Widmann, P.

1996-02-01

Modern large-area precision tracking detectors require increasing accuracy for the alignment of their components. A novel multi-point laser alignment system has been developed for such applications. The position of detector components with respect to reference laser beams is monitored by semi-transparent optical position sensors which work on the principle of silicon strip photodiodes. Two types of custom designed transparent strip sensors, based on crystalline and on amorphous silicon as active material, have been studied. The sensors are optimized for the typical diameters of collimated laser beams of 3-5 mm over distances of 10-20 m. They provide very high position resolution, on the order of 1 μm, uniformly over a wide measurement range of several centimeters. The preparation of the sensor surfaces requires special attention in order to achieve high light transmittance and minimum distortion of the traversing laser beams. At selected wavelengths, produced by laser diodes, transmission rates above 90% have been achieved. This allows to position more than 30 sensors along one laser beam. The sensors will be equipped with custom designed integrated readout electronics.

Neutron beam optimization based on a 7Li(p,n)7Be reaction for treatment of deep-seated brain tumors by BNCT

NASA Astrophysics Data System (ADS)

Zahra Ahmadi, Ganjeh; S. Farhad, Masoudi

2014-10-01

Neutron beam optimization for accelerator-based Boron Neutron Capture Therapy (BNCT) is investigated using a 7Li(p,n)7Be reaction. Design and optimization have been carried out for the target, cooling system, moderator, filter, reflector, and collimator to achieve a high flux of epithermal neutron and satisfy the IAEA criteria. Also, the performance of the designed beam in tissue is assessed by using a simulated Snyder head phantom. The results show that the optimization of the collimator and reflector is critical to finding the best neutron beam based on the 7Li(p,n)7Be reaction. Our designed beam has 2.49×109n/cm2s epithermal neutron flux and is suitable for BNCT of deep-seated brain tumors.

Design of axisymmetrical tailored concentrators for LED light source applications

NASA Astrophysics Data System (ADS)

Van Giel, Bart; Meuret, Youri; Thienpont, Hugo

2006-04-01

In our contribution we present a solution to an important question in the design of a LED-based illumination engine for projection systems: the collimation of the LED light. We tested the principle in the modification of a common device in non-imaging optics, the compound Parabolic Concentrator. This CPC-like achieves a collection of 72% (ideal reflective coating presumed). This CPC-like was tailored by numerically solving an differential equation. This approach has some serious drawbacks. For a compact collection device with high collimation, an other approach is required. A more elegant design strategy will rely fully on geometrical principles. The result of our work is a compound collection lens that achieves a collection efficiency of 87%, assuming an ideal reflective coating and neglecting Fresnel losses. We study the performance of this device in detail. Further enhancements are suggested.

Simulator for beam-based LHC collimator alignment

NASA Astrophysics Data System (ADS)

Valentino, Gianluca; Aßmann, Ralph; Redaelli, Stefano; Sammut, Nicholas

2014-02-01

In the CERN Large Hadron Collider, collimators need to be set up to form a multistage hierarchy to ensure efficient multiturn cleaning of halo particles. Automatic algorithms were introduced during the first run to reduce the beam time required for beam-based setup, improve the alignment accuracy, and reduce the risk of human errors. Simulating the alignment procedure would allow for off-line tests of alignment policies and algorithms. A simulator was developed based on a diffusion beam model to generate the characteristic beam loss signal spike and decay produced when a collimator jaw touches the beam, which is observed in a beam loss monitor (BLM). Empirical models derived from the available measurement data are used to simulate the steady-state beam loss and crosstalk between multiple BLMs. The simulator design is presented, together with simulation results and comparison to measurement data.

Analysis investigation of supporting and restraint conditions on the surface deformation of a collimator primary mirror

NASA Astrophysics Data System (ADS)

Chan, Chia-Yen; You, Zhen-Ting; Huang, Bo-Kai; Chen, Yi-Cheng; Huang, Ting-Ming

2015-09-01

For meeting the requirements of the high-precision telescopes, the design of collimator is essential. The diameter of the collimator should be larger than that of the target for the using of alignment. Special supporting structures are demanded to reduce the deformation of gravity and to control the surface deformation induced by the mounting force when inspecting large-aperture primary mirrors. By using finite element analysis, a ZERODUR® mirror of a diameter of 620 mm will be analyzed to obtain the deformation induced by the supporting structures. Zernike polynomials will also be adopted to fit the optical surface and separate corresponding aberrations. Through the studies under different boundary conditions and supporting positions of the inner ring, it is concluded that the optical performance will be excellent under a strong enough supporter.

Red maple (Acer rubrum) leaf toxicosis in horses: a retrospective study of 32 cases.

PubMed

Alward, Ashley; Corriher, Candice A; Barton, Michelle H; Sellon, Debra C; Blikslager, Anthony T; Jones, Samuel L

2006-01-01

Ingestion of wilted red maple leaves by horses can result in severe hemolytic anemia and methemoglobinemia. Little is known about what factors influence the outcome of red maple leaf toxicosis in horses. Our hypothesis was that physical examination findings, clinicopathologic variables or therapeutic modalities may predict outcome in horses with red maple leaf toxicity. Horses with red maple leaf toxicosis presented to referral hospitals in the southeast region of the United States. A multi-institutional retrospective study was designed to identify factors that predict mortality in horses with red maple toxicosis. Thirty-two horses with red maple toxicosis were identified, 19 of which died. Twenty-nine horses presented with anemia and 24 had clinicopathologic evidence of systemic inflammation. Renal insufficiency was identified in 12/30 (41%) horses. Laminitis (9/28) and colic (13/30) also were identified in horses with red maple toxicosis, but development of these 2 conditions did not have a negative effect on short-term survival. Horses with red maple toxicosis that survived to discharge were likely to have developed pyrexia during hospitalization (P = .030). Horses that were treated with a corticosteroid had a significantly increased likelihood of death (P = .045). There was no significant relationship between initial serum hemoglobin concentration, methemoglobin concentration, or percentage methemoglobin and mortality in this horse series. This study suggests that information obtained on initial examination cannot be used to accurately predict survival in horses with red maple toxicosis, but horses that receive corticosteroids are unlikely to survive.

Inverse-collimated proton radiography for imaging thin materials

NASA Astrophysics Data System (ADS)

Freeman, Matthew S.; Allison, Jason; Andrews, Malcolm; Ferm, Eric; Goett, John J.; Kwiatkowski, Kris; Lopez, Julian; Mariam, Fesseha; Marr-Lyon, Mark; Martinez, Michael; Medina, Jason; Medina, Patrick; Merrill, Frank E.; Morris, Chris L.; Murray, Matthew M.; Nedrow, Paul; Neukirch, Levi P.; Prestridge, Katherine; Rigg, Paolo; Saunders, Alexander; Schurman, Tamsen; Tainter, Amy; Trouw, Frans; Tupa, Dale; Tybo, Josh; Vogan-McNeil, Wendy; Wilde, Carl

2017-01-01

Relativistic, magnetically focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam and is inherently well-suited to imaging dense objects, at areal densities >20 g cm-2. However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm-2. Here, this inverse-collimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm-2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ˜25 mg cm-2 to 100 g cm-2, exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

Inverse-collimated proton radiography for imaging thin materials.

PubMed

Freeman, Matthew S; Allison, Jason; Andrews, Malcolm; Ferm, Eric; Goett, John J; Kwiatkowski, Kris; Lopez, Julian; Mariam, Fesseha; Marr-Lyon, Mark; Martinez, Michael; Medina, Jason; Medina, Patrick; Merrill, Frank E; Morris, Chris L; Murray, Matthew M; Nedrow, Paul; Neukirch, Levi P; Prestridge, Katherine; Rigg, Paolo; Saunders, Alexander; Schurman, Tamsen; Tainter, Amy; Trouw, Frans; Tupa, Dale; Tybo, Josh; Vogan-McNeil, Wendy; Wilde, Carl

2017-01-01

Relativistic, magnetically focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam and is inherently well-suited to imaging dense objects, at areal densities >20 g cm -2 . However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm -2 . Here, this inverse-collimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm -2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ∼25 mg cm -2 to 100 g cm -2 , exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

Free-form surface design method for a collimator TIR lens.

PubMed

Tsai, Chung-Yu

2016-04-01

A free-form (FF) surface design method is proposed for a general axial-symmetrical collimator system consisting of a light source and a total internal reflection lens with two coupled FF boundary surfaces. The profiles of the boundary surfaces are designed using a FF surface construction method such that each incident ray is directed (refracted and reflected) in such a way as to form a specified image pattern on the target plane. The light ray paths within the system are analyzed using an exact analytical model and a skew-ray tracing approach. In addition, the validity of the proposed FF design method is demonstrated by means of ZEMAX simulations. It is shown that the illumination distribution formed on the target plane is in good agreement with that specified by the user. The proposed surface construction method is mathematically straightforward and easily implemented in computer code. As such, it provides a useful tool for the design and analysis of general axial-symmetrical optical systems.

BOMBOLO: a Multi-Band, Wide-field, Near UV/Optical Imager for the SOAR 4m Telescope

NASA Astrophysics Data System (ADS)

Angeloni, R.; Guzmán, D.; Puzia, T. H.; Infante, L.

2014-10-01

BOMBOLO is a new multi-passband visitor instrument for SOAR observatory. The first fully Chilean instrument of its kind, it is a three-arms imager covering the near-UV and optical wavelengths. The three arms work simultaneously and independently, providing synchronized imaging capability for rapid astronomical events. BOMBOLO will be able to address largely unexplored events in the minute-to-second timescales, with the following leading science cases: 1) Simultaneous Multiband Flickering Studies of Accretion Phenomena; 2) Near UV/Optical Diagnostics of Stellar Evolutionary Phases; 3) Exoplanetary Transits and 4) Microlensing Follow-Up. BOMBOLO optical design consists of a wide field collimator feeding two dychroics at 390 and 550 nm. Each arm encompasses a camera, filter wheel and a science CCD230-42, imaging a 7 x 7 arcmin field of view onto a 2k x 2k image. The three CCDs will have different coatings to optimise the efficiencies of each camera. The detector controller to run the three cameras will be Torrent (the NOAO open-source system) and a PanView application will run the instrument and produce the data-cubes. The instrument is at Conceptual Design stage, having been approved by the SOAR Board of Directors as a visitor instrument in 2012 and having been granted full funding from CONICYT, the Chilean State Agency of Research, in 2013. The Design Phase is starting now and will be completed in late 2014, followed by a construction phase in 2015 and 2016A, with expected Commissioning in 2016B and 2017A.

THE MULTI-OBJECT, FIBER-FED SPECTROGRAPHS FOR THE SLOAN DIGITAL SKY SURVEY AND THE BARYON OSCILLATION SPECTROSCOPIC SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smee, Stephen A.; Gunn, James E.; Uomoto, Alan

2013-07-12

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measuremore » redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-alpha absorption of 160,000 high redshift quasars over 10,000 square degrees of sky, making percent level measurements of the absolute cosmic distance scale of the Universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near ultraviolet to the near infrared, with a resolving power R = \\lambda/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 < \\lambda < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.« less

The optical design and simulation of the collimated solar simulator

NASA Astrophysics Data System (ADS)

Zhang, Jun; Ma, Tao

2018-01-01

The solar simulator is a lighting device that can simulate the solar radiation. It has been widely used in the testing of solar cells, satellite space environment simulation and ground experiment, test and calibration precision of solar sensor. The solar simulator mainly consisted of short—arc xenon lamp, ellipsoidal reflectors, a group of optical integrator, field stop, aspheric folding mirror and collimating reflector. In this paper, the solar simulator's optical system basic size are given by calculation. Then the system is optically modeled with the Lighttools software, and the simulation analysis on solar simulator using the Monte Carlo ray -tracing technique is conducted. Finally, the simulation results are given quantitatively by diagrammatic form. The rationality of the design is verified on the basis of theory.

Comparison of Hyperspectral and Multispectral Satellites for Forest Alliance Classification in the San Francisco Bay Area

NASA Astrophysics Data System (ADS)

Clark, M. L.

2016-12-01

The goal of this study was to assess multi-temporal, Hyperspectral Infrared Imager (HyspIRI) satellite imagery for improved forest class mapping relative to multispectral satellites. The study area was the western San Francisco Bay Area, California and forest alliances (e.g., forest communities defined by dominant or co-dominant trees) were defined using the U.S. National Vegetation Classification System. Simulated 30-m HyspIRI, Landsat 8 and Sentinel-2 imagery were processed from image data acquired by NASA's AVIRIS airborne sensor in year 2015, with summer and multi-temporal (spring, summer, fall) data analyzed separately. HyspIRI reflectance was used to generate a suite of hyperspectral metrics that targeted key spectral features related to chemical and structural properties. The Random Forests classifier was applied to the simulated images and overall accuracies (OA) were compared to those from real Landsat 8 images. For each image group, broad land cover (e.g., Needle-leaf Trees, Broad-leaf Trees, Annual agriculture, Herbaceous, Built-up) was classified first, followed by a finer-detail forest alliance classification for pixels mapped as closed-canopy forest. There were 5 needle-leaf tree alliances and 16 broad-leaf tree alliances, including 7 Quercus (oak) alliance types. No forest alliance classification exceeded 50% OA, indicating that there was broad spectral similarity among alliances, most of which were not spectrally pure but rather a mix of tree species. In general, needle-leaf (Pine, Redwood, Douglas Fir) alliances had better class accuracies than broad-leaf alliances (Oaks, Madrone, Bay Laurel, Buckeye, etc). Multi-temporal data classifications all had 5-6% greater OA than with comparable summer data. For simulated data, HyspIRI metrics had 4-5% greater OA than Landsat 8 and Sentinel-2 multispectral imagery and 3-4% greater OA than HyspIRI reflectance. Finally, HyspIRI metrics had 8% greater OA than real Landsat 8 imagery. In conclusion, forest alliance classification was found to be a difficult remote sensing application with moderate resolution (30 m) satellite imagery; however, of the data tested, HyspIRI spectral metrics had the best performance relative to multispectral satellites.

Synchronized parameter optimization of the double freeform lenses illumination system used for the CF-LCoS pico-projectors

NASA Astrophysics Data System (ADS)

Chen, Enguo; Liu, Peng; Yu, Feihong

2012-10-01

A novel synchronized optimization method of multiple freeform surfaces is proposed and applied to double lenses illumination system design of CF-LCoS pico-projectors. Based on Snell's law and the energy conservation law, a series of first-order partial differential equations are derived for the multiple freeform surfaces of the initial system. By assigning the light deflection angle to each freeform surface, multiple surfaces can be obtained simultaneously by solving the corresponding equations, meanwhile the restricted angle on CF-LCoS is guaranteed. In order to improve the spatial uniformity, the multi-surfaces are synchronously optimized by using simplex algorithm for an extended LED source. Design example shows that the double lenses based illumination system, which employs a single 2 mm×2 mm LED chip and a CF-LCoS panel with a diagonal of 0.59 inches satisfies the needs of pico-projector. Moreover, analytical result indicates that the design method represents substantial improvement and practical significance over traditional CF-LCoS projection system, which could offer outstanding performance with both portability and low cost. The synchronized optimization design method could not only realize collimating and uniform illumination, but also could be introduced to other specific light conditions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gromov, R.; Bailey, J.; Virgo, M.

Argonne National Laboratory, in cooperation with Los Alamos National Laboratory, is developing technology with NorthStar Medical Technologies to produce 99Mo from the γ,n reaction on a 100Mo target in an electron accelerator. During production runs and thermal testing of the helium-cooled target, it became obvious that a production-scale beam-line configuration would need a collimator to protect the target from accidental beam misplacement or a beam-profile change. A prototype high-power collimator and beam stop were designed and fabricated. Testing indicated that they will be able to operate at full power in the production-scale accelerator.

Development of Prior Image-Based, High-Quality, Low-Dose Kilovoltage Cone Beam CT for Use in Adaptive Radiotherapy of Prostate Cancer

DTIC Science & Technology

2011-05-01

for the research in the next year. The aims in the next year include further develop- ment of the prior image- based , narrowly collimated CBCT imaging...further investigation planned for the next year. 5 BODY 1 Research Accomplishments 1.1 Implement narrow beam collimation for CBCT ROI imaging I have...noise level to mimic different mAs used in clinical and research modes of the CBCT system. Based upon experiences with the numerical phantom, I designed

Potential of discrete Gaussian edge feathering method for improving abutment dosimetry in eMLC-delivered segmented-field electron conformal therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eley, John G.; Hogstrom, Kenneth R.; Matthews, Kenneth L.

2011-12-15

Purpose: The purpose of this work was to investigate the potential of discrete Gaussian edge feathering of the higher energy electron fields for improving abutment dosimetry in the planning volume when using an electron multileaf collimator (eMLC) to deliver segmented-field electron conformal therapy (ECT). Methods: A discrete (five-step) Gaussian edge spread function was used to match dose penumbras of differing beam energies (6-20 MeV) at a specified depth in a water phantom. Software was developed to define the leaf eMLC positions of an eMLC that most closely fit each electron field shape. The effect of 1D edge feathering of themore » higher energy field on dose homogeneity was computed and measured for segmented-field ECT treatment plans for three 2D PTVs in a water phantom, i.e., depth from the water surface to the distal PTV surface varied as a function of the x-axis (parallel to leaf motion) and remained constant along the y-axis (perpendicular to leaf motion). Additionally, the effect of 2D edge feathering was computed and measured for one radially symmetric, 3D PTV in a water phantom, i.e., depth from the water surface to the distal PTV surface varied as a function of both axes. For the 3D PTV, the feathering scheme was evaluated for 0.1-1.0-cm leaf widths. Dose calculations were performed using the pencil beam dose algorithm in the Pinnacle{sup 3} treatment planning system. Dose verification measurements were made using a prototype eMLC (1-cm leaf width). Results: 1D discrete Gaussian edge feathering reduced the standard deviation of dose in the 2D PTVs by 34, 34, and 39%. In the 3D PTV, the broad leaf width (1 cm) of the eMLC hindered the 2D application of the feathering solution to the 3D PTV, and the standard deviation of dose increased by 10%. However, 2D discrete Gaussian edge feathering with simulated eMLC leaf widths of 0.1-0.5 cm reduced the standard deviation of dose in the 3D PTV by 33-28%, respectively. Conclusions: A five-step discrete Gaussian edge spread function applied in 2D improves the abutment dosimetry but requires an eMLC leaf resolution better than 1 cm.« less

Evaluation of dual γ-ray imager with active collimator using various types of scintillators.

PubMed

Lee, Wonho; Lee, Taewoong; Jeong, Manhee; Kim, Ho Kyung

2011-10-01

The performance of a specialized dual γ-ray imager using both mechanical and electronic collimation was evaluated by Monte Carlo simulation (MCNP5). The dual imager consisted of an active collimator and a planar detector that were made from scintillators. The active collimator served not only as a coded aperture for mechanical collimation but also as a first detector for electronic collimation. Therefore, a single system contained both mechanical and electronic collimation. Various types of scintillators were tested and compared with each other in terms of their angular resolution, efficiency, and background noise. In general, a BGO active collimator had the best mechanical collimation performance, and an LaCl₃(Ce) active collimator provided the best electronic collimation performance. However, for low radiation energies, the mechanical collimation images made from both scintillators showed the same quality, and, for high radiation energies, electronic collimation images made from both scintillators also show similar quality. Therefore, if mechanical collimation is used to detect low-energy radiation and electronic collimation is applied to reconstruct a high-energy source, either LaCl₃(Ce) or BGO would be appropriate for the active collimator of a dual γ-ray imager. These results broaden the choice of scintillators for the active collimator of the dual γ-ray imager, which makes it possible to consider other factors, such as machinability and cost, in making the imager. As a planar detector, BGO showed better performance than other scintillators since its radiation detection efficiency was highest of all. Copyright © 2011 Elsevier Ltd. All rights reserved.

Design and performance evaluation of a new high energy parallel hole collimator for radioiodine planar imaging by gamma cameras: Monte Carlo simulation study.

PubMed

Moslemi, Vahid; Ashoor, Mansour

2017-05-01

In addition to the trade-off between resolution and sensitivity which is a common problem among all types of parallel hole collimators (PCs), obtained images by high energy PCs (HEPCs) suffer from hole-pattern artifact (HPA) due to further septa thickness. In this study, a new design on the collimator has been proposed to improve the trade-off between resolution and sensitivity and to eliminate the HPA. A novel PC, namely high energy extended PC (HEEPC), is proposed and is compared to HEPCs. In the new PC, trapezoidal denticles were added upon the septa in the detector side. The performance of the HEEPCs were evaluated and compared to that of HEPCs using a Monte Carlo-N-particle version5 (MCNP5) simulation. The point spread functions (PSF) of HEPCs and HEEPCs were obtained as well as the various parameters such as resolution, sensitivity, scattering, and penetration ratios, and the HPA of the collimators was assessed. Furthermore, a Picker phantom study was performed to examine the effects of the collimators on the quality of planar images. It was found that the HEEPC D with an identical resolution to that of HEPC C increased sensitivity by 34.7%, and it improved the trade-off between resolution and sensitivity as well as to eliminate the HPA. In the picker phantom study, the HEEPC D indicated the hot and cold lesions with the higher contrast, lower noise, and higher contrast to noise ratio (CNR). Since the HEEPCs modify the shaping of PSFs, they are able to improve the trade-off between the resolution and sensitivity; consequently, planar images can be achieved with higher contrast resolutions. Furthermore, because the HEEPC S reduce the HPA and produce images with a higher CNR, compared to HEPCs, the obtained images by HEEPCs have a higher quality, which can help physicians to provide better diagnosis.

Miniaturized CARS microendoscope probe design for label-free intraoperative imaging

NASA Astrophysics Data System (ADS)

Chen, Xu; Wang, Xi; Xu, Xiaoyun; Cheng, Jie; Liu, Zhengfan; Weng, Sheng; Thrall, Michael J.; Goh, Alvin C.; McCormick, Daniel T.; Wong, Kelvin; Wong, Stephen T. C.

2014-03-01

A Coherent Anti-Stokes Raman Scattering (CARS) microendoscope probe for early stage label-free prostate cancer diagnosis at single cell resolution is presented. The handheld CARS microendoscope probe includes a customized micro-electromechanical systems (MEMS) scanning mirror as well as miniature optical and mechanical components. In our design, the excitation laser (pump and stokes beams) from the fiber is collimated, reflected by the reflecting mirror, and transmitted via a 2D MEMS scanning mirror and a micro-objective system onto the sample; emission in the epi-direction is returned through the micro-objective lens, MEMS and reflecting mirror, and collimation system, and finally the emission signal is collected by a photomultiplier tube (PMT). The exit pupil diameter of the collimator system is designed to match the diameter of the MEMS mirror and the entrance pupil diameter of the micro-objective system. The back aperture diameter of the micro-objective system is designed according to the largest MEMS scanning angle and the distance between the MEMS mirror and the back aperture. To increase the numerical aperture (NA) of the micro-objective system in order to enhance the signal collection efficiency, the back aperture diameter of the micro-objective system is enlarged with an upfront achromatic wide angle Keplerian telescope beam expander. The integration of a miniaturized micro-optics probe with optical fiber CARS microscopy opens up the possibility of in vivo molecular imaging for cancer diagnosis and surgical intervention.

Explicit Nonlinear Finite Element Geometric Analysis of Parabolic Leaf Springs under Various Loads

PubMed Central

Kong, Y. S.; Omar, M. Z.; Chua, L. B.; Abdullah, S.

2013-01-01

This study describes the effects of bounce, brake, and roll behavior of a bus toward its leaf spring suspension systems. Parabolic leaf springs are designed based on vertical deflection and stress; however, loads are practically derived from various modes especially under harsh road drives or emergency braking. Parabolic leaf springs must sustain these loads without failing to ensure bus and passenger safety. In this study, the explicit nonlinear dynamic finite element (FE) method is implemented because of the complexity of experimental testing A series of load cases; namely, vertical push, wind-up, and suspension roll are introduced for the simulations. The vertical stiffness of the parabolic leaf springs is related to the vehicle load-carrying capability, whereas the wind-up stiffness is associated with vehicle braking. The roll stiffness of the parabolic leaf springs is correlated with the vehicle roll stability. To obtain a better bus performance, two new parabolic leaf spring designs are proposed and simulated. The stress level during the loadings is observed and compared with its design limit. Results indicate that the newly designed high vertical stiffness parabolic spring provides the bus a greater roll stability and a lower stress value compared with the original design. Bus safety and stability is promoted, as well as the load carrying capability. PMID:24298209

Explicit nonlinear finite element geometric analysis of parabolic leaf springs under various loads.

PubMed

Kong, Y S; Omar, M Z; Chua, L B; Abdullah, S

2013-01-01

This study describes the effects of bounce, brake, and roll behavior of a bus toward its leaf spring suspension systems. Parabolic leaf springs are designed based on vertical deflection and stress; however, loads are practically derived from various modes especially under harsh road drives or emergency braking. Parabolic leaf springs must sustain these loads without failing to ensure bus and passenger safety. In this study, the explicit nonlinear dynamic finite element (FE) method is implemented because of the complexity of experimental testing A series of load cases; namely, vertical push, wind-up, and suspension roll are introduced for the simulations. The vertical stiffness of the parabolic leaf springs is related to the vehicle load-carrying capability, whereas the wind-up stiffness is associated with vehicle braking. The roll stiffness of the parabolic leaf springs is correlated with the vehicle roll stability. To obtain a better bus performance, two new parabolic leaf spring designs are proposed and simulated. The stress level during the loadings is observed and compared with its design limit. Results indicate that the newly designed high vertical stiffness parabolic spring provides the bus a greater roll stability and a lower stress value compared with the original design. Bus safety and stability is promoted, as well as the load carrying capability.

Analysis and experimental demonstration of conformal adaptive phase-locked fiber array for laser communications and beam projection applications

NASA Astrophysics Data System (ADS)

Liu, Ling

The primary goal of this research is the analysis, development, and experimental demonstration of an adaptive phase-locked fiber array system for free-space optical communications and laser beam projection applications. To our knowledge, the developed adaptive phase-locked system composed of three fiber collimators (subapertures) with tip-tilt wavefront phase control at each subaperture represents the first reported fiber array system that implements both phase-locking control and adaptive wavefront tip-tilt control capabilities. This research has also resulted in the following innovations: (a) The first experimental demonstration of a phase-locked fiber array with tip-tilt wave-front aberration compensation at each fiber collimator; (b) Development and demonstration of the fastest currently reported stochastic parallel gradient descent (SPGD) system capable of operation at 180,000 iterations per second; (c) The first experimental demonstration of a laser communication link based on a phase-locked fiber array; (d) The first successful experimental demonstration of turbulence and jitter-induced phase distortion compensation in a phase-locked fiber array optical system; (e) The first demonstration of laser beam projection onto an extended target with a randomly rough surface using a conformal adaptive fiber array system. Fiber array optical systems, the subject of this study, can overcome some of the draw-backs of conventional monolithic large-aperture transmitter/receiver optical systems that are usually heavy, bulky, and expensive. The primary experimental challenges in the development of the adaptive phased-locked fiber-array included precise (<5 microrad) alignment of the fiber collimators and development of fast (100kHz-class) phase-locking and wavefront tip-tilt control systems. The precise alignment of the fiber collimator array is achieved through a specially developed initial coarse alignment tool based on high precision piezoelectric picomotors and a dynamic fine alignment mechanism implemented with specially designed and manufactured piezoelectric fiber positioners. Phase-locking of the fiber collimators is performed by controlling the phases of the output beams (beamlets) using integrated polarization-maintaining (PM) fiber-coupled LiNbO3 phase shifters. The developed phase-locking controllers are based on either the SPGD algorithm or the multi-dithering technique. Subaperture wavefront phase tip-tilt control is realized using piezoelectric fiber positioners that are controlled using a computer-based SPGD controller. Both coherent (phase-locked) and incoherent beam combining in the fiber array system are analyzed theoretically and experimentally. Two special fiber-based beam-combining testbeds have been built to demonstrate the technical feasibility of phase-locking compensation prior to free-space operation. In addition, the reciprocity of counter-propagating beams in a phase-locked fiber array system has been investigated. Coherent beam combining in a phase-locking system with wavefront phase tip-tilt compensation at each subaperture is successfully demonstrated when laboratory-simulated turbulence and wavefront jitters are present in the propagation path of the beamlets. In addition, coherent beam combining with a non-cooperative extended target in the control loop is successfully demonstrated.

Complex carbon cycle responses to multi-level warming and supplemental summer rain in the high Arctic.

PubMed

Sharp, Elizabeth D; Sullivan, Patrick F; Steltzer, Heidi; Csank, Adam Z; Welker, Jeffrey M

2013-06-01

The Arctic has experienced rapid warming and, although there are uncertainties, increases in precipitation are projected to accompany future warming. Climate changes are expected to affect magnitudes of gross ecosystem photosynthesis (GEP), ecosystem respiration (ER) and the net ecosystem exchange of CO2 (NEE). Furthermore, ecosystem responses to climate change are likely to be characterized by nonlinearities, thresholds and interactions among system components and the driving variables. These complex interactions increase the difficulty of predicting responses to climate change and necessitate the use of manipulative experiments. In 2003, we established a long-term, multi-level and multi-factor climate change experiment in a polar semidesert in northwest Greenland. Two levels of heating (30 and 60 W m(-2) ) were applied and the higher level was combined with supplemental summer rain. We made plot-level measurements of CO2 exchange, plant community composition, foliar nitrogen concentrations, leaf δ(13) C and NDVI to examine responses to our treatments at ecosystem- and leaf-levels. We confronted simple models of GEP and ER with our data to test hypotheses regarding key drivers of CO2 exchange and to estimate growing season CO2 -C budgets. Low-level warming increased the magnitude of the ecosystem C sink. Meanwhile, high-level warming made the ecosystem a source of C to the atmosphere. When high-level warming was combined with increased summer rain, the ecosystem became a C sink of magnitude similar to that observed under low-level warming. Competition among our ER models revealed the importance of soil moisture as a driving variable, likely through its effects on microbial activity and nutrient cycling. Measurements of community composition and proxies for leaf-level physiology suggest GEP responses largely reflect changes in leaf area of Salix arctica, rather than changes in leaf-level physiology. Our findings indicate that the sign and magnitude of the future High Arctic C budget may depend upon changes in summer rain. © 2013 Blackwell Publishing Ltd.

Collimating lens for light-emitting-diode light source based on non-imaging optics.

PubMed

Wang, Guangzhen; Wang, Lili; Li, Fuli; Zhang, Gongjian

2012-04-10

A collimating lens for a light-emitting-diode (LED) light source is an essential device widely used in lighting engineering. Lens surfaces are calculated by geometrical optics and nonimaging optics. This design progress does not rely on any software optimization and any complex iterative process. This method can be used for any type of light source not only Lambertian. The theoretical model is based on point source. But the practical LED source has a certain size. So in the simulation, an LED chip whose size is 1 mm*1 mm is used to verify the feasibility of the model. The mean results show that the lenses have a very compact structure and good collimating performance. Efficiency is defined as the ratio of the flux in the illuminated plane to the flux from LED source without considering the lens material transmission. Just investigating the loss in the designed lens surfaces, the two types of lenses have high efficiencies of more than 90% and 99%, respectively. Most lighting area (possessing 80% flux) radii are no more than 5 m when the illuminated plane is 200 m away from the light source.

Optical design of a robotic TV camera probe for minimally invasive abdominal surgery

NASA Astrophysics Data System (ADS)

Todaro, Susanna; He, Weiyi; Killinger, Dennis

2011-03-01

Minimally invasive techniques are a promising new field of surgery; however, they limit the surgeon's access points and maneuverability. In order to increase the number of access points in minimally invasive abdominal surgery, a proposed implantable medical probe braces to the abdominal wall and provides illumination and video signal. The probe is cylindrical, about 25 mm long and 10 mm in diameter. A ring of LEDs on the end of the probe illuminates the tissue, and the resulting image is focused onto an HD video detector. It was necessary to apply beam-shaping reflectors to collimate the light onto a small target area, to avoid illuminating areas not picked up by the video. These reflectors were designed and simulated using the optical ray tracing software TracePro. Two LED chip geometries and three types of reflector geometries were analyzed, and the parameters for each geometry were optimized. For the straight-edged reflectors, the intensity patterns and optimization were compared to experimental results. Although parabolic reflectors produced the best collimation, cone reflectors with a 20-degree half-angle produced significant collimation at a much cheaper price. This work was supported by NSF REU program (award No DMR-1004873).

Metamaterial-based lossy anisotropic epsilon-near-zero medium for energy collimation

NASA Astrophysics Data System (ADS)

Shen, Nian-Hai; Zhang, Peng; Koschny, Thomas; Soukoulis, Costas M.

2016-06-01

A lossy anisotropic epsilon-near-zero (ENZ) medium may lead to a counterintuitive phenomenon of omnidirectional bending-to-normal refraction [S. Feng, Phys. Rev. Lett. 108, 193904 (2012), 10.1103/PhysRevLett.108.193904], which offers a fabulous strategy for energy collimation and energy harvesting. Here, in the scope of effective medium theory, we systematically investigate two simple metamaterial configurations, i.e., metal-dielectric-layered structures and the wire medium, to explore the possibility of fulfilling the conditions of such an anisotropic lossy ENZ medium by playing with materials' parameters. Both realistic metamaterial structures and their effective medium equivalences have been numerically simulated, and the results are in excellent agreement with each other. Our study provides clear guidance and therefore paves the way towards the search for proper designs of anisotropic metamaterials for a decent effect of energy collimation and wave-front manipulation.

Reflector automatic acquisition and pointing based on auto-collimation theodolite.

PubMed

Luo, Jun; Wang, Zhiqian; Wen, Zhuoman; Li, Mingzhu; Liu, Shaojin; Shen, Chengwu

2018-01-01

An auto-collimation theodolite (ACT) for reflector automatic acquisition and pointing is designed based on the principle of autocollimators and theodolites. First, the principle of auto-collimation and theodolites is reviewed, and then the coaxial ACT structure is developed. Subsequently, the acquisition and pointing strategies for reflector measurements are presented, which first quickly acquires the target over a wide range and then points the laser spot to the charge coupled device zero position. Finally, experiments are conducted to verify the acquisition and pointing performance, including the calibration of the ACT, the comparison of the acquisition mode and pointing mode, and the accuracy measurement in horizontal and vertical directions. In both directions, a measurement accuracy of ±3″ is achieved. The presented ACT is suitable for automatic pointing and monitoring the reflector over a small scanning area and can be used in a wide range of applications such as bridge structure monitoring and cooperative target aiming.

Reflector automatic acquisition and pointing based on auto-collimation theodolite

NASA Astrophysics Data System (ADS)

Luo, Jun; Wang, Zhiqian; Wen, Zhuoman; Li, Mingzhu; Liu, Shaojin; Shen, Chengwu

2018-01-01

An auto-collimation theodolite (ACT) for reflector automatic acquisition and pointing is designed based on the principle of autocollimators and theodolites. First, the principle of auto-collimation and theodolites is reviewed, and then the coaxial ACT structure is developed. Subsequently, the acquisition and pointing strategies for reflector measurements are presented, which first quickly acquires the target over a wide range and then points the laser spot to the charge coupled device zero position. Finally, experiments are conducted to verify the acquisition and pointing performance, including the calibration of the ACT, the comparison of the acquisition mode and pointing mode, and the accuracy measurement in horizontal and vertical directions. In both directions, a measurement accuracy of ±3″ is achieved. The presented ACT is suitable for automatic pointing and monitoring the reflector over a small scanning area and can be used in a wide range of applications such as bridge structure monitoring and cooperative target aiming.

Content addressable memory project

NASA Technical Reports Server (NTRS)

Hall, J. Storrs; Levy, Saul; Smith, Donald E.; Miyake, Keith M.

1992-01-01

A parameterized version of the tree processor was designed and tested (by simulation). The leaf processor design is 90 percent complete. We expect to complete and test a combination of tree and leaf cell designs in the next period. Work is proceeding on algorithms for the computer aided manufacturing (CAM), and once the design is complete we will begin simulating algorithms for large problems. The following topics are covered: (1) the practical implementation of content addressable memory; (2) design of a LEAF cell for the Rutgers CAM architecture; (3) a circuit design tool user's manual; and (4) design and analysis of efficient hierarchical interconnection networks.

Thermal and epithermal neutron fluence rate gradient measurements by PADC detectors in LINAC radiotherapy treatments-field

NASA Astrophysics Data System (ADS)

Barrera, M. T.; Barros, H.; Pino, F.; Dávila, J.; Sajo-Bohus, L.

2015-07-01

LINAC VARIAN 2100 is where energetic electrons produce Bremsstrahlung radiation, with energies above the nucleon binding energy (E≈5.5MeV). This radiation induce (γ,n) and (e,e'n) reactions mainly in the natural tungsten target material (its total photoneutron cross section is about 4000 mb in a energy range from 9-17 MeV). These reactions may occur also in other components of the system (e.g. multi leaf collimator). During radiation treatment the human body may receive an additional dose inside and outside the treated volume produced by the mentioned nuclear reactions. We measured the neutron density at the treatment table using nuclear track detectors (PADC-NTD). These covered by a boron-converter are employed, including a cadmium filter, to determine the ratio between two groups of neutron energy, i.e. thermal and epithermal. The PADC-NTD detectors were exposed to the radiation field at the iso-center during regular operation of the accelerator. Neutron are determined indirectly by the converting reaction 10B(n,α)7Li the emerging charged particle leave their kinetic energy in the PADC forming a latent nuclear track, enlarged by chemical etching (6N, NaOH, 70°C). Track density provides information on the neutron density through calibration coefficient (˜1.6 104 neutrons /track) obtained by a californium source. We report the estimation of the thermal and epithermal neutron field and its gradient for photoneutrons produced in radiotherapy treatments with 18 MV linear accelerators. It was obsered that photoneutron production have higher rate at the iso-center.

SU-E-T-113: Dose Distribution Using Respiratory Signals and Machine Parameters During Treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imae, T; Haga, A; Saotome, N

Purpose: Volumetric modulated arc therapy (VMAT) is a rotational intensity-modulated radiotherapy (IMRT) technique capable of acquiring projection images during treatment. Treatment plans for lung tumors using stereotactic body radiotherapy (SBRT) are calculated with planning computed tomography (CT) images only exhale phase. Purpose of this study is to evaluate dose distribution by reconstructing from only the data such as respiratory signals and machine parameters acquired during treatment. Methods: Phantom and three patients with lung tumor underwent CT scans for treatment planning. They were treated by VMAT while acquiring projection images to derive their respiratory signals and machine parameters including positions ofmore » multi leaf collimators, dose rates and integrated monitor units. The respiratory signals were divided into 4 and 10 phases and machine parameters were correlated with the divided respiratory signals based on the gantry angle. Dose distributions of each respiratory phase were calculated from plans which were reconstructed from the respiratory signals and the machine parameters during treatment. The doses at isocenter, maximum point and the centroid of target were evaluated. Results and Discussion: Dose distributions during treatment were calculated using the machine parameters and the respiratory signals detected from projection images. Maximum dose difference between plan and in treatment distribution was −1.8±0.4% at centroid of target and dose differences of evaluated points between 4 and 10 phases were no significant. Conclusion: The present method successfully evaluated dose distribution using respiratory signals and machine parameters during treatment. This method is feasible to verify the actual dose for moving target.« less

Measurement and Monte Carlo simulation for energy- and intensity-modulated electron radiotherapy delivered by a computer-controlled electron multileaf collimator.

PubMed

Jin, Lihui; Eldib, Ahmed; Li, Jinsheng; Emam, Ismail; Fan, Jiajin; Wang, Lu; Ma, C-M

2014-01-06

The dosimetric advantage of modulated electron radiotherapy (MERT) has been explored by many investigators and is considered to be an advanced radiation therapy technique in the utilization of electrons. A computer-controlled electron multileaf collimator (MLC) prototype, newly designed to be added onto a Varian linac to deliver MERT, was investigated both experimentally and by Monte Carlo simulations. Four different electron energies, 6, 9, 12, and 15 MeV, were employed for this investigation. To ensure that this device was capable of delivering the electron beams properly, measurements were performed to examine the electron MLC (eMLC) leaf leakage and to determine the appropriate jaw positioning for an eMLC-shaped field in order to eliminate a secondary radiation peak that could otherwise appear outside of an intended radiation field in the case of inappropriate jaw positioning due to insufficient radiation blockage from the jaws. Phase space data were obtained by Monte Carlo (MC) simulation and recorded at the plane just above the jaws for each of the energies (6, 9, 12, and 15 MeV). As an input source, phase space data were used in MC dose calculations for various sizes of the eMLC shaped field (10 × 10 cm2, 3.4 × 3.4 cm2, and 2 × 2 cm2) with respect to a water phantom at source-to-surface distance (SSD) = 94 cm, while the jaws, eMLC leaves, and some accessories associated with the eMLC assembly as well were modeled as modifiers in the calculations. The calculated results were then compared with measurements from a water scanning system. The results showed that jaw settings with 5 mm margins beyond the field shaped by the eMLC were appropriate to eliminate the secondary radiation peak while not widening the beam penumbra; the eMLC leaf leakage measurements ranged from 0.3% to 1.8% for different energies based on in-phantom measurements, which should be quite acceptable for MERT. Comparisons between MC dose calculations and measurements showed agreement within 1%/1 mm based on percentage depth doses (PDDs) and off-axis dose profiles for a range of field sizes for each of the electron energies. Our current work has demonstrated that the eMLC and other relevant components in the linac were correctly modeled and simulated via our in-house MC codes, and the eMLC is capable of accurately delivering electron beams for various eMLC-shaped field sizes with appropriate jaw settings. In the next stage, patient-specific verification with a full MERT plan should be performed.

Measurement and Monte Carlo simulation for energy‐ and intensity‐modulated electron radiotherapy delivered by a computer‐controlled electron multileaf collimator

PubMed Central

Eldib, Ahmed; Li, Jinsheng; Emam, Ismail; Fan, Jiajin; Wang, Lu; Ma, C‐M

2014-01-01

The dosimetric advantage of modulated electron radiotherapy (MERT) has been explored by many investigators and is considered to be an advanced radiation therapy technique in the utilization of electrons. A computer‐controlled electron multileaf collimator (MLC) prototype, newly designed to be added onto a Varian linac to deliver MERT, was investigated both experimentally and by Monte Carlo simulations. Four different electron energies, 6, 9, 12, and 15 MeV, were employed for this investigation. To ensure that this device was capable of delivering the electron beams properly, measurements were performed to examine the electron MLC (eMLC) leaf leakage and to determine the appropriate jaw positioning for an eMLC‐shaped field in order to eliminate a secondary radiation peak that could otherwise appear outside of an intended radiation field in the case of inappropriate jaw positioning due to insufficient radiation blockage from the jaws. Phase space data were obtained by Monte Carlo (MC) simulation and recorded at the plane just above the jaws for each of the energies (6, 9, 12, and 15 MeV). As an input source, phase space data were used in MC dose calculations for various sizes of the eMLC shaped field (10×10 cm2, 3.4×3.4 cm2, and 2×2 cm2) with respect to a water phantom at source‐to‐surface distance (SSD)=94cm, while the jaws, eMLC leaves, and some accessories associated with the eMLC assembly as well were modeled as modifiers in the calculations. The calculated results were then compared with measurements from a water scanning system. The results showed that jaw settings with 5 mm margins beyond the field shaped by the eMLC were appropriate to eliminate the secondary radiation peak while not widening the beam penumbra; the eMLC leaf leakage measurements ranged from 0.3% to 1.8% for different energies based on in‐phantom measurements, which should be quite acceptable for MERT. Comparisons between MC dose calculations and measurements showed agreement within 1%/1mm based on percentage depth doses (PDDs) and off‐axis dose profiles for a range of field sizes for each of the electron energies. Our current work has demonstrated that the eMLC and other relevant components in the linac were correctly modeled and simulated via our in‐house MC codes, and the eMLC is capable of accurately delivering electron beams for various eMLC‐shaped field sizes with appropriate jaw settings. In the next stage, patient‐specific verification with a full MERT plan should be performed. PACS number: 87.55.ne PMID:24423848

Key Elements of a Low Voltage, Ultracompact Plasma Spectrometer

NASA Technical Reports Server (NTRS)

Scime, E. E.; Barrie, A.; Dugas, M.; Elliott, D.; Ellison, S.; Keesee, A. M.; Pollock, C. J.; Rager, A.; Tersteeg, J.

2016-01-01

Taking advantage of technological developments in wafer-scale processing over the past two decades, such as deep etching, 3-D chip stacking, and double-sided lithography, we have designed and fabricated the key elements of an ultracompact 1.5cm (exp 3)plasma spectrometer that requires only low-voltage power supplies, has no microchannel plates, and has a high aperture area to instrument volume ratio. The initial design of the instrument targets the measurement of charged particles in the 3-20keV range with a highly directional field of view and a 100 duty cycle; i.e., the entire energy range Is continuously measured. In addition to reducing mass, size, and voltage requirements, the new design will affect the manufacturing process of plasma spectrometers, enabling large quantities of identical instruments to be manufactured at low individual unit cost. Such a plasma spectrometer is ideal for heliophysics plasma investigations, particularly for small satellite and multispacecraft missions. Two key elements of the instrument have been fabricated: the collimator and the energy analyzer. An initial collimator transparency of 20 with 3deg x 3deg angular resolution was achieved. The targeted 40 collimator transparency appears readily achievable. The targeted energy analyzer scaling factor of 1875 was achieved; i.e.20 keV electrons were selected for only a 10.7V bias voltage in the energy analyzer.

The NuSTAR Mission: Implementation and Science Prospects

NASA Technical Reports Server (NTRS)

Zhang, William W.

2009-01-01

NuSTAR is NASA's next X-ray observatory scheduled to be launched in 2011. It will have two multi-layered X-ray mirror assemblies capable of focusing X-rays in the band of 5 to 80 keV, providing unprecedented detection and imaging sensitivity in a band that only coded-mask or collimated detection has been possible. In this talk I will describe the instrumentation and the prospects of using it to perform various kinds of astronomical studies.

Leaf shape: genetic controls and environmental factors.

PubMed

Tsukaya, Hirokazu

2005-01-01

In recent years, many genes have been identified that are involved in the developmental processes of leaf morphogenesis. Here, I review the mechanisms of leaf shape control in a model plant, Arabidopsis thaliana, focusing on genes that fulfill special roles in leaf development. The lateral, two-dimensional expansion of leaf blades is highly dependent on the determination of the dorsoventrality of the primordia, a defining characteristic of leaves. Having a determinate fate is also a characteristic feature of leaves and is controlled by many factors. Lateral expansion is not only controlled by general regulators of cell cycling, but also by the multi-level regulation of meristematic activities, e.g., specific control of cell proliferation in the leaf-length direction, in leaf margins and in parenchymatous cells. In collaboration with the polarized control of leaf cell elongation, these redundant and specialized regulating systems for cell cycling in leaf lamina may realize the elegantly smooth, flat structure of leaves. The unified, flat shape of leaves is also dependent on the fine integration of cell proliferation and cell enlargement. Interestingly, while a decrease in the number of cells in leaf primordia can trigger a cell volume increase, an increase in the number of cells does not trigger a cell volume decrease. This phenomenon is termed compensation and suggests the existence of some systems for integration between cell cycling and cell enlargement in leaf primordia via cell-cell communication. The environmental adjustment of leaf expansion to light conditions and gravity is also summarized.

The dosimetric impact of inversely optimized arc radiotherapy plan modulation for real-time dynamic MLC tracking delivery.

PubMed

Falk, Marianne; Larsson, Tobias; Keall, Paul; Chul Cho, Byung; Aznar, Marianne; Korreman, Stine; Poulsen, Per; Munck Af Rosenschold, Per

2012-03-01

Real-time dynamic multileaf collimator (MLC) tracking for management of intrafraction tumor motion can be challenging for highly modulated beams, as the leaves need to travel far to adjust for target motion perpendicular to the leaf travel direction. The plan modulation can be reduced by using a leaf position constraint (LPC) that reduces the difference in the position of adjacent MLC leaves in the plan. The purpose of this study was to investigate the impact of the LPC on the quality of inversely optimized arc radiotherapy plans and the effect of the MLC motion pattern on the dosimetric accuracy of MLC tracking delivery. Specifically, the possibility of predicting the accuracy of MLC tracking delivery based on the plan modulation was investigated. Inversely optimized arc radiotherapy plans were created on CT-data of three lung cancer patients. For each case, five plans with a single 358° arc were generated with LPC priorities of 0 (no LPC), 0.25, 0.5, 0.75, and 1 (highest possible LPC), respectively. All the plans had a prescribed dose of 2 Gy × 30, used 6 MV, a maximum dose rate of 600 MU/min and a collimator angle of 45° or 315°. To quantify the plan modulation, an average adjacent leaf distance (ALD) was calculated by averaging the mean adjacent leaf distance for each control point. The linear relationship between the plan quality [i.e., the calculated dose distributions and the number of monitor units (MU)] and the LPC was investigated, and the linear regression coefficient as well as a two tailed confidence level of 95% was used in the evaluation. The effect of the plan modulation on the performance of MLC tracking was tested by delivering the plans to a cylindrical diode array phantom moving with sinusoidal motion in the superior-inferior direction with a peak-to-peak displacement of 2 cm and a cycle time of 6 s. The delivery was adjusted to the target motion using MLC tracking, guided in real-time by an infrared optical system. The dosimetric results were evaluated using gamma index evaluation with static target measurements as reference. The plan quality parameters did not depend significantly on the LPC (p ≥ 0.066), whereas the ALD depended significantly on the LPC (p < 0.001). The gamma index failure rate depended significantly on the ALD, weighted to the percentage of the beam delivered in each control point of the plan (ALD(w)) when MLC tracking was used (p < 0.001), but not for delivery without MLC tracking (p ≥ 0.342). The gamma index failure rate with the criteria of 2% and 2 mm was decreased from > 33.9% without MLC tracking to <31.4% (LPC 0) and <2.2% (LPC 1) with MLC tracking. The results indicate that the dosimetric robustness of MLC tracking delivery of an inversely optimized arc radiotherapy plan can be improved by incorporating leaf position constraints in the objective function without otherwise affecting the plan quality. The dosimetric robustness may be estimated prior to delivery by evaluating the ALD(w) of the plan.

Design optimization of an ironless inductive position sensor for the LHC collimators

NASA Astrophysics Data System (ADS)

Danisi, A.; Masi, A.; Losito, R.; Perriard, Y.

2013-09-01

The Ironless Inductive Position Sensor (I2PS) is an air-cored displacement sensor which has been conceived to be totally immune to external DC/slowly-varying magnetic fields. It can thus be used as a valid alternative to Linear Variable Differential Transformers (LVDTs), which can show a position error in magnetic environments. In addition, since it retains the excellent properties of LVDTs, the I2PS can be used in harsh environments, such as nuclear plants, plasma control and particle accelerators. This paper focuses on the design optimization of the sensor, considering the CERN LHC Collimators as application. In particular, the optimization comes after a complete review of the electromagnetic and thermal modeling of the sensor, as well as the proper choice of the reading technique. The design optimization stage is firmly based on these preliminary steps. Therefore, the paper summarises the sensor's complete development, from its modeling to its actual implementation. A set of experimental measurements demonstrates the sensor's performances to be those expected in the design phase.

Evaluation of a commercially‐available block for spatially fractionated radiation therapy

PubMed Central

Buckey, Courtney; Cashon, Ken; Gutierrez, Alonso; Esquivel, Carlos; Shi, Chengyu; Papanikolaou, Nikos

2010-01-01

In this paper, we present the dosimetric characteristics of a commercially‐produced universal GRID block for spatially fractioned radiation therapy. The dosimetric properties of the GRID block were evaluated. Ionization chamber and film measurements using both Kodak EDR2 and Gafchromic EBT film were performed in a solid water phantom to determine the relative output of the GRID block as well as its spatial dosimetric characteristics. The surface dose under the block and at the openings was measured using ultra thin TLDs. After introducing the GRID block into the treatment planning system, a treatment plan was created using the GRID block and also by creating a GRID pattern using the multi‐leaf collimator. The percent depth doses measured with film showed that there is a shift of the dmax towards shallower depths for both energies (6 MV and 18 MV) under investigation. It was observed that the skin dose at the GRID openings was higher than the corresponding open field by a factor as high as 50% for both photon energies. The profiles showed the transmission under the block was in the order of 15–20% for 6 MV and 30% for 18 MV. The MUs calculated for a real patient using the block were about 80% less than the corresponding MUs for the same plan using the multileaf collimator to define the GRID. Based on this investigation, this brass GRID compensator is a viable alternative to other solid compensators or MLC‐based fields currently in use. Its ease of creation and use give it decided advantages. Its ability to be created once and used for multiple patients (by varying the collimation of the linear accelerator jaws) makes it attractive from a cost perspective. We believe this compensator can be put to clinical use, and will allow more centers to offer GRID therapy to their patients. PACS number: 87.53.Mr

Simultaneous identification of optical constants and PSD of spherical particles by multi-wavelength scattering-transmittance measurement

NASA Astrophysics Data System (ADS)

Zhang, Jun-You; Qi, Hong; Ren, Ya-Tao; Ruan, Li-Ming

2018-04-01

An accurate and stable identification technique is developed to retrieve the optical constants and particle size distributions (PSDs) of particle system simultaneously from the multi-wavelength scattering-transmittance signals by using the improved quantum particle swarm optimization algorithm. The Mie theory are selected to calculate the directional laser intensity scattered by particles and the spectral collimated transmittance. The sensitivity and objective function distribution analysis were conducted to evaluate the mathematical properties (i.e. ill-posedness and multimodality) of the inverse problems under three different optical signals combinations (i.e. the single-wavelength multi-angle light scattering signal, the single-wavelength multi-angle light scattering and spectral transmittance signal, and the multi-angle light scattering and spectral transmittance signal). It was found the best global convergence performance can be obtained by using the multi-wavelength scattering-transmittance signals. Meanwhile, the present technique have been tested under different Gaussian measurement noise to prove its feasibility in a large solution space. All the results show that the inverse technique by using multi-wavelength scattering-transmittance signals is effective and suitable for retrieving the optical complex refractive indices and PSD of particle system simultaneously.

A Maximum NEC Criterion for Compton Collimation to Accurately Identify True Coincidences in PET

PubMed Central

Chinn, Garry; Levin, Craig S.

2013-01-01

In this work, we propose a new method to increase the accuracy of identifying true coincidence events for positron emission tomography (PET). This approach requires 3-D detectors with the ability to position each photon interaction in multi-interaction photon events. When multiple interactions occur in the detector, the incident direction of the photon can be estimated using the Compton scatter kinematics (Compton Collimation). If the difference between the estimated incident direction of the photon relative to a second, coincident photon lies within a certain angular range around colinearity, the line of response between the two photons is identified as a true coincidence and used for image reconstruction. We present an algorithm for choosing the incident photon direction window threshold that maximizes the noise equivalent counts of the PET system. For simulated data, the direction window removed 56%–67% of random coincidences while retaining > 94% of true coincidences from image reconstruction as well as accurately extracted 70% of true coincidences from multiple coincidences. PMID:21317079

Characterization of equipment for shaping and imaging hadron minibeams

NASA Astrophysics Data System (ADS)

Pugatch, V.; Brons, S.; Campbell, M.; Kovalchuk, O.; Llopart, X.; Martínez-Rovira, I.; Momot, Ie.; Okhrimenko, O.; Prezado, Y.; Sorokin, Yu.

2017-11-01

For the feasibility studies of spatially fractionated hadron therapy prototypes of the equipment for hadron minibeams shaping and monitoring have been designed, built and tested. The collimators design was based on Monte Carlo simulations (Gate v.6.2). Slit and matrix collimators were used for minibeams shaping. Gafchromic films, micropixel detectors Timepix in a hybrid as well as metal mode were tested for measuring hadrons intensity distribution in minibeams. An overall beam profile was measured by the metal microstrip detector. The performance of a mini-beams shaping and monitoring equipment was characterized exploring low energy protons at the KINR Tandem generator as well as high energy carbon and oxygen ion beams at HIT (Heidelberg). The results demonstrate reliable performance of the tested equipment for shaping and imaging hadron mini-beam structures.

Optimization of leaf margins for lung stereotactic body radiotherapy using a flattening filter-free beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wakai, Nobuhide, E-mail: wakai@naramed-u.ac.jp; Sumida, Iori; Otani, Yuki

Purpose: The authors sought to determine the optimal collimator leaf margins which minimize normal tissue dose while achieving high conformity and to evaluate differences between the use of a flattening filter-free (FFF) beam and a flattening-filtered (FF) beam. Methods: Sixteen lung cancer patients scheduled for stereotactic body radiotherapy underwent treatment planning for a 7 MV FFF and a 6 MV FF beams to the planning target volume (PTV) with a range of leaf margins (−3 to 3 mm). Forty grays per four fractions were prescribed as a PTV D95. For PTV, the heterogeneity index (HI), conformity index, modified gradient indexmore » (GI), defined as the 50% isodose volume divided by target volume, maximum dose (Dmax), and mean dose (Dmean) were calculated. Mean lung dose (MLD), V20 Gy, and V5 Gy for the lung (defined as the volumes of lung receiving at least 20 and 5 Gy), mean heart dose, and Dmax to the spinal cord were measured as doses to organs at risk (OARs). Paired t-tests were used for statistical analysis. Results: HI was inversely related to changes in leaf margin. Conformity index and modified GI initially decreased as leaf margin width increased. After reaching a minimum, the two values then increased as leaf margin increased (“V” shape). The optimal leaf margins for conformity index and modified GI were −1.1 ± 0.3 mm (mean ± 1 SD) and −0.2 ± 0.9 mm, respectively, for 7 MV FFF compared to −1.0 ± 0.4 and −0.3 ± 0.9 mm, respectively, for 6 MV FF. Dmax and Dmean for 7 MV FFF were higher than those for 6 MV FF by 3.6% and 1.7%, respectively. There was a positive correlation between the ratios of HI, Dmax, and Dmean for 7 MV FFF to those for 6 MV FF and PTV size (R = 0.767, 0.809, and 0.643, respectively). The differences in MLD, V20 Gy, and V5 Gy for lung between FFF and FF beams were negligible. The optimal leaf margins for MLD, V20 Gy, and V5 Gy for lung were −0.9 ± 0.6, −1.1 ± 0.8, and −2.1 ± 1.2 mm, respectively, for 7 MV FFF compared to −0.9 ± 0.6, −1.1 ± 0.8, and −2.2 ± 1.3 mm, respectively, for 6 MV FF. With the heart inside the radiation field, the mean heart dose showed a V-shaped relationship with leaf margins. The optimal leaf margins were −1.0 ± 0.6 mm for both beams. Dmax to the spinal cord showed no clear trend for changes in leaf margin. Conclusions: The differences in doses to OARs between FFF and FF beams were negligible. Conformity index, modified GI, MLD, lung V20 Gy, lung V5 Gy, and mean heart dose showed a V-shaped relationship with leaf margins. There were no significant differences in optimal leaf margins to minimize these parameters between both FFF and FF beams. The authors’ results suggest that a leaf margin of −1 mm achieves high conformity and minimizes doses to OARs for both FFF and FF beams.« less

Image quality phantom and parameters for high spatial resolution small-animal SPECT

NASA Astrophysics Data System (ADS)

Visser, Eric P.; Harteveld, Anita A.; Meeuwis, Antoi P. W.; Disselhorst, Jonathan A.; Beekman, Freek J.; Oyen, Wim J. G.; Boerman, Otto C.

2011-10-01

At present, generally accepted standards to characterize small-animal single photon emission tomographs (SPECT) do not exist. Whereas for small-animal positron emission tomography (PET), the NEMA NU 4-2008 guidelines are available, such standards are still lacking for small-animal SPECT. More specifically, a dedicated image quality (IQ) phantom and corresponding IQ parameters are absent. The structures of the existing PET IQ phantom are too large to fully characterize the sub-millimeter spatial resolution of modern multi-pinhole SPECT scanners, and its diameter will not fit into all scanners when operating in high spatial resolution mode. We therefore designed and constructed an adapted IQ phantom with smaller internal structures and external diameter, and a facility to guarantee complete filling of the smallest rods. The associated IQ parameters were adapted from NEMA NU 4. An additional parameter, effective whole-body sensitivity, was defined since this was considered relevant in view of the variable size of the field of view and the use of multiple bed positions as encountered in modern small-animal SPECT scanners. The usefulness of the phantom was demonstrated for 99mTc in a USPECT-II scanner operated in whole-body scanning mode using a multi-pinhole mouse collimator with 0.6 mm pinhole diameter.

Analysis on the electromagnetic scattering properties of crops at multi-band

NASA Astrophysics Data System (ADS)

Wu, Tao; Wu, Zhensen; Liu, Xiaoyi

2014-12-01

The vector radiative transfer (VRT) theory for active microwave remote sensing and Rayleigh-Gans approximation (GRG) are applied in the study, and an iterative algorithm is used to solve the RT equations, thus we obtain the zeroorder and first-order equation for numerical results. The Michigan Microwave Canopy Scattering (MIMICS) model is simplified to adapt to the crop model, by analyzing body-surface bistatic scattering and backscattering properties between a layer of soybean or wheat consisting of stems and leaves and different underlying soil surface at multi-band (i.e. P, L, S, X, Ku-band), we obtain microwave scattering mechanisms of crop components and the effect of underlying ground on total crop scattering. Stem and leaf are regard as a needle and a circular disk, respectively. The final results are compared with some literature data to verify our calculating method, numerical results show multi-band crop microwave scattering properties differ from scattering angle, azimuth angle and moisture of vegetation and soil, which offer the part needed information for the design of future bistatic radar systems for crop sensing applications.

Objective comparison of lesion detectability in low and medium-energy collimator iodine-123 mIBG images using a channelized Hotelling observer

NASA Astrophysics Data System (ADS)

Gregory, Rebecca A.; Murray, Iain; Gear, Jonathan; Aldridge, Matthew D.; Levine, Daniel; Fowkes, Lucy; Waddington, Wendy A.; Chua, Sue; Flux, Glenn

2017-01-01

Iodine-123 mIBG imaging is widely regarded as a gold standard for diagnostic studies of neuroblastoma and adult neuroendocrine cancer although the optimal collimator for tumour imaging remains undetermined. Low-energy (LE) high-resolution (HR) collimators provide superior spatial resolution. However due to septal penetration of high-energy photons these provide poorer contrast than medium-energy (ME) general-purpose (GP) collimators. LEGP collimators improve count sensitivity. The aim of this study was to objectively compare the lesion detection efficiency of each collimator to determine the optimal collimator for diagnostic imaging. The septal penetration and sensitivity of each collimator was assessed. Planar images of the patient abdomen were simulated with static scans of a Liqui-Phil™ anthropomorphic phantom with lesion-shaped inserts, acquired with LE and ME collimators on 3 different manufacturers’ gamma camera systems (Skylight (Philips), Intevo (Siemens) and Discovery (GE)). Two-hundred normal and 200 single-lesion abnormal images were created for each collimator. A channelized Hotelling observer (CHO) was developed and validated to score the images for the likelihood of an abnormality. The areas under receiver-operator characteristic (ROC) curves, Az, created from the scores were used to quantify lesion detectability. The CHO ROC curves for the LEHR collimators were inferior to the GP curves for all cameras. The LEHR collimators resulted in statistically significantly smaller Azs (p  <  0.05), of on average 0.891  ±  0.004, than for the MEGP collimators, 0.933  ±  0.004. In conclusion, the reduced background provided by MEGP collimators improved 123I mIBG image lesion detectability over LEHR collimators that provided better spatial resolution.

Optimal Shape of a Gamma-ray Collimator: single vs double knife edge

NASA Astrophysics Data System (ADS)

Metz, Albert; Hogenbirk, Alfred

2017-09-01

Gamma-ray collimators in nuclear waste scanners are used for selecting a narrow vertical segment in activity measurements of waste vessels. The system that is used by NRG uses tapered slit collimators of both the single and double knife edge type. The properties of these collimators were investigated by means of Monte Carlo simulations. We found that single knife edge collimators are highly preferable for a conservative estimate of the activity of the waste vessels. These collimators show much less dependence on the angle of incidence of the radiation than double knife edge collimators. This conclusion also applies to cylindrical collimators of the single knife edge type, that are generally used in medical imaging spectroscopy.

Extending the generality of leaf economic design principles in the cycads, an ancient lineage.

PubMed

Zhang, Yong-Jiang; Cao, Kun-Fang; Sack, Lawren; Li, Nan; Wei, Xue-Mei; Goldstein, Guillermo

2015-04-01

Cycads are the most ancient lineage of living seed plants, but the design of their leaves has received little study. We tested whether cycad leaves are governed by the same fundamental design principles previously established for ferns, conifers and angiosperms, and characterized the uniqueness of this relict lineage in foliar trait relationships. Leaf structure, photosynthesis, hydraulics and nutrient composition were studied in 33 cycad species from nine genera and three families growing in two botanical gardens. Cycads varied greatly in leaf structure and physiology. Similarly to other lineages, light-saturated photosynthetic rate per mass (Am ) was related negatively to leaf mass per area and positively to foliar concentrations of chlorophyll, nitrogen (N), phosphorus and iron, but unlike angiosperms, leaf photosynthetic rate was not associated with leaf hydraulic conductance. Cycads had lower photosynthetic N use efficiency and higher photosynthetic performance relative to hydraulic capacity compared with other lineages. These findings extend the relationships shown for foliar traits in angiosperms to the cycads. This functional convergence supports the modern synthetic understanding of leaf design, with common constraints operating across lineages, even as they highlight exceptional aspects of the biology of this key relict lineage. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

WE-G-16A-01: Evolution of Radiation Treatment Planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rothenberg, L; Mohan, R; Van Dyk, J

Welcome and Introduction - Lawrence N. Rothenberg This symposium is one a continuing series of presentations at AAPM Annual Meetings on the historical aspects of medical physics, radiology, and radiation oncology that have been organized by the AAPM History Committee. Information on previous presentations including “Early Developments in Teletherapy” (Indianapolis 2013), “Historical Aspects of Cross-Sectional Imaging” (Charlotte 2012), “Historical Aspects of Brachytherapy” (Vancouver 2011), “50 Years of Women in Medical Physics” (Houston 2008), and “Roentgen's Early Investigations” (Minneapolis 2007) can be found in the Education Section of the AAPM Website. The Austin 2014 History Symposium will be on “Evolution ofmore » Radiation Treatment Planning.” Overview - Radhe Mohan Treatment planning is one of the most critical components in the chain of radiation therapy of cancers. Treatment plans of today contain a wide variety of sophisticated information conveying the potential clinical effectiveness of the designed treatment to practitioners. Examples of such information include dose distributions superimposed on three- or even four-dimensional anatomic images; dose volume histograms, dose, dose-volume and dose-response indices for anatomic structures of interest; etc. These data are used for evaluating treatment plans and for making treatment decisions. The current state-of-the-art has evolved from the 1940s era when the dose to the tumor and normal tissues was estimated approximately by manual means. However, the symposium will cover the history of the field from the late-1950's, when computers were first introduced for treatment planning, to the present state involving the use of high performance computing and advanced multi-dimensional anatomic, functional and biological imaging, focusing only on external beam treatment planning. The symposium will start with a general overview of the treatment planning process including imaging, structure delineation, assignment of dose requirements, consideration of uncertainties, selection of beam configurations and shaping of beams, and calculations, optimization and evaluation of dose distributions. This will be followed by three presentations covering the evolution of treatment planning, which parallels the evolution of computers, availability of advanced volumetric imaging and the development of novel technologies such as dynamic multi-leaf collimators and online image guidance. This evolution will be divided over three distinct periods - prior to 1970's, the 2D era; from 1980 to the mid-1990's, the 3D era; and from the mid 1990's to today, the IMRT era. When the World was Flat: The Two-Dimensional Radiation Therapy Era” - Jacob Van Dyk In the 2D era, anatomy was defined with the aid of solder wires, special contouring devices and projection x-rays. Dose distributions were calculated manually from single field, flat surface isodoses on transparencies. Precalculated atlases of generic dose distributions were produced by the International Atomic Energy Agency. Massive time-shared main frames and mini-computers were used to compute doses at individual points or dose distributions in a single plane. Beam shapes were generally rectangular, with wedges, missing tissue compensators and occasional blocks to shield critical structures. Dose calculations were measurement-based or they used primary and scatter calculations based on scatter-air ratio methodologies. Dose distributions were displayed on line printers as alpha-numeric character maps or isodose patterns made with pen plotters. More than Pretty Pictures: 3D Treatment Planning and Conformal Therapy - Benedick A. Fraass The introduction of computed tomography allowed the delineation of anatomy three-dimensionally and, supported partly by contracts from the National Cancer Institute, made possible the introduction and clinical use of 3D treatment planning, leading to development and use of 3D conformal therapy in the 1980's. 3D computer graphics and 3D anatomical structure definitions made possible Beam's Eye View (BEV) displays, making conformal beam shaping and much more sophisticated beam arrangements possible. These conformal plans significantly improved target dose coverage as well as normal tissue sparing. The use of dose volume histograms, gross/clinical/planning target volumes, MRI and PET imaging, multileaf collimators, and computer-controlled treatment delivery made sophisticated planning approaches practical. The significant improvements in dose distributions and analysis achievable with 3D conformal therapy made possible formal dose escalation and normal tissue tolerance clinical studies that set new and improved expectations for improved local control and decreasing complications in many clinical sites. From the Art to the State of the Art: Inverse Planning and IMRT - Thomas R. Bortfeld While the potential of intensity modulation was recognized in the mid- 1980's, intensity-modulated radiotherapy (IMRT) did not become a reality until the mid-1990's. Broad beams of photons could be sub-divided into narrow beamlets whose intensities could be determined using sophisticated optimization algorithms to appropriately balance tumor dose with normal tissue sparing. The development of dynamic multi-leaf collimators (on conventional linear accelerators as well as in helical delivery devices) enabled the efficient delivery of IMRT. The evolution of IMRT planning is continuing in the form of Volumetric Modulated Arc Therapy (VMAT) and through advanced optimization tools, such as multi-criteria optimization, automated IMRT planning, and robust optimization to protect dose distributions against uncertainties. IMRT also facilitates “dose painting” in which different sub-volumes of the target are prescribed different doses. Clearly, these advancements are being made possible by the increasing power and lower cost of computers and developments in other fields such as imaging and operations research. Summary - Radhe Mohan The history does not end here. The advancement of treatment planning is expected to continue, leading to further automation and improvements in conformality and robustness of dose distributions, particularly in the area of particle therapy. Radiobiological modeling will gain emphasis as part of the planning process. Learning Objectives: The scope of changes in technology and the capabilities of radiation treatment planning The impact of these changes in the quality of treatment plans and optimality of dose distributions The impact of development in other fields (imaging, computers, operations research, etc.) on the evolution of radiation treatment planning.« less

Effect of Multiangular Observations on Crop Chlorophyll Content Retrieval Using Field Top-Of Spectrometer Data

NASA Astrophysics Data System (ADS)

Jiao, Q.; Liu, L.; Zhang, B.

2017-12-01

Leaf chlorophyll content is an important indicator of crop growth condition that determines final crop yield. A lot of research on remote sensing of leaf chlorophyll content were based on reflectance data acquired from nadir direction. However, reflectance data at nadir may be affected by soil background. In fact, many satellite sensors with capability of chlorophyll retrieval, like the 68.5 degrees field-of-view MERIS, have produced large multiangular data. This study tries to assess the anisotropic effect on the retrieval of leaf chlorophyll content using field hyperspectral data of wheat canopy. The field multi-angle observation experiment of winter wheat was carried out in April 2017 in Xiaotangshan agriculture demonstration study site in Beijing. Field canopy spectra and leaf chlorophyll content of winter wheat were measured. The most used indices for chlorophyll content retrieval, such as CIred-edge, REP, MTCI, MCARI/OSAVI[705,750], TCARI/OSAVI[705,750], were calculated based on the filed multiangular reflectance. The ratio index TCARI/OSAVI owned the best results in estimating leaf chlorophyll content (R2 of 0.62) among all the selected indices, when using the top-of-canopy reflectance at nadir. The determination coefficient of the relationship of TCARI/OSAVI with chlorophyll content reached its peak (R2 of 0.70) at angle of 15 degrees, and the minimum R2 value of only 0.25 at angle of 60 degrees. The MTCI got the peak of determination coefficient (R2 of 0.63) at angle of 15 degrees and the minimum value (R2 of 0.57) for 60 degrees. Our results showed the MTCI could keep a more satisfactory correlation with leaf chlorophyll content of winter wheat, however the mean values of the MTCI basically decreased as the observation angle increases. This work shows the strong anisotropic effects of top-of-canopy reflectance which influences most of selected popular chlorophyll indices. If spectral index selection is proper, multiangular remote sensing could produce higher accuracy for leaf chlorophyll content retrieval than only using nadir observation. Multi-angular remote sensing has the potential of leaf chlorophyll content retrieval for diagnosis of crop nitrogen stress or water stress.

Incorporating geometric ray tracing to generate initial conditions for intensity modulated arc therapy optimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oliver, Mike; Gladwish, Adam; Craig, Jeff

2008-07-15

Purpose and background: Intensity modulated arc therapy (IMAT) is a rotational variant of Intensity modulated radiation therapy (IMRT) that is achieved by allowing the multileaf collimator (MLC) positions to vary as the gantry rotates around the patient. This work describes a method to generate an IMAT plan through the use of a fast ray tracing technique based on dosimetric and geometric information for setting initial MLC leaf positions prior to final IMAT optimization. Methods and materials: Three steps were used to generate an IMAT plan. The first step was to generate arcs based on anatomical contours. The second step wasmore » to generate ray importance factor (RIF) maps by ray tracing the dose distribution inside the planning target volume (PTV) to modify the MLC leaf positions of the anatomical arcs to reduce the maximum dose inside the PTV. The RIF maps were also segmented to create a new set of arcs to improve the dose to low dose voxels within the PTV. In the third step, the MLC leaf positions from all arcs were put through a leaf position optimization (LPO) algorithm and brought into a fast Monte Carlo dose calculation engine for a final dose calculation. The method was applied to two phantom cases, a clinical prostate case and the Radiological Physics Center (RPC)'s head and neck phantom. The authors assessed the plan improvements achieved by each step and compared plans with and without using RIF. They also compared the IMAT plan with an IMRT plan for the RPC phantom. Results: All plans that incorporated RIF and LPO had lower objective function values than those that incorporated LPO only. The objective function value was reduced by about 15% after the generation of RIF arcs and 52% after generation of RIF arcs and leaf position optimization. The IMAT plan for the RPC phantom had similar dose coverage for PTV1 and PTV2 (the same dose volume histogram curves), however, slightly lower dose to the normal tissues compared to a six-field IMRT plan. Conclusion: The use of a ray importance factor can generate initial IMAT arcs efficiently for further MLC leaf position optimization to obtain more favorable IMAT plan.« less

Determination of Spring Onset and Growing Season Duration using Satellite Measurements

NASA Technical Reports Server (NTRS)

Min, Q.; Lin, Bing

2006-01-01

An integrated approach to retrieve microwave emissivity difference vegetation index (EDVI) over land regions has been developed from combined multi-platform/multi-sensor satellite measurements, including SSM/I measurements. A possible relationship of the remotely sensed EDVI and the leaf physiology of canopy is exploited at the Harvard Forest site for two growing seasons. This study finds that the EDVI is sensitive to leaf development through vegetation water content of the crown layer of the forest canopy, and has demonstrated that the spring onset and growing season duration can be determined accurately from the time series of satellite estimated EDVI within uncertainties about 3 and 7 days for spring onsets and growing season duration, respectively, compared to in-situ observations. The leaf growing stage may also be quantitatively monitored by a normalized EDVI. Since EDVI retrievals from satellite are generally possible during both daytime and nighttime under non-rain conditions, the EDVI technique studied here may provide higher temporal resolution observations for monitoring the onset of spring and the duration of growing season compared to currently operational satellite methods.

On the use of an analytic source model for dose calculations in precision image-guided small animal radiotherapy.

PubMed

Granton, Patrick V; Verhaegen, Frank

2013-05-21

Precision image-guided small animal radiotherapy is rapidly advancing through the use of dedicated micro-irradiation devices. However, precise modeling of these devices in model-based dose-calculation algorithms such as Monte Carlo (MC) simulations continue to present challenges due to a combination of very small beams, low mechanical tolerances on beam collimation, positioning and long calculation times. The specific intent of this investigation is to introduce and demonstrate the viability of a fast analytical source model (AM) for use in either investigating improvements in collimator design or for use in faster dose calculations. MC models using BEAMnrc were developed for circular and square fields sizes from 1 to 25 mm in diameter (or side) that incorporated the intensity distribution of the focal spot modeled after an experimental pinhole image. These MC models were used to generate phase space files (PSFMC) at the exit of the collimators. An AM was developed that included the intensity distribution of the focal spot, a pre-calculated x-ray spectrum, and the collimator-specific entrance and exit apertures. The AM was used to generate photon fluence intensity distributions (ΦAM) and PSFAM containing photons radiating at angles according to the focal spot intensity distribution. MC dose calculations using DOSXYZnrc in a water and mouse phantom differing only by source used (PSFMC versus PSFAM) were found to agree within 7% and 4% for the smallest 1 and 2 mm collimator, respectively, and within 1% for all other field sizes based on depth dose profiles. PSF generation times were approximately 1200 times faster for the smallest beam and 19 times faster for the largest beam. The influence of the focal spot intensity distribution on output and on beam shape was quantified and found to play a significant role in calculated dose distributions. Beam profile differences due to collimator alignment were found in both small and large collimators sensitive to shifts of 1 mm with respect to the central axis.

Cleaning Insertions and Collimation Challenges

NASA Astrophysics Data System (ADS)

Redaelli, S.; Appleby, R. B.; Bertarelli, A.; Bruce, R.; Jowett, J. M.; Lechner, A.; Losito, R.

High-performance collimation systems are essential for operating efficiently modern hadron machine with large beam intensities. In particular, at the LHC the collimation system ensures a clean disposal of beam halos in the superconducting environment. The challenges of the HL-LHC study pose various demanding requests for beam collimation. In this paper we review the present collimation system and its performance during the LHC Run 1 in 2010-2013. Various collimation solutions under study to address the HL-LHC requirements are then reviewed, identifying the main upgrade baseline and pointing out advanced collimation concept for further enhancement of the performance.

Radiography by selective detection of scatter field velocity components

NASA Technical Reports Server (NTRS)

Dugan, Edward T. (Inventor); Jacobs, Alan M. (Inventor); Shedlock, Daniel (Inventor)

2007-01-01

A reconfigurable collimated radiation detector, system and related method includes at least one collimated radiation detector. The detector has an adjustable collimator assembly including at least one feature, such as a fin, optically coupled thereto. Adjustments to the adjustable collimator selects particular directions of travel of scattered radiation emitted from an irradiated object which reach the detector. The collimated detector is preferably a collimated detector array, where the collimators are independently adjustable. The independent motion capability provides the capability to focus the image by selection of the desired scatter field components. When an array of reconfigurable collimated detectors is provided, separate image data can be obtained from each of the detectors and the respective images cross-correlated and combined to form an enhanced image.

Simple luminosity normalization of greenness, yellowness and redness/greenness for comparison of leaf spectral profiles in multi-temporally acquired remote sensing images.

PubMed

Doi, Ryoichi

2012-09-01

Observation of leaf colour (spectral profiles) through remote sensing is an effective method of identifying the spatial distribution patterns of abnormalities in leaf colour, which enables appropriate plant management measures to be taken. However, because the brightness of remote sensing images varies with acquisition time, in the observation of leaf spectral profiles in multi-temporally acquired remote sensing images, changes in brightness must be taken into account. This study identified a simple luminosity normalization technique that enables leaf colours to be compared in remote sensing images over time. The intensity values of green and yellow (green+red) exhibited strong linear relationships with luminosity (R2 greater than 0.926) when various invariant rooftops in Bangkok or Tokyo were spectralprofiled using remote sensing images acquired at different time points. The values of the coefficient and constant or the coefficient of the formulae describing the intensity of green or yellow were comparable among the single Bangkok site and the two Tokyo sites, indicating the technique's general applicability. For single rooftops, the values of the coefficient of variation for green, yellow, and red/green were 16% or less (n=6-11), indicating an accuracy not less than those of well-established remote sensing measures such as the normalized difference vegetation index. After obtaining the above linear relationships, raw intensity values were normalized and a temporal comparison of the spectral profiles of the canopies of evergreen and deciduous tree species in Tokyo was made to highlight the changes in the canopies' spectral profiles. Future aspects of this technique are discussed herein.

SWIMRT: A graphical user interface using the sliding window algorithm to construct a fluence map machine file

PubMed Central

Chow, James C.L.; Grigorov, Grigor N.; Yazdani, Nuri

2006-01-01

A custom‐made computer program, SWIMRT, to construct “multileaf collimator (MLC) machine” file for intensity‐modulated radiotherapy (IMRT) fluence maps was developed using MATLAB® and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment‐planning system such as Pinnacle3 or create his or her own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and the dimension of the imported fluence field, the user can use associated image‐processing tools such as field resizing and edge trimming to modify the imported map. When the processed fluence map is suitable, a “MLC machine” file is generated for our Varian 21 EX linear accelerator with a 120‐leaf Millennium MLC. This machine file is transferred to the MLC console of the LINAC to control the continuous motions of the leaves during beam irradiation. An IMRT field is then irradiated with the 2D intensity profiles, and the irradiated profiles are compared to the imported or modified fluence map. This program was verified and tested using film dosimetry to address the following uncertainties: (1) the mechanical limitation due to the leaf width and maximum traveling speed, and (2) the dosimetric limitation due to the leaf leakage/transmission and penumbra effect. Because the fluence map can be edited, resized, and processed according to the requirement of a study, SWIMRT is essential in studying and investigating the IMRT technique using the sliding window algorithm. Using this program, future work on the algorithm may include redistributing the time space between segmental fields to enhance the fluence resolution, and readjusting the timing of each leaf during delivery to avoid small fields. Possible clinical utilities and examples for SWIMRT are given in this paper. PACS numbers: 87.53.Kn, 87.53.St, 87.53.Uv PMID:17533330

A time-domain fluorescence diffusion optical tomography system for breast tumor diagnosis

NASA Astrophysics Data System (ADS)

Zhang, Wei; Gao, Feng; Wu, LinHui; Ma, Wenjuan; Yang, Fang; Zhou, Zhongxing; Zhang, Limin; Zhao, Huijuan

2011-02-01

A prototype time-domain fluorescence diffusion optical tomography (FDOT) system using near-infrared light is presented. The system employs two pulsed light sources, 32 source fibers and 32 detection channels, working separately for acquiring the temporal distribution of the photon flux on the tissue surface. The light sources are provided by low power picosecond pulsed diode lasers at wavelengths of 780 nm and 830 nm, and a 1×32-fiber-optic-switch sequentially directs light sources to the object surface through 32 source fibers. The light signals re-emitted from the object are collected by 32 detection fibers connected to four 8×1 fiber-optic-switch and then routed to four time-resolved measuring channels, each of which consists of a collimator, a filter wheel, a photomultiplier tube (PMT) photon-counting head and a time-correlated single photon counting (TCSPC) channel. The performance and efficacy of the designed multi-channel PMT-TCSPC system are assessed by reconstructing the fluorescent yield and lifetime images of a solid phantom.

MuSICa image slicer prototype at 1.5-m GREGOR solar telescope

NASA Astrophysics Data System (ADS)

Calcines, A.; López, R. L.; Collados, M.; Vega Reyes, N.

2014-07-01

Integral Field Spectroscopy is an innovative technique that is being implemented in the state-of-the-art instruments of the largest night-time telescopes, however, it is still a novelty for solar instrumentation. A new concept of image slicer, called MuSICa (Multi-Slit Image slicer based on collimator-Camera), has been designed for the integral field spectrograph of the 4-m European Solar Telescope. This communication presents an image slicer prototype of MuSICa for GRIS, the spectrograph of the 1.5-m GREGOR solar telescope located at the Observatory of El Teide. MuSICa at GRIS reorganizes a 2-D field of view of 24.5 arcsec into a slit of 0.367 arcsec width by 66.76 arcsec length distributed horizontally. It will operate together with the TIP-II polarimeter to offer high resolution integral field spectropolarimetry. It will also have a bidimensional field of view scanning system to cover a field of view up to 1 by 1 arcmin.

Algorithm for retrieving vegetative canopy and leaf parameters from multi- and hyperspectral imagery

NASA Astrophysics Data System (ADS)

Borel, Christoph

2009-05-01

In recent years hyper-spectral data has been used to retrieve information about vegetative canopies such as leaf area index and canopy water content. For the environmental scientist these two parameters are valuable, but there is potentially more information to be gained as high spatial resolution data becomes available. We developed an Amoeba (Nelder-Mead or Simplex) based program to invert a vegetative canopy radiosity model coupled with a leaf (PROSPECT5) reflectance model and modeled for the background reflectance (e.g. soil, water, leaf litter) to a measured reflectance spectrum. The PROSPECT5 leaf model has five parameters: leaf structure parameter Nstru, chlorophyll a+b concentration Cab, carotenoids content Car, equivalent water thickness Cw and dry matter content Cm. The canopy model has two parameters: total leaf area index (LAI) and number of layers. The background reflectance model is either a single reflectance spectrum from a spectral library() derived from a bare area pixel on an image or a linear mixture of soil spectra. We summarize the radiosity model of a layered canopy and give references to the leaf/needle models. The method is then tested on simulated and measured data. We investigate the uniqueness, limitations and accuracy of the retrieved parameters on canopy parameters (low, medium and high leaf area index) spectral resolution (32 to 211 band hyperspectral), sensor noise and initial conditions.

Unveiling Members of Colletotrichum acutatum Species Complex Causing Colletotrichum Leaf Disease of Hevea brasiliensis in Sri Lanka.

PubMed

Hunupolagama, D M; Chandrasekharan, N V; Wijesundera, W S S; Kathriarachchi, H S; Fernando, T H P S; Wijesundera, R L C

2017-06-01

Colletotrichum is an important fungal genus with great diversity, which causes anthracnose of a variety of crop plants including rubber trees. Colletotrichum acutatum and Colletotrichum gloeosporioides have been identified as the major causative agents of Colletotrichum leaf disease of rubber trees in Sri Lanka based on morphology, pathogenicity, and the analysis of internally transcribed spacer sequences of the nuclear ribosomal DNA. This study has been conducted to investigate the members of the C. acutatum species complex causing rubber leaf disease using a morphological and multi gene approach. For the first time in Sri Lanka, Colletotrichum simmondsii, Colletotrichum laticiphilum, Colletotrichum nymphaeae, and Colletotrichum citri have been identified as causative agents of Colletotrichum leaf disease in addition to C. acutatum s. str. Among them, C. simmondsii has been recognized as the major causative agent.

Simulations and measurements of beam loss patterns at the CERN Large Hadron Collider

NASA Astrophysics Data System (ADS)

Bruce, R.; Assmann, R. W.; Boccone, V.; Bracco, C.; Brugger, M.; Cauchi, M.; Cerutti, F.; Deboy, D.; Ferrari, A.; Lari, L.; Marsili, A.; Mereghetti, A.; Mirarchi, D.; Quaranta, E.; Redaelli, S.; Robert-Demolaize, G.; Rossi, A.; Salvachua, B.; Skordis, E.; Tambasco, C.; Valentino, G.; Weiler, T.; Vlachoudis, V.; Wollmann, D.

2014-08-01

The CERN Large Hadron Collider (LHC) is designed to collide proton beams of unprecedented energy, in order to extend the frontiers of high-energy particle physics. During the first very successful running period in 2010-2013, the LHC was routinely storing protons at 3.5-4 TeV with a total beam energy of up to 146 MJ, and even higher stored energies are foreseen in the future. This puts extraordinary demands on the control of beam losses. An uncontrolled loss of even a tiny fraction of the beam could cause a superconducting magnet to undergo a transition into a normal-conducting state, or in the worst case cause material damage. Hence a multistage collimation system has been installed in order to safely intercept high-amplitude beam protons before they are lost elsewhere. To guarantee adequate protection from the collimators, a detailed theoretical understanding is needed. This article presents results of numerical simulations of the distribution of beam losses around the LHC that have leaked out of the collimation system. The studies include tracking of protons through the fields of more than 5000 magnets in the 27 km LHC ring over hundreds of revolutions, and Monte Carlo simulations of particle-matter interactions both in collimators and machine elements being hit by escaping particles. The simulation results agree typically within a factor 2 with measurements of beam loss distributions from the previous LHC run. Considering the complex simulation, which must account for a very large number of unknown imperfections, and in view of the total losses around the ring spanning over 7 orders of magnitude, we consider this an excellent agreement. Our results give confidence in the simulation tools, which are used also for the design of future accelerators.

Investigating a multi-purpose target for electron linac based photoneutron sources for BNCT of deep-seated tumors

NASA Astrophysics Data System (ADS)

Masoudi, S. Farhad; Rasouli, Fatemeh S.

2015-08-01

Recent studies in BNCT have focused on investigating appropriate neutron sources as alternatives for nuclear reactors. As the most prominent facilities, the electron linac based photoneutron sources benefit from two consecutive reactions, (e, γ) and (γ, n). The photoneutron sources designed so far are composed of bipartite targets which involve practical problems and are far from the objective of achieving an optimized neutron source. This simulation study deals with designing a compact, optimized, and geometrically simple target for a photoneutron source based on an electron linac. Based on a set of MCNPX simulations, tungsten is found to have the potential of utilizing as both photon converter and photoneutron target. Besides, it is shown that an optimized dimension for such a target slows-down the produced neutrons toward the desired energy range while keeping them economy, which makes achieving the recommended criteria for BNCT of deep-tumors more available. This multi-purpose target does not involve complicated designing, and can be considered as a significant step toward finding application of photoneutron sources for in-hospital treatments. In order to shape the neutron beam emitted from such a target, the beam is planned to pass through an optimized arrangement of materials composed of moderators, filters, reflector, and collimator. By assessment with the recommended in-air parameters, it is shown that the designed beam provides high intensity of desired neutrons, as well as low background contamination. The last section of this study is devoted to investigate the performance of the resultant beam in deep tissue. A typical simulated liver tumor, located within a phantom of human body, was subjected to the irradiation of the designed spectrum. The dosimetric results, including evaluated depth-dose curves and carried out in-phantom parameters show that the proposed configuration establishes acceptable agreement between the appropriate neutron intensity, and penetrating deep in tissue in a reasonable treatment time.

Investigation of converging and collimated beam instrument geometry on specular gloss measurements

NASA Astrophysics Data System (ADS)

Zwinkels, Joanne C.; Côté, Éric; Morgan, John

2018-02-01

Specular gloss is an important appearance property of a wide variety of manufactured goods. Depending upon the application, e.g. paints, paper, ceramics, etc. different instrument designs and measurement geometries are specified in standard test methods. For a given specular angle, these instrument designs can be broadly classified as converging beam (TAPPI method) and collimated beam (DIN method). In recent comparisons of specular gloss measurements using different glossmeters, very large standard deviations have been reported, well exceeding the manufacturers claims. In this paper, we investigate the effect of instrument beam geometry on gloss measurements. These results indicate that this difference in beam geometry can give the magnitude of gloss differences reported in these comparisons and highlights the importance of educating the user community of best measurement practices and obtaining appropriate traceability for their glossmeters.

The effect of environmental uncertainty on morphological design and fluid balance in Sarracenia purpurea L.

PubMed

Kingsolver, Joel

1981-03-01

To explore principles of organismic design in fluctuating environments, morphological design of the leaf of the pitcher-plant, Sarracenia purpurea, was studied for a population in northern Michigan. The design criterion focused upon the leaf shape and minimum size which effectively avoids leaf desiccation (complete loss of fluid from the leaf cavity) in the face of fluctuating rainfall and meteorological conditions. Bowl- and pitcher-shaped leaves were considered. Simulations show that the pitcher geometry experiences less frequent desiccation than bowls of the same size. Desiccation frequency is inversely related to leaf size; the size distribution of pitcher leaves in the field shows that the majority of pitchers desiccate only 1-3 times per season on average, while smaller pitchers may average up to 8 times per season. A linear filter model of an organism in a fluctuating environment is presented, in which the organism selectively filters the temporal patterns of environmental input. General measures of rainfall predictability based upon information theory and spectral analysis are consistent with the model of a pitcher leaf as a low-pass (frequency) filter which avoids desiccation by eliminating high-frequency rainfall variability.

Automated assembly of fast-axis collimation (FAC) lenses for diode laser bar modules

NASA Astrophysics Data System (ADS)

Miesner, Jörn; Timmermann, Andre; Meinschien, Jens; Neumann, Bernhard; Wright, Steve; Tekin, Tolga; Schröder, Henning; Westphalen, Thomas; Frischkorn, Felix

2009-02-01

Laser diodes and diode laser bars are key components in high power semiconductor lasers and solid state laser systems. During manufacture, the assembly of the fast axis collimation (FAC) lens is a crucial step. The goal of our activities is to design an automated assembly system for high volume production. In this paper the results of an intermediate milestone will be reported: a demonstration system was designed, realized and tested to prove the feasibility of all of the system components and process features. The demonstration system consists of a high precision handling system, metrology for process feedback, a powerful digital image processing system and tooling for glue dispensing, UV curing and laser operation. The system components as well as their interaction with each other were tested in an experimental system in order to glean design knowledge for the fully automated assembly system. The adjustment of the FAC lens is performed by a series of predefined steps monitored by two cameras concurrently imaging the far field and the near field intensity distributions. Feedback from these cameras processed by a powerful and efficient image processing algorithm control a five axis precision motion system to optimize the fast axis collimation of the laser beam. Automated cementing of the FAC to the diode bar completes the process. The presentation will show the system concept, the algorithm of the adjustment as well as experimental results. A critical discussion of the results will close the talk.

Optical elements design of optical pick-up with characteristics of read-out spot for high density optical storage

NASA Astrophysics Data System (ADS)

Li, Lihua; Ma, Jianshe; Liu, Lin; Pan, Longfa; Zhang, Jianyong; Lu, Junhui

2005-09-01

It is well known that the optical pick-up (OPU) plays a very important role in optical storage system. And the quality of OPU can be measured by the characteristics of OPU read-out spot for high density optical storage. Therefore this paper mainly designs an OPU model for high density optical storage to study the characteristics of OPU read-out spot. Firstly it analyses the optical read-out principle in OPU and contrives an optical read-out system based on the hereinbefore theory. In this step it chiefly designs the grating, splitter, collimator lens and objective lens. Secondly based on the aberrations analysis and theory involved by the splitter, the collimator lens and the optical lens, the paper uses the software CODE V to calculate the aberrations and to optimize the optical read-out system. Then the author can receive an ideal OPU read-out spot for high density optical storage and obtain the characteristics of the ideal OPU read-out spot. At the same time this paper analyses some influence factors which can directly affect the characteristics of the OPU read-out spot. Thirdly according to the up data the author practically manufactures a real optical pick-up to validate the hereinbefore designed optical read-out system. And it uses the Optical Spot Analyzer to get the image of the read-out spot. Comparing the ideal image to the actual image of the designed optical read-out system, the author finds out that the upwards analyses and design is suitable for high density storage and can be used in the actual production. And the author also receives the conclusion that the mostly influences on characteristics of OPU read-out spot for high density optical storage factors is not only the process of designing the grating, splitter, collimator lens and objective lens, but also the assembling work precision

Dose characteristics of in-house-built collimators for stereotactic radiotherapy with a linear accelerator.

PubMed

Norrgård, F S; Sipilä, P M; Kulmala, J A; Minn, H R

1998-06-01

Dose characteristics of a stereotactic radiotherapy unit based on a standard Varian Clinac 4/100 4 MV linear accelerator, in-house-built Lipowitz collimators and the SMART stereotactic radiotherapy treatment planning software have been determined. Beam collimation is constituted from the standard collimators of the linear accelerator and a tertiary collimation consisting of a replaceable divergent Lipowitz collimator. Four collimators with isocentre diameters of 15, 25, 35 and 45 mm, respectively, were constructed. Beam characteristics were measured in air, acrylic or water with ionization chamber, photon diode, electron diode, diamond detector and film. Monte Carlo simulation was also applied. The radiation leakage under the collimators was less than 1% at 50 mm depth in water. Specific beam characteristics for each collimator were imported to SMART and dose planning with five non-coplanar converging 140 degrees arcs separated by 36 degrees angles was performed for treatment of a RANDO phantom. Dose verification was made with TLD and radiochromic film. The in-house-built collimators were found to be suitable for stereotactic radiotherapy and patient treatments with this system are in progress.

A small-angle x-ray scattering system with a vertical layout

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhen; Chen, Xiaowei; Meng, Lingpu

A small-angle x-ray scattering (SAXS) system with a vertical layout (V-SAXS) has been designed and constructed for in situ detection on nanostructures, which is well suitable for in situ study on self-assembly of nanoparticles at liquid interface and polymer processing. A steel-tower frame on a reinforced basement is built as the supporting skeleton for scattering beam path and detector platform, ensuring the system a high working stability and a high operating accuracy. A micro-focus x-ray source combining parabolic three-dimensional multi-layer mirror and scatteringless collimation system provides a highly parallel beam, which allows us to detect the very small angle range.more » With a sample-to-detector distance of 7 m, the largest measurable length scale is 420 nm in real space. With a large sample zone, it is possible to install different experimental setups such as film stretching machine, which makes the system perfect to follow the microstructures evolution of materials during processing. The capability of the V-SAXS on in situ study is tested with a drying experiment of a free latex droplet, which confirms our initial design.« less

MSE spectrograph optical design: a novel pupil slicing technique

NASA Astrophysics Data System (ADS)

Spanò, P.

2014-07-01

The Maunakea Spectroscopic Explorer shall be mainly devoted to perform deep, wide-field, spectroscopic surveys at spectral resolutions from ~2000 to ~20000, at visible and near-infrared wavelengths. Simultaneous spectral coverage at low resolution is required, while at high resolution only selected windows can be covered. Moreover, very high multiplexing (3200 objects) must be obtained at low resolution. At higher resolutions a decreased number of objects (~800) can be observed. To meet such high demanding requirements, a fiber-fed multi-object spectrograph concept has been designed by pupil-slicing the collimated beam, followed by multiple dispersive and camera optics. Different resolution modes are obtained by introducing anamorphic lenslets in front of the fiber arrays. The spectrograph is able to switch between three resolution modes (2000, 6500, 20000) by removing the anamorphic lenses and exchanging gratings. Camera lenses are fixed in place to increase stability. To enhance throughput, VPH first-order gratings has been preferred over echelle gratings. Moreover, throughput is kept high over all wavelength ranges by splitting light into more arms by dichroic beamsplitters and optimizing efficiency for each channel by proper selection of glass materials, coatings, and grating parameters.

SU-F-T-671: Effects of Collimator Material On Proton Minibeams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, E; Sandison, G; Cao, N

2016-06-15

Purpose: To investigate the dosimetric effects of collimator material on spatially modulated proton minibeams (pMBRT). Methods: pMBRT holds promise to exhibit shallow depth normal-tissue sparing effects similar to synchrotron based microbeams while also retaining potential for uniform dose distributions for tumor targets. TOPAS Monte Carlo simulations were performed for a 5cm thick multislit collimator with 0.3mm slits and 1mm center-to-center spacing for a 50.5MeV proton minibeam while varying collimator material between brass, tungsten, and iron. The collimator was placed both “flush” at the water phantom surface and at 5cm distance to investigate the effects on surface dose, peak-to-valley-dose-ratio (PVDR) andmore » neutron contribution. Results: For flush placement, the neutron dose at the phantom surface for the tungsten collimator was approximately 20% higher than for brass and iron. This was not reflected in the overall surface dose, which was comparable for all materials due to the relatively low neutron contribution of <0.1%. When the collimator was retracted, the overall neutron contribution was essentially identical for all three collimators. Surface dose dropped by ∼40% for all collimator materials with air gap compared to being flush with the phantom surface. This surface dose reduction was at the cost of increase in valley dose for all collimator materials due to increased angular divergence of the mini-beams at the surface and their consequent geometric penumbra at depth. When the collimator was placed at distance from the phantom surface the PVDR decreased. The peak-to-entrance-dose ratio was highest for the iron collimator with 5cm air gap. Conclusion: The dosimetric difference between the collimator materials is minimal despite the relatively higher neutron contribution at the phantom surface for the tungsten collimator when placed flush. The air gap between the collimator and phantom surface strongly influences all dosimetry parameters due to the influence of scatter on the narrow spatial modulation.« less

Radiation beam collimation system and method

DOEpatents

Schmidt, Oliver A.; Ramanathan, Mohan

2015-08-18

The invention provides a method for collimating a radiation beam, the method comprising subjecting the beam to a collimator that yaws and pitches, either separately or simultaneously relative to the incident angle of the beam. Also provided is a system for collimating radiation beams, the system comprising a collimator body, and a stage for pitching and yawing the body. A feature of the invention is that a single, compact mask body defines one or a plurality of collimators having no moving surfaces relative to each other, whereby the entire mask body is moved about a point in space to provide various collimator opening dimensions to oncoming radiation beams.

Sci-Thur PM – Brachytherapy 05: Surface Collimation Applied to Superficial Flap High Dose-Rate Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Derek; Sabondjian, Eric; Lawrence, Kailin

Purpose: To apply surface collimation for superficial flap HDR skin brachytherapy utilizing common clinical resources and to demonstrate the potential for OAR dose reduction within a clinically relevant setting. Methods: Two phantom setups were used. 3 mm lead collimation was applied to a solid slab phantom to determine appropriate geometries relating to collimation and dwell activation. The same collimation was applied to the temple of an anthropomorphic head phantom to demonstrate lens dose reduction. Each setup was simulated and planned to deliver 400 cGy to a 3 cm circular target to 3 mm depth. The control and collimated irradiations weremore » sequentially measured using calibrated radiochromic films. Results: Collimation for the slab phantom attenuated the dose beyond the collimator opening, decreasing the fall-off distances by half and reducing the area of healthy skin irradiated. Target coverage can be negatively impacted by a tight collimation margin, with the required margin approximated by the primary beam geometric penumbra. Surface collimation applied to the head phantom similarly attenuated the surrounding normal tissue dose while reducing the lens dose from 84 to 68 cGy. To ensure consistent setup between simulation and treatment, additional QA was performed including collimator markup, accounting for collimator placement uncertainties, standoff distance verification, and in vivo dosimetry. Conclusions: Surface collimation was shown to reduce normal tissue dose without compromising target coverage. Lens dose reduction was demonstrated on an anthropomorphic phantom within a clinical setting. Additional QA is proposed to ensure treatment fidelity.« less

Panoramic, large-screen, 3-D flight display system design

NASA Technical Reports Server (NTRS)

Franklin, Henry; Larson, Brent; Johnson, Michael; Droessler, Justin; Reinhart, William F.

1995-01-01

The report documents and summarizes the results of the required evaluations specified in the SOW and the design specifications for the selected display system hardware. Also included are the proposed development plan and schedule as well as the estimated rough order of magnitude (ROM) cost to design, fabricate, and demonstrate a flyable prototype research flight display system. The thrust of the effort was development of a complete understanding of the user/system requirements for a panoramic, collimated, 3-D flyable avionic display system and the translation of the requirements into an acceptable system design for fabrication and demonstration of a prototype display in the early 1997 time frame. Eleven display system design concepts were presented to NASA LaRC during the program, one of which was down-selected to a preferred display system concept. A set of preliminary display requirements was formulated. The state of the art in image source technology, 3-D methods, collimation methods, and interaction methods for a panoramic, 3-D flight display system were reviewed in depth and evaluated. Display technology improvements and risk reductions associated with maturity of the technologies for the preferred display system design concept were identified.

Quench protection studies of the 11-T Nb 3Sn dipole for the LHC upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bermudez, Susana Izquierdo; Auchmann, Bernhard; Bajas, Hugues

The planned upgrade of the LHC collimation system foresees additional collimators to be installed in the dispersion suppressor areas. Fermilab and CERN are developing an 11 T Nb 3Sn dipole to replace some 8.33 T-15-m-long Nb-Ti LHC main dipoles providing longitudinal space for the collimators. In case of a quench, the large stored energy and the low copper stabilizer fraction make the protection of the 11 T Nb 3Sn dipoles challenging. This paper presents the results of quench protection analysis, including quench protection heater design and efficiency, quench propagation and coil heating. The numerical results are compared with the experimentalmore » data from the 2-m-long Nb 3Sn dipole models. Here, the validated model is used to predict the current decay and hot spot temperature under operating conditions in the LHC and the presently foreseen magnet protection scheme is discussed.« less

Quench protection studies of the 11-T Nb 3Sn dipole for the LHC upgrade

DOE PAGES

Bermudez, Susana Izquierdo; Auchmann, Bernhard; Bajas, Hugues; ...

2016-06-01

The planned upgrade of the LHC collimation system foresees additional collimators to be installed in the dispersion suppressor areas. Fermilab and CERN are developing an 11 T Nb 3Sn dipole to replace some 8.33 T-15-m-long Nb-Ti LHC main dipoles providing longitudinal space for the collimators. In case of a quench, the large stored energy and the low copper stabilizer fraction make the protection of the 11 T Nb 3Sn dipoles challenging. This paper presents the results of quench protection analysis, including quench protection heater design and efficiency, quench propagation and coil heating. The numerical results are compared with the experimentalmore » data from the 2-m-long Nb 3Sn dipole models. Here, the validated model is used to predict the current decay and hot spot temperature under operating conditions in the LHC and the presently foreseen magnet protection scheme is discussed.« less

The development of large-aperture test system of infrared camera and visible CCD camera

NASA Astrophysics Data System (ADS)

Li, Yingwen; Geng, Anbing; Wang, Bo; Wang, Haitao; Wu, Yanying

2015-10-01

Infrared camera and CCD camera dual-band imaging system is used in many equipment and application widely. If it is tested using the traditional infrared camera test system and visible CCD test system, 2 times of installation and alignment are needed in the test procedure. The large-aperture test system of infrared camera and visible CCD camera uses the common large-aperture reflection collimator, target wheel, frame-grabber, computer which reduces the cost and the time of installation and alignment. Multiple-frame averaging algorithm is used to reduce the influence of random noise. Athermal optical design is adopted to reduce the change of focal length location change of collimator when the environmental temperature is changing, and the image quality of the collimator of large field of view and test accuracy are also improved. Its performance is the same as that of the exotic congener and is much cheaper. It will have a good market.

Performance evaluation for pinhole collimators of small gamma camera by MTF and NNPS analysis: Monte Carlo simulation study

NASA Astrophysics Data System (ADS)

Jeon, Hosang; Kim, Hyunduk; Cha, Bo Kyung; Kim, Jong Yul; Cho, Gyuseong; Chung, Yong Hyun; Yun, Jong-Il

2009-06-01

Presently, the gamma camera system is widely used in various medical diagnostic, industrial and environmental fields. Hence, the quantitative and effective evaluation of its imaging performance is essential for design and quality assurance. The National Electrical Manufacturers Association (NEMA) standards for gamma camera evaluation are insufficient to perform sensitive evaluation. In this study, modulation transfer function (MTF) and normalized noise power spectrum (NNPS) will be suggested to evaluate the performance of small gamma camera with changeable pinhole collimators using Monte Carlo simulation. We simulated the system with a cylinder and a disk source, and seven different pinhole collimators from 1- to 4-mm-diameter pinhole with lead. The MTF and NNPS data were obtained from output images and were compared with full-width at half-maximum (FWHM), sensitivity and differential uniformity. In the result, we found that MTF and NNPS are effective and novel standards to evaluate imaging performance of gamma cameras instead of conventional NEMA standards.

Thermostructural characterization and structural elastic property optimization of novel high luminosity LHC collimation materials at CERN

NASA Astrophysics Data System (ADS)

Borg, M.; Bertarelli, A.; Carra, F.; Gradassi, P.; Guardia-Valenzuela, J.; Guinchard, M.; Izquierdo, G. Arnau; Mollicone, P.; Sacristan-de-Frutos, O.; Sammut, N.

2018-03-01

The CERN Large Hadron Collider is currently being upgraded to operate at a stored beam energy of 680 MJ through the High Luminosity upgrade. The LHC performance is dependent on the functionality of beam collimation systems, essential for safe beam cleaning and machine protection. A dedicated beam experiment at the CERN High Radiation to Materials facility is created under the HRMT-23 experimental campaign. This experiment investigates the behavior of three collimation jaws having novel composite absorbers made of copper diamond, molybdenum carbide graphite, and carbon fiber carbon, experiencing accidental scenarios involving the direct beam impact on the material. Material characterization is imperative for the design, execution, and analysis of such experiments. This paper presents new data and analysis of the thermostructural characteristics of some of the absorber materials commissioned within CERN facilities. In turn, characterized elastic properties are optimized through the development and implementation of a mixed numerical-experimental optimization technique.

Diamond-anvil high-pressure cell with improved X-ray collimation system

DOEpatents

Schiferl, David; Olinger, Barton W.; Livingston, Robert W.

1986-01-01

An adjustable X-ray collimation system for a diamond-anvil high-pressure cell of the type including a cooperable piston and cylinder and a pair of opposing diamonds located between the head of the piston and the head of the cylinder. The X-ray collimation system includes a tubular insert which contains an X-ray collimator. The insert is engageable in the bore of the piston. The collimator is mounted within the insert by means of an elastomeric O-ring at the end closest the opposed diamonds, and by means of a set of adjustable set screws at the opposite end. By adjustment of the set screws the collimator can be pivoted about the O-ring and brought into alignment with the opposed diamonds and the sample contained therein. In the preferred embodiment there is further provided a set of plugs which are insertable in the bore of the collimator. The plugs have bores of different diameters. By successively inserting plugs of progressively smaller bore diameters and adjusting the alignment of the collimator with each plug, the collimator can be quickly brought into accurate alignment with the diamonds. The collimation system allows alignment of the collimator either before or after the cell has been loaded and pressurized.

Slit-Slat Collimator Equipped Gamma Camera for Whole-Mouse SPECT-CT Imaging

NASA Astrophysics Data System (ADS)

Cao, Liji; Peter, Jörg

2012-06-01

A slit-slat collimator is developed for a gamma camera intended for small-animal imaging (mice). The tungsten housing of a roof-shaped collimator forms a slit opening, and the slats are made of lead foils separated by sparse polyurethane material. Alignment of the collimator with the camera's pixelated crystal is performed by adjusting a micrometer screw while monitoring a Co-57 point source for maximum signal intensity. For SPECT, the collimator forms a cylindrical field-of-view enabling whole mouse imaging with transaxial magnification and constant on-axis sensitivity over the entire axial direction. As the gamma camera is part of a multimodal imaging system incorporating also x-ray CT, five parameters corresponding to the geometric displacements of the collimator as well as to the mechanical co-alignment between the gamma camera and the CT subsystem are estimated by means of bimodal calibration sources. To illustrate the performance of the slit-slat collimator and to compare its performance to a single pinhole collimator, a Derenzo phantom study is performed. Transaxial resolution along the entire long axis is comparable to a pinhole collimator of same pinhole diameter. Axial resolution of the slit-slat collimator is comparable to that of a parallel beam collimator. Additionally, data from an in-vivo mouse study are presented.

Diamond-anvil high-pressure cell with improved x-ray collimation system

DOEpatents

Schiferl, D.; Olinger, B.W.; Livingston, R.W.

1984-03-30

An adjustable x-ray collimation system for a diamond-anvil high-pressure cell of the type including a cooperable piston and cylinder and a pair of opposing diamonds located between the head of the piston and the head of the cylinder. The x-ray collimation system includes a tubular insert which contains an x-ray collimator. The insert is engageable in the bore of the piston. The collimator is mounted within the insert by means of an elastomeric o-ring at the end closest the opposed diamonds, and by means of a set of adjustable set screws at the opposite end. By adjustment of the set screws the collimator can be pivoted about the o-ring and brought into alignment with the opposed diamonds and the sample contained therein. In the preferred embodiment there is further provided a set of plugs which are insertable in the bore of the collimator. The plugs have bores of different diameters. By successively inserting plugs of progressively smaller bore diameters and adjusting the alignment of the collimator with each plug, the collimator can be quickly brought into accurate alignment with the diamonds. The collimation system allows alignment of the collimator either before or after the cell has been loaded and pressurized.

Multileaf collimator performance monitoring and improvement using semiautomated quality control testing and statistical process control.

PubMed

Létourneau, Daniel; Wang, An; Amin, Md Nurul; Pearce, Jim; McNiven, Andrea; Keller, Harald; Norrlinger, Bernhard; Jaffray, David A

2014-12-01

High-quality radiation therapy using highly conformal dose distributions and image-guided techniques requires optimum machine delivery performance. In this work, a monitoring system for multileaf collimator (MLC) performance, integrating semiautomated MLC quality control (QC) tests and statistical process control tools, was developed. The MLC performance monitoring system was used for almost a year on two commercially available MLC models. Control charts were used to establish MLC performance and assess test frequency required to achieve a given level of performance. MLC-related interlocks and servicing events were recorded during the monitoring period and were investigated as indicators of MLC performance variations. The QC test developed as part of the MLC performance monitoring system uses 2D megavoltage images (acquired using an electronic portal imaging device) of 23 fields to determine the location of the leaves with respect to the radiation isocenter. The precision of the MLC performance monitoring QC test and the MLC itself was assessed by detecting the MLC leaf positions on 127 megavoltage images of a static field. After initial calibration, the MLC performance monitoring QC test was performed 3-4 times/week over a period of 10-11 months to monitor positional accuracy of individual leaves for two different MLC models. Analysis of test results was performed using individuals control charts per leaf with control limits computed based on the measurements as well as two sets of specifications of ± 0.5 and ± 1 mm. Out-of-specification and out-of-control leaves were automatically flagged by the monitoring system and reviewed monthly by physicists. MLC-related interlocks reported by the linear accelerator and servicing events were recorded to help identify potential causes of nonrandom MLC leaf positioning variations. The precision of the MLC performance monitoring QC test and the MLC itself was within ± 0.22 mm for most MLC leaves and the majority of the apparent leaf motion was attributed to beam spot displacements between irradiations. The MLC QC test was performed 193 and 162 times over the monitoring period for the studied units and recalibration had to be repeated up to three times on one of these units. For both units, rate of MLC interlocks was moderately associated with MLC servicing events. The strongest association with the MLC performance was observed between the MLC servicing events and the total number of out-of-control leaves. The average elapsed time for which the number of out-of-specification or out-of-control leaves was within a given performance threshold was computed and used to assess adequacy of MLC test frequency. A MLC performance monitoring system has been developed and implemented to acquire high-quality QC data at high frequency. This is enabled by the relatively short acquisition time for the images and automatic image analysis. The monitoring system was also used to record and track the rate of MLC-related interlocks and servicing events. MLC performances for two commercially available MLC models have been assessed and the results support monthly test frequency for widely accepted ± 1 mm specifications. Higher QC test frequency is however required to maintain tighter specification and in-control behavior.

Neutron measurement at the thermal column of the Malaysian Triga Mark II reactor using gold foil activation method and TLD

NASA Astrophysics Data System (ADS)

Shalbi, Safwan; Salleh, Wan Norhayati Wan; Mohamad Idris, Faridah; Aliff Ashraff Rosdi, Muhammad; Syahir Sarkawi, Muhammad; Liyana Jamsari, Nur; Nasir, Nur Aishah Mohd

2018-01-01

In order to design facilities for boron neutron capture therapy (BNCT), the neutron measurement must be considered to obtain the optimal design of BNCT facility such as collimator and shielding. The previous feasibility study showed that the thermal column could generate higher thermal neutrons yield for BNCT application at the TRIGA MARK II reactor. Currently, the facility for BNCT are planned to be developed at thermal column. Thus, the main objective was focused on the thermal neutron and epithermal neutron flux measurement at the thermal column. In this measurement, pure gold and cadmium were used as a filter to obtain the thermal and epithermal neutron fluxes from inside and outside of the thermal column door of the 200kW reactor power using a gold foil activation method. The results were compared with neutron fluxes using TLD 600 and TLD 700. The outcome of this work will become the benchmark for the design of BNCT collimator and the shielding

FLUKA Monte Carlo simulations and benchmark measurements for the LHC beam loss monitors

NASA Astrophysics Data System (ADS)

Sarchiapone, L.; Brugger, M.; Dehning, B.; Kramer, D.; Stockner, M.; Vlachoudis, V.

2007-10-01

One of the crucial elements in terms of machine protection for CERN's Large Hadron Collider (LHC) is its beam loss monitoring (BLM) system. On-line loss measurements must prevent the superconducting magnets from quenching and protect the machine components from damages due to unforeseen critical beam losses. In order to ensure the BLM's design quality, in the final design phase of the LHC detailed FLUKA Monte Carlo simulations were performed for the betatron collimation insertion. In addition, benchmark measurements were carried out with LHC type BLMs installed at the CERN-EU high-energy Reference Field facility (CERF). This paper presents results of FLUKA calculations performed for BLMs installed in the collimation region, compares the results of the CERF measurement with FLUKA simulations and evaluates related uncertainties. This, together with the fact that the CERF source spectra at the respective BLM locations are comparable with those at the LHC, allows assessing the sensitivity of the performed LHC design studies.

Evaluation of radiation exposure with Tru-Align intraoral rectangular collimation system using OSL dosimeters.

PubMed

Goren, Arthur D; Bonvento, Michael J; Fernandez, Thomas J; Abramovitch, Kenneth; Zhang, Wenjian; Roe, Nadine; Seltzer, Jared; Steinberg, Mitchell; Colosi, Dan C

2011-03-01

A pilot study to compare radiation exposure with the Tru-Align rectangular collimation system to round collimation exposures was undertaken. Radiation exposure at various points within the cross sections of the collimators and entrance, intraoral and exit dose measurements were measured using InLight OSL dosimeters. Overall dose reduction with the use of the rectangular collimation system was estimated by taking into account the ratios of collimator openings and the average radiation exposure at the measurement points. Use of the Tru-Align system resulted in an average radiation exposure within the perimeter of the projected outline of the rectangular collimator of 36.1 mR, compared to 148.5 mR with the round collimator. Our calculations indicate a dose reduction by a factor of approximately 3.2 in the case of the Tru-Align system compared to round collimation. The Tru-Align system was easy to use, but in some situations failed to allow Xray coverage of the entire surface of the image receptor, leading to cone cuts.

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

DOE PAGES

Varela, J.; Oak Ridge National Lab.; Brun, S.; ...

2017-05-01

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varela, J.; Oak Ridge National Lab.; Brun, S.

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Karman-Sodium dynamo experiment. The aim of the study is to analyze influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Karman-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbersmore » between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller than with a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.« less

Effects of turbulence, resistivity and boundary conditions on helicoidal flow collimation: Consequences for the Von-Kármán-Sodium dynamo experiment

NASA Astrophysics Data System (ADS)

Varela, J.; Brun, S.; Dubrulle, B.; Nore, C.

2017-05-01

We present hydrodynamic and magneto-hydrodynamic simulations of a liquid sodium flow using the compressible MHD code PLUTO to investigate the magnetic field regeneration in the Von-Kármán-Sodium dynamo experiment. The aim of the study is to analyze the influence of the fluid resistivity and turbulence level on the collimation by helicoidal motions of a remnant magnetic field. We use a simplified Cartesian geometry to represent the flow dynamics in the vicinity of one cavity of a multi-blades impeller inspired by those used in the Von-Kármán-Sodium (VKS) experiment. We perform numerical simulations with kinetic Reynolds numbers up to 1000 for magnetic Prandtl numbers between 30 and 0.1. Our study shows that perfect ferromagnetic walls favour enhanced collimation of flow and magnetic fields even if the turbulence degree of the model increases. More specifically, the location of the helicoidal coherent vortex in between the blades changes with the impinging velocity. It becomes closer to the upstream blade and the impeller base if the flow incident angle is analogous to the TM73 impeller configuration rotating in the unscooping direction. This result is also obtained at higher kinetic Reynolds numbers when the helicoidal vortex undergoes a precessing motion, leading to a reinforced effect in the vortex evolution and in the magnetic field collimation when using again perfect ferromagnetic boundary conditions. Configurations with different materials used for the impeller blades and the impeller base confirm a larger enhancement of the magnetic field when perfect ferromagnetic boundary conditions are used compared with the perfect conductor case, although smaller compared to a perfect ferromagnetic impeller, as it was observed in the VKS experiment. We further estimate the efficiency of a hypothetical dynamo loop occurring in the vicinity of the impeller and discuss the relevance of our findings in the context of mean field dynamo theory.

Beam halo collimation in heavy ion synchrotrons

NASA Astrophysics Data System (ADS)

Strašík, I.; Prokhorov, I.; Boine-Frankenheim, O.

2015-08-01

This paper presents a systematic study of the halo collimation of ion beams from proton up to uranium in synchrotrons. The projected Facility for Antiproton and Ion Research synchrotron SIS100 is used as a reference case. The concepts are separated into fully stripped (e.g., 238U92+ ) and partially stripped (e.g., 238U28+ ) ion collimation. An application of the two-stage betatron collimation system, well established for proton accelerators, is intended also for fully stripped ions. The two-stage system consists of a primary collimator (a scattering foil) and secondary collimators (bulky absorbers). Interaction of the particles with the primary collimator (scattering, momentum losses, and nuclear interactions) was simulated by using fluka. Particle-tracking simulations were performed by using mad-x. Finally, the dependence of the collimation efficiency on the primary ion species was determined. The influence of the collimation system adjustment, lattice imperfections, and beam parameters was estimated. The concept for the collimation of partially stripped ions employs a thin stripping foil in order to change their charge state. These ions are subsequently deflected towards a dump location using a beam optical element. The charge state distribution after the stripping foil was obtained from global. The ions were tracked by using mad-x.

Iodine-131 imaging using 284 keV photons with a small animal CZT-SPECT system dedicated to low-medium-energy photon detection.

PubMed

Kojima, Akihiro; Gotoh, Kumiko; Shimamoto, Masako; Hasegawa, Koki; Okada, Seiji

2016-02-01

Iodine-131 is widely used for radionuclide therapy because of its β-particle and for diagnostic imaging employing its principal gamma ray. Since that principal gamma ray has the relatively high energy of 364 keV, small animal single-photon emission computed tomography (SPECT) imaging systems may be required to possess the ability to image such higher energy photons. The aim of this study was to investigate the possibility of imaging I-131 using its 284 keV photons instead of its 364 keV photons in a small animal SPECT imaging system dedicated to the detection of low-medium-energy photons (below 300 keV). The imaging system used was a commercially available preclinical SPECT instrument with CZT detectors that was equipped with multi-pinhole collimators and was accompanied by a CT imager. An energy window for I-131 imaging was set to a photopeak of 284 keV with a low abundance compared with 364 keV photons. Small line sources and two mice, one of each of two types, that were injected with NaI-131 were scanned. Although higher counts occurred at the peripheral region of the reconstructed images due to the collimator penetration by the 364 keV photons, the shape of the small line sources could be well visualized. The measured spatial resolution was relatively poor (~1.9 mm for full width at half maximum and ~3.9 mm for full width at tenth maximum). However, a good linear correlation between SPECT values and the level of I-131 radioactivity was observed. Furthermore, the uptake of NaI-131 to the thyroid gland for the two mice was clearly identified in the 3D-SPECT image fused with the X-ray CT image. We conclude that the use of an energy window set on the photopeak of 284 keV and the multi-pinhole collimator may permit I-131 imaging for a preclinical CZT-SPECT system that does not have the ability to acquire images using the 364 keV photons.

MO-G-17A-02: Computer Simulation Studies for On-Board Functional and Molecular Imaging of the Prostate Using a Robotic Multi-Pinhole SPECT System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, L; Duke University Medical Center, Durham, NC; Fudan University Shanghai Cancer Center, Shanghai

Purpose: To investigate prostate imaging onboard radiation therapy machines using a novel robotic, 49-pinhole Single Photon Emission Computed Tomography (SPECT) system. Methods: Computer-simulation studies were performed for region-of-interest (ROI) imaging using a 49-pinhole SPECT collimator and for broad cross-section imaging using a parallel-hole SPECT collimator. A male XCAT phantom was computersimulated in supine position with one 12mm-diameter tumor added in the prostate. A treatment couch was added to the phantom. Four-minute detector trajectories for imaging a 7cm-diameter-sphere ROI encompassing the tumor were investigated with different parameters, including pinhole focal length, pinhole diameter and trajectory starting angle. Pseudo-random Poisson noise wasmore » included in the simulated projection data, and SPECT images were reconstructed by OSEM with 4 subsets and up to 10 iterations. Images were evaluated by visual inspection, profiles, and Root-Mean- Square-Error (RMSE). Results: The tumor was well visualized above background by the 49-pinhole SPECT system with different pinhole parameters while it was not visible with parallel-hole SPECT imaging. Minimum RMSEs were 0.30 for 49-pinhole imaging and 0.41 for parallelhole imaging. For parallel-hole imaging, the detector trajectory from rightto- left yielded slightly lower RMSEs than that from posterior to anterior. For 49-pinhole imaging, near-minimum RMSEs were maintained over a broader range of OSEM iterations with a 5mm pinhole diameter and 21cm focal length versus a 2mm diameter pinhole and 18cm focal length. The detector with 21cm pinhole focal length had the shortest rotation radius averaged over the trajectory. Conclusion: On-board functional and molecular prostate imaging may be feasible in 4-minute scan times by robotic SPECT. A 49-pinhole SPECT system could improve such imaging as compared to broadcross-section parallel-hole collimated SPECT imaging. Multi-pinhole imaging can be improved by considering pinhole focal length, pinhole diameter, and trajectory starting angle. The project is supported by the NIH grant 5R21-CA156390.« less

SHIELDING CONSIDERATIONS FOR THE SMALL ANIMAL RADIATION RESEARCH PLATFORM (SARRP)

PubMed Central

Sayler, Elaine; Dolney, Derek; Avery, Stephen; Koch, Cameron

2014-01-01

The Small Animal Radiation Research Platform (SARRP) is a commercially available platform designed to deliver conformal, image-guided radiation to small animals using a dual-anode kV x-ray source. At the University of Pennsylvania, a free-standing 2 m3 enclosure was designed to shield the SARRP according to federal code regulating cabinet x-ray systems. The initial design consisted of 4.0-mm-thick lead for all secondary barriers and proved wholly inadequate. Radiation levels outside the enclosure were 15 times higher than expected. Additionally, the leakage appeared to be distributed broadly within the enclosure, so concern arose that a subject might receive significant doses outside the intended treatment field. Thus, a detailed analysis was undertaken to identify and block all sources of leakage. Leakage sources were identified by Kodak X-OmatV (XV) film placed throughout the enclosure. Radiation inside the enclosure was quantified using Gafchromic film. Outside the enclosure, radiation was measured using a survey meter. Sources of leakage included (1) an unnecessarily broad beam exiting the tube, (2) failure of the secondary collimator to confine the primary beam entirely, (3) scatter from the secondary collimator, (4) lack of beam-stop below the treatment volume, and (5) incomplete shielding of the x-ray tube. The exit window was restricted, and a new collimator was designed to address problems (1–3). A beam-stop and additional tube shielding were installed. These modifications reduced internal scatter by more than 100-fold. Radiation outside the enclosure was reduced to levels compliant with federal regulations, provided the SARRP is operated using tube potentials of 175 kV or less. In addition, these simple and relatively inexpensive modifications eliminate the possibility of exposing a larger animal (such as a rat) to significant doses outside the treatment field. PMID:23532076

Collimator with attachment mechanism and system

DOEpatents

Kross, Brian J [Yorktown, VA; McKisson, John [Hampton, VA; Stolin, Aleksandr [Morgantown, WV; Weisenberger, Andrew G [Yorktown, VA; Zorn, Carl [Yorktown, VA

2012-07-10

A self-aligning collimator for a radiation imaging device that is secured and aligned through the use of a plurality of small magnets. The collimator allows for the rapid exchange, removal, or addition of collimators for the radiation imaging device without the need for tools. The accompanying method discloses the use of magnets and accompanying magnetic fields to align and secure collimators in a radiation imaging assembly.

Impact of plant shoot architecture on leaf cooling: a coupled heat and mass transfer model

PubMed Central

Bridge, L. J.; Franklin, K. A.; Homer, M. E.

2013-01-01

Plants display a range of striking architectural adaptations when grown at elevated temperatures. In the model plant Arabidopsis thaliana, these include elongation of petioles, and increased petiole and leaf angles from the soil surface. The potential physiological significance of these architectural changes remains speculative. We address this issue computationally by formulating a mathematical model and performing numerical simulations, testing the hypothesis that elongated and elevated plant configurations may reflect a leaf-cooling strategy. This sets in place a new basic model of plant water use and interaction with the surrounding air, which couples heat and mass transfer within a plant to water vapour diffusion in the air, using a transpiration term that depends on saturation, temperature and vapour concentration. A two-dimensional, multi-petiole shoot geometry is considered, with added leaf-blade shape detail. Our simulations show that increased petiole length and angle generally result in enhanced transpiration rates and reduced leaf temperatures in well-watered conditions. Furthermore, our computations also reveal plant configurations for which elongation may result in decreased transpiration rate owing to decreased leaf liquid saturation. We offer further qualitative and quantitative insights into the role of architectural parameters as key determinants of leaf-cooling capacity. PMID:23720538

Proton Therapy Facility Planning From a Clinical and Operational Model.

PubMed

Das, Indra J; Moskvin, Vadim P; Zhao, Qingya; Cheng, Chee-Wai; Johnstone, Peter A

2015-10-01

This paper provides a model for planning a new proton therapy center based on clinical data, referral pattern, beam utilization and technical considerations. The patient-specific data for the depth of targets from skin in each beam angle were reviewed at our center providing megavoltage photon external beam and proton beam therapy respectively. Further, data on insurance providers, disease sites, treatment depths, snout size and the beam angle utilization from the patients treated at our proton facility were collected and analyzed for their utilization and their impact on the facility cost. The most common disease sites treated at our center are head and neck, brain, sarcoma and pediatric malignancies. From this analysis, it is shown that the tumor depth from skin surface has a bimodal distribution (peak at 12 and 26 cm) that has significant impact on the maximum proton energy, requiring the energy in the range of 130-230 MeV. The choice of beam angles also showed a distinct pattern: mainly at 90° and 270°; this indicates that the number of gantries may be minimized. Snout usage data showed that 70% of the patients are treated with 10 cm snouts. The cost of proton beam therapy depends largely on the type of machine, maximum beam energy and the choice of gantry versus fixed beam line. Our study indicates that for a 4-room center, only two gantry rooms could be needed at the present pattern of the patient cohorts, thus significantly reducing the initial capital cost. In the USA, 95% and 100% of patients can be treated with 200 and 230 MeV proton beam respectively. Use of multi-leaf collimators and pencil beam scanning may further reduce the operational cost of the facility. © The Author(s) 2014.

Thermal and epithermal neutron fluence rate gradient measurements by PADC detectors in LINAC radiotherapy treatments-field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barrera, M. T., E-mail: mariate9590@gmail.com; Barros, H.; Pino, F.

2015-07-23

LINAC VARIAN 2100 is where energetic electrons produce Bremsstrahlung radiation, with energies above the nucleon binding energy (E≈5.5MeV). This radiation induce (γ,n) and (e,e’n) reactions mainly in the natural tungsten target material (its total photoneutron cross section is about 4000 mb in a energy range from 9-17 MeV). These reactions may occur also in other components of the system (e.g. multi leaf collimator). During radiation treatment the human body may receive an additional dose inside and outside the treated volume produced by the mentioned nuclear reactions. We measured the neutron density at the treatment table using nuclear track detectors (PADC-NTD). Thesemore » covered by a boron-converter are employed, including a cadmium filter, to determine the ratio between two groups of neutron energy, i.e. thermal and epithermal. The PADC-NTD detectors were exposed to the radiation field at the iso-center during regular operation of the accelerator. Neutron are determined indirectly by the converting reaction {sup 10}B(n,α){sup 7}Li the emerging charged particle leave their kinetic energy in the PADC forming a latent nuclear track, enlarged by chemical etching (6N, NaOH, 70°C). Track density provides information on the neutron density through calibration coefficient (∼1.6 10{sup 4} neutrons /track) obtained by a californium source. We report the estimation of the thermal and epithermal neutron field and its gradient for photoneutrons produced in radiotherapy treatments with 18 MV linear accelerators. It was obsered that photoneutron production have higher rate at the iso-center.« less

Response analysis of TLD-300 dosimeters in heavy-particle beams

NASA Astrophysics Data System (ADS)

Loncol, Th; Hamal, M.; Denis, J. M.; Vynckier, S.; Wambersie, A.; Scalliet, P.

1996-09-01

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65)+Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (C) and peak 5 (C) response of :Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental C-12 heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to Co-60, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the Co-60 reference radiation to the C-12 heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

Feasibility study of an intensity-modulated radiation model for the study of erectile dysfunction.

PubMed

Koontz, Bridget F; Yan, Hui; Kimura, Masaki; Vujaskovic, Zeljko; Donatucci, Craig; Yin, Fang-Fang

2011-02-01

Preclinical studies of radiotherapy (RT) induced erectile dysfunction (ED) have been limited by radiation toxicity when using large fields. To develop a protocol of rat prostate irradiation using techniques mimicking the current clinical standard of intensity modulated radiotherapy (IMRT). Quality assurance (QA) testing of plan accuracy, animal health 9 weeks after RT, and intracavernosal pressure (ICP) measurement on cavernosal nerve stimulation. Computed tomography-based planning was used to develop a stereotactic radiosurgery (SRS) treatment plan for five young adult male Sprague-Dawley rats. Two treatment planning strategies were utilized to deliver 20 Gy in a single fraction: three-dimensional dynamic conformal arc and intensity-modulated arc (RapidArc). QA testing was performed for each plan type. Treatment was delivered using a NovalisTX (Varian Medical Systems) with high-definition multi-leaf collimators using on-board imaging prior to treatment. Each animal was evaluated for ED 2 months after treatment by nerve stimulation and ICP measurement. The mean prostate volume and target volume (5 mm expansion of prostate) for the five animals was 0.36 and 0.66 cm3, respectively. Both conformal and RapidArc plans provided at least 95% coverage of the target volume, with rapid dose fall-off. QA plans demonstrated strong agreement between doses of calculated and delivered plans, although the conformal arc plan was more homogenous in treatment delivery. Treatment was well tolerated by the animals with no toxicity out to 9 weeks. Compared with control animals, significant reduction in ICP/mean arterial pressure, maximum ICP, and ICP area under the curve were noted. Tightly conformal dynamic arc prostate irradiation is feasible and results in minimal toxicity and measurable changes in erectile function. © 2010 International Society for Sexual Medicine.

SU-F-T-295: MLCs Performance and Patient-Specific IMRT QA Using Log File Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osman, A; American University of Biuret Medical Center, Biuret; Maalej, N

2016-06-15

Purpose: To analyze the performance of the multi-leaf collimators (MLCs) from the log files recorded during the intensity modulated radiotherapy (IMRT) treatment and to construct the relative fluence maps and do the gamma analysis to compare the planned and executed MLCs movement. Methods: We developed a program to extract and analyze the data from dynamic log files (dynalog files) generated from sliding window IMRT delivery treatments. The program extracts the planned and executed (actual or delivered) MLCs movement, calculates and compares the relative planned and executed fluences. The fluence maps were used to perform the gamma analysis (with 3% dosemore » difference and 3 mm distance to agreement) for 3 IMR patients. We compared our gamma analysis results with those obtained from portal dose image prediction (PDIP) algorithm performed using the EPID. Results: For 3 different IMRT patient treatments, the maximum difference between the planned and the executed MCLs positions was 1.2 mm. The gamma analysis results of the planned and delivered fluences were in good agreement with the gamma analysis from portal dosimetry. The maximum difference for number of pixels passing the gamma criteria (3%/3mm) was 0.19% with respect to portal dosimetry results. Conclusion: MLC log files can be used to verify the performance of the MLCs. Patientspecific IMRT QA based on MLC movement log files gives similar results to EPID dosimetry results. This promising method for patient-specific IMRT QA is fast, does not require dose measurements in a phantom, can be done before the treatment and for every fraction, and significantly reduces the IMRT workload. The author would like to thank King Fahd University of petroleum and Minerals for the support.« less

The accuracy of the out-of-field dose calculations using a model based algorithm in a commercial treatment planning system

NASA Astrophysics Data System (ADS)

Wang, Lilie; Ding, George X.

2014-07-01

The out-of-field dose can be clinically important as it relates to the dose of the organ-at-risk, although the accuracy of its calculation in commercial radiotherapy treatment planning systems (TPSs) receives less attention. This study evaluates the uncertainties of out-of-field dose calculated with a model based dose calculation algorithm, anisotropic analytical algorithm (AAA), implemented in a commercial radiotherapy TPS, Varian Eclipse V10, by using Monte Carlo (MC) simulations, in which the entire accelerator head is modeled including the multi-leaf collimators. The MC calculated out-of-field doses were validated by experimental measurements. The dose calculations were performed in a water phantom as well as CT based patient geometries and both static and highly modulated intensity-modulated radiation therapy (IMRT) fields were evaluated. We compared the calculated out-of-field doses, defined as lower than 5% of the prescription dose, in four H&N cancer patients and two lung cancer patients treated with volumetric modulated arc therapy (VMAT) and IMRT techniques. The results show that the discrepancy of calculated out-of-field dose profiles between AAA and the MC depends on the depth and is generally less than 1% for in water phantom comparisons and in CT based patient dose calculations for static field and IMRT. In cases of VMAT plans, the difference between AAA and MC is <0.5%. The clinical impact resulting from the error on the calculated organ doses were analyzed by using dose-volume histograms. Although the AAA algorithm significantly underestimated the out-of-field doses, the clinical impact on the calculated organ doses in out-of-field regions may not be significant in practice due to very low out-of-field doses relative to the target dose.

Fluence field modulated CT on a clinical TomoTherapy radiation therapy machine

NASA Astrophysics Data System (ADS)

Szczykutowicz, Timothy P.; Hermus, James

2015-03-01

Purpose: The multi-leaf collimator (MLC) assembly present on TomoTherapy (Accuray, Madison WI) radiation therapy (RT) and mega voltage CT machines is well suited to perform fluence field modulated CT (FFMCT). In addition, there is a demand in the RT environment for FFMCT imaging techniques, specifically volume of interest (VOI) imaging. Methods: A clinical TomoTherapy machine was programmed to deliver 30% imaging dose outside predefined VOIs. Four different size ROIs were placed at varying distances from isocenter. Projections intersecting the VOI received "full dose" while those not intersecting the VOI received 30% of the dose (i.e. the incident fluence for non VOI projections was 30% of the incident fluence for projections intersecting the VOI). Additional scans without fluence field modulation were acquired at "full" and 30% dose. The noise (pixel standard deviation) was measured inside the VOI region and compared between the three scans. Results: The VOI-FFMCT technique produced an image noise 1.09, 1.05, 1.05, and 1.21 times higher than the "full dose" scan for ROI sizes of 10 cm, 13 cm, 10 cm, and 6 cm respectively within the VOI region. Conclusions: Noise levels can be almost unchanged within clinically relevant VOIs sizes for RT applications while the integral imaging dose to the patient can be decreased, and/or the image quality in RT can be dramatically increased with no change in dose relative to non-FFMCT RT imaging. The ability to shift dose away from regions unimportant for clinical evaluation in order to improve image quality or reduce imaging dose has been demonstrated. This paper demonstrates that FFMCT can be performed using the MLC on a clinical TomoTherapy machine for the first time.

Quantitative evaluation of patient-specific quality assurance using online dosimetry system

NASA Astrophysics Data System (ADS)

Jung, Jae-Yong; Shin, Young-Ju; Sohn, Seung-Chang; Min, Jung-Whan; Kim, Yon-Lae; Kim, Dong-Su; Choe, Bo-Young; Suh, Tae-Suk

2018-01-01

In this study, we investigated the clinical performance of an online dosimetry system (Mobius FX system, MFX) by 1) dosimetric plan verification using gamma passing rates and dose volume metrics and 2) error-detection capability evaluation by deliberately introduced machine error. Eighteen volumetric modulated arc therapy (VMAT) plans were studied. To evaluate the clinical performance of the MFX, we used gamma analysis and dose volume histogram (DVH) analysis. In addition, to evaluate the error-detection capability, we used gamma analysis and DVH analysis utilizing three types of deliberately introduced errors (Type 1: gantry angle-independent multi-leaf collimator (MLC) error, Type 2: gantry angle-dependent MLC error, and Type 3: gantry angle error). A dosimetric verification comparison of physical dosimetry system (Delt4PT) and online dosimetry system (MFX), gamma passing rates of the two dosimetry systems showed very good agreement with treatment planning system (TPS) calculation. For the average dose difference between the TPS calculation and the MFX measurement, most of the dose metrics showed good agreement within a tolerance of 3%. For the error-detection comparison of Delta4PT and MFX, the gamma passing rates of the two dosimetry systems did not meet the 90% acceptance criterion with the magnitude of error exceeding 2 mm and 1.5 ◦, respectively, for error plans of Types 1, 2, and 3. For delivery with all error types, the average dose difference of PTV due to error magnitude showed good agreement between calculated TPS and measured MFX within 1%. Overall, the results of the online dosimetry system showed very good agreement with those of the physical dosimetry system. Our results suggest that a log file-based online dosimetry system is a very suitable verification tool for accurate and efficient clinical routines for patient-specific quality assurance (QA).

Collimator application for microchannel plate image intensifier resolution improvement

DOEpatents

Thomas, Stanley W.

1996-02-27

A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution.

Numerical Calculations of Short-Range Wakefields of Collimators

NASA Astrophysics Data System (ADS)

Ng, C. K.

2001-12-01

The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic structures. In this paper, numerical methods using codes such as MAFIA are used to determine a series of tapered collimators with rectangular apertures that have been built for studies at SLAC (Stanford Linear Accelerator Center). We will study the dependences of the wakefield on the collimator taper angle, the collimator gap as well as the bunch length. Calculations are also compared with measurements.

Orthogonal strip HPGe planar SmartPET detectors in Compton configuration

NASA Astrophysics Data System (ADS)

Boston, H. C.; Gillam, J.; Boston, A. J.; Cooper, R. J.; Cresswell, J.; Grint, A. N.; Mather, A. R.; Nolan, P. J.; Scraggs, D. P.; Turk, G.; Hall, C. J.; Lazarus, I.; Berry, A.; Beveridge, T.; Lewis, R.

2007-10-01

The evolution of Germanium detector technology over the last decade has lead to the possibility that they can be employed in medical and security imaging. The potential of excellent energy resolution coupled with good position information that Germanium affords removes the necessity for mechanical collimators that would be required in a conventional gamma camera system. By removing this constraint, the overall dose to the patient can be reduced or the throughput of the system can be increased. An additional benefit of excellent energy resolution is that tight gates can be placed on energies from either a multi-lined gamma source or from multi-nuclide sources increasing the number of sources that can be used in medical imaging. In terms of security imaging, segmented Germanium gives directionality and excellent spectroscopic information.

Management of three-dimensional intrafraction motion through real-time DMLC tracking.

PubMed

Sawant, Amit; Venkat, Raghu; Srivastava, Vikram; Carlson, David; Povzner, Sergey; Cattell, Herb; Keall, Paul

2008-05-01

Tumor tracking using a dynamic multileaf collimator (DMLC) represents a promising approach for intrafraction motion management in thoracic and abdominal cancer radiotherapy. In this work, we develop, empirically demonstrate, and characterize a novel 3D tracking algorithm for real-time, conformal, intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)-based radiation delivery to targets moving in three dimensions. The algorithm obtains real-time information of target location from an independent position monitoring system and dynamically calculates MLC leaf positions to account for changes in target position. Initial studies were performed to evaluate the geometric accuracy of DMLC tracking of 3D target motion. In addition, dosimetric studies were performed on a clinical linac to evaluate the impact of real-time DMLC tracking for conformal, step-and-shoot (S-IMRT), dynamic (D-IMRT), and VMAT deliveries to a moving target. The efficiency of conformal and IMRT delivery in the presence of tracking was determined. Results show that submillimeter geometric accuracy in all three dimensions is achievable with DMLC tracking. Significant dosimetric improvements were observed in the presence of tracking for conformal and IMRT deliveries to moving targets. A gamma index evaluation with a 3%-3 mm criterion showed that deliveries without DMLC tracking exhibit between 1.7 (S-IMRT) and 4.8 (D-IMRT) times more dose points that fail the evaluation compared to corresponding deliveries with tracking. The efficiency of IMRT delivery, as measured in the lab, was observed to be significantly lower in case of tracking target motion perpendicular to MLC leaf travel compared to motion parallel to leaf travel. Nevertheless, these early results indicate that accurate, real-time DMLC tracking of 3D tumor motion is feasible and can potentially result in significant geometric and dosimetric advantages leading to more effective management of intrafraction motion.

Ion source with improved primary arc collimation

DOEpatents

Dagenhart, W.K.

1983-12-16

An improved negative ion source is provided in which a self-biasing, molybdenum collimator is used to define the primary electron stream arc discharge from a filament operated at a negative potential. The collimator is located between the anode and the filament. It is electrically connected to the anode by means of an appropriate size resistor such that the collimator is biased at essentially the filament voltage during operation. Initially, the full arc voltage appears across the filament to collimator until the arc discharge strikes. Then the collimator biases itself to essentially filament potential due to current flow through the resistor thus defining the primary electron stream without intercepting any appreciable arc power. The collimator aperture is slightly smaller than the anode aperture to shield the anode from the arc power which, in the past, has caused overheating and erosion of the anode collimator during extended time pulsed-beam operation of the source. With the self-biasing collimator of this invention, the ion source may be operated from short pulse periods to steady-state without destroying the anode.

Ion source with improved primary arc collimation

DOEpatents

Dagenhart, William K.

1985-01-01

An improved negative ion source is provided in which a self-biasing, molybdenum collimator is used to define the primary electron stream arc discharge from a filament operated at a negative potential. The collimator is located between the anode and the filament. It is electrically connected to the anode by means of an appropriate size resistor such that the collimator is biased at essentially the filament voltage during operation. Initially, the full arc voltage appears across the filament to collimator until the arc discharge strikes. Then the collimator biases itself to essentially filament potential due to current flow through the resistor thus defining the primary electron stream without intercepting any appreciable arc power. The collimator aperture is slightly smaller than the anode aperture to shield the anode from the arc power, thereby preventing the exposure of the anode to the full arc power which, in the past, has caused overheating and erosion of the anode collimator during extended time pulsed-beam operation of the source. With the self-biasing collimator of this invention, the ion source may be operated from short pulse periods to steady-state without destroying the anode.

Multi-focus beam shaping of high power multimode lasers

NASA Astrophysics Data System (ADS)

Laskin, Alexander; Volpp, Joerg; Laskin, Vadim; Ostrun, Aleksei

2017-08-01

Beam shaping of powerful multimode fiber lasers, fiber-coupled solid-state and diode lasers is of great importance for improvements of industrial laser applications. Welding, cladding with millimetre scale working spots benefit from "inverseGauss" intensity profiles; performance of thick metal sheet cutting, deep penetration welding can be enhanced when distributing the laser energy along the optical axis as more efficient usage of laser energy, higher edge quality and reduction of the heat affected zone can be achieved. Building of beam shaping optics for multimode lasers encounters physical limitations due to the low beam spatial coherence of multimode fiber-coupled lasers resulting in big Beam Parameter Products (BPP) or M² values. The laser radiation emerging from a multimode fiber presents a mixture of wavefronts. The fiber end can be considered as a light source which optical properties are intermediate between a Lambertian source and a single mode laser beam. Imaging of the fiber end, using a collimator and a focusing objective, is a robust and widely used beam delivery approach. Beam shaping solutions are suggested in form of optics combining fiber end imaging and geometrical separation of focused spots either perpendicular to or along the optical axis. Thus, energy of high power lasers is distributed among multiple foci. In order to provide reliable operation with multi-kW lasers and avoid damages the optics are designed as refractive elements with smooth optical surfaces. The paper presents descriptions of multi-focus optics as well as examples of intensity profile measurements of beam caustics and application results.

Calculations of safe collimator settings and β* at the CERN Large Hadron Collider

NASA Astrophysics Data System (ADS)

Bruce, R.; Assmann, R. W.; Redaelli, S.

2015-06-01

The first run of the Large Hadron Collider (LHC) at CERN was very successful and resulted in important physics discoveries. One way of increasing the luminosity in a collider, which gave a very significant contribution to the LHC performance in the first run and can be used even if the beam intensity cannot be increased, is to decrease the transverse beam size at the interaction points by reducing the optical function β*. However, when doing so, the beam becomes larger in the final focusing system, which could expose its aperture to beam losses. For the LHC, which is designed to store beams with a total energy of 362 MJ, this is critical, since the loss of even a small fraction of the beam could cause a magnet quench or even damage. Therefore, the machine aperture has to be protected by the collimation system. The settings of the collimators constrain the maximum beam size that can be tolerated and therefore impose a lower limit on β*. In this paper, we present calculations to determine safe collimator settings and the resulting limit on β*, based on available aperture and operational stability of the machine. Our model was used to determine the LHC configurations in 2011 and 2012 and it was found that β* could be decreased significantly compared to the conservative model used in 2010. The gain in luminosity resulting from the decreased margins between collimators was more than a factor 2, and a further contribution from the use of realistic aperture estimates based on measurements was almost as large. This has played an essential role in the rapid and successful accumulation of experimental data in the LHC.

Radiation leakage dose from Elekta electron collimation system

PubMed Central

Hogstrom, Kenneth R.; Carver, Robert L.

2016-01-01

This study provided baseline data required for a greater project, whose objective was to design a new Elekta electron collimation system having significantly lighter electron applicators with equally low out‐of field leakage dose. Specifically, off‐axis dose profiles for the electron collimation system of our uniquely configured Elekta Infinity accelerator with the MLCi2 treatment head were measured and calculated for two primary purposes: 1) to evaluate and document the out‐of‐field leakage dose in the patient plane and 2) to validate the dose distributions calculated using a BEAMnrc Monte Carlo (MC) model for out‐of‐field dose profiles. Off‐axis dose profiles were measured in a water phantom at 100 cm SSD for 1 and 2 cm depths along the in‐plane, cross‐plane, and both diagonal axes using a cylindrical ionization chamber with the 10×10 and 20×20 cm2 applicators and 7, 13, and 20 MeV beams. Dose distributions were calculated using a previously developed BEAMnrc MC model of the Elekta Infinity accelerator for the same beam energies and applicator sizes and compared with measurements. Measured results showed that the in‐field beam flatness met our acceptance criteria (±3% on major and ±4% on diagonal axes) and that out‐of‐field mean and maximum percent leakage doses in the patient plane met acceptance criteria as specified by the International Electrotechnical Commission (IEC). Cross‐plane out‐of‐field dose profiles showed greater leakage dose than in‐plane profiles, attributed to the curved edges of the upper X‐ray jaws and multileaf collimator. Mean leakage doses increased with beam energy, being 0.93% and 0.85% of maximum central axis dose for the 10×10 and 20×20 cm2 applicators, respectively, at 20 MeV. MC calculations predicted the measured dose to within 0.1% in most profiles outside the radiation field; however, excluding modeling of nontrimmer applicator components led to calculations exceeding measured data by as much as 0.2% for some regions along the in‐plane axis. Using EGSnrc LATCH bit filtering to separately calculate out‐of‐field leakage dose components (photon dose, primary electron dose, and electron dose arising from interactions in various collimating components), MC calculations revealed that the primary electron dose in the out‐of‐field leakage region was small and decreased as beam energy increased. Also, both the photon dose component and electron dose component resulting from collimator scatter dominated the leakage dose, increasing with increasing beam energy. We concluded that our custom Elekta Infinity with the MLCi2 treatment head met IEC leakage dose criteria in the patient plane. Also, accuracy of our MC model should be sufficient for our use in the design of a new, improved electron collimation system. PACS number(s): 87.56.nk, 87.10.Rt, 87.56.J PMID:27685101

SU-F-T-350: Continuous Leaf Optimization (CLO) for IMRT Leaf Sequencing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, T; Chen, M; Jiang, S

Purpose: To study a new step-and-shoot IMRT leaf sequencing model that avoids the two main pitfalls of conventional leaf sequencing: (1) target fluence being stratified into a fixed number of discrete levels and/or (2) aperture leaf positions being restricted to a discrete set of locations. These assumptions induce error into the sequence or reduce the feasible region of potential plans, respectively. Methods: We develop a one-dimensional (single leaf pair) methodology that does not make assumptions (1) or (2) that can be easily extended to a multi-row model. The proposed continuous leaf optimization (CLO) methodology takes in an existing set ofmore » apertures and associated intensities, or solution “seed,” and improves the plan without the restrictiveness of 1or (2). It then uses a first-order descent algorithm to converge onto a locally optimal solution. A seed solution can come from models that assume (1) and (2), thus allowing the CLO model to improve upon existing leaf sequencing methodologies. Results: The CLO model was applied to 208 generated target fluence maps in one dimension. In all cases for all tested sequencing strategies, the CLO model made improvements on the starting seed objective function. The CLO model also was able to keep MUs low. Conclusion: The CLO model can improve upon existing leaf sequencing methods by avoiding the restrictions of (1) and (2). By allowing for more flexible leaf positioning, error can be reduced when matching some target fluence. This study lays the foundation for future models and solution methodologies that can incorporate continuous leaf positions explicitly into the IMRT treatment planning model. Supported by Cancer Prevention & Research Institute of Texas (CPRIT) - ID RP150485.« less

Monte Carlo modeling and simulations of the High Definition (HD120) micro MLC and validation against measurements for a 6 MV beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borges, C.; Zarza-Moreno, M.; Heath, E.

2012-01-15

Purpose: The most recent Varian micro multileaf collimator (MLC), the High Definition (HD120) MLC, was modeled using the BEAMNRC Monte Carlo code. This model was incorporated into a Varian medical linear accelerator, for a 6 MV beam, in static and dynamic mode. The model was validated by comparing simulated profiles with measurements. Methods: The Varian Trilogy (2300C/D) accelerator model was accurately implemented using the state-of-the-art Monte Carlo simulation program BEAMNRC and validated against off-axis and depth dose profiles measured using ionization chambers, by adjusting the energy and the full width at half maximum (FWHM) of the initial electron beam. Themore » HD120 MLC was modeled by developing a new BEAMNRC component module (CM), designated HDMLC, adapting the available DYNVMLC CM and incorporating the specific characteristics of this new micro MLC. The leaf dimensions were provided by the manufacturer. The geometry was visualized by tracing particles through the CM and recording their position when a leaf boundary is crossed. The leaf material density and abutting air gap between leaves were adjusted in order to obtain a good agreement between the simulated leakage profiles and EBT2 film measurements performed in a solid water phantom. To validate the HDMLC implementation, additional MLC static patterns were also simulated and compared to additional measurements. Furthermore, the ability to simulate dynamic MLC fields was implemented in the HDMLC CM. The simulation results of these fields were compared with EBT2 film measurements performed in a solid water phantom. Results: Overall, the discrepancies, with and without MLC, between the opened field simulations and the measurements using ionization chambers in a water phantom, for the off-axis profiles are below 2% and in depth-dose profiles are below 2% after the maximum dose depth and below 4% in the build-up region. On the conditions of these simulations, this tungsten-based MLC has a density of 18.7 g cm{sup -3} and an overall leakage of about 1.1 {+-} 0.03%. The discrepancies between the film measured and simulated closed and blocked fields are below 2% and 8%, respectively. Other measurements were performed for alternated leaf patterns and the agreement is satisfactory (to within 4%). The dynamic mode for this MLC was implemented and the discrepancies between film measurements and simulations are within 4%. Conclusions: The Varian Trilogy (2300 C/D) linear accelerator including the HD120 MLC was successfully modeled and simulated using the Monte Carlo BEAMNRC code by developing an independent CM, the HDMLC CM, either in static and dynamic modes.« less

Collimator application for microchannel plate image intensifier resolution improvement

DOEpatents

Thomas, S.W.

1996-02-27

A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution. 2 figs.

Pixelated gamma detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolinsky, Sergei Ivanovich; Yanoff, Brian David; Guida, Renato

2016-12-27

A pixelated gamma detector includes a scintillator column assembly having scintillator crystals and optical transparent elements alternating along a longitudinal axis, a collimator assembly having longitudinal walls separated by collimator septum, the collimator septum spaced apart to form collimator channels, the scintillator column assembly positioned adjacent to the collimator assembly so that the respective ones of the scintillator crystal are positioned adjacent to respective ones of the collimator channels, the respective ones of the optical transparent element are positioned adjacent to respective ones of the collimator septum, and a first photosensor and a second photosensor, the first and the secondmore » photosensor each connected to an opposing end of the scintillator column assembly. A system and a method for inspecting and/or detecting defects in an interior of an object are also disclosed.« less

Design of TIR collimating lens for ordinary differential equation of extended light source

NASA Astrophysics Data System (ADS)

Zhan, Qianjing; Liu, Xiaoqin; Hou, Zaihong; Wu, Yi

2017-10-01

The source of LED has been widely used in our daily life. The intensity angle distribution of single LED is lambert distribution, which does not satisfy the requirement of people. Therefore, we need to distribute light and change the LED's intensity angle distribution. The most commonly method to change its intensity angle distribution is the free surface. Generally, using ordinary differential equations to calculate free surface can only be applied in a point source, but it will lead to a big error for the expand light. This paper proposes a LED collimating lens based on the ordinary differential equation, combined with the LED's light distribution curve, and adopt the method of calculating the center gravity of the extended light to get the normal vector. According to the law of Snell, the ordinary differential equations are constructed. Using the runge-kutta method for solution of ordinary differential equation solution, the curve point coordinates are gotten. Meanwhile, the edge point data of lens are imported into the optical simulation software TracePro. Based on 1mm×1mm single lambert body for light conditions, The degrees of collimating light can be close to +/-3. Furthermore, the energy utilization rate is higher than 85%. In this paper, the point light source is used to calculate partial differential equation method and compared with the simulation of the lens, which improve the effect of 1 degree of collimation.

Micro-crystallography developments at GM/CA CAT at the APS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, S.; Makarov, O.; Benn, R.

2010-01-01

Recently, several important structures have been solved using micro-crystallographic techniques that previously could not have been solved with conventional crystallography. At GM/CA-CAT we continue to develop micro-crystallographic capabilities for difficult problems such as small crystals of large macromolecular complexes or membrane proteins grown in the lipidic cubic phase. This paper will describe three major upgrades to our arsenal of tools, 'mini-beam' collimators, active beamstop, and an improved goniostat. Our 'mini-beam' collimators have evolved to a new triple-collimator fabricated from molybdenum as a uni-body. This has significantly improved the robustness, ease of initial alignment, and reduction of background. More recently, twomore » prototypes of a quad-collimator have been developed and fabricated to provide a selection of mini-beams of 5, 10, 20 {mu}m and a 300 {mu}m scatter-guard on a single body. The smaller beams and samples have increased the demand on the tolerances of our goniostat. To meet these challenges we have designed and implemented a goniostat with a 1-micron peak-to-peak sphere of confusion. This is a significant improvement over the previous 6 micron sphere of confusion of the commercially available air-bearing and XY stages. Finally, an 'active beamstop' has been constructed. This will provide non-invasive, real time feedback at the sample during data collection.« less

Micro-Crystallography Developments at GM/CA-CAT at the APS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu Shenglan; Makarov, Oleg; Benn, Rich

2010-06-23

Recently, several important structures have been solved using micro-crystallographic techniques that previously could not have been solved with conventional crystallography. At GM/CA-CAT we continue to develop micro-crystallographic capabilities for difficult problems such as small crystals of large macromolecular complexes or membrane proteins grown in the lipidic cubic phase. This paper will describe three major upgrades to our arsenal of tools, 'mini-beam' collimators, active beamstop, and an improved goniostat. Our 'mini-beam' collimators have evolved to a new triple-collimator fabricated from molybdenum as a uni-body. This has significantly improved the robustness, ease of initial alignment, and reduction of background. More recently, twomore » prototypes of a quad-collimator have been developed and fabricated to provide a selection of mini-beams of 5, 10, 20 {mu}m and a 300 {mu}m scatter-guard on a single body. The smaller beams and samples have increased the demand on the tolerances of our goniostat. To meet these challenges we have designed and implemented a goniostat with a 1-micron peak-to-peak sphere of confusion. This is a significant improvement over the previous 6 micron sphere of confusion of the commercially available air-bearing and XY stages. Finally, an 'active beamstop' has been constructed. This will provide non-invasive, real time feedback at the sample during data collection.« less

Inverse-collimated proton radiography for imaging thin materials

DOE PAGES

Freeman, Matthew S.; Allison, Jason; Andrews, Malcolm; ...

2017-01-01

Relativistic, magnetically-focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam, and is inherently well-suited to imaging dense objects, at areal densities >20 g cm -2. However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm -2. Here, this inversecollimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an arealmore » density change of just 49 mg cm-2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ~25 mg cm -2 to 100 g cm -2, exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system, as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.« less

Illumination design for semiconductor backlight inspection and application extensions

NASA Astrophysics Data System (ADS)

Zhou, Wei; Rutherford, Todd; Hart, Darcy

2013-09-01

High speed strobe based illumination scheme is one of the most critical factors for high throughput semiconductor defect inspection applications. HB LEDs are always the first and best options for such applications due to numerous unique advantages such as excellent spatial and temporal stability, fast responding time, large and linear intensity dynamic range and no heat issue for the extremely low duty cycle applications. For some applications where a large area is required to be illuminated simultaneously, it remains a great challenge to efficiently package a large amount of HB-LEDs in a highly confined 3D space, to generate a seamless illuminated area with high luminance efficiency and spatial uniformity. A novel 3D structured collimation lens is presented in this paper. The non-circular edge shape reduces the intensity drop at the channel boundaries, while the secondary curvatures on the top of the collimator lens efficiently guides the light into desired angular space. The number of the edges and the radius of the top surface curvature are control parameters for the system level performance and the manufacture cost trade-off. The proposed 3D structured LED collimation lens also maintains the benefits of traditional LED collimation lens such as coupling efficiency and mold manufacture capability. The applications can be extended into other non-illumination area like parallelism measurement and solar panel concentrator etc.

Study Of Boosted W-Jets And Higgs-Jets With the SiFCC Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Shin-Shan; Chekanov, Sergei; Gray, Lindsey

We study the detector performance in the reconstruction of hadronically-decaying W bosons and Higgs bosons at very high energy proton colliders using a full GEANT4 simulation of the SiFCC detector. The W and Higgs bosons carry transverse momentum in the multi-TeV range, which results in collimated decay products that are reconstructed as a single jet. We present a measurement of the energy response and resolution of boosted W-jets and Higgs-jets and show the separation of two sub-jets within the boosted boson jet.

The new neutron radiography/tomography/imaging station DINGO at OPAL

NASA Astrophysics Data System (ADS)

Garbe, U.; Randall, T.; Hughes, C.

2011-09-01

A new neutron imaging instrument will be built to support the area of neutron imaging research (neutron radiography/tomography) at ANSTO. The instrument will be designed for an international user community and for routine quality control for defence, industrial, mining, space and aircraft applications. It will also be a useful tool for assessing oil and water flow in sedimentary rock reservoirs (like the North West Shelf), assessing water damage in aircraft components, and the study of hydrogen distribution and cracking in steel. The instrument is planned to be completed by the end of June 2013 and is currently in the design stage. The usable neutron flux is mainly determined by the neutron source, but it also depends on the instrument position and the resolution. The designated instrument position for DINGO is the beam port HB-2 in the reactor hall. The estimated flux for an L/ D of approximately 250 at HB-2 is calculated by Mcstas simulation in a range of 4.75×10 7 n/cm 2 s, which is in the same range of other facilities like ANSTARES (FRM II; Schillinger et al., 2004 [1]) or BT2 (NIST; Hussey et al., 2005 [2]). A special feature of DINGO is the in-pile collimator place in front of the main shutter at HB-2. The collimator offers two pinholes with a possible L/ D of 250 and 1000. A secondary collimator will separate the two beams and block one. The whole instrument will operate in two different positions, one for high resolution and the other for high speed.