| 1. |
- Andreassen, Björn, 1975-, et al.
(författare)
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Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 612:1, s. 201-208
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Tidskriftsartikel (refereegranskat)abstract
- Due to the clinical advantages of Intensity Modulated Radiation Therapy (IMRT) high flexibility and accuracy in intensity modulated dose delivery is desirable to really maximize treatment outcome. Although it is possible to deliver IMRT by using broad beams in combination with dynamic multileaf collimation the process is rather time consuming and inefficient. By using narrow scanned high energy photon beams the treatment outcome can be improved, the treatment time reduced and accurate 3D in vivo dose delivery monitoring is possible by PET-CT based dose delivery imaging of photo nuclear reactions in human tissues. Narrow photon beams can be produced by directing a low emittance high energy electron beam on a thin target, and then cleaning the therapeutic photon beam from transmitted high energy electrons, and photon generated charged leptons, with a dedicated purging magnet placed directly downstream of the target. To have an effective scanning and purging magnet system the purging magnet should be placed immediately after the bremsstrahlung target to deflect the transmitted electrons to an efficient electron stopper. In the static electron stopper the electrons should be safely collected independent of the desired direction of the therapeutic scanned photon beam. The SID (Source to Isocentre Distance) should preferably be short while retaining the ability to scan over a large area on the patient and consequently there are severe requirements both on the strength and the geometry of the scanning and purging magnets. In the present study an efficient magnet configuration with a purging and scanning magnet assembly is developed for electron energies in the 50-75 MeV range and a SID of 75 cm. For a bremsstrahlung target of 3mm Be these electron energies produce a photon beam of 25-17 mm FWHM (Full Width Half Maximum) at a SID of 75 cm. The magnet system was examined both in terms of the efficiency in scanning the narrow bremsstrahlung beam and the deflection of transmitted and photon generated electrons. The simulations show that its is possible to have a scan area on the patient of up to 43 x 40 cm2 for an incident electron energy of 50 MeV and 28 x 40 cm2 at 75 MeV, while at the same time adequately deflecting the transmitted electron beam.
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| 2. |
- Andreassen, Björn, et al.
(författare)
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Fast IMRT with narrow high energy scanned photon beams
- 2011
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 38:8, s. 4774-4784
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Since the first publications on intensity modulated radiation therapy (IMRT) in the early 1980s almost all efforts have been focused on fairly time consuming dynamic or segmental multileaf collimation. With narrow fast scanned photon beams, the flexibility and accuracy in beam shaping increases, not least in combination with fast penumbra trimming multileaf collimators. Previously, experiments have been performed with full range targets, generating a broad bremsstrahlung beam, in combination with multileaf collimators or material compensators. In the present publication, the first measurements with fast narrow high energy (50 MV) scanned photon beams are presented indicating an interesting performance increase even though some of the hardware used were suboptimal. Methods: Inverse therapy planning was used to calculate optimal scanning patterns to generate dose distributions with interesting properties for fast IMRT. To fully utilize the dose distributional advantages with scanned beams, it is necessary to use narrow high energy beams from a thin bremsstrahlung target and a powerful purging magnet capable of deflecting the transmitted electron beam away from the generated photons onto a dedicated electron collector. During the present measurements the scanning system, purging magnet, and electron collimator in the treatment head of the MM50 racetrack accelerator was used with 3-6 mm thick bremsstrahlung targets of beryllium. The dose distributions were measured with diodes in water and with EDR2 film in PMMA. Monte Carlo simulations with GEANT4 were used to study the influence of the electrons transmitted through the target on the photon pencil beam kernel. Results: The full width at half-maximum (FWHM) of the scanned photon beam was 34 mm measured at isocenter, below 9.5 cm of water, 1 m from the 3 mm Be bremsstrahlung target. To generate a homogeneous dose distribution in a 10 x 10 cm(2) field, the authors used a spot matrix of 100 equal intensity beam spots resulting in a uniformity of collimated 80%-20% penumbra of 9 mm at a primary electron energy of 50 MeV. For the more complex cardioid shaped dose distribution, they used 270 spots, which at a pulse repetition frequency of 200 Hz is completed every 1.36 s. Conclusions: The present measurements indicate that the use of narrow scanned photon beams is a flexible and fast method to deliver advanced intensity modulated beams. Fast scanned photon IMRT should, therefore, be a very interesting modality in the delivery of biologically optimized radiation therapy with the possibility for in vivo treatment verification with PET-CT imaging.
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| 3. |
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| 4. |
- Brahme, Anders, et al.
(författare)
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Application of Geant4 in the development of new radiation therapy treatment methods
- 2006
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Ingår i: Proceedings of the 9th Conference, Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications. - 5 Toh Tuck Link, singapore : World Scientific Publishing Co. Pte. Ltd.. - 9812567984 ; , s. 451-461
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Konferensbidrag (refereegranskat)abstract
- There is a very fast development of new radiation treatment methods today, from advanced use of intensity modulated photon and electron beams to light ion therapy with narrow scanned beam based treatment units. Accurate radiation transport calculations are a key requisite for these developments where Geant4 is a very useful Monte Carlo code for accurate design of new treatment units. Today we cannot only image the tumor by PET-CT imaging before the treatment but also determine the tumor sensitivity to radiation and even measure in vivo the delivered absorbed dose in three dimensions in the patient. With such methods accurate Monte Carlo calculations will make radiation therapy an almost exact science where the curative doses can be calculated based on patient individual response data. In the present study results from the application of Geant4 are discussed and the comparisons between Geant4 and experimental and other Monte Carlo data are presented.
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| 5. |
- Fang, Zhao, 1986, et al.
(författare)
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TiO2 nanoparticle interactions with supported lipid membranes – an example of removal of membrane patches
- 2016
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Ingår i: RSC Advances. - 2046-2069. ; 6:94, s. 91102-91110
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for different levels of model systems for effect studies of engineered nanoparticles and the development of nanoparticle structure–activity relationships in biological systems. Descriptors for nanoparticles based on their interactions in molecular model systems may become useful to predict toxicological responses of the nanoparticles in cells. Towards this end, we report on nanoparticle-induced formation of holes in supported model membranes. Specifically, TiO2 nanoparticle – lipid membrane interactions were studied under low ionic strength, basic conditions (pH 8), using different membrane compositions and several surface-sensitive analytical techniques. It was found that for mixed POPC/POPG (PG fractions ≥ 35%) membranes on silica supports, under conditions where electrostatic repulsion was expected, the addition of TiO2 nanoparticles resulted in transient interaction curves, consistent with the removal of part of the lipid membrane. The formation of holes was inferred from quartz crystal microbalance with dissipation (QCM-D) monitoring, as well as from optical measurements by reflectometry, and also verified by atomic force microscopy (AFM) imaging. The interaction between the TiO2 nanoparticles and the PG-containing membranes was dependent on the presence of Ca2+ ions. A mechanism is suggested where TiO2 nanoparticles act as scavengers of Ca2+ ions associated with the supported membrane, leading to weakening of the interaction between the membrane and the support and subsequent removal of lipid mass as TiO2 nanoparticles spontaneously leave the surface. This mechanism is consistent with the observed formation of holes in the supported lipid membranes.
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| 6. |
- Holmberg, Rickard, et al.
(författare)
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Development of Methods for the Design of Electron Collection Systems for Scanned Thin-target Bremsstrahlung IMRT
- 2007
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Ingår i: 9th Biennial ESTRO Meeting on Physics and Radiation Technology for Clinical Radiotherapy, 8-13 Spetember, Barcelona, Spain.
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Purpose: Driven by the need for more accurate and cost-effective therapeutic methods, IMRT is rapidly being deployed at radiation therapy departments. An effecient way of conducting IMRT is by using narrow scanned photon beams, produced from thin bremsstrahlung production targets. Thereby the photon penumbra and pencil beam half width are minimized, while the mean photon energy in the beam is increased, thus enhancing the quality of PET-CT dosimetry. This approach, however, imposes the additional problem of deflecting and stopping an intense stream of high-energy transmitted electrons. In this work, methods for resolving this problem was developed and applied to different treatment unit configurations.Materials/Method: To optimize the geometrical shape of the electron collector together with the scanning and purging magnetic fields, a composite framework, including CAD (Solid Edge 3D), electromagnetic field simulation (Opera 3D) and Monte Carlo simulation (GEANT4), has been set up. Codes have been developed to integrate the geometry from the CAD software as well as the magnetic fields from the electromagnetic design software in the Monte Carlo simulation, so that all three components have one common description of the physical device investigated. Additionally, software has been developed to enable the results from the Monte Carlo simulation to be directly fed back into the CAD model, permitting the use of analytical models for the electron collector shape as a function of transmitted electron fluence from the target. A major consideration in the choice of GEANT4 as the Monte Carlo simulation software was the ability to simulate all relevant kinds of produced radiation in the electron collector.Results: The integration of the geometries and the magnetic fields in the different software applications has been thouroughly verified by several means. For example, tracking a 50 MeV electron through the magnetic fields independently in GEANT4 and Opera 3D gives a maximum disagreementof about 500 nm - well within the expected numerical accuracy. The leakage radiation from a number of different collector designs is evaluated and compared to the ICRP 33 recommendations.Conclusions: A framework integrating CAD, FEM simulations and Monte Carlo transport was developed. The framework, which is more generelly applicable, was here applied to the modelling and simulation of electron collectors for scanned, narrow photon beam IMRT. Relevant physical quantities, including leakage radiation, was computed and evaluated.
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| 7. |
- Holsanova, Jana, et al.
(författare)
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Läsning i gamla och nya medier.
- 2008
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Ingår i: Tekniken bakom språket. - 9789172276307 - 9172276304 - 9789113045351 ; Språkrådets skrifter, 1654-0433 ; 9, s. 144-167
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Jemt, Anders, 1985-, et al.
(författare)
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Evaluation of methods for whole genome and transcriptome sequencing from nanograms of FFPE samples
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The most widely used method for the preservation of clinical tissue specimens is formalin fixation and paraffin embedding (FFPE). Simultaneous analysis of RNA and DNA from samples preserved using this method have long proved problematic, primarily due to lack of material. Here, we describe an attempt to build a complete analysis package for RNA and DNA extracted from single tissue sections. The workflow includes quality control of the extracted material, library preparation and data analysis. We extract DNA with varying integrity from FFPE sections and subject them to whole genome sequencing using two library preparation methods, Illumina TruSeq Nano using the Illumina NeoPrep and Rubicon Genomics ThruPlex. We are able to obtain some usable data, albeit with high duplication rates, demonstrating both the possibilities and challenges of sequencing damaged DNA. Two different approaches to transcriptome sequencing are assessed, the TruSeq RNA Access library preparation kit from Illumina and the SMARTer Stranded Total RNA-Seq Kit - Pico Input from Clonetech. The sequence capture approach of the TruSeq kit is shown to be more robust to low integrity RNA compared to the SMARTer kit. However, the SMARTer kit needs much less starting material and is able to yield data about all transcripts, not just protein coding mRNA.
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| 9. |
- Källman, Hans-Erik, et al.
(författare)
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Source modeling for Monte Carlo dose calculation of CT examinations with a radiotherapy treatment planning system
- 2016
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 43:11, s. 6118-6128
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Tidskriftsartikel (refereegranskat)abstract
- Purpose:Radiation dose to patients undergoing examinations with Multislice Computed Tomography (MSCT) as well as Cone Beam Computed Tomography (CBCT) is a matter of concern. Risk management could benefit from efficient replace rational dose calculation tools. The paper aims to verify MSCT dose calculations using a Treatment Planning System (TPS) for radiotherapy and to evaluate four different variations of bow-tie filter characterizations for the beam model used in the dose calculations.Methods:A TPS (RayStation™, RaySearch Laboratories, Stockholm, Sweden) was configured to calculate dose from a MSCT (GE Healthcare, Wauwatosa, WI, USA). The x-ray beam was characterized in a stationary position the by measurements of the Half-Value Layer (HVL) in aluminum and kerma along the principal axes of the isocenter plane perpendicular to the beam. A Monte Carlo source model for the dose calculation was applied with four different variations on the beam-shaping bow-tie filter, taking into account the different degrees of HVL information but reconstructing the measured kerma distribution after the bow-tie filter by adjusting the photon sampling function. The resulting dose calculations were verified by comparison with measurements in solid water as well as in an anthropomorphic phantom.Results:The calculated depth dose in solid water as well as the relative dose profiles was in agreement with the corresponding measured values. Doses calculated in the anthropomorphic phantom in the range 26–55 mGy agreed with the corresponding thermo luminescence dosimeter (TLD) measurements. Deviations between measurements and calculations were of the order of the measurement uncertainties. There was no significant difference between the different variations on the bow-tie filter modeling.Conclusions:Under the assumption that the calculated kerma after the bow-tie filter replicates the measured kerma, the central specification of the HVL of the x-ray beam together with the kerma distribution can be used to characterize the beam. Thus, within the limits of the study, a flat bow-tie filter with an HVL specified by the vendor suffices to calculate the dose distribution. The TPS could be successfully configured to replicate the beam movement and intensity modulation of a spiral scan with dose modulation, on the basis of the specifications available in the metadata of the digital images and the log file of the CT.
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| 10. |
- Scheffel, Jan, 1954-, et al.
(författare)
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Introducing the Novatron, a novel reactor concept
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A new magnetic mirror design is described – the Novatron – with the potential to confine fully stable compact mirror-cusp fusion plasmas. The novel design features an axisymmetric magnetic field configuration with concave curvature throughout, as seen from the outside. Moreover, the Novatron is designed to be self-stabilized against the drift cyclotron loss-cone modes (DCLC). This paper describes the fundamental topology of the magnetic field and presents an outline for the design of the magnet system.
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