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| 2. |
- Bjoreland, Anders, et al.
(författare)
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Liquid ionization chamber calibrated gel dosimetry in conformal stereotactic radiotherapy of brain lesions
- 2008
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Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 47:6, s. 1099-1109
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Tidskriftsartikel (refereegranskat)abstract
- Hypofractionated conformal stereotactic radiotherapy (HCSRT) is an established method of treating brain lesions such as arteriovenous malformations (AVMs) and brain metastases. The aim of this study was to investigate the reliability of treatment plans in the terms of dose distribution and absorbed dose for HCSRT. Methods and materials. Treatment plans for three different clinical intracerebral targets, AVMs, were transferred to a CT study of a spherical water filled phantom simulating the human head and recalculated for the phantom geometry using a standard treatment planning system utilizing a pencil beam algorithm for dose calculation. The calculated absorbed dose, relative three dimensional (3D) dose distribution and dose conformity were investigated using gel dosimetry normalized to liquid ionization chamber (LIC) measurements. Results. The measured absorbed dose to the dose reference point was found to be within 2% of the calculated dose for all three targets. The measured dose distribution was found to be within 3% and 2 mm of the calculated dose for more than 93% of all points in the target volume for all three targets. Conclusions. The results show that the investigated standard treatment planning system can correctly predict the absorbed dose and dose distribution in different types of intracerebral targets and that the treatment can be delivered according to the plan.
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| 4. |
- Karlsson, Jenny, et al.
(författare)
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RoadOpt : a decision support system for road upgrading in forestry
- 2006
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 21:S7. 7, s. 5-15
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Tidskriftsartikel (refereegranskat)abstract
- Road blocking due to thawing or heavy rains annually contributes to a considerable loss of profit in Swedish forestry. Companies have to build large stocks of sawlogs and pulplogs to secure a continuous supply during periods where the accessibility of the road network is uncertain. This storage leads to quality deterioration, which means loss in profit. One approach to reduce the losses due to blocked roads is to upgrade the road network to a standard that guarantees accessibility throughout the year. This article describes a decision support system called RoadOpt for the planning of forest road upgrading. The planning horizon is about one decade. The system uses a Geographical Information System (GIS)-based map user interface to present and analyse data and results. Two important modules are the Swedish road database, which provides detailed information about the road network, and an optimization module consisting of a mixed integer linear programming model. A case study from a major Swedish company is presented.
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| 6. |
- Karlsson, Mikael, et al.
(författare)
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Beyond the limits: On Violated Environmental Quality Standards and Health Effects from Particles in Sweden
- 2006
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Konferensbidrag (refereegranskat)abstract
- The present levels of particles in the air present a serious health problem in Sweden and legal quality standards for particles are violated. The article analyses if the environmental quality standard is possible to maintain by present legislation, if the standard is based on scientific facts concerning which types of particles that are most hazardous, and if the proposed legally based action programme for counteracting particle concentrations in Stockholm beyond the limits is effective. It suggests developed legislation, a new standard for fine particles and increased focus on traffic reducing measures, if the standards are to be maintained
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| 7. |
- Karlsson, Mikael, et al.
(författare)
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Dedicated magnetic resonance imaging in the radiotherapy clinic
- 2009
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Ingår i: International journal of radiation oncology, biology, physics. - : Elsevier BV. - 1879-355X .- 0360-3016. ; 74:2, s. 644-651
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To introduce a novel technology arrangement in an integrated environment and outline the logistics model needed to incorporate dedicated magnetic resonance (MR) imaging in the radiotherapy workflow. An initial attempt was made to analyze the value and feasibility of MR-only imaging compared to computed tomography (CT) imaging, testing the assumption that MR is a better choice for target and healthy tissue delineation in radiotherapy. METHODS AND MATERIALS: A 1.5-T MR unit with a 70-cm-bore size was installed close to a linear accelerator, and a special trolley was developed for transporting patients who were fixated in advance between the MR unit and the accelerator. New MR-based workflow procedures were developed and evaluated. RESULTS: MR-only treatment planning has been facilitated, thus avoiding all registration errors between CT and MR scans, but several new aspects of MR imaging must be considered. Electron density information must be obtained by other methods. Generation of digitally reconstructed radiographs (DRR) for x-ray setup verification is not straight forward, and reliable corrections of geometrical distortions must be applied. The feasibility of MR imaging virtual simulation has been demonstrated, but a key challenge to overcome is correct determination of the skeleton, which is often needed for the traditional approach of beam modeling. The trolley solution allows for a highly precise setup for soft tissue tumors without the invasive handling of radiopaque markers. CONCLUSIONS: The new logistics model with an integrated MR unit is efficient and will allow for improved tumor definition and geometrical precision without a significant loss of dosimetric accuracy. The most significant development needed is improved bone imaging.
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| 8. |
- Karlsson, Mikael, et al.
(författare)
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MR-only procedures for improved overall precision in radiotherapy
- 2009
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Ingår i: International Journal of Radiation Oncology Biology Physics. - : Elsevier BV. - 0360-3016. ; , s. S656-S656
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Konferensbidrag (refereegranskat)abstract
- Purpose/Objective(s) To reduce the overall geometrical uncertainty in radiotherapy by introducing a novel technology arrangement based on a dedicated MR in an integrated workflow. A new logistics model needed to incorporate MR in this way was developed and clinically evaluated. Testing the assumption that MR is a better choice for target and healthy tissue delineation in radiotherapy, the suggested procedure was analyzed with respect to feasibility and precision of MR-only imaging compared to CT. The focus of the present study was on the geometrical uncertainty which is connected to the required margins between PTV and CTV. Materials/Methods A 1.5-T “open bore” MR unit with a 70-cm-bore size, Siemens Espree, was installed in close proximity to a treatment unit. A new MR-based workflow procedure was developed where all target drawing and treatment planning was performed on MR-data only. For non-fixed soft tissue targets, e.g. prostate, a special trolley was developed for transporting patients, who were immobilized, between the MR unit and the accelerator. The geometrical uncertainty using the transport solution was added to the uncertainty originating from the target definition process and compared with the total uncertainty in a more conventional CT based workflow. Results MR-only treatment planning has been facilitated, thus avoiding all registration errors between CT and MR data, but several new aspects of MR imaging must be considered. Reliable corrections of geometrical distortions must be applied and electron density information must be obtained by other methods. The feasibility of MR virtual simulation has previously been demonstrated. However, a key challenge is improve the visualization of skeletal structures, which is often needed for the traditional approach of set-up verification. The trolley solution allows for a highly precise setup of soft tissue targets without the invasive handling of fiducial markers. In the overall analyses of geometrical uncertainties it was shown that the combined uncertainty is reduced with the MR based workflow, mostly because of reduced systematic uncertainties when the CT-image registration is avoided. Conclusions The new logistics model is efficient and will allow for improved tumor definition and geometrical precision without a significant loss of dosimetric accuracy. Treatment planning directly on MR images is a way to reduce the geometrical uncertainty for e.g. prostate treatments. MR aided patient positioning does not require implanted fiducial markers and will be facilitated by rigid MR-MR registration. Less precise soft tissue CT-CT or CT-MR registrations will thus be avoided.
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| 9. |
- Nyholm, Tufve, et al.
(författare)
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MR based treatment workflow for external radiotherapy of prostate cancer
- 2009
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Ingår i: World Congress on Medical Physics and Biomedical Engineering, September 7 - 12, 2009, Munich, Germany. - Berlin : Springer. ; , s. 60-63
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Konferensbidrag (refereegranskat)abstract
- The requirements on spatial accuracy are high in external radiotherapy of prostate cancer. The technical achievements in image guided radiotherapy (IGRT) during the recent years have lead to a significant improvement of teh daily positioning accuracy. Improved accuracy has made it possible to reduce the margin between the clinical target volume and the planning target volume, thus reduce the risk for normal tissue complications.MRI is to prefer to CT for delineation of the prostate target because of superior soft tissue contrast. Recent studies have shown that the dosimetric accuracy of dose calculations on MR material is acceptable. In the present work we analyze the spatial uncertainties that are connected to workflows where the CT has been excluded.We found that accuracy increase with a fully MR based workflow. The main reason is that the MR based workflow does not require any registration between MR and CT to enable target delineation on the MR series. Two different methodologies for patient positioning with MR as baseline were identified: A. Implanted fiducial markers with portal imaging at each treatment session. B. Imaging of the patient in the MR at every treatment session to localize the prostate. We found that the two positioning methods give equivalent spatial accuracy. The estimated required margins for the MR based workflows was around 8 mm, corresponding numbers for a CT based workflow using the same assessment methods was around 10 mm.
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| 10. |
- Nyholm, Tufve, et al.
(författare)
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MR based workflow for external radiotherapy of prostate cancer.
- 2009
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Ingår i: IFMBE Proceedings 25/1. - Berlin, Heidelberg : Springer Verlag. - 9783642034725 ; , s. 60-63
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Bokkapitel (refereegranskat)abstract
- The requirements on spatial accuracy are high in external radiotherapy of prostate cancer. The technical achievements in image guided radiotherapy (IGRT) during the recent years have lead to a significant improvement of the daily positioning accuracy. Improved accuracy has made it possible to reduce the margin between the clinical target volume and the planning target volume, thus reduce the risk for normal tissue complications. MRI is to prefer to CT for delineation of the prostate target because of superior soft tissue contrast. Recent studies have shown that the dosimetric accuracy of dose calculations on MR material is acceptable. In the present work we analyze the spatial uncertainties that are connected to workflows where the CT has been excluded. We found that accuracy increase with a fully MR based workflow. The main reason is that the MR based workflow does not require any registration between MR and CT to enable target delineation on the MR series. Two different methodologies for patient positioning with MR as baseline were identified: A. Implanted fiducial markers with portal imaging at each treatment session. B. Imaging of the patient in the MR at every treatment session to localize the prostate. We found that the two positioning methods give equivalent spatial accuracy. The estimated required margins for the MR based workflows was around 8 mm, corresponding numbers for a CT based workflow using the same assessment methods was around 10 mm.
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