| 1. |
- Georg, Dietmar, et al.
(författare)
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Clinical evaluation of monitor unit software and the application of action levels
- 2007
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 85:2, s. 306-315
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was the clinical evaluation of an independent dose and monitor unit verification (MUV) software which is based on sophisticated semi-analytical modelling. The software was developed within the framework of an ESTRO project. Finally, consistent handling of dose calculation deviations applying individual action levels is discussed. MATERIALS AND METHODS: A Matlab-based software ("MUV") was distributed to five well-established treatment centres in Europe (Vienna, Graz, Basel, Copenhagen, and Umeå) and evaluated as a quality assurance (QA) tool in clinical routine. Results were acquired for 226 individual treatment plans including a total of 815 radiation fields. About 150 beam verification measurements were performed for a portion of the individual treatment plans, mainly with time variable fluence patterns. The deviations between dose calculations performed with a treatment planning system (TPS) and the MUV software were scored with respect to treatment area, treatment technique, geometrical depth, radiological depth, etc. RESULTS: In general good agreement was found between calculations performed with the different TPSs and MUV, with a mean deviation per field of 0.2+/-3.5% (1 SD) and mean deviations of 0.2+/-2.2% for composite treatment plans. For pelvic treatments less than 10% of all fields showed deviations larger than 3%. In general, when using the radiological depth for verification calculations the results and the spread in the results improved significantly, especially for head-and-neck and for thorax treatments. For IMRT head-and-neck beams, mean deviations between MUV and the local TPS were -1.0+/-7.3% for dynamic, and -1.3+/-3.2% for step-and-shoot IMRT delivery. For dynamic IMRT beams in the pelvis good agreement was obtained between MUV and the local TPS (mean: -1.6+/-1.5%). Treatment site and treatment technique dependent action levels between +/-3% and +/-5% seem to be clinically realistic if a radiological depth correction is performed, even for dynamic wedges and IMRT. CONCLUSION: The software MUV is well suited for patient specific treatment plan QA applications and can handle all currently available treatment techniques that can be applied with standard linear accelerators. The highly sophisticated dose calculation model implemented in MUV allows investigation of systematic TPS deviations by performing calculations in homogeneous conditions
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| 2. |
- Georg, Dietmar, et al.
(författare)
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Patient-specific IMRT verification using independent fluence-based dose calculation software : experimental benchmarking and initial clinical experience
- 2007
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 52:16, s. 4981-4992
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Tidskriftsartikel (refereegranskat)abstract
- Experimental methods are commonly used for patient-specific intensity-modulated radiotherapy (IMRT) verification. The purpose of this study was to investigate the accuracy and performance of independent dose calculation software ( denoted as 'MUV' ( monitor unit verification)) for patient-specific quality assurance (QA). 52 patients receiving step-and-shoot IMRT were considered. IMRT plans were recalculated by the treatment planning systems (TPS) in a dedicated QA phantom, in which an experimental 1D and 2D verification (0.3 cm(3) ionization chamber; films) was performed. Additionally, an independent dose calculation was performed. The fluence-based algorithm of MUV accounts for collimator transmission, rounded leaf ends, tongue-and-groove effect, backscatter to the monitor chamber and scatter from the flattening filter. The dose calculation utilizes a pencil beam model based on a beam quality index. DICOM RT files from patient plans, exported from the TPS, were directly used as patient-specific input data in MUV. For composite IMRT plans, average deviations in the high dose region between ionization chamber measurements and point dose calculations performed with the TPS and MUV were 1.6 +/- 1.2% and 0.5 +/- 1.1% ( 1 S. D.). The dose deviations between MUV and TPS slightly depended on the distance from the isocentre position. For individual intensity-modulated beams ( total 367), an average deviation of 1.1 +/- 2.9% was determined between calculations performed with the TPS and with MUV, with maximum deviations up to 14%. However, absolute dose deviations were mostly less than 3 cGy. Based on the current results, we aim to apply a confidence limit of 3% ( with respect to the prescribed dose) or 6 cGy for routine IMRT verification. For off-axis points at distances larger than 5 cm and for low dose regions, we consider 5% dose deviation or 10 cGy acceptable. The time needed for an independent calculation compares very favourably with the net time for an experimental approach. The physical effects modelled in the dose calculation software MUV allow accurate dose calculations in individual verification points. Independent calculations may be used to replace experimental dose verification once the IMRT programme is mature.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Nyholm, Tufve, et al.
(författare)
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Modelling lateral beam quality variations in pencil kernel based photon dose calculations
- 2006
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 51:16, s. 4111-4118
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Tidskriftsartikel (refereegranskat)abstract
- Standard treatment machines for external radiotherapy are designed to yield flat dose distributions at a representative treatment depth. The common method to reach this goal is to use a flattening filter to decrease the fluence in the centre of the beam. A side effect of this filtering is that the average energy of the beam is generally lower at a distance from the central axis, a phenomenon commonly referred to as off-axis softening. The off-axis softening results in a relative change in beam quality that is almost independent of machine brand and model. Central axis dose calculations using pencil beam kernels show no drastic loss in accuracy when the off-axis beam quality variations are neglected. However, for dose calculated at off-axis positions the effect should be considered, otherwise errors of several per cent can be introduced. This work proposes a method to explicitly include the effect of off-axis softening in pencil kernel based photon dose calculations for arbitrary positions in a radiation field. Variations of pencil kernel values are modelled through a generic relation between half value layer (HVL) thickness and off-axis position for standard treatment machines. The pencil kernel integration for dose calculation is performed through sampling of energy fluence and beam quality in sectors of concentric circles around the calculation point. The method is fully based on generic data and therefore does not require any specific measurements for characterization of the off-axis softening effect, provided that the machine performance is in agreement with the assumed HVL variations. The model is verified versus profile measurements at different depths and through a model self-consistency check, using the dose calculation model to estimate HVL values at off-axis positions. A comparison between calculated and measured profiles at different depths showed a maximum relative error of 4% without explicit modelling of off-axis softening. The maximum relative error was reduced to 1% when the off-axis softening was accounted for in the calculations.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Nyholm, Tufve, et al.
(författare)
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Pencil kernel correction and residual error estimation for quality-index-based dose calculations
- 2006
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 51:23, s. 6245-6262
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data from 593 photon beams were used to quantify the errors in dose calculations using a previously published pencil kernel model. A correction of the kernel was derived in order to remove the observed systematic errors. The remaining residual error for individual beams was modelled through uncertainty associated with the kernel model. The methods were tested against an independent set of measurements. No significant systematic error was observed in the calculations using the derived correction of the kernel and the remaining random errors were found to be adequately predicted by the proposed method.
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| 9. |
- Nyholm, Tufve, et al.
(författare)
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Photon pencil kernel parameterisation based on beam quality index
- 2006
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 78:3, s. 347-351
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Tidskriftsartikel (refereegranskat)abstract
- Background and purposeNew treatment techniques in radiotherapy employ increasing dose calculation complexity in treatment planning. For an adequate check of the results coming from a modern treatment planning system, clinical tools with almost the same degree of generality and accuracy as the planning system itself are needed. To fulfil this need we propose a photon pencil kernel parameterization based on a minimum of input data that can be used for phantom scatter calculations. Through scatter integration the pencil kernel model can calculate common parameters, such as TPR or phantom scatter factors, used in various dosimetric QA (quality assurance) procedures.Material and methodsThe proposed model originates from an already published radially parameterized pencil kernel. A depth parameterization of the pencil kernel parameters has been introduced, based on a large database containing commissioned beam data for a commercial treatment planning system. The entire pencil kernel model demands only one photon beam quality index, TPR20,10, as input.ResultsBy comparing the dose calculation results to the extensive experimental data set in the database, it has been possible to make a thorough analysis of the resulting accuracy. The errors in calculated doses, normalized to the reference geometry, are in most cases smaller than 2%.ConclusionsThe investigation shows that a pencil kernel model based only on TPR20,10 can be used for dosimetric verification purposes in megavoltage photon beams at depths below the range of contaminating electrons.
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| 10. |
- Nyholm, Tufve, et al.
(författare)
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Systematisation of spatial uncertainties for comparison between a MR and a CT-based radiotherapy workflow for prostate treatments
- 2009
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Ingår i: Radiation Oncology. - 1748-717X .- 1748-717X. ; 4:54
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Tidskriftsartikel (refereegranskat)abstract
- Background: In the present work we compared the spatial uncertainties associated with a MR-based workflow for external radiotherapy of prostate cancer to a standard CT-based workflow. The MR-based workflow relies on target definition and patient positioning based on MR imaging. A solution for patient transport between the MR scanner and the treatment units has been developed. For the CT-based workflow, the target is defined on a MR series but then transferred to a CT study through image registration before treatment planning, and a patient positioning using portal imaging and fiducial markers. Methods: An "open bore" 1.5T MRI scanner, Siemens Espree, has been installed in the radiotherapy department in near proximity to a treatment unit to enable patient transport between the two installations, and hence use the MRI for patient positioning. The spatial uncertainty caused by the transport was added to the uncertainty originating from the target definition process, estimated through a review of the scientific literature. The uncertainty in the CT-based workflow was estimated through a literature review.Results: The systematic uncertainties, affecting all treatment fractions, are reduced from 3-4 mm (ISd) with a CT based workflow to 2-3 mm with a MR based workflow. The main contributing factor to this improvement is the exclusion of registration between MR and CT in the planning phase of the treatment.
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