| 1. |
- Andersen, C. E., et al.
(författare)
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Medical proton dosimetry using radioluminescence from aluminium oxide crystals attached to optical-fiber cables
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 580:1, s. 466-468
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Tidskriftsartikel (refereegranskat)abstract
- The prime objective of this study is to investigate if radioluminescence (RL) from carbon-doped aluminum oxide (Al2O3:C) crystals potentially can be used for absorbed dose-rate measurements during proton radiotherapy. The RL from two separate (2 mg) Al2O3:C crystals attached to optical-fiber cables were recorded during irradiations in water in a 175 MeV clinical proton beam. The RL response for low-LET protons in the plateau region of the Bragg curve was found to closely resemble that observed for a clinical 6 MV X-ray beam. An identical response was found in the Bragg peak (where the dose-averaged LET is about 4 keV/mu m) for absorbed doses less than 0.3 Gy. For doses in the range of 0.3-3Gy, we observed a significant decrease in luminescence efficiency with LET. At 3 Gy, the luminescence efficiency was about 60% in the Bragg-peak region. The study implies that the RL-signal from Al2O3:C could potentially be suitable for medical proton dosimetry in the 0-0.3 Gy range even without any LET-dependent correction factors.
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| 2. |
- Aznar, Marianne C., et al.
(författare)
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A Monte Carlo study of the energy dependence of Al2O3:C crystals for real-time in vivo dosimetry in mammography
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:Nos 1-3, s. 444-449
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Tidskriftsartikel (refereegranskat)abstract
- In a previous experimental study, a novel method for in vivo dosimetry has been investigated, based on radioluminescence (RL) and optically stimulated luminescence (OSL). However, because of the large difference in atomic composition between the detector material and the breast tissue, relatively large energy dependence in low-energy X-ray beams can be expected. In the present work, the energy dependence of Al2O3:C crystals was modelled with the Monte Carlo code EGSnrc using three types of X-ray spectra. The results obtained (5.6-7.3%) agree with a previously determined experimental result (9%) within the combined standard uncertainty of the two methods. The influence of the size of the crystal on the energy dependence was investigated together with the effect of varying the thickness of the surrounding light-protective material. The results obtained indicate a minor effect owing to the thickness of the light-protective material, and a somewhat larger effect from reducing the diameter of the crystal. The outcome of this study can be used to improve the future design of the RL/OSL dosimetry system for use in mammography.
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| 3. |
- Andersen, C. E., et al.
(författare)
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An algorithm for real-time dosimetry in intensity-modulated radiation therapy using the radioluminescence signal from Al2O3 : C
- 2006
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 120:1-4, s. 41468-41468
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Tidskriftsartikel (refereegranskat)abstract
- Although the radioluminescence (RL) signal from optical fibre Al2O3:C dosemeters used in medical applications is essentially proportional to dose rate, the crystals used so far are imperfect in the sense that their RL sensitivity changes with accumulated dose. A computational algorithm has been developed that corrects for these sensitivity changes. We further report on a new system that effectively separates the RL signal generated in the crystal from fluorescence and Cerenkov emission generated in the optical fibre cable using a gating technique in connection with pulsed linear accelerator radiation beams. The dosimetry system has been used for dose measurements in a phantom during an intensity-modulated radiation therapy (IMRT) treatment with 6 MV photons. The RL measurement results are in excellent agreement (i.e. within 1%) with both the OSL results and the dose delivered according to the treatment planning system. RL signals from Al2O3:C can be used for real-time dose rate measurements with a time resolution of similar to 0.1 s and a spatial resolution only limited by the size of the detector (< 0.5 mm).
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| 4. |
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| 5. |
- Aznar, MC, et al.
(författare)
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In vivo absorbed dose measurements in mammography using a new real-time luminescence technique
- 2005
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 78:928, s. 328-334
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Tidskriftsartikel (refereegranskat)abstract
- A dosimetry system based on radioluminescence (RL) and optically stimulated luminescence (OSL) from carbon doped aluminium oxide (Al2O3:C) crystals was developed for in vivo absorbed dose measurements in mammography. A small cylindrical crystal of Al2O3:C (diameter 0.48 mm and length 2 mm) was coupled to the end of a 1 mm diameter optical fibre cable. Owing to their small size and characteristic shape, these probes can be placed on the body surface in the field of view during the examination, without compromising the reading of the mammogram. Our new technique was tested with a mammography unit (Siemens Mammomat 3000) and screen-film technique over a range of clinically relevant X-ray energies. The results were compared with those obtained from an ionization chamber usually used for the determination of absorbed dose in mammography. The reproducibility of measurements was around 3% (1 standard deviation) at 4.5 mGy for both RL and OSL data. The dose response was found to be linear between 4.5 mGy and 30 mGy. The energy dependence of the system is around 18% between 23 kV and 35 kV. In vivo measurements were performed during three patient examinations. It was shown that entrance and exit doses could be measured. The presence of the small probes did not significantly interfere with the diagnostic quality of the images. Entrance doses estimated by RL/OSL results agreed within 3% with entrance surface dose values calculated from the ionization chamber measurements. These results indicate a considerable potential for use in routine control and in vivo dose measurements in mammography.
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| 6. |
- Aznar, MC, et al.
(författare)
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Real-time optical-fibre luminescence dosimetry for radiotherapy: physical characteristics and applications in photon beams
- 2004
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 49:9, s. 1655-1669
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Tidskriftsartikel (refereegranskat)abstract
- A new optical-fibre radiation dosimeter system, based on radioluminescence and optically stimulated luminescence from carbon-doped aluminium oxide, was developed and tested in clinical photon beams. This prototype offers several features, such as a small detector (1 x 1 x 2 mm), high sensitivity, real-time read-out and the ability to measure both dose rate and absorbed dose. The measurements describing reproducibility and output dependence on dose rate, field size and energy all had standard deviations smaller than 1%. The signal variation with the angle of incidence was smaller than 2% (1 SD). Measurements performed in clinical situations suggest the potential of using this real-time system for in vivo dosimetry in radiotherapy.
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| 7. |
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| 8. |
- Bäck, Sven, et al.
(författare)
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Ferrous sulphate gel dosimetry and MRI for proton beam dose measurements
- 1999
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 44:8, s. 1983-1996
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Tidskriftsartikel (refereegranskat)abstract
- Ferrous sulphate gel dosimetry has the potential for measurement of absorbed dose distributions in proton therapy. The chemical properties of the gel are altered according to the radiation dose and these changes can be evaluated in three dimensions using MRI. The purpose of this work was to investigate the properties of a ferrous gel used with clinical proton beams. The gel was irradiated with both monoenergetic and range-modulated proton beams. It was then evaluated using MRI. The depth dose by means of the 1/T1 distribution was studied and compared with data from a plane-parallel plate ionization chamber. 1/T1 was shown to be proportional to the dose at a mean proton energy of approximately 90 MeV. The dose response was no different from that obtained using photon beams. However, on normalization at the entrance, the relative 1/T1 at the Bragg peak was 15-20% lower than the corresponding ionization chamber data for the monoenergetic proton beam. Better agreement was found for the modulated beam, but with significant differences close to the distal edge of the 1/T1 distribution. The change in sensitivity with depth was explained by means of a linear energy transfer dependence. This property was further studied using Monte Carlo methods.
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| 9. |
- Ceberg, Sofie, et al.
(författare)
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RapidArc™ treatment verification using polymer gel dosimetry
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 164:1
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to verify a novel volumetric arc therapy technique, RapidArc". Polymer gel dosimetry system was used to measure the advanced inhomogeneous 3D dose distribution produced using the technique RapidArc". A preclinical installation of the novel beam delivery approach was set up on a linear accelerator at Rigshospitalet in Copenhagen. A prostate treatment plan was delivered to a 1.3 l nPAG gel phantom using one single arc rotation from 200 to 160 degrees, and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using the 1.5 T scanner and MATLAB was used for image processing and 3D rendering. The difference in relative absorbed dose between the treatment planning system (TPS) and gel measurement was calculated voxel by voxel within the 80% and the 95% isodose volume, respectively. Measurements agreed well with the TPS within the treated volume. Within both isodose volumes 90% of the voxels showed a deviation less or equal to 5%. This study shows that the 3D gel dosimetry system is a useful tool for dose verification of advanced treatment delivery techniques.
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| 10. |
- Ceberg, Sofie, et al.
(författare)
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Tumor-tracking radiotherapy of moving targets; verification using 3D polymer gel, 2D ion-chamber array and biplanar diode array
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 250:1, s. 235-239
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to carry out a dosimetric verification of a dynamic multileaf collimator (DMLC)-based tumor-tracking delivery during respiratory-like motion. The advantage of tumor-tracking radiation delivery is the ability to allow a tighter margin around the target by continuously following and adapting the dose delivery to its motion. However, there are geometric and dosimetric uncertainties associated with beam delivery system constraints and output variations, and several investigations have to be accomplished before a clinical integration of this tracking technique. Two types of delivery were investigated in this study I) a single beam perpendicular to a target with a one dimensional motion parallel to the MLC moving direction, and II) an intensity modulated arc delivery (RapidArc®) with a target motion diagonal to the MLC moving direction. The feasibility study (I) was made using an 2D ionisation chamber array and a true 3D polymer gel. The arc delivery (II) was verified using polymer gel and a biplanar diode array. Good agreement in absorbed dose was found between delivery to a static target and to a moving target with DMLC tracking using all three detector systems. However, due to the limited spatial resolution of the 2D array a detailed comparison was not possible. The RapidArc® plan delivery was successfully verified using the biplanar diode array and true 3D polymer gel, and both detector systems could verify that the DMLC-based tumor-tracking delivery system has a very good ability to account for respiratory target motion.
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| 11. |
- Edvardsson, Anneli, et al.
(författare)
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Verification of motion induced thread effect during tomotherapy using gel dosimetry
- 2015
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Ingår i: 8th International Conference on 3D Radiation Dosimetry (IC3DDOSE). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 573, s. 012048-012048
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Konferensbidrag (refereegranskat)abstract
- The purpose of the study was to evaluate how breathing motion during tomotherapy (Accuray, CA, USA) treatment affects the absorbed dose distribution. The experiments were carried out using gel dosimetry and a motion device simulating respiratory-like motion (HexaMotion, ScandiDos, Uppsala, Sweden). Normoxic polyacrylamide gels (nPAG) were irradiated, both during respiratory-like motion and in a static mode. To be able to investigate interplay effects the static absorbed dose distribution was convolved with the motion function and differences between the dynamic and convolved static absorbed dose distributions were interpreted as interplay effects. The expected dose blurring was present and the interplay effects formed a spiral pattern in the lower dose volume. This was expected since the motion induced affects the preset pitch and the theoretically predicted thread effect may emerge. In this study, the motion induced thread effect was experimentally verified for the first time.
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| 12. |
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| 13. |
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| 14. |
- Hemdal, Bengt, et al.
(författare)
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Can the average glandular dose in routine digital mammography screening be reduced? A pilot study using revised image quality criteria.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 383-8
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for tools that in a simple way can be used for the evaluation of image quality related to clinical requirements in mammography. The aim of this work was to adjust the present European image quality criteria to be relevant also for digital mammography images, and to use as simple and as few criteria as possible. A pilot evaluation of the new set of criteria was made with mammograms of 28 women from a General Electric Senographe 2000D full-field digital mammography system. One breast was exposed using the standard automatic exposure mode, the other using about half of that absorbed dose. Three experienced radiologists evaluated the images using visual grading analysis technique. The results indicate that the new quality criteria can be used for the evaluation of image quality related to clinical requirements in digital mammography in a simple way. The results also suggest that absorbed doses for the mammography system used may be substantially reduced.
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| 15. |
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| 16. |
- Hemdal, Bengt, et al.
(författare)
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Clinical evaluation of a new set of image quality criteria for mammography.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 389-94
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Tidskriftsartikel (refereegranskat)abstract
- The European Commission (EC) quality criteria for screen-film mammography are used as a tool to assess image quality. A new set of criteria was developed and initially tested in a previous study. In the present study, these criteria are further evaluated using screen-film mammograms that have been digitised, manipulated to simulate different image quality levels and reprinted on film. Expert radiologists have evaluated these manipulated images using both the original (EC) and the new criteria. A comparison of three different simulated dose levels reveals that the new criteria yield a larger separation of image criteria scores than the old ones. These results indicate that the new set of image quality criteria has a higher discriminative power than the old set and thus seems to be more suitable for evaluation of image quality in mammography.
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| 17. |
- Lerner, Minna, et al.
(författare)
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Clinical validation of a commercially available deep learning software for synthetic CT generation for brain
- 2021
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Ingår i: Radiation Oncology. - : Springer Science and Business Media LLC. - 1748-717X. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Most studies on synthetic computed tomography (sCT) generation for brain rely on in-house developed methods. They often focus on performance rather than clinical feasibility. Therefore, the aim of this work was to validate sCT images generated using a commercially available software, based on a convolutional neural network (CNN) algorithm, to enable MRI-only treatment planning for the brain in a clinical setting. Methods: This prospective study included 20 patients with brain malignancies of which 14 had areas of resected skull bone due to surgery. A Dixon magnetic resonance (MR) acquisition sequence for sCT generation was added to the clinical brain MR-protocol. The corresponding sCT images were provided by the software MRI Planner (Spectronic Medical AB, Sweden). sCT images were rigidly registered and resampled to CT for each patient. Treatment plans were optimized on CT and recalculated on sCT images for evaluation of dosimetric and geometric endpoints. Further analysis was also performed for the post-surgical cases. Clinical robustness in patient setup verification was assessed by rigidly registering cone beam CT (CBCT) to sCT and CT images, respectively. Results: All sCT images were successfully generated. Areas of bone resection due to surgery were accurately depicted. Mean absolute error of the sCT images within the body contour for all patients was 62.2 ± 4.1 HU. Average absorbed dose differences were below 0.2% for parameters evaluated for both targets and organs at risk. Mean pass rate of global gamma (1%/1 mm) for all patients was 100.0 ± 0.0% within PTV and 99.1 ± 0.6% for the full dose distribution. No clinically relevant deviations were found in the CBCT-sCT vs CBCT-CT image registrations. In addition, mean values of voxel-wise patient specific geometric distortion in the Dixon images for sCT generation were below 0.1 mm for soft tissue, and below 0.2 mm for air and bone. Conclusions: This work successfully validated a commercially available CNN-based software for sCT generation. Results were comparable for sCT and CT images in both dosimetric and geometric evaluation, for both patients with and without anatomical anomalies. Thus, MRI Planner is feasible to use for radiotherapy treatment planning of brain tumours.
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| 18. |
- Lerner, Minna, et al.
(författare)
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MRI-only based treatment with a commercial deep-learning generation method for synthetic CT of brain
- 2020
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Ingår i: ; , s. 47-47
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Konferensbidrag (refereegranskat)abstract
- ObjectivesTo show feasibility of synthetic computed tomography (sCT) images generated using a commerciallyavailable software, enabling MRI-only treatment planning for the brain in a clinical setting.Patients and Methods20 and 16 patients with brain malignancies, including post-surgical cases, were included for validationand treatment, respectively. Dixon MR images of the skull were exported to the MRI Planner software(Spectronic Medical AB), which utilizes convolutional neural network algorithms for sCT generation.In the validation study, sCT images were rigidly registered and resampled to CT geometry for eachpatient. Treatment plans were optimized on CT and retrospectively recalculated on sCT images forevaluation of dosimetric and geometric endpoints. Clinical robustness in patient setup verification wasassessed by rigidly registering cone beam CT (CBCT) to sCT and CT images, respectively.The treatment study was performed on sCT images, using CT solely for QA purposes.ResultsAll sCT images were successfully generated in the validation study. Mean absolute error of the sCTimages within the body contour for all patients was 62.2 ± 4.1 HU. Average absorbed dose differenceswere below 0.2%. Mean pass rate of global gamma (1%/1mm) for all patients was 100.0 ± 0.0 % withinPTV and 99.1 ± 0.6 % for the full dose distribution. No clinically relevant deviations were found in theCBCT-sCT vs CBCT-CT image registrations. Areas of bone resection due to surgery were accuratelydepicted in the sCT images. Finally, treatment success rate was 15/16. One patient was excluded due tosCT artifacts from a haemostatic substance injected during surgery.Conclusion15 patients have successfully received MRI-only RT for brain tumours using the validated commerciallyavailable sCT software. Validation showed comparable results between sCT and CT images for bothdosimetric and geometric endpoints
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| 19. |
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| 20. |
- Lerner, Minna, et al.
(författare)
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Prospective Clinical Feasibility Study for MRI-Only Brain Radiotherapy
- 2022
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Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: MRI-only radiotherapy (RT) provides a workflow to decrease the geometric uncertainty introduced by the image registration process between MRI and CT data and to streamline the RT planning. Despite the recent availability of validated synthetic CT (sCT) methods for the head region, there are no clinical implementations reported for brain tumors. Based on a preceding validation study of sCT, this study aims to investigate MRI-only brain RT through a prospective clinical feasibility study with endpoints for dosimetry and patient setup. Material and Methods: Twenty-one glioma patients were included. MRI Dixon images were used to generate sCT images using a CE-marked deep learning-based software. RT treatment plans were generated based on MRI delineated anatomical structures and sCT for absorbed dose calculations. CT scans were acquired but strictly used for sCT quality assurance (QA). Prospective QA was performed prior to MRI-only treatment approval, comparing sCT and CT image characteristics and calculated dose distributions. Additional retrospective analysis of patient positioning and dose distribution gamma evaluation was performed. Results: Twenty out of 21 patients were treated using the MRI-only workflow. A single patient was excluded due to an MRI artifact caused by a hemostatic substance injected near the target during surgery preceding radiotherapy. All other patients fulfilled the acceptance criteria. Dose deviations in target were within ±1% for all patients in the prospective analysis. Retrospective analysis yielded gamma pass rates (2%, 2 mm) above 99%. Patient positioning using CBCT images was within ± 1 mm for registrations with sCT compared to CT. Conclusion: We report a successful clinical study of MRI-only brain radiotherapy, conducted using both prospective and retrospective analysis. Synthetic CT images generated using the CE-marked deep learning-based software were clinically robust based on endpoints for dosimetry and patient positioning.
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| 21. |
- Lorin, Stefan, et al.
(författare)
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Development of a compact proton scanning system in Uppsala with a moveable second magnet
- 2000
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 45, s. 1151-
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Tidskriftsartikel (refereegranskat)abstract
- A scanned proton beam yields dose distributions that in most cases are superior to passively scattered proton beams and to other external radiation treatment modalities. The present paper gives a description of the scanning system that has been developed at the Svedberg Laboratory (TSL) in Uppsala. The scanning technique and the technical design are described. The solution with a small pole gap of the magnets and a moveable second magnet results in a very compact scanning head, which can therefore be incorporated in a gantry of relatively limited size. A prototype was constructed that has been used to realize various dose distributions with a scanned beam of 180 MeV protons at TSL.
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| 22. |
- Lorin, Stefan, et al.
(författare)
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Reference dosimetry in a scanned pulsed proton beam using ionisation chambers and a Faraday cup
- 2008
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 53:13, s. 3519-3529
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Tidskriftsartikel (refereegranskat)abstract
- In order to give the correct dose to a patient, the monitor chamber for a proton scanning system has to be calibrated. As recombination of ion pairs occurs in the monitor chamber, the relation between the number of particles traversing it per time unit and the ionization chamber signal is not linear. A method developed for a scanned pulsed proton beam taking the nonlinear monitor signal into account is described. A vital part of the reference dosimetry procedure is to determine the absorbed dose under reference conditions, which is recommended to be done with an ionization chamber. For a scanned pulsed proton beam, the recombination in the ionization chamber is not negligible and the signal from the ionization chamber has to be corrected. In this work, it is shown that although the pulse length is comparable to the ion transit time the beam can be considered as continuously scanned if the applied high voltage is not too small. Also shown is that the two-voltage formula for a continuous beam is under some conditions applicable for a continuous scanned beam as well.
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| 23. |
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| 24. |
- Medin, Joakim, et al.
(författare)
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Experimental determination of k Qfactors for two types of ionization chambers in scanned proton beams
- 2022
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 67:5
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Tidskriftsartikel (refereegranskat)abstract
- Objective. Experimental determination of beam quality k Q factors for two types of Farmer ionization chambers, NE2571 and IBA FC65-G, in a scanned proton beam for three nominal energies (140 MeV, 180 MeV and 220 MeV) based on water calorimetry. Approach. Beam quality correction factors were determined comparing the results obtained with water calorimetry and ionometry. Water calorimetry was performed to determine the absorbed dose at a depth of measurement in water of 5 g cm-2, limited by the extension of the calorimeter glass vessel used. For the ionometry, two chambers of each type were included in the study. The ionization chambers were calibrated in terms of absorbed dose to water in 60Co at the Swedish Secondary Standard Dosimetry Laboratory, directly traceable to the BIPM, and were used according to the IAEA TRS-398 Code of Practice. Main results. The k Q values determined in the present work have been compared with the values tabulated in TRS-398 and its forthcoming update and also with those obtained in previous water calorimetric measurements and Monte Carlo calculations. All results were found to agree within the combined uncertainties of the different data. Significance. It is expected that the present work will serve as an experimental contribution to k Q -factors for the two chamber types and three scanned proton beam qualities used.
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| 25. |
- Medin, Joakim
(författare)
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Implementation of water calorimetry in a 180 MeV scanned pulsed proton beam including an experimental determination of k(Q) for a Farmer chamber
- 2010
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 55:12, s. 3287-3298
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Tidskriftsartikel (refereegranskat)abstract
- Water calorimetric measurements have been performed in a 180 MeV scanned pulsed proton beam and the absorbed dose determined has been compared with the results obtained using two NE2571 Farmer chambers and the IAEA TRS-398 code of practice. The depth of measurement in water corresponded to a residual range of R-res = 16.5 cm, corresponding to a mean energy of about 150 MeV. Ionization chambers were calibrated in terms of the absorbed dose to water in Co-60 at the Swedish Secondary Standard Dosimetry Laboratory, directly traceable to Bureau International des Poids et Mesures. The present experimental investigation has shown that water calorimetry is feasible in a high-energy scanned pulsed proton beam. When comparing the results obtained with water calorimetry and ionometry, the beam quality correction factor, k(Q), could be determined for the two NE2571 ionization chambers used. The k(Q)-factor was found to be 1.032 +/- 0.013, which is in good agreement with the factor tabulated in IAEA TRS-398 for this chamber type (1.039 +/- 0.018). The present result has also been compared with a previously obtained result in a passively scattered proton beam having similar energy. This comparison yielded a 1.1% deviation, which is not significant considering the combined uncertainties of the two experimental determinations of k(Q). The dominating contribution to the combined uncertainty stems from the correction factor for ion recombination in the scanned proton beam (1%), and further studies are required in order to reduce this uncertainty and reveal any possible differences in the k(Q)-factor between these two proton beam delivery techniques.
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