| 1. |
- Almén, Anja, 1964, et al.
(author)
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A CONCEPTUAL FRAMEWORK FOR MANAGING RADIATION DOSE TO PATIENTS IN DIAGNOSTIC RADIOLOGY USING REFERENCE DOSE LEVELS
- 2016
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 17-23
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Journal article (peer-reviewed)abstract
- The overall aim of the present work was to develop a conceptual framework for managing radiation dose in diagnostic radiology with the intention to support optimisation. An optimisation process was first derived. The framework for managing radiation dose, based on the derived optimisation process, was then outlined. The outset of the optimisation process is four stages: providing equipment, establishing methodology, performing examinations and ensuring quality. The optimisation process comprises a series of activities and actions at these stages. The current system of diagnostic reference levels is an activity in the last stage, ensuring quality. The system becomes a reactive activity only to a certain extent engaging the core activity in the radiology department, performing examinations. Three reference dose levels-possible, expected and established-were assigned to the three stages in the optimisation process, excluding ensuring quality. A reasonably achievable dose range is also derived, indicating an acceptable deviation from the established dose level. A reasonable radiation dose for a single patient is within this range. The suggested framework for managing radiation dose should be regarded as one part of the optimisation process. The optimisation process constitutes a variety of complementary activities, where managing radiation dose is only one part. This emphasises the need to take a holistic approach integrating the optimisation process in different clinical activities.
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| 2. |
- Almén, Anja, et al.
(author)
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Challenges assessing radiation risk in image-guided treatments-implications on optimisation of radiological protection
- 2018
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In: Journal of Radiological Protection. - : IOP Publishing. - 0952-4746 .- 1361-6498. ; 38:3, s. 1064-1076
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Journal article (peer-reviewed)abstract
- The present work explores challenges when assessing organ dose and effective dose concerning image-guided treatments. During these treatments considerable x-ray imaging is employed using technically advanced angiographic x-ray equipment. Thus, the radiation dose to organs and the related radiation risk are relatively difficult to assess. This has implications on the optimisation process, in which assessing radiation dose is one important part. In this study, endovascular aortic repair treatments were investigated. Organ dose and effective dose were assessed using Monte Carlo calculations together with a detailed specification of the exposure situation and patient size. The resulting normalised organ dose and effective dose with respect to kerma-area product for patient sizes and radiation qualities representative for the patient group were evaluated. The variability and uncertainty were investigated and their possible impact on optimisation of radiation protection was discussed. Exposure parameters, source to detector distances etc varied between treatments and also varied between image acquisitions during one treatment. Thus the derived normalised organ dose and effective dose exhibited a large range of values depending greatly on used exposure parameters and patient configuration. The derived normalised values for effective dose varied approximately between 0.05 and 0.30 mSv per Gy.cm(2) when taking patient sizes and exposure parameters into consideration, the values for organ doses exhibited even larger variation. The study shows a possible systematic error for derived organ doses and effective dose up to a factor of 7 if detailed exposure or patient characteristics are not known and/or not taken into consideration. The intra-treatment variability was also substantial and the normalised dose values varied up to a factor of 2 between image acquisitions during one treatment. The study shows that the use of conversion factors that are not adapted to the clinic can cause the radiation dose to be exaggerated or underestimated considerably. A conclusion from the present study is that the systematic error could be large and should be estimated together with random errors. A large uncertainty makes it difficult to detect true differences in radiation dose between methods and technology-a prerequisite for optimising radiation protection for image-guided treatments.
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| 3. |
- Almén, Anja, 1964, et al.
(author)
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OPTIMISATION OF OCCUPATIONAL RADIATION PROTECTION IN IMAGE-GUIDED INTERVENTIONS: EXPLORING VIDEO RECORDINGS AS A TOOL IN THE PROCESS
- 2016
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 425-429
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Journal article (peer-reviewed)abstract
- The overall purpose of this work was to explore how video recordings can contribute to the process of optimising occupational radiation protection in image-guided interventions. Video-recorded material from two image-guided interventions was produced and used to investigate to what extent it is conceivable to observe and assess dose-affecting actions in video recordings. Using the recorded material, it was to some extent possible to connect the choice of imaging techniques to the medical events during the procedure and, to a less extent, to connect these technical and medical issues to the occupational exposure. It was possible to identify a relationship between occupational exposure level to staff and positioning and use of shielding. However, detailed values of the dose rates were not possible to observe on the recordings, and the change in occupational exposure level from adjustments of exposure settings was not possible to identify. In conclusion, the use of video recordings is a promising tool to identify dose-affecting instances, allowing for a deeper knowledge of the interdependency between the management of the medical procedure, the applied imaging technology and the occupational exposure level. However, for a full information about the dose-affecting actions, the equipment used and the recording settings have to be thoroughly planned.
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| 4. |
- Almén, Anja, 1964, et al.
(author)
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Optimisation of occupational radiological protection in image-guided interventions: potential impact of dose rate measurements.
- 2015
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In: Journal of radiological protection : official journal of the Society for Radiological Protection. - : IOP Publishing. - 1361-6498. ; 35:1, s. 47-62
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Journal article (peer-reviewed)abstract
- The optimisation of occupational radiological protection is challenging and a variety of factors have to be considered. Physicians performing image-guided interventions are working in an environment with one of the highest radiation risk levels in healthcare. Appropriate knowledge about the radiation environment is a prerequisite for conducting the optimisation process. Information about the dose rate variation during the interventions could provide valuable input to this process. The overall purpose of this study was to explore the prerequisite and feasibility to measure dose rate in scattered radiation and to assess the usefulness of such data in the optimisation process.Using an active dosimeter system, the dose rate in the unshielded scattered radiation field was measured in a fixed point close to the patient undergoing an image-guided intervention. The measurements were performed with a time resolution of one second and the dose rate data was continuously timed in a data log. In two treatment rooms, data was collected during a 6 month time period, resulting in data from 380 image-guided interventions and vascular treatments in the abdomen, arms and legs. These procedures were categorised into eight types according to the purpose of the treatment and the anatomical region involved.The dose rate varied substantially between treatment types, both regarding the levels and the distribution during the procedure. The maximum dose rate for different types of interventions varied typically between 5 and 100 mSv h(-1), but substantially higher and lower dose rates were also registered. The average dose rate during a complete procedure was however substantially lower and varied typically between 0.05 and 1 mSv h(-1). An analysis of the distribution disclosed that for a large part of the treatment types, the major amount of the total accumulated dose for a procedure was delivered in less than 10% of the exposure time and in less than 1% of the total procedure time.The present study shows that systematic dose rate measurements are feasible. Such measurements can be used to give a general indication of the exposure level to the staff and could serve as a first risk assessment tool when introducing new treatment types or x-ray equipment in the clinic. For example, it could provide an indication for when detailed eye dose measurements are needed. It also gives input to risk management considerations and the development of efficient routines for other radiological protection measures.
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| 5. |
- Almén, Anja, 1964, et al.
(author)
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The process of optimisation of radiological protection – the significance of diagnostic reference levels
- 2015
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In: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Conference paper (other academic/artistic)abstract
- The system of diagnostic reference levels in medicine has been presented as a tool to advice on when a local review of the procedures and equipment is warranted in order to determine whether the protection has been adequately optimised. The system is somewhat country specific, presumably due to different national regulations or guidelines, but as a whole relies on the same principles and standards. Diagnostic reference levels are typically set for standardised patients and procedures with minor considerations of the need to manage individual patient characteristics or specific medical tasks in the optimisation process. Optimisation of radiological protection should involve key aspects influencing the radiation dose to the patients and also include the needs of optimising the protection for each patient individually. The actual given radiation dose to the patient is affected by a number of factors, amongst other things equipment specific features and training of staff performing the examinations. This emphases the need to take a holistic approach and integrate different clinical processes - e.g. purchasing of equipment or the implementation of new examination protocols in the clinic – in the process of optimisation. Taking this approach gives the opportunity to evaluate the significance of the current system of diagnostic reference levels in the process of optimisation and to identify other reference levels supporting the process of optimisation. This paper will investigate the optimisation process and identify key instances where reference levels could provide support to the optimisation process. The issue of optimising the individual examination with regard to patient characteristics and medical indication will be specifically addressed.
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| 6. |
- Andersson, Peter, 1975, et al.
(author)
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Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams
- 2023
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In: Biomedical Engineering & Physics Express. - : Institute of Physics. - 2057-1976. ; 9:2
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Journal article (peer-reviewed)abstract
- Purpose. To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98-1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54-0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99-1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92-0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses. © 2023 The Author(s).
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| 7. |
- Arvidsson, Jonathan, et al.
(author)
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Image Fusion of Reconstructed Digital Tomosynthesis Volumes From a Frontal and a Lateral Acquisition
- 2016
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 410-415
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Journal article (peer-reviewed)abstract
- Digital tomosynthesis (DTS) has been used in chest imaging as a low radiation dose alternative to computed tomography (CT). Traditional DTS shows limitations in the spatial resolution in the out-of-plane dimension. As a first indication of whether a dual-plane dual-view (DPDV) DTS data acquisition can yield a fair resolution in all three spatial dimensions, a manual registration between a frontal and a lateral image volume was performed. An anthropomorphic chest phantom was scanned frontally and laterally using a linear DTS acquisition, at 120 kVp. The reconstructed image volumes were resampled and manually co-registered. Expert radiologist delineations of the mediastinal soft tissues enabled calculation of similarity metrics in regard to delineations in a reference CT volume. The fused volume produced the highest total overlap, implying that the fused volume was a more isotropic 3D representation of the examined object than the traditional chest DTS volumes.
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| 8. |
- Arvidsson, Jonathan, et al.
(author)
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Image fusion of two FBP-reconstructed digital tomosynthesis volumes from frontal and lateral acquisitions
- 2015
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In: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Conference paper (other academic/artistic)abstract
- Purpose: Digital tomosynthesis (DTS) has been used in chest imaging as a low radiation dose alternative to computed tomography (CT). DTS can to a certain degree separate overlapping anatomical structures at different depth levels using traditional filtered back projection (FBP) reconstruction schemes. However, the spatial resolution remains limited in the out-of-plane dimension. The aim of this work was to investigate if utilizing information from both a frontal and lateral DTS acquisition will give a more accurate 3D representation of the examined object. Method: As a first indication of whether a dual-view DTS data acquisition can yield a fair resolution in the three spatial dimensions, a manual registration between two reconstructed DTS volumes, one being a frontal data acquisition and the other a lateral one, was performed. An anthropomorphic chest phantom was scanned using a linear DTS acquisition in frontal and lateral directions, at 120 kVp. The two corresponding volumes where reconstructed, downsampled to a lower resolution and manually co-registered. Being manual, the registration step was subjective and thus included identifying suitable landmarks that could be used to ensure that the correct rigid transformation between the two volumes was found. Finally a CT examination of the phantom, used as a ground truth 3D representation, was manually co-registered to the DTS data. The reconstruction, downsampling and co-registering was performed using both commercial and freely available software. Major Findings: The resulting co-registered volume gave a more accurate isotropic 3D representation of the examined object than the two original reconstructions. Oblique planes were more accurately reproduced by the co-registered volume whereas coronal and sagittal planes were better reproduced by the original frontally and laterally reconstructed volumes. Conclusions: The proposed method shows that fusing frontally and laterally reconstructed DTS volumes is possible and yields a more accurate isotropic 3D representation of the examined object than original DTS reconstructions. By utilizing a dual-view DTS acquisition geometry some advantages of including DTS data from orthogonal projection angles were illustrated. The findings are encouraging for further work on reconstruction algorithms using a dual-view DTS acquisition geometry.
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| 9. |
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| 10. |
- Ásgeirsdóttir, Helga, et al.
(author)
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Depiction of anatomic structures of relevance for scoring of cystic fibrosis changes by chest tomosynthesis and computed tomography
- 2014
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In: Journal of Cystic Fibrosis. 37th European Cystic Fibrosis Conference, 11-14 June 2014, Gothenburg, Sweden. ; 13:Suppl. 2
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Conference paper (other academic/artistic)abstract
- Introduction: Chest radiography (CR) and computed tomography (CT) are commonly used for imaging of patients with cystic fibrosis, and scoring is applied to assess disease severity. Chest tomosynthesis (CTS) is a new imaging modality providing better anatomic visualization than CR at radiation doses and costs lower than CT. Objective: To compare visibility and size of anatomic structures of relevance for scoring in CTS and CT images. Methods: 21 adult patients with cystic fibrosis were examined both with CTS (VolumeRAD; GE Healthcare) and volumetric CT (LightSpeed Pro 16, LightSpeed VCT, Discovery CT750HD; GE healthcare and Somatom Definition, Siemens Medical Solutions). The average effective dose for a standard patient was 0.13 and 4.5 mSv for CTS and CT, respectively. Comparison of visibility and manual measurements of diameters of the central and peripheral bronchi and their accompanying artery, as well as bronchial wall thickness (BWT), were performed in a non-blinded fashion. Results: All central structures could be evaluated. Mean difference in diameter of central bronchi, accompanying artery and BWT between CTS and CT was −0.6 (SD 0.6), −0.7 (SD 0.7) and −0.4 (SD 0.2) mm, respectively. Peripheral structures were more difficult to assess by CTS. Peripheral bronchial diameter, BWT and diameter of accompanying artery could be assessed by CTS in 20, 15 and 4 cases, respectively and mean difference between measurements was −0.5 (SD 0.5), −0.3 (SD 0.3) and −0.4 (SD 0.4) mm, respectively. Conclusion: This study indicates that peripheral structures are more difficult to evaluate by CTS and that CTS slightly underestimate size of structures in comparison to CT
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