| 1. |
- 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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| 2. |
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| 3. |
- Dance, David, et al.
(författare)
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Influence of anode/filter material and tube potential on contrast, signal-to-noise ratio and average absorbed dose in mammography: a Monte Carlo study
- 2000
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Ingår i: British Journal of Radiology. - 0007-1285. ; 73, s. 1056-1067
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Tidskriftsartikel (refereegranskat)abstract
- The comparative performance of mammographic X-ray systems that use different anode/filter combinations has been assessed for screen±®lm and digital imaging. Monte Carlo techniques have been used to calculate average glandular dose as well as contrast and signal-tonoise ratio for imaging two test details. Five anode/filter combinations have been studied to establish the potential for dose saving or image quality improvement. For screen±film mammography, it was found that little bene®t is gained by changing from a standard 28 kV molybdenum/molybdenum spectrum for breasts up to 6 cm thick. For thicker breasts, where the tube potential for the standard technique might be increased, 20% improvement in contrast can be achieved without dose penalty using molybdenum/rhodium or rhodium/rhodium spectra, whereas dose savings of more than 50% can be attained whilst maintaining contrast using tungsten/rhodium or rhodium/aluminium spectra. In digital mammography, a molybdenum/ molybdenum spectrum delivers the lowest dose for a 2 cm breast, but gives the highest dose for thicker breasts. Tungsten/rhodium or rhodium/aluminium spectra provide the lowest doses at greater thicknesses. It is concluded that for screen±film mammography, molybdenum/ molybdenum is the spectrum of choice for all but the thickest or most glandular breasts. In digital mammography, an alternative spectrum is preferable for breasts thicker than 2 cm.
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| 5. |
- Ekestubbe, Annika, 1953, et al.
(författare)
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Effective and organ doses from scanography and zonography: a comparison with periapical radiography.
- 2004
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Ingår i: Dento maxillo facial radiology. - : British Institute of Radiology. - 0250-832X. ; 33:2, s. 87-92
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To compare absorbed and effective doses from scanographic and zonographic examinations performed in the Scanora unit with intraoral periapical radiography. METHODS: Absorbed dose measurements were made on an anthropomorphic phantom head with LiF thermoluminescent dosemeters in the regions of the pituitary gland, eye lenses, parotid glands, submandibular glands, thyroid gland and skin. Energy imparted was calculated from the measurements of air collision kerma and effective doses by using the quotient 24 mSv J-1 between energy imparted and effective dose. The upper and lower third molar region was examined with intraoral radiographs and with ramus scanograms, dental scanograms and dental zonograms. Radiation dose measurements were also performed for Scanora panoramic radiography (jaw and dental). RESULTS: The effective doses for the ramus and dental scanograms were 0.01 mSv, similar or lower than for intraoral radiography. Zonography yielded the highest effective dose (0.03 mSv). Except for the skin doses, the salivary glands received the highest doses. Salivary gland doses were slightly higher from narrow beam than from intraoral radiography. CONCLUSIONS: Detail narrow beam radiography with the Scanora is an alternative to periapical radiography and is preferred, from a radiation dose point of view, over zonography.
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| 7. |
- Granlund, Christina, et al.
(författare)
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Absorbed organ and effective doses from digital intra-oral and panoramic radiography applying the ICRP 103 recommendations for effective dose estimations
- 2016
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 89:1066
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Tidskriftsartikel (refereegranskat)abstract
- Objective: During dental radiography, the salivary and thyroid glands are at radiation risk. In 2007, the International Commission on Radiological Protection (ICRP) updated the methodology for determining the effective dose, and the salivary glands were assigned tissue-specific weighting factors for the first time. The aims of this study were to determine the absorbed dose to the organs and to calculate, applying the ICRP publication 103 tissue-weighting factors, the effective doses delivered during digital intraoral and panoramic radiography. Methods: Thermoluminescent dosemeter measurements were performed on an anthropomorphic head and neck phantom. The organ-absorbed doses were measured at 30 locations, representing different radiosensitive organs in the head and neck, and the effective dose was calculated according to the ICRP recommendations. Results: The salivary glands and the oral mucosa received the highest absorbed doses from both intraoral and panoramic radiography. The effective dose from a fullmouth intraoral examination was 15mSv and for panoramic radiography, the effective dose was in the range of 19-75 mSv, depending on the panoramic equipment used. Conclusion: The effective dose from a full-mouth intraoral examination is lower and that frompanoramic radiography is higher than previously reported. Clinicians should be aware of the higher effective dose delivered during panoramic radiography and the risk-benefit profile of this technique must be assessed for the individual patient.
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| 8. |
- Hammarstedt, Lilian, et al.
(författare)
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Adrenal lesions: variability in attenuation over time, between scanners, and between observers.
- 2013
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Ingår i: Acta radiologica (Stockholm, Sweden : 1987). - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 54:7, s. 817-826
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundMeasurements of attenuation (in Hounsfield units [HU]) and contrast wash-out are widely used to characterize adrenal lesions as benign or indeterminate/malignant at computed tomography (CT). Clinical experience suggests that such measurements of adrenal lesions may vary over time and between observers, making evaluation difficult.PurposeTo investigate the change over time of adrenal lesion size, attenuation, and contrast wash-out at CT, to determine inter-observer variability, and to analyze other factors underlying the variability.Material and MethodsIn a cohort of patients, with or without malignant disease, undergoing CT, adrenal lesions were prospectively analyzed. Lesions with growth >20% or >5 mm over 6 months were excluded. Non-enhanced attenuation and contrast medium wash-out over 2-year follow-up were analyzed. An inter-observer analysis with five observers and a phantom study of eight different CT scanners were performed to assess measurement variability.ResultsMean adrenal lesion non-enhanced attenuation values decreased by 0.5 HU/year during follow-up. Using 10 HU or 40% relative wash-out as threshold values for benign versus indeterminate lesions, 27 (20%) and 39 (29%) of 136 lesions, respectively, would be reclassified at some occasion during follow-up. In the observer analysis 37 of 40 lesions demonstrated agreement between all observers, using established threshold values. The phantom study showed an intra-scanner variability of 1-3 HU, but an inter-scanner variability of up to 8 HU for water.ConclusionThe clinically widespread use of specific attenuation threshold values for characterizing adrenal lesions must be used with great caution, considering that multiple factors, related to patient, equipment, scanning technique, and observer influence the outcome.
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| 9. |
- Hansson, Jonny, et al.
(författare)
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Comparison of three methods for determining CT dose profile: presenting the tritium method
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 434-438
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present work was to describe a method of using an imaging plate from a computed radiography system to determine the computed tomography (CT) dose profile (the tritium method) and to compare this method with point-dose measurements using a solid-state detector (CT Dose Profiler; RTI Electronics, Mölndal, Sweden) and the indirect method of comparing the air kerma-length product (P(KL)) at different beam collimations. The three methods were used to determine the full width at half maximum (FWHM) of the dose profile of a multi-slice CT at different nominal beam collimations. For all beam collimations, the obtained deviation between the tritium method and the CT Dose Profiler was smaller than 0.1 mm. The maximum relative error was 2 %. For the P(KL) method, the deviation from the CT Dose Profiler was between 0.2 and 0.4 mm, resulting in a relative error larger than 10 % for the smallest beam collimation even after normalisation to a known FWHM. In conclusion, the proposed method of using an imaging plate to determine the FWHM of the CT dose profile has a high accuracy and shows good agreement with the more advanced method of point-dose measurements using a solid-state detector.
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