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Dose Management in Diagnostic Radiology - application of the DICOM imaging standard and a Monte Carlo dose engine for exposure surveillance
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för immunologi, genetik och patologi.ORCID-id: 0000-0002-2602-599X
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Ionizing radiation is used in diagnostic radiology with a large contribution to the health of the patients. The regulations to limit the detrimental effects, e.g. cancer induction, are based on recommendations from the International Commission on Radiological Protection (ICRP). Epidemiological evidence for radiation induced cancer is expressed as a function of absorbed dose in the irradiated organs. The committee for Biological Effects of Ionizing Radiation has favored the use of Lifetime Attributable Risk, a risk estimator applicable to individuals exposed in medical applications. The imaging in radiology complies with a technical standard that potentiates the retrieval of exposure information that can be used in optimization of patient exposure. The information can also be used as input in organ dose calculations.

The aims were to apply the benefits of the technical image standard to radiation safety management by automated collection and analysis of exposure data and to adapt a Therapy Planning System (TPS) for radiotherapy to calculate dose for a Computed Tomography (CT) machine.

An automated workflow for extraction, communication and analysis of exposure data from the image files in the central image archive was defined and implemented at the institution (papers I-II). A source model for Monte Carlo simulation of the CT was developed taking into consideration the energy spectrum of the photons, the spiral movement of the X-ray beam, the beam shaping filter and the tube current modulation (paper III). The source model was used exploring the possibilities to utilize the tissue characterization methods and segmentation tools available in the TPS to devise a strategy to automate organ dose calculations for patients undergoing thorax examinations in a CT (paper IV).

The exposure data workflow was finalized showing that the technical standard for images could supply a framework for automated assembly and analysis of the data, supporting the local implementation of optimization. The CT was modeled with regard to its irradiation characteristics with uncertainties in the dose calculations below 4%. Dose calculations with the tissue characterization methods available in the TPS deviated by less than 2% from measurements and a strategy for automation of organ dose calculations was devised that could facilitate individual risk estimates in CT.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2017. , s. 44
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1407
Nyckelord [en]
Radiology, metadata, DICOM, radiation safety, Monte Carlo, source model, patient model, optimization, justification
Nationell ämneskategori
Övrig annan medicin och hälsovetenskap
Forskningsämne
Medicinsk radiofysik
Identifikatorer
URN: urn:nbn:se:uu:diva-335575ISBN: 978-91-513-0179-2 (tryckt)OAI: oai:DiVA.org:uu-335575DiVA, id: diva2:1163425
Disputation
2018-02-02, Lecture hall, Falu lasarett, Lasarettsvägen 10, Falun, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-01-08 Skapad: 2017-12-07 Senast uppdaterad: 2018-03-07
Delarbeten
1. DICOM Metadata repository for technical information in digital medical images
Öppna denna publikation i ny flik eller fönster >>DICOM Metadata repository for technical information in digital medical images
2009 (Engelska)Ingår i: Acta Oncologica, Vol. 48, nr 2, s. 285-288Artikel i tidskrift (Refereegranskat) Published
Ort, förlag, år, upplaga, sidor
Taylor & Francis, 2009
Nationell ämneskategori
Annan fysik
Identifikatorer
urn:nbn:se:uu:diva-335529 (URN)
Tillgänglig från: 2017-12-06 Skapad: 2017-12-06 Senast uppdaterad: 2017-12-08
2. Automated detection of changes in patient exposure in digital projection radiography using exposure index from DICOM header metadata
Öppna denna publikation i ny flik eller fönster >>Automated detection of changes in patient exposure in digital projection radiography using exposure index from DICOM header metadata
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2011 (Engelska)Ingår i: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 50, nr 6, s. 960-965Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Purpose. Automated collection of image data from DICOM headers enables monitoring of patient dose and image quality parameters. Manual monitoring is time consuming, owing to the large number of exposure scenarios, thus automated methods for monitoring needs to be investigated. The aim of the present work was to develop and optimise such a method. Material and methods. Exposure index values from digital systems in projection radiography were collected over a period of five years, representing data from 1.2 million projection images. The exposure index values were converted to detector dose and an automated method for detection of sustained level shifts in the resulting detector dose time series was applied using the statistical analysis tool R. The method combined handling of outliers, filtering and estimation of variation in combination with two different statistical rank tests for level shift detection. A set of 304 time series representing central body parts was selected and the level shift detection method was optimised using level shifts identified by ocular evaluation as the gold standard. Results. Two hundred and eighty-one level changes were identified that were deemed in need of further investigation. The majority of these changes were abrupt. The sensitivity and specificity of the optimised and automated detection method concerning the ocular evaluation were 0.870 and 0.997, respectively, for detected abrupt changes. Conclusions. An automated analysis of exposure index values, with the purpose of detecting changes in exposure, can be performed using the R software in combination with a DICOM header metadata repository containing the exposure index values from the images. The routine described has good sensitivity and acceptable specificity for a wide range of central body part projections and can be optimised for more specialised purposes.

Nationell ämneskategori
Radiologi och bildbehandling
Identifikatorer
urn:nbn:se:uu:diva-156931 (URN)10.3109/0284186X.2011.579622 (DOI)000292841500029 ()
Tillgänglig från: 2011-08-20 Skapad: 2011-08-11 Senast uppdaterad: 2017-12-08Bibliografiskt granskad
3. Source modeling for Monte Carlo dose calculation of CT examinations with a radiotherapy treatment planning system
Öppna denna publikation i ny flik eller fönster >>Source modeling for Monte Carlo dose calculation of CT examinations with a radiotherapy treatment planning system
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2016 (Engelska)Ingår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 43, nr 11, s. 6118-6128Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Purpose: Radiation dose to patients undergoing examinations with Multislice Computed Tomography (MSCT) as well as Cone Beam Computed Tomography (CBCT) is a matter of concern. Risk management could benefit from efficient replace rational dose calculation tools. The paper aims to verify MSCT dose calculations using a Treatment Planning System (TPS) for radiotherapy and to evaluate four different variations of bow-tie filter characterizations for the beam model used in the dose calculations. Methods: A TPS (RayStation (TM), RaySearch Laboratories, Stockholm, Sweden) was configured to calculate dose from a MSCT (GE Healthcare, Wauwatosa, WI, USA). The x-ray beam was characterized in a stationary position the by measurements of the Half-Value Layer (HVL) in aluminum and kerma along the principal axes of the isocenter plane perpendicular to the beam. A Monte Carlo source model for the dose calculation was applied with four different variations on the beam-shaping bow-tie filter, taking into account the different degrees of HVL information but reconstructing the measured kerma distribution after the bow-tie filter by adjusting the photon sampling function. The resulting dose calculations were verified by comparison with measurements in solid water as well as in an anthropomorphic phantom. Results: The calculated depth dose in solid water as well as the relative dose profiles was in agreement with the corresponding measured values. Doses calculated in the anthropomorphic phantom in the range 26-55 mGy agreed with the corresponding thermo luminescence dosimeter (TLD) measurements. Deviations between measurements and calculations were of the order of the measurement uncertainties. There was no significant difference between the different variations on the bow-tie filter modeling. Conclusions: Under the assumption that the calculated kerma after the bow-tie filter replicates the measured kerma, the central specification of the HVL of the x-ray beam together with the kerma distribution can be used to characterize the beam. Thus, within the limits of the study, a flat bow-tie filter with an HVL specified by the vendor suffices to calculate the dose distribution. The TPS could be successfully configured to replicate the beam movement and intensity modulation of a spiral scan with dose modulation, on the basis of the specifications available in the metadata of the digital images and the log file of the CT.

Nyckelord
radiation exposure, radiation oncology, tomography, x-ray computed, Monte Carlo method, risk management
Nationell ämneskategori
Radiologi och bildbehandling
Identifikatorer
urn:nbn:se:uu:diva-310771 (URN)10.1118/1.4965043 (DOI)000387007500033 ()27806588 (PubMedID)
Tillgänglig från: 2016-12-19 Skapad: 2016-12-19 Senast uppdaterad: 2017-12-08Bibliografiskt granskad
4. Towards automated and personalized organ dose determination in CT examinations – influence of tissue data representations for Monte Carlo dose calculation with a Therapy Planning System
Öppna denna publikation i ny flik eller fönster >>Towards automated and personalized organ dose determination in CT examinations – influence of tissue data representations for Monte Carlo dose calculation with a Therapy Planning System
(Engelska)Ingår i: Medical physics (Lancaster), ISSN 0094-2405Artikel i tidskrift (Refereegranskat) Submitted
Nationell ämneskategori
Annan fysik
Identifikatorer
urn:nbn:se:uu:diva-335555 (URN)
Tillgänglig från: 2017-12-06 Skapad: 2017-12-06 Senast uppdaterad: 2017-12-08

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