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Malusek, A., Sandborg, M. & Alm Carlsson, G. (2016). ACCURATE KAP METER CALIBRATION AS A PREREQUISITE FOR OPTIMISATION IN PROJECTION RADIOGRAPHY. Radiation Protection Dosimetry, 169(1-4), 353-359
Open this publication in new window or tab >>ACCURATE KAP METER CALIBRATION AS A PREREQUISITE FOR OPTIMISATION IN PROJECTION RADIOGRAPHY
2016 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, no 1-4, p. 353-359Article in journal (Refereed) Published
Abstract [en]

Modern X-ray units register the air kerma–area product, PKA, with a built-in KAP meter. Some KAP meters show an energydependent bias comparable with the maximum uncertainty articulated by the IEC (25 %), adversely affecting dose-optimisation processes. To correct for the bias, a reference KAP meter calibrated at a standards laboratory and two calibration methods described here can be used to achieve an uncertainty of <7 % as recommended by IAEA. A computational model of the reference KAP meter is used to calculate beam quality correction factors for transfer of the calibration coefficient at the standards laboratory, Q0, to any beam quality, Q, in the clinic. Alternatively, beam quality corrections are measured with an energy-independent dosemeter via a reference beam quality in the clinic, Q1, to beam quality, Q. Biases up to 35 % of built-in KAP meter readings were noted. Energy-dependent calibration factors are needed for unbiased PKA. Accurate KAP meter calibration as a prerequisite for optimisation in projection radiography.

Place, publisher, year, edition, pages
Oxford University Press, 2016
National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-124662 (URN)10.1093/rpd/ncv524 (DOI)000383492100056 ()26743261 (PubMedID)
Note

Funding agencies: Swedish Radiation Safety Authority, SSM [SSM 2014-1204]

Available from: 2016-02-09 Created: 2016-02-09 Last updated: 2017-05-02Bibliographically approved
Kardell, M., Magnusson, M., Sandborg, M., Alm Carlsson, G., Jeuthe, J. & Malusek, A. (2016). AUTOMATIC SEGMENTATION OF PELVIS FOR BRACHYTHERAPYOF PROSTATE. Radiation Protection Dosimetry, 169(1-4), 398-404
Open this publication in new window or tab >>AUTOMATIC SEGMENTATION OF PELVIS FOR BRACHYTHERAPYOF PROSTATE
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2016 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, no 1-4, p. 398-404Article in journal (Refereed) Published
Abstract [en]

Advanced model-based iterative reconstruction algorithms in quantitative computed tomography (CT) perform automatic segmentation of tissues to estimate material properties of the imaged object. Compared with conventional methods, these algorithms may improve quality of reconstructed images and accuracy of radiation treatment planning. Automatic segmentation of tissues is, however, a difficult task. The aim of this work was to develop and evaluate an algorithm that automatically segments tissues in CT images of the male pelvis. The newly developed algorithm (MK2014) combines histogram matching, thresholding, region growing, deformable model and atlas-based registration techniques for the segmentation of bones, adipose tissue, prostate and muscles in CT images. Visual inspection of segmented images showed that the algorithm performed well for the five analysed images. The tissues were identified and outlined with accuracy sufficient for the dual-energy iterative reconstruction algorithm whose aim is to improve the accuracy of radiation treatment planning in brachytherapy of the prostate.

National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-122978 (URN)10.1093/rpd/ncv461 (DOI)000383492100063 ()26567322 (PubMedID)
Funder
Swedish Cancer Society, CAN 2012/764Swedish Cancer Society, CAN 2014/691
Note

Funding agencies: Swedish Cancer Foundation [CAN 2012/764, CAN 2014/691]; Medical Faculty, Linkoping University; ALF Grants, Region Ostergotland [LiO-438731]

Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2017-12-01
Örtenberg, A., Magnusson, M., Sandborg, M., Alm Carlsson, G. & Malusek, A. (2016). PARALLELISATION OF THE MODEL-BASED ITERATIVE RECONSTRUCTION ALGORITHM DIRA. Radiation Protection Dosimetry, 169(1-4), 405-409
Open this publication in new window or tab >>PARALLELISATION OF THE MODEL-BASED ITERATIVE RECONSTRUCTION ALGORITHM DIRA
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2016 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, no 1-4, p. 405-409Article in journal (Refereed) Published
Abstract [en]

New paradigms for parallel programming have been devised to simplify software development on multi-core processors and many-core graphical processing units (GPU). Despite their obvious benefits, the parallelisation of existing computer programs is not an easy task. In this work, the use of the Open Multiprocessing (OpenMP) and Open Computing Language (OpenCL) frameworks is considered for the parallelisation of the model-based iterative reconstruction algorithm DIRA with the aim to significantly shorten the code’s execution time. Selected routines were parallelised using OpenMP and OpenCL libraries; some routines were converted from MATLAB to C and optimised. Parallelisation of the code with the OpenMP was easy and resulted in an overall speedup of 15 on a 16-core computer. Parallelisation with OpenCL was more difficult owing to differences between the central processing unit and GPU architectures. The resulting speedup was substantially lower than the theoretical peak performance of the GPU; the cause was explained.

Place, publisher, year, edition, pages
Oxford university press: , 2016
National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:liu:diva-123009 (URN)10.1093/rpd/ncv430 (DOI)000383492100064 ()26454270 (PubMedID)
Funder
Swedish Cancer Society, CAN 2012/764Swedish Cancer Society, CAN 2014/691
Note

Funding agencies: Swedish Cancer Foundation [CAN 2012/764, CAN 2014/691]

Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2018-01-10
Malusek, A., Helmrot, E., Sandborg, M., Grindborg, J.-E. & Alm Carlsson, G. (2014). In-situ calibration of clinical built-in KAP meters with traceability to a primary standard using a reference KAP meter. Physics in Medicine and Biology, 59(23), 7195-7210
Open this publication in new window or tab >>In-situ calibration of clinical built-in KAP meters with traceability to a primary standard using a reference KAP meter
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2014 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, no 23, p. 7195-7210Article in journal (Refereed) Published
Abstract [en]

The air kerma-area product (KAP) is used for settings of diagnostic reference levels. The International Atomic Energy Agency (IAEA) recommends that doses in diagnostic radiology (including the KAP values) be estimated with an accuracy of at least +/- 7% (k = 2). Industry standards defined by the International Electrotechnical Commission (IEC) specify that the uncertainty of KAP meter measurements should be less than +/- 25% (k = 2). Medical physicists willing to comply with the IAEAs recommendation need to apply correction factors to KAP values reported by x-ray units. The aim of this work is to present and evaluate a calibration method for built-in KAP meters on clinical x-ray units. The method is based on (i) a tandem calibration method, which uses a reference KAP meter calibrated to measure the incident radiation, (ii) measurements using an energy-independent ionization chamber to correct for the energy dependence of the reference KAP meter, and (iii) Monte Carlo simulations of the beam quality correction factors that correct for differences between beam qualities at a standard laboratory and the clinic. The method was applied to the KAP meter in a Siemens Aristos FX plus unit. It was found that values reported by the built-in KAP meter differed from the more accurate values measured by the reference KAP meter by more than 25% for high tube voltages (more than 140 kV) and heavily filtered beams (0.3 mm Cu). Associated uncertainties were too high to claim that the IECs limit of 25% was exceeded. Nevertheless the differences were high enough to justify the need for a more accurate calibration of built-in KAP meters.

Place, publisher, year, edition, pages
IOP Publishing: Hybrid Open Access, 2014
Keywords
KAP-meter; kerma-area product; calibration
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-112993 (URN)10.1088/0031-9155/59/23/7195 (DOI)000345254000010 ()25369212 (PubMedID)
Note

Funding Agencies|Swedish Radiation Safety Authority

Available from: 2015-01-12 Created: 2015-01-08 Last updated: 2017-12-05
Kubancak, J., Ambrozova, I., Buetikofer, R., Kudela, K., Langer, R., Davidkova, M., . . . Malusek, A. (2014). Liulin silicon semiconductor spectrometers as cosmic ray monitors at  the high mountain observatories Jungfraujoch and Lomnický štít. Journal of Instrumentation, 9(P07018)
Open this publication in new window or tab >>Liulin silicon semiconductor spectrometers as cosmic ray monitors at  the high mountain observatories Jungfraujoch and Lomnický štít
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2014 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 9, no P07018Article in journal (Refereed) Published
Abstract [en]

Currently, most cosmic ray data are obtained by detectors on satellites, aircraft, high-altitude balloons and ground (neutron monitors). In our work, we examined whether Liulin semiconductor spectrometers (simple silicon planar diode detectors with spectrometric properties) located at high mountain observatories could contribute new information to the monitoring of cosmic rays by analyzing data from selected solar events between 2005 and 2013. The decision thresholds and detection limits of these detectors placed at Jungfraujoch (Switzerland; 3475 m a.s.l.; vertical cut-off rigidity 4.5 GV) and Lomnicky. stit (Slovakia; 2633 m a.s.l.; vertical cut-off rigidity 3.84 GV) highmountain observatories were determined. The data showed that only the strongest variations of the cosmic ray flux in this period were detectable. The main limitation in the performance of these detectors is their small sensitive volume and low sensitivity of the PIN photodiode to neutrons.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
Keywords
Dosimetry concepts and apparatus; Spectrometers; Analysis and statistical methods
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110981 (URN)10.1088/1748-0221/9/07/P07018 (DOI)000340050700039 ()
Note

Funding Agencies|project INGO of Ministry of Education, Youth and Sports of the Czech Republic; IEP SAS in Kosice; Slovak grant agency VEGA [2/0040/13]; [SGS12/200/OHK4/3T/14]

Available from: 2014-10-01 Created: 2014-10-01 Last updated: 2017-12-05Bibliographically approved
Malusek, A., Magnusson, M., Sandborg, M., Westin, R. & Alm Carlsson, G. (2014). Prostate tissue decomposition via DECT using the modelbased iterative image reconstruction algorithm DIRA. In: Bruce R. Whiting; Christoph Hoeschen; Despina Kontos (Ed.), Medical Imaging 2014: Physics of Medical Imaging. Paper presented at Medical Imaging 2014 - Physics of Medical Imaging, San Diego, California, United States, 17–20 February 2014 (pp. Art.nr. 90333H). SPIE - International Society for Optical Engineering, 9033(90333H)
Open this publication in new window or tab >>Prostate tissue decomposition via DECT using the modelbased iterative image reconstruction algorithm DIRA
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2014 (English)In: Medical Imaging 2014: Physics of Medical Imaging / [ed] Bruce R. Whiting; Christoph Hoeschen; Despina Kontos, SPIE - International Society for Optical Engineering, 2014, Vol. 9033, no 90333H, p. Art.nr. 90333H-Conference paper, Published paper (Refereed)
Abstract [en]

Better knowledge of elemental composition of patient tissues may improve the accuracy of absorbed dose delivery in brachytherapy. Deficiencies of water-based protocols have been recognized and work is ongoing to implement patient-specific radiation treatment protocols. A model based iterative image reconstruction algorithm DIRA has been developed by the authors to automatically decompose patient tissues to two or three base components via dual-energy computed tomography. Performance of an updated version of DIRA was evaluated for the determination of prostate calcification. A computer simulation using an anthropomorphic phantom showed that the mass fraction of calcium in the prostate tissue was determined with accuracy better than 9%. The calculated mass fraction was little affected by the choice of the material triplet for the surrounding soft tissue. Relative differences between true and approximated values of linear attenuation coefficient and mass energy absorption coefficient for the prostate tissue were less than 6% for photon energies from 1 keV to 2 MeV. The results indicate that DIRA has the potential to improve the accuracy of dose delivery in brachytherapy despite the fact that base material triplets only approximate surrounding soft tissues.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2014
Series
Progress in Biomedical Optics and Imaging, ISSN 1605-7422 ; Vol. 9033
Keywords
Dual energy computed tomography, model based iterative reconstruction algorithm, brachytherapy, prostate calcification
National Category
Clinical Medicine
Identifiers
urn:nbn:se:liu:diva-107506 (URN)10.1117/12.2043445 (DOI)000338775800120 ()2-s2.0-84901613219 (Scopus ID)
Conference
Medical Imaging 2014 - Physics of Medical Imaging, San Diego, California, United States, 17–20 February 2014
Available from: 2014-06-13 Created: 2014-06-13 Last updated: 2015-08-20Bibliographically approved
Malusek, A., Karlsson, M., Magnusson, M. & Alm Carlsson, G. (2013). The potential of dual-energy computed tomography for quantitative decomposition of soft tissues to water, protein and lipid in brachytherapy. Physics in Medicine and Biology, 58(4), 771-785
Open this publication in new window or tab >>The potential of dual-energy computed tomography for quantitative decomposition of soft tissues to water, protein and lipid in brachytherapy
2013 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 4, p. 771-785Article in journal (Refereed) Published
Abstract [en]

Dosimetric accuracy of radiation treatment planning in brachytherapy depends on knowledge of tissue composition. It has been speculated that soft tissues can be decomposed to water, lipid and protein. The aim of our work is to evaluate the accuracy of such tissue decomposition. Selected abdominal soft tissues, whose average elemental compositions were taken from literature, were decomposed using dual energy computed tomography to water, lipid and protein via the three-material decomposition method. The quality of the decomposition was assessed using relative differences between (i) mass energy absorption and (ii) mass energy attenuation coefficients of the analyzed and approximated tissues. It was found that the relative differences were less than 2% for photon energies larger than 10 keV. The differences were notably smaller than the ones for water as the transport and dose scoring medium. The choice of the water, protein and lipid triplet resulted in negative elemental mass fractions for some analyzed tissues. As negative elemental mass fractions cannot be used in general purpose particle transport computer codes using the Monte Carlo method, other triplets should be used for the decomposition. These triplets may further improve the accuracy of the approximation as the differences were mainly caused by the lack of high-Z materials in the water, protein and lipid triplet.

Place, publisher, year, edition, pages
Institute of Physics, 2013
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-89734 (URN)10.1088/0031-9155/58/4/771 (DOI)000314396800004 ()
Note

Funding Agencies|Swedish Cancer Society (Cancerfonden)|100 512|

Available from: 2013-03-05 Created: 2013-03-05 Last updated: 2017-12-06
Pachnerova Brabcova, K., Ambrozova, I., Koliskova, Z. & Malusek, A. (2013). Uncertainties in linear energy transfer spectra measured with track-etched detectors in space. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 713, 5-10
Open this publication in new window or tab >>Uncertainties in linear energy transfer spectra measured with track-etched detectors in space
2013 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 713, p. 5-10Article in journal (Refereed) Published
Abstract [en]

Polyallyldiglycol carbonate-based track-etched detectors can measure linear energy transfer (LET) spectra of charged particles. Accuracy of the spectra is affected by many factors whose effects are difficult to quantify. Typically, only uncertainty arising from the randomness of particle detection is reported in scientific literature. The aim of this paper is to classify the sources of uncertainties of an LET spectrum measurement and provide a simple model for the calculation of the combined uncertainty. The model was used for a spectrum measured with the track-etched detector (Harzlas TD-1) on board of the International Space Station from May-October 2009. For some spectrum bins the largest contribution to the combined uncertainty came from the uncertainty arising from the randomness of particle detection. For other bins it came from the uncertainty of the calibration curve. Contribution from the cross talk between bins was small for most of the bins as the width of the bins was relatively large compared to the intrinsic resolution of the track-etched detector. The analysis showed that sources of uncertainties other than the randomness of particle detection should not, in general, be neglected.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
CR-39, Linear energy transfer, Uncertainty model, Space dosimetry
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94594 (URN)10.1016/j.nima.2013.03.012 (DOI)000319239300002 ()
Note

Funding Agencies||GACR 205/09/0171||IAA 100480902 ASCR||GAAV KJB100480901||GACR 202/09/H086||SGS 10/212/OHK4/2T/14|

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-12-06
Mukhopadhyay, N. D., Sampson, A. J., Deniz, D., Alm Carlsson, G., Williamson, J. & Malusek, A. (2012). Estimating statistical uncertainty of Monte Carlo efficiency-gain in the context of a correlated sampling Monte Carlo code for brachytherapy treatment planning with non-normal dose distribution. Applied Radiation and Isotopes, 70(1), 315-323
Open this publication in new window or tab >>Estimating statistical uncertainty of Monte Carlo efficiency-gain in the context of a correlated sampling Monte Carlo code for brachytherapy treatment planning with non-normal dose distribution
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2012 (English)In: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 70, no 1, p. 315-323Article in journal (Refereed) Published
Abstract [en]

Correlated sampling Monte Carlo methods can shorten computing times in brachytherapy treatment planning. Monte Carlo efficiency is typically estimated via efficiency gain, defined as the reduction in computing time by correlated sampling relative to conventional Monte Carlo methods when equal statistical uncertainties have been achieved. The determination of the efficiency gain uncertainty arising from random effects, however, is not a straightforward task specially when the error distribution is non-normal. The purpose of this study is to evaluate the applicability of the F distribution and standardized uncertainty propagation methods (widely used in metrology to estimate uncertainty of physical measurements) for predicting confidence intervals about efficiency gain estimates derived from single Monte Carlo runs using fixed-collision correlated sampling in a simplified brachytherapy geometry. A bootstrap based algorithm was used to simulate the probability distribution of the efficiency gain estimates and the shortest 95% confidence interval was estimated from this distribution. It was found that the corresponding relative uncertainty was as large as 37% for this particular problem. The uncertainty propagation framework predicted confidence intervals reasonably well; however its main disadvantage was that uncertainties of input quantities had to be calculated in a separate run via a Monte Carlo method. The F distribution noticeably underestimated the confidence interval. These discrepancies were influenced by several photons with large statistical weights which made extremely large contributions to the scored absorbed dose difference. The mechanism of acquiring high statistical weights in the fixed-collision correlated sampling method was explained and a mitigation strategy was proposed.

Place, publisher, year, edition, pages
UK: Pergamon, 2012
Keywords
Monte Carlo, Correlated sampling, Efficiency, Uncertainty, Bootstrap
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-72277 (URN)10.1016/j.apradiso.2011.09.015 (DOI)000297901400052 ()
Available from: 2011-11-28 Created: 2011-11-24 Last updated: 2017-12-08Bibliographically approved
Malusek, A. & Alm Carlsson, G. (2011). Analysis of the tandem calibration method for kerma area meters vis Monte Carlo simulations. In: Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS).  Proceedings of an International Symposium held in Vienna, Austria 9-12 November 2010 (2 Volumes): . Paper presented at International Dosimetry Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS), IAEA, November 9-12, Vienna, Austria (pp. 129-136). IAEA
Open this publication in new window or tab >>Analysis of the tandem calibration method for kerma area meters vis Monte Carlo simulations
2011 (English)In: Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS).  Proceedings of an International Symposium held in Vienna, Austria 9-12 November 2010 (2 Volumes), IAEA , 2011, p. 129-136Conference paper, Published paper (Refereed)
Abstract [en]

The IAEA recommends that uncertainties of dosimetric measurements in diagnostic radiology for risk assessment and quality assurance should be less than 7% on the confidence level of 95%. This accuracy is difficult to achieve with kerma area product (KAP) meters currently used in clinics. The reasons range from the high energy dependence of KAP meters to the wide variety of configurations in which KAP meters are used and calibrated. The tandem calibration method introduced by Pöyry, Komppa and Kosunen in 2005 has the potential to make the calibration procedure simpler and more accurate compared to the traditional beam-area method. In this method, two positions of the reference KAP meter are of interest: (a) a position close to the field KAP meter and (b) a position 20 cm above the couch. In the close position, the distance between the two KAP meters should be at least 30 cm to reduce the effect of back scatter. For the other position, which is recommended for the beam-area calibration method, the distance of 70 cm between the KAP meters was used in this study. The aim of this work was to complement existing experimental data comparing the two configurations with Monte Carlo (MC) simulations. In a geometry consisting of a simplified model of the VacuTec 70157 type KAP meter, the MCNP code was used to simulate the kerma area product, PKA, for the two (close and distant) reference planes. It was found that PKA values for the tube voltage of 40 kV were about 2.5% lower for the distant plane than for the close one. For higher tube voltages, the difference was smaller. The difference was mainly caused by attenuation of the X ray beam in air. Since the problem with high uncertainties in PKA measurements is also caused by the current design of X ray machines, possible solutions are discussed.

Place, publisher, year, edition, pages
IAEA, 2011
Series
International Atomic Energy Agency, ISSN 0074-1884 ; Vol. 1
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-75344 (URN)978-92-0-116210-6 (ISBN)
Conference
International Dosimetry Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS), IAEA, November 9-12, Vienna, Austria
Available from: 2012-03-01 Created: 2012-02-27 Last updated: 2016-07-01Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1257-2383

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