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Olofsson, Jörgen
Publications (10 of 22) Show all publications
Lundman, J. A., Johansson, A., Olofsson, J., Axelsson, J., Larsson, A. & Nyholm, T. (2017). Effect of gradient field nonlinearity distortions in MRI-based attenuation maps for PET reconstruction. Physica medica (Testo stampato), 35, 1-6
Open this publication in new window or tab >>Effect of gradient field nonlinearity distortions in MRI-based attenuation maps for PET reconstruction
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2017 (English)In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 35, p. 1-6Article in journal (Refereed) Published
Abstract [en]

Purpose: Attenuation correction is a requirement for quantification of the activity distribution in PET. The need to base attenuation correction on MRI instead of CT has arisen with the introduction of integrated PET/MRI systems. The aim was to describe the effect of residual gradient field nonlinearity distortions on PET attenuation correction.

Methods: MRI distortions caused by gradient field nonlinearity were simulated in CT images used for attenuation correction in PET reconstructions. The simulations yielded radial distortion of up to  at 15 cm from the scanner isocentre for distortion corrected images. The mean radial distortion of uncorrected images were 6.3 mm at the same distance. Reconstructions of PET data were performed using the distortion corrected images as well as the images where no correction had been applied.

Results: The mean relative difference in reconstructed PET uptake intensity due to incomplete distortion correction was less than ±5%. The magnitude of this difference varied between patients and the size of the distortions remaining after distortion correction.

Conclusions: Radial distortions of 2 mm at 15 cm radius from the scanner isocentre lead to PET attenuation correction errors smaller than 5%. Keeping the gradient field nonlinearity distortions below this limit can be a reasonable goal for MRI systems used for attenuation correction in PET for quantification purposes. A higher geometrical accuracy may, however, be warranted for quantification of peripheral lesions. These distortions can, e.g., be controlled at acceptance testing and subsequent quality assurance intervals.

Keywords
MRI, PET, Quality assurance, Attenuation correction, MRI distortions
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-133798 (URN)10.1016/j.ejmp.2017.02.019 (DOI)000397945200001 ()28283354 (PubMedID)
Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2018-06-09Bibliographically approved
Benedek, H., Isacsson, U., Olevik-Dunder, M., Westermark, M., Hållström, P., Olofsson, J. & Gustafsson, M. (2015). Strategies for quality assurance of intensity modulated radiation therapy. In: 8TH INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY (IC3DDOSE): . Paper presented at 8th International Conference on 3D Radiation Dosimetry (IC3DDose), SEP 04-07, 2014, Ystad, SWEDEN (pp. 012015). Institute of Physics (IOP), 573, Article ID 012015.
Open this publication in new window or tab >>Strategies for quality assurance of intensity modulated radiation therapy
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2015 (English)In: 8TH INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY (IC3DDOSE), Institute of Physics (IOP), 2015, Vol. 573, p. 012015-, article id 012015Conference paper, Published paper (Refereed)
Abstract [en]

In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2015
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 573(2015):1
National Category
Other Medical Sciences not elsewhere specified
Identifiers
urn:nbn:se:umu:diva-103174 (URN)10.1088/1742-6596/573/1/012015 (DOI)000352600500015 ()
Conference
8th International Conference on 3D Radiation Dosimetry (IC3DDose), SEP 04-07, 2014, Ystad, SWEDEN
Available from: 2015-05-28 Created: 2015-05-18 Last updated: 2018-06-07Bibliographically approved
Kadesjö, N., Nyholm, T. & Olofsson, J. (2011). A practical approach to diode based in vivo dosimetry for intensity modulated radiotherapy. Radiotherapy and Oncology, 98(3), 378-381
Open this publication in new window or tab >>A practical approach to diode based in vivo dosimetry for intensity modulated radiotherapy
2011 (English)In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 98, no 3, p. 378-381Article in journal (Refereed) Published
Abstract [en]

A method for in vivo entrance dosimetry, using point detectors, in intensity modulated radiotherapy has been clinically evaluated. Diode dosimetry was performed for treatments of the head and neck and prostate regions. The results were good; 92.2% of the measurements showed deviations within ±5% of the expected values.

Keywords
IMRT, In vivo dosimetry, diodes, entrance dose
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-40713 (URN)10.1016/j.radonc.2010.12.018 (DOI)21295879 (PubMedID)
Available from: 2011-03-07 Created: 2011-03-07 Last updated: 2018-06-08Bibliographically approved
Nyholm, T., Olofsson, J., Ahnesjö, A. & Karlsson, M. (2011). Corrigendum to ‘‘Photon pencil kernel parameterisation based on beam qualityindex’’ [Radiother. Oncol. 78 (2006) 347–351]. Radiotherapy and Oncology, 98(2), 286
Open this publication in new window or tab >>Corrigendum to ‘‘Photon pencil kernel parameterisation based on beam qualityindex’’ [Radiother. Oncol. 78 (2006) 347–351]
2011 (English)In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 98, no 2, p. 286-Article in journal (Refereed) Published
National Category
Cancer and Oncology Other Clinical Medicine
Identifiers
urn:nbn:se:umu:diva-40261 (URN)10.1016/j.radonc.2010.12.003 (DOI)
Available from: 2011-02-21 Created: 2011-02-21 Last updated: 2018-06-08Bibliographically approved
Karlsson, M., Ahnesjö, A., Georg, D., Nyholm, T. & Olofsson, J. (2010). Beam modelling and dose calculations (1ed.). In: Independent Dose Calculations - Concepts and Models: Booklet 10 (pp. 39-66). Bryssel: ESTRO
Open this publication in new window or tab >>Beam modelling and dose calculations
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2010 (English)In: Independent Dose Calculations - Concepts and Models: Booklet 10, Bryssel: ESTRO , 2010, 1, p. 39-66Chapter in book (Other academic)
Place, publisher, year, edition, pages
Bryssel: ESTRO, 2010 Edition: 1
Identifiers
urn:nbn:se:umu:diva-39975 (URN)90-804532-9 (ISBN)
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
Karlsson, M., Ahnesjö, A., Georg, D., Nyholm, T. & Olofsson, J. (2010). Dosimetric tolerance limits and action limits (1ed.). In: Independent Dose Calculations - Concepts and Models: Booklet 10 (pp. 13-24). Bryssel: ESTRO
Open this publication in new window or tab >>Dosimetric tolerance limits and action limits
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2010 (English)In: Independent Dose Calculations - Concepts and Models: Booklet 10, Bryssel: ESTRO , 2010, 1, p. 13-24Chapter in book (Other academic)
Place, publisher, year, edition, pages
Bryssel: ESTRO, 2010 Edition: 1
Identifiers
urn:nbn:se:umu:diva-39973 (URN)90-804532-9 (ISBN)
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
Karlsson, M., Ahnesjö, A., Georg, D., Nyholm, T. & Olofsson, J. (2010). Measured data for verification and dose calculations (1ed.). In: Independent Dose Calculations - Concepts and Models: Booklet 10 (pp. 67-76). Bryssel: ESTRO
Open this publication in new window or tab >>Measured data for verification and dose calculations
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2010 (English)In: Independent Dose Calculations - Concepts and Models: Booklet 10, Bryssel: ESTRO , 2010, 1, p. 67-76Chapter in book (Other academic)
Place, publisher, year, edition, pages
Bryssel: ESTRO, 2010 Edition: 1
Identifiers
urn:nbn:se:umu:diva-39977 (URN)90-804532-9 (ISBN)
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
Karlsson, M., Ahnesjö, A., Georg, D., Nyholm, T. & Olofsson, J. (2010). Statistical analysis (1ed.). In: Independent Dose Calculations - Concepts and Models: Booklet 10 (pp. 25-38). Bryssel: ESTRO
Open this publication in new window or tab >>Statistical analysis
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2010 (English)In: Independent Dose Calculations - Concepts and Models: Booklet 10, Bryssel: ESTRO , 2010, 1, p. 25-38Chapter in book (Other academic)
Place, publisher, year, edition, pages
Bryssel: ESTRO, 2010 Edition: 1
Identifiers
urn:nbn:se:umu:diva-39974 (URN)90-804532-9 (ISBN)
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
Karlsson, M., Ahnesjö, A., Georg, D., Nyholm, T. & Olofsson, J. (2010). The concept of independent dose calculation (1ed.). In: Independent Dose Calculations - Concepts and Models: Booklet 10 (pp. 5-12). Mounierlaan 83/12 – 1200 Brussels (Belgium): ESTRO
Open this publication in new window or tab >>The concept of independent dose calculation
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2010 (English)In: Independent Dose Calculations - Concepts and Models: Booklet 10, Mounierlaan 83/12 – 1200 Brussels (Belgium): ESTRO , 2010, 1, p. 5-12Chapter in book (Other academic)
Place, publisher, year, edition, pages
Mounierlaan 83/12 – 1200 Brussels (Belgium): ESTRO, 2010 Edition: 1
Identifiers
urn:nbn:se:umu:diva-39884 (URN)90-804532-9 (ISBN)
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
Georg, D., Nyholm, T., Olofsson, J., Kjaer-Kristoffersen, F., Schnekenburger, B., Winkler, P., . . . Karlsson, M. (2007). Clinical evaluation of monitor unit software and the application of action levels. Radiotherapy and Oncology, 85(2), 306-315
Open this publication in new window or tab >>Clinical evaluation of monitor unit software and the application of action levels
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2007 (English)In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 85, no 2, p. 306-315Article in journal (Refereed) Published
Abstract [en]

Purpose: The aim of this study was the clinical evaluation of an independent dose and monitor unit verification (MUV) software which is based on sophisticated semi-analytical modelling. The software was developed within the framework of an ESTRO project. Finally, consistent handling of dose calculation deviations applying individual action levels is discussed.

Materials and methods: A Matlab-based software ("MUV") was distributed to five well-established treatment centres in Europe (Vienna, Graz, Basel, Copenhagen, and Umea) and evaluated as a quality assurance (QA) tool. in clinical routine. Results were acquired for 226 individual treatment plans including a total of 815 radiation fields. About 150 beam verification measurements were performed for a portion of the individual treatment plans, mainly with time variable fluence patterns. The deviations between dose calculations performed with a treatment planning system (TPS) and the MUV software were scored with respect to treatment area, treatment technique, geometrical depth, radiological depth, etc.

Results: In general good agreement was found between calculations performed with the different TPSs and MUV, with a mean deviation per field of 0.2 +/- 3.5% (1 SD) and mean deviations of 0.2 +/- 2.2% for composite treatment plans. For pelvic treatments less than 10% of all fields showed deviations larger than 3%. In general, when using the radiological depth for verification calculations the results and the spread in the results improved significantly, especially for head-and-neck and for thorax treatments. For IMRT head-and-neck beams, mean deviations between MUV and the local TPS were -1.0 +/- 7.3% for dynamic, and -1.3 +/- 3.2% for step-and-shoot IMRT delivery. For dynamic IMRT beams in the pelvis good agreement was obtained between MUV and the local TIPS (mean: -1.6 +/- 1.5%). Treatment site and treatment technique dependent action levels between 3% and 5% seem to be clinically realistic if a radiological depth correction is performed, even for dynamic wedges and IMRT.

Conclusion: The software MUV is well suited for patient specific treatment plan QA applications and can handle all currently available treatment techniques that can be applied with standard linear accelerators. The highly sophisticated dose calculation model implemented in MUV allows investigation of systematic TIPS deviations by performing calculations in homogeneous conditions. (c) 2007 Elsevier Ireland Ltd. All rights reserved.

Keywords
Dose calculation accuracy, action level, independent dose calculation
Identifiers
urn:nbn:se:umu:diva-39900 (URN)10.1016/j.radonc.2007.04.035 (DOI)000252201400020 ()
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2018-06-08Bibliographically approved
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