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  • 1.
    Andersson, Karin M.
    et al.
    Örebro University, School of Health Sciences. The Skandion Clinic, Uppsala, Sweden.
    Vallhagen Dahlgren, Christina
    The Skandion Clinic, Uppsala, Sweden.
    Reizenstein, Johan
    Department of Oncology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Cao, Yang
    Örebro University, School of Medical Sciences. Örebro University Hospital. Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Ahnesjö, Anders
    Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics.
    Evaluation of two commercial CT metal artifact reduction algorithms for use in proton radiotherapy treatment planning in the head and neck area2018In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, no 10, p. 4329-4344Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To evaluate two commercial CT metal artifact reduction (MAR) algorithms for use in proton treatment planning in the head and neck (H&N) area.

    METHODS: An anthropomorphic head phantom with removable metallic implants (dental fillings or neck implant) was CT-scanned to evaluate the O-MAR (Philips) and the iMAR (Siemens) algorithms. Reference images were acquired without any metallic implants in place. Water equivalent thickness (WET) was calculated for different path directions and compared between image sets. Images were also evaluated for use in proton treatment planning for parotid, tonsil, tongue base, and neck node targets. The beams were arranged so as to not traverse any metal prior to the target, enabling evaluation of the impact on dose calculation accuracy from artifacts surrounding the metal volume. Plans were compared based on γ analysis (1 mm distance-to-agreement/1% difference in local dose) and dose volume histogram metrics for targets and organs at risk (OARs). Visual grading evaluation of 30 dental implant patient MAR images was performed by three radiation oncologists.

    RESULTS: In the dental fillings images, ΔWET along a low-density streak was reduced from -17.0 to -4.3 mm with O-MAR and from -16.1 mm to -2.3 mm with iMAR, while for other directions the deviations were increased or approximately unchanged when the MAR algorithms were used. For the neck implant images, ΔWET was generally reduced with MAR but residual deviations remained (of up to -2.3 mm with O-MAR and of up to -1.5 mm with iMAR). The γ analysis comparing proton dose distributions for uncorrected/MAR plans and corresponding reference plans showed passing rates >98% of the voxels for all phantom plans. However, substantial dose differences were seen in areas of most severe artifacts (γ passing rates of down to 89% for some cases). MAR reduced the deviations in some cases, but not for all plans. For a single patient case dosimetrically evaluated, minor dose differences were seen between the uncorrected and MAR plans (γ passing rate approximately 97%). The visual grading of patient images showed that MAR significantly improved image quality (P < 0.001).

    CONCLUSIONS: O-MAR and iMAR significantly improved image quality in terms of anatomical visualization for target and OAR delineation in dental implant patient images. WET calculations along several directions, all outside the metallic regions, showed that both uncorrected and MAR images contained metal artifacts which could potentially lead to unacceptable errors in proton treatment planning. ΔWET was reduced by MAR in some areas, while increased or unchanged deviations were seen for other path directions. The proton treatment plans created for the phantom images showed overall acceptable dose distributions differences when compared to the reference cases, both for the uncorrected and MAR images. However, substantial dose distribution differences in the areas of most severe artifacts were seen for some plans, which were reduced by MAR in some cases but not all. In conclusion, MAR could be beneficial to use for proton treatment planning; however, case-by-case evaluations of the metal artifact-degraded images are always recommended.

  • 2.
    Andersson, Karin
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Öhman, Johan
    Örebro University, School of Humanities, Education and Social Sciences.
    Moral relations in encounters with nature2015In: Journal of Adventure Education and Outdoor Learning, ISSN 1472-9679, E-ISSN 1754-0402, Vol. 15, no 4, p. 310-329Article in journal (Refereed)
    Abstract [en]

    The overall aim of this article is to develop in-depth knowledge about the connection between outdoor experiences and moral attitudes towards nature. The study focuses on processes in which moral relations are at stake in encounters between students and nature. The purpose is to identify such events, describe their specific circumstances and clarify how moral relations are established in these events. The empirical material consists of video-recordings of activities in three different outdoor education practices. In order to identify and categorise moral situations, an analytical tool called the ethical tendency is used. This tool is based on Wittgenstein’s language game method. The findings show that in the investigated outdoor education practices, moral relations towards nature are established in several different ways. The article concludes with four educational implications: responsibility when dealing with moral reactions; bring- ing ethical questions to the fore; different educational conditions create different encounters with nature; and the consequences of different language games. 

  • 3.
    Öhman, Johan
    et al.
    Örebro University, School of Humanities, Education and Social Sciences.
    Andersson, Karin
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Sandberg, Mattias
    Göteborgs universitet, Göteborg, Sverige.
    Barns möte med naturen2013In: Friluftsliv i förändring: resultat från ett forskningsprogram: slutrapport / [ed] Peter Fredman, Marie Stenseke, Klas Sandell, Anders Mossing, Stockhom: Rapport (Statens naturvårdsverk) , 2013, p. 115-130Chapter in book (Other academic)
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