Received: 18 October 2018
Accepted: 25 April 2019
First Online: 16 May 2019
Ethics approval and consent to participate
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required.
: Not applicable.
: CB has a research cooperation with Elekta AB, Stockholm, Sweden. The other authors declare that they have no competing interests.
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