Text and Data Mining valid from 2018-10-01
Received: 6 December 2017
Revised: 6 August 2018
Accepted: 21 September 2018
First Online: 1 October 2018
Compliance with ethical standards
: All authors (Takayuki Okamoto, Takashi Ohnishi, Hiroshi Kawahira, Olga Dergachyova, Pierre Jannin and Hideaki Haneishi) have no conflict of interest or financial ties to disclose.