Received: 13 February 2020
Accepted: 13 April 2020
First Online: 22 May 2020
Ethics approval and consent to participate
: The retrospective analysis was approved by the Ethics Committee Campus Charité Mitte (EA1/233/18) and by Comitato Ethico Interaziendale Messina (80/19). Consent to participate is not applicable for a retrospective study.
: Not applicable.
: There is no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Dr. Conti and Dr. Romanelli received research and travel grants from Accuray Inc., Sunnyvale, CA, USA.