> My question is whether it is possible to either put the Captions above or below the radiobuttons, or to place the first button's caption to its left.
The only way to do that would be to (a) leave all the /options blank
/ options = (""; ""; ""; ""; ""; "")
and (b) set up two separate <caption> elements
/ caption = "stimme gar nicht zu"
/ caption = "stimme völlig zu"
use their /position attributes to position them properly, and display them along with the <radiobuttons> via your <surveypage>'s /questions attribute
/ questions = [1=ncc1; 2=leftcaption; 3=rightcaption]
If you have only a single <radiobuttons> element on a given <surveypage>, you may want to consider using <likert> trials instead of <surveypage> / <radiobuttons>.