How to add parameter to a command line depending of checkbox state POWERSHELL

This is simple, well i think. But can't figure out how to proceed for this.

On a button AddClick, i have this line (i won't explain what it executes, i don't think that it is relevant for my question

QATests -v $SelectionCBBversion -b $SelectionCBBbuild -rev $SelectionCBBrev -e $SelectionCBBequipe -rtf -c LISTS-SPMT\$SelectionCBBlist –rio 

The -rtf parameter should be written in the command line only if a certain checkbox is checked. How would you proceed ? This parameter will create .rtf files instead of .docx files witch is the default one.

Thank you !