Unfortunately, there is no straightforward answer to the question.
Regulations for shielding during C-arm use vary across a number of factors, including site location, location of the C-arm within the site, and the type of usage the C-arm will see. Some states don't require any shielding at all, but have other requirements that must be met. Take Texas, for instance: a C-arm doesn't need to be shielded, but its dose must be monitored for a year after installation. Other states, like Ohio, require a physicist to visit your site and advise specific shielding measures for your individual building.