I do not believe a hospital outpatient setting can bill any CPT code with professional or TC modifiers without using those modifiers. That is to say, a global billing is only available to freestanding settings. Doesn’t matter if physician is employed or does his own professional billing.
But, I never said an MD didn’t have to be there at all during image acquisition. Well, I did sort of: CMS approves of an NP, PA, etc, supervising the IGRT instead of an MD. (Right now, virtual supervision provides this level of direct supervision; if it goes away, an MD or APP would need to be there for IGRT image acquisitions, but not for other radiation therapy activities… like treatments.)