Different places do this in different ways. Anyone can feel free to correct me on this, but this is my Cliff's notes version...keep in mind much of the terminology and billing is based upon old traditional flouroscopic or conventional sims which have been amended to reflect current rad onc practice....
A conventional ct simulation is considered a "complex simulation" and coded as CPT code 77290. The vast majority of practices I've ever seen (and my current practice - hospital based private practice) requires the physician to be physically present at the CT simulator to help supervise...though I believe within the medicare guidelines it still falls under "direct supervision," which leaves some gray area as to where exactly in the building one has to be. However, most places have the attending present for CT sim.
However, for verification sim (coded as a "simple simulation", CPT code 77280) some places deal with the physical presence of a physician in different ways. The patient undergoes a cone beam or their setup films, portal/MLC films, and marks on their skin are updated. But they don't actually receive their first treatment that day. Some places only have the doc review the films on verification day (ie the day before the patient receives his/her first fraction) and the doc isn't physically present at the linac - as mentioned by medgator above. My practice used to be this way until my administrators got all hot and bothered and declared I needed to be present at the linac (they're hyper-conservative on billing stuff). Other academic centers with residents sometimes send a resident to the verification sim and may or may not bill it. Attendings would review the films later in the day, but physically at the linac at time of films only the resident is present. If a patient is receiving daily image guidance (you're billing a 77014 charge), then you cannot bill both a verification simulation and an image guidance charge on the same day, so many practices choose to do a verification simulation with no treatment on the day prior to starting a patient's XRT. There are also work flow issues/benefits to doing a verification sim prior to starting XRT as well.
Hope that helps.
