I came from a Varian show site and now work in a full Elekta environment at UC Davis. Things operate slightly different with the equipment however I have not experienced major differences in the utilization of AlignRT with Elekta vs. Varian. We treat SBRT patient routinely in our clinic and the therapist have a great workflow for utilizing Hexapod, AlignRT and CBCT together. Here are the steps for a typical SBRT patient:
1) Align patient in room using AlignRT. The therapist really like to utilize postural alignment for this as it helps with determining whether the patient is in the proper position within the vaclok.
2) Perform Motion view if requested by the physician.
3) Perform CBCT and make adjustments. We have created a policy within our department to identify how much rotational shift we would actual like to allow with Hexapod. If over that value the therapist go back into the room and reset patient (this is a very rare occurrence). The reason for setting this policy in place because as you mentioned the amount of translation shift that the precise couch top makes in relation to the hexapod can be pretty significant and concerning.
4) while waiting for the physician to approve shifts and images therapist #2 will go into the room and retract the imaging arms and get the gantry into position for treatment. Most of the time the driving therapist will have sent shifts by this time and it gives the therapist a great opportunity to apply shifts from in the room and verify clearance.
5) Once shifts are made, a new SGRT capture is taken. Beam hold can be turned on at this point and patient gets treated.
During CBCT we do see occlusion somewhere starting around 15 deg- 25deg and 340ish on the opposite side. Once we start treatment we do not seem to have issue with gantry occlusion. This is very similar to what I would see occur when using Varian equipment as well. I have found it helpful to create an upside T, making sure to include enough laterally as well.
Overall we have not found that retracting imaging arms adds a significant amount of time to our treatments. Our SBRTs are typically scheduled in a 30 min time slot.
I agree with Ben’s summary as well.