We use AlignRT with Elekta in Birmingham, England. You are correct in as much as you certainly need to put the XVI tube and panel away. If you don’t they will block the camera view. This is true for CBCT acquisition and treatment delivery. And you can see it happen by the light projection being on the back of the panel/tube rather than the patient, as well as the deltas changing erratically. This is all we’ve known as we have only ever used AlignRT with Elekta and it would be nice to see the next generation Elekta Linacs have a remote camera and panel retraction option.
So the only thing it really creates for us is a blip in monitoring the patient when acquiring a CBCT. But you can see when the cameras are able to see the patient based on the projection so when we have known camera block during acquisition, we watch the deltas and if they jump out of tolerance we don’t panic. As soon as the known camera block is over (maybe 10 seconds later), if the deltas come back in to tolerance, then the patient hasn’t moved. If they stay out of tolerance and you are sure the camera block is over, then we interrupt as it is likely that the patient has moved.
We also optimise our ROI for VMAT deliveries to let AlignRT see more of the patient. This avoids blips at certain gantry angles.
I can see how the height of the patient could reduce the camera view as it can create a shallower angle (depending on patient anatomy) but whether the patient is further in or out of the gantry shouldn’t make a difference as the area you are treating will still be at the isocentre.
Don’t worry if there’s camera block when acquiring a CBCT – just ensure the deltas move back when the camera block is over.
Put the tube and panel away when treating (or you’ll have to deal with camera block issues during treatment which we don’t feel is the best way to use the system).
Fingers crossed for more automation of panel and tube on Elektas part in the future.
I hope this help.