I didn't get to see the procedure for the mask making, but the radiologist showed us a sample of one. It's like a hard netting made of what looks to be a ploymer or silicon material, moulded exactly to fit over the face, so each mask is unique to the wearer.
Guess if the area to be zapped were on some other part of the body, there would be other means of immobilizing said part. But the head tends to roll around a lot, firstly because the neck is a relatively unstable base, and because any distraction or moment of inattention will cause the target area to shift significantly in orientation, causing unnecessary and undesirable collateral damage to the surrounding tissue.
Tomorrow should be the fitting of the mask, some discussion of customization and modification for optimal comfort, and also a sort of calibrating rehearsal on the machine -- a dry-run, so to speak. Unfortunately, I won't be able to perform my usual chauffeur duty as my day-job is calling me back from the mid-term break.
Transport will have to be taken over by a free shuttle service for such contingencies, though at the moment the Patient is on a waiting list. Public transport for now, but hopefully the shuttle will be able to accommodate when the treatment begins for real in a couple of weeks' time.