The radiation treatment for TED is only effective in the early phases of TED, so no, this wouldn't be something to save for later. TED has a well-defined disease curve, though the length of the overall process can vary. There is an initial phase when the symptoms and bulging can change frequently, followed by a period of relative stability, followed by a period of gradual improvement, and finally complete stability. The early part of the curve is very steep, the end part is shallower. Directed radiation to the eye is typically only effective in that first phase, and it works mostly to minimize bulging. Oral steroids can be another option to attain the same result during that period. Oral steroids and directed radiation carry some risks, so sometimes doctors will use a little of each to minimize the risk of both. Last I heard, patients who respond well to one of these two will likely also respond well to the other, but if the symptoms do NOT respond to one of these, they are not likely to respond to the other either.
It's difficult to say how a patient's TED will progress, so there's some art to this, but there is a school of thought that suggests using one or both of these treatments (steroids and/or directed radiation) can keep the outcome from being worse by keeping the changes to a minimum and waiting out the early phase.
Once a patient gets to the very end of the disease curve, what they call the “cold phase” (diagnosed in hindsight), then surgical interventions can be pursued. If the early treatments work well to keep the eyes from changing a lot, then hopefully it either eliminates the need for surgical corrections, or minimizes the procedures that will be needed to correct the changes.
I hope this helps!
Good luck to you, this can be a tough road – keep in mind that people who suffer the very worst symptoms of TED are in a very tiny minority of patients overall, so the odds are on your side. If it get really bad, though, you've got a great community here of people who completely understand what you're going through, and that will help.
GDATF Online Facilitator