In Europe at least, many insurances cover it if you have the right criterias.

From my visits, they mostly focus on children that have some very nasty cancers, the IBA hospitals are all designed with children in mind (to avoid stressing them), and from my memory, a unique hospital is often enough to treat a whole country for the kind of cancer they target.

Now, if it is on par with classical radiotherapy BUT it gives less subsequent problems, it might be worth the cost as subsequent problems can be as expensive or even more than the original treatment. It becomes an actuarial issue to know where is the tradeoff.