We have been doing lots of treatments for arthritis.
Response is variable. The longer the disease has been there, the tougher it may be to produce a good, durable response to RT. We generally say that 80% of patients respond to some degree and around 50% can expect to be pain–free or almost pain–free.
Second malignancy has not been reported in the literature, at least as far as I know. Perhaps it has to do with the low doses used (3–6Gy) and the generally elder patients receiving it.
There is no problem with surgery, since the dose is low.
Good book by one of the German experts:
Radiotherapy for Non-Malignant Disorders
Seegenschmiedt, M.H., Makoski, H.-B., Trott, K.-R., Brady, L.W. (Eds.)
You can use a linac for all indications. We use an orthovoltage machine with 100kV for fingers. If they are really thick, we give 0.5 Gy from both sides ––> 0.5 Gy in the middle.
Last but not least:
Raising interest in your ortho colleagues may give rise to additional referrals. They also see quite few painful heel spurs and heterotopic ossifications certainly.