Long-term efficacy of radon spa therapy in rheumatoid arthritis–a randomized, sham-controlled study and follow-up.

Franke A, Reiner L, Pratzel HG, Franke T, Resch KL
Rheumatology (Oxford). 2000 Aug;39(8):894-902

https://www.ncbi.nlm.nih.gov/pubmed/10952746