RF of sufficient intensity to cause ALOT of heating over large body areas has been used medically for over 75 years. Back alot more than that if you include spark diathermy that was developed in the late 1800's. Today the technique is mainly used for physial therapy, but it can have a number of other uses. A typical treatment might last 30 to 45 minutes and cause a very noticeable temperature rise.

The FCC's business in all of this is that communications are not interfered with. Medical effects are not their business, but people involved with radio always assume that it is.