Good question, Pat.
Stereotactic radiosurgery (SRS) is the general term for precise delivery of focused radiation beams to treat tumors and other problems in the brain, neck, lungs, liver, spine and other parts of the body.

Gamma Knife machines use 192 or 201 small beams of gamma rays to target and treat cancerous and noncancerous brain abnormalities. Gamma Knife machines are used primarily for small to medium tumors and lesions in the brain associated with a variety of conditions.

Proton beam therapy (charged particle radiosurgery) is the newest type of stereotactic radiosurgery and is available in only a few research centers in the U.S, although the number of centers offering proton beam therapy has greatly increased in the last few years. Proton beam therapy can treat brain cancers in a single session using stereotactic radiosurgery, or it can use fractionated stereotactic radiotherapy to treat body tumors over several sessions.

Read more here: https://www.mayoclinic.org/tests-procedures/stereotactic-radiosurgery/about/pac-20384526
and
https://www.mayoclinic.org/tests-procedures/brain-stereotactic-radiosurgery/about/pac-20384679
Gamma Knife radiosurgery is offered at all Mayo Clinic locations.

Proton beam therapy at Mayo Clinic is currently offered in MN and AZ. Florida will soon have proton beam. https://www.mayoclinic.org/departments-centers/proton-beam-therapy-program/sections/proton-therapy-facilities/gnc-20187682