Hi, and welcome back!
Proton/Ion Therapy is used in the fight against cancer. It allows beams to be targetted directly to the cancer cells, the goal being to lessen the impact on healthy cells. The beam itself is made of protons, which are positively charged particles that are found in the nucleus of every atom. The beam damages the DNA in the cancer cell, killing it or preventing it from dividing.
This website has lots more information about the therapy:
It is available in the US, for example, at the MD Anderson Center in Houston, Texas:
It is also available at Mass General Hospital in Boston, MA:
I hope this helps. Let me know if you have any questions about this,