Metastasized liver cancer

Is proton beam therapy used for liver cancer that has metastasized? Has anyone been through this experience? How does the proton beam find which cells are cancer and which cells are not? What happens to the cancer that has been treated with proton beam therapy? Is there a risk that proton beam therapy will spread the cancer and make it worse? If the cancer came from a resection of the colon, they would have to take that out too, right?