I thought it was just one. It is a form of external-beam radiation treatment. Proton radiation is delivered by the second method. The physician can shape the beam to match the shape of a tumor, so most of the radiation is delivered to the tumor, not to the surrounding normal tissue.
Protons deposit their radiation dose differently.
Protons, which are positively charged subatomic particles, deposit energy differently than x-ray beams do. X-ray beams deposit most of their dose in tissues in front of the tumor and in front of a substantial amount of malignant tissue. Because of the number of patients treated and the amount of follow-up data available, we can assess the effectiveness of proton beams for treating cancer. Loma Linda University and Harvard University are currently performing studies sponsored by the NCI to determine the best or optimal proton dose for certain cancers, such as prostate cancer and a variety of brain tumors. The studies are being done to find out the best ways to use this tool against cancer.