Summary
This randomized phase III trial studies proton beam radiation therapy (proton therapy) compared to photon beam radiation therapy (photon therapy) in treating patients with breast cancer that has not spread to other places in the body (non-metastatic). Radiation therapy is an important treatment for breast cancer, however, radiation goes to other organs, such as heart, causing heart problems. Proton therapy is a type of radiation therapy that uses multiple beams of protons (tiny particles with a positive charge) to kill tumor cells. Photon therapy is also a type of radiation therapy which uses multiple x-ray beams to kill tumor cells. Proton therapy is theorized to deposit less radiation to healthy tissues beyond the cancer tumor. However, it is not yet known whether proton therapy is more effective than photon therapy in treating patients with non-metastatic breast cancer without causing heart damage.