Study Overview: This research is focused on women with breast cancer who need radiation therapy. The study compares two methods: a shorter 3-week treatment versus a traditional 5-week treatment. Both use a special type of radiation called proton therapy, which targets cancer cells more precisely. Key Points:

• Participants will receive radiation therapy for either 3 weeks or 5 weeks.
• The study aims to see if the shorter treatment has similar side effects as the longer one.
• The trial is designed for women who have had breast surgery and need further radiation.

Proton therapy is a type of radiation that more accurately targets the cancer, potentially reducing damage to surrounding healthy tissue. The study is for women with Stage I-III breast cancer who had surgery and need radiation. They should not have certain health issues like skin ulceration, active skin rash, or certain genetic mutations. It's important to be able to start the treatment within 12 weeks after surgery or chemotherapy. Participants will be closely monitored for side effects, especially on the skin and soft tissues, to ensure the shorter treatment is as safe and effective as the longer one.