Can radiotherapy cure fibrosarcoma and angiosarcoma?

Yes: Usually radiotherapy is used following surgery in the treatment of sarcomas, but both of these sarcomas may respond to radiotherapy.

Yes and no: Small tumors can be surgically resected then treated with radiation to "clean up" any malignant cells that may have remained, giving an excellent outcome. Radiation by itself generally cannot cure such tumors by itself, although my experience tells me angiosarcoma responds better than fibrosarcoma.