RATIONALE: Monoclonal antibodies, such as trastuzumab, can block tumor growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry tumor-killing substances to them. Radiation therapy uses high-energy x-rays to kill tumor cells. Trastuzumab may make tumor cells more sensitive to radiation therapy. Giving trastuzumab together with radiation therapy may kill more tumor cells.