RATIONALE: Radiation therapy uses high-energy x-rays to kill tumor cells. Specialized radiation therapy that delivers a high dose of radiation directly to the tumor may kill more tumor cells and cause less damage to normal tissue. Giving radiation therapy after surgery may kill any tumor cells that remain after surgery. It is not yet known whether intensity-modulated radiation therapy or 3-dimensional conformal radiation therapy is more effective in decreasing hearing loss in patients undergoing radiation therapy for parotid gland cancer.