Patients must have undergone definitive RT for histologically confirmed NPC years before. They were required to have at least two consecutive magnetic resonance imaging (MRI) study supporting the diagnosis of CRN with an interval of 3-4 months, with the second MRI showing progressive disease compared with the first MRI. The necrotic mass shown on MRI must be measured in two dimensions in order to define the response to treatment. Other radiologic studies were also required to support the non-existence of local or regional recurrence, distant metastasis. Patients must have undergone mental status examinations and had progressive neurologic symptoms or signs. In addition, they were required to have a Karnofsky performance status of at least 70 and were supposed to live more than 6 months.