The purpose of this study is to determine whether postoperative conformal radiotherapy are effective in the treatment of Masaoka stage II-III B type thymoma.

The role of postoperative radiotherapy in thymoma is controversial. Some retrospective studies were for the radiotherapy, but others were against. However, more inherent biases existed in these trials. Resection, Masaoka stage and pathology were widely accepted as the prognostic factors for thymoma. Furthermore, the frequency of local failure after radical resection was still high in Masaoka stage II-III B type thymoma. With the conformal technique appearing, conformal radiotherapy can escalate the dose without increasing the risk of normal tissue toxicities.

Inclusion Criteria:

• Age 18-75, Zubrod-ECOG-WHO 0-2, the interval of surgery to radiotherapy < 2months, Masaoka stage II-III and WHO B type thymoma

Exclusion Criteria:

• No second primary tumor, no serious comorbidity, no neoadjuvant anticancer treatment, no adjuvant chemotherapy.