Objective:To observe the effects of the new technique of flexible 3D-conformal radiotherapy with combination of photon and electron (3DCRT) in the treatment of the patients with diffuse malignant pleural mesothelioma (MPM),and carry out the comparative study between flexible 3DCRT and hemithoracic conventional radiotherapy (CRT).Methods:From January 2004 to October 2007,8 patients with MPM were treated with flexible 3DCRT.5 patients had received cycles of chemotherapy before radiation.New technique of flexible 3DCRT with combination of photon and electron was used in our study,and DT 32.2-64 Gy with conventional split were delivered.CRT technique was mimicked to compare with 3DCRT technique to predict the possibility of lung damage in two methods.Results:One patient reached CR and other 7 patients got PR after radiation.Two patients died during the follow-up.The median survival time (MST) was 15.4 months and it was 18.8 months for sequential chemotherapy and radiotherapy group and 9.7 months for radiotherapy alone group.The V20,V30,and ipsilateral and centralateral median lung dosage (MLD) were 20.5%,15.6%,18.8 Gy and 2.2 Gy respectively when the flexible 3DCRT technique was used,whereas they were 36.8%,27.9%,31.1 Gy and 1.2 Gy respectively when the CRT technique was used.They were statistically different for the lung V20,V30 and ipsilateral MLD between the two techniques (P＜0.01),whereas there was no different for the contralateral MLD (P＝0.08).All patients received radiation were found to have lung fibrosis and classified as grades 1-2 radiation pneumonitis.The quality of life was increased from score 2.83 to 3.76 and it was significantly different (P＜0.01).Conclusion:MPM is moderately sensitive to radiation.The flexible 3DCRT technique is feasible in the treatment of MPM and lung damage is reduced apparently comparing with the CRT technique.The quality of life of patients with MPM is improved after irradiation.