Abstract: Objective:To investigate target volume delineation after four cycles of induction chemotherapy in locoregionally advanced nasopharyngeal cancer (NPC).Methods:From August2009to August 2013, 57patients with stage Ⅲ- ⅣNPC were treated with induc -tion-concurrent chemotherapy and intensity-modulated radiotherapy. The primary gross tumor volume (GTV), including retropharyn -geal lymph node metastasis before and after induction chemotherapy, was defined as GTVnx- pre and GTVnx- post, respectively, and the clinical target volume (CTV) was divided into two parts: CTV1 and CTV2. The CTVnx 1 was defined as the GTVnx-post plus a10-mm margin, covering the region of GTVnx-pre. The contouring of neck lymph nodes was similar to the primary gross tumor, with the neck lymph nodes GTV and CTV defined as GTVnd- pre, GTVnd- post, and CTVnd1, respectively. CTV 2 was defined as CTVnx1 and CTVnd1 plus a 5- mm margin together with the bilateral cervical selective lymph drainage respectively areas. Treatment outcome and toxicity were determined in all patients.Results:The GTVnx- post was significantly smaller than the GTVnx- pre ( 21. 8 cm3 vs . 63. 7 cm3 , P<0. 01), whereas the GTVnd-post was significantly smaller than the GTVnd-pre (21. 7 cm3 vs . 7. 5 cm3, P<0. 01). With a median follow-up of 60. 0 months, the 5-year overall survival (OS), locoregional relapse-free survival (LRFS), distant metastasis-free survival (DMFS), and progres -sion-free survival (PFS) rates were 49/57(86. 0%),53/57(93. 0%),52/57(91. 2%), and53/57(93. 0%) respectively. All locoregional fail ures occurred in the GTVnx-post or GTVnd-post field with no relapses in the CTVnx1 or CTVnd 1. Conclusion: Four cycles of IC can signif -icantly reduce tumor volume. The target volume delineation according to the tumor volume after IC has encouraging long-term treat -ment outcome.