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Objective Patients with nasopharyngeal carcinoma ( NPC) undergoing intensity-modulated radiation therapy ( IMRT) may experience significant volumetric and dosimetric variations throughout the treatment course. However, neoadjuvant chemotherapy may reduce the extent of these variations. This study was carried out to evaluate volumetric and dosimetric changes in target volumes and organs at risk ( OARs ) during IMRT in patients with locally advanced NPC who received concurrent chemoradiotherapy ( CCRT ) alone or in combination with neoadjuvant chemotherapy ( NACT ) . Methods 35 NPC patients were recruited for this study and divided into the NACT ( n=15 ) and CCRT ( n=20 ) groups. Computed tomography (CT) scans were performed before neoadjuvant chemotherapy,before IMRT,before the 24th fraction of IMRT, and after treatment. The original plan (plan 0) was based on CT images collected before IMRT. Hybrid plan 1 (plan 1) and hybrid plan 2 (plan 2) were generated by applying the beam configurations of plan0 to the CT scans collected before the 24th fraction of IMRT and after treatment. Volumetric and dosimetric variations were assessed by comparing the results of plan 0 with those of plan 1 and plan 2. Results In the NACT group,compared with that in plan 0,the primary gross tumor volume (GTVnx) decreased by 33. 2％±18. 4％ and 50. 5％±12. 6％ in plan1 and plan 2,respectively. In the CCRT group, the corresponding reduction rates in plan 1 and plan 2 were 49. 4％±8. 0％ and 77. 8％±28. 1％,respectively. The volume decrease rates in the NACT group were less than those in the CCRT group (P<0. 001). In the NACT group,compared with that of plan 0,the dose to 95％ of the volume (D95) for the planning target volume of the primary tumor (PTVnx) decreased by 1. 0％±0. 7％ and 0. 6％±0. 6％ in plan 1 and plan 2,respectively. In the CCRT group,the corresponding decrease rates in plan 1 and plan 2 were 4. 2％±3. 8％ and 6. 1％±6. 3％,respectively. The decrease rate of D95 for PTVnx in the NACT group was less than that in the CCRT group (P<0. 001). Similar results among the plans were found in terms of D99,Dmean, V93 for PTVnx and PTVnd ,and Dmean for the parotid glands. Conclusion Neoadjuvant chemotherapy reduces the extent of volu-metric and dosimetric variations in target volumes and OARs during IMRT and,thus,helps achieve better target volume cover-age,protects adjacent important structures,and minimizes unnecessary replanning during radiotherapy.