Treatment planning for NPC can be challenging due to the proximity of the target to organs at risk (OAR) and the need to compromise coverage in order to limit toxicity to OARs. One direct benefit of reduced PTV margins is decreased dose to OAR. The purpose is to assess different reduced planning target volume (PTV) margin schema for nasopharyngeal carcinoma (NPC), using clinical image guided radiation therapy (IGRT) data, deformable image registration (DIR) and dose accumulation. A retrospective re-planning study of 10 NPC patients who received 70Gy in 35 fractions (high dose), 63 Gy (intermediate dose) and 56 Gy (low dose) with daily cone beam CT (CBCT) guidance. Intensity modulated radiation therapy (IMRT) plans were generated for clinical use with uniform 5 mm PTV margins. These plans together with images, structures and dose were imported into RayStation v.4.5.2. New plans were made for three different reduced PTV margin schemas applied to the primary high dose disease (CTVp70), 1) 3 mm isotropic, 2) 3 mm in all directions except for 0 mm posteriorly and 3) 1 mm isotropic. The goal of the re-plans was to achieve at least the same target coverage and OAR sparing as the clinical plan. For each patient, the re-plans were normalized to CTVp70 receiving prescription dose (V70Gy) in the clinical plan. The impact of daily set-up variation and anatomical changes on target coverage and dose to the OARs was calculated as the difference between the estimated delivered dose (using DIR and dose accumulation) and the planned dose (delivered – planned). A comparison between the reduced margin schema and current clinical margins illustrates the benefits of reduced target volume in lower OAR dose (maximum point dose (Dmax). The average reduction in Dmax for the brainstem, optic chiasm, and optic nerves, respectively for the three schema were 1) 4.3, 6.2, 6.1 Gy, 2) 4.1, 7.0, 5.0 Gy and 3) 3.8, 11.2, 8.5 Gy. All plans had V70Gy >99% for CTVp70 except for the two bulkiest tumors. After dose accumulation, the mean difference in CTVp70 coverage (V70Gy) was 1.3%(±1.1) for the clinical margins, with similar results for new schema of 1) 1.1%(±0.9), 2) 0.9% (±0.9) and 3) 0.4% (±0.8). Overall, there were small differences in OAR dose. For example, Dmax for brainstem had a small decrease on averagex for the clinical plan (-0.34 Gy ± 0.97) and each of the three schema ( 1) -0.32 Gy ± 0.85, 2) -1.0 Gy ± 1.7 and 3) -0.30 Gy ± 0.94). Our analysis of accumulated dose demonstrates that all three margin schemas are sufficient to maintain target coverage while reducing OAR dose, using current institutional IGRT practices. Further evaluation of this schema on a larger patient cohort will be conducted to determine which schema is optimal for clinical implementation.