Abstract: Background and purpose: Head and neck lymphedema (HNL) is a common side effect of intensitymodulated (IMRT) radiotherapy for nasopharyngeal carcinoma (NPC), but few studies have been reported. The purpose of this study was to explore a method to prevent or mitigate HNL after radiotherapy for NPC patients and to study its dosimetric feasibility. Methods: Two groups of plans were designed for 20 NPC patients. Plan A included simplified intensity-modulated radiotherapy (sIMRT) plans by conventional method, and plan B included sIMRT plans using the anterior head and neck lymphatic drainage protection area. Dose distributions of the target, dose-volume parameters of organs at risk (OAR) and the total monitor units (MU) were compared between the two groups. Results: The target dose distributions of the two groups all met the clinical requirements. The indicators of planning target volume 1 (PTV1) had no significant difference between the two groups. In plan A, D_98%, V_100% (%), V_95% (%) and homogeneity index (HI) of PTV2 were superior to those in plan B (t=4.134, 3.455, 2.423 and -2.410, P<0.05). D_mean of left and right parotid gland and V₃₀ of left parotid gland in plan A were lower than those in plan B (t =-2.454, -2.113 and -4.651, P<0.05). For oral cavity, D_mean and V50 were higher in plan A (t=4.639 and 2.237, P<0.05). Similarly, D_mean and V₅₀ of larynx were also higher in plan A (t=10.934 and 4.624, P<0.05). Compared with plan A, the total MU of plan B increased slightly, but the differences were not statistically significant. Conclusion: The plan design of the anterior head and neck lymphatic drainage protection is feasible in dosimetry for NPC patients. Without sacrificing the target coverage, a low-dose (<20 Gy) lymphatic drainage area can be reserved to the front of head and neck while oral cavity and larynx are better protected.

Key words: Nasopharyngeal carcinoma, Head and neck lymphedema, Simplified intensity-modulated radiotherapy, Organ at risk