Selectively Irradiation of the Supraclavicular Area in Nasopharyngeal Carcinoma Treated with Intensity Modulated Radiotherapy

Abstract

The application of intensity-modulated radiotherapy (IMRT) has significantly improved the locoregional control and overall survival of patients with nasopharyngeal carcinoma (NPC), but how to deescalate the intensity of treatment to further reduce the side effects while ensuring the efficacy is the main concern of clinicians. Decreasing radiation volume is one of the hot research topics. Whole-neck irradiation is recommended for patients with cervical lymph node involvement, which includes levels IVb and Vc. Since the implementation of IMRT in our clinic, patients with only upper cervical lymph node invasion have not been irradiated in the levels IVb and Vc, and the regional control rate is comparable to that of other centers. This study intends to retrospectively analyze the feasibility of omitting levels IVb and Vc in patients with only upper cervical lymph node invasion, and provide a basis for the revision of international guideline for the delineation of the clinical target volume (CTV). Patients with histologically confirmed NPC who completed IMRT successfully at our attending group between January 2014 to March 2018 were candidates for this study. Other eligibility criteria for analysis were as follows: (1) The first patient without distant metastasis; (2) Only patients with upper cervical lymph node invasion (only N1, N2, because the maximum diameter of the upper neck 6cm diagnosed as N3 patients were not included) (AJCC staging system, 8th edition); (3) Having complete baseline imaging data; (4) Over 3 months of follow-up; (5) Patients without previous history of malignant tumor and secondary cancer. According to the delineation of CTV in our protocol for patients with stage N1 and N2, levels IVb and Vc are not irradiated (i.e., retaining the original supraclavicular area). The main endpoints of the study were regional recurrence-free survival (RRFS) and recurrence rates in levels IVb and Vc. In all, 363 patients with NPC and median follow-up of 61.9 months (range, 3.67-93.3) met the study inclusion criteria and comprise the dataset for the analysis. The overall survival, survival without local recurrence, survival without regional recurrence, and survival without distant metastasis at 3 and 5 years were 94.6% and 91.1%, 97.7% and 96.5%, 98.6% and 98.0%, 93.5% and 91.1%. At the final follow-up, 11 cases showed regional recurrence, and only one case (0.28%) showed recurrence in regions IVb and Vc, which were field recurrences, while the rest were intra-field recurrences. Omitting levels Ⅳb and Ⅴc IMRT should be safe and feasible for patients who only had involvement of upper neck LNs. Further well-designed multicenter prospective trials should be conducted to confirm our results and further optimize the recommendation of the International Guideline.