3657 - Refining the Radiologic Criteria of Parotid Node Groups Metastasis in Nasopharyngeal Carcinoma

Q. Guo¹, X. Yang², Z. Yan², X. Chen², J. Pan³, and S. Lin^4,5; ¹Department of Radiation Oncology, Fujian Medical University Cancer Hospital, Fujian Cancer Hospital, Fuzhou, China, ²Department of Radiation Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou, Fujian, China., Fuzhou, China, ³Fujian Key Laboratory of Translational Cancer Medicine, Fuzhou, China, ⁴Fujian Provincial Cancer Hospital, Fuzhou, China, ⁵Department of Radiation Oncology, Fujian Medical University Cancer Hospital, Fujian Cancer Hospital, Fuzhou, Fujian, China

Purpose/Objective(s): Growing evidence reported that parotid nodes groups(PNG, nominated as level VIII) was the major out-field site of regional failure after curative intensity modulated radiotherapy(IMRT) in nasopharyngeal carcinoma(NPC) patients, and a majority of them presented with sub-centimeter lymph nodes(<10mm) in level VIII at their baseline magnetic resonance imaging (MRI). This situation raised the concern for reconsidering the diagnostic criteria of level VIII lymph nodes (LNs) metastasis. This study was conducted to evaluate the rationality of current radiologic criteria of metastatic PNG, and provide evidence for possible refinement. Materials/

Methods: Patients with histologically-proven NPC who received curative IMRT with or without chemotherapy at our attending group between January 2014 and March 2018 were candidates for this study. Other eligible criteria were listed as following: (1) has no history of previous treatment or prior malignancy; (2) has available imaging data for re-staging according to the TNM-8 and evaluating the status of PNG. Of note, PNGs with the minimal axial diameter (MAD) = 5 mm of the largest lymph node at baseline MRI were all recorded. Survival outcome focus on regional relapse free survival (RRFS) and the incidence of PNG were analyzed.
Results: A total of 627 patients were finally included for this analysis. With a median following up time of 69 months, 5-year OS and RRFS, LRFS and DMFS were reported to be 89.5%, 95.6%, 97.2%, and 88.4%, respectively. At time of censorship, 20 cases developed regional recurrence, of which 9 were located at level VIII. Notably, 8 out of the 9 patients with level VIII failure had sub-centimeter lymph nodes (<10 mm) in situ at baseline MRI. After re-evaluation the baseline imaging data for the whole cohort of patients, a total of 72 patients presented to have sub-centimeter lymph nodes at baseline, among them, 4 cases received PLNs-covering IMRT and did not experience level VIII recurrence. Of the remaining 68 patients who underwent PLNs-sparing IMRT, 53 cases were recorded as = 5 mm but <6mm, 1(1.9%) out of these 53 patients developed level VIII relapse. For the 15 patients who had sub-centimeter lymph nodes of =6mm at baseline, 5(33.3%, 5/15) of them occurred regional relapse at level VIII. Five out of the 68 patients had baseline sub-centimeter lymph nodes of 7mm or larger, two of them experience in situ recurrence in level VIII. All the three patients with sub-centimeter lymph nodes of =8mm at diagnosis experienced in situ recurrence(100%).
Conclusion: Current radiologic criteria(=10 mm) for assessing PNGs should be implemented with caution, as a substantial proportion of patients with sub-centimeter lymph nodes of >6mm at baseline occurred in situ regional failure at level VIII. Pathological puncture was recommended for patients with sub-centimeter lymph nodes of =6mm at baseline. Well-designed prospective multi-center study is warranted to confirm our findings.