2755 - Long-Term Outcome in Nasopharyngeal Carcinoma Following IMRT with Modified Nodal CTV Cranially Based on the International Guideline: A Single Center Experience
Presenter(s)
Q. Guo1, Z. Yan2, X. Yang1, K. Lin2, J. Pan3, J. Chen2, and S. Lin1; 1Department of Radiation Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou, Fujian, China, 2Department of Radiation Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou, China, 3Oncology Department, Zhangzhou Zhengxing Hospital, Zhangzhou, Fujian, China
Purpose/Objective(s): Although the International Guideline for the delineation of clinical target volume (CTV) in nasopharyngeal carcinoma (NPC) has provided important reference for clinical practice, there are marked variations in practice among different institutions. The international guideline put forward that the cranial border of nodal CTV (CTVn) should be extend to the skull base, with only 64% experts agreed, some suggested that the cranial boundary of CTVn should be contoured at the caudal edge of the lateral process of C1, and ensure a 2cm margin cranially of GTVn. The purpose of this study was to evaluate the long-term outcomes of NPC patients whose cranial boundary of CTVn were contoured at the caudal edge of the lateral process of C1, and ensure a 1cm margin cranially of GTVn.
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 or serious coexisting diseases; (2) has available imaging data for re-staging according to the TNM-8. All patients were re-staged according to the TNM-8 staging system. All patients received radical IMRT. CTVn was defined as GTVn + 3-5 mm + corresponding elective prophylactic neck area. It is worth noting that the cranial border of CTVn was defined as the caudal edge of the lateral process of C1, and ensure a 1cm margin cranially of GTVn.
Results: A total of 627 patients were included, of which 80 cases presented with a GTVn extending upward over the caudally edge of the lateral process of C1, while the remaining 547 cases were diagnosed as N0 or presented with their GTVn not over the caudally edge of the lateral process of C1. With a median follow-up of 73 months, the 5-year OS, LRFS, RRFS, DMFS for the whole cohort were 89.5%, 95.6%, 97.2%, 88.4%, respectively. Twenty (3.2%) patients experienced regional failure at time of censorship. Among these patients, 13 cases developed outside CTVn failure: level VIII (7 cases), level Ib (4 cases) and level IV(2 cases). Among the 12 cases who experienced inside CTVn failure, 7 occurred at level II, with the recurrence site in 6 out of 7 cased located below the caudal edge of the lateral process of C1. Only one patient had recurrence GTVn in level IIb extending upward over the caudal edge of the lateral process of C1 but below the skull base, of note, this specific case has in situ positive LN in level IIb at baseline MRI data, which was almost overlapped with the recurrent GTVn, and should be defined as inside GTVn failure.
Conclusion: The excellent clinical outcomes of the current study supported the feasibility of our policy that the cranial boundary of CTVn could be settled at the caudal edge of the lateral process of C1 and ensure a minimal margin of 1cm above GTVn. Further well-designed multi-center prospective trials should be conducted to confirm our results.