Prognostic value of MRI-derived residual retropharyngeal lymph node after intensity-modulated radiotherapy in nasopharyngeal carcinoma and a nomogram for the prediction of it

Abstract

Background: In nasopharyngeal carcinoma (NPC) patients with retropharyngeal lymph node (RLN) metastasis who receive intensity‐modulated radiotherapy (IMRT), the incidence of magnetic resonance imaging (MRI)‐derived residual retropharyngeal lymph node (RRLN) is not rare and its prognostic value is uncertain. In present study, we aim to investigate the prognostic value of MRI‐derived RRLN and sought to develop a nomogram for the prediction of it. Methods: A total of 922 patients with RLN metastasis without distant metastasis NPC treated with IMRT were enrolled in present study. The Kaplan‐Meir survival curves and cox proportional regression model were used to assess the prognostic value of RRLN. The patients were then randomly assigned into the training cohort (n=645) and the validation cohort (n=277). Factors significantly associated with RRLN were identified and used to construct nomogram with multivariate logistic regression model. The discrimination and performance of nomogram were evaluated in training cohort and confirmed in validation cohort. Results: The incidence of RRLN was 28.2%. The 5‐year OS, DFS, DMFS, LRRFS of the RRLN group and non‐RRLN group were 84.1% vs. 93.2%, 65.1% vs. 87.3%, 71.2% vs. 94.2% and 87.8% vs. 95.6%, respectively (for all rates, P<0.05). Necrosis, extra‐nodal neoplastic spread (ENS), minimum axial dimeter (MAD) and the percentage volume of the GTVnx receiving 95% of the prescribed dose (GTVnx V95%) were identified as independent factors associated with RRLN and used to construct the nomogram. The nomogram showed favorable calibration and discrimination in training cohort (AUC, 0.746) and validation cohorts (AUC, 0.738). Patients with high‐risk scores had a higher probability of developing RRLN than patients with low‐risk scores in training cohort (OR, 5.183, 95% CI 2.845‐8.525) and validation cohort (OR, 6.977, 95% CI 3.990‐ 12.200). Conclusions: MRI‐derived RRLN was a negative independent prognostic factor for OS, PFS, DMFS and LRRFS in NPC patients with RLN metastasis who received IMRT. We constructed a nomogram based on clinical and radiological characteristics that predicted an individual's risk of RRLN.