Can Parameters Other than Minimal Axial Diameter in MRI and PET/CT Further Improve Diagnostic Accuracy for Equivocal Retropharyngeal Lymph Nodes in Nasopharyngeal Carcinoma?

Yu-Wen Wang,Yu-Kang Chang,Chin-Shun Wu,Keng-Ren Lin,Kuo-Sheng Cheng,Chih-Han Chang,Li-Ching Lin,Tsair-Wei Chien,Guo-Yi Zhang,Wei-Jen Yao,Jeremy J.W Chen

doi:10.1371/journal.pone.0163741

Abstract

PurposeMinimal axial diameter (MIAD) in magnetic resonance imaging (MRI) was recognized as the most useful parameter in diagnosing lateral retropharyngeal lymph (LRPL) nodes in nasopharyngeal carcinoma (NPC). This study aims to explore the additional nodal parameters in MRI and positron emission tomography–computed tomography for increasing the prediction accuracy.Materials and MethodsA total of 663 LRPL nodes were retrospectively collected from 335 patients with NPC. The LRPL nodes ascertained on follow-up MRI were considered positive for metastases. First, the optimal cutoff value of each parameter was derived for each parameter. In addition, neural network (NN) nodal evaluation was tested for all combinations of three parameters, namely MIAD, maximal axial diameter (MAAD), and maximal coronal diameter (MACD). The optimal approach was determined through brute force attack, and the results of two methods were compared using a bootstrap sampling method. Second, the mean standard uptake value (NSUVmean) was added as the fourth parameter and tested in the same manner for 410 nodes in 219 patients.ResultsIn first and second analysis, the accuracy rate (percentage) for the MIAD was 89.0% (590/663) and 89.0% (365/410), with the optimal cutoff values being 6.1 mm and 6.0 mm, respectively. With the combination of all three and four parameters, the accuracy rate of the NN was 89% (288/332) and 88.8% (182/205), respectively. In prediction, the optimal combinations of the three and four parameters resulted in correct identification of three (accuracy: 593/663, 89.4%) and six additional nodes (371/410, 90.5%), representing 4% (3/73) and 13.3% (6/45) decreases in incorrect prediction, respectively.ConclusionNPC LRPL nodes with an MIAD ≥ 6.1 mm are positive. Among nodes with an MIAD < 6.1 mm, if the NSUVmean ≥ 2.6 or MACD ≥ 25 mm and MAAD ≥ 8 mm, the nodes are positive; otherwise, they are negative.

Highlights

Identification of positive lateral retropharyngeal lymph (LRPL) nodes in nasopharyngeal carcinoma (NPC) is crucial
NPC LRPL nodes with an minimal axial diameter (MIAD) ! 6.1 mm are positive
In stage I, this paper describes an evaluation of nodal parameters by using a neural network (NN) and an exhaustive key search of 663 LRPL nodes in NPC for testing whether higher accuracy than that of MIAD alone can be attained by employing a combination of MIAD, maximal axial diameter (MAAD), and maximal coronal diameter (MACD)

Summary

Introduction

Identification of positive lateral retropharyngeal lymph (LRPL) nodes in nasopharyngeal carcinoma (NPC) is crucial. Most physicians use minimal axial diameter (MIAD) in MRI to evaluate nodal metastasis [4, 5]. The net additional contribution of PET/CT used to complement MRI has not been addressed in the literature on LRPL nodal metastasis in NPC. For equivocal LRPL nodes in NPC patients, whose chemoradiation decisions can solely be based on image information in the absence of feasible tissue proof, it is imperative for improving the accuracy of node diagnosis [2, 5, 10, 11, 13, 14]. In stage I, this paper describes an evaluation of nodal parameters by using a neural network (NN) and an exhaustive key search of 663 LRPL nodes in NPC for testing whether higher accuracy than that of MIAD alone can be attained by employing a combination of MIAD, MAAD, and MACD. In stage II, 410 nodes were jointly evaluated using the method applied in stage I to determine whether superior results could be attained by adding the nodal mean standard uptake value (NSUVmean) as a parameter

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