ESTRO 2021 Abstract Book

S841

ESTRO 2021

PO-1012 proposal of new N stage scheme and comparison between seven N schemes in nasopharyngeal carcinoma W. Peng 1 , C. Hu 1 , T. Xu 1 , X. Zhou 2 1 Fudan University Shanghai Cancer Center, Radiation Oncology, Shanghai, China; 2 Fudan University Shanghai Cancer Center,, Radiation Oncology, Shanghai, China Purpose or Objective To identify the prognostic value of the nodal features and evaluate the performance of seven N stage schemes of nasopharyngeal carcinoma (NPC) patients. Materials and Methods Data from 1638 non-distant metastatic NPC patients who received IMRT in Fudan University Shanghai Cancer Center between 2013 and 2015 were retrospectively reviewed. Nomograms using nodal features to predict OS and DMFS were constructed. Features in the final predictive modal were put into multivariable analysis and then corporated into a new N stage scheme. Performances of nomogram-based N stage were assessed against five newly proposed N stage system and current 8th N stage using a quantitative model(autoRPA platform) to compare hazard consistency, discrimination, outcome predicting and sample size balance. Results Various nodal features, i.e., RLN (retropharyngeal lymph node) laterality and size; CLN (cervical lymph node) laterality, level, size—measured as maximal axial diameters (MAD) and maximal diameter at three plane (Dmax), extranodal extension (ENE) measured as different grades, central nodal necrosis (CNN) measured as different grades, grouping and total nodes number, were taken into factor selection. Nomograms to predict OS and DMFS were constructed using ENE infiltrating surrounding structures (ENEmax), MAD, big RLN (minimal axial diameter >1.5cm), multiple CNN, CLN laterality and level (not shown here). Multivariate analysis showed ENEmax, MAD>3cm, Big RLN, multiple CNN and lower neck involvement were also independently associated with OS(p<0.05). We proposed to use big RLN and MAD>3cm as N2 factor, ENEmax and lower neck involvement as N3 factor(abbr.Nomo).

Since publication of 8 th UICC/AJCC stage(th8N), five N schemes were proposed to improve the staging performance--more than 9 positive LNs as N3 (N93), MAD >4 cm as N3 (MAD43), ENEmax as N3 (ENE3), bilateral RLN metastasis as N2 (RLN2), upstage cases with CNN (CNNup). We used a staging comparison model developed by Groome et al(http://rpa.renlab.org) to quantify the staging differences in four aspects. Among seven N stage schemes, our nomogram-based N scheme and upgrading ENEmax to N3 scheme (ENE3) ranked top two in overall comparison with elevated outcome predicting value (highest c-index). The 8 th N staging showed best hazard discrimination. N93 showed best hazard consistency. CNNup showed best sample size balance. In all, RLN2, N93, MAD43 and CNNup were not superior than th8N. However, the best one--ENE3 showed no difference in OS and DMFS(p>0.05) between N0 and N1, N1 and N2 subgroups.