ICHNO-ECHNO 2022 - Abstract Book

S17

ICHNO-ECHNO 2022

The average change in Δ NTCP from the comparative proton plan to the clinical proton plan was -1.3% [-10.2 to 7.0%] and - 1.8% [-8.3 to 5.5%] for xerostomia and dysphagia, respectively.

Conclusion The pilot study of the DAHANCA 35 demonstrated that the plan comparison in local treatment centres can be used to select patients for proton treatment based on Δ NTCP. However, the comparative proton plan seems to slightly overestimate the benefit of the clinical proton plan, perhaps due to the precautionary principle of a clinical treatment plan and due to variations in target and OAR contouring. Continuous quality assurance of the delineation procedures and an optimal patient flow is crucial in this randomized clinical trial setting.

OC-0029 Radiologic Extranodal Extension and Its Role in Clinical N Classification in Nasopharyngeal Cancer

S.H. Huang 1 , O. Chin 2 , E. Yu 3 , J. Su 4 , A. Tellier 5 , L. Siu 6 , J. Waldron 1 , J. Kim 1 , A. Hansen 6 , A. Hope 1 , J. Cho 1 , M. Giuliani 1 , J. Ringash 1 , A. Spreafico 6 , S. Bratman 1 , A. Hosni 1 , E. Hahn 1 , L. Tong 1 , W. Xu 4 , B. O'Sullivan 1 1 Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada; 2 University of Toronto, Neuroradiology , Toronto, Canada; 3 Princess Margaret Cancer Centre, Neuroradiology and Head and Neck Imaging, Toronto, Canada; 4 Princess Margaret Cancer Centre, Biostatistics, Toronto, Canada; 5 University of Toronto, Neuroradiology, Toronto, Canada; 6 Princess Margaret Cancer Centre, Medical Oncology, Toronto, Canada Purpose or Objective The aim of the study is to confirm the prognostic value of radiologic extranodal extension (rENE) and its role in clinical N classification in nasopharyngeal cancer (NPC) treated in a western institution. Materials and Methods NPC cases treated between 2010-2017 were reviewed. Pre-treatment MRI were evaluated by (OC and AT) for unequivocal rENE and its grade: grade-1: tumour invading through any part of nodal capsule but confined to perinodal fat; grade-2: ≥ 2 adjacent nodes forming a coalescent nodal mass; grade-3: tumour extending beyond perinodal fat to invade/encase adjacent structures. Inter-rater kappa was calculated against a very experienced neuroradiologist (EY) for 100 randomly selected samples. Overall survival (OS) and disease-free survival (DFS) were compared between rENE-positive (rENE+) and rENE-negative (rENE–) patients. Multivariable analysis (MVA) confirmed the prognostic importance of rENE and its grade. Stage schemas incorporating rENE in the N-classification were proposed and performance evaluated. Results A total of 274 patients were eligible (43 cN0; 231 cN-positive). rENE was identified in 83/231 (36%) cN-positive, including grade-1, grade-2, and grade-3 rENE in 14, 58, and 11 cases, respectively. Inter-rater kappas for rENE (yes vs no), grade-1, grade-2, and grade-3 were 0.79, 0.36, 0.60, and 0.69, respectively. Compared to rENE–, rENE+ experienced lower OS (68% vs 89%, p<0.001) and DFS (58% vs 80%, p <0.001). MVA confirmed the adverse prognosis of both grade-2 [HR: OS: 2.85 (p=0.005); DFS: 2.89 (p<0.001)] and grade-3 rENE [HR: OS 5.28 (p=0.004); DFS 3.86 (p=0.005)]; a trend existed for grade-1 vs rENE– [HR: OS 2.63 (p=0.13); DFS 1.49 (p=0.520)]. We considered any rENE as cN3 ( Proposal-I ) or any grade-2/grade-3 rENE as cN3 ( Proposal-II ). The stage schema using Proposal-I cN ranked highest for both OS and DFS compared to TNM-8, and 3 other stage schemas.