2789 - Assessing the Safety of Delayed Elective Nodal Irradiation through Pre-Treatment Nodal Kinetics in High-Risk OPSCC
Presenter(s)
G. J. Li1, D. Hindle1, M. H. Bin Johari2, S. H. Huang1, E. Taylor1, T. Tadic1, E. Yu2, A. Spreafico3, J. de Almeida4, S. V. Bratman1, J. Cho1, E. Hahn1, A. J. Hope1, A. Hosni1, J. H. J. Kim1, N. Malik1, B. O'Sullivan1, C. J. Tsai4, J. N. Waldron1, and A. McPartlin1; 1Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 2Department of Medical Imaging, University of Toronto, Toronto, ON, Canada, 3Department of Medical Oncology, University of Toronto, Toronto, ON, Canada, 4Princess Margaret Cancer Centre, Toronto, ON, Canada
Purpose/Objective(s): Delayed neck elective nodal irradiation (dENI) potentiates immune-mediated response in animal models via initial sparing of radiosensitive draining lymph nodes. The risk of occult disease progression from dENI is poorly described, limiting clinical investigation. We report pre-treatment nodal kinetics in a high-risk population of oropharyngeal squamous cell carcinoma (OPSCC).
Materials/Methods: All T4, node-positive, p16-negative OPSCC patients treated with definitive radiotherapy between 2008-2021 were identified from an institutional database. To quantify kinetics, nodal volumes were contoured and compared on diagnostic and planning imaging. Association of nodal kinetics and oncologic outcomes were assessed using regression models.
Results: Seventy-nine patients with available imaging were identified, with median follow-up of 17 months. N-category included N1 (n=12, 15%), N2a/b (n=32, 40%), N2c (n=33, 42%) and N3 (n=2, 3%), with median total nodal volume of 8.6 cc (IQR 3.5-17.2) at diagnosis. Median interval between diagnostic and planning imaging was 30 days (IQR 18-40), with median overall growth of 0.5 cc (IQR 0.1-2.5) and growth rate of 0.3% per day (IQR 0.05-1.2%). No new radiological nodal disease developed between scans. Two-year cumulative incidence of local failure (LF) was 26%, regional failure (RF) 14%, and distant failure (DF) 23%. All regional failures occurred within treated gross nodal volumes. Median PFS and OS were 14 and 32 months. Time between imaging, absolute and relative nodal growth rates, were not associated with outcomes. Total volume of nodal disease at diagnosis, but not N-category, was associated with RF (HR 1.05 [1.02-1.08]), DF (HR 1.04 [1.02-1.07]), and OS (HR 1.02 [1.01-1.04]).
Conclusion: Despite locally advanced OPSCC, nodal disease volume, but not pre-treatment kinetics, was prognostic. All regional failures occurred within initially treated nodal disease. During the median 30-day interval prior to treatment, no new nodal disease developed, and nodal growth was minimal. This supports the safety of dENI studies for OPSCC.