3622 - Outcomes and Characteristics of Patients Receiving Pre-Operative vs. Post-Operative Radiotherapy for Sinonasal Squamous Cell Carcinoma

R. Chelvarajah¹, S. H. Huang², J. Su³, J. Ringash², I. Witterick¹, J. de Almeida⁴, E. Montero¹, A. Spreafico⁵, J. N. Waldron⁶, B. OSullivan¹, A. Hosni Abdalaty¹, S. V. Bratman⁶, J. Cho², A. Hope⁷, J. Kim², A. McPartlin⁸, C. J. Tsai⁹, W. Xu¹⁰, and E. Hahn¹; ¹Princess Margaret Cancer Centre, Toronto, ON, Canada, ²Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ³Department of Biostatistics, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁴Department of Otolaryngology-Head & Neck Surgery, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁵Department of Medical Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁶Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, ⁷Department of Radiation Oncology, University Health Network, Toronto, ON, Canada, ⁸Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, ⁹University of Toronto, Toronto, ON, Canada, ¹⁰Department of Biostatistics, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada

Purpose/Objective(s): Resectable sinonasal squamous cell carcinoma (SNSCC) is often managed by surgery +/- post-operative radiation (postop-RT), guided by surgical pathology. In our institution, pre-operative radiation (preop-RT) has been used in select cases after multidisciplinary input due to advantages of lower dose and defined volumes, important for disease adjacent to optic structures. We report our experience with preop-RT in SNSCC, focusing on oncologic outcomes and patient selection. Materials/

Methods: All newly diagnosed SNSCC treated with preop-RT or postop-RT from 2005 to 2021 were included. SNSCC treated with surgery alone was excluded. Clinical characteristics and outcomes were compared between preop-RT vs postop-RT. Actuarial rates of overall survival (OS), disease-free survival (DFS), locoregional control (LRC), local control (LC), distant control (DC), and late toxicity were estimated.
Results: A total of 71 patients were eligible: 25 received preop-RT and 46 postop-RT. The preop-RT cohort comprised more ethmoid sinus primary sites (32% vs 0%, p<0.001) and T3-T4 diseases (versus T1-2) at presentation (96% vs 65%, p<0.04; mean tumor size 62 cc vs 49 cc, p=0.02). The remaining baseline characteristics were similar between the preop-RT vs postop-RT cohorts. The reasons for preop-RT included reduction of dose and volume of critical organs (n=16, 64%), avoidance of orbital exenteration (n=2, 8%), maximizing the likelihood of achieving clear resection margins (n=5, 20%) and other (n=2, 8%). All patients in the preop-RT cohort received 50 Gy/25f to the primary site, and 7 received a simultaneous boost to 60 Gy for gross/equivocal nodal disease to spare a neck dissection (n=4, 57%), or high-risk surgical regions with a high likelihood of a R1 resection based on a pre-RT discussion with the surgical team (n=3, 43%). Patients in the postop-RT cohort received 60-70 Gy/30-35f. Eight (32%) preop-RT patients had a pathological complete response (pCR). Five (20%) patients in the preop-RT cohort had local failure (1 residual, 4 recurrence) vs 16 (35%) in the postop-RT cohort. The median follow-up was 5.5 and 5.2 years for the preop-RT and postop-RT cohort, respectively. Oncologic outcomes and late toxicity at 5-years were similar between cohorts (Table 1).
Conclusion: Nearly 1/3 of patients with SNSCC treated with preop-RT achieved a pCR. Preop-RT was associated with similar oncologic outcomes as postop-RT despite larger tumor sizes with higher T-categories. In the setting of collaborative high-volume center, pre-op RT in the management of locally advanced SNSCC is a reasonable option in select patients to minimize dose to optic structures, reduce the radiated volume, and improve margin clearance. Abstract 3622 – Table 1: Oncologic outcomes

	Postop-RT (n=46) (%)	Preop-RT (n=25) (%)	P value
5-year Outcomes
OS	65 (52-81)	76 (61-95)	0.91
DFS	57 (44-74)	66 (49-89)	0.49
LRC	64 (47-76)	78 (50-90)	0.11
LC	78 (50-90)	67 (49-78)	0.16
DC	81 (65-90)	92 (69-98)	0.52
Late toxicity	0.12 (0.04-0.23)	0.18 (0.05-0.36)	0.39