3719 - Impact of Post-Operative Radiotherapy Neck Volume on Unstimulated Saliva Flow in Oral Cavity Squamous Cell Carcinoma

C. Rooney¹, S. H. Huang², E. Watson³, M. Glogauer³, J. Su⁴, A. Hosni⁵, J. Irish⁶, D. Goldstein⁶, J. de Almeida⁷, S. V. Bratman⁵, J. Cho⁸, E. Hahn⁵, A. J. Hope⁹, J. Kim⁵, B. OSullivan¹⁰, C. J. Tsai⁵, J. Waldron⁵, A. Spreafico¹¹, and A. McPartlin²; ¹Department of Radiation Oncology, Princes Margaret Cancer Centre, Toronto, ON, Canada, ²Department of Radiation Oncology, Princess Margaret Cancer Centre, Toronto, ON, Canada, ³University of Toronto Faculty of Dentistry, Princess Margaret Cancer Centre, Toronto, ON, Canada, ⁴Department of Biostatistics, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁵Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁶Department of Otolaryngology-Head & Neck Surgery, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁷Department of Otolaryngology – Head & Neck Surgery/Surgical Oncology, Princess Margaret Cancer Centre, Toronto, ON, Canada, ⁸Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, ⁹Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, ¹⁰CHUM (The University of Montreal Hospital Centre), Montreal, QC, Canada, ¹¹Department of Medical Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada

Purpose/Objective(s): Hyposalivation is a common sequelae of oral cavity carcinoma (OSCC) surgery and post-operative radiotherapy (PORT). The relative contribution of both treatment modalities to long term xerostomia is poorly described. Quantification of the effect of bilateral neck PORT on saliva dysfunction can inform decisions regarding adjuvant PORT volumes. We compare change in unstimulated salivary function, measured via 3-minute modified Schirmer test (MST), in OSCC patients following an ipsilateral neck dissection (IND) stratified by PORT neck volumes. Materials/

Methods: We reviewed a prospectively assembled cohort of OSCC patients who underwent IND with intensity modulated PORT between 2005-21 and who had a routine 3-minute MST measurement pre-RT and 6 and/or 12 months post-PORT. Change in saliva flow and prevalence of hyposalivation, (defined as MST <25mm) was compared by PORT neck volumes (bilateral vs unilateral/no). Multivariable linear regression analysis (MVA) was performed to identify predictors for hyposalivation.
Results: A total of 165 patients were eligible; 88 (53%) bilateral, 66 (40%) ipsilateral, and 11 (7%) no neck PORT. Baseline characteristics were similar between groups, except more N2b/N2c with bilateral PORT (60% vs 31%, p<0.001). Similar proportions had baseline hyposalivation after surgery prior to PORT (26% vs 28%, p=0.97). The median absolute change in MST (mm) compared to baseline was greater in the bilateral vs ipsilateral/no neck PORT at 6 (21 vs 5) and 12 (21 vs 0) months (both p<0.001). Hyposalivation occurred more in bilateral vs ipsilateral/no neck PORT at 6 months (90% vs 54%) and 12 months (90% vs 44%) (both p<0.001). MVA identified bilateral neck PORT and higher smoker pack-years as predictors for hyposalivation at 6/12 months (Table 1).
Conclusion: About a quarter OSCC patients have baseline unstimulated salivary hypofunction following IND prior to PORT. Rates of hyposalivation at 6- and 12-months post-PORT nearly doubles following bilateral neck PORT compared to unilateral or no neck PORT. Incidence of hyposalivation following bilateral PORT was stable at 6 and 12 months, suggesting little long term recovery of function. Further investigation with correlation of irradiation dosimetry to the salivary gland structures may help guide dose optimization strategies. Abstract 3719 – Table 1: Multivariate analysis displaying odds ratio for occurrence of hyposalivation following PORT

	Odd Ratio (95% CI)	p-value
IMRT Neck Volume		<0.001
Unilateral/No	Reference
Bilateral	6.25 (2.56-16.67)
Age at Diagnosis	1.01 (0.97-1.04)	0.63
Gender		0.58
Female	Reference
Male	0.78 (0.33-1.86)
Smoking Pack-Years (continuous)	1.05 (1.01-1.09)	0.018
Stage (by TNM-7)		0.30
I/II	Reference
III/IV	1.71 (0.63-4.69)
Chemotherapy		0.67
No	Reference
Yes	1.30 (0.39-4.35)