ESTRO 2023 - Abstract Book

S968

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ESTRO 2023

PO-1211 Adjuvant Radiotherapy in Node-negative Parotid Gland Malignancies: A Multi-institutional Analysis

J.B. Park 1 , H. Wu 1 , J.H. Kim 1 , J.H. Lee 1 , S. Ahn 2 , E. Chung 2 , K. Eom 3 , W. Jeong 4 , T. Kwon 5 , S. Kim 6 , C.W. Wee 6

1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of; 2 Seoul National University Hospital, Otorhinolaryngology-Head and Neck Surgery, Seoul, Korea Republic of; 3 Seoul National University Bundang Hospital, Radiation Oncology, Seongnam, Korea Republic of; 4 Seoul National University Bundang Hospital, Otorhinolaryngology-Head and Neck Surgery , Seongnam, Korea Republic of; 5 SMG-SNU Boramae Medical Center, Otorhinolaryngology-Head and Neck Surgery, Seoul, Korea Republic of; 6 SMG-SNU Boramae Medical Center, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective To determine the role of adjuvant radiotherapy (ART) in parotid gland cancer without nodal metastasis, we evaluated the survival outcomes, prognostic factors, and dose-response relationships in patients with node-negative salivary gland malignancies of the parotid gland patients who underwent curative parotidectomy. Materials and Methods Patients who underwent curative surgery and were pathologically diagnosed with parotid gland cancer without regional or distant metastases between 2004 and 2019 were reviewed. Histological type and grade were reclassified according to the 2022 World Health Organization classification. The benefit of ART in terms of locoregional control (LRC) and progression free survival (PFS) were evaluated. Results In total, 261 patients were included in the analysis. Among those patients, 45.2% received ART. The median follow-up period was 66.8 months. Multivariate analysis revealed that histological grade and ART were independent prognostic factors for LRC and PFS (all p < .05) ( Figure 1 ). For patients with high-grade histology, ART was associated with a significant improvement in 5-year LRC (adjusted hazard ratio [HR], 0.17; 95% confidence interval [CI], 0.05–0.58; p = .005) and PFS (HR, 0.25; 95% CI, 0.09–0.71; p = .009) in multivariate analysis ( Figure 2 ). Among patients who complete ART and had a high-grade histology, higher biologic effective dose ( ≥ 77 Gy10) significantly increased PFS (HR, 0.10 per 1-Gy increase; 95% CI, 0.02-0.58; p = .010). ART significantly improved LRC (HR, 0.18; 95% CI, 0.04–0.92; p = .039) in patients with low-to intermediate histological grade as well per multivariate analysis. Subgroup analyses revealed patients with T3–4 stage and close/positive resection margins (< 1 mm) would benefit from ART. Figure 1. [A] Locoregional control and [B] progression-free survival in all patients