S568
Clinical – Head & neck
ESTRO 2026
1 Otorhinolaryngology, Juntendo University, Tokyo, Japan. 2 Radiation Oncology, Juntendo University, Tokyo, Japan Purpose/Objective: Salivary gland carcinoma (SGC) is a rare and histologically diverse malignancy with limited preoperative biomarkers for risk stratification. Although diffusion-weighted MRI (DWI) provides functional insights into tumor cellularity, its clinical implementation has been hindered by methodological variability and lack of standardization. This study aimed to evaluate the prognostic and metastatic risk significance of preoperative, volume-based apparent diffusion coefficient (ADC) analysis in SGC using an automated software platform that enables reproducible whole-tumor quantification. Material/Methods: Sixty-five consecutive patients with SGC who underwent radical surgery between 2014 and 2024 were retrospectively analyzed. Quantitative DWI analysis was performed using dedicated software (Attractive BD Score, PixSpace Inc., Japan), which automatically segmented voxels with ADC values between 0.3 and 2.0 × 10 ⁻ ³ mm ² /s. Histogram analysis yielded median ADC and entropy as volumetric parameters. Local control (LC), disease-free survival (DFS), and overall survival (OS) were evaluated using the Kaplan–Meier method. Prognostic factors were assessed with log-rank tests, Spearman’s rank correlation, and Cox proportional hazards modeling. Results: The median patient age was 57 years, and 84.6% of tumors originated in the parotid gland. At two years, LC remained excellent across all stages (89.3% for stage I–II vs. 92.3% for stage III–IV), whereas DFS was significantly worse in advanced disease (77.7% vs. 46.9%, p = 0.047). In univariate analyses, advanced stage, high pathological grade, preoperative facial nerve palsy, and low median ADC were significantly associated with poorer DFS. Spearman’s analysis demonstrated a negative correlation between pathological grade and median ADC ( ρ = –0.38, p = 0.002). Multivariate analysis identified median ADC as an independent predictor of DFS (HR = 0.25, 95% CI 0.07–0.98, p = 0.046), suggesting that low ADC value primarily reflects metastatic potential rather than local progression. Entropy did not correlate with outcomes. The automated, volume-based ADC approach enabled consistent whole-lesion analysis. Conclusion: This study demonstrates that preoperative, volume- based ADC quantification independently predicts DFS in SGC, serving as a potential imaging biomarker of metastatic risk. While ADC was not associated with local control, its integration into preoperative evaluation may enhance risk stratification and support
were conducted using Kaplan–Meier estimates and log-rank testing. Results:
Baseline characteristics were well balanced between groups, except for a higher prevalence of prior malignancies in the definitive RT cohort (23% vs. 3%, p=0.002). Systemic therapy was more frequently administered in the definitive RT group. After a median follow-up of 32.7 months, OS did not differ significantly between groups (5-year OS: 63.9% vs. 60.0%, p=0.7). Trends favouring adjuvant RT were observed for PFS (5-year: 58.7% vs. 48.1%, p=0.09) and LRFS (5-year: 85.8% vs. 74.6%, p=0.08), though not statistically significant. MFS was comparable between groups (5-year: 59.6% vs. 51.7%, p=0.2). Treatment- related toxicities were similar; however, lymphedema was more common following adjuvant RT (33% vs. 13%, p=0.017). Other acute/late effects including mucositis, xerostomia, dysphagia, fatigue, and dermatitis showed no significant differences. Locoregional recurrences were numerically higher
after definitive RT (23% vs. 12%, p=0.149), predominantly within high-dose regions. Conclusion:
In this matched analysis, adjuvant and definitive RT achieved comparable survival outcomes for patients with locally advanced pharyngeal and laryngeal SCC. Adjuvant RT showed a trend toward improved disease control but was associated with increased lymphedema. These findings highlight the importance of individualized, multidisciplinary treatment selection and warrant further prospective validation. Keywords: definitive RT, adjuvant RT, matching
Digital Poster 1537
Preoperative Volume-Based Apparent Diffusion Coefficient as a Predictor of Disease-Free Survival and Metastatic Risk in Salivary Gland Carcinoma Tomo Arai 1 , Noriyuki Okonogi 2 , Yasuo Kosugi 2 , Jun Takatsu 2 , Yoshifumi Matsumoto 1 , Shinichi Oba 1 , Naoya Murakami 2 , Naoto Shikama 2 , Fumihiko Matsumoto 1
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