S644
Clinical – Head & neck
ESTRO 2026
corresponding to relative reductions of 5.5% and 11%, respectively. No significant differences were observed for hypothyroidism (p=0.10), and mucositis reduction was minimal but statistically significant ( Δ 0.0 pp, p<0.01) due to lower mean oral cavity doses. Nearly half the patients would have benefited from volume adaptation either by inclusion of atypical drainage levels or omission of the contralateral neck. Conclusion: SLNB-guided postoperative RT planning for OTSCC is a promising approach to individualize treatment and reducing radiation volumes in majority of patients. Integrating SLNB findings enables both safer target coverage in cases with atypical drainage and significant dose reductions to organs at risk when contralateral drainage is absent. This strategy may enhance treatment safety and patient quality of life without compromising oncologic security. Prospective validation in a controlled clinical setting is warranted. References: 1. Bark, R., et al., Sentinel node-assisted neck dissection in advanced oral squamous cell carcinoma- A new protocol for staging and treatment. Cancer Med, 2023. 12(11): p. 12524-12534.2. Koyfman, S.A., et al., Management of the Neck in Squamous Cell Carcinoma of the Oral Cavity and Oropharynx: ASCO Clinical Practice Guideline. J Clin Oncol, 2019. 37(20): p. 1753-1774.3. Gregoire, V., et al., Delineation of the neck node levels for head and neck tumors: a 2013 update. DAHANCA, EORTC, HKNPCSG, NCIC CTG, NCRI, RTOG, TROG consensus guidelines. Radiother Oncol, 2014. 110(1): p. 172-81.4. Langendijk, J.A., et al., National Protocol for Model-Based Selection for Proton Therapy in Head and Neck Cancer. Int J Part Ther, 2021. 8(1): p. 354-365. Keywords: SLNB, radiotherapy, individualized treatment Digital Poster 4014 Assessment of Radiation Dose and Volume Changes in the Masticatory Apparatus and Clinical Correlation with Trismus in Oral Cavity Cancer Patients Maham Khan, Laraib Khan, Mariam Hina, Tooba Ali, Fabiha Shakeel, Maria Tariq, Asim Hafiz, Ahmed Nadeem Abbasi, Nasir Ali, Bilal Mazhar Qureshi Radiation Oncology, Aga Khan University Hospital, Karachi, Pakistan Purpose/Objective: Oral cavity squamous cell carcinoma (OSCC) is the most common head and neck malignancy in South Asia, where adjuvant radiotherapy is integral to management. Trismus is a frequent complication that impairs nutrition, speech, and quality of life. While
Digital Poster 3992
Sentinel node–modified adjuvant radiotherapy for oral tongue squamous cell carcinoma (OTSCC): Retrospective analysis using NTCP models Einar Björgvinsson 1,2 , Aeneas Kolev 3,4 , Eva Onjukka 5,2 , Mattias Hedman 6,2 , Gregori Margolin 3,4 , Åsa Carlsson Tedgren 5,2 , Lars Södergren 5 , Michael Gubanski 6,2 1 Head and neck oncology, Karolinska University Hospital, Stockholm, Sweden. 2 Oncology-Pathology, Karolinska Institute, Stockholm, Sweden. 3 Head and neck surgery, Karolinska University Hospital, Stockholm, Sweden. 4 Clinical science, intervention and technique, Karolinska Institute, Stockholm, Sweden. 5 Nuclear medicine, Karolinska University Hospital, Stockholm, Sweden. 6 Radiotherapy, Karolinska University Hospital, Stockholm, Sweden Purpose/Objective: To investigate whether sentinel lymph node biopsy (SLNB) results can be used to individualize postoperative radiotherapy (RT) in patients with oral tongue squamous cell carcinoma (OTSCC), with the aim of improving safety and reducing toxicity. Specifically, we evaluated the frequency of aberrant lymphatic drainage patterns detected by SLNB, their potential impact on RT target definition, and the estimated reduction in treatment-related side effects using normal tissue complication probability (NTCP) models. Material/Methods: This retrospective study included 42 consecutive OTSCC patients treated with curative intent surgery, SLNB, and postoperative RT at Karolinska University Hospital between 2016–2021. Treatment RT plans were compared with modified ones according to each patient’s SLNB results. Two groups were defined: (1) patients with sentinel nodes (SNs) outside standard elective neck levels or contralateral drainage, and (2) patients with no contralateral drainage and pN0 status, for whom the contralateral neck was omitted. All plans were generated using the same RapidPlan™ knowledge-based model to ensure comparability. NTCP was calculated for xerostomia, dysphagia, hypothyroidism, and oral mucositis based on published models, and compared using Wilcoxon signed-rank tests. Results: Aberrant lymphatic drainage outside standard target volumes was observed in 45% of patients, most frequently in ipsilateral levels IV–V. Contralateral drainage was absent in 83%, suggesting that contralateral irradiation could eventually safely be omitted in a large subset. The SLNB-adapted plans showed significantly reduced median NTCP values for xerostomia (7.7% → 6.2%, Δ –0.4 pp, p<0.01) and dysphagia (8.9% → 6.2%, Δ –1.0 pp, p<0.01),
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