S605
Clinical – Head & neck
ESTRO 2026
Purpose/Objective: This study aimed to evaluate the clinical outcomes, local tumor control, overall survival, and treatment- related toxicity of patients with bulky head-and-neck tumors treated with VMAT Lattice radiotherapy, and to perform a dosimetric analysis of delivered doses to tumor vertices (VTV) and gross tumor volume (GTV) Material/Methods: Forty patients treated between 2020 and 2025 with VMAT Lattice radiotherapy for bulky head-and-neck tumors were included. Treatment planning was performed in Eclipse TPS using VMAT with 6 MV photon beams. Clinical, dosimetric, and volumetric parameters were analyzed, including VTV dose, prescribed dose to GTV, number of vertices, number of fractions, baseline and post-treatment tumor volumes, volumetric reduction, toxicity, and clinical outcomes. Overall survival was calculated from treatment start to death or last follow-up. Descriptive analysis and a simple linear model were used to assess associations between dose and survival. TNM stage and recurrence were also considered. Results: Most patients had stage IV disease (55.6%) or recurrence (27.8%). The mean number of VTV was 8 (2- 30), the mean VolumeVTV/VolumeGTV ratio was 1.4% (0.4–3.7%) with a VTV dose of 15.0 or 18.0 Gy and a prescribed GTV dose between 45.0 and 72.0 Gy. The mean initial VolumeGTV was 257.8 cc (48.0–976.0), decreasing to 165.2 cc (0.0–629.0) post-treatment. The mean volumetric reduction was 27.2% (–76.5% to 100%), with tumor growth observed in two patients (5%)—paranasal sinus and facial bone carcinoma— and complete response in two cases (laryngeal carcinoma and tumor of indeterminate origin). Median overall survival for the entire cohort was 6.3 months (range 0.4–31.2). Survival varied by tumor site, with the longest outcomes observed in laryngeal carcinoma (31.2 months), followed by parotid (10.2), paranasal sinus (8.5), hypopharynx (6.6), and indeterminate origin (6.1). When stratified by stage, mean survival was 7.1 months for both stage IV and III disease, and 6.2 months for recurrent cases. The most frequent acute toxicities were mucosal (n=22) and dermal (n=12), while gastrointestinal toxicity occurred in 7 patients. Grade ≥ 3 toxicity was uncommon (GI n=0, dermal n=7, mucosal n=11). Conclusion: VMAT Lattice radiotherapy for bulky head-and-neck tumors was feasible, safe, and well tolerated, achieving meaningful volumetric responses with low early progression. Most patients showed tumor reduction or stabilization, including isolated complete responses, without major toxicity. These findings support the possible use of Lattice as a dose- intensification strategy for locally advanced or recurrent disease. Larger prospective studies with
longer follow-up are warranted to confirm these results. References: Amendola BE, Perez NC, Wu X, et al. Improved outcome of treating locally advanced lung cancer with the use of Lattice Radiotherapy (LRT): a case report. Clin Transl Radiat Oncol. 2018;12:68–71. https://doi.org/10.1016/j.ctro.2018.01.003Bentzen SM, et al. Randomized Controlled Trial of Hypofractionated vs. Normo-fractionated Locally Advanced Head and Neck Squamous Cell Carcinoma (HYPNO). Int J Radiat Oncol Biol Phys. 2023;117(4):e2. https://doi.org/10.1016/j.ijrobp.2023.08.026Mohiuddin M, Stevens JH, Reiff JE, Huq MS, Suntharalingam N. Spatially fractionated (GRID) radiation for palliative treatment of advanced cancer. Radiat Oncol Investig. 1996;4:41–47. https://doi.org/10.1002/(SICI)1520- 6823(1996)4:1<41::AID-ROI7>3.0.CO;2-M Keywords: VMAT Lattice radiotherapy, bulky head neck tumors Evaluation of recurrences after postoperative observation as a management strategy in stage I and II oral cavity cancers Anjali Uniyal 1 , Sanjay Deshmukh 2 , Vrushab Rao 3,4 , Manjiri Joshi 5 , Manish Akare 6 , Parul Gupta 1 , Darshana Kawale 1 , Bhooshan Zade 1 1 Department of Radiation Oncology, Indrayani Hospital and Cancer Institute, Pune, India. 2 Department of Surgical Oncology, Indrayani Hospital and Cancer Institute, Pune, India. 3 Department of Radiation Oncology, Tata Memorial Centre (TMH/ACTREC), Mumbai, India. 4 Department of CyberKnife Radiosurgery and Radiation Oncology, Ruby Hall Clinic, Pune, India. 5 Department of Digital Poster 2845 Epidemiology, Indrayani Hospital and Cancer Institute, Pune, India. 6 Department of Histopathology, Indrayani Hospital and Cancer Institute, Pune, India Purpose/Objective: Observation after surgery in stage I and II oral cavity cancers is a viable strategy as it offers favorable survival outcomes with reduced morbidity compared to post-operative radiotherapy. In India, less than a third of head and neck cancers are diagnosed in early stages (I and II), and risk stratification is a key consideration before opting for observation after surgery. Surgery with adequate margins and lymph node dissection achieves significantly comparable disease-specific and overall survival, while avoiding additional treatment-related toxicity and functional impairments from adjuvant radiation in low-risk cases. This study aims to assess the recurrences after observation post surgery and its association with
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