S1052
Clinical – Sarcoma, skin cancer, malignant melanoma
ESTRO 2026
80% isodose to the peaks, with peripheral doses of 2– 7Gy. FDG-PET was used for targeting and follow-up in
cemiplimab in advanced cutaneous squamous-cell carcinoma. N Engl J Med. 2018 Jul 26;[2] Hughes BG, Munoz-Couselo E, Mortier L, Stanka J, De La Cruz- Merino L, Gutzmer R, et al. Pembrolizumab for locally advanced and recurrent/metastatic cutaneous squamous cell carcinoma (KEYNOTE-629 Study): an open-label, nonrandomized, multicenter, phase II trial. J Am Acad Dermatol. 2025;[3] Challapalli A, Smith B, Jones C, et al. A novel phase 2 study of targeted therapy in non-small cell lung cancer. J Clin Oncol. 2024; Keywords: Cemiplimab, Cutaneous SCC, Immunotherapy LATTICE Radiotherapy for Advanced Sarcomas: Feasibility, Efficacy and Safety in 21 Patients with No Therapeutic Alternative marie-pierre Sunyach 1 , luca mulcahy 1,2 , Waissie Waisse 3 , Camille Roukos 1 , Vanina Isnardi 4 , Magalie Sandt 1 , Marie-Claude Biston 1,2 1 radiotherapy, Centre Leon Berard, Lyon, France. 2 CREATIS, Université Lyon 1, Lyon, France. 3 Lyon - INSERM U1052-CNRS5286, Centre Leon Berard, lyon, France. 4 NUCLEAR MEDECINE, Centre Leon Berard, LYON, France Purpose/Objective: Sarcomas in therapeutic impasse represent a major challenge due to limited treatment options. Lattice radiotherapy (LRT) delivers spatially fractionated high- dose peaks (10–25Gy) surrounded by low-dose valleys (<5Gy), leveraging bystander and apoptotic effects. This study evaluates the feasibility, efficacy, and safety of Lattice technique in 21 patients with advanced sarcomas. Material/Methods: Between 2022-2025, 21 patients with advanced sarcomas (15 abdominal, 2 intrathoracic, 3 limb roots, 1 foot, 1 abdominal wall) were treated using LRT. Histologies included undifferentiated sarcoma (n=5), solitary fibrous tumor (n=2), synovial sarcoma (n=1), chondrosarcoma (n=2), chordoma (n=2), Digital Poster 4733 osteosarcoma (n=1), MPNST (n=1), fibrosarcoma (n=1), and liposarcoma (n=7). Six patients were treated for recurrence, 5 in a preoperative setting (ultimately inoperable), and 10 were deemed inoperable. Treatment planning involved MIM Maestro (MIM software inc.) for manual sphere positioning and Monaco treatment planning system (Elekta). Spheres were placed within the GTV, maintaining a 15mm margin from organs-at-risk. A 4D CT was used for thoracic/abdominal tumors. Treatment was delivered on a Versa HD linac using 6MV FFF beams and VMAT technique (3 arcs). Prescribed dose was 12 Gy at the
3 cases. Results:
Lattice was feasible in all cases, including reirradiation and complex anatomical sites. Tumor response was assessed by volumetric reduction. Results showed: 1 progressive disease, 6 non-evaluable, 6 patients with 0–20% reduction, 4 with 20–50%, and 4 with 70–90%. Eight patients died by the end of the study. No toxicity >3 was observed. Partial responses were observed in 9 patients, with follow-up ranging from 5-18 months. Two patients had stable disease for 5 and 18 months, both showing symptom improvement. Six patients were not locally evaluated—five due to death from metastatic progression and one pending assessment. Local control was achieved in two patients despite subsequent death from metastases. Additionally, one patient remained stable with symptom improvement before later progression requiring retreatment, and another maintained local control for 16 months before relapse. Conclusion: LATTICE radiotherapy is a feasible, safe, and potentially effective option for advanced sarcomas with no therapeutic alternative. The technique allows for high-dose delivery while sparing normal tissues, with encouraging tumor response rates and minimal toxicity. Further investigations are underway to optimize sphere positioning using metabolic imaging alongside morphological data. Prospective studies are also warranted to refine patient selection and improve long-term outcomes. References: Duriseti S, Kavanaugh J, Goddu S et al. Spatially fractionated stereotactic body radiation therapy (Lattice) for large tumors. Adv Radiat Oncol. 2021;6(3):100639Borzov E, Bar-Deroma R, Lutsyk M. Physical aspects of a spatially fractionated radiotherapy technique for large soft tissue sarcomas. Phys Imaging Radiat Oncol. 2022 May 4;22:63-66. doi: 10.1016/j.phro.2022.04.010. PMID: 35572042; PMCID: PMC9092247. Bekker, R.A., Obertopp, N., Redler, G. et al. Spatially fractionated GRID radiation potentiates immune-mediated tumor control. Radiat Oncol 19, 121 (2024). https://doi.org/10.1186/s13014-024-02514-6 Keywords: Lattice, feasability, inoperable sarcoma
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