S1032
Clinical – Sarcoma, skin cancer, malignant melanoma
ESTRO 2026
Purpose/Objective: Patients with large, unresectable, or metastatic soft tissue tumours (STT) face limited local treatment options, with conventional radiotherapy often constrained by toxicity and modest efficacy. Lattice Radiotherapy (LRT) is an emerging spatially fractionated technique that delivers ablative “vertices” within the tumour, promoting immunogenic cell death and cytoreduction while sparing surrounding normal tissue. Although international reports show safety and encouraging local control, experience from the Middle East remains scarce. This study presents our initial institutional experience, describing treatment technique, tolerance, and early outcomes. Material/Methods: A retrospective review was performed of all patients treated with LRT for STT at our centre between 2023 and 2025. Clinical records, imaging, and dosimetric data were analysed for feasibility, radiologic and symptomatic response, and toxicity (CTCAE v5.0). Tumour response was assessed by volumetric change at 3 months. Results: Five female patients (median age 41 years, range 22– 91) with large or metastatic STT were analysed. Histologies included desmoid fibromatosis (n=1), undifferentiated high-grade sarcoma (n=1), malignant peripheral nerve sheath tumour (n=1), synovial sarcoma (n=1), and spindle cell sarcoma (n=1). Four cases were treated palliatively and one definitively.Median gross tumour volume (GTV) was 1,758 cc (range 180–2,340 cc). All plans used VMAT- based LRT delivered in 1–3 fractions to a total dose of 12–18 Gy. The median number of vertices was 23, with mean vertex diameter 1 cm and median centre-to- centre spacing 2.6 cm (range 2–4 cm).All patients completed treatment without interruption. LRT was well tolerated, with only Grade 1–2 dermatitis or transient pain and no Grade ≥ 3 acute or late toxicity. Symptomatic relief, mainly pain and pressure reduction, occurred in all evaluable patients within 1–3 weeks.At a median follow-up of 5 months (range 3–10), radiologic assessment showed partial response or stable disease in four assessable patients, with a median tumour volume reduction of 28% (range –6% to –55%). All demonstrated intratumoral necrosis on post-treatment imaging, and one previously unresectable patient underwent successful surgical resection.
OS was 34% [95% CI 24–44%] for SBRT and 38% [95% CI 30–42%] for surgery, with no significant difference between the two modalities. Conclusion: Available evidence suggests that SBRT and surgery achieve comparable oncologic outcomes for sarcoma- derived PM, and SBRT should not be regarded merely as a fallback for patients with high surgical risk or contraindications. Reported toxicities favor SBRT, though comparisons are limited by retrospective design of the majority of the studies, heterogeneous indications, and incomplete reporting. Treatment choice should be individualized within a multidisciplinary sarcoma team, integrating clinical factors, patient preferences, and modality-specific advantages. Well-designed prospective trials are urgently needed to clarify the relative safety and efficacy of both approaches. References: Bonvalot S, Tetreau R, Llacer-Moscardo C, Roland C. The Landmark Series: Multimodal Management of Oligometastatic Sarcoma. Ann Surg Oncol. 2024;31(12):7930-7942. doi: 10.1245/s10434-024- 16103-0.Smolle MA, van Praag VM, Posch F, Bergovec M, Leitner L, Friesenbichler J, et al. Surgery for metachronous metastasis of soft tissue sarcoma - A magnitude of benefit analysis using propensity score methods. Eur J Surg Oncol. 2019;45(2):242-248. doi: 10.1016/j.ejso.2018.06.019.Tetta C, Londero F, Micali LR, Parise G, Algargoush AT, Algargoosh M, et al. Stereotactic Body Radiotherapy Versus Metastasectomy in Patients With Pulmonary Metastases From Soft Tissue Sarcoma. Clin Oncol (R Coll Radiol). 2020;32(5):303-315. doi: 10.1016/j.clon.2020.01.005. Keywords: Pulmonary metastasis, SBRT, Surgery Early Clinical Experience of Lattice Radiotherapy (LRT) in Bulky, Unresectable Soft Tissue Tumours: A Single-Center Cohort from Oman Khadiga Mohammed 1 , Syeda Sara Tajammul 1 , Mahmoud Alfishawy 2 , Boris Itkin 3 , Iqbal Abdullah AlAmri 2 , Tauseef Ali 1 , Zahid Almandhari 1 1 Radiation oncology, Sultan Qaboos Comprehensive Cancer Care and Research Centre (SQCCCRC)/ University Medical City (UMC), Muscat, Oman. 2 Medical Physicist, Sultan Qaboos Comprehensive Cancer Care and Research Centre (SQCCCRC)/ University Medical City (UMC), Muscat, Oman. 3 Medical Oncologist, Sultan Qaboos Comprehensive Cancer Care and Research Centre (SQCCCRC)/ University Medical City (UMC), Muscat, Oman Digital Poster 438
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