Role of Spatially Fractionated Radiotherapy (LATTICE) Treatment in Inoperable Bulky Soft-Tissue Sarcomas.

Background: The clinical outcome of inoperable sarcoma patients treated with LATTICE (LRT) is limited and therefore the objective of our study was to report treatment response, overall survival (OS), local-recurrence free survival (LRFS) and toxicity. Methods: This retrospective observational study includes 15 histologically proven inoperable non-extremity sarcoma patients with no treatment options or no response to systemic therapy, treated at our institution between 2020 and 2024. The patients were treated with a combination of LRT and normo- or hypo-fractionated external beam radiotherapy. Treatment response was evaluated by RECIST1.1 criteria, toxicity by CTCAE 5.0 and OS and LRFS by Kaplan-Meier curves. Results: The median follow-up (F-UP) since the beginning of the treatment was 10 months (range 4-32). Nine patients were male and six female. Their mean age was 60 years. The median gross tumor volume (GTV) was 1058 cm3 (range 142-6103 cm3). The median number of spheres was 9 (4-30). All patients with symptoms reported symptoms' relief. Based on RECIST1.1 criteria, 10 patients (67%) had stable local disease at 1-2 months F-UP on computed tomography (CT). Surgical resection was feasible in five patients. Three of them are alive without disease and two died due to metastatic progression. From 10 (67%) non operated patients, 5 patients died (50%) due to disease. The remaining five patients (50%) are alive, three with stable disease at 21, 22, and 32 months of F-UP and two with disease progression who are currently receiving palliative chemotherapy treatment. Reported G2 toxicity was as follows: gastrointestinal (2), asthenia (1). Two patients had G3 toxicity: esophagitis (1) and inguinal dermatitis (1). No acute or chronic G4-G5 toxicity was observed. Conclusions: LRT is a feasible and well-tolerated radiation technique for inoperable bulky soft-tissue sarcomas. Further studies are needed to establish protocols to determine which patients could benefit from palliative or preoperative treatment.