Impressive Results after "Metabolism-Guided" Lattice Irradiation in Patients Submitted to Palliative Radiation Therapy: Preliminary Results of LATTICE_01 Multicenter Study

Simple Summary: The lattice technique is a particular form of spatially fractionated radiation therapy, which was demonstrated to be safe and effective for treating advanced cancers. Bulky tumor disease is difficult to treat. In this clinical scenario, radiotherapy has a role in the palliation of symptoms. The lattice technique allows high doses to be delivered within tumor masses. Combining lattice delivery with IMRT/VMAT to bulky tumors offers optimal symptom control and could emerge as the best therapeutic option in this setting of patients. Purpose: To evaluate feasibility, toxicities, and clinical response in Stage IV patients treated with palliative "metabolism-guided" lattice technique. Patients and Methods: From June 2020 to December 2021, 30 consecutive clinical stage IV patients with 31 bulky lesions were included in this study. All patients received palliative irradiation consisting of a spatially fractionated high radiation dose delivered in spherical deposits (vertices, Vs) within the bulky disease. The Vs were placed at the edges of tumor areas with different metabolisms at the PET exam following a non-geometric arrangement. Precisely, the Vs overlapped the interfaces between the tumor areas of higher F-18-FDG uptake (>75% SUV max) and areas with lower F-18-FDG uptake. A median dose of 15 Gy/1 fraction (range 10-27 Gy in 1/3 fractions) was delivered to the Vs. Within 7 days after the Vs boost, all the gross tumor volume (GTV) was homogeneously treated with hypo-fractionated radiation therapy (RT). Results: The rate of symptomatic response was 100%, and it was observed immediately after lattice RT delivery in 3/30 patients, while 27/30 patients had a symptomatic response within 8 days from the end of GTV irradiation. Radiation-related acute grade >= 1 toxicities were observed in 6/30 (20%) patients. The rate of overall clinical response was 89%, including 23% of complete remission. The 1-year overall survival rate was 86.4%. Conclusions: "Metabolism-guided" lattice radiotherapy is feasible and well-tolerated, being able to yield very impressive results both in terms of symptom relief and overall clinical response rate in stage IV bulky disease patients. These preliminary results seem to indicate that this kind of therapy could emerge as the best therapeutic option for this patient setting.