S886
Clinical - Mixed sites & palliation
ESTRO 2026
Purpose/Objective: Lattice Radiotherapy (LRT), 3D Spatially Fractionated Radiotherapy (SFRT), allows to treat unresectable bulky cancers in palliative settings with a heterogeneous high-gradient dose distribution and a safe dose escalation. Multiple localized high-dose islands (vertices, Vs) are created within the tumor, alternated with a certain degree of separation from lower dose regions (valleys). LRT enhances its action inducing bystander and abscopal effects. Material/Methods: Between December 2023 and June 2025, 34 patients (pts) with bulky tumors were recruited (total of 35 treatments). A geometric arrangement (through a grid tool of the Treatment Planning System) was used to create from 1 to 32 cylindrical vertices, with a diameter of 1/1.2 cm and a separation of 1.5/2.0 cm between each vertex and the next in the axial plane. Treatment planning was realized with Monte Carlo–based Monaco treatment planning system (version 5.51, Elekta AB, Stockholm, Sweden) in Volumetric Modulated Arc Therapy (VMAT) and delivered with a Elekta Versa HD linear accelerator (Elekta AB, Stockholm, Sweden). Mean Vertices (CTVert) volume was 6 cm3 (from 1 to 40 cm3), mean CTV volumes 308 cm3, (from 14 to 1400 cm3), mean CTVert/CTVT volumes ratio 2,8 % (from 1.5% to 6%). Dose to CTVert varied from 5 Gy/1 fr to 50 Gy/4fr and dose to CTV from 8 Gy/1 fr to 70 Gy/35 fr. Goal of planning was to achieve ≥ 95% prescription dose coverage to at least 95% of the targets. Normally employed constraints for Organs At Risk (OAR) were used. Treatments were delivered in concomitant mode: 2 as a simultaneous integrated boost, 1 as Strip-Therapy, and 1 treatment was delivered twice daily (Lattice – 6h lag – VMAT). Results: LRT permits to deliver ablative doses to bulky tumors, where Stereotactic Body Radiation Therapy (SBRT) is not feasible limiting the dose to OAR and avoiding excessive toxicity to the surrounding normal tissues, compared with standard treatment. 31 pts completed the treatment without related toxicities, 4 pts died from chemo and immunotherapy-related toxicity. Relief of initial symptoms (dyspnea, pain, functional impotence) was always observed after one month after radiotherapy; 22 out of 31 patients were alive after 18 months, and 4 after 36 months. Conclusion: LTR has proven to be safe and effective for bulky cancers. It delivers a very high dose inside the tumor providing a higher local control without adding extra toxicity to the normal tissues. More patients must be recruited and experience must grow to turn palliative treatments into curative treatments.
Conclusion: The GTV-based target volume concept was associated with improved local control and decreased risk of vertebral compression fracture as compared to the segment-based target volume concept. References: 1. Cox BW, Spratt DE, Lovelock M, et al. International spine radiosurgery consortium consensus guidelines for target volume definition in spinal stereotactic radiosurgery. Int J Radiat Oncol Biol Phys 2012;83:e597-605. Keywords: Spinal SBRT, target volume definition Digital Poster 2801 Applications in clinical practice of the Lattice Radiation Therapy: results and future possibilities Davide Di Gennaro 1 , Bruno Curcio 1 , Ernesto Falcone 1 , Diana Laslo 1 , Arturo Losco 1 , Giuseppe Scimone 1 , Immacolata Vivone 1 , Immacolata Anna Maria Pilotti 2 , Silvio Maffei 2 , Pierluigi D'Andria 2 , Carolina Mainardi 2 , Antonio Orientale 2 1 U.O.C. Radioterapia, A.O.U. San Giovanni di Dio e Ruggi D'Aragona, Salerno, Italy. 2 U.O. Fisica Sanitaria, A.O.U. San Giovanni di Dio e Ruggi D'Aragona, Salerno, Italy
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