Spatially fractionated radiotherapy: Dosimetric and clinical report

Abstract

Aim: Lattice is a three-dimensional technical development of the two-dimensional grid technology, which forms high-dose “islands” amid a “sea” of lower dose. When compared to grid, lattice offers enhanced dose distribution and organs-at-risk (OAR) sparing, which may be useful for big or deep-seated cancers. In this study, we used a Halcyon 2.0 (6MV) linear accelerator to treat the palliative cases with lattice radiation using volumetric modulated arc treatment (VMAT). With new machines and techniques, it's becoming more difficult to adapt and reinvent traditional grid radiation. In our study, we used VMAT to deliver high-dose radiation to the tumor while sparing the surrounding areas and normal tissues. New methodologies and the same thing we showed in our study are bringing development to lattice planning. Materials and Methods: Four patients were treated with grid technique. All the structures of respective patients were manually contoured on Eclipse SomaVision for lattice planning, important parameters include the vertex volume diameter and center-to-center spacing. Spheres were contoured in the axial slice inside the gross tumor volume. VMAT was planned with a single isocenter and multiple arcs (full arcs 360°). Optimization was set giving high priorities to the target volume, ensuring that the tumor received the required dose and that the OARs were met. Results: VMAT lattice therapy as a strategy to improve initial responsiveness while reducing OAR toxicity. All the target spheres achieved >95% of the prescription dose and dose fall-off outside the target sphere was achieved due to the ring shape sphere constraints. Conclusions: Bulky tumors were treated with lattice radiation with a high dose per fraction in this study, with the vertices receiving the specified dose and the region between the vertices being spared. As it was a task for physicists to design a lattice radiation considering the vertices and periphery regions and to achieve the OARs according to the dose constraint protocol, the VMAT plan was well realized using optimization and computation.

Keywords

• grid
• lattice
• valley
• vertex
• volumetric modulated arc treatment