Spatially fractionated stereotactic body radiotherapy (Lattice SBRT) for large tumors

Stereotactic body radiotherapy (SBRT) has demonstrated clinical benefit for patients with metastatic and/or unresectable cancer. Technical considerations of treatment delivery and sensitive organs at risk (OARs) limit the use of SBRT in large tumors or those in unfavorable locations. Spatially fractionated radiotherapy (SFRT) delivers high-dose radiation to discrete sub-volume vertices within a tumor target while restricting the remainder of the target to low dose. SFRT has been utilized for treatment of large tumors with reported dramatic tumor response and minimal side effects. Lattice is a modern approach to SFRT that can be delivered with arc-based therapy, which allows for the rapid dose fall-off required for high quality SBRT. In order to overcome the limitations of SBRT for large tumors, we developed Lattice SBRT. Here we report the results of a dosimetry and quality assurance (QA) feasibility study of Lattice SBRT in 11 patients with 12 tumor targets, each ≥ 10 cm in an axial dimension. Prior CT simulation scans were used to generate volumetric-modulated arc therapy (VMAT) Lattice SBRT plans that were then delivered on clinically available Linacs. QA testing included external portal imaging device (EPID) and ion chamber (IC) analysis. All generated plans were able to meet the standard SBRT dose constraints, such as those from AAPM Task Group 101. Additionally, we provide a step-by-step approach for generating and delivering Lattice SBRT plans using commercially available treatment technology. Lattice SBRT is currently being tested in a prospective trial for patients with metastatic cancer needing palliation of a large tumor (NCT04133415).