Lattice Radiotherapy Using Photon Minibeams: A Spatial Fractionation Approach for Small-to-Medium Tumors
Abstract
Purpose
Lattice radiotherapy (LRT) is a spatially fractionated radiation technique that creates three-dimensional arrays of high-dose vertices within tumor volumes. Current LRT implementations face geometric constraints in small and medium-sized tumors, primarily due to large beam dimensions that limit the formation of optimal lattice configurations. This study evaluates a novel photon minibeam-based lattice radiotherapy (mini-LRT) approach developed to address the geometric limitations of conventional LRT and enable spatially fractionated treatment of small and medium-sized tumors.
Methods
Three brain cases with clinical target volumes of 12.4 cc, 28.7 cc, and 23.5 cc were selected for comparative treatment planning between conventional LRT and mini-LRT. A multi-collimator delivery approach utilizing shifted slit configurations was employed to accomplish complementary spatial coverage. Dose computation and plan optimization were conducted using Monte Carlo simulations (GATE/GEANT4) and resolved through an iterative convex relaxation algorithm.
Results
Mini-LRT produced denser lattice structures in all cases, generating 6-9 vertices compared to only 1-2 vertices achievable with conventional LRT. Vertex diameters were reduced from 15 mm to 4–6 mm, and vertex-to-vertex distances decreased from 25 mm to 12.4–20.5 mm. Mini-LRT yielded better normal tissue sparing with whole-body dose reductions of 10.5%, 26.7%, and 41.7% across the three cases. Brainstem sparing was improved, with mean doses decreased by an average of 44.6% and maximum doses reduced by 7.0%–15.4%.
Conclusion
Mini-LRT successfully overcomes geometric and dosimetric constraints of conventional LRT. This new technique maintains 3D spatially fractionation dose distribution and achieves better organ-at-risk sparing, potentially expanding the clinical applicability of LRT beyond large tumor indications.