KEY POINTS
- This proof-of-concept planning study compared photon minibeam-based LATTICE with conventional LATTICE in three brain and three lung cases, with CTVs ranging from 12.34 to 40.88 cm³. Dose calculation used Monte Carlo simulations and iterative convex optimization.
- Mini-LATTICE used a custom multi-slit tungsten collimator with 0.7-mm slit width, 5-mm centre-to-centre spacing, and multiple laterally shifted configurations. The nominal peak and valley objectives were 15 Gy and 5 Gy, respectively.
- Conventional LATTICE could accommodate only 1–3 vertices with 15-mm diameter and 25-mm spacing, whereas mini-LATTICE produced 5–11 vertices with diameters of only 3–4 mm and 12.5-mm spacing.
- Despite the larger number of vertices, high-dose occupancy was markedly reduced: lattice-volume ratios were 0.68–1.07% with mini-LATTICE versus 8.64–22.50% with conventional LATTICE. Peak-to-valley dose ratios increased from 1.75–2.34 to 2.19–2.94.
- OAR exposure decreased in all three brain cases. Brainstem mean dose fell by approximately 62.5%, 43.4%, and 44.8%, and in two cases brainstem D0.03cc fell from >16 Gy with conventional LATTICE to <6.8 Gy with mini-LATTICE.
- Conventional reference SBRT plans prescribed 50 Gy in 5 fractions and achieved CTV D95=50 Gy in all six cases, but selected anatomically constrained cases showed high near-maximum OAR doses. The mini-LATTICE robustness analysis included ±3-mm translational errors and showed only modest degradation of peak-to-valley separation, but it did not model continuous gantry dynamics, respiratory interplay, mechanical timing, or actual treatment delivery.
CLINICAL TAKEAWAY
Photon minibeams may extend spatially fractionated LATTICE concepts into much smaller tumors where conventional centimetre-scale vertices are geometrically impractical. For now this remains a planning concept rather than a clinical technique: experimental dosimetry, deliverability, motion studies, radiobiological validation, and patient data are all still required.