KEY POINTS
- Investigators developed PATLESL, a proton arc lattice framework combining three optimization layers: simulated-annealing energy-layer selection, adaptive sparse spot assignment and explicit LET optimization. It was tested retrospectively in 18 patients previously treated with photon lattice radiotherapy.
- Lattice target volumes consisted of 3–19 spherical vertices, generally 1–1.5 cm in diameter, placed within the gross tumor with separation from its edge and nearby organ-at-risk planning volumes. The study prescribed 60 Gy(RBE) in five fractions to the lattice vertices.
- Compared with the previous PATseq proton-arc lattice approach, PATLESL increased mean peak-to-valley dose ratio from 16.90 ± 18.04 to 41.85 ± 29.69 (p<0.01), producing substantially steeper spatial dose modulation.
- Adaptive spot assignment increased target spot coverage by 44.12% while reducing the total number of spots by 93.78%. The combination of fewer spots and optimized energy sequencing shortened calculated beam delivery time by 37.43% in the primary comparison.
- LET optimization increased mean dose-averaged LET within the lattice target from 2.84 ± 0.38 to 3.59 ± 0.26 keV/μm (p<0.01), concentrating higher-LET regions within the high-dose vertices rather than relying on physical dose alone.
- The authors additionally report a 35.71% reduction in normal-tissue integral dose with the integrated framework and incorporated setup/range robustness directly into optimization, aiming to preserve the planned spatial and LET pattern under clinically realistic uncertainty.
- End-to-end film measurements confirmed deliverability, although performance depended strongly on how low-dose regions were analyzed. At 3%/2 mm, gamma passing was 90.99% for PATLESL at a 20% threshold, but fell to 74.94% when the threshold was reduced to 10%, reflecting the particular measurement challenges of highly heterogeneous lattice dose distributions.
CLINICAL TAKEAWAY
This is a sophisticated attempt to exploit both the spatial dose heterogeneity and variable biological effectiveness of proton arcs rather than treating lattice therapy as purely a physical-dose problem. The gains in PVDR, LET localization and delivery efficiency are substantial, but there are no patient outcome data demonstrating that this added optimization translates into better tumor response or toxicity.
SOURCE
International Journal of Radiation Oncology, Biology, Physics