Integrity of delivered dose in temporally fractionated lattice radiotherapy amid anatomical changes and setup uncertainties.

Abstract

To investigate the impact of anatomical changes and setup uncertainties on lattice integrity and delivered target dose in spatially and temporally fractionated Lattice Radiation Therapy (LRT). Sixteen patients with large-volume tumors underwent 5-fraction LRT, receiving 20  Gy to the target planning volume (PTV) and a simultaneous integrated boost of 66.7  Gy to lattice-arranged high-dose spheres within the gross tumor volume (GTV_2000). Delivered dose was reconstructed by computing fraction doses on CBCTs, followed by deformable registration and accumulation onto the planning CT. Planned and delivered doses were compared in terms of GTV_2000 coverage, peak-to-valley dose ratio (PVDR), preservation of high-dose volumes, and organ-at-risk doses. Dose accumulation was prospectively performed for 80 fractions. The average GTV_2000 vol was 1580  cm³ (range: 139-3183 cm³), with a mean of 12 (range: 1-33) high-dose spheres per lattice. Among the 12 patients not requiring replanning, the average delivered GTV_2000 Dmean, D98%, and PVDR were 27.7  Gy, 19.2  Gy, and 3.25, respectively, representing minor decreases of 1.0 Gy, 0.6 Gy and 3.5%. High-dose volumes (V66.7 Gy and V60Gy) showed larger reductions of 41.5% and 25.2%. The 4 patients requiring replanning demonstrated greater dosimetric deviations. Delivered organ-at-risk doses were largely in agreement with the planned doses and stayed within dose tolerance limits. CBCT-guided, temporally fractionated LRT can maintain high spatial and dosimetric accuracy. Despite anatomical changes, PVDR and lattice integrity were generally preserved, particularly in patients not requiring replanning. Consistent lattice delineation across scans was critical in patients requiring replanning to preserve lattice spatial dose integrity.