Presenter(s)
S. Unterkirhers1, C. Rohrer Bley2, T. Streller3, C. Glanzmann4, and G. Studer3; 1Institute for Radiotherapy, Klinik Hirslanden, Zurich, Switzerland, 2Division of Radiation Oncology, Vetsuisse-Faculty University of Zurich, Zurich, Zurich, Switzerland, 3Kantonsspital Luzern, Luzern, Switzerland, 4Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
Purpose/Objective(s): Spatially fractionated lattice SBRT intensifies dose within bulky tumors using discrete intratumoral boost “vertices”; however, manual template-based vertex contouring is time-consuming and can under-fill irregular targets. We evaluated whether an automated, principal component analysis (PCA)-aligned, geometry-adaptive lattice method, originally developed to address complex tumors geometries in canine sarcoma patients, improves boost packing compared with manually contoured lattices in bulky human sarcomas.
Materials/Methods: The tumor-geometry–adjusted, PCA-aligned lattice workflow was translated to four representative bulky human sarcoma patients (median 1926 cm3, range 1419-3090 cm3) previously treated with SFRT plans using manually contoured 5.0 mm radius lattice vertices. Each case was replanned using automated PCA-guided vertex placement; vertex radii of 5.0 and 7.5 mm were evaluated, and the radius providing the best peak–valley dose pattern selected for comparison. Consistent with the original workflow, vertex diameters were automatically reduced near the GTV periphery to maintain an internal margin. Plans were optimized as simultaneous integrated boost lattice SBRT (66.7 Gy to vertices with 20 Gy background in 5 fractions). DVH metrics were extracted via scripting, including total vertexes volume, vertex volume as a percentage of GTV, vertex and void mean doses, peak-to-valley dose ratio (PVDR), and OAR DVH metrics. Paired comparisons are reported descriptively as median (range).
Results: Use of automated PCA-based lattices increased total boost vertex volume from 7.4 cm³ (6.7–11.5) to 31.4 cm³ (19.1–56.6), a median 3.9× increase (2.8–5.7). Vertex volume as a fraction of GTV increased from 0.41% (0.29–0.56) to 1.66% (1.56–1.83), a median 4.2× increase (3.0–5.7). Vertex mean dose was maintained (manual 71.2 Gy [69.0–71.8] vs automated 71.3 Gy [70.5–72.0]). PCA-based replanning increased mean GTV dose from 27.0 Gy (23.9–30.1) to 30.8 Gy (28.5–33.0), corresponding to a median paired increase of +3.7 Gy (2.5–5.1). Automated plans achieved void mean doses of 22.3 Gy (21.2–23.1) with PVDR 3.20 (3.09–3.37). Across evaluated OARs, median change in Dmax was +0.8 Gy (range -3.8 to +28.3).
Conclusion: PCA-aligned, geometry-adaptive lattice generation substantially increased intratumoral boost packing and was associated with higher mean GTV dose in bulky human sarcomas while maintaining vertex dose and producing consistent PVDR. This approach may reduce manual contouring burden and enable more standardized lattice SBRT planning; larger retrospective series and prospective evaluation are warranted.