Author: Joshua Misa, Damodar Pokhrel, William St. Clair π¨βπ¬
Affiliation: University of Kentucky, Department of Radiation Medicine π
Purpose: Development of a novel spatially fractionated radiotherapy (SFRT) lattice deployment method featuring a large high-dose sphere at the tumorβs center, surrounded by smaller diameter spheres. We hypothesize that this will amplify the ablative dose delivered to the tumor, encouraging further debulking and sensitization for large bulky tumors for future combination therapy.
Methods: Thirty previously treated extracranial SFRT patients were selected (115.7-2150.6 cc). Eleven novel patterns were investigated and benchmarked against the standard lattice pattern (1.5cm diameter, 3cm spacing) and clinically delivered SFRT plans. Clinical plans consist of a cylindrical dose distribution with a diameter of 1cm and spacing of 2cm. The 11 patterns consist of a large core diameter (C) of 2-4cm, 2-4cm spacing (S), and a smaller peripheral diameter (P) of 1-2cm. All replans used four full VMAT arcs, collimator angles of +/-15Β°, and a 6MV-FFF beam. Metrics evaluated were D50%, Dmean, V50%, D2cm, V75%/V50% and V15Gy.
Results: All differential hole-size patterns produced clinically acceptable plans and statistically outperformed the standard lattice pattern in terms of D50%, Dmean, V50%, V75%/V50%, and V15Gy. These novel patterns produced statistically significant decreases in D2cm compared to the clinical plan but statistical increases compared to the standard lattice pattern. The differential hole-size patterns also gave lower Dmax to adjacent critical organs compared to clinical SFRT plans. One pattern (C = 3cm, S = 2cm, P = 1.5cm) statistically improved on D50% (Ξ=1.6Gy, p<0.001; Ξ=5.4Gy, p<0.001), Dmean (Ξ=1.4Gy, p<0.001; Ξ=4.8Gy, p<0.001), V50% (Ξ=16%, p<0.001; Ξ=47%, p<0.001), V75%/V50% (Ξ=0.205, p<0.001; Ξ=0.144, p<0.001), and V15Gy (Ξ=6.2%, p<0.001; Ξ=6.3%, p<0.001), compared to clinical SFRT and standard lattice plans, respectively.
Conclusion: This novel lattice deployment for SFRT enhances ablative dose delivery to large deep-seated tumors, improving direct cell kill for potential increases in tumor local control rates and sensitization for combination therapy while maintaining normal tissue doses.