Journal Article

Demonstration of an enhanced dosing pattern for debulking large and bulky unresectable tumors via differential hole‐size spatially fractionated radiotherapy

St. Clair, William, Pokhrel, Damodar, Misa, Joshua

2025

Overview

Purpose/objective We propose a novel lattice deployment for spatially fractionated radiotherapy (SFRT) treatments. In this approach, a larger diameter high‐dose sphere is centrally placed in the bulky tumor mass and surrounded by smaller diameter high‐dose spheres. Materials/methods Thirty SFRT patients (10 head and neck [HN], 10 abdominal/pelvis, and 10 chest/lung cases) treated with an MLC‐based crossfire method were retrospectively analyzed. Eleven differential hole‐size lattice patterns were benchmarked against the clinically delivered SFRT plans (1 cm diameter cylinders, 2 cm spacing) and the standard uniform lattice pattern (1.5 cm diameter spheres, 3 cm spacing). These patterns varied in core diameter (C: 2–4 cm), spacing (S: 2–4 cm), and peripheral diameter (P: 1–2 cm). In addition to peak‐to‐valley‐dose ratio (PVDR), tumor dose metrics (D50%, V50%, Dmean), Dmax to nearby critical organs, and ablative dose (V75%/V50% and V15Gy) were evaluated. Results 10 out of 11 differential hole‐size patterns showed increases in D50%, Dmean, and V50% compared to the standard lattice pattern. One pattern (C = 3 cm, S = 2 cm, P = 1.5 cm) outperformed the clinical SFRT plans in D50% (Δ = 1.8 Gy, p = 0.003; Δ = 2.0 Gy, p = 0.015; Δ = 0.9 Gy, p = 0.045), Dmean (Δ = 1.6 Gy, p = 0.003; Δ = 1.7 Gy, p = 0.021; Δ = 0.7 Gy, p = 0.042), and V50% (Δ = 20.4%, p < 0.001; Δ = 16.6%, p = 0.008; Δ = 10.3%, p = 0.079) for the HN, abdominal/pelvis, and chest/lung SFRT patients, respectively. This pattern also demonstrated average increases to D5% D10%, D90% across all 30 patients compared to both benchmarked patterns. However, this pattern showed reduced PVDR compared to the clinical and standard SFRT plans but still achieved a ratio > 3.0. All differential hole‐size patterns demonstrated decreases in Dmax to critical organs compared to the clinical SFRT plans. Moreover, compared to the clinical SFRT and the standard lattice plans, 9 out of 11 differential hole‐size patterns demonstrated increases in V75%/V50% and V15Gy. Conclusion All differential hole‐size SFRT replans were clinically acceptable, with C = 3 cm, S = 2 cm, and P = 1.5 cm providing the optimal setting for select tumors. Differential lattice patterns enhanced the ablative dose to the bulky tumors while restricting the maximum dose to adjacent critical organs.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc
• Subject: Abdomen / Abdominal Neoplasms - radiotherapy / Abdominal Neoplasms - surgery / Dose Fractionation, Radiation / Head and Neck Neoplasms - pathology / Head and Neck Neoplasms - radiotherapy / Head and Neck Neoplasms - surgery / hole‐size / hole‐spacing / Humans / indirect cell kill / large and bulky tumors / lattice pattern / Lung Neoplasms - pathology / Lung Neoplasms - radiotherapy / Lung Neoplasms - surgery / Neoplasms - pathology / Neoplasms - radiotherapy / Neoplasms - surgery / Organs at Risk - radiation effects / Patients / Pelvic Neoplasms - radiotherapy / Pelvic Neoplasms - surgery / Planning / Radiation therapy / Radiotherapy Dosage / Radiotherapy Planning, Computer-Assisted - methods / Radiotherapy, Intensity-Modulated - methods / Retrospective Studies / SFRT / Simulation / Spheres / Tumors