Coplanar DCA-based hypofractionated stereotactic radiotherapy for very small brain metastasis from non-small cell lung cancer: treatment planning comparison with coplanar VMAT and preliminary clinical outcome.

Abstract

To assess the clinical outcome of single-arc coplanar dynamic conformal arc (C-DCA) in three-fraction hypofractionated stereotactic radiotherapy (3F-HSRT) for single very small brain metastasis (BM; gross tumor volume [GTV] ≤ 1 cm³) from non-small cell lung cancer (NSCLC) and to compare treatment planning with single-arc coplanar volumetric modulated arc therapy (C-VMAT). From December 2019 to May 2023, twenty NSCLC patients with single BM treated with 3F-HSRT (24-39 Gy/3f) using C-DCA were enrolled in this study. Each plan was replanned using C-VMAT, and relevant planning indices were compared. Clinical outcome was evaluated following C-DCA treatment. C-VMAT yielded a higher homogeneity index (1.41 vs. 1.16, p < 0.001) and GTV D_98% (38.10 Gy vs. 32.72 Gy, p = 0.008), with slightly smaller normal brain tissue (NBT) V_23Gy, and V_21Gy. However, C-DCA offered 31.37% lower monitor units (p = 0.008) and 36.55% shorter beam on time (p = 0.007) while achieving a significantly higher gamma passing rate for the 2%/1 mm criterion (p = 0.001). As of October 2023, the median follow-up time was 9.2 months. The intracranial disease control rate was 70%, with a median intracranial progression-free survival of 11.4 (95% CI 4.5-18.3) months and a 1-year intracranial control rate of 45.4%. The intracranial local disease control rate was 95%. Only two irradiated lesions progressed at the end of follow-up. The cerebral radiation necrosis rate of all patients was 5%. For small BM, C-DCA provided nearly equivalent target coverage and NBT sparing to the C-VMAT while maintaining higher delivery efficiency and accuracy. C-DCA HSRT also provided good local control and limited toxicity.