Hypofractionated stereotactic radiotherapy using coplanar VMAT for single small brain metastasis: dosimetric analysis and clinical outcomes

TL;DR

This study shows that hypofractionated stereotactic radiotherapy using coplanar VMAT is effective and safe for treating small brain metastases.

Contribution

The study evaluates dosimetric and clinical outcomes of HSRT for small brain metastases using a 3-mm PTV margin and C-VMAT.

Findings

C-VMAT achieved high delivery accuracy with a gamma passing rate ≥90%.

Local control rates at 1 and 2 years were 91.5% and 83.2%, respectively.

The cerebral radiation necrosis rate was 7.4% with minimal lesion progression.

Abstract

To evaluate the dosimetric parameters and clinical outcomes of hypofractionated stereotactic radiotherapy (HSRT) for small brain metastases [BMs; planning target volume (PTV) ≤ 4 cm3) via coplanar volumetric modulated arc therapy (C-VMAT).

Between March 2019 and February 2023, 68 patients with a single BM treated with Linac-based HSRT (24–39 Gy in three fractions) via C-VMAT and a 3-mm PTV margin were enrolled in this retrospective analysis. A frameless head–neck–shoulder thermoplastic mask, whose immobilization accuracy is inferior to that of specialized mask fixation systems, was used to immobilize patients. Dosimetric parameters and clinical outcomes were evaluated.

C-VMAT provided clinically satisfactory treatment plans, with median gradient index, conformity index, homogeneity index, and PTV coverage values of 4.30, 1.05, 1.28, and 98%, respectively. The median volumes of normal brain tissue receiving 18 Gy, 21 Gy, and 23 Gy were 7.29 cm3, 5.33 cm3, and 4.40 cm3, respectively. High delivery accuracy was observed, with a gamma passing rate ≥90% for all plans. As of June 2023, the median follow-up time was 9.1 months. The intracranial objective response rate and disease control rate were 64% and 96%, respectively. The median intracranial progression-free survival was 26.9 (95% CI, 12.7–41.1) months. The 1- and 2-year local control (LC) rates were 91.5% (95% CI, 80.1%–100%) and 83.2% (95% CI, 64.6%–100%), respectively. The 1- and 2-year intracranial control rates were 70.9% (95% CI, 55.2%–86.6%) and 51.2% (95% CI, 32.6%–69.8%), respectively. Only four irradiated lesions progressed at the end of follow-up. The cerebral radiation necrosis rate of all patients was 7.4%.

C-VMAT HSRT combined with a 3-mm PTV margin is an effective and safe treatment modality for small BMs.

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