Contrast-enhanced T2-fluid-attenuated inversion recovery magnetic resonance imaging for radiotherapy target delineation in brain metastases: A narrative review

Table 2 Comparison of different imaging modalities in brain metastases target delineation

Imaging modality	Advantages	Limitations	Clinical applications in BM radiotherapy
T1WI + C	Standard reference; excellent for enhancing lesions; widely available	Vascular enhancement can obscure cortical/CSF-adjacent lesions; signal interference from blood vessels	Primary sequence for GTV delineation; standard for response assessment
T2-FLAIR	Suppresses CSF signal; excellent for edema visualization; detects non-enhancing tumor	No contrast enhancement; may miss small lesions	Assessing peritumoral edema; visualizing non-enhancing tumor components
T2-FLAIR + C	CSF suppression; superior detection of cortical/meningeal lesions; high sensitivity to low-dose contrast; reduces vascular interference	Variable availability; technical standardization lacking; limited evidence base for target delineation	Delineating lesions near CSF/cortex; detecting leptomeningeal disease; possible role in target delineation
CT	Fast; widely available; excellent for bone anatomy; essential for dose calculation	Poor soft tissue contrast; low sensitivity for small metastases	Simulation and localization; electron density mapping for dose calculation
PET-CT	Metabolic information; distinguishes active tumor from necrosis/edema	Limited spatial resolution; higher cost; radiation exposure	Problem-solving in equivocal cases; detecting active disease
DCE-MRI	Assesses vascular permeability; biological information	Longer acquisition; specialized processing; not standard in routine practice	Research applications; understanding tumor biology
DSC-MRI	Assesses perfusion and angiogenesis; helps differentiate RN from TP	Requires specialized software; prone to artifacts	Differentiating radiation necrosis from tumor progression

T1WI + C: Contrast-enhanced T1-weighted imaging; T2-FLAIR: T2-fluid-attenuated inversion recovery; T2-FLAIR + C: Contrast-enhanced T2-fluid-attenuated inversion recovery; CT: Computed tomography; PET-CT: Positron emission tomography-computed tomography; DCE-MRI: Dynamic contrast-enhanced magnetic resonance imaging; DSC-MRI: Dynamic susceptibility contrast magnetic resonance imaging; BM: Brain metastases; CSF: Cerebrospinal fluid; GTV: Gross Tumor Volume; RN: Radiation necrosis; TP: Tumor progression.