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

Table 1 An ASTRO clinical practice guideline for brain metastases radiotherapy

KQ	Population	Intervention	Comparator	Outcomes
1	What are the indications for SRS alone for patients with intact BM?
	Patients with intact BM	Observation WBRT	SRS	Intracranial control; progression-free survival; overall survival; neurocognitive function; patient-reported outcomes
2	What are the indications for observation, preoperative SRS or WBRT in patients with resected BM?
	Patients with resected BM	Observation WBRT	SRS	Intracranial control; progression-free survival; overall survival; neurocognitive function; patient-reported outcomes
3	What are the indications for WBRT for patients with intact BM?
	Patients with intact BM	Observation WBRT	Conventional WBRT; HA-WBRT; HA-WBRT plus memantine	Intracranial control; progression-free survival; overall survival; neurocognitive function; patient-reported outcomes
4	What are the risks of symptomatic radionecrosis with WBRT and/or SRS for patients with BM?
	Patients with BM	WBRT	SRS	Symptomatic radionecrosis; other adverse effects

BM: Brain metastases; KQ: Key question; SRS: Stereotactic radiosurgery; WBRT: Whole-brain radiation therapy; HA-WBRT: Hippocampal-avoidance whole-brain radiation therapy.

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.

Table 3 Summary of key clinical studies of contrast-enhanced T2-fluid-attenuated inversion recovery sequence in brain metastases

Ref.	Population	Sample size	Contrast agent/dose	Acquisition setting	Comparator	Primary outcome	Key limitations
Jin et al[33]	Patients with suspected BM	82	Half-dose	Diagnostic	Standard-dose T1WI + C	Lesion detection rate; contrast-to-noise ratio comparison	Single-center; no radiotherapy contouring endpoint
Ahn et al[31]	Patients with small BM	121	Double-dose	Diagnostic	Conventional 3D T1WI + C	Detection sensitivity for small BM	Diagnostic cohort only; no radiotherapy application
Sun et al[18]	Lung cancer patients with BM	156	Standard-dose	Diagnostic	T1WI + C alone	Overall lesion detection rate	Diagnostic study; no target delineation analysis
Heyn et al[123]	BM patients post-radiotherapy	98	Standard-dose	Diagnostic follow-up	DSC-MRI	Differentiation of radiation necrosis vs tumor progression	Retrospective; single-center
Ohira et al[53]	BM patients undergoing SRS	41	Standard-dose	Radiotherapy simulation	CT simulation	Geometric distortion and dosimetric impact	Focused on distortion, not contour accuracy

All available evidence is derived from diagnostic imaging or geometric distortion studies. No prospective study has directly evaluated the impact of contrast-enhanced T2-fluid-attenuated inversion recovery on Gross Tumor Volume contouring accuracy, interobserver variability, dosimetric outcomes, or patient survival. T1WI + C: Contrast-enhanced T1-weighted imaging; CT: Computed tomography; DSC-MRI: Dynamic susceptibility contrast magnetic resonance imaging; BM: Brain metastases; SRS: Stereotactic radiosurgery.