KEY POINTS
- Four trained radiology residents independently delineated 354 intact brain metastases from 149 patients on pretreatment contrast-enhanced three-dimensional T1-weighted magnetic resonance imaging.
- Median Dice similarity coefficient was 0.85, and median mean distance to agreement was 0.34 mm.
- Lesions with perilesional oedema and larger volumes showed greater proportional overlap by Dice.
- Larger lesions also had greater absolute boundary differences, reflected by increasing mean distance to agreement.
- Imaging at 3 tesla was associated with slightly better agreement, while other acquisition parameters and organ-at-risk proximity did not show consistent multivariable associations.
CLINICAL TAKEAWAY
Overall agreement was good after structured observer training, but different metrics captured different aspects of uncertainty: larger lesions had better proportional overlap yet larger absolute boundary deviations. Standardized magnetic resonance imaging protocols, training and peer review remain justified in stereotactic workflows.