Dynamic susceptibility contrast MRI-derived oxygen metabolism and perfusion metrics for distinguishing radiation necrosis from tumor progression in irradiated brain metastases

PURPOSE: The purpose of this study was to determine the capabilities of dynamic susceptibility contrast (DSC)‑derived microvascular and oxygen metabolism metrics to distinguish radiation necrosis (RN) from tumor progression (TP) in irradiated brain metastases. MATERIALS AND METHODS: Fifty‑eight patients who completed cranial irradiation and underwent DSC perfusion MRI between August 2014 and August 2024 were retrospectively included. There were 31 men and 27 women, with a median age of 60.5 years (first quartile [Q1], 52.3; third quartile [Q3], 68.8). Perfusion, microvascular, and metabolic maps were generated with commercially available software. Lesion‑to‑white‑matter ratios were computed for all DSC-derived microvascular and oxygenation metrics including relative cerebral blood volume (rCBV) and oxygen extraction fraction (rOEF). Reference diagnoses were histopathology (n = 11) or multidisciplinary follow‑up (n = 47). Logistic regression analysis was used to identify metrics associated with RN versus TP, and receiver operating characteristic curve analysis was used to estimate diagnostic performance. For prognosis, overall survival was analyzed using Cox proportional hazards models. RESULTS: A total of 58 brain lesions were studied, including 34 TPs and 24 RNs. Patients with RN had longer overall survival than those with TP (median not reached vs. 22 months; P = 0.01). Among all metrics, only rCBV and rOEF differed significantly. TP showed higher median rCBV (1.8; Q1, 1.2; Q3, 2.8) than RN (1.1; Q1, 0.6; Q3, 1.9) (P = 0.02). RN exhibited greater median rOEF (1.9; Q1, 1.4; Q3, 2.1) than TP (1.5; Q1, 1.3; Q3, 1.8, P = 0.03). rCBV achieved an area under the receiver operating characteristic curve (AUC) of 0.69 (95 % confidence interval [CI]: 0.54-0.83), rOEF an AUC of 0.66 (95 % CI: 0.52-0.81), and their combination and AUC of 0.74 (95 % CI: 0.60-0.87) without significant differences (P ≥ 0.19). After adjusting for rCBV in multivariable analysis, rOEF remained significantly associated with RN (odds ratio, 0.23; 95 % CI: 0.06-0.72; P = 0.02). A greater rOEF was also associated with a longer overall survival in Cox analysis (adjusted hazard ratio, 0.72; 95 % CI: 0.55-0.95. P = 0.02). CONCLUSION: Elevated rCBV is in favor of the diagnosis of TP whereas increased rOEF is in favor of the diagnosis of RN in patients with irradiated brain metastases. Although combining metrics did not confer significant diagnostic advantages, rOEF shows an independent association with longer overall survival.