Differentiating between changes after radiotherapy and radionecrosis during the follow-up of brain metastasis remains challenging. Hybrid positron-emission tomography/magnetic resonance imaging is a relatively novel imaging modality that integrates advanced magnetic resonance imaging sequences with metabolic data from positron-emission tomography. This study ailed to evaluate retrospectively the contribution of hybrid ( ¹⁸ F)-fluorodeoxyglucose positron-emission tomography/magnetic resonance imaging in distinguishing radionecrosis from recurrent cerebral metastatis, comparing the diagnosis performance of ( ¹⁸ F)-fluorodeoxyglucose positron-emission tomography and magnetic resonance imaging independently, without relying clinical or prior imaging data.

Over a one-year period, we included 72 patients with brain metastases undergoing evaluation for differential diagnosis between recurrence and radionecrosis. Two senior nuclear medicine physicians and two senior radiologists independently analysed positron-emission tomography and magnetic resonance images. For semi-quantitative positron-emission tomography, analysis maximum standardized uptake value was measured at 30 min and 4 h postinjection and retention indices were calculated. Reading correlations between physicians was assessed using Cohen's Kappa coefficients. Clinical and imaging follow-up, considered the gold standard, was used to classify the lesion. For discordant cases, a joint interdisciplinary reading was conducted.

A total of 142 treated brain metastases from 90 hybrid ( ¹⁸ F)-fluorodeoxyglucose positron-emission tomography/magnetic resonance imaging scans of 72 patients were analysed. Based on the gold standard for diagnosis, the 142 lesions were categorized into two groups: 47 recurrences and 95 cases of radionecrosis. The sensibility and sensitivity of hybrid ( ¹⁸ F)-fluorodeoxyglucose positron-emission tomography/magnetic resonance imaging were 97.9 and 100 %, respectively, outperforming both magnetic resonance imaging and positron-emission tomography alone.

Dual time-point ( ¹⁸ F)-fluorodeoxyglucose positron-emission tomography, with retention index calculation, shows significant in differentiating radionecrosis from recurrence. Technological advancements, such as hybrid positron-emission tomography/magnetic resonance imaging, enhance diagnostic accuracy in substantial patients’ cohorts. Further studies incorporating histological confirmation as the gold standard is warranted to validate these findings.