Evaluation of response to stereotactic radiosurgery in brain metastases using multiparametric MRI

Abstract

BACKGROUND

Following stereotactic radiosurgery (SRS), brain metastases initially increase in size in up to a third of cases, suggesting treatment failure. Current imaging using structural MRI cannot differentiate between tumour recurrence and SRS-induced changes, creating difficulties with patient management. Combining multiparametric MRI techniques, which assess tissue physiological and metabolic information has shown promise for answering this clinical question.

MATERIALS AND METHODS

Multiparametric MRI techniques including spectroscopy, diffusion and perfusion imaging were used for differentiation of radiation-induced necrosis and tumour recurrence after SRS for intracranial metastases in six cases. All patients presented with enlargement of the treated lesion, an increase in perilesional brain oedema, and aggravation or appearance of neurological signs and symptoms from 7–29 weeks after primary treatment.

RESULTS

Multiparametric imaging helped to differentiate features of tumour progression (n=4) from radiation-induced necrosis (n=2). A low apparent diffusion coefficient (ADC) <1000 x 10 ^–6 mm ²/s, high relative cerebral blood volume (rCBV) ratio >2.1, high choline:creatine (Cho:Cr) ratio >1.8 suggested tumour recurrence. A high ADC >1000 x 10 ^–6 mm ²/s, low rCBV ratio <2.1, Cho:Cr ratio <1.8 suggested SRS-induced radiation changes. Multiparametric MRI diagnosis was confirmed by histology or radiological and clinical follow up.

CONCLUSION

Multiparametric MRI is helpful in the early identification of radiation-induced necrosis and tumour recurrence, which can be used for monitoring treatment changes in intracranial neoplasms after SRS treatment.