P11.42.A Short course of Bevacizumab for differential diagnosis of tumor progression and radionecrosis or pseudoprogression after brain metastasis SRS

Abstract

Abstract Background Despite use of modern MRI techniques (perfusion, spectroscopy, TRAMs, radiomics), PET and SPECT the differential diagnosis of radio-necrosis and tumor progression is still difficult in malignant gliomas and brain metastasis after radiotherapy or radiosurgery. For patients who have enlargement of brain metastasis after radiosurgery we suggest a new strategy to discriminate pseudoprogression and true progression - two intravenous infusions Bevacizumab in 5-7 mg/kg with 2-3 week interval and new contrast MR. Material and Methods We present 3 relevant clinical cases, all after LINAC-based SRS for brain metastasis.1st case - 49 y.o. female with ovarian cancer underwent SRS for two small closely seated metastases in temporal lobe, both metastasis had shrunk and remained stable until 34 months after radiosurgery a new asymptomatic contrasting lesion with edema developed on MRI adjacent to one of metastasis. Patient developed no other new brain or extracranial mets, so we proposed radionecrosis, but MR-perfusion data was ambiguous. 2nd case - 67 y.o. female with lung adenocarcinoma underwent SRS (27 Gy in 3 fractions) for solitary brain metastasis. 4 months after SRS metastasis partially regressed, but 4 months later a new contrast enhancement zone appeared on its periphery with edema. 18F-FET PET failed to differentiate recurrence and pseudoprogression. 3d case - 48 y.o. female with breast cancer underwent SRS (27 Gy in 3 fractions) for 3 brain metastases. All mets regressed during the next 7 months, but 3 months later one of them showed significant symptomatic enlargement with edema on MRI. All patients received two intravenous infusions Bevacizumab in 5-7 mg/kg with 2-3 week interval and new contrast MRI (1-2 week after second infusion). Results 1st case - after two infusions of 6 mg/kg with a 3-week interval new contrasting zone disappeared and did not develop again for at least 6 months (with no chemotherapy), so we confirmed necrosis. 2nd case - substantial regression of pathological MRI changes was noted, which was stable for 3 months, diagnostic for pseudoprogression. 3d case - MRI showed substantial regress of contrasting lesion (diagnostic for necrosis), symptoms also regressed and 1 month later methionine PET showed no active tumor. Conclusion Our preliminary data suggest that use of two infusions of Bevacizumab and routine contrast MRI have very promising diagnostic value to rule out tumor growth after SRS of brain metastasis.