ИСТИНА

Whereas use of Bevacizumab to treat symptomatic brain radionecrosis is widely known, the differential diagnosis of necrosis and tumor progression is still difficult in some cases. For patients who have enlargement of brain metastasis after radiosurgery we suggest a new strategy to discriminate radionecrosis and true progression – a short course of intravenous Bevacizumab in 5-7 mg/kg with 2-3 week interval and new contrast MR. We present 3 relevant clinical cases. 1st case – 49 y.o. female with ovarian cancer underwent LINAC-based SRS for two small closely seated metastases in temporal lobe, both metastasis had shrunk and remained stable, but 34 months after radiosurgery a new asymptomatic contrasting lesion developed adjacent to one of metastasis, 11 millimeters in diameter, and surrounded with an edema. Patient developed no other new brain or extracranial mets. We proposed radionecrosis, which was too small to use PET to discriminate for regrowth or necrosis. MR-perfusion data was not convincing, so a decision to use Bevacizumab was made. After two infusions of 6 mg/kg with a 3-week interval this new zone disappeared and did not develop again for at least 10 months (with no chemotherapy), so we confirmed necrosis. 2nd case – 67 y.o. female with lung adenocarcinoma underwent LINAC-based 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 some edema. 18F-FET PET failed to differentiate tumor recurrence and pseudoprogression, so we prescribed two infusions of Bevacizumab 7 mg/kg with a 3-week interval. 1 month later a good response to Bevacizumab therapy as a substantial regression of pathological MRI changes were noted, diagnostic for pseudoprogression. 3d case – 48 y.o. female with breast cancer underwent LINAC-based 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. After two infusions of Bevacizumab 5 mg/kg with 2-week interval, this lesion and symptoms substantially regressed. After a second infusion methionine PET showed no active tumor. Conclusion - our preliminary data suggest that use of two infusions of Bevacizumab and routine contrast MRI have promising diagnostic value to rule out tumor growth without use of PET during the first year after SRS of brain metastasis.