SERIAL MR-IMAGING OF INTRACRANIAL METASTASES AFTER RADIOSURGERY

Purpose: To evaluate the spatiotemporal evolution of radiosurgical ind uced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. Methods and Ma terials: Thirty-five intracranial metastases of different primaries we re treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-thr ee follow-up MR studies were performed in these patients including T-2 - and contrast-enhanced T-1-weighted MR images. The average follow-up time was 9 +/- 5 months (mean +/- standard deviation [SD]). Based on c ontrast-enhanced T-1-weighted MR images, tumor response was radiologic ally classified in the following four groups: stable disease was assum ed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial r emission as a shrinkage of tumor size of more than 50%, a disappearanc e of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we an alysed signal changes on T-2-weighted images in brain parenchyma adjac ent to the enhancing metastases. Results: The overall mean survival ti me was 10.5 +/- 7 months, with a 1-year actuarial survival rate of 40% . Stable disease, partial or complete remission of the metastatic tumo r was observed in 22 patients (88%). Central or homogeneous loss of co ntrast enhancement appeared to be a good prognostic sign for stable di sease or partial remission. This association was statistically signifi cant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, sig nal changes on T-2-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T -2-weighted images was seen in seven of the eight patients between 3 a nd 6 months after therapy, followed by a signal regression 6-18 months after irradiation. Conclusion: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adja cent parenchymal changes following radiosurgery. Loss of homogeneous o r central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T-2-weighted images see m to be self limited. (C) 1997 Elsevier Science Inc.