What predicts early volumetric edema increase following stereotactic radiosurgery for brain metastases?

A volumetric analysis of pre- and post-radiosurgery (PreSRS and PostSRS) edema in patients with cerebral metastases was performed to determine factors of a predictive model assessing the risk of developing increased edema relatively early after SRS. One-hundred-fourteen metastases in 55 patients were analyzed. Selection for this analysis required an MRI ≤ 30 days before SRS and an MRI ≤ 100 days after SRS. Tumor volumes were calculated on PreSRS, SRS, and PostSRS T1-weighted postgadolinium images while edema volumes were calculating using PreSRS and PostSRS fluid-attenuated inversion recovery MR images. An increase in edema was defined as an increase in measurable edema of at least 5%. We developed and evaluated a model predicting the relative risk (RR) of increased edema after SRS. Peritumoral edema increased in 18% (21/114) of the analyzed lesions. Melanoma/renal histology, recursive partitioning analysis class III, and prior WBRT carried RRs of developing postSRS edema increase of 2.45, 2.48, and 3.16, respectively (all P values <0.05). The PreSRS edema/tumor ratio predicted for a RR of 1.007/ratio unit, and steroid dose at time of SRS predicted for a RR of 0.89/mg (all P values <0.05). A predictive model for assessing the RR of increased edema after SRS was developed based from these data and may be useful in identifying patients who might benefit from prophylactic anti-edema therapies before, during, or after SRS. This model could be used as the basis of inclusion criteria for prospective trials investigating novel anti-edema therapies.