A nomogram for predicting distant brain failure in patients treated with gamma knife stereotactic radiosurgery without whole brain radiotherapy

Background. We review our single institution experience to determine predictive factors for early and delayed distant brain failure (DBF) after radiosurgery without whole brain radiotherapy (WBRT) for brain metastases. Materials and methods. Between January 2000 and December 2010, a total of 464 patients were treated with Gamma Knife stereotactic radiosurgery (SRS) without WBRT for primary management of newly diagnosed brain metastases. Histology, systemic disease, RPA class, and number of metastases were evaluated as possible predictors of DBF rate. DBF rates were determined by serial MRI. Kaplan-Meier method was used to estimate rate of DBF. Multivariate analysis was performed using Cox Proportional Hazard regression. Results. Median number of lesions treated was 1 (range 1-13). Median time to DBF was 4.9 months. Twenty-seven percent of patients ultimately required WBRT with median time to WBRT of 5.6 months. Progressive systemic disease (chi(2) = 16.748, P < . 001), number of metastases at SRS (chi(2) = 27.216, P < .001), discovery of new metastases at time of SRS (chi(2) = 9.197, P < . 01), and histology (chi(2) = 12.819, P < .07) were factors that predicted for earlier time to distant failure. High risk histologic subtypes (melanoma, her2 negative breast, chi(2) = 11.020, P < . 001) and low risk subtypes (her2 + breast, chi(2) = 11.343, P < . 001) were identified. Progressive systemic disease (chi(2) = 9.549, P < . 01), number of brain metastases (chi 2 = 16.953, P < .001), minimum SRS dose (chi(2) = 21.609, P < . 001), and widespread metastatic disease (chi(2) = 29.396, P < .001) were predictive of shorter time to WBRT. Conclusion. Systemic disease, number of metastases, and histology are factors that predict distant failure rate after primary radiosurgical management of brain metastases.