RADIOSURGERY FOR BRAIN METASTASES - RELATIONSHIP OF DOSE AND PATTERN OF ENHANCEMENT TO LOCAL-CONTROL

Purpose: This study aimed to analyze dose, initial pattern of enhancem ent, and other factors associated with freedom from progression (FFP) of brain metastases after radiosurgery (RS). Methods and Materials: Al l brain metastases treated with gamma-knife RS at the University of Ca lifornia, San Francisco, from 1991 to 1994 were reviewed. Evaluable le sions were those with follow-up magnetic resonance or computed tomogra phic imaging. Actuarial FFP was calculated using the Kaplan-Meier meth od, measuring FFP from the date of RS to the first imaging study showi ng tumor progression. Controlled lesions were censored at the time of the last imaging study. Multivariate analyses were performed using a s tepwise Cox proportional hazards model. Results: Of 261 lesions treate d in 119 patients, 219 lesions in 100 patients were evaluable. Major h istologies included adenocarcinoma (86 lesions), melanoma (77), renal cell carcinoma (21), and carcinoma not otherwise specified (17). The m edian prescribed RS dose was 18.5 Gy (range, 10-22) and the median tum or volume was 1.3 mi (range, 0.02-30.9). The initial pattern of contra st enhancement was homogeneous in 68% of lesions, heterogeneous in 12% , and ring-enhancing in 19%. The actuarial FFP was 82% at 6 months and 77% at 1 year for all lesions, and 93 and 90%, respectively, for 145 lesions receiving greater than or equal to 18 Gy. Multivariate analysi s showed that longer FFP was significantly associated with higher pres cribed RS dose, a homogeneous pattern of contrast enhancement, and a l onger interval between primary diagnosis and RS. Adjusted for these fa ctors, adenocarcinomas had longer FFP than melanomas. No significant d ifferences in FFP were noted among lesions undergoing RS for recurrenc e after prior radiotherapy (119 lesions), RS alone as initial treatmen t (45), or RS boost (55). Conclusion: A minimum prescribed radiosurgic al dose greater than or equal to 18 Gy yields excellent local control of brain metastases. The influence of pattern of enhancement on local control, a new finding in this retrospective analysis, needs to be con firmed. (C) 1997 Elsevier Science Inc.