Background
The role of stereotactic radiosurgery (SRS) for recurrent glioblastoma and the radionecrosis risk in this setting remain unclear.
Objective
To perform a large retrospective study to help inform proper indications, efficacy, and anticipated complications of SRS for recurrent glioblastoma.
Methods
We retrospectively analyzed patients who underwent Gamma Knife SRS between 1991 and 2013. We used the partitioning deletion/substitution/addition (partDSA) algorithm to identify potential predictor covariate cut points and Kaplan-Meier and proportional hazards modeling to identify factors associated with post-SRS and post-diagnosis survival.
Results
174 glioblastoma patients (median age 54.1 years) underwent SRS a median of 8.7 months after initial diagnosis. Seventy-five percent had one treatment target (range = 1–6) and median target volume, and prescriptions were 7.0 cm3 (range 0.3–39.0) and 16.0 Gy (range 10–22), respectively. Median overall survival was 10.6 months following SRS and 19.1 months after diagnosis. Kaplan-Meier and multivariable modeling revealed that younger age at SRS, higher prescription dose, and longer interval between original surgery and SRS are significantly associated with improved post-SRS survival. Forty-six patients (26%) underwent salvage craniotomy after SRS, with 63% showing radionecrosis or mixed tumor/necrosis versus 35% showing purely recurrent tumor. The necrosis/mixed group had lower mean isodose prescription compared to the tumor group (16.2 vs 17.8 Gy, P = .0031) and larger mean treatment volume (10.0 vs 5.4 cm3, P = .0091).
Conclusion
Gamma Knife may benefit a subset of focally recurrent patients, particularly those who are younger with smaller recurrences. Higher prescriptions are associated with improved post-SRS survival and do not seem to have greater risk of symptomatic treatment effect.