Experiences on two different stereotactic radiosurgery modalities of Gamma Knife and Cyberknife in treating brain metastases.

Abstract

In this study, we compared the dosimetric properties between Gamma Knife (GK) and Cyberknife (CK), and investigated the clinical implications in treating brain metastases (BMs). Between 2011 and 2013, 77 patients treated with either single-fraction GK for small BMs (n = 40) or fractionated CK for large BMs >3 cm (n = 37) were analyzed. Among a total of 160 lesions, 81 were treated with GK (median, 22 Gy) and 38 (large lesions) with three- or five-fraction CK (median, 35 Gy). The median tumor volume was 1.0 cc (IQR, 0.12-4.4 cc) for GK and 17.6 cc (IQR, 12.8-23.7 cc) for fractionated CK. A lesion-to-lesion dosimetric comparison was performed using the identical contour set in both systems. The mean dose to tumor was significantly higher in GK by 1.25-fold (P < 0.001), whereas normal tissue volume receiving 90-10 % of prescription dose was significantly larger in CK by 1.26-fold (P < 0.001). Nevertheless, no differences were observed in local tumor control (rates at 1 year, 89.7 % vs 87.0 %; P = 0.594) and overall survival (median, 14 vs 16 months; P = 0.493) between GK and fractionated CK groups. The incidences of radiation necrosis were also not different (12.3 % vs 15.8 %; P = 0.443). Despite slightly inferior dosimetric properties of CK, fractionated CK for large BMs appears to be as effective and safe as single-fraction GK for small BMs, representing fractionation as an effective strategy for enhancing efficacy and moderating toxicity in stereotactic radiosurgery for BMs.