Comparing Gamma Knife and CyberKnife in patients with brain metastases

Terence T. Sio, Sunyoung Jang, Sung Woo Lee, Bruce Curran, Anil P. Pyakuryal, Edward S. Sternick

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The authors compared the relative dosimetric merits of Gamma Knife (GK) and CyberKnife (CK) in 15 patients with 26 brain metastases. All patients were initially treated with the Leksell GK 4C. The same patients were used to generate comparative CK treatment plans. The tissue volume receiving more than 12 Gy (V12), the difference between V12 and tumor volume (V12net), homogeneity index (HI), and gradient indices (GI25, GI50) were calculated. Peripheral dose falloff and three conformity indices were compared. The median tumor volume was 2.50 cm3 (range, 0.044-19.9). A median dose of 18 Gy (range, 15-22) was prescribed. In GK and CK plans, doses were prescribed to the 40-50% and 77-92% isodose lines, respectively. Comparing GK to CK, the respective parametric values (median ± standard deviation) were: minimum dose (18.2 ± 3.4 vs. 17.6 ± 2.4 Gy, p = 0.395); mean dose (29.6 ± 5.1 vs. 20.6 ± 2.8 Gy, p < 0.00001); maximum dose (40.3 ± 6.5 vs. 22.7 ± 3.3 Gy, p < 0.00001); and HI (2.22 ± 0.19 vs. 1.18 ± 0.06, p < 0.00001). The median dosimetric indices (GK vs. CK, with range) were: RTOG_CI, 1.76 (1.12-4.14) vs. 1.53 (1.16-2.12), p = 0.0220; CI, 1.76 (1.15-4.14) vs. 1.55 (1.18-2.21), p = 0.050; nCI, 1.76 (1.59-4.14) vs. 1.57 (1.20-2.30), p = 0.082; GI50, 2.91 (2.48-3.67) vs. 4.90 (3.42-11.68), p < 0.00001; GI25, 6.58 (4.18-10.20) vs. 14.85 (8.80-48.37), p < 0.00001. Average volume ratio (AVR) differences favored GK at multiple normalized isodose levels (p < 0.00001). We concluded that in patients with brain metastases, CK and GK resulted in dosimetrically comparable plans that were nearly equivalent in several metrics, including target coverage and minimum dose within the target. Compared to GK, CK produced more homogenous plans with significantly lower mean and maximum doses, and achieved more conformal plans by RTOG_CI criteria. By GI and AVR analyses, GK plans had sharper peripheral dose falloff in most cases.

Original languageEnglish (US)
Pages (from-to)14-26
Number of pages13
JournalJournal of applied clinical medical physics
Issue number1
StatePublished - 2014

All Science Journal Classification (ASJC) codes

  • Radiation
  • Instrumentation
  • Radiology Nuclear Medicine and imaging


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