Dosimetric comparison of volumetric modulated arc therapy with TrueBeam LINAC and hypofractionated radiosurgery with gamma knife ICON for large (>10 cm3) skull base meningiomas

BACKGROUND: Multi Fractionated stereotactic radiosurgery (MF-SRS) of Linac has an essential role in the treatment of skull base meningiomas (sbMNG). However, Gamma Knife Icon (GK) allows MF-SRS using mask immobilization with onboard image guidance. OBJECTIVE: This dosimetric study aims to investigate whether equivalent plan quality can be achieved with Volumetric Modulated Arc Therapy (VMAT) in patients with large sbMNG (>10 cm(3)) previously treated with GK. METHODS: Twenty patients with the median target volume of 19.7cm(3) are re-planned by using VMAT with 20 Gy in 5 fractions. Plan qualities are compared to tumor coverage, paddick conformity index (PCI), gradient index (GI), V4 Gy, V10 Gy, V12 Gy, optic chiasm V20 Gy, brainstem V23 Gy, optic nerve V25 Gy volumes, and maximum doses for all. Additionally, beam-on time and approximate planning time are also analyzed and compared. RESULTS: All plans provide adequate clinical requirements. First, the CI is comparable for the GK and VMAT (0.99 +/- 0.01 vs. 1.13 +/- 0.20; p = 0.18). Second, VMAT has a significantly higher GI than GK (3.81 +/- 0.35 vs. 2.63 +/- 0.09; p < 0.001). Third, the PCI is significantly higher in GK than VMAT (0.76 +/- 0.05 vs. 0.70 +/- 0.07; p < 0.001). The lower GI of the GK also results in significantly lower V4 Gy (156.1 +/- 43.8 vs. 207.5 +/- 40.1 cm(3), p < 0.001) and V10 Gy (26.1 +/- 9.0 vs. 28.9 +/- 7.7 cm(3), p < 0.001) compared to VMAT. Last, the VMAT reduces beam-on time (4.8 +/- 0.5 vs. 19 +/- 1.1 min.; p < 0.001). CONCLUSION: Although both systems have succeeded in creating effective plans in clinical practice, the GK reveals more effective lower normal brain tissue doses. However, the shorter treatment time with LINAC, excluding the total procedure time, can be considered advantageous over GK.