Table 2. Details of the failed cases of the VMAT plans with a gamma criterion of 2%/1 mm and a tolerance level of the global gamma passing rate of 90% for two years.

Failed case	Treatment sites	Prescription (Gy)	Fraction number	MIs	%GP with 2%/1 mm	%GP with 2%/2 mm
1	T-spine	13	1	3.63	84.6	100
2	Lung	60	4	5.73	89.0	100
3	L-spine	20	1	12.03	87.5	97.1
4	C-spine	16	1	14.18	88.7	95.6

Abbreviations: VMAT, volumetric modulated arc therapy; MI_s, modulation index evaluating the speed of multi-leaf collimator; %GP with 2%/1 mm, global gamma passing rate with a gamma criterion of 2%/1 mm; %GP with 2%/2 mm, global gamma passing rate with a gamma criterion of 2%/2 mm.