The dose statistics of the plans were based on dose-volume histogram (DVH) analysis. For PTV, the dose of 2% and 98% volume (D2, D98), the volume receiving 107% and 110% of the prescribed dose (V107 and V110) and the mean dose (Dmean) were analysed. The conformity index (CI) and the homogeneity index (HI) of the PTV were calculated according to the following formula:

TVPV represents the volume of the PTV wrapped by the prescription dose, the TV represents the volume of the PTV, and the PV represents the total volume wrapped by the prescription dose. Larger CI values indicate the better conformity of the target [13].

Dp represents the prescribed dose. Lower HI values indicate the better uniformity of the target [14].

For OARs, the VX and mean doses were analysed. VX represents the irradiated volume of X Gy dose.

The number of MUs was analysed for all plans. The delivery times of T-4arc, T-8arc, H-4arc and H-8arc were recorded. The delivery time was recorded from the first field beam on to the last field beam off, excluding the positioning time.