ESTRO 2023 - Abstract Book

S1817

Digital Posters

ESTRO 2023

counterclockwise arcs with collimator angle345) with a flattening-filter-free 10MV photons. Moreover, volume of PTV receiving 95% of the prescription dose in VMAT plans was normalized to be similar to the CK plans. Dose indices related to target coverage, dose-volume histogram parameters for the target and organs at risk(OAR), as well as Conformity index(CI) and new Conformity index(nCI), Gradient index(GI), and Homogeneity index(HI) were compared. The number of monitor units (MU) and the estimated treatment delivery times of each plan were also reported. Results The dose distribution of two techniques was shown in Figure 1. The volume of PTV received 36.25 Gy for VMAT was higher than CK (VMAT:97.25 1.14%, CK:96.46 1.24%) but did not reach statistically significant(p=0.079). The doses conformed to PTV of VMAT were better than CK with statistically significant in nCI (VMAT: CI1.01 0.06 and nCI1.07 0.05, CK: CI1.03 0.04 and nCI1.10 0.04, p=0.377 and 0.028 respectively); however, the dose rapid falloff of CK-SBRT was not statistically differenced VMAT-SBRT (CK: GI3.40 0.35, VMAT: GI3.52 0.22, p=0.062). The dose homogeneity of VMAT-SBRT was higher than CK (VMAT: HI0.05 0.01, CK: HI0.12 0.06, p<0.001). In terms of OARs sparing, VMAT was reduced dose to OARs greater than CK, as shown in Table 1. Nevertheless, VMAT provides the number of MU and treatment delivery times less than CK (VMAT: MU2303.49 193.07 and delivery time1.80 0.02 mins, CK: MU2878.59 382.36 and delivery time12.25 1.12 mins, p<0.001)