VMAT Optimization for Cervical Cancer Radiotherapy

17 patients were treated with a Versa HD linear accelerator (Elekta Medical Systems Co., Stockholm, Sweden) of 6 MV photon beams. The VMAT plan of a 360^o full bow with 2 arcs was designed for every patient based on Smart Arc inverse optimization. The objective functions were shown in Table 1. The doses were calculated with the Collapsed Cone Convolution (CCC) algorithm [18 (link)]. The planning prescription setting was as follows: the PTV prescription being 45.0–50.0Gy/25 fractions, and the PGTV prescription being 60.0–62.5Gy/25 fractions.
Table 1

Dose-volume criteria used in the cervix cancer VMAT plans

Volume of interest	Dose-volume criteria (cGy)
PGTV	MinD = 95%PD, VPD ≥ 95%, MaxD = 107%PD
PTV	MinD = 95%PD, VPD ≥ 95%, MaxD = 107%PD
Rectum	V40 < 60%, D33% < 45Gy
Bladder	V40 < 40%, D33% < 45Gy
L-Femur	V45 < 5%, V30 < 30%
R-Femur	V45 < 5%, V30 < 30%
Intestine	V30 < 30%
Cord	MaxD = 45Gy

Note: PD is the prescribed dose

All VMAT physical schemes were designed with Pinnacle TPS (version 9.10). When the default value was DCGS = 4.0 mm, the planners optimized and adjusted the treatment plans for cervical cancer patients based on their own previous experience. After all the indicators of the plans met the clinical requirements, changed the DCGS (from 2.0 mm to 5.0 mm) and recalculated dose in the target volumes and OARs.