# Analysis of the effect of dual reference lines on first positioning accuracy in intensity‐modulated radiotherapy for cervical cancers

## TL;DR

Using dual reference lines in radiotherapy improves positioning accuracy and reduces target volume for cervical cancer treatment.

## Contribution

Introduces dual-reference lines to enhance precision and efficiency in VMAT for cervical cancer.

## Key findings

- Dual-reference lines reduced linear and rotational positioning errors compared to single-reference lines.
- Median positioning time was shorter in the dual-reference line group.
- Modified planning target volumes were smaller with dual-reference lines.

## Abstract

To investigate the use of dual‐reference lines to reduce positioning errors and optimize modified planning target volume (MPTV) in volume modulated arc therapy (VMAT) for cervical cancers.

Thirty‐seven patients with FIGO stage IIB‐IVA cervical cancer and no distant metastasis, who underwent radiotherapy in a tertiary hospital from June 15 2022 to September 15 2023, were selected and randomly divided into dual positioning reference line group (dual‐line group, 21 cases) and single positioning reference line group (single‐line group, 16 cases). A single reference line was made in pelvic region in single‐line group, while dual reference lines were made in stable abdominopelvic region in dual‐line group. The cone‐beam computed tomography (CBCT) was conducted to determine the positioning errors and calculate MPTV.

Linear error in Y direction, rotational errors in the rotation around Y‐axis (RY)/Z‐axis (RZ) (0.27 ± 0.12 cm, 0.60 ± 0.42°, 0.48 ± 0.44°) in dual‐line group were smaller than those (0.35 ± 0.22 cm, 0.78 ± 0.45°, 0.85 ± 0.66°) in single‐line group (p < 0.05). The thresholds of 0.4 cm and 1.4° were set as the boundary values for linear and rotational errors, respectively. There were significant statistical differences in the distribution of positioning errors in the six directions between the two groups (p < 0.001), with higher positioning error rates in the Y (77.78%), RY (41.46%), and RZ (53.66%) directions, respectively. Median total positioning time in dual‐line group (8.27 min, interquartile rang [IQR]: 7.65–8.63) was shorter than that (8.75 min, IQR: 7.89–9.45) in single‐line group (Z = 3.53998, p < 0.001). MPTVs in X, Y, and Z directions (0.25, 0.37, and 0.10 cm) in dual‐line group were smaller than those (0.31, 0.56, and 0.11 cm) in single‐line group.

Dual‐reference lines improve positioning accuracy, reduce MPTV, and enhance efficiency in VMAT for middle and advanced cervical cancers, offering a clinically practical solution for precision radiotherapy.