# Evaluation of the accuracy of a surface-guided radiotherapy system for patient positioning in radiotherapy of breast cancer

## TL;DR

This study shows that a surface-guided system can accurately position breast cancer patients for radiotherapy, comparable to traditional imaging methods.

## Contribution

The study validates marker-free surface-guided radiotherapy as a reliable setup method for breast cancer treatment.

## Key findings

- Surface-guided positioning deviations were within 3 mm/3° in all directions.
- No significant differences were found between SGRT and CBCT for longitudinal and lateral translations.
- CBCT-based corrections showed statistically significant differences compared to SGRT.

## Abstract

•Accuracy of surface-guided positioning evaluated for breast cancer radiotherapy.•Deviations within 3 mm/3° in all directions after surface matching.•Surface scanning found to be a reliable setup method for breast cancer radiotherapy.

Accuracy of surface-guided positioning evaluated for breast cancer radiotherapy.

Deviations within 3 mm/3° in all directions after surface matching.

Surface scanning found to be a reliable setup method for breast cancer radiotherapy.

The accuracy of a surface-guided radiotherapy (SGRT) system for patient positioning in free-breathing breast cancer radiotherapy (RT) was evaluated against cone-beam computed tomography (CBCT)-based image registration.

A total of 106 treatment fractions from 20 patients who received breast RT in free-breathing in our institution were analysed. Patient positioning was performed using an SGRT system, without initial alignment to skin markers. The positioning deviations were reduced to within our clinical tolerance of ± 3.0 mm (translations) and ± 3.0° (rotations) before CBCT acquisition. CBCT-based setup corrections were calculated using bony anatomy registration between the CBCT and planning computed tomography (CT) images. The translational and rotational corrections derived from SGRT were compared with those from CBCT. A two-sample paired t-test with a significance level of 0.05 was performed.

No significant differences were observed between SGRT and CBCT for longitudinal (p = 0.42) and lateral translations (p = 0.70). Vertical translation and rotations about all three axes were within clinical tolerance levels with SGRT, while CBCT-based corrections showed statistically significant differences (p < 0.05).

The results support the feasibility of marker-free SGRT with CBCT verification as a reliable setup method in free-breathing breast cancer RT.