# Potential of margin reduction for cervical cancer radiotherapy in an online adaptive image-guided workflow

## TL;DR

Adaptive radiotherapy improves cervical cancer treatment by reducing target margins and protecting nearby organs from unnecessary radiation.

## Contribution

Online adaptive radiotherapy enables significant margin reduction and better organ sparing in cervical cancer treatment.

## Key findings

- Adaptive radiotherapy reduced geometric miss volume by 85.1% compared to IGRT.
- ART improved rectum sparing with 4.39% lower gEUD and 52.27% lower NTCP.
- ART achieved 99.2% target coverage in fractions compared to 75.0% with IGRT.

## Abstract

•Adaptive radiotherapy enabled target volume margin reduction in cervical cancer.•Adaptive radiotherapy assured target volume coverage while reduced organ irradiation.•Bladder-filling drinking protocol enhanced small-bowel sparing during radiotherapy.•Adaptive radiotherapy reduced the normal tissue complication probability of organs.

Adaptive radiotherapy enabled target volume margin reduction in cervical cancer.

Adaptive radiotherapy assured target volume coverage while reduced organ irradiation.

Bladder-filling drinking protocol enhanced small-bowel sparing during radiotherapy.

Adaptive radiotherapy reduced the normal tissue complication probability of organs.

Adaptive radiotherapy (ART) manages anatomical variations through real-time plan adjustments. Herein, we aimed to evaluate the efficacy of ART in improving target coverage and reducing organ-at-risk (OAR) irradiation doses in cervical cancer.

A prospective single-arm study enrolled 15 patients with cervical cancer. Participants received definitive chemoradiotherapy (45–50 Gy/25Fractions) using cone-beam computed tomography-guided online ART workflow. Endpoints included geometric miss volume (target volume underdosed), planning target volume (PTV) coverage (V100%), OAR sparing (generalized equivalent uniform dose [gEUD] and normal tissue complication probability [NTCP]), and dose homogeneity/conformity parameters (coefficient of variation [CV], Paddick Index [PI]). Mixed-effects models compared ART and simulated image-guided radiotherapy (IGRT) plans, with Wilcoxon signed-rank and Mann-Whitney U tests for statistical analysis.

Among 375 adaptive sessions, ART outperformed IGRT, reduced geometric miss volume by 85.1% (0.28 cm3 vs. 1.88 cm3; P < 0.001) and achieved V100% ≥ 99% in 99.2% of fractions (vs. 75.0% with IGRT; P < 0.001). ART improved PTV dose homogeneity (median CV: −0.29% vs. 3.89%; P < 0.001) and conformity (median PI: 0.75 vs. 0.60; P < 0.001). Additionally, ART reduced rectum gEUD by 4.39% (P < 0.001) and NTCP by 52.27% (P < 0.001), with similar benefits for other OARs (P < 0.001). ART maintained robustness against intrafractional anatomical changes, with minimal target coverage loss and stable OAR doses despite bladder/rectum volume fluctuations. Patients exhibited 100% complete response and mild acute side effects (no grade ≥ 3 enteritis; no cystitis).

Online ART with 3-mm isotropic margins is feasibile for cervical cancer, achieved high target coverage while reduced OAR doses and NTCP.