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

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 (V_100%), 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 V_100% ≥ 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.