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

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Background and purpose 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. Materials and methods 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. Results Among 375 adaptive sessions, ART outperformed IGRT, reduced geometric miss volume by 85.1% (0.28 cm 3 vs. 1.88 cm 3 ; 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). Conclusions Online ART with 3-mm isotropic margins is feasibile for cervical cancer, achieved high target coverage while reduced OAR doses and NTCP.