Evaluation of variability in applicator position and organs at risk dose in fractionated intracavitary brachytherapy for cervical cancer.

Background: Cervical cancer remains a major cause of mortality in low- and middle-income countries (LMICs). Intracavitary brachytherapy (ICBT) is critical for curative radiotherapy; however, inter-fractional variability in applicator positioning may compromise treatment reproducibility and organ-at-risk (OAR) sparing.

Objective: This study assessed inter-fractional applicator positional stability and its dosimetric impact on OARs during fractionated ICBT for cervical cancer.

Materials and methods: A prospective analysis of 60 treatment plans from 20 patients receiving three ICBT fractions was conducted. Applicator shifts along the X, Y, and Z axes and corresponding bladder and rectal doses were evaluated. Descriptive statistics and repeated measures ANOVA determined positional reproducibility and dose variability, while correlation analysis examined associations between applicator displacement and OAR dose changes.

Results: Applicator positioning was reproducible across fractions, with no significant differences in any axis p > 0.05). Bladder dose, however, demonstrated significant variation (p = 0.027), progressively increasing across fractions. Moderate correlations (r ≈ 0.39) were observed between bladder dose escalation and applicator shifts along the X and Y axes, especially in the Y-axis. Rectal dose remained stable (p = 0.776).

Conclusion: Although applicator positioning was geometrically stable, significant bladder dose variability occurred. Adaptive replanning and real-time imaging are recommended to optimize treatment precision in fractionated ICBT.