Integrating ultrasound into cervical brachytherapy planning: A technical note with an illustrative case

To describe the feasibility of ultrasound as an alternative imaging modality for intracavitary brachytherapy in cervical cancer, particularly in resource-limited settings. This technical note describes the integration of ultrasound into two-dimensional (2D) and three-dimensional (3D) cervical brachytherapy workflows, illustrated through a representative case, demonstrating how ultrasound-derived anatomical measurement may assist applicator placement and dose optimization.

Ultrasound was used to guide applicator insertion, reducing uterine perforation risk and confirming tandem position. In the 2D workflow, ultrasound measurements of the cervix width, uterine fundus width, and tandem-to-wall distance guided optimization of the initial point A plan. In the 3D workflow, baseline ultrasound measurements obtained during the first CT-planned fraction were recorded. In subsequent fractions, ultrasound was used to reproduce the initial applicator geometry, potentially avoiding repeat CT-based adaptive planning when measurements were consistent.

A representative case was used to illustrate the workflows. The initial 2D plan exceeded bladder and rectal limits. Ultrasound-planned 2D optimization reduced D2cc from 855 to 639 cGy and rectum D2cc from 533 to 421 cGy while maintaining high-risk clinical target volume D90% of 772 cGy. In the 3D workflow, ultrasound was used to reproduce the initial applicator geometry across fractions, enabling reproducible positioning and achieving dosimetry comparable to fully CT-guided plans (bladder D2cc: 639 vs 618 cGy; rectum D2cc: 421 vs 398 cGy; high-risk clinical target volume D90%: 772 vs 744 cGy).

In this representative case, ultrasound guidance may facilitate patient-specific 2D dose optimization and reproducible applicator positioning, facilitating optimization of bladder and rectal doses. Further studies are warranted to validate these findings.