Automatic contouring using deformable image registration for tandem-ring or tandem-ovoid brachytherapy

Area of Science:

• Radiation Oncology
• Medical Imaging
• Gynecologic Oncology

Background:

• Image-guided brachytherapy (IGBT) is crucial for cervical cancer treatment.
• Accurate contouring of targets and organs at risk (OARs) is essential for optimal dose delivery.
• Manual contouring is time-consuming and subject to inter-observer variability.

Purpose of the Study:

• To evaluate the efficacy of deformable image registration (DIR)-based automatic contouring in 3D computed tomography (CT)-based IGBT for cervical cancer.
• To compare DIR-based automatic contouring with manual contouring for tandem-ring (T-R) and tandem-ovoid (T-O) applicators.
• To assess the dosimetric impact of DIR-based contouring on treatment plans.

Main Methods:

• Retrospective analysis of CT images from 28 cervical cancer patients undergoing IGBT with T-R or T-O insertion.
• Hybrid DIR performed between the first fraction CT and subsequent CTs, using the first CT as the reference.
• Evaluation of contour similarity using Dice Similarity Coefficient (DSC) and comparison of mean volumes; dosimetric analysis of dose-volume parameters.

Main Results:

• DIR-based automatic contours generally showed larger volumes than manual contours, with statistical significance for the small bowel.
• Lower DSC scores were observed for the small bowel and sigmoid.
• DIR-based contouring was less accurate for the rectum with T-O applicators compared to T-R.
• Volume differences did not significantly impact dose-volume parameters, and treatment plans covered DIR contours.
• DIR significantly reduced contouring time (2.0 ±0.1 min) compared to manual contouring (14.0 ±0.4 min) (p < 0.001).

Conclusions:

• DIR-based automatic contouring is a successful and safe method for T-R and T-O applications in cervical IGBT.
• The technique significantly decreases contouring time, enhancing efficiency in clinical practice.
• Automatic contouring using DIR is a time-saving and viable approach for image-guided brachytherapy.