Automatic Contouring Using Deformable Image Registration for Tandem-Ring or Tandem-Ovoid Brachytherapy

Abstract

To investigate the effectiveness of deformable image registration (DIR)-based automatic contouring for tandem-ring (T-R) or tandem-ovoid (T-O) 3-dimensional computed tomography (CT)-based image-guided brachytherapy (IGBT).CT images of 28 patients with intact cervical cancer were retrospectively analyzed. The selected group had T-R or T-O insertion for IGBT. The hybrid DIR was performed between the first fraction CT and the subsequent CTs of the IGBT. The first IGBT CT images were the reference images. All DIRs were performed based on these 1st IGBT CT scans. The contour similarities between the manual and automated segmentations were evaluated with Dice Similarity Coefficient (DSC) score. Mean volumes of the structures delineated manually and automatically were compared. Finally, dosimetric comparisons were performed in order to obtain how contour differences affect the target and organs at risk (OARs) doses.In general, mean volumes of the automatic contours were larger than manual contours for both T-R and T-O insertions. However, the difference in the volume was statistically significant for the small bowel only (P < 0.05 and P < 0.01 for T-R and T-O, respectively). The DSC scores were small for small bowel and sigmoid in both applicator sets. When the two different applicator sets were compared, the performance of DIR-based contour propagation for the rectum was worse in the T-O than the T-R application. Dosimetric comparisons showed that the volume differences between the manual and propagated contours did not affect the dose distributions. The plans based on manually contoured targets also covered the DIR contours well. The average time for DIR was 2 ± 0.1 minutes per fraction compared to 14 ± 0.in manual contouring (P < 0.001).DIR-based automatic contouring of the structures seems successful for both the T-R and T-O applications in cervical IGBT. DIR significantly decreased the time for contouring. Our results indicate that automatic contouring in IGBT is safe and time-saving.