Seroma Visualization and Implant Accuracy in Permanent Breast Seed Implant Brachytherapy

This study aimed to evaluate the relationship between seroma visualization and seed placement accuracy in permanent breast seed implant brachytherapy (PBSI).

At the time of planning computed tomography (CT), 10 patients receiving PBSI were imaged with spatially co-registered 3-dimensional ultrasound (US). Seromas were independently contoured by 3 radiation oncologists on CT and US scans. Intra- and interuser conformity indices (CIs) were used as a surrogate for seroma visualization. Intermodality visualization differences were assessed by defining consensus contours, clinical target volume (CTV)_CT and CTV_US, and evaluating the CI and the centroid position and volume differences. Seed placement accuracy was represented by the differences between the planned and implanted seed positions (displacements). Correlations among total, systematic, and random seed displacements and seroma visualization metrics were assessed.

The median (range) intra-user CI of CT seroma contouring was 0.60 (0.46-0.72), and the median interuser CIs were 0.46 (0.38-0.58) and 0.50 (0.29-0.67) on CT and US, respectively. The CTV_US was a mean 68% ± 12% smaller than CTV_CT and differed in centroid position by 8 ± 3 mm. Seeds were placed, on average, 10 ± 5 mm from their planned positions, and intrapatient systematic displacements were observed. The mean seed displacements for the implants were shown to correlate with interuser CI on CT (r = .74; P = .01) and volume differences between CTV_CT and CTV_US (r = .65; P = .04), but not with intrauser CI, intermodality CI or centroid differences. Systematic displacements were correlated with interuser CT CI (r = .67; P = .03) and intermodality volume difference (r = .64; P = .04), but random seed displacements were independent of all evaluated metrics.

Consistency in seroma delineation in treatment planning and differences between seroma visualized on CT and US scans are associated with seed placement accuracy in PBSI. Efforts to enhance seroma visualization in treatment planning and implant guidance may have a positive impact on treatment quality and should be pursued to facilitate the widespread implementation of this technique.