  Among all types of cancer, gynecological malignancies belong to the 4th most
frequent type of cancer among women. Besides chemotherapy and external beam
radiation, brachytherapy is the standard procedure for the treatment of these
malignancies. In the progress of treatment planning, localization of the tumor
as the target volume and adjacent organs of risks by segmentation is crucial to
accomplish an optimal radiation distribution to the tumor while simultaneously
preserving healthy tissue. Segmentation is performed manually and represents a
time-consuming task in clinical daily routine. This study focuses on the
segmentation of the rectum/sigmoid colon as an Organ-At-Risk in gynecological
brachytherapy. The proposed segmentation method uses an interactive,
graph-based segmentation scheme with a user-defined template. The scheme
creates a directed two dimensional graph, followed by the minimal cost closed
set computation on the graph, resulting in an outlining of the rectum. The
graphs outline is dynamically adapted to the last calculated cut. Evaluation
was performed by comparing manual segmentations of the rectum/sigmoid colon to
results achieved with the proposed method. The comparison of the algorithmic to
manual results yielded to a Dice Similarity Coefficient value of 83.85+/-4.08%,
in comparison to 83.97+/-8.08% for the comparison of two manual segmentations
of the same physician. Utilizing the proposed methodology resulted in a median
time of 128 seconds per dataset, compared to 300 seconds needed for pure manual
segmentation.
