Among all types of cancer, gynecological malignancies belong to the 4 th 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 userdefined 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.
DESCRIPTION OF PURPOSEGynecological malignancies which include endometrial, vaginal/vulvar and cervical cancers represent the 4 th most frequent type of cancer among women and a major cause of death around the world 1 . The standard procedure for primary or recurrent treatments of these types of cancer consists of external-beam radiation (EBR) followed by brachytherapy. During the brachytherapy procedure needle like catheters carrying a radiation source are inserted into the patient in close proximity to the tumor in order to directly irradiate the malignant tissue 2 . A crucial step in planning the applied amount and distribution of radiation is the segmentation of the tumor and adjacent organs-at-risk (OAR) potentially exposed to radiation. The most common OAR segmented in gynecological brachytherapy include the urinary bladder and the rectum/sigmoid colon. In general cases, the performing physician might have to outline several structures in more than 80 slices, which is a tedious task.Over the last decades various fully automatic segmentation methods have been proposed to support this timeconsuming segmentation process. However, the development of fully automatic segmentation tools remains problematic due to variability in pelvic organ shape and poor soft tissue depiction. None of these automatic analysis tools can guarantee robust results or achieved clinical approval. Moreover, they mostly lack necessary intervention methodologies and provide little final control by the medical do...