The next step is to propagate

this contour from the midgland to the remaining slices (Fig. 1c). To do so, two ellipsoids are fitted to the midgland contour, one to act as a guide selleck chemical for the volume superior to the midgland and one for the volume inferior. These ellipsoids are uniquely defined by the midgland ellipse and the intersection of the longitudinal axis of the prostate passing through the center of the midgland contour and the base-1 (one slice superior to the base slice) and apex + 1 (one slice inferior to the apex) slices. The intersection of these ellipsoids with the image slices create elliptical contours, which are used as the initial estimates of the prostate boundary on those slices. These contours,

similar to what was done in the midgland image, serve as a guide to the IMMPDA edge detection algorithm to obtain image-based elliptical contours for each image slice. To ensure smoothness in the axial direction find more (i.e., from one slice to the next), a tapered ellipsoid is fitted to the contours of all images. This shape has an elliptical cross-section with tapering along its longitudinal axis. Finally, the 3D volume is sliced at image depths and the elliptical contours are tapered and warped using the initial values to match the original images ( Fig. 1d). Further details and mathematical equations of the algorithm can be found in our earlier reports [16] and [17]. We will hereafter refer to the algorithm and the resulting contours

as the “tapered ellipsoid segmentation (TES) algorithm” and “TES contours.” Figure 2 shows a snapshot of the graphical user interface used in the VCC for prostate contouring using the TES method. This algorithm has been routinely used to support clinical treatment planning at VCC since January 2009 and to this date more than 600 cases have been planned using our proposed method. LDR brachytherapy is indicated at the BCCA for low- and intermediate-risk prostate cancer (all of: pretreatment DOK2 prostate-specific antigen level ≤20, Gleason score ≤7, clinical stage ≤T2c [International Union Against Cancer (UICC) 1997]). Three to four weeks before the implant, a radiation oncologist (RO) performs a volume study in which 2D ultrasound images are obtained at 5 mm intervals with the use of a transrectal ultrasound probe (B&K Pro-Focus System B-series ultrasound machine; BK Medical, Peabody, MA, with the MFI Biplane Transducer, 640 × 480 pixels image size, 0.15 mm × 0.15 mm pixel size). The patient is in the dorsal lithotomy position during imaging. For applying the TES algorithm on these clinical images, appropriate institutional and ethics committee approval have been obtained. The TES algorithm is initiated by a radiation therapist to produce a CTV called the “Raw TES CTV.