Background: Delineation of the target volume is a time-consuming task in radiotherapy treatment planning, yet\r\nessential for a successful treatment of cancers such as prostate cancer. To facilitate the delineation procedure, the\r\npaper proposes an intuitive approach for 3D modeling of the prostate by slice-wise best fitting ellipses.\r\nMethods: The proposed estimate is initialized by the definition of a few control points in a new patient. The method\r\nis not restricted to particular image modalities but assumes a smooth shape with elliptic cross sections of the object.\r\nA training data set of 23 patients was used to calculate a prior shape model. The mean shape model was evaluated\r\nbased on the manual contour of 10 test patients. The patient records of training and test data are based on axial\r\nT1-weighted 3D fast-field echo (FFE) sequences. The manual contours were considered as the reference model.\r\nVolume overlap (Vo), accuracy (Ac) (both ratio, range 0-1, optimal value 1) and Hausdorff distance (HD) (mm, optimal\r\nvalue 0) were calculated as evaluation parameters.\r\nResults: The median and median absolute deviation (MAD) between manual delineation and deformed mean best\r\nfitting ellipses (MBFE) was Vo (0.9 �± 0.02), Ac (0.81 �± 0.03) and HD (4.05 �± 1.3)mm and between manual delineation\r\nand best fitting ellipses (BFE) was Vo (0.96 �± 0.01), Ac (0.92 �± 0.01) and HD (1.6 �± 0.27)mm. Additional results show a\r\nmoderate improvement of the MBFE results after Monte Carlo Markov Chain (MCMC) method.\r\nConclusions: The results emphasize the potential of the proposed method of modeling the prostate by best fitting\r\nellipses. It shows the robustness and reproducibility of the model. A small sample test on 8 patients suggest possible\r\ntime saving using the model
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