In this article, we provide an extensive clinical validation of the segmentation method from our earlier work (17), which is being used as a part of the LDR prostate brachytherapy procedure at the Vancouver Cancer Center and BC Cancer Agency (BCCA). Currently, the semiautomatic contour is first approved and modified, if required, before treatment planning. The results from our earlier work (17) suggested that such modifications are so minor that

they Vemurafenib in vitro may not be necessary in many cases. Indeed, a volumetric study showed that the semiautomatic segmentation error is within the range of inter- and intraobserver variability of manual contours in most regions of the prostate, which suggests that on average, no greater variation is introduced by using the algorithm than would be expected if a different oncologist performed the contour. The aim of this article is to extend the volumetric analysis conducted in our earlier work (17) to a larger data set and to show that the segmentation error leads to a dose error that is negligible. For the sake of readability SB431542 cost and completeness, we will provide a summary of

the segmentation algorithm from our earlier report (17). As per the BCCA protocol, the contouring algorithm assumes that a smooth and symmetric CTV is the aim of the oncologist, who consequently positions the prostate symmetrically across the midsagittal plane during TRUS image acquisition. The use of symmetric contours for treatment planning is widely practiced as part of the popular Seattle preplanning technique (6). Symmetric contours lead to simple treatment plans that are also simple to change to ensure adequate dose coverage should the shape, size, or position of the prostate change significantly with respect to the volume study. By maintaining symmetry during the preoperative volume study, reproducing the prostate image intraoperatively is relatively simple because the body’s long axis can be identified easily in the dorsolithotomy position and does not change over time or in response

to shifting leg positions and tissue relaxation. However, replicating a specific arrangement of misalignment is not easily accomplished because there are numerous ways to misalign the axes of the TRUS probe and of the prostate, 4��8C each of which creates a somewhat different visual pattern of asymmetry on the TRUS images. We emphasize the need to maintain proper body alignment throughout both the TRUS image acquisition and intraoperatively because, in most cases, maintaining this is sufficient to achieve symmetry on all slices. Effective implementation of a symmetric planning approach is demonstrated by our 2009 population-based report with only 35 recurrence events among the first 1006 consecutive BCCA prostate brachytherapy patients who underwent implant between July 1998 and October 2003 (18).