Analysis of Cross-site Heterogeneity
We first evaluated prostate segmentation performance using mean intersection over union (IoU), in order to ensure that the prostate regions can be predicted accurately. The IoU indicates the intersection between the predicted prostate contour and the ground truth mask label, which was measured on the test split of I2CVB. The mean IoU of prostate region, central gland, and peripheral zone are 0.843, 0.781, and 0.516, respectively. These results are comparable with the work of Alkadi, Taher, El-Baz and Werghi [4] which attained an IoU of 0.673 and 0.599 for the central gland and peripheral zone, respectively. It implies that the training set containing MR[5] images from 36 patients is already sufficient for accurate prostate segmentation. Additionally, the segmentation results are found to be promising on the image obtained from either 1.5-T or 3.0-T MRI[6] machine, indicating that the IoU measuring is not sensitive to the scanner types (see details in Supplementary Figure 1).