Fig. 2

Tumor segmentation process on MRI. First, we manually segmented the whole tumor on axial T2WI images and labeled it as the intratumoral area. Second, “shrink” was defined as the tumor border automatically shrinking by 1 mm on the inside. “Dilate” was defined as automated dilation of the tumor border by 2 mm on the outside. “Dilate-shrink” resulted in a ring with a thickness of 3 mm. Thus, the peritumoral 3 mm area was obtained, including the most peripheral portion of the tumor and the surrounding tissues. Moreover, the peritumoral-mesorectal fat (MRF) area was obtained by drawing along the mesorectal fascia