Data collection and preparation
Cancer
MAY, RECTAL CANCER, CANCER
As a plot study approved by the institutional review board a cohort of 141 patients treated at our institute (Peking University Cancer Hospital) between March 2020 and May 2022 were retrospectively included in this study. The patients were diagnosed with Stage II to III rectal cancer, and received neoadjuvant chemoradiotherapy, which is the standard treatment for locally advanced rectal cancer. The cohort were categorized into training group (121/141) and testing group (20/141) by random sampling (Fisher-yates shuffle). Over the training group, 69 were female and 52 were male, and the ages ranged from 33 to 74 with the median value of 61. Over the testing group, 13 were female and 7 were male, and the ages ranged from 39 to 72 with the median value of 63.All the patients were immobilized by pelvis thermoplastic in the supine posture and received CT and MRI simulations respectively. The CT images were acquired on a big-bore RT-specific CT scanner (Somation Sensation Open, Siemens Healthineers, Germany) with 5-mm slice thickness, and MRI T2 and T1 images on a 3.0-T MR-Sim scanner (MAGNETOM Skyra, Siemens Healthineers, Germany) with 5-mm slice thickness as well. The CT and MRI images were imported into the Eclipse Treatment Planning System (Varian Medical System Inc., USA) for target and organs-at-risk (OAR) delineation. Due to the different imaging contrast properties between CT and MRI, CTV structures were contoured in CT images, and GTV structures in MRI T2 images. Note that the CTV and GTV definitions in this study were consistent with the NCCN and ESMO guideline. The CTV and GTV contours of all the patients were reviewed by two senior physicians, and therefore were used as ground truth (GT) herein.