In the screening and identifying of colon and rectum malignancy, computed tomography colonography (CTC) is a highly effective imaging technique, albeit patients receiving a significant effective dose. Accordingly, patient dose evaluation is an important need, seeking to ensure benefits outweigh the projected cancer risk. Objective: For CTC procedures carried out in the Radiology Department, Medical Imaging Operation Services, King Fahad Medical City (KFMC), evaluation is done using the current American College of Radiology (ACR) imaging protocol and concomitant patient-effective doses. Study is carried out on a sample size of 55 CTC procedures, involving 25 males (45%) and 30 females (55%). The patients were classified as follows: two groups based on CT machine; four groups based on the applied protocol; and three groups based on the procedure results. All procedures were carried out using two machines, the products of two different vendors (a GE Healthcare DISCOVERY CT 750 HD 64 slices dual-energy scanner and a Philips Brilliance CT 64 slices scanner). The overall mean, standard deviation (SD), median, and range of the effective dose (in mSv) were 11.57 ± 7.75, 9.25 (2.17–31.93). Automatic tube current modulation (ATCM) shows a significant increase in CTDIvol up to 69% and effective dose (mSv) up to 95% than the manual tube current (mA) compared to the standard protocol. The CT protocol variation results in a three-fold variation in patient-effective dose. The technologist role is crucial in selecting a noise reference based on patient weight and adjusting tube current per slice to avoid overexposure during ATCM protocol.