In this prospective, open, multicenter, multi-arm, observational controlled study, the investigators investigated the impact of different pelvic radiation doses of anal cancer and rectal cancer patients on the dynamic changes of anal function, and analyzed the correlation between the changes of anal function and the score of anal incontinence in the radiation dose≤50Gy group and \>50Gy group. The study population includes 124 patients with anal canal cancer or rectal cancer who have received sphincter preservation treatments (including radiochemotherapy), aged from 18 to 75 years old undergoing sphincter preservation treatments at The Sixth Affiliated Hospital, Sun Yat-sen University and Nanfang Hospital, Southern Medical University. The primary outcome is the average resting pressure of anal sphincter. The secondary outcomes are maximum anal sphincter contraction pressure and Wexner continence score. Evaluations will be carried out at the following stages: baseline (T1), after radiotherapy or chemotherapy (before surgery, T2), after surgery (before closing the temporary stoma, T3), and at follow-up visits (every 3 to 6 months, T4, T5……). Follow-up for each patient will be at least 2 years.