RecruitingPhase 3Radiation therapyA Clinical Trial Comparing Long-Course Versus Short-Course Radiotherapy Followed by Immunotherapy Combined With Total Neoadjuvant Therapy (TNT) to Long-Course Radiotherapy Followed by TNT in Locally Advanced Rectal CancerThis study is a national multicenter, prospective randomized, placebo- controlled Phase III clinical trial designed to investigate the potential therapeutic benefit of immunotherapy combined with total neoadjuvant therapy (TNT) and to compare the efficacy of different radiotherapy modalities followed by immunotherapy.