RecruitingPhase 2Radiation therapyA Pilot Study Evaluating β-hydroxybutyrate Supplementation Concomitant to Short-Course Radiotherapy Followed by Immunotherapy Combined With CAPEOX Neoadjuvant Therapy in Patients With Locally Advanced Rectal CancerThis study is a prospective phase II clinical trial aimed at exploring the potential benefits of supplementing β-hydroxybutyrate with existing short course radiotherapy sequential immunotherapy and CAPEOX therapy.