Simultaneous Boost in Neoadjuvant Radiotherapy for Rectal Cancer

Inclusion Criteria: 1. Age ≥18 and \<80 years 2. Histologically confirmed rectal adenocarcinoma 3. Tumor located within 10 cm from the anal verge 4. MRI staging: T3-T4 and/or N+, M0 (AJCC 8th edition) 5. ECOG performance status 0-2 6. Adequate bone marrow function: WBC ≥3×10⁹/L, ANC ≥1.5×10⁹/L, PLT ≥100×10⁹/L, Hb ≥90 g/L 7. Adequate liver function: TBIL ≤1.5 × ULN, ALT/AST ≤2.5 × ULN 8. Adequate renal function: Cr ≤1.5 × ULN or CCr ≥60 mL/min 9. Signed informed consent Exclusion Criteria: 1. Prior rectal cancer surgery 2. Prior induction chemotherapy, immunotherapy, or pelvic radiotherapy 3. History of other malignancies 4. History of chronic colitis, ulcerative colitis, or nonspecific proctitis 5. Pregnant or breastfeeding women 6. Active infection or fever 7. Severe uncontrolled comorbidities (e.g., unstable heart disease, renal disease, chronic hepatitis, uncontrolled diabetes, psychiatric disorders) 8. Inability to comply with study protocol