Based on preliminary findings on the motion error of the clinical target volume (CTV) in MR-guided adaptive radiotherapy (MRgART) for locally advanced rectal cancer (LARC), this study aims to reduce CTV-to-PTV margins and evaluate the complete response (CR) rate following MRgART in LARC patients. Additionally, it will investigate the safety and tolerability of MRgART, as well as its impact on:
3-year organ preservation rate
Local recurrence rate in patients under a "watch-and-wait" approach
3-year overall survival (OS), disease-free survival (DFS), and local progression-free survival (LPFS).
Furthermore, by analyzing ADC maps of the gross tumor volume (GTV), this study will characterize treatment responses and spatial deformation in metabolically active tumor subregions. These insights may inform future dose-escalation strategies for LARC radiotherapy, with the ultimate goal of improving prognosis and quality of life in this patient population.
Age 18-75 years, regardless of gender;
Staged as II/III (cT3-T4N0 or cT2-4N+, no distant metastasis) by MRI or endoscopic ultrasound (according to the AJCC Cancer Staging Manual, 8th Edition);
Fibrocolonoscopy or digital rectal examination confirms the lower border of the lesion is ≤10 cm from the anal verge;
Pathologically confirmed or reviewed diagnosis of rectal adenocarcinoma;
Presence of MRI-incompatible metal implants or claustrophobia;
Previous treatment with anti-PD-1/L1, anti-CTLA-4 immunotherapy, or other experimental immunotherapeutic drugs;
History of severe autoimmune diseases, including active inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis), rheumatoid arthritis, scleroderma, systemic lupus erythematosus, autoimmune vasculitis (e.g., Wegener's granulomatosis), etc.;
Symptomatic interstitial lung disease or active infectious/non-infectious pneumonia;
Single group
short course radiotherapy using MR-linac
RadiationPatients in the MRgART group will receive standard total neoadjuvant therapy (TNT) and surgical treatment, including short-course radiotherapy and chemotherapy, with the addition of immunotherapy at the investigator's discretion based on individual patient characteristics.
complete response (CR)
Absence of residual cancer cells on the final analysis of the tumor and lymph node
adverse events (AE)
Toxicity including anorexia, nausea, vomiting, diarrhoea, dermatitis, proctitis, urinary frequency/urgency according to CTCAE criteria v5.0
organ preservation rate
Sphincter Preservation rates 8 weeks post chemoradiotherapy at surgery.Percentage of patients who underwent sphincter salvage surgery after chemoradiotherapy
local recurrence rate (LCR)
disease-free survival (DFS)
Time from study entry to disease recurrence or death
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