THeragnostic Utilities for Neoplastic DisEases of the Rectum by MRI Guided Radiotherapy

Neoadjuvant chemoradiation therapy (nCRT) is the standard treatment modality for locally advanced rectal cancer (LARC), and patients achieving complete response (CR) generally have improved local control, metastasis-free survival, and overall survival. The aim of this clinical trial is to investigate the impact of radiotherapy dose escalation in rectal cancer by identifying poor responders during treatment using the Early Tumor Regression Index (ERI). Patients are treated using magnetic resonance-guided radiotherapy (MRgRT). ERI is calculated at fraction 10. Patients with an ERI value below 13.1 continue the standard treatment schedule, whereas patients with an ERI value above 13.1 undergo adaptive replanning with dose escalation up to 60.1 Gy to the residual tumor volume. Concomitant chemotherapy consists of fluoropyrimidine-based treatment, with oxaliplatin permitted in patients at high risk of recurrence. In selected high-risk patients, consolidation chemotherapy with three cycles of FOLFOX may be administered during the interval before surgery. Following protocol amendments, the study was expanded to include a total planned enrollment of 179 patients. Additional blood samples for circulating tumor DNA (ctDNA) analysis and stool samples for gut microbiome profiling are collected at predefined time points. These longitudinal multi-omics data are integrated with magnetic resonance imaging-based delta-radiomics features to develop composite biomarker models for prediction of treatment response. The primary outcome measures are complete response, defined as ypT0N0 after Total Mesorectal Excision (TME), ypT0 ycN0 after Local Excision (LE), or ycT0N0 in patients managed with Watch and Wait, and the prospective validation of the magnetic resonance-guided radiotherapy delta-radiomics predictive model.

Inclusion Criteria: * Histological proven adenocarcinoma of the rectum; * cT2-4, or cN0-2 (also extramesorectal nodes), or mesorectal fascia involvement for tumor (MRF+) or extramural venous invasion (EMVI+); * cM0; * No prior radiotherapy in pelvic region; * Tumour located between 0 and 15 cm above the anal verge; * Not mesorectal fascia involvement for tumor; * No extramesorectal nodes involvement; * No extramural venous invasion (EMVI); * No rectal mucinous adenocarcinoma histology; * No contra-indications for MRI; * ECOG 0-1; * Age over 18 years; * Adequate hematological function: granulocyte count \> 1500/microl, Hemoglobin level \> 10 g/dl, Platelet count \> 100000/microl, ALT/AST: 7-45 UI/L; * No other malignancies in the previous history (except skin and initial cervical cancer); * Absence of important comorbidities: severe cardiac or coagulative disease, moderate or severe restrictive/obstructive lung deficit, severe cognitive impairment, moderate and severe renal and hepatic impairment; * Absence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with the patient before registration in the trial; * Absence of pregnancy or lactating female patients; * Written informed consent. Exclusion Criteria: * Distant metastases (cM1); * Prior radiotherapy in the pelvic region; * Tumour located lower than 0 cm or higher than 15 cm above the anal verge; * Rectal mucinous adenocarcinoma histology; * Contra-indications for Magnetic Resonance Imaging (MRI); * Eastern Cooperative Oncology Group (ECOG) performance status score \>= 2; * Age under 18 years; * Inadequate hematological function (Granulocyte count \