Organ Preservation in Rectal Cancer by Dose Escalated MR Guided Adaptive Radiotherapy (MARS)

This study is testing whether radiation delivered with MRI guidance using a so-called MR-linac in distal rectal cancer can result in a high rate of organ preservation. Patients will receive radiotherapy together with standard chemotherapy.

Study Overview

• Status: Recruiting
• Conditions: Rectal Cancer
• Intervention / Treatment: Radiation: Dose escalated radiotherapy using a 1.5 T MR-Linac

• Study Type: Interventional
• Enrollment (Estimated): 100
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Cihan Gani, MD; Phone Number: +4970712982165; Email: cihan.gani@med.uni-tuebingen.de

Study Locations

• Germany
  • Baden-Wurttemberg
    • Tübingen, Baden-Wurttemberg, Germany, 72074
      • Recruiting
      • University Hospital Tübingen

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Patients with histologically confirmed diagnosis of rectal cancer localized between dentate line and 12 cm from the anocutaneous line
• Any MRI staged rectal cancer meeting the following criteria
• cT1-cT3 and
• cN0 -cN1 and
• cM0
• Inclusion of UICC Stage I tumors only if unsuitable for endoscopic resection or if primary surgery would require permanent colostomy or deep anastomosis with expected poor organ function.
• Tumor affects less than 70% of the rectal circumference.
• Maximum longitudinal extension of the tumor less than 8 cm on MRI

• MR-Staging requirements: High-resolution, thin-sliced (i.e.

  ≤3mm) magnetic resonance imaging (MRI) of the pelvis.

• Cross-sectional imaging of the abdomen and chest to exclude distant metastases.
• Aged at least 18 years. No upper age limit.
• WHO/ECOG Performance Status ≤ 1
• Adequate hematological, hepatic, renal and metabolic function parameters
• Informed consent of the patient

Exclusion Criteria:

• Lower border of the tumor localised more than 12 cm from the anocutaneous line as measured by rigid rectoscopy
• Distant metastases
• Preexisting fecal incontinence for solid stool
• Prior antineoplastic therapy for rectal cancer
• Prior radiotherapy of the pelvic region
• Subject pregnant or breast feeding, or planning to become pregnant within 6 months after the end of treatment.
• Subject (male or female) is not willing to use highly effective methods of contraception (per institutional standard) during treatment and for 6 months (male or female) after the end of treatment (adequate: oral contraceptives, intrauterine device or barrier method in conjunction with spermicidal jelly).
• Other concomitant antineoplastic therapy
• Serious concurrent diseases, including neurologic or psychiatric disorders (incl. dementia and uncontrolled seizures), active,uncontrolled infections, active, disseminated coagulation disorder
• Other primary tumors with an estimated life expectancy of less than three years
• Contraindications for treatment with 5-Fluorouracil or Capecitabine
• Psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule (these conditions should be discussed with the patient before registration in the trial).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: MR guided dose escalated radiotherapy; A dose of 65 Gy is delivered to the primary tumor and affected lymph nodes.	Radiation: Dose escalated radiotherapy using a 1.5 T MR-Linac; Dose escalated radiotherapy using a 1.5 T MR-Linac is given to the primary tumor and affected lymph nodes in an online adaptive manner

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Two year TME-free survival	Patients alive and without TME-surgery	Two years from the start of radiotherapy

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Clincal complete response rate	Patients who have no evidence of residual tumor on MRI and rectoscopy	three months after the end of radiotherapy

Collaborators and Investigators

• Sponsor: University Hospital Tuebingen

Study record dates

Study Major Dates

• Study Start (Actual): January 7, 2026
• Primary Completion (Estimated): January 1, 2029
• Study Completion (Estimated): January 1, 2029

Study Registration Dates

• First Submitted: January 1, 2026
• First Submitted That Met QC Criteria: January 1, 2026
• First Posted (Actual): January 13, 2026

Study Record Updates

• Last Update Posted (Actual): February 17, 2026
• Last Update Submitted That Met QC Criteria: February 14, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Keywords: organ preservation
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Intestinal Diseases; Gastrointestinal Neoplasms; Digestive System Neoplasms; Digestive System Diseases; Gastrointestinal Diseases; Colorectal Neoplasms; Intestinal Neoplasms; Rectal Diseases; Rectal Neoplasms
• Other Study ID Numbers: 311/2025BO1

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: Data will be shared if a sound scientific proposal if provided.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No