Higher Radiation Dose to the Tumor May Help Avoid Surgery in Rectal Cancer Patients (REBOOT)

REctal Organ Preservation With a BOost Approach Using CBCT-based Online Adaptive radioTherapy

The goal of this prospective study is to evaluate if a higher radiation dose to the tumor can increase the organ preservation rate in non-locally advanced rectal cancer.

Study Overview

• Status: Recruiting
• Conditions: Rectal Cancer; Radiation Oncology
• Intervention / Treatment: Radiation: Simultaneous integrated boost to the tumor and positive mesorectal lymph nodes

Detailed Description

Rationale:

Organ preservation has emerged as a promising alternative to total mesorectal excision (TME) for non-locally advanced rectal cancer, aiming to reduce long-term functional impairments and improve quality of life. While magnetic resonance (MR)-guided radiotherapy boosts have shown potential in enhancing organ preservation rates, their high costs, prolonged treatment times and limited accessibility prevent widespread adoption. To address this gap in current treatment options, this study investigates a more accessible online adaptive boost strategy based on cone-beam computed tomography (CBCT) imaging, with the aim of expanding organ-preserving treatment options for rectal cancer patients.

Objective:

The primary objective of this study is to evaluate the organ preservation rate at two-year follow-up in patients with non-locally advanced rectal cancer. Secondary objectives include the assessment of clinical and pathological response rates, recurrence and survival outcomes, biological effects, treatment-related toxicities, bowel function, quality of life, tumor regression, CBCT-based workflow, and target and organ motion during treatment.

Study design:

This study is designed as a non-randomized, single arm, monocenter, phase II clinical trial.

Study population:

Patients (n=25) older than 18 years with non-locally advanced rectal cancer (defined as cT1-3N0-IM0) and a wish for organ preservation, who are referred for treatment.

Intervention (if applicable):

Addition of a simultaneous integrated boost (SIB) to the standard chemoradiotherapy (CRT) scheme of 2.0 Gy to the mesorectum. The radiotherapy scheme consists of 25 fractions, delivering 2.0 Gy per fraction to the mesorectum and 2.4 Gy per fraction to the tumor and positive mesorectal lymph nodes.

Main study parameters/endpoints:

This study aims to demonstrate that the investigated treatment approach results in an increased organ preservation rate of 70% at two year follow-up compared to historical data.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

Preclinical data confirmed the feasibility of the investigated SIB-CRT approach, demonstrating limited and clinically acceptable increases in organ at risk doses compared to the standard CRT scheme, all remaining well within clinical constraints. Furthermore, current literature supports the safety of dose escalation CRT strategies for rectal cancer, reporting manageable acute toxicity profiles, with symptoms typically returning to baseline after treatment. Based on these data, the investigated SIB-CRT strategy is expected to result in only minimal additional toxicities compared to standard CRT therapy.

The additional burden for the participants includes five MRI scans (approximately five hours total), scheduled alongside routine visits to minimize inconvenience. Patients will also be asked to complete three questionnaires at five time points, requiring approximately two hours in total, and to provide one additional 20 mL blood sample during three routine blood withdrawals.

The principal investigators consider the additional potential risk and burden for patients in the study to be acceptable. This study aims to significantly improve organ preservation rates, offering a meaningful benefit to individual patients by potentially avoiding TME surgery.

• Study Type: Interventional
• Enrollment (Estimated): 25
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Netherlands
  • South Holland
    • Rotterdam, South Holland, Netherlands, 3015 GD
      • Recruiting
      • Erasmus MC
      • Contact: Judith Sluijter, MSc; Phone Number: +31107035792; Email: j.sluijter@erasmusmc.nl
      • Principal Investigator: Claudia Schuurhuizen, PhD, MD

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Age ≥18 years
• Eastern cooperative oncology group (ECOG) performance status ≤2
• Histologically confirmed rectal adenocarcinoma
• Non-locally advanced rectal cancer, defined as (magnetic resonance imaging (MRI)-based) T1-3, N0/N1 (≤3 positive mesorectal lymph nodes), MX/M0
• Indication for curative treatment with organ preservation
• Discussed in the multidisciplinary tumor board (MTB)
• Written informed consent

Exclusion Criteria:

• Previous radiotherapy in the pelvic area
• Other malignancies, except for adequately treated basal cell carcinoma (BCC), at time of inclusion or within 3 years prior to inclusion
• Contra-indications for (chemo)radiotherapy or surgery
• Presence of lateral lymph nodes, cN2 status, extramural vascular invasion (EMVI) or mesorectal fascia involvement as seen on MRI
• Mucinous defined tumor on MRI
• Prior local excision of the primary tumor
• DPD (dihydropyrimidine dehydrogenase) deficiency
• Unable to understand the requirements of the study and to give written informed consent, as determined by the treating physician

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: Simultaneous integrated boost; Treatment arm, in which all participating patients will receive the simultaneous integrated boost (SIB)	Radiation: Simultaneous integrated boost to the tumor and positive mesorectal lymph nodes; Addition of a simultaneous integrated boost (SIB) to the standard chemoradiotherapy (CRT) scheme of 2.0 Gy to the mesorectum. The radiotherapy scheme consists of 25 fractions, delivering 2.0 Gy per fraction to the mesorectum and 2.4 Gy per fraction to the tumor and positive mesorectal lymph nodes.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Organ preservation	Organ preservation is considered unsuccessful if the rectum is surgically removed, a stoma is present, or a non-salvageable locoregional cancer recurrence is developed.	During two-year follow-up

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Rate of clinical complete response	Defined as the proportion of patients showing complete resolution of the tumor, assessed through endoscopy and MRI	Assessed at the two response assessments (14-16 weeks and 26 weeks after the start of treatment)
Rate of pathological complete response	Evaluated in patients undergoing surgical resection who did not achieve cCR. pCR is defined as the absence of any residual tumor in surgical specimens, assessed via histopathological examination.	During two-year follow-up
Local progression-free survival	Defined as the absence of tumor regrowth at or near the primary tumor site. Assessed through clinical evaluation and radiological imaging during the follow-up period.	During two-year follow-up
Distant progression-free survival	Defined as the absence of distant metastasis or death from any cause. Monitored with regular imaging and clinical evaluations during the follow-up period.	During three-year follow-up
Overall survival	Defined as the time from the start of treatment to death from any cause.	During three-year follow-up
Biological effect of the treatment	Blood analyses to assess circulating tumor DNA (ctDNA) as a potential biomarker to predict treatment response.	An additional 20 mL blood sample will be collected during scheduled blood withdrawal moments at three time points: (1) at baseline, (2) 2 weeks after start of treatment, and (3) 14-16 weeks after start of treatment.
Toxicities	Acute and late toxicities will be evaluated using the Common Terminology Criteria for Adverse Events (CTCAE) version 6.0. Both patient- and clinician-reported toxicity will be assessed during regular follow-up visits. Toxicities will be scored using the CTCAE scale, which ranges from Grade 0 (no toxicity) to Grade 5 (death), with higher grades indicating more severe adverse outcomes.	During two-year follow-up
Bowel function	Evaluated using the low anterior resection syndrome (LARS) score, completed by the patient through a self-administered questionnaire. by a questionnaire which the patient fills in by themself. The total score ranges from 0 to 42 points, with higher scores indicating more severe symptoms. The following categories are used: 0-20 points: No LARS, 21-29 points: Minor LARS, 30-42 points: Major LARS	Baseline and 3, 6, 12 and 24 months after start of treatment
Quality of Life (QoL)	Measured using the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 questionnaire, filled in by the patient. All of the scales and single-item measures range in score from 0 to 100. A high score for the functional scale and functional single-items represents a high or healthy level of functioning. A high score for the global health status/QoL scale represents a high QoL, whereas a high score for the symptom scale and single items represents a high level of symptomatology or problems.	Baseline and 3, 6, 12 and 24 months after start of treatment
Quality of Life (QoL)	Measured using the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-CR29 questionnaire, filled in by the patient. All of the scales and single-item measures range in score from 0 to 100. A high score for the functional scale and functional single-items represents a high or healthy level of functioning, whereas a high score for the symptom scales and single-items represents a high level of symptomatology or problems.	Baseline and 3, 6, 12 and 24 months after start of treatment
Tumor regression during treatment, monitored through weekly MRI scans	Weekly information to evaluate tumor regression during treatment. This includes five MRI scans in total, each requiring approximately one hour, including waiting time. Retrospectively, these scans will also be used to assess inter- and intrafractional motion of the target and OARs to investigate the potential for further margin reduction.	Baseline, and treatment week 2, 3, 4 and 5
Target and organ intra- and interfraction motion	Daily CBCT scans acquired pre-, intra-, and post-treatment will be retrospectively analyzed to assess inter- and intrafractional motion of the target and OARs to investigate the potential for further margin reduction in millimeters.	CBCT data is gathered daily as standard-of-care during the 5-week treatment
Feasibility of the CBCT-based SIB online adaptive workflow	Feasibility of the CBCT-based SIB online adaptive workflow including treatment time in minutes will be evaluated using treatment logs.	During the 5-week treatment course

Collaborators and Investigators

• Sponsor: Claudia Schuurhuizen

Study record dates

Study Major Dates

• Study Start (Actual): January 27, 2026
• Primary Completion (Estimated): August 1, 2029
• Study Completion (Estimated): August 1, 2030

Study Registration Dates

• First Submitted: March 13, 2026
• First Submitted That Met QC Criteria: May 29, 2026
• First Posted (Actual): June 1, 2026

Study Record Updates

• Last Update Posted (Actual): June 1, 2026
• Last Update Submitted That Met QC Criteria: May 29, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Rectal cancer; Radiation Oncology; 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: NL-010517

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

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