Erectile Function PRESERVation in Definitive Radiotherapy for Prostate Cancer by MRI-Enhanced Adaptive Sparing of the Neurovascular Bundle (EF-PRESERVE)

October 29, 2026 updated by: University of Zurich

Radiotherapy is a standard and highly effective treatment for prostate cancer that is confined to the prostate gland. One modern approach, called stereotactic body radiotherapy (SBRT), delivers treatment in just five sessions and has been shown to control prostate cancer as well as longer treatment schedules. Large clinical studies have demonstrated excellent cancer control rates after SBRT.

Although SBRT is effective, some men experience worsening erectile function after treatment. Researchers believe that reducing radiation exposure to the nerves and blood vessels involved in erections, known as the neurovascular bundles (NVBs), may help preserve sexual function.

The EF-PRESERVE study is evaluating whether a specialized MRI-guided treatment approach can safely reduce radiation dose to these structures while still delivering effective treatment to the prostate cancer.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Stereotactic body radiotherapy (SBRT) has evolved from an experimental modality into a guideline-supported treatment option for localized prostate cancer. Initial pooled consortium data across 1,100 patients demonstrated high efficacy and acceptable toxicity, which was subsequently confirmed by prospective phase III trials. The HYPO-RT-PC trial established the non-inferiority of 42.7 Gy in seven fractions, while PACE-B showed that 5-fraction SBRT without androgen deprivation therapy (ADT) achieved equivalent 5-year biochemical or clinical failure-free survival compared to conventional or moderately hypofractionated schedules (95.8% vs. 94.6%). Nevertheless, erectile dysfunction remains a frequent late toxicity, with clinician-reported CTCAE Grade more than 2 erectile dysfunction rising from 18% at baseline to 26.4% five years post-SBRT in PACE-B.

To mitigate this functional decline, the EF-PRESERVE study incorporates daily adaptive magnetic resonance imaging (MRI). Because standard cone-beam computed tomography (CBCT) lacks sufficient soft-tissue resolution to visualize structures like the neurovascular bundle (NVB), the ARTEMIS workflow acts as a scaleable alternative to integrated MR-linacs.

Patients are scanned on a dedicated MRI simulator to adjust target and NVB contours daily, then transferred via a dedicated shuttle system directly to a CE-marked CBCT linear accelerator for radiotherapy delivery.

Study Type

Interventional

Enrollment (Estimated)

48

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

  • Name: Matthias Guckenberger, Prof. Dr. med
  • Phone Number: +41 44 255 29 30

Study Locations

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

Male

Description

Inclusion Criteria:

  • Age ≥18 years

  • Histologically confirmed, low- or intermediate risk localized prostate cancer eligible for definitive prostate SBRT according to NCCN criteria as (Appendix 1):

    • cT1-cT2 and
    • PSA <20 ng/ml and
    • Gleason <8

  • At least at one side the DIL ≥5 mm from the NVB

  • WHO/ECOG performance status 0-2

  • Sexually active patients (i.e. satisfactory penetrative intercourse over the last 4 weeks)

  • Life expectancy >5 years

  • If ADT planned during radiotherapy:

    • Only short-course ADT for in total ≤6 months using oral GnRH-antagonists (e.g. Relugolix) for rapid testosterone recovery.

Exclusion Criteria:

  • DIL within <5 mm to NVB at both sides

  • High risk localized prostate cancer according to NCCN criteria as:

    • cT3-cT4 or
    • PSA ≥20 ng/ml or
    • Gleason ≥8

  • Non-localized prostate cancer (i.e. cN1 or cM1)

  • Insufficient erectile function preventing satisfactory penetrative intercourse (i.e. erectile dysfunction CTCAE (v6.0) Grade 3)

  • Sexually inactive patients (i.e. no penetrative intercourse over the last 4 weeks).

  • Previous pelvic radiotherapy (at any time)

  • Previous definitive treatment for prostate cancer (radiotherapy or prostatectomy at any time)

  • Contraindication to repeated MRI

  • Unable to lie in a supine position for estimated 30 min

  • Inability or contraindications to undergo the investigated intervention,

  • Clinically significant concomitant diseases,

  • Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

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

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Adaptive MR-Enhanced SBRT with NVB Sparing

Participants undergo ultra-hypofractionated stereotactic body radiotherapy (SBRT) delivered in 5 fractions. Prior to each fraction, patients are imaged on a MRI simulator to evaluate and adapt target volumes and neurovascular bundle (NVB) contours. Using the ARTEMIS transfer shuttle system, patients are moved directly to a standard C-arm CBCT linear accelerator. The NVB will be spared during radiotherapy delivery while maintaining a minimum target dose of 40 Gy to the dominant intraprostatic lesion (DIL). If clinically indicated, concurrent short-course androgen deprivation therapy (under 6 months) is limited strictly to oral GnRH antagonists (e.g., Relugolix).
Radiation: Daily Adaptive MR-Enhanced SBRT with Neurovascular Bundle Sparing

Patients receive daily adaptive ultra-hypofractionated SBRT (5 fractions) utilizing the ARTEMIS workflow. Before each fraction, patients undergo low-field MRI to adapt target and neurovascular bundle (NVB) contours based on daily anatomical changes. Patients are transferred in treatment position to a standard CBCT linear accelerator via a shuttle system. Radiotherapy intentionally spares the NVB (unilaterally or bilaterally depending on tumor proximity) to preserve erectile function, while ensuring the dominant intraprostatic lesion (DIL) receives at least 40Gy. Additional erection-related structures (internal pudendal artery, penile bulb, corpus cavernosum) are contoured for dosimetric analysis. Concurrent short-course ADT (not more than 6 months), if indicated, is restricted to oral GnRH antagonists (Relugolix) to allow rapid testosterone recovery.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Proportion of Patients with CTCAE v6.0 Grade ≥2 Erectile Dysfunction at 1 Year Post-SBRT
Time Frame: 1 year post-SBRT

Evaluates the proportion of sexually active patients who develop clinician-reported moderate to severe erectile dysfunction (defined as CTCAE v6.0 Grade ≥2) 1 year following the completion of adaptive MR-enhanced prostate SBRT with neurovascular bundle (NVB) sparing. The rate will be evaluated against historical controls from the PACE-B trial benchmark.
1 year post-SBRT

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Patient-Reported Erectile Function Change via IIEF-5 Score
Time Frame: Baseline, every 3 months for the first 1 year, and annually thereafter up to 5 years post-SBRT

Evaluates changes in patient-reported erectile function using the 5-item International Index of Erectile Function (IIEF-5) questionnaire. Scores range from 5 to 25, with lower scores indicating more severe erectile dysfunction (ED). The mean score change from baseline, the proportion of patients maintaining potency, and the proportion experiencing a clinically meaningful decline (≥4 point drop in IIEF-5 score) will be evaluated across time points.
Baseline, every 3 months for the first 1 year, and annually thereafter up to 5 years post-SBRT
Biochemical progression-free survival
Time Frame: Baseline, every 3 months for the first 1 year, and annually thereafter up to 5 years post-SBRT

Measurement of PSA, biochemical progression is defined according to phoenix criteria.
Baseline, every 3 months for the first 1 year, and annually thereafter up to 5 years post-SBRT

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Zurich

Investigators

  • Principal Investigator: Tiuri Kroese, MD PhD, University Hospital Zurich / University of Zurich

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

December 1, 2026

Primary Completion (Estimated)

December 1, 2029

Study Completion (Estimated)

December 1, 2033

Study Registration Dates

First Submitted

October 29, 2026

First Submitted That Met QC Criteria

October 29, 2026

First Posted (Actual)

November 4, 2026

Study Record Updates

Last Update Posted (Actual)

November 4, 2026

Last Update Submitted That Met QC Criteria

October 29, 2026

Last Verified

October 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • EF-PRESERVE

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

UNDECIDED

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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