ABlative Radiotherapy (for) Unfavorable Prostate Tumors 2.0 (ABRUPT 2)

February 9, 2026 updated by: Stefano Arcangeli, University of Milano Bicocca

Single-Dose Image-Guided Radiotherapy (IGRT) With Focal Boost to the MRI-defined Macroscopic Tumor Volume for Intermediate Unfavorable and High Risk Prostate Cancer

Published clinical evidence confirms that a single dose of 24 Gy provides unprecedented long-term local control in primary and metastatic prostate cancer with safe toxicity profiles, provided that exposure of surrounding healthy tissues is critically assessed with fulfillment of strict constraints and dose distribution is accomplished using image guidance and tracking tools. In the present trial, intermediate unfavorable and selected high-risk organ-confined prostate cancer patients will undergo Single Dose Radiation Therapy (SDRT) With Focal Boost to the MRI-defined Macroscopic Tumor Volume by means of image-guided volumetric intensity-modulated arc radiotherapy (IGRT-VMAT) and state-of-the-art treatment-planning and quality assurance procedures. Androgen Deprivation Therapy (ADT) type and duration has been set as per standard of care, in accordance with current recommendations and guidelines. The results of the study will enable us to find out if the new, shorter treatment (1 doses of radiotherapy), has a similar level of side effects as the 5 dose treatment and is suitable for further study.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

ABRUPT 2.0 is a non-comparative, randomized phase II trial focusing on acute genitourinary (GU) toxicity as the primary endpoint in a similar patient population. Acute GU toxicity was selected because it has been shown to be predictive of late GU toxicity and represents a clinically meaningful early safety endpoint. Using PACE-C as a benchmark, the trial is designed to test the hypothesis that acute GU toxicity in each treatment arm will remain within predefined clinically acceptable limits. Patients are randomized in a 1:1 ratio to receive either 36.25 Gy SBRT in five fractions over two weeks or 24 Gy SDRT with urethra-sparing and a focal isotoxic GTV boost up to 27 Gy. Randomization is performed using a minimization algorithm balanced for NCCN risk group (intermediate-unfavorable vs selected high-risk) and incorporating a random element. Treatment allocation is not masked. All participants are treated at a single institution (Fondazione IRCCS San Gerardo dei Tintori and University of Milan-Bicocca).

All patients undergo non-contrast-enhanced CT and mpMRI simulation on the same day. Anatomic reproducibility is ensured through rectal micro-enema administration. In the SDRT arm, the bladder is filled with 150 mL of saline solution via a 16-F Foley catheter before simulation and treatment delivery. In the five-fraction SBRT arm, bladder preparation consists of drinking 500 mL of still water 30-45 minutes before simulation and each fraction. The use of a hyaluronic acid rectal spacer is encouraged and left at physician's discretion. Patients are positioned supine with arms placed over the chest. CT images and T2-weighted 3D MRI scans are fused for target and OAR delineation. The GTV was defined as the visible tumor lesion on mpMRI in collaboration with an experienced radiologist. The clinical target volume (CTV) encompasses the entire prostate gland and seminal vesicles. The PTV is generated by applying a 3-mm isotropic margin to the CTV. OARs include the urethra, bladder, bladder trigone, rectum, femoral heads, penile bulb, bowel, and neurovascular bundles. In the SDRT arm, a 3-mm isotropic margin is added to the urethra, bladder, and rectum to generate planning OAR volumes (PRV), and the minimum prescribed dose to the GTV and PTV is constrained by OAR dose limits. In the five-fraction SBRT arm, the treatment prescription consists of 36.25 Gy administered in five fractions over two weeks on alternate days, with a mandatory additional CTV dose target of 40 Gy. Both dose levels are prescribed to the isodose covering 95% of the target volume, with controlled dose heterogeneity within the target and a maximum PTV dose of 42 Gy to protect the urethra by limiting its estimated dose to ≤95Gy EQD2. No focal boost is delivered to the GTV in this arm. In both arms, treatment plans are optimized using a 10-MV flattening-filter-free single partial arc (140°-220°), allowing a substantial reduction in treatment time.

In order to preserve identical 3-mm PTV margins in both treatment arms, continuous intrafraction motion monitoring is systematically implemented. Two distinct non-ionizing real-time tracking systems are employed. In the SDRT arm, prostate motion is monitored using an electromagnetic transmitter embedded within a urethral catheter. In the five-fraction SBRT arm, real-time tracking is performed using a 4D transperineal ultrasound system. All treatments are delivered on a linear accelerator. Initial patient positioning is verified using cone-beam CT with soft-tissue matching. Beam delivery is interrupted and patient positioning corrected whenever prostate displacement exceeds 2.5 mm in any of the three spatial directions.

The sample size has been determined using a Simon two-stage minimax design, independently powered for each treatment group to test whether the incidence of acute G2+ toxicity is significantly different from 51% (null hypothesis), using a one-sided 0.05-level test with 90% power to detect a true toxicity rate of 25%. Each group includes 29 patients (stage 1: 25 patients, and stage 2: 4 patients). The trial continued to complete stage 2 as 9 or fewer patients among the first 25 will develop G2+ GU toxicity within 3 months after treatment. If 10 patients or fewer in a group will develop G2+ GU toxicity, this would allow rejecting the null hypothesis of a 51% toxicity rate, which is 1.5 times higher than the rate observed in the PACE-C trial. Under the two-stage design, interim analysis will be provided after 10 patients are treated in each group to ensure that acute toxicity rates are within acceptable limits before proceeding to full accrual. The trial is not powered to detect statistical differences between the two treatment groups; therefore, data will be analysed descriptively.

Study Type

Observational

Enrollment (Estimated)

58

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 Locations

  • Italy
    • MB
      • Monza, MB, Italy, 20900
        • Recruiting
        • Radiation Oncology, Fondazione IRCCS San Gerardo dei Tintori
        • Contact:

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

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Probability Sample

Study Population

Unfavorable Intermediate and Selected High Risk Prostate Cancer (no cT3b and PSA > 20 ng/mL allowed), as per NCCN definition

Description

Inclusion Criteria:

  • Histologically proven prostate adenocarcinoma;
  • Intermediate and High risk disease, as per the NCCN definition;
  • a PI-RADS 3-5 dominant intraprostatic lesion on multiparametric MRI (mpMRI);
  • N0M0 at staging with standard techniques (Bone Scan and Abdominal CT) or (preferably) PSMA PET-CT;
  • World Health Organization performance status 0-1;
  • Life expectancy of > 5 years, in the opinion of the investigator;
  • IPSS score must be ≤ 15 (alpha blockers allowed);
  • Prostate gland volume ≤100 g as estimated by computed tomography (CT), ultrasound, or MRI.

Exclusion Criteria:

  • ≥T3b disease according to the 8th AJCC classification;
  • PSA>20 ng/ml;
  • Previous local treatment of the prostate with surgery (radical prostatectomy or cryotherapy) or transurethral resection;
  • Previous radiotherapy to the pelvis;
  • Presence of a periurethral dominant lesion;
  • Previous invasive malignancy unless disease free for a minimum of 5 years;
  • Active Crohn's Disease or Ulcerative Colitis;
  • Presence of hip prostheses.

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

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
5 Fx SBRT
Patients will receive 36.25 Gy SBRT in five fractions over two weeks
Radiation: SBRT
Stereotactic Body Radiotherapy. Ultrahypofractionated radiotherapy.
1 Fx SDRT
Patients will receive 24 Gy SDRT with urethra-sparing and a focal isotoxic GTV boost up to 27 Gy
Radiation: SDRT
Single Dose Radiation Therapy. Ultrahypofractionated radiotherapy.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Number of participants with acute genitourinary treatment-related adverse events as assessed by CTCAE v.5.0
Time Frame: 3 months
The primary endpoint is the cumulative incidence of acute CTCAE v5.0 grade ≥2 genitourinary (GU) toxicity from the start of radiotherapy to 3 months post-treatment. Toxicity assessments are performed at baseline, end of treatment, and at 1, 2, and 3 months after radiotherapy.
3 months

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Number of participants with late genitourinary treatment-related adverse events as assessed by CTCAE v.5.0
Time Frame: 1, 2 and 5 years
To assess treatment related late genitourinary (GU) toxicity
1, 2 and 5 years
Number of participants with treatment-related adverse gastrointestinal events as assessed by CTCAE v.5.0
Time Frame: 3 months, 1, 2 and 5 years
To assess treatment related gastrointestinal (GI) acute and late toxicity
3 months, 1, 2 and 5 years
QUALITY OF LIFE (QOL) assessed by EORTC QLQ-C30. For QoL domain minimum score (=0) means worst QoL and maximum score (=100) means best QoL.
Time Frame: 3 months, 1, 2 and 5 years
To measure symptom scores for each QOL domain (overall QoL) by EORTC Questionnaire
3 months, 1, 2 and 5 years
Number of participants with voiding symptoms assessed by International Prostatic Symptoms Score (IPSS), ranging from 0 (best) to 35 (worst)
Time Frame: 3 months, 1, 2 and 5 years
To assess voiding symptoms using IPSS
3 months, 1, 2 and 5 years
Number of participants with erectile dysfunction assessed by International Index of Erectile Function Questionnaire ranging from 5 (worst ) to 25 (best)
Time Frame: 2 and 5 years
To assess erectile function using IIEF 5
2 and 5 years
Number of participants with biochemical relapse assessed by PSA (Phoenix definition)
Time Frame: 2 and 5 years
To assess biochemical outcome using serum PSA levels
2 and 5 years
QUALITY OF LIFE (QOL) assessed by EORTC PR-25. For QoL domain minimum score (=0) means best QoL symptoms and maximum score (=100) means worst QoL symptoms
Time Frame: 3 months, 1, 2 and 5 years
To measure symptom scores for each QOL domain (urinary incontinence and bowel dysfunction) by EORTC Questionnaire
3 months, 1, 2 and 5 years

Collaborators and Investigators

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

Sponsor

University of Milano Bicocca

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 (Actual)

January 28, 2026

Primary Completion (Estimated)

July 31, 2029

Study Completion (Estimated)

July 31, 2034

Study Registration Dates

First Submitted

January 29, 2026

First Submitted That Met QC Criteria

February 9, 2026

First Posted (Actual)

February 12, 2026

Study Record Updates

Last Update Posted (Actual)

February 12, 2026

Last Update Submitted That Met QC Criteria

February 9, 2026

Last Verified

February 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • ABRUPT 2.0

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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