Patients With Metastasized Prostate Cancer Whose Prostate-specific Antigen-level (PSA) Remains >0,2 ng/ml After Six Months of Dual Antihormonal Therapy Will Receive Radiotherapy to the Prostate and Radiotherapy to Refractory Metastases (RIALTO)

RIALTO: Radiotherapy in Primarily Metastasized Prostate Cancer - Image-guided Local AbLaTion of Prostate and Oligoresidual Disease

The goal of this clinical trial is to learn if radiotherapy to the prostate and PET-positive (positron emission tomography) metastasis will lead to radiological response on PSMA-PET (prostate specific membrane antigen-PET). Patients who receive combined androgen deprivation therapy for de novo metastasized prostate cancer and show an incomplete PSA-response (>0,2 ng/ml after six months) and exhibit at least four bone metastases on PET-imaging at this time point (without metastases to organs) can take part in this study.

The main questions it aims to answer are:

• Does radiotherapy to the prostate and PET-positive metastases lead to a radiological response one year after radiotherapy? Researchers will analyze PET-imaging prior to radiotherapy to the prostate and metastases and one yeare thereafter.

Participants will:

• Continue taking combined androgen-deprivation therapy
• Receive a total of three PSMA-PET/CT scans
• Receive radiotherapy to the prostate and PET-positive metastases
• Visit the clinic every three months for 36 months
• Complete quality of life questionnaires at every visit

Study Overview

• Status: Not yet recruiting
• Conditions: Prostate Cancer; Prostate Cancer Metastatic Disease; Prostate Cancer Metastatic to Bone
• Intervention / Treatment: Radiation: Radiotherapy to the prostate and to PSMA-PET positive metastases

• Study Type: Interventional
• Enrollment (Estimated): 27
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Elgin Hoffmann, MD, Dr. med.; Phone Number: 4970712982165; Email: ROinfo@med.uni-tuebingen.de
• Study Contact Backup: Name: Maximilian Niyazi, MD, Prof. Dr. Dipl.-Phys.

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Prostate adenocarcinoma
• de novo metastasized prostate cancer (at least 4 osseous metastases +/- lymphonodal metastases)
• first-line combined antihormonal therapy (ADT + ARPI) for six months
• PSA > 0,2 ng/ml after six months of combined ADT/ARPI therapy
• multimetastasized disease stage without visceral metastases on imaging at first diagnosis (PET, CT, or bone scan)
• <16 osseous/lymphnodal metastases on response assessment imaging (PSMA-PET/CT) after six months of combined antihormonal therapy

Exclusion Criteria:

• neuroendocrine histology
• visceral metastases (M1c)
• prior radiotherapy to the pelvis
• PSA < 0,2 ng/ml after 6 months of combined antihormonal therapy
• prior prostatectomy
• contraindication against PSMA-PET/CT and/or radiotherapy to the prostate/metastases
• HIFU or TUR-P within 6 months of study treatment
• other active malignancy two years prior to study inclusion (except skin cancer in remission)
• relevant GU/GI condition (active fistula or other)
• known tumor predisposition syndrome

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• 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: Radiotherapy to the prostate and PSMA-PET/CT guided radiotherapy of refractory metastases; Radiotherapy to the prostate and refractory metastases on PSMA-PET/CT	Radiation: Radiotherapy to the prostate and to PSMA-PET positive metastases; Patients will receive radiotherapy to the prostate and to PSMA-PET postivie Metastases

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Radiological Progression-Free Survival	Radiological Progression-Free Survival as determined on PSMA-PET/CT according to RECIP criteria, defined as 30% response in PSA-volume	12 months after radiotherapy of metastases

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Lesion-specific response on imaging		12 months after radiotherapy to metastases
Prostate specific antigen (PSA)	Prostate specific antigen	up to 36 months after radiotherapy to the prostate
Objective response rate		12 months after radiotherapy to metastases
Time to next systemic therapy		up to 36 months after radiotherapy to the prostate
Overall survival		up to 36 months after radiotherapy to the prostate
Failure-free survival		up to 36 months after radiotherapy to the prostate
Progression-free survival		up to 36 months after radiotherapy to the prostate
Metastasis-free survival		up to 36 months after radiotherapy to the prostate
Prostate-cancer specific survival		up to 36 months after radiotherapy to the prostate

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Quality of life questionnaires	EORTC QLQ-C30 Prostate	up to 36 months after radiotherapy of the prostate
Organ-specific side effects	CTCAEv5	up to 36 months after radiotherapy of the prostate
Organ function	IPS-Score	up to 36 months after radiotherapy of the prostate
Choice of next systemic therapy	Documentation of systemic treatment in case of progression	up to 36 months after radiotherapy to the prostate
Reason for change in systemic therapy	Documentation in case of change in systemic therapy	up to 36 months after radiotherapy to the prostate
Quality of Life questionnaire	QLQ-PR25	up to 36 months after end of radiotherapy of the prostate
Quality of life questionnaire	EQ-D5	up to 36 months after radiotherapy to the prostate
Organ-specific side effects	RTOG questionnaire	up to 36 months after end of radiotherapy
Organ function	ICIQScore	up to 36 months after radiotherapy to the prostate
Organ-specific function	NCI-PRO-CTCAE	up to 36 months after radiotherapy to the prostate
Organ-specific function	IIEF	up to 36 months after radiotherapy to the prostate

Collaborators and Investigators

• Sponsor: University Hospital Tuebingen
• Collaborators: Ludwig-Maximilians - University of Munich; University Hospital Freiburg; University Hospital Dresden; University Hospital Augsburg; Uniklinikum Giessen und Marburg
• Investigators: Principal Investigator: Elgin Hoffmann, MD, Department of Radiation Oncology, University Hospital Tübingen

Study record dates

Study Major Dates

• Study Start (Estimated): July 1, 2026
• Primary Completion (Estimated): July 1, 2027
• Study Completion (Estimated): February 1, 2031

Study Registration Dates

• First Submitted: June 1, 2026
• First Submitted That Met QC Criteria: June 8, 2026
• First Posted (Actual): June 12, 2026

Study Record Updates

• Last Update Posted (Actual): June 12, 2026
• Last Update Submitted That Met QC Criteria: June 8, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: radiotherapy; mHSPC; local therapy; insufficient PSA-response to dual antihormonal treatment
• Additional Relevant MeSH Terms: Urogenital Diseases; Genital Diseases; Genital Neoplasms, Male; Urogenital Neoplasms; Neoplasms by Site; Neoplasms; Genital Diseases, Male; Prostatic Diseases; Male Urogenital Diseases; Prostatic Neoplasms
• Other Study ID Numbers: 430/2025BO1; DRKS00038018 (Registry Identifier: Deutsches Register Klinischer Studien (German clinical trial registry))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Depending on national data security legislation for sharing individual data, providing IPD might not be permitted without explicit consent by the patients enrolled in this study.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No