PRO-BOOST-N: Prostate-First Versus Combined Prostate and Nodal Dose Escalation in PSMA PET-Staged Node-Positive Prostate Cancer

Summary

Patients with prostate cancer and pelvic lymph node involvement (cN1M0) identified on PSMA PET imaging represent a biologically aggressive yet potentially curable disease population. Contemporary management relies on multimodality treatment combining definitive radiotherapy to the prostate and pelvic lymph nodes with long-term androgen deprivation therapy (ADT), often intensified with androgen receptor pathway inhibitors. Despite these advances, a substantial proportion of patients still develop distant metastatic disease, highlighting the need to optimize local-regional treatment strategies in the era of molecular imaging.

The introduction of PSMA PET has fundamentally altered staging accuracy in prostate cancer, enabling earlier and more precise detection of pelvic nodal disease. However, most existing evidence guiding radiotherapy dose prescription in node-positive prostate cancer originates from the pre-PSMA era. As a result, it remains unclear how best to integrate prostate-directed and nodal-directed dose escalation strategies when disease extent is defined by modern molecular imaging. In particular, it is unknown whether long-term disease control is primarily driven by durable intraprostatic tumor eradication, by aggressive treatment of involved lymph nodes, or by a combination of both.

PRO-BOOST-N is a prospective, multicenter, randomized phase II/III clinical trial designed to address this critical evidence gap. The trial evaluates prostate-first versus combined prostate and nodal dose escalation strategies in patients with PSMA PET-staged node-positive (cN1M0) prostate cancer treated within a standardized ultrahypofractionated whole-pelvis radiotherapy framework. All enrolled patients indicated for definitive treatment undergo mandatory baseline PSMA PET/CT to confirm pelvic lymph node involvement and exclude distant metastatic disease.

All patients receive a uniform radiotherapy backbone consisting of ultrahypofractionated whole-pelvis radiotherapy delivered in five fractions, combined with long-term ADT. Use of androgen receptor pathway inhibitors is permitted and encouraged according to contemporary clinical practice and local availability, ensuring the relevance of the trial to real-world treatment settings.

Using a 2×2 factorial randomized design, PRO-BOOST-N evaluates two independent treatment factors. The primary randomized comparison assesses whether ablative prostate dose escalation improves oncologic outcomes compared with contemporary SBRT-based definitive prostate radiotherapy without additional boost. Prostate dose escalation may be delivered using one of three protocol-defined modalities-high-dose-rate brachytherapy, low-dose-rate brachytherapy, or single-fraction SBRT-according to institutional expertise. This comparison directly tests the hypothesis that durable intraprostatic disease control is the dominant determinant of long-term systemic disease suppression in node-positive prostate cancer.

The key secondary, hierarchically tested comparison evaluates the role of nodal dose escalation by comparing two predefined dose levels delivered to PSMA PET-positive pelvic lymph nodes. These dose levels reflect intermediate versus higher nodal boost strategies based on biologically effective dose concepts specific to prostate cancer radiobiology. To ensure patient safety and protocol feasibility, organ-at-risk-driven nodal dose de-escalation is permitted within the higher-dose arm, without altering randomization assignment.

The primary endpoint of the trial is metastasis-free survival. Secondary endpoints include overall survival, radiographic progression-free survival assessed primarily using PSMA PET imaging, intraprostatic and regional nodal control, time to castration-resistant prostate cancer, time to next systemic therapy, treatment-related toxicity graded according to CTCAE version 5.0, and patient-reported outcomes assessing urinary, bowel, sexual, and global quality of life.

By prospectively and hierarchically evaluating prostate and nodal dose escalation strategies within a modern PSMA PET-guided and ultrahypofractionated radiotherapy platform, PRO-BOOST-N aims to define the optimal radiotherapy intensification approach for patients with node-positive prostate cancer. The results of this study are expected to directly inform clinical practice, guideline development, and future treatment individualization in the PSMA PET era.

Conditions

• Prostate Cancer
• Brachytherapy
• Stereotactic Body Radiation Therapy (SBRT)
• Dose Escalation: Solid Tumors
• Regionally Advanced Prostate Cancer

Interventions

RADIATION

Ultrahypofractionated Whole-Pelvis Radiotherapy

Whole-pelvis external beam radiotherapy delivered using VMAT or IMRT techniques to elective pelvic lymph node volumes and the prostate. Treatment is prescribed as 25 Gy in 5 fractions and delivered with daily image guidance, serving as the standardized radiotherapy backbone for all study arms.

RADIATION

SBRT-Based Prostate Radiotherapy (No Boost)

Definitive prostate radiotherapy delivered as a simultaneous integrated boost within the ultrahypofractionated whole-pelvis radiotherapy plan. The prostate receives a total dose of 36.25 Gy in 5 fractions without additional prostate boost beyond this dose.

RADIATION

Ablative Prostate Boost

Ablative prostate dose escalation delivered after completion of ultrahypofractionated whole-pelvis radiotherapy. The prostate boost is delivered using one of the following protocol-defined modalities according to institutional expertise: high-dose-rate brachytherapy (15 Gy in 1 fraction), low-dose-rate brachytherapy (110 Gy permanent implant), or single-fraction stereotactic body radiotherapy boost (15 Gy in 1 fraction).

RADIATION

Intermediate Nodal Dose Escalation

Dose escalation to PSMA PET-positive pelvic lymph nodes delivered using a simultaneous integrated boost technique within the ultrahypofractionated whole-pelvis radiotherapy plan. The prescribed nodal boost dose is 27.75 Gy in 5 fractions.

RADIATION

Higher Nodal Dose Escalation

Dose escalation to PSMA PET-positive pelvic lymph nodes delivered using a simultaneous integrated boost technique within the ultrahypofractionated whole-pelvis radiotherapy plan. The prescribed nodal boost dose is 30 Gy in 5 fractions, with protocol-defined organ-at-risk-driven dose de-escalation permitted if required.

DRUG

Androgen Deprivation Therapy (ADT)

Androgen deprivation therapy administered as long-term systemic treatment in all study arms. ADT is delivered using luteinizing hormone-releasing hormone (LHRH) agonists or antagonists according to institutional practice and protocol-defined duration. ADT is initiated before or during radiotherapy and continued after completion of radiotherapy as specified in the study protocol.

DRUG

Androgen Receptor Pathway Inhibitors (ARPIs)

Androgen receptor pathway inhibitors may be administered in combination with androgen deprivation therapy according to contemporary clinical practice, local availability, and patient-specific considerations. The use of ARPIs is permitted but not randomized and includes approved agents targeting androgen receptor signaling.

Sponsors & Collaborators

• Affidea Nu-med Center of Oncological DIagnostics and Therapy

  lead OTHER

Principal Investigators

• Mateusz Bilski, MD, PhD · Affidea Nu-med Center of Oncological DIagnostics and Therapy

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

NONE

Model

FACTORIAL

Eligibility

Min Age

18 Years

Sex

MALE

Healthy Volunteers

No

Timeline & Regulatory

Start

2026-03-19

Primary Completion

2033-12-01

Completion

2035-12-01

Countries

• Poland

Study Locations