PRO-BOOST-LC is a prospective, multicenter, randomized clinical trial designed for patients with localized prostate cancer who do not have evidence of lymph node or distant metastases based on modern PSMA PET imaging.
Prostate cancer is one of the most common cancers in men. For patients with disease confined to the prostate, radiotherapy is a well-established and effective curative treatment option. Over the past decades, research has shown that delivering higher radiation doses to the prostate can improve cancer control and reduce the risk of disease recurrence. However, higher radiation doses may also increase the risk of side effects affecting urinary, bowel, and sexual function. For this reason, different radiation techniques have been developed to safely deliver higher doses while protecting surrounding healthy organs.
Several approaches to radiation dose escalation are currently used in clinical practice. These include stereotactic body radiotherapy (SBRT), which delivers radiation in a small number of highly precise treatments, as well as brachytherapy, where radioactive sources are placed directly inside the prostate for a short time (high-dose-rate brachytherapy) or permanently (low-dose-rate brachytherapy). Although all these approaches are accepted and widely used, it is not known which strategy provides the best balance between cancer control, treatment-related side effects, and long-term quality of life, particularly when modern imaging techniques are used to accurately stage the disease.
The PRO-BOOST-LC study aims to directly compare different radiation dose escalation strategies using a standardized treatment framework. All participants enrolled in the study will have localized prostate cancer staged with PSMA PET imaging to exclude metastatic disease. Participants will then be randomly assigned to one of four treatment groups. One group will receive SBRT alone to the prostate. The other three groups will receive a short course of external beam radiotherapy followed by an additional focused radiation boost delivered using one of three methods: high-dose-rate brachytherapy, low-dose-rate brachytherapy, or SBRT. All treatment approaches used in this study are established methods routinely applied in clinical practice.
Randomization ensures that each participant has an equal chance of being assigned to any of the treatment groups. This allows the study to fairly compare outcomes between the different strategies. The main objective of the trial is to determine whether adding a radiation boost improves treatment outcomes compared with SBRT alone. The primary outcome measure is failure-free survival, which includes cancer recurrence, disease progression, the need for additional cancer treatment, or death from any cause. Secondary outcomes include the development of distant metastases, overall survival, treatment-related side effects, and patient-reported quality of life.
Participants will be closely monitored throughout the study. Before treatment, patients will undergo clinical evaluation, blood tests including prostate-specific antigen (PSA), imaging studies, and quality-of-life assessments. During and after treatment, participants will attend regular follow-up visits. These visits will include clinical examinations, PSA testing, assessment of treatment-related side effects, and completion of standardized questionnaires evaluating urinary, bowel, and sexual function, as well as overall quality of life. Imaging studies, including PSMA PET scans, will be performed when clinically indicated to assess for possible disease recurrence or progression.
The study is designed to follow participants for many years in order to capture both early and long-term outcomes. By using modern radiotherapy techniques, standardized treatment protocols, and comprehensive follow-up, PRO-BOOST-LC aims to generate high-quality evidence that will help guide future treatment decisions for patients with localized prostate cancer. The results of this trial are expected to improve understanding of how best to use radiation dose escalation to maximize cancer control while minimizing side effects and preserving quality of life in the era of advanced imaging and precision radiotherapy.
Participation in this study does not involve experimental or unproven treatments. All radiation techniques used in PRO-BOOST-LC are approved, widely available, and considered standard of care in many treatment centers worldwide. The study focuses on optimizing how these existing techniques are combined and delivered, rather than introducing new drugs or devices. Participation may involve additional follow-up assessments and questionnaires compared with routine care, but treatment decisions are made within established clinical practice guidelines. Patients may or may not directly benefit from participation, but the information gained from this study may help improve future treatment strategies for men with localized prostate cancer.
Male patients aged ≥18 years.
Histologically confirmed adenocarcinoma of the prostate.
Localized or locally advanced prostate cancer classified as cT1-4, cN0, cM0.
Negative pelvic nodal and distant metastatic disease on baseline PSMA PET.
Evidence of pelvic nodal (cN1) or distant metastatic disease (cM1) on baseline imaging.
Prior definitive local treatment for prostate cancer, including prostatectomy, brachytherapy, or definitive external beam radiotherapy.
Prior pelvic radiotherapy for any malignancy.
Prior systemic therapy for prostate cancer other than protocol-allowed neoadjuvant ADT.
Parallel
Stereotactic Body Radiotherapy (SBRT) Monotherapy
RadiationStereotactic body radiotherapy (SBRT) delivered to the prostate as definitive monotherapy using an ultrahypofractionated schedule. Treatment is planned with highly conformal techniques and daily image guidance according to protocol-defined target coverage objectives and organ-at-risk constraints. This intervention represents a non-invasive definitive radiotherapy strategy without additional intraprostatic boost.
External Beam Radiotherapy (EBRT) Backbone
RadiationUltrahypofractionated external beam radiotherapy delivered to the prostate using volumetric modulated arc therapy (VMAT) or equivalent intensity-modulated techniques. This intervention serves as a standardized treatment backbone prior to intraprostatic dose escalation and is delivered according to protocol-defined target volumes, margins, and dose constraints.
High-Dose-Rate Brachytherapy Boost
RadiationIntraprostatic high-dose-rate brachytherapy delivered as a single-fraction boost following completion of external beam radiotherapy. The procedure involves transperineal catheter placement with afterloading and is performed according to protocol-defined technical, dosimetric, and safety criteria to achieve focal dose escalation while respecting organ-at-risk constraints.
Low-Dose-Rate Brachytherapy Boost
RadiationIntraprostatic low-dose-rate permanent seed brachytherapy delivered as a boost following completion of external beam radiotherapy. Radioactive seeds are implanted transperineally according to protocol-defined planning and implantation guidelines to provide continuous low-dose-rate irradiation while maintaining predefined target coverage and organ-at-risk constraints.
Stereotactic Body Radiotherapy (SBRT) Boost
RadiationIntraprostatic stereotactic body radiotherapy delivered as a single-fraction boost following completion of external beam radiotherapy. This intervention provides non-invasive dose escalation using highly conformal planning and image guidance according to protocol-defined coverage objectives and organ-at-risk constraints.
Androgen Deprivation Therapy (ADT)
DrugAndrogen deprivation therapy (ADT) administered according to protocol-defined risk group and standard clinical practice. ADT may include luteinizing hormone-releasing hormone (LHRH) agonists or antagonists, with or without short-course antiandrogens, delivered as neoadjuvant, concurrent, and/or adjuvant therapy in accordance with contemporary clinical guidelines. ADT is not randomized and is applied uniformly within each risk group across all treatment arms.
Failure-Free Survival (FFS)
Failure-Free Survival (FFS) is defined as the time from randomization to the earliest occurrence of any of the following events: biochemical recurrence according to the Phoenix definition (PSA nadir + 2 ng/mL), confirmed local recurrence within the prostate, regional pelvic nodal progression, distant metastatic disease, initiation of salvage therapy, or death from any cause. Local recurrence is defined by radiologic progression on multiparametric MRI or PSMA PET/CT confirmed on repeat imaging ≥6 months later, or biopsy-proven viable adenocarcinoma in the presence of radiologic progression. Regional nodal progression includes pelvic nodal relapse (obturator, internal iliac, external iliac, presacral nodes). Patients without an event will be censored at the date of last disease assessment.
Metastasis-Free Survival (MFS) hierarchical
Metastasis-Free Survival (MFS) is defined as the time from randomization to the occurrence of distant metastatic disease or death from any cause, whichever occurs first. Distant metastases are defined as non-pelvic nodal disease (including common iliac nodes) or visceral or bone metastases detected preferentially by PSMA PET/CT and confirmed according to protocol-defined imaging criteria. MFS is analyzed as a key confirmatory endpoint within a hierarchical testing strategy and will be formally tested only if the primary comparison for Failure-Free Survival is statistically significant. MFS is assessed in accordance with EAU/ASTRO/STRATOS consensus definitions and is recognized as a validated surrogate for overall survival in localized and locally advanced prostate cancer.
Intraprostatic Local Control (iLC)
Intraprostatic local control is defined as the time from randomization to confirmed local recurrence within the prostate gland. Local recurrence is determined by radiologic progression on multiparametric MRI or PSMA PET/CT confirmed on repeat imaging performed at least 6 months later, or by biopsy-proven viable adenocarcinoma in the presence of radiologic progression. This endpoint evaluates the effectiveness of intraprostatic dose escalation strategies.
Regional Pelvic Nodal Control (rNC)
Regional pelvic nodal control is defined as the time from randomization to pelvic nodal progression detected on imaging. Pelvic nodal progression includes involvement of obturator, internal iliac, external iliac, or presacral lymph nodes. Progression in common iliac lymph nodes is classified as distant metastatic disease and is not considered a regional nodal event. Nodal progression must be confirmed on imaging according to protocol-defined criteria.
Acute Genitourinary and Gastrointestinal Toxicity
Acute genitourinary (GU) and gastrointestinal (GI) toxicity is defined as treatment-related adverse events occurring within 90 days from completion of radiotherapy. Toxicity will be graded according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5.0. The incidence and severity of acute adverse events will be systematically recorded at scheduled follow-up visits.
Late Genitourinary and Gastrointestinal Toxicity
Late genitourinary (GU) and gastrointestinal (GI) toxicity is defined as treatment-related adverse events occurring more than 90 days after completion of radiotherapy. Toxicity will be graded using CTCAE version 5.0. This endpoint assesses long-term safety and tolerability of dose-escalated and boost-based radiotherapy strategies.
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