Interim Phase II Trial: 68Ga-PSMA-PET and Transponder-Guided Salvage Radiotherapy Post-Prostatectomy

Overview

This prospective Phase II study evaluated 3-year outcomes of salvage radiotherapy (SRT) guided by 68Ga-PSMA-PET imaging and electromagnetic transponders in men with biochemical recurrence of prostate cancer after prostatectomy. The study demonstrated promising freedom from biochemical relapse rates with low toxicity and preserved quality of life in patients treated to the prostate bed alone without androgen deprivation therapy.

Background

Approximately one-third of men undergoing radical prostatectomy for prostate cancer experience biochemical recurrence within 10 years, often detected by rising PSA levels. Salvage radiotherapy to the prostate bed is the standard treatment at early biochemical recurrence, ideally at PSA levels below 0.5 ng/mL. Conventional imaging has limited sensitivity at low PSA levels, complicating treatment decisions. 68Ga-PSMA-PET imaging improves detection of local recurrence and can refine patient selection for targeted salvage therapy. Implantable electromagnetic transponders enable real-time tracking of the prostate bed during radiotherapy, potentially reducing toxicity and improving treatment accuracy.

Data Highlights

Key Findings

• Patients with negative or prostate bed-only positive 68Ga-PSMA-PET underwent SRT without ADT.
• Real-time electromagnetic transponder tracking was used to optimize radiotherapy delivery in suitable patients.
• Freedom from biochemical relapse was the primary endpoint, defined as PSA rise >0.2 ng/mL above nadir with confirmatory test.
• Low acute and late toxicity rates were observed, assessed by CTCAE v4.03 criteria.
• Patient-reported quality of life, measured by SF-12 and EPIC-26, showed stability from baseline through follow-up.
• Use of 68Ga-PSMA-PET altered treatment planning by identifying patients suitable for prostate bed-only SRT, potentially reducing overtreatment.

Clinical Implications

68Ga-PSMA-PET imaging combined with transponder-guided SRT allows precise targeting of the prostate bed in men with biochemical recurrence post-prostatectomy, potentially avoiding unnecessary androgen deprivation therapy. This approach may reduce treatment-related toxicity and preserve quality of life while maintaining effective disease control. Clinicians should consider integrating advanced imaging and real-time tracking technologies to optimize salvage radiotherapy strategies.

Conclusion

Interim 3-year results support the feasibility and efficacy of 68Ga-PSMA-PET-directed, transponder-guided salvage radiotherapy to the prostate bed without ADT in selected patients, demonstrating favorable biochemical control and low toxicity. Longer-term follow-up will further clarify oncological outcomes and quality of life benefits.

References

1. Epworth Human Research Ethics Committee 675-15 -- Study Approval
2. Common Terminology Criteria for Adverse Events v4.03 -- Toxicity Assessment
3. Calypso® localisation system (Varian Medical Systems) -- Real-time Target Tracking