PSA and PSMA Kinetics After PSMA-PET and MR Guided Prostate Stereotactic Body Radiation Therapy With Focal Boost: Results From the Phase 2 PROBE Trial
Abstract
Purpose: To evaluate prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) kinetics following PSMA-positron emission tomography (PET) and magnetic resonance (MR) guided stereotactic body radiation therapy (SBRT) and short-term androgen deprivation therapy with dominant intraprostatic lesion (DIL) boost in localized prostate cancer.
Methods and materials: This prespecified analysis from the phase 2 PROBE trial (IRB approval: IEC 900917) included patients with intermediate- or high-risk prostate cancer treated with 5-fraction SBRT (36.25 Gy to prostate; 40 to 42.5 Gy to PSMA/MRI-defined DIL) and 6 months of androgen deprivation therapy. PSA kinetics relied on 3-monthly PSA levels. Longitudinal metabolic response, based on the adapted PET Response Criteria in Solid Tumors, was assessed using 68Ga-PSMA-PET/computed tomography done at SBRT completion, 3 to 6 months, and 9 to 12 months after SBRT completion. Cumulative genitourinary/gastrointestinal toxicities were reported per National Cancer Institute Common Terminology Criteria for Adverse Events v5.0.
Results: Thirty enrolled patients (54% intermediate risk, 46% high risk) were included. A PSA <0.1 ng/mL was achieved in 79% of patients at 6 months and 50% at 12 months. The mean maximum standardized uptake value (SUVmax) decreased from 12.2 (range, 4.0-39.6) pretreatment to 3.2 at 3 to 6 months and 1.8 at 9 to 12 months. Complete response (CR) rates increased from 17% at SBRT completion to 48% at 3 to 6…
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Evidence Hub reads this as a clinical trial, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence.
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