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Updated: Mar 1, 2026
A Whole Body Dosimetry Protocol for Peptide-Receptor Radionuclide Therapy PRRT: 2D Planar Image and Hybrid 2D+3D SPECT/CT Image Methods
Published on: April 24, 2020
PSA and PSMA Kinetics After PSMA-PET and MR Guided Prostate Stereotactic Body Radiation Therapy With Focal Boost:
Maneesh Singh1, Suchismita Ghosh2, Aparna Katdare3
1Department of Radiation Oncology, Tata Memorial Hospital and Advanced Centre for Treatment Research and Education in Cancer (ACTREC), Homi Bhabha National Institute, Mumbai, India.
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 months and 65% at 9 to 12 months. Patients achieving CR at 3 to 6 months reached a lower mean PSA (0.04 vs 0.3 ng/mL, P = .009). Those with PSA <0.1 ng/mL at 6 months were more likely to attain CR at 12 months (76% vs 28%, P = .003). An early standardized uptake value (SUV) "flare" was observed in 4 (14%) patients, resolving by 9 to 12 months. No National Cancer Institute Common Terminology Criteria for Adverse Events grade ≥3 genitourinary/gastrointestinal toxicity was seen.
Conclusions:
PSMA-PET and MR guided prostate SBRT with DIL boost achieved deep PSA nadirs, gradual PSMA kinetics, and a favorable safety profile. About 80% of patients achieved a PSA <0.1 ng/mL at 6 months, with two-thirds achieving CR by 12 months post-SBRT. Achieving a PSA <0.1 ng/mL could potentially predict PSMA-CR. Early PSMA-CR at 3 to 6 months may predict durable PSA response and warrants further evaluation as a biomarker for risk-adapted strategies in localized prostate cancer.
