Samuel Chao, MD from the Cleveland Clinic, Case Comprehensive Cancer Center speaks about the ASTRO 2020 abstract 18F-Fluciclovine PET to Distinguish Tumor Progression From Radiation Necrosis.
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Purpose / Objective(s): To determine whether 18F Fluciclovine PET CT, a widely available FDA approved amino acid radiotracer for a suspected recurrence of prostate cancer, is useful in separating radiation necrosis (RN) from tumor progression (TP) from stereotactic radiosurgery (SRS)-treated brain metastases. Descriptive updates of an ongoing pilot clinical trial are being published.
Materials / Methods: The primary objective is to estimate the precision of 18F Fluciclovine PET CT in the separation between RN and TP. We included adult brain metastasis patients who underwent previous SRS and had a follow-up brain MRI (with DSC MR perfusion), which was equivocal for RN versus TP. Patients were grouped by the study neuroradiologist as equivocal but suspicious for either RN or TP, or genuinely equivocal, based on equivocal MRI and prior to PET.
Patients underwent 18F Fluciclovine PET CT on a Siemens Biograph mCT scanner with a 10 mCi bolus dose within 30 days of equivocal MRI of the brain immediately prior to PET. PET data were collected in a 25-minute post-injection list mode and reconstructed as a static 10-25-minute post-injection data image and as a dynamic sequence of four 5-minute frames between 5-25 minutes post-injection. Quantitative metrics, including SUV max, SUV mean, SUV peak, and normal brain SUV mean, were recorded for each lesion. Lesion was measured at standard brain ratios.
Clinical follow-up with MRI of the brain (with DSC MR perfusion) every 2-4 months before multidisciplinary consensus (or tissue confirmation) for RN versus TP diagnosis was the reference norm.
Results: 10 of 16 expected subjects enrolled from 7/2019-2/2020, 2 patients withdrew consent, and 8 patients with 15 lesions underwent 18F Fluciclovine PET CT. Primary histology was breast in 3 of the 8 imaged patients, lung adenocarcinoma in 3, and melanoma in 2 patients. SUV max, 2.05-12.10; SUV mean, 1.14-7.37; SUV peak, 0.97-4.45; regular brain SUV mean, 0.19-0.35; SUV max / regular ratio, 6.9-43.2; SUV mean / normal ratio, 3.8-17.7; and SUV peak / normal ratio, 3.1-26.4. Of all 15 imaged lesions, the quantitative measurement ranges were:
Conclusion: In this population, 18F Fluciclovine creates a wide range of quantitative metric lesion values and low normal brain uptake, allowing precise discrimination to occur. In order to determine whether 18F Fluciclovine is useful for distinguishing RN from TP among patients with brain metastases treated with SRS, ongoing accrual and follow-up is required.