PURPOSE/OBJECTIVE(S) To report descriptive updates of an ongoing pilot trial assessing whether 18F-Fluciclovine PET/CT, a widely available amino-acid radiotracer, is useful to distinguish radiation necrosis (RN) from tumor progression (TP) among patients with brain metastases. MATERIALS/METHODS The primary objective is to estimate the accuracy of 18F-Fluciclovine PET/CT in distinguishing RN from TP. We included adults with brain metastases who underwent prior stereotactic radiosurgery and presented with a follow-up MRI brain (with DSC-MR perfusion) which was equivocal for RN versus TP. Within 30 days of equivocal MRI, patients underwent 18F-Fluciclovine PET/CT on a Siemens Biograph mCT scanner with a 10 mCi bolus dose immediately prior to PET. PET data were collected in list-mode for 25 mins post-injection and were reconstructed as a static image of data 10-25 mins post-injection, and as a dynamic series of four 5-min frames between 5-25 mins post-injection. Quantitative metrics for each lesion were documented. Lesion to normal brain ratios were calculated. The reference standard was clinical follow-up with MRI brain (with DSC-MR perfusion) every 2-4 months until multidisciplinary consensus (or tissue confirmation) for diagnosis of RN versus TP. RESULTS From 7/2019-6/2020, 12 of 16 planned subjects with 17 lesions underwent 18F-Fluciclovine PET/CT. Primary histology was non-small cell lung cancer in 5 patients, breast in 4, melanoma in 2, and endometrial in 1. Among all 17 lesions, ranges of quantitative metrics were: SUVmax, 2.18-12.10; SUVmean, 1.16-7.37; SUVpeak, 1.06-4.45; normal brain SUVmean, 0.19-0.44; SUVmax/normal ratio, 7.50-45.40; SUVmean/normal ratio, 4.20-26.30; and SUVpeak/normal ratio, 3.90-26.40. Follow-up was completed for 5 patients (6 lesions). No adverse events have occurred. CONCLUSION In this population, 18F-Fluciclovine produces a wide range of lesion quantitative metric values and uniformly low uptake in normal brain, which may allow accurate discrimination. Ongoing additional accrual and follow up is required.
PURPOSE/OBJECTIVE(S) To assess the ability of 18F-Fluciclovine PET/CT to distinguish radiation necrosis (RN) from tumor progression (TP) among patients with brain metastases (BM) treated with stereotactic radiosurgery (SRS) in a prospective pilot study. MATERIALS/METHODS Adults with post-SRS BM presenting with follow-up brain MRI equivocal for RN versus TP underwent 18F-Fluciclovine PET/CT within 30 days of equivocal MRI. PET images were reconstructed using a point-spread-function algorithm. Three physician reviewers independently performed qualitative analyses of each lesion using a three-point visual score relative to PET-avidity of blood pool and parotid. Quantitative metrics for each lesion were documented. Reference standard was clinical follow-up with brain MRI until tumor board consensus or tissue confirmation. Nonparametric estimates of area under the receiver operating characteristic curve (AUC) for clustered data were estimated, with diagnostic performance based on visual score. RESULTS In 15 subjects with 20 lesions, final diagnosis was RN in 16 (80%) lesions and TP in 4 (20%). Visual score significantly correlated with final diagnosis (AUC range 0.836-0.906 [p≤0.037]). A threshold score of 2 (lesion 18F-fluciclovine uptake above blood pool to parotid) and higher produced sensitivities and specificities of 75-100% and 38-56% respectively among the reviewer majority. Conversely, a threshold of 3 (uptake higher than parotid) produced sensitivities and specificities of 50-75% and 100% respectively. CONCLUSION In this prospective pilot, basic visual analysis of 18F-Fluciclovine PET/CT provided high sensitivity and specificity in detection of TP in post-SRS BM based on different threshold scores, suggesting room for visual threshold optimization. A low TP event rate limited the ability to estimate sensitivity/specificity and to perform combined qualitative/quantitative analyses. Further study to refine interpretation criteria is ongoing.
PURPOSE To estimate the accuracy of 18F-Fluciclovine PET/CT in distinguishing radiation necrosis (RN) from tumor progression (TP) among patients with brain metastases (BM) having undergone prior stereotactic radiosurgery (SRS) who presented with a follow-up MRI brain (with DSC-MR perfusion) which was equivocal for RN versus TP. METHODS Within 30 days of equivocal MRI brain, subjects underwent 18F-Fluciclovine PET/CT on a Siemens Biograph mCT scanner with a 10 mCi bolus dose immediately prior to PET. Data were collected in list mode for 25 minutes post-injection and were reconstructed as a static image of data 10–25 minutes post-injection, and as a dynamic series of four 5-minute frames between 5–25 minutes post-injection. Quantitative metrics for each lesion were documented including SUVmax, SUVmean, SUVpeak, and normal brain SUVmean. Lesion to normal brain ratios were calculated. The reference standard was clinical follow-up with MRI brain (with DSC-MR perfusion) every 2–4 months until multidisciplinary consensus (or tissue confirmation) for diagnosis of RN versus TP. RESULTS From 7/2019-11/2020, 16 of 16 planned subjects enrolled and underwent 18F-Fluciclovine PET/CT for evaluation of 21 brain lesions. Primary histology included NSCLC (n=7), breast (n=5), melanoma (n=3), and endometrial (n=1). Ranges of quantitative metrics were: SUVmax, 2.18–12.1; SUVmean, 1.16–7.37; SUVpeak, 1.06–5.14; normal brain SUVmean, 0.19–0.50; SUVmax/normal ratio, 7.5–45.4; SUVmean/normal ratio, 4.2–26.3; and SUVpeak/normal ratio, 3.9–26.4. Among the patients 10 patients with 12 lesions who completed follow up, estimates of the area under the receiver operating characteristic curve for SUVmax, SUVmean, and SUVpeak were: 0.93, 0.93, and 0.82, respectively. CONCLUSION In this population, 18F-Fluciclovine PET/CT favorably produces a wide range of lesion quantitative metric values, low uptake in the normal brain, and promising accuracy to distinguish RN from TP. Completion of follow-up for all patients is required. Phase II and III studies are under development.
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