Clinical radiology · 2026
Delayed 18F-FDG PET for the evaluation of suspected recurrent disease in brain metastases treated with radiation.
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Ciavarra B, Krayyem A, Ansari S, Shindell E, Gule-Monroe M K, Patel C B, Johnson J M
Аннотация
BACKGROUND AND PURPOSE: Differentiating progressive disease (PD) from radiation necrosis (RN) after treatment of brain metastases remains challenging. We evaluated the diagnostic utility of dual-timepoint 18F-FDG PET in distinguishing PD from RN in patients with treated brain metastases showing suspicious MRI findings.
MATERIALS AND METHODS: Thirty-four patients with suspicious MRI enhancement following radiation therapy were retrospectively analyzed. Seventeen had PD and 17 had RN, confirmed by a composite reference standard of clinical and radiologic follow-up (all 34 patients) or histopathology (10 patients, 29%). All underwent dual-timepoint 18F-FDG PET imaging (early at ∼77 minutes and delayed at ∼293 minutes post-injection). Tumor-to-background SUVmax ratios (T/B ratios) were calculated for each timepoint.
RESULTS: T/B SUVmax ratios were significantly higher in PD compared to RN at both early (1.3 ± 0.6 vs. 0.9 ± 0.3, P = .01) and delayed (2.0 ± 1.1 vs. 1.1 ± 0.3, P = .004) imaging, with greater absolute increase from early to delayed imaging in PD (0.7 ± 0.6 vs. 0.2 ± 0.2, P = .007). The delayed T/B ratio achieved an AUC of 0.772 (95% CI: 0.582-0.921). A delayed T/B ratio ≥ 1.5 achieved 94.1% specificity (95% CI: 71.3%-99.9%) with moderate sensitivity (58.8%; 95% CI: 32.9%-81.6%). While no single PET metric outperformed MRI overall, PET correctly reclassified three of four MRI misdiagnoses.
CONCLUSION: Dual-timepoint 18F-FDG PET may improve differentiation of PD from RN in equivocal MRI cases, particularly by reducing false-positive diagnoses, with a number needed to image of 8 (95% CI: 3-272). However, all thresholds were data-driven and confidence intervals are wide. Prospective validation with standardized protocols and pre-specified thresholds is warranted.
MATERIALS AND METHODS: Thirty-four patients with suspicious MRI enhancement following radiation therapy were retrospectively analyzed. Seventeen had PD and 17 had RN, confirmed by a composite reference standard of clinical and radiologic follow-up (all 34 patients) or histopathology (10 patients, 29%). All underwent dual-timepoint 18F-FDG PET imaging (early at ∼77 minutes and delayed at ∼293 minutes post-injection). Tumor-to-background SUVmax ratios (T/B ratios) were calculated for each timepoint.
RESULTS: T/B SUVmax ratios were significantly higher in PD compared to RN at both early (1.3 ± 0.6 vs. 0.9 ± 0.3, P = .01) and delayed (2.0 ± 1.1 vs. 1.1 ± 0.3, P = .004) imaging, with greater absolute increase from early to delayed imaging in PD (0.7 ± 0.6 vs. 0.2 ± 0.2, P = .007). The delayed T/B ratio achieved an AUC of 0.772 (95% CI: 0.582-0.921). A delayed T/B ratio ≥ 1.5 achieved 94.1% specificity (95% CI: 71.3%-99.9%) with moderate sensitivity (58.8%; 95% CI: 32.9%-81.6%). While no single PET metric outperformed MRI overall, PET correctly reclassified three of four MRI misdiagnoses.
CONCLUSION: Dual-timepoint 18F-FDG PET may improve differentiation of PD from RN in equivocal MRI cases, particularly by reducing false-positive diagnoses, with a number needed to image of 8 (95% CI: 3-272). However, all thresholds were data-driven and confidence intervals are wide. Prospective validation with standardized protocols and pre-specified thresholds is warranted.