Correlating kinetic ¹⁸F-FDOPA uptake to quantitative MRI markers in primary and metastatic brain tumors to predict patient outcomes with hybrid PET/MRI

Purpose: Post-radiation changes in the brain can mimic tumor recurrence on MRI, requiring multiple short term follow-ups to differentiate tumor progression from radiation necrosis. We propose to combine functional and anatomic imaging with dynamic FDOPA PET and clinical grade MR imaging of brain tumors with quantitative post-processing. Materials and Methods: Sixteen adult patients treated with radiation therapy were identified - four with metastatic disease from breast and lung cancer and twelve with primary brain glioma (IDH wildtype glioblastoma). Patients were scanned on hybrid PET-MRI (GE Healthcare) with clinical MRI brain sequences and dynamic FDOPA uptake. Dynamic FDOPA uptake within these tumors over 45 minutes after tracer injection was analyzed and compared to ADC histogram analysis. Results: Sixteen patients had successful [¹⁸F]FDOPA PET and clinical quality MRI on hybrid PET-MRI with three patients having six month follow up and five patients having 4 month follow up. Successful dynamic FDOPA uptake within the tumor was seen in all patients and ratio of tumor to contralateral ROI were found to range from 1.8-4.5. One of the patients with metastatic breast cancer within cerebellum demonstrated increase in size of the metastatic lesion by 68% over a six month period, which on resection was found to be 25% recurrent tumor and 75% radiation changes. The lesion raw SUVmax values ranged from 2.07 - 3.93 over 45 minute acquisition. The T/C SUVmax ratios ranged from 1.22-1.81 over 45 minute acquisition period. Second patient with metastatic breast cancer that was found to be mostly recurrent tumor with no change in lesion size over 1 month period, demonstrated raw SUVmax values 1.66-3.98 over 45 minutes with T/C SUVmax ratios ranging 1.62-2.57. Raw SUV values did not differentiate recurrent tumor from radiation changes in glioblastoma, but T/C SUVmax rations were found to be 1.12-2.42 in treated hypoxic tumor that showed no evidence of disease progression. On the other hand, T/C values in glioblastoma demonstrating active radiation changes were elevated ranging from 0.71-4.09 over 45 minutes. Conclusion:MRI imaging characteristics are critical for interpretation of dynamic [18F]FDOPA uptake within the tumor and FDOPA uptake within 3D tumor predicts patient outcome at 6 months.

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