BMET-30ACCURACY OF SCREENING FOR BRAIN METASTASES WITH WHOLE-BODY FDG PET IN INITIAL STAGING OF NON-CENTRAL NERVOUS SYSTEM MALIGNANCY

Abstract

BACKGROUND: Fluorodeoxyglucose (FDG) positron emission tomography (PET) is often used in the initial staging of non-CNS primaries to detect distant metastases. Previous studies suggested moderate sensitivity in detecting brain metastasis; however, samples sizes were small to modest. We chose to evaluate FDG-PET in a larger sample of patients to better assess the sensitivity in detecting brain metastases. METHODS: We retrospectively evaluated 172 adult patients with a variety of non-CNS primaries undergoing FDG-PET of the whole body (from vertex to at least mid-thigh) and MRI of the brain with a maximum interval of 30 days. Studies were acquired between January-2010 to March-2015. The presence of brain metastases for each imaging method was assessed. We excluded primary CNS malignancies, lymphoma, H&N primaries(except melanoma) and test intervals greater than 30 days. No patients were treated with surgery, radiation or chemotherapy in between the studies. Statistical analysis was done by Pearson chi-square test. RESULTS: Of 172 patients majority were: non-small cell(65) and small cell(23) lung carcinoma, melanoma(39), breast(13), unknown primaries(4) and renal cell carcinoma (3). PET and MRI revealed 47 and 75 cases with brain metastasis respectively. Overall sensitivity and specificity of PET in detecting brain metastases with the reference of MRI brain was 54.7% and 93.8% respectively. PPV and NPV of PET were 87.2% (95%CI: 74.8%- 94%) and 72.8% (64.4%-79.8%) respectively. Pre-test probability (prevalence) was 43.6% and accuracy of the PET was 76.7%. Pearson chi-square test is 50.06 and it is statistically significant with p-value < 0.00001. Pearson correlation coefficient between tests is 0.54. CONCLUSION: Sensitivity of FDG-PET in our evaluation is 54.7% sensitivity for brain metastasis compared to MRI brain. Our finding is similar to previously reported sensitivities. More sensitive screening FDG-PET protocols need to be employed (such as dedicated brain table position and/or MR/PET registration) to rely on FDG-PET as a screening method for the brain.