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Scientific Session 26 — SS26: Nuclear Medicine

Friday, April 27, 2018

Abstracts 2830-3544



2830. Regional Changes in Brain FDG Uptake After Cranial Irradiation May Reflect Functional Changes

Eshghi N1*,  Garland L1,  Hsu C1,  Choudhary G2,  Kuo P1 1. University of Arizona, Tucson, AZ; 2. University of Alabama, Birmingham, AL

Address correspondence to N. Eshghi (neshghi@radiology.arizona.edu)

Objective: Chemotherapy followed by prophylactic cranial irradiation (PCI) is associated with increased survival in patients with small cell lung cancer (SCLC) but is associated with fatigue and cognitive difficulties. This retrospective study evaluated for regional differences in FDG uptake of the brain before and after PCI. The null hypothesis is that direct toxic effects on the brain from chemotherapy and PCI should be symmetric and thus asymmetric changes may reflect functional changes due to therapy.

Materials and Methods: Electronic medical record from 2013 to 2015 was searched for patients with SCLC, MRI of brain negative for metastasis, and FDG PET/CT before and after PCI. As standard of care, patients received first-line chemotherapy followed by PCI. The closest PET/CT scans before and after PCI were selected. All FDG PET/CT scans were performed at our facility and extended from vertex to thigh. 16 patients met these criteria. Commercially available PET software was utilized to register and subtract the PET scans before and after PCI to obtain difference maps. Registration was performed by auto rigid alignment method, manual correction, or both. For each patient, regions of the brain with differences greater than 2.5 SD were recorded. Occipital region was excluded from the final analysis given known high variability from visual stimuli. A chi-square test was used for statistical analysis.

Results:

One patient was excluded from the final analysis because of poor registration, so 15/16 patients were successfully analyzed. Statistically significant alterations in regional brain FDG uptake before and after PCI were found in 14/15 patients. Thirteen patients had cerebral changes. Only one patient had significant changes exclusively in the cerebellum and no cerebral changes. Eleven patients showed significant changes unilaterally in at least one region. Three patients showed bilateral regional changes and no region with unilateral change. Chi-square test for unilateral regional difference on the patient level resulted in χ2 = 4.58 with p < 0.05 and thus were statistically significant. Another observation is that the most commonly affected brain region was the frontal. Also, the temporal region only had changes in three patients but was the only region to be exclusively affected on the left.



Conclusion: This retrospective, exploratory study found regional alterations in FDG uptake of the brain in patients with SCLC before and after PCI. Significantly more patients had unilateral rather than bilateral regional differences. This suggests that functional changes are being observed, since direct toxicity alone from chemotherapy and PCI would be symmetric. The most commonly affected region was the frontal which may suggest an etiology for cognitive difficulties after therapy.