Impact of chemotherapy with Temozolomide on physiological brain 18F-DOPA uptake in patients with glioma

Purpose: To investigate the effects of temozolomide chemo-therapy on the physiological uptake of 18F-DOPA. Subjects and Methods: The analysis included 155 consecutive studies from 121 patients with glioma referred for F-DOPA PET/CT at our institution between July 2010 and February 2017. Patients had been previously treated with surgery, temozolomide che-motherapy, stereotactic radiotherapy, or a combination thereof. To obtain the average background uptake (SUVbckr), a large hemispherical ROI including both gray and white matter was placed above the lateral ventricles, controlateral to the tumor lesion. A semi-automatic threshold-based VOI segmentation tool (Hermes Medical Solutions) was used to delineate tumor (>1.6 x background uptake) and controlateral basal ganglia (>2.0 x background uptake). In some cases manual adjustment was needed. Average tumor and basal ganglia uptakes (SUVt and SUVbg, respectively) were calculated within each given VOI. Tumor-to-background (TBR) and tumor-to-basal-ganglia (TBG) ratios were defined as SUVt/SUVbckr and SUVt/SUVbg, respectively. All studies were divided into three groups based on chemotherapy status: ongoing treatment (Group A, n=57); treatment completed >1 months before PET (Group B, n=50); no previous treatment (Group C, n=48). Differences between groups were assessed by ANOVA with Turkey’s test for multiple comparisons. Results: There were significant effects of chemo-therapy on SUVbckr and SUVbg (p=0.02 and p=0.05, respective-ly, ANOVA) In particular, mean SUVbckr was significantly lower in Group A than in Group B (1.005 ± 0.2458 vs 1.144 ± 0.309, p=0.01,Turkey’s test), while the difference between Group A and Group C (1.067 ± 0.2099) was not significant (p=0.43, Turkey’s test). As regards SUVbg, comparisons between Groups A (2.073 ± 0.4255) and B (2.262 ± 0.5684) and between Groups B and C (2.055 ± 0.3912) showed a trend towards significance (p values: 0.09 and 0.07 for A vs B and B vs C, respectively, Turkey’s test). Prior radiotherapy had no effect on both SUVbckr and SUVbg (data not shown). In 92 patients with PET+ tumors, temozolo-mide chemotherapy affected TBR (and not TBG) (p=0.02, ANO-VA). In particular, mean TBR was significantly higher in Group A than in Group B (2.374 ± 0.537, n=41 vs 2.093 ± 0.375, n=27; p=0.03, Turkey’s test) Conclusion: Normal brain and basal gan-glia F-DOPA uptake is decreased in patients with ongoing te-mozolomide. As a consequence, these patients appear to have increased TBR compared to patients who never underwent or already concluded chemotherapy. This has to be taken into ac-count when interpreting F-DOPA PET images.