18F-DOPA uptake parameters in glioma: effects of patients' characteristics and prior treatment history

Objective: In amino acid positron emission tomography brain tumour imaging, tumour-to-background uptake parameters are often used for treatment monitoring. We studied the effects of patients' characteristics and anticancer treatments on F-18-fluoro-l-phenylalanine uptake of normal brain and tumour lesions, with particular emphasis on temozolomide (TMZ) chemotherapy. Methods: 155 studies from 120 patients with glioma were analysed. Average uptake of normal background (standardized uptake value, SUVbckgr) and basal ganglia (SUVbg), as well as tumour-to-brain ratios (TBR) were compared between positron emission tomography/CT studies acquired before (Group A, n = 48), after (Group B, n = 50) or during (Group C, n = 57) TMZ treatment, using analysis of variance. Results: Overall, mean SUVbckgr and mean SUVbg were 1.06 +/- 0.26 and 2.12 +/- 0.47, respectively. Female had significantly higher SUVbckgr (p = 0.002) and SUVbg fA = 0.012) than male patients. Age showed a positive correlation with SUVbg (p = 0.001). In the overall cohort, there were significant effects of TMZ on SUVbckgr (p = 0.0237) and TBR (p = 0.0138). In particular, SUVbckgr was lower in Group C than in Group B (1.00 +/- 0.25 vs 1.14 +/- 0.31, p = 0.0173). Significant variations of SUVbckr could be observed in female only. TBR was significantly higher in Group C than in Group B (2.37 +/- 0.54 vs 2.06 +/- 0.38, p = 0.010). Variations of SUVbg between groups slightly missed significance (p = 0.0504). Conclusion: Temozolomide chemotherapy and patients' characteristics, including gender and age, affect physiological [F-18]-fluoro-l-phenylalanine uptake and, consequently, the calculation of TBRs. Advances in knowledge: For the first time, the effects of past or concurrent temozolomide chemotherapy on brain physiological amino acid uptake have been investigated. Such effects are relevant and should be taken into account when evaluating tumour-to-background ratios.