Aims: We aim to reveal an effect of residual activity leftover within the medical materials other than the empty syringe used for injection of the tracer on SUV measurements and, consequently, the effect on possible treatment response. Background: The staging and follow-up of pediatric lymphoma patients is mainly achieved with the help of PET/CT scans. Making an optimal imaging technique for interpreting individual images and assessing treatment response is crucial. Objective: Standardized uptake value measurement is an important quantification parameter in PET/CT scanning of childhood lymphomas. A low dose of activity in pediatric oncology patients makes them vulnerable to small input value changes for subsequent metabolic parameters Methods: Sixty-eight pediatric lymphoma patients below 50 kg were included in the study. SUVmax, and SUVpeak values of the most metabolically active lesions, along with liver and mediastinum, were recorded. Metabolic parameters of the lesions/lymph nodes, mediastinum and liver parenchyma were compared before and after counts from medical materials other than empty syringes were taken into account. Wilcoxon signed-rank test was used for non-parametric paired sampled tests for the groups. Results: There were statistically significant differences between the whole 6 above-mentioned groups confirming the importance of residual counts on metabolic parameters (p<0.001). Conclusion: Our study demonstrated residual radioactivity in medical materials such as serum line tubes, i.v. catheters, three-way stopcock and also butterfly needles used during intravenous injection should also be included for optimum quantitative metabolic parameter values and to minimize their adverse effect on treatment response evaluation, especially in borderline lesions.

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AimTo determine the impact of 18 F-FDG PET/computed tomography (CT) on clinical staging in bladder cancer with comparison to conventional CT and MRI.Methods A total of 142 patients who underwent 18 F-FDG PET/CT imaging with a diagnosis of bladder cancer between 1 June 2019 and 31 December 2020 were screened retrospectively. Seventy patients who underwent diagnostic CT or MRI within 2 months before or after PET/CT were included in the study. The N and M stages determined by CT, MRI and PET/CT according to the eighth version of the TNM staging system were recorded. T-test was used to determine the levels of significant difference, and univariate logistic regression analysis was used to evaluate the impact of the T stage on nodal up-staging. ResultsAccording to the PET/CT, the N stage increased in 19 patients (27.14%) and decreased in seven patients (10%). Likewise, the M stage increased in 16 patients (22.86%) and decreased in seven patients (10%). The N stage determined by PET/CT was confirmed by pathologic examination in all cases in which the two modalities were inconsistent. In muscle-invasive cases, the rate of increase in the N stage after PET/CT (36.95%) was found to be significantly higher than in that of cases without invasion (8.33%) (P = 0.011). Increasing T stage was associated with an increase in the N stage after PET/CT (odds ratio: 2.33, 95% confidence interval: 1.02-5.28, P = 0.042).Conclusion 18 F-FDG PET/CT can potentially change the clinical stage determined by CT and MRI when used for staging in bladder cancer, and can lead to nodal up-staging particularly in cases with muscle-invasive bladder cancer.