Abstract
PurposeTo investigate the reproducibility of tracer uptake measurements, including volume metrics, such as metabolic tumor volume (MTV) and tumor lesion glycolysis (TLG) obtained by TOF-PET-CT and TOF-PET-MR.Materials and MethodsEighty consecutive patients with different oncologic diagnoses underwent TOF-PET-CT (Discovery 690; GE Healthcare) and TOF-PET-MR (SIGNA PET-MR; GE Healthcare) on the same day with single dose−18F-FDG injection. The scan order, PET-CT following or followed by PET-MR, was randomly assigned. A spherical volume of interest (VOI) of 30 mm was placed on the liver in accordance with the PERCIST criteria. For liver, the maximum and mean standard uptake value for body weight (SUV) and lean body mass (SUL) were obtained. For tumor delineation, VOI with a threshold of 40 and 50% of SUVmax was used (VOI40 and VOI50). The SUVmax, SUVmean, SUVpeak, MTV and TLG were calculated. The measurements were compared between the two scanners.ResultsIn total, 80 tumor lesions from 35 patients were evaluated. There was no statistical difference observed in liver regions, whereas in tumor lesions, SUVmax, SUV mean, and SUVpeak of PET-MR were significantly underestimated (p < 0.001) in both VOI40 and VOI50. Among volume metrics, there was no statistical difference observed except TLG on VOI50 (p = 0.03). Correlation between PET-CT and PET-MR of each metrics were calculated. There was a moderate correlation of the liver SUV and SUL metrics (r = 0.63–0.78). In tumor lesions, SUVmax and SUVmean had a stronger correlation with underestimation in PET-MR on VOI 40 (SUVmax and SUVmean; r = 0.92 and 0.91 with slope = 0.71 and 0.72, respectively). In the evaluation of MTV and TLG, the stronger correlations were observed both on VOI40 (MTV and TLG; r = 0.75 and 0.92) and VOI50 (MTV and TLG; r = 0.88 and 0.95) between PET-CT and PET-MR.ConclusionPET metrics on TOF-PET-MR showed a good correlation with that of TOF-PET-CT. SUVmax and SUVpeak of tumor lesions were underestimated by 16% on PET-MRI. MTV with % threshold can be regarded as identical volumetric markers for both TOF-PET-CT and TOF-PET-MR.
Highlights
18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is used routinely in the diagnosis, staging, restaging, and treatment monitoring of various cancers [1]
In order to achieve a more detailed assessment of tumor characteristics, recent studies have focused on demonstrating the prognostic value of positron emission tomography (PET)-based volumetric parameters, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG) [2–6]
Among volume metrics consisting of MTV and TLG, there was no statistical difference observed except for the TLG of VOI50 (p = 0.03)
Summary
18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is used routinely in the diagnosis, staging, restaging, and treatment monitoring of various cancers [1]. In order to achieve a more detailed assessment of tumor characteristics, recent studies have focused on demonstrating the prognostic value of positron emission tomography (PET)-based volumetric parameters, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG) [2–6]. MTV is defined as the sum of the volume of voxels, and TLG is the product of the MTV and SUVmean These indicators can be used for prognostication as they reflect the activity of glucose metabolism in the entire tumor compared to SUVmax which only reflects a single voxel value. In clinical or research settings, several PET machines were used for identical clinical and research purposes In such a situation, reproducibility among scanners remains an issue to be solved [11, 12]. In the case of time-of-flight (TOF)-PET-MR instruments, no study has evaluated the volumetric parameters In these machines, the effect of the MRAC error is reduced by TOF-reconstruction [32–34]
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