Abstract
Introduction: Hybrid positron emission tomography/computed tomography (PET/CT) has now become available, as well as whole body, low dose multi-detector row computed tomography (MDCT) or magnetic resonance imaging (MRI). The usefulness of 18F-fluorodeoxyglucose (FDG) PET/CT in evaluating multiple myeloma (MM) has been proven for several years but its sensitivity is imperfect. In a pilot study, we showed that 18F-fluorocholine (FCH) could have some advantages compared to FDG in suspected relapsing or progressive MM, since it is able to pinpoint lesions with a less intense metabolism and/or located in the skull, which are not revealed by FDG. The aim of the present study was to compare the diagnostic performance of PET/CT using FCH and FDG, in various settings of MM: staging, follow-up or suspected relapse.
Methods: FDG and FCH PET/CTs were both performed within few days (less than 30 and without specific treatment in the meanwhile) in 77 consecutive patients with MM referred between November 2015 and June 2017. For each patient and each tracer, two blind readers determined the number of foci (intraosseous and extraosseous), measured their intensity of uptake by their SUVmax and by the corresponding target/non-target ratio (T/NT). A consensus reading was made between the two masked readers. Bone spread was divided into three patterns: innumerable foci (more than 10), countable bone foci (less or equal to 10) or diffuse bone marrow infiltration.
Results: The 77 patients (average age = 67.3 year old) underwent 95 couples of FDG and FCH PET/CTs, all within 30 days: 17 for staging, 45 for follow-up (some patients had iterative PET/CTs) and 33 for suspected relapse. Among the 45 follow-up PET/CTs, 13 were intended purely to monitor treatment. No foci were found in 41 PET/CTs (6 for staging, 22 for follow-up and 13 for suspected relapse). Uncountable foci were observed in 10 cases with both tracers, but mismatched FDG/FCH foci in 1 case. Concerning countable foci, in 5 staging PET/CTs FDG showed 21 foci vs. 22 FCH foci, in 18 follow-up PET/CTs 32 FDG foci vs. 41 FCH foci, in 14 cases of suspected relapse 26 FDG foci vs. 55 FCH foci (+53%). Median SUVmax and T/NT was overall greater for FCH than for FDG, significantly in case of suspected relapse. There was no significant difference for median SUVmax and T/NT between FDG and FCH PET/CTs performed for staging. Of the 7 cases of diffuse bone marrow infiltration, 2 were better detected with FDG and 5 with FCH. Extramedullary spread was detected in 2 patients, foci of similar intensity being visible with both tracers. In all PET/CTs monitoring treatment for efficacy evaluation, FCH showed as reliable results as did FDG. FCH had better specificity than FDG, without some misleading foci of FDG in cases of inflammation (two cases), brown fat (one case) or post-traumatic fracture (one case). In 3 patients, the management decided on basis of FDG PET/CT was changed in view of FCH PET/CT.
Conclusions: These findings suggest that FCH PET/CT could have a role in all settings of MM, in particular in case of suspected relapse or progression, because it would reveal more lesions than FDG and avoid some pitfalls. Further investigations are needed to determine significance of mismatched FDG and FCH foci, and in which patients it is worthwhile to complete the exploration with FCH, or whether using FCH instead of FDG would lead to detrimental decisions in some patients.
Garderet: Amgen: Honoraria; Takeda: Honoraria.
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