18f-Fludeoxyglucose and 11c-Methionine PET/CT Scans in Patients with Multiple Myeloma Following Autologous Stem-Cell Transplantation (auto-HSCT)
Authors: Solovev Maxim V. , Mendeleeva Larisa P. , Firsova Maiia V. , Aslanidi Irakly P. , Mukhortova Olga V. , Savchenko Valery G. 
Published: October 2019

Abstract
Introduction: Over the past years, possible use of PET/CT scan for diagnosis of multiple myeloma has been intensively studied; there is evidence that the use of 11C-methionine instead of 18F-fludeoxyglucose (18F-FDG) in multiple myeloma patients promotes the decrease in false negative PET/CT scan results. Comparative evaluation of the efficacy of detection of residual tumor lesions in MM patients following auto-HSCT using different radiopharmaceuticals for PET/CT scans is an important task.
Goal of the study: To compare the results of tumor imaging using 18F-FDG and 11C-methionine PET/CT scan in MM patients following auto-HSCT.
Materials and methods: Over the period from December 2016 to March 2018, 27 MM patients (8 males and 19 females) aged 32 to 64 years (median=57) were enrolled into a prospective study designed to evaluate efficacy of detection of tumor lesions using PET/CT scan technique. The disease stage according to the International Staging System (ISS) was I, II and III in 10, 7 and 10 patients, respectively. The onset of myeloma cast nephropathy was diagnosed in 4 (18%) patients, intraosseous plasmacytomas were found in 18 (67%) patients, extramedullary brain lesions was observed in 1 case. All patients received induction therapy with bortezomib; immunomodulatory drugs were used in 6 cases. Mobilization of CD34+ blood cells was carried out according to the regimen Cyclophosphamide 4 g/m2 + G-CSF. While using high-dose melphalan (200 mg/m2), a single (n=21) or tandem (n=6) auto-HSCT was conducted. On Day 100 after the initiation of auto-HSCT, PET/CT scan with two radiopharmaceuticals - 18F-FDG and 11C-methionine was performed. The obtained images were evaluated by visual inspection and semi-quantitative analysis. There were foci of increased accumulation of each agent (areas of hypermetabolism) not related to its physiological distribution. For each of the radiopharmaceuticals, the standardized uptake value (SUVmax) in the lesions was estimated automatically. The results of PET/CT and anti-tumor response achieved following auto-HSCT were compared according to the criteria developed by the International Myeloma Working Group. Statistical analysis was performed using Statistica 10 software. The quantitative values were expressed as the mean value ± standard deviation or the median value. Comparison of the respective measurements was carried out using the Student's t-test. To compare frequencies of data between independent groups, the Fisher's exact test or chi-square test were used.
Results: Following auto-HSCT, 60% of patients demonstrated complete remission (CR). When using 18F-FDG, abnormal accumulation was observed in 37% (n=10) cases, PET-negative results were obtained in 63% (n=17) patients. Following administration of 11C-methionine, hypermetabolic foci were revealed in 67% (n=18) cases, lack of accumulation was observed in 33% (n=9) patients (Fig. 1). When using 11C-methionine, MM patients were found 1.8 times more likely to demonstrate abnormal accumulation of the radiopharmaceutical (p<0.02).
Following administration of 18F-FDG, PET/CT scans of MM patients demonstrated 1 to 6 (mean value = 1±1.5) foci of abnormal fixation, while the use of 11C-methionine allowed revealing 1 to 12 (mean value=2.5±3.1) lesions. When using 11C-methionine, the number of lesions demonstrating abnormal accumulation of the radiopharmaceutical was 2.5 times that of 18F-FDG (p<0.05).
Mean value of SUVmax for 18F-FDG was 1.02±1.6, while the mean value of SUVmax for 11C-methionine was 2.29±2.04. When using 11C-methionine, the values of SUVmax significantly exceeded the respective parameter associated with the use of 18F-FDG (p=0.02).
Discussion: The results of our study have demonstrated a significant role of 11C-methionine for detection of tumor lesions in MM patients following auto-HSCT. The use of 11C-methionine PET/CT scan allows improving the accuracy of diagnosis of tumor lesions in MM patients following auto-HSCT.

Disclosures
No relevant conflicts of interest to declare.