Background-aim: As extensively shown in the literature, 18F-FDG biodistribution in normal and neoplastic tissues is proportional to their glucose metabolism. Therefore its semi-quantitative estimate (SUV) has quickly become the most widely used parameter for tumor detection, staging, restaging and therapy response evaluation in clinical oncology. The SUV calculation, however, is influenced by several parameters that are closely related to both physical charac- teristics of the tomograph and processing softwares used for images reconstruction. The aim of our study was thus to evaluate the role that may have different reconstruction algorithms on the SUV and volume lesion estimates and, consequently, determine their possible impact in the interpretation of PET-CT images. Methods: We retrospectively analyzed 189 PET-CT lesions in lung cancer (92 pulmonary nodules, 67 metastatic lymph nodes) and lymphoma patients (30 Hodgkin or Non-Hodgkin pathologic lymph nodes). SUVmax and volumes were calculated for all lesions with both a standard iterative reconstruction algorithm (IR) and the new True-X-TOF (Siemens Medical Solutions, Erlangen, Germany) method. The distribution of SUVmax, in relation to the reconstruction method used, was statistically analyzed by linear regression (fre- quency distribution curves and scatter plots). The relationship between volume and ratio between SUVmax True-X-TOF and IR (SUVr) was evaluated and shown with box-plots. Results: The SUV ratio ‘‘True-X-TOF/IR’’ (SUVr) was used to stratify the lesions in three groups: I 1.0 B x B 1.5, II 1.5 \ x B 2.0, III x [ 2.0, inside which regression correlation stays excellent (R = 0.996, 0.996 and 0.993 respectively). Among the three groups a statistically significant stratification of ratios between lesion volumes and SUVr values was observed (p \ 0.001): smaller volumes were associated to greater SUVr, while larger volumes ([2 cm3) were associated to SUVr closer to 1. Pulmonary lesions and lymph nodes represented 70 and 30% respectively of findings in group I, and 45 and 55% in group II and III combined. Conclusions: FDG PET-CT SUV is determined by a lot of parame- ters, among which acquisition modalities and reconstruction techniques can play a pivotal role. Our preliminary data, obtained from a daily clinical setting, demonstrated that True-X ? TOF shows greater SUV values in comparison to IR method. However, greater differential SUVmax values were identified in small lesions compared to larger ones, probably meaning that IR underestimates SUV in smaller lesions. Therefore, True-X ? TOF reconstruction algorithm seems to allow more sensitive metabolic characterization of small lesions in comparison to iterative methods making the impact of that feature more relevant in staging and prognostic stratification of lymph nodes than of generally larger pulmonary lesions. Moreover our study highlights the risk to compare PET-CT scans obtained with different reconstruction methods during clinical follow-up and so the impor- tance of standardization in PET-CT imaging. Larger clinical prospective trials are mandatory to confirm these preliminary findings and to assess their potential impact in clinical practice.
Technical aspects related to different reconstruction algorithms in FDG PET-CT imaging: a correlation study between SUVmax and volume in neoplastic lesions
C. Cittanti;SCHINCAGLIA, VANESSA;M. Bartolomei
2017
Abstract
Background-aim: As extensively shown in the literature, 18F-FDG biodistribution in normal and neoplastic tissues is proportional to their glucose metabolism. Therefore its semi-quantitative estimate (SUV) has quickly become the most widely used parameter for tumor detection, staging, restaging and therapy response evaluation in clinical oncology. The SUV calculation, however, is influenced by several parameters that are closely related to both physical charac- teristics of the tomograph and processing softwares used for images reconstruction. The aim of our study was thus to evaluate the role that may have different reconstruction algorithms on the SUV and volume lesion estimates and, consequently, determine their possible impact in the interpretation of PET-CT images. Methods: We retrospectively analyzed 189 PET-CT lesions in lung cancer (92 pulmonary nodules, 67 metastatic lymph nodes) and lymphoma patients (30 Hodgkin or Non-Hodgkin pathologic lymph nodes). SUVmax and volumes were calculated for all lesions with both a standard iterative reconstruction algorithm (IR) and the new True-X-TOF (Siemens Medical Solutions, Erlangen, Germany) method. The distribution of SUVmax, in relation to the reconstruction method used, was statistically analyzed by linear regression (fre- quency distribution curves and scatter plots). The relationship between volume and ratio between SUVmax True-X-TOF and IR (SUVr) was evaluated and shown with box-plots. Results: The SUV ratio ‘‘True-X-TOF/IR’’ (SUVr) was used to stratify the lesions in three groups: I 1.0 B x B 1.5, II 1.5 \ x B 2.0, III x [ 2.0, inside which regression correlation stays excellent (R = 0.996, 0.996 and 0.993 respectively). Among the three groups a statistically significant stratification of ratios between lesion volumes and SUVr values was observed (p \ 0.001): smaller volumes were associated to greater SUVr, while larger volumes ([2 cm3) were associated to SUVr closer to 1. Pulmonary lesions and lymph nodes represented 70 and 30% respectively of findings in group I, and 45 and 55% in group II and III combined. Conclusions: FDG PET-CT SUV is determined by a lot of parame- ters, among which acquisition modalities and reconstruction techniques can play a pivotal role. Our preliminary data, obtained from a daily clinical setting, demonstrated that True-X ? TOF shows greater SUV values in comparison to IR method. However, greater differential SUVmax values were identified in small lesions compared to larger ones, probably meaning that IR underestimates SUV in smaller lesions. Therefore, True-X ? TOF reconstruction algorithm seems to allow more sensitive metabolic characterization of small lesions in comparison to iterative methods making the impact of that feature more relevant in staging and prognostic stratification of lymph nodes than of generally larger pulmonary lesions. Moreover our study highlights the risk to compare PET-CT scans obtained with different reconstruction methods during clinical follow-up and so the impor- tance of standardization in PET-CT imaging. Larger clinical prospective trials are mandatory to confirm these preliminary findings and to assess their potential impact in clinical practice.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
