Impact of PET and CT in PET/CT studies for staging and evaluating treatment response in bone and soft tissue sarcomas.

Purpose: Study impact of F-18 FDG PET/CT on initial staging, restaging, and evaluating treatment response (ETR) in bone and soft tissue sarcomas (BSTS), focusing on discrepancy between CT and PET portions.

Patients And Methods: Ninety-three BSTS patients having 204 F-18 FDG PET/CT studies were retrospectively reviewed. They were divided into 4 groups. Group I for initial staging included 16 patient studies. The other 3 groups were divided according to the time interval from last treatment received. Group II for ETR up to 2 months included 83 studies. Group III was for early restaging after 2 to 6 months included 45 studies. Group IV was for long-term follow-up after 6 months included 60 studies. All results were confirmed either by pathology, or by clinical follow-up.

Results: Sixteen studies for initial staging were concordant in 14 and discordant in 2 patients (48 lesions, 46 concordant, and 2 discordant). PET showed 97.2% sensitivity and 100% specificity versus 100% and 91.6% on CT. Regarding the other 3 groups, 498 lesions were detected; PET and CT were concordant in 436/498 (88%) and discordant in 62/498 (12%). In group II for ETR, PET and CT were concordant in 64/83 (77%) and discordant in 19/83(23%) studies-13 showed excellent to complete response on PET with partial response (PR) or stable disease (SD) on CT; 6 studies in PET showed PR versus SD or progression of disease (PD) on CT. In group III, for early restaging of disease 36/45 (80%) concordant and 9/45 (20%) discordant (3 showed excellent to complete response and 2 PR on PET versus CT SD, 3 PET PR versus CT PD, and 1 PET study showed PD while CT showed SD). In group IV, for long-term restaging, 49/60 (82%) were concordant and 11/60 (18%) were discordant; 9 PET studies were negative for active disease versus CT positive and 2 PET studies showed PD, CT was negative. PET alone showed 94.1% sensitivity and 94.6% specificity versus 97.2% and 63.5% for CT, 100% and 95.9% for PET/CT.

Conclusions: In BSTS for the purpose of initial staging, ETR, short-term, or long-term restaging, FDG-PET is more accurate than CT. Combined PET/CT has higher accuracy than either alone.