Discrepancy between CT & PET in evaluating treatment response (ETR) & follow-up (FU) in patients (pts) with soft tissue sarcomas (STS)

Abstract

648

Objectives: STS are rare mesenchymal tumors with a wide array of histologic subtypes & biologic behavior which contribute to difficulty in predicting natural history & patterns of treatment response. To evaluate impact of both F-18 FDG PET & low dose CT components in PET/CT studies (std) performed for initial staging (I.S.), ETR post-surgery, radio or chemotherapy, short & long range FU & restaging in pts with STS, & focus on discrepancy between CT & PET findings. Methods: 58 pts with STS underwent 111 std: 7 I.S., 43 ETR up to 2 months(mo), 27 early FU from 2-6 mo & 34 long-term FU (>6 mo) were included. Histologic subtypes: 16 lipo, 21 leiomyo, 6 rhabdomyo, 3 synovial , 4 fibro, 3 hemangio, 1 chondro, 1 Schwanona, 1 GIST, 1 neuroectodermal sarcomas & 1 metastatic STS from unknown primary. All underwent PET/CT between 60-90 min following 10-15 mCi of 18F-FDG on GE Discovery PET/CT. Oral contrast was given. Findings were confirmed by clinical FU. Studies read by Nuclear Medicine & Radiology specialists. Results: 264 lesions detected, 235 concordant between PET & CT portions of PET/CT & 2911%) discordant. I.S. (7 std) CT & PET concordant in 5 & discordant in 2. ETR (43 std) PET/CT concordant in 35 (24 complete, 1 partial response(resp), 2 no resp, 3 progression & 5 mixed resp). Discordance found in 8(19%) (5 complete & 2 partial resp in PET & no change on corresponding CT, 1 study PET showed partial resp vs no changes on CT). PET identified bone marrow hyperplasia in 4 std before end of first mo after therapy. 27 std performed for early FU (2-6 mo) were concordant in 23 (complete resp 8, partial 2, progression 9 & mixed resp 4). Discordance observed in 4 std(15%) (1 complete resp, 2 partial resp in PET vs CT showing no resp in these 3 & 1 partial resp on PET vs CT progression of dx). 34 std for long term FU showed concordance in 30 std (11 free of dx, 3 stable & 16 recurrence or progression). Discordance was seen in 4(12%) (3 PET negative vs CT recurrence & 1 PET positive vs CT free of dx). Conclusions: In ETR, either short or long term FU, although combined PET/CT had higher accuracy than either alone, FDG PET is more accurate than CT alone.