Correlation of Tc-99m MIBI washout rate with tissue necrosis after neoadjuvant therapy in sarcomas

Objectives Tc-99m MIBI was evaluated to predict the response of neoadjuvant therapy in bone and soft-tissue sarcomas before it is initiated

Methods 31 patients, 17 with osteosarcomas (OS) and 14 with various soft-tissue sarcomas (STS) were included. Scintigraphy with IV injection of 370-630 MBq of Tc-99m MIBI was done before starting the therapy. Static images were taken at 10 (early) and 60 (delayed) min. post-injection. Lesions to normal ratios (L/N) were calculated. Therapy response was assessed by percent necrosis in specimen taken after amputation or limb salvage surgery. It was correlated and compared with washout rate (WR%) calculated from scintigraphic study

Results Necrosis after chemotherapy was 71.35±20.20% with 8 patients showing good response (necrosis ≥90%) and 23 had poor response (necrosis <90%). The response was higher in STS compared to OS (36% vs. 18% respectively). L/Ns were statistically not different in good and poor responders. Poor correlation of both early and delayed L/N with percent necrosis was seen. WR% was found to be 26.13±11.25% with median of 29% which was taken as cut-off value. There was a weak and negative correlation between percent values of necrosis in post-therapy specimen and WR%. However WR% of good responders was significantly lower than the poor responders (P=0.003). 88% of good responders had WR% < then 29% while only 35% poor responders showed WR% > than this cut-off value.

Conclusions Washout rate of Tc-99m MIBI is a reliable parameter to identify poor responders to neoadjuvant therapy in patients with bone and soft tissue sarcoma