is tc99m-mibi scintigraphy a predictor of response to pre-operative neoadjuvant chemotherapy in osteosarcoma?

objectives: multidrug resistance (mdr), which may be due to the over expression of p-glycoprotein (pgp) and/or mrp, is a major problem in neoadjuvant chemotherapy of osteosarcoma. the aim of this study was to investigate the role of tc-99m mibi scan for predicting the response to pre-operative chemotherapy. materials and methods: twenty-five patients (12 males and 13 females, aged between 8 and 52y) with osteosarcoma were studied. before the chemotherapy, planar 99mtc-mibi anterior and posterior images were obtained 10-min [tumor-to-background ratio: (t1/b1)10min] and 3-hr after tracer injection. after completion of chemotherapy, again 99mtc-mibi scan was performed at 10-min after tracer injection. in addition to calculation of decay corrected tumor to background (t/b) ratios ,  using the 10-min and 3-hr images of the pre-chemotherapy scintigraphy , percent wash-out rate (wr%) of 99mtc-mibi was calculated. using the 10-min images of the pre- and post-chemotherapy scans, the percent reduction in uptake at the tumor site after treatment (red%) was also calculated. then after surgical resection, tumor response was assessed by percentage of necrosis. results: all patients showed significant 99mtc-mibi uptake in early images. only 9 patients showed good response to chemotherapy (necrosis≥90%) while 16 patients were considered as non-responder (necrosis<90%). there was no statistical significant difference between non-responders and responders in (t1/b1)10min.there was a significant negative correlation between wr% and percentage of necrosis (p=0.001). on the other hand, there was a significant correlation between red% and percentage of necrosis (p<0.001).there was also statistical significant difference in wr% and red% between non-responders and responders (both p< 0.001). conclusion: washout rate of 99mtc-mibi in pre-chemotherapy scintigraphy as well as red% using pre- and post-chemotherapy mibi scintigraphy are useful methods for predicting response to neoadjuvant chemotherapy.