USE OF TC-99M-MIBI SCINTIGRAPHY IN THE EVALUATION OF THE RESPONSE OF OSTEOSARCOMA TO CHEMOTHERAPY

The use of gamma camera scintigraphy with technetium-99m hexakis-2-met hoxyisobutylisonitrile (Tc-99m-MIBI) for assessment of the response of high-grade osteosarcoma to preoperative chemotherapy was evaluated. T welve patients with osteosarcoma of the extremities underwent planar e xamination with Tc-99m-MIBI before and after preoperative chemotherapy according to the recommendations of the Scandinavian Sarcoma Group. A fter calculating a quotient for the tumour and the average activity of both extremities and correcting for background activity, the change i n uptake between the two examinations was assessed. This was compared with histological examination of the ultimately resected specimen in 1 1 patients and progressive clinical disease in one. All the 11 tumours undergoing histological examination showed cellular necrosis of betwe en 50% and 100% as well as a reduced uptake of Tc-99m-MIBI, while the single progressive tumour showed an increased uptake. There was a corr elation between the reduction of radiopharmaceutical uptake and the hi stological response in the entire series, while the Variation was too large to allow conclusions in individual patients, This Variation may have biological reasons or may be due to the planar imaging technique, which only allows semiquantitative evaluation. The technique reflects response to therapy but is not yet clinically applicable for the iden tification of poor responders, which would serve as a basis for altera tion of the chemotherapy regimen. In order to evaluate whether such a role could be fulfilled, further studies using single-photon emission tomography with correction for attenuation and scattering of photons a re necessary.