[Changes in metabolism and peritumoral circulation after radiosurgery of metastatic brain tumors: evaluation by three dimensional dual isotope SPECT].

Concurrent use of two different isotopes, 201T1C1 and 123I-IMP, in SPECT is useful in separative evaluation of tumor metabolism and peritumoral circulation. Three dimensional SPECT employed in our study has an obvious advantage over two dimensional SPECT for its accurate imaging of tumors and peritumoural areas. Changes of tumor metabolism and regional circulation in peritumoral edematous tissues were investigated by fused 3-D SPECT images using 201T1C1 and 123I-IMP. In this study, the volume of isotope accumulative and isotope defective regions were measured. Fusion of SPECT images was performed by the use of panning visualization software; Application Visualization System Medical View (K.G.T.). The threshold of 3-D rendering was determined by conforming the volume of the hemisphere and of the tumor estimated on CT to the volume of 123I-IMP and 201T1C1 accumulating area respectively. Accumulative volume of 201T1C1 in the tumor decreased remarkably at 7 days after radiosurgery (p < 0.01). Defective volume of peritumoral hypoperfusion was measured on 3-D SPECT. The average volume was 80.5 + 32.5cm3 before radiosurgery. It decreased by approximately 60% at 7 days after radiosurgery (p < 0.05). Analysis of 3-D SPECT images using two different isotope tracers is reliable and useful to evaluate early the changes of metabolism and peritumoral circulation in or around intracerebral tumors.