TL-201 VERSUS TECHNETIUM-99M-MIBI SPECT IN EVALUATION OF CHILDHOOD BRAIN-TUMORS - A WITHIN-SUBJECT COMPARISON

We previously found that Tl-201 SPECT is a highly specific agent for d etection of metabolic activity of childhood brain tumors. To compare t he relative diagnostic accuracy of Tl-201 and a technetium-based tumor -avid agent, we have obtained SPECT in 19 children using Tl-201 (37-11 1 MBq) followed immediately by Tc-99m-methoxyisobutylisonitrile (MIBI) (370-740 MBq) intravenously. Moderate to intense focal uptake of both tracers characterized true positive cases (n = 6). Lesion boundaries were better defined by MIBI. Uptake of MIBI by choroid plexus occurred despite pretreatment with potassium perchlorate (6 mg/ kg) and compli cated interpretation of deep/paraventricular lesions. Preliminary asse ssment indicated sensitivity approximately 67% (Tl and MIBI); specific ity approximately 91% (Tl); approximately 100% (MIBI). Two tumors (med ulloblastoma, dysgerminoma) were Tl/MIBI nonavid. Semi-quantitative as sessment of tracer uptake was made using a ratio of radioactivity in t umor-containing areas compared to uninvolved brain. Ratio values were (mean +/- s.d.) 7.88 +/- 7.70 (Tl) and 27.1 +/- 36.41 (MIBI). The spec trum of tumor activity is similar for Tl and MIBI. Clearer identificat ion of boundaries by MIBI may be an advantage in applications, e.g., r adiotherapy port planning.