Quantitative thallium-201 scintigraphy in childhood osteosarcoma: Comparison with technetuim-99m MDP and magnetic resonance imaging in the evaluation of chemotherapeutic response.

The aim of this study was to assess early (15 min) and late 2 h) thallium-201 (201Tl) uptake in children with osteosarcoma and to compare these findings with magnetic resonance imaging (MRI) and technetium-99m methylenediphosphonate (99mTc MDP), with emphasis on evaluating tumor viability before and after chemotherapy. Fifteen patients with biopsy-proven osteosarcoma received standard preoperative chemotherapy with a combination of cisplatin, Adriamycin, and high-dose methotrexate. Their ages ranged between 7 and 18 years (median 14.5 years). All patients had 201Tl, 99mTc MDP, and MRI studies. Thallium scintigraphy was performed at 15 min and 2 h after IV injection of 92 MBq of thallium. Thallium uptake ratio was calculated by dividing the count density of the lesion (L) by that of the controlateral normal (N) area. The percent reduction of 201Tl uptake ratio (alteration ratio) was calculated by [100x(prechemotherapy L/N-postchemotherapy L/N)/prechemotherapy L/N]. Pathologic changes were graded on the basis of % tumor necrosis as defined histologically. Scintigraphic comparisons demonstrated a high-degree of correlation with late 201Tl alteration ration and poor correlation with both early 201Tl and 99mTc MDP alteration ratios. Late 201Tl images were superior to early 201Tl, 99mTc MDP, and MRI in predicting tumor response to chemotherapy as determined by % tumor necrosis (p<.01). The authors found that late 201Tl was an accurate test for evaluating the response to specific therapeutic regimens and it can be useful planning surgery or choosing alternative chemotherapeutic regimens.