Thallium-201 scintigraphy for the evaluation of tumor response to preoperative chemotherapy in patients with osteosarcoma

Abstract

BACKGROUND. The degree of tumor necrosis after preoperative intravenous chemotherapy is likely to be an indicator of prognosis for patients with primary osteosarcoma. This study was undertaken to evaluate the efficacy of thallium-201 (Tl-201) scintigraphy in assessing response to chemotherapy in patients with osteosarcoma and to correlate the findings with the degree of tumor necrosis assessed histologically. METHODS. Twenty-four patients with biopsy-proven osteosarcoma underwent Tl201 imaging before and immediately after preoperative intravenous chemotherapy. The maximum pixel counts taken over the tumor divided by those taken of a background region yielded a tumor- to-background ratio. The percentage of change in the tumor-to-background ratio before and after chemotherapy, defined as the alteration ratio, was correlated with the percentage of tumor necrosis. The percentages of tumor necrosis were classified into 4 grades: Grade 1, <50%; Grade 2, 5089%; Grade 3, 90- 99%; Grade 4, 100%. RESULTS. Three patients with Grade 1 histologic response had an alteration ratio of 31% ± 4 (mean ± standard deviation). Three patients with Grade 2 response had an alteration ratio of 76% ± 9. Nine patients with Grade 3 response had an alteration ratio of 84% ± 11. Nine patients with Grade 4 response had an alteration ratio of 96% ± 5. These ratios correlated well with the histologic grades (P < 0.001). CONCLUSIONS. The results of this study suggest that Tl-201 scintigraphy is a powerful tool in the evaluation of tumor response to chemotherapy in patients with osteosarcoma.