Thallium bone imaging as an indicator of response and outcome in nonmetastatic primary extremity osteosarcoma

Purpose. We investigated one Tl-201 bone scintigraphy method as a predictor of histologic response and event-free survival (EFS) of nonmetastatic extr emity osteosarcoma. Materials and methods. We evaluated images of the primary tumor to determin e whether they exhibited a donut of avidity for 40 patients enrolled on a s ingle institutional protocol. Participants underwent three serial Tl-201 bo ne scintigraphy studies during preoperative neoadjuvant chemotherapy. Intra - and interobserver variability of the method was assessed, and the presenc e of the donut of avidity was examined as a predictor of EFS and histologic response. Results. Fifty-three percent of patients were female and 75% were Caucasian ; the median age at diagnosis was 13.5 years. Intraobserver agreement was m oderate to very good, ranging from 0.595 to 0.865. Interobserver agreement was moderate to good for all time points, ranging from 0.576 to 0.708. Ther e was a significant difference in EFS among patients with and without the d onut-shape at any of the three time points (P = 0.049); patients whose tumo rs displayed a donutshape had inferior EFS. Conclusion. The pattern of donut avidity in extremity OS is a predictor of lower EFS, but does not correlate with histologic response to therapy.