European Journal of Nuclear Medicine Short communication Quantitative evaluation of thallium-201 uptake in predicting chemotherapeutic response of osteosarcoma Joanna Lin 1, Wai-tong Leung 1, Stephen K. W. Ho ~, K. C. Ho 2, S. M. Kumta 3, Con Metreweli2, Philip J. Johnson 1 1 Department of Clinical Oncology, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong 2 Department of Diagnostic Radiology and Organ Imaging, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong 3 Department of Orthopaedics and Traumatology, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Received 28 November 1994 and in revised form 12 February 1995 Abstract. Thallium-201 has been shown to be useful in predicting tumour viability in patients undergoing neo- adjuvant chemotherapy for osteogenic sarcoma. Early studies relied upon qualitative assessment of analog im- ages to obtain predictive results. Recently, the lesion to normal tissue uptake ratio of 2°1T1 has been used in eval- uating bone and soft tissue sarcomas. This study at- tempts to quantitate changes in tumour to normal tissue ratio following chemotherapy. Eight consecutive patients with classical osteosarcoma received standard preopera- tive chemotherapy with a combination of cisplatin, adriamycin and high-dose methotrexate. 2°lT1 gamma scintigraphic images were obtained both before and after chemotherapy. The average counts taken over the tumour divided by that from the contralateral normal tissue area yielded a tumour-to-normal tissue (T/N) ratio. The per- centage change in the T/N ratio before and after preoper- ative chemotherapy was correlated with the percentage of tumour necrosis from pathological section. The medi- an post-chemotherapy T/N ratio was 1.85 (range 0.5-7.7). The median percentage change in T/N ratio af- ter chemotherapy was -58% (range +26% to -83%). The median percentage of necrosis from pathological section was 80% (range 0%-95%). There was a good correlation between the percentage of tumour necrosis and the percentage change in T/N ratio (rank correlation coefficient r=0.84, P=0.0085). Quantitative assessment of changes in 201T1 uptake by osteosarcoma correlates well with tumour necrosis after preoperative chemother- apy. This method may be used to predict response to chemotherapy at an earlier stage, enabling the clinician to consider alternative chemotherapeutic regimens or salvage surgery. Key words: Osteogenic sarcoma - Thallium-201 - Che- motherapy Correspondence to: W. T. Leung Eur J Nucl Med (1995) 22:553-555 Introduction Osteogenic sarcoma is at present optimally treated by a combination of neoadjuvant chemotherapy and surgery. Preoperative chemotherapy has been part of this treat- ment programme in most centres. The response of the tumour to preoperative chemotherapy, as defined by the degree of tumour necrosis, has been found to be one of the best prognostic indicators for this disease [1]. How- ever, this information can only be obtained by detailed histological examination after the tumour has been re- sected. Recently, there have been attempts to predict the tumour response to chemotherapy, before surgical resec- tion, by various imaging techniques. Radionuclide imaging is a sensitive method of detect- ing bone lesions. Several radioactive substances have been used, the most common being technetium-99m la- belled medronate (99mTc-MDP), but this cannot accu- rately predict tumour viability as it reflects bone metab- olism and increased MDP uptake may be related to other pathological processes such as fracture. Gallium-67 ci- trate does give more information regarding the metabolic activity of tumour tissue but the inflammatory compo- nents of the tumour may also take up gallium. Gamma scintigraphy using thallium-201 chloride has been used to detect soft tissue and bone sarcomas, to as- sess viable tumour burden and for evaluation of response to preoperative chemotherapy [2-7]. It has been shown that it is superior to 99mTc-MDP and 67Ga citrate in as- sessing tumour viability and predicting tumour necrosis after chemotherapy. Tumour-to-normal tissue (T/N) up- take ratios from quantitating images have been suggest- ed as an indicator of viable tumour [2, 3]. We have attempted, in this prospective study, to ob- tain a quantitative assessment of tumour response by cal- culating the pre- and post-chemotherapy T/N uptake ra- European Journal of Nuclear Medicine Vol. 22, No. 6, June 1995 - © Springer-Verlag 1995