Thallium-201 for oncological imaging in children.

Many pediatric centers are beginning to accumulate a large experience in the use of thallium-201 (201Tl) imaging with 201Tl requires a state-of-the-art high-resolution gamma camera computer system with single photon emission computed tomography (SPECT) capability and a physician-directed tailored examination. Tumor imaging with 201Tl, with its multifactorial localization mechanisms that are different from those for gallium-67, offers a distinct advantage over gallium tumor imaging with a short total imaging time. Tumors are variable in avidity and intensity of thallium uptake. Primary and metastatic disease can be detected with 201Tl scintigraphy. Baseline pretreatment determination of thallium avidity is crucial to its efficacy in therapeutic response assessment. Adjunctive SPECT imaging provides greater sensitivity for lesion detection and direct comparison of physiology (thallium uptake) with anatomy (computed tomography and magnetic resonance imaging). The sensitivity and specificity for detection of pediatric brain tumors has been reported as 77% and 93%, respectively. Thallium-201 brain SPECT also provides a less expensive and more readily available alternative to positron emission tomography for assessing the functional state of pediatric brain tumors. Extremity osteogenic sarcoma and Ewing's sarcoma have 100% sensitivity for 201Tl uptake pretreatment. Early results confirm an association between 201Tl uptake and histological tumor response. The determination of residual/recurrent disease versus thymic rebound and other nonneoplastic change in thallium-avid lymphoma, rhabdomyosarcoma, and germ cell tumors that involve the thorax can be confirmed with a 201Tl SPECT examination. Soft-tissue tumors elsewhere in the body may be detected with 201Tl scintigraphy. Thallium-201 does not exhibit 100% specificity for tumors. False-positive 201Tl uptake has been seen in histiocytosis X, benign bone tumors, stress fractures, and inflammation.