sites is fundamental to the definition of response—most series suggest that 50-60% of those patients do not have viable disease. Both gallium and FDG have high sensitivity and specificity in defining the presence of active tumor and are the investigations of choice.
Repeating the gallium imaging after 2 cycles of chemotherapy may predict treatment failure if gallium uptake persists. Positive gallium uptake at the end of treatment also appears to predict reduced survival and reduced disease free interval. The same parameters for predicting treatment failure can probably be applied to PET. In children a confounding feature is uptake within a hyperplastic thymus; this
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