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may be differentiated by tomographic imaging where a characteristic "H" pattern of uptake is seen on coronal sections.

Evaluating Relapse and Restaging

With more aggressive—and successful—salvage protocols, early detection of recurrence has become important in the management of these patients. Gallium and FDG have very high clinical accuracy in confirming the presence of active tumor and defining the extent of disease burden. Both radiopharmaceuticals are useful in evaluating a residual mass on CT, functionally defining a CT abnormality, and whole

Figure 14. Anterior 18F-FDG scan of a patient with extensive mediastinal lymphoma (arrows). Metastases to pelvic lymph nodes are also present (arrowheads). (Courtesy of ADAC Labs and Dr. A. Alavi, University of Pennsylvania, Philadelphia, USA).

body screening in high risk patients or those with palpable nodes. Standard of care in this patient population should include imaging with either gallium or FDG.

As PET imaging becomes routinely available, FDG will almost certainly replace gallium as the investigation of choice. If the preliminary data supporting its role as a predictive assay of response are confirmed, it will be routinely performed prior to treatment, after 1 or 2 cycles of therapy, and during follow-up.

Melanoma

Melanoma is increasing in incidence in most of the developed world, and in countries such as Australia the incidence is doubling every ten years. At presentation the most important prognostic indicator is tumor thickness as described by the Breslow classification.

Five year survival in patients with Stage IIB (tumor thickness > 4.00mm) or worse is poor—chances of curative therapy depend entirely on the accuracy of staging and the completeness of radical dissection. Locoregional recurrence is high and restaging at recurrence carries the same requirements as at presentation. Interferon alpha-2a (IFN alpha-2a) is efficacious as adjuvant therapy in stage IIB and III melanoma, but is toxic and expensive. Accurate staging is therefore required before embarking on a course of therapy.

Lymphoscintigraphy

Lymphoscintigraphy with sentinel node mapping has revolutionized the staging of patients with melanoma, providing the surgeon with an accurate localization of sentinel nodes. Orderly and sequential drainage to the sentinel node and then to the

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