Gallium scintigraphypositron emission tomography

67Gallium scintigraphy and PET are often used to both accurately stage HL and assess response to treatment. Conventional CT scanning has not proven to be very sensitive for occult abdominal disease during the staging evaluation of HL. In addition, assessment of a residual mediastinal mass at the completion of therapy can be problematic with this modality. 67Ga scintigra-phy has proven to be more sensitive than CT in the posttreatment evaluation of HL, provided that the patient has a gallium-avid tumor at diagnosis.33-35 The positive and negative predictive values of 67Ga scintigraphy following treatment range from 92 to 100% and from 83 to 90%, respectively,36'37 compared to 48% and 83% with CT.36 PET scan using the glucose analog 2-(18F)-fluoro-2-deoxy-D-glucose (18F-FDG) has emerged as a very useful tool in the evaluation and

Table 72.4 Cotswolds update of the Ann Arbor staging system30

Stage Description

Stage I Involvement of a single lymph node region or lymphoid structure (e.g., spleen, thymus, Waldeyer's ring) or involvement of a single extralymphatic site (ie)_

Stage II Involvement of two or more lymph node regions on the same side of the diaphragm (the mediastinum is a single site; hilar nodes, when involved on both sides, constitute stage II disease); localized contiguous involvement of only one extranodal organ or site and lymph node region on the same side of the diaphragm (IIE). The number of anatomic regions involved should be designated by a subscript (e.g., II3)

Stage III Involvement of lymph node regions on both sides of the diaphragm, which may also be accompanied by involvement of the spleen (IIIS) or by localized contiguous involvement of only one extranodal organ (IIIE) or both (IIISE)

1111 With or without involvement of splenic, hilar, celiac, or portal nodes

1112 With involvement of para-aortic, iliac, and mesen-teric nodes

Stage IV Diffuse or disseminated involvement of one or more extranodal organs or tissues, with or without associated lymph node involvement

Designations applicable to any disease stage

A No symptoms

B Fever (temperature >38°C), drenching night sweats, unexplained weight loss of more than 10% of body weight in the preceding 6 months

X Bulky disease (>1/3 widening of the mediastinum or the presence of a nodal mass >10 cm)

E Involvement of single extranodal site that is con tiguous or proximal to known nodal site of disease monitoring of response in HL. In terms of diagnostic evaluation, in a small study of 11 patients undergoing staging laparotomy, the sensitivity and specificity of 18F-FDG PET were both 100%, compared to 20% and 83%, respectively, with CT scans.38 In a larger study of 45 patients with Hodgkin's and non-Hodgkin's lymphoma (NHL), PET scanning altered the staging in 16% of patients, although it understaged 7% of patients.39 Even more data exist regarding the impact of PET imaging on response assessment. In 54 patients with HL (19 patients) or NHL (35 patients), all 6 patients with a positive 18F-FDG PET relapsed—a positive predictive value of 100%, compared to 42% with conventional CT.40 The negative predictive value of 18F-FDG PET in this trial was 83%, with eight patients relapsing despite a negative study. In a second study in 48 patients previously treated for HL, the positive and negative predictive values of 18F-FDG PET were both equal to 92%.41 However, while 67Ga scintigraphy and

18F-FDG PET may both guide staging and treatment decisions, false positives do occur. For example, in patients younger than 25 years, a regenerating thymus can be gallium- or 18F-FDG avid, following completion of treatment of HL.42,43 Therefore, these noninvasive radiographic modalities do have utility in the diagnostic and response evaluation of HL; however, the results need to be interpreted in conjunction with the clinical circumstances, other laboratory evaluations, and CT results. In situations where PET or 67Ga scintigraphy results contradict the clinical picture or are inconclusive, biopsy may be warranted.

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