Has the 67Ga-SPET a Role in Monitoring Hodgkin and Primary Mediastinal Lymphoma in the PET-FDG Age?.

Background and aims Present data indicate that FDG-PET has a superior accuracy than gallium scan (Ga-S) in staging and post-therapy restaging of malignant lymphomas. However in Hodgkin’s lymphoma (HL) with a predominant mediastinal involvement and in primary mediastinal lymphoma (ML), this latter, less expensive, nuclear imaging technique might still have a diagnostic value. The aims of this prospective study were to assess: the accuracy of SPET Ga-S in detecting residual tumour in the upper diaphragm nodal regions mainly in the mediastinal site and its predictive value in terms of disease free survival (DFS) and overall survival (OS). Methods Since 1989, 68 patients (pts) with HL (60) or ML (8) were enrolled: 24 male and 44 female. Median age was 28 (range 12-80) years. Ann Arbor stage distribution was: stage IIA in 18 pts, IIB in 23 pts, IIIA in 4 pts, IIIB in 6 pts, IVA in 4 pts and IVB in 13 pts. Histology subgroups included 43 SN, 11 CM, 1 DL, 2 LP, 3 unclassified HL and 8 large B-cell ML. Bulky mediastinal disease was detected in 22 HL and all of ML cases. 44 patients received conventional chemotherapy, 4 non-myeloablative and 20 myeloablative chemotherapy with peripheral blood stem cells support because of unfavourable disease or resistant or relapsing to primary treatment disease. Ga-SPET was performed in all patients 72 hours after the intravenous injection of 370 MBq (8–10 mCi) of 67Ga cirate. SPET data acqusiton included a 360° rotation, with 60 projections at rate of 20 s per projection. The matrix size was 64x64 and a Butterworth filter (0.4–0.6) was used. Results A total of 107 Ga-SPET/TC restaging were obtained after chemotherapy and/or chemo-radiotherapy completion in 64/68 evaluable pts. Despite 84/107 CT evaluations were suggestive of persistent disease in the mediastinal region, 61/107 simultaneous Ga-SPET exams were negative. Instead Ga-SPET indicated the presence of active disease only in 5 cases although the CT was interpreted as negative. Concordant results were documented in the remaining 41 evaluations. The difference in the final post-therapy findings between Ga-SPET and TC were less frequent in upper diaphragm nodal region other than mediastinum, with concordant and discordant results respectively in 51/71 and 20/71 scans. Sensitivity, specificity and accuracy were 89%, 93% and 92% for the Ga-SPET, while they were 100%, 27% and 37% for the CT when the mediastinal area was considered. After a median follow-up of 34 (4–138) months, DFS and OS for patients with a positive Ga-SPET at the end of treatment program were 9 (2–57) and 24,5 (9–67) months, respectively. In contrast, the Corresponding figures have not been reached for patiens with a negative Ga-SPET after a median time of 31,5+ (3–136) months and 49,5+ (4–144) monhs respectively. The median values of DSF and OS of patients with a CT compatible with absent or persistent disease have not been reached at 31+ (3–89) vs 27+ (3–136) months and 46+ (11–108) vs 40+ (4–144) months. Conclusions Thus, Ga-SPET is still a useful, sensitive and not expensive method to determine the presence of eventual active post-therapy disease in the mediastinum.