Depending on the histology and risk factors, 30% to 75% of patients with advanced HD and aggressive NHL can be cured with front-line treatment[1
]. However, patients who do not achieve complete remission (CR) at the end of first-line treatment or who have a relapse after CR, have a poor prognosis regardless of any further conventional treatment[1
]. Treatment with high-dose chemotherapy combined with stem cell transplantation increases survival[2
] and response to treatment is currently assessed on the basis of clinical, radiologic, and pathologic criteria. Computed tomography remains the standard for the evaluation of nodal disease. However, defining response criteria based on conventional radiographic characteristics remains difficult because lymphoma patients treated with chemotherapy often present with residual masses of uncertain significance. These residual masses may consist of fibrotic tissue or viable tumor and CT cannot differentiate between active tumor and fibrosis[11
]. In the management of lymphoma, GS has been used with some success in differentiating residual disease from fibrotic masses after treatment[11
]. Role of GS in the follow-up has been studied immensely as well, all showing better performance over CT[11
]. However, few studies have been conducted on the value of GS after high dose chemotherapy and ASCT. In this study, GS obtained before and 100 days after high dose chemotherapy in addition to ASCT were compared with CT scans within the same time intervals. The predictive value of the scans was evaluated for these patients as well.
The follow-up of 25 patients with normal GS findings on D-100 post-ASCT revealed that they were all in CR, except 3. One of them had normal findings on GS and CT, both on D-100 and D-200, developed MDS and was lost eventually on 42 months post-ASCT. The second patient who developed acute myeloid leukemia and died 40 months post-ASCT, had normal GS but abnormal CT findings in the pretracheal area but these lesions disappeared in the control CT scans on D-200. The last patient had normal Ga-67 and CT scan, relapsed 18 months later and died 36 months post-ASCT. So this patient was considered false negative of GS, but to the best of our knowledge there is no knowledge of how long a GS could predict event free survival.
Written reports of CT and GS were used to establish the predictive values of these tests. Using written reports might have put GS at a relative disadvantage compared to conventional imaging due to the diverse experience of the readers for the distribution of Ga-67 in the body. Pitfalls in the interpretation of GS are very well established, because of various reasons. The false positive results in this study is mainly due to the prominent hilar uptake of Ga-67, which is usually seen in patients with a history of cigarette smoking, and after cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy regimens. Although bilateral mild hilar uptake, which is less than the original disease, of Ga-67 is very well described in the literature sometimes as in this study asymmetrical severe uptake can be misleading. Asymmetrical uptake of Ga-67 not only in the hilar region but also in the breast came up to be false positive on the follow-up clinically as well.
GS is being replaced by a newer technique in centers that have the appropriate facilities for FDG imaging. As in the case of Ga-67, FDG is a tumor viability agent and its uptake indicates the presence of active disease[14,15]. FDG has already been found to overcome some of the limitations of GS in the evaluation in lymphoma patients. However, dedicated FDG–PET is currently still of limited availability. SPECT systems are commonly used in the routine practice of nuclear medicine. The limitations and pitfalls of GS have been elaborated in large number of patients and currently do not interfere with image interpretation by physicians with appropriate knowledge and expertise. GS is a good functional imaging modality for lymphoma, it may detect relapse earlier than conventional imaging modalities and identifies patients with refractory disease. The current study demonstrates that GS can be used to predict the outcome of patients undergoing ASCT with lymphoma accurately. In contrast, CT was unable to reliably predict disease-free survival, mainly due to its poor specificity. We hope that our data regarding the use of GS in the evaluation of patients with lymphoma undergoing ASCT is useful and is added to the list of GS utilization list.