F-18-FDG PET in the evaluation of residual masses in patients with Hodgkin Disease

Residual masses are frequently observed in patients with Hodgkin disease (HD) after therapy and discrimination between active tumor tissue and fibrotic residues remains a clinical challenge. In the large percentage of patients (> 60%) conventional imaging methods show remaining tumor masses at the end of therapy, although only a small percentage of these patients still have active disease and eventually will relapse. AIM: The aim of this study was to asses the value of the F-18-FDG PET in detecting residual disease in patients with residual masses after completed therapy, in comparison to the tumor masses volume changes according to the CT after therapy. METHODS: 66 patients with HD and residual masses (size1.2-5.2 cm in diameter) after completed initial or second line therapy were retrospectively included in our study (29 male ; 37 female), median age 29.5 (range 13-80 years). All lesions have been confirmed by histological examinations before treatment and patients staged according to Ann Arbor classification. They were assigned for FDG PET at least 3 weeks after chemotherapy and 12 weeks after radiotherapy. Using computed tomography patients were divided in four groups according to the changes in volume of tumor mass after the therapy (I- tumor reduction < 30% ; II- tumor reduction 30-50% ; III- tumor reduction > 50-70% ; IV- tumor reduction > 70%). RESULTS: PET negative residual mass were observed in 42 patients (64%) and positive findings were observed in residual masses of 19 patients (29%). Five patients had equivocal findings (7%). Although the percentage of PET positive findings were the highest in the first two groups with lowest regression, in comparison with the other groups in which higher percentage of tumor volume reduction was noticed (I – 32% positive ; II – 61% positive ; III 12, 5% positive and IV- 17% positive findings). CONCLUSIONS: Changes in volume of tumor mass, as documented with computed tomography, are neither sensitive nor specific enough for accurate evaluation of residual disease. FDG PET is superior to conventional imaging for detection of residual active disease at the end of treatment what has great influence on further management. In our study, 17% of patients with almost complete regression of tumor masses had residual disease after therapy and should be further treated. Contrary, even 58% patients with minimal tumor shrinkage had not active disease and should not be additionally treated.