Utility of PET/CT after cryoablation for early identification of local tumor progression in osseous metastatic disease

OBJECTIVE. The purpose of this study is to evaluate the utility of combined PET/CT for the detection of early local tumor progression after cryoablation of bone metastases. MATERIALS AND METHODS. A retrospective single-institution review revealed 61 consecutive patients with 80 separate bone metastases treated with cryoablation who were evaluated with a preablation PET/CT and at least two postablation PET/CT examinations between September 2007 and July 2015. Patients were excluded if they had local therapy or pathologic fracture after ablation. The patients were grouped according to postcryoablation disease status (i.e., local tumor progression or not) and PET radiotracer (i.e., ¹¹C-choline or ¹⁸F-FDG) used. The maximum standardized uptake value (SUV_max) ratio (i.e., ratio of SUV_max to blood pool) was calculated within each osseous metastasis before and after cryoablation, and these were then compared between groups. RESULTS. Of the 61 patients and 80 ablations performed, 32 patients were imaged with FDG PET/CT and 29 were imaged with ¹¹C-choline PET/CT. Twenty-three patients imaged with FDG and 13 patients imaged with ¹¹C-choline had evidence of local tumor progression on all postablation PET/CT examinations. The SUV_max ratio was significantly higher in patients with local tumor progression on the first and most remote postcryoablation PET/CT examinations for both FDG and ¹¹C-choline (p < 0.001 in all cases). There was no significant difference in the postablation systemic therapy between the groups with and without local tumor progression. CONCLUSION. Increased SUV_max ratio in patients after cryoablation for osseous metastatic disease should raise concern about local tumor progression independently of time after ablation.