Assessment of response of brain metastases to radiotherapy by PET imaging of apoptosis with 18F-ML-10

Early assessment of tumor response to therapy is vital for treatment optimization for the individual cancer patient. Induction of apoptosis is an early and nearly universal effect of anticancer therapies. The purpose of this study was to assess the performance of F-18-ML-10, a novel PET radiotracer for apoptosis, as a tool for the early detection of response of brain metastases to whole-brain radiation therapy (WBRT). Ten patients with brain metastases treated with WBRT at 30 Gy in ten daily fractions were enrolled in this trial. Each patient underwent two F-18-ML-10 PET scans, one prior to the radiation therapy (baseline scan), and the second after nine or ten fractions of radiotherapy (follow-up scan). MRI was performed at 6-8 weeks following completion of the radiation therapy. Early treatment-induced changes in tumor F-18-ML-10 uptake on the PET scan were measured by voxel-based analysis, and were then evaluated by correlation analysis as predictors of the extent of later changes in tumor anatomical dimensions as seen on MRI scans 6-8 weeks after completion of therapy. In all ten patients, all brain lesions were detected by both MRI and the F-18-ML-10 PET scan. A highly significant correlation was found between early changes on the F-18-ML-10 scan and later changes in tumor anatomical dimensions (r = 0.9). These results support the potential of F-18-ML-10 PET as a novel tool for the early detection of response of brain metastases to WBRT.