Prediction of tumour necrosis fractions using metabolic and volumetric 18F-FDG PET/CT indices, after one course and at the completion of neoadjuvant chemotherapy, in children and young adults with osteosarcoma
The utility of combined metabolic and volumetric 18F-FDG PET/CT indices for predicting tumour necrosis fractions following neoadjuvant chemotherapy has not been extensively studied in osteosarcoma. Furthermore, little is known of the early PET/CT responses after only one chemotherapy course. Enrolled in the study were 20 children and young adults with resectable osteosarcoma who had undergone 18F-FDG PET/CT scans before and after neoadjuvant chemotherapy. Maximum standardized uptake value (mSUV), metabolic tumour volume (MTV), and total lesion glycolysis (TLG) were measured. From among the 20 patients, 14 were prospectively recruited and underwent an additional PET/CT scan after one chemotherapy course. Histopathological necrosis fractions were compared with the above-mentioned PET/CT indices and their ratios. MTV at the SUV threshold of 2 g/ml was closely correlated with the magnetic resonance image volumes before therapy (r = 0.91). In the prospective cohort, five patients were classified as good responders and nine as poor responders. All the metabolic indices (mSUV and its ratio) and combined metabolic/volumetric indices (MTV, TLG, and their ratios) except the mSUV ratio determined after therapy showed significant differences between good and poor responders (P <0.05). Differences were also noted for all of these indices determined after one chemotherapy course. Furthermore, most of these indices determined after therapy as well as after one chemotherapy course had good sensitivity, specificity, positive predictive value and negative predictive value with respect to predicting histological response to chemotherapy. In our osteosarcoma patient population, 18F-FDG PET/CT indices (either combined metabolic/volumetric or metabolic indices) determined after neoadjuvant chemotherapy were useful in predicting tumour responses. This held true after only one chemotherapy course.