Introduction: Radiographic assessment of cerebral metastasis after stereotactic radiosurgery (SRS) remains a major challenge in neuro-oncology. It is often difficult to distinguish tumor progression (TP) from radiation necrosis (RN) in this setting using conventional MRI. The objective of this study is to compare the diagnostic sensitivity and specificity of different functional imaging modalities for detecting tumor recurrence after SRS.
Methods: We retrospectively reviewed patients treated between 2007 and 2010 and identified 14 patients with cerebral metastasis who suffered clinical or radiographic progression following SRS and were imaged with arterial spin labeling (ASL), FDG-PET, and Thallium-SPECT imaging prior to stereotactic biopsy. Diagnostic accuracy, specificity, sensitivity, positive predictive value, and negative predictive value were calculated for each imaging modality using pathologic diagnosis as gold standard.
Results: Six patients (42%) suffered tumor progression while eight (58%) developed radiation necrosis. FDG-PET and ASL were equally sensitive in detecting tumor progression (83%). However, the specificity of ASL was superior to that of FDG-PET or SPECT (100%, 75%, and 50% respectively). The positive and negative predictive values of ASL were also superior to those of FDG-PET or SPECT. Combination of modalities did not significantly augment the sensitivity, specificity, PPV, or NPV of ASL.
Conclusions: In our series, ASL positivity closely associates with pathological diagnosis of tumor progression after SRS. Validation of this finding in a large series is warranted.
Patient Care: Improved assessment of post-radiation radiological changes will better guide decision making regarding invasive work-up procedures as well as aid biopsy target selective when invasive procedures are warranted
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe limitations in imaging surveillance of radiation treated brain tumors, 2) Discuss the advantages and disadvantages of current structural and functional imaging modalities used in surveillance of tumor recurrence, 3) Identify most appropriate diagnostic imaging to order in cases of suspected tumor recurrence