Appropriate use criteria for ¹⁸F-FDG PET/CT in restaging and treatment response assessment of malignant disease

Precision medicine is evolving to include a variety of data to optimize patient care and improve outcome. Multimodality imaging is paving the way toward this goal. PET/CT with 18F-FDG is now established as an important imaging modality in many clinical conditions, particularly in oncology (1,2). Many tumors demonstrate high glucose metabolism as one of the hallmarks of cancer (3). PET/CT provides combined anatomic and physiologic (glucose metabolism) information that may be used for initial diagnosis, staging, restaging, treatment response assessment, and prognosis in patients with cancer. Moreover, PET information can contribute significantly when other imaging modalities are equivocal. This document describes the appropriate use of PET/CT∗ in the response assessment and restaging of patients with cancer. Our focus is on common cancers in which the use of PET/CT has been most relevant for clinical practice. Restaging is broadly defined to include the phase of the disease after initial diagnosis and treatment, which may entail local recurrence, distant metastatic disease, and assessment of response to treatments after disease recurrence. The goal of these recommendations is to guide the appropriate use of PET/CT in assessing treatment response after therapy and in evaluating imaging of patients with suspected recurrent cancer. Although the terms response assessment and restaging are frequently used in the discussion of cancer treatment, no consensus definition exists regarding the time frame that differentiates these 2 terms. Indeed, the time interval at which a patient transitions from response assessment to restaging likely varies in relation to tumor biology, therapeutic regimen, and other factors. In this work, the term assessment of response is taken to mean the period in which the intended target of the therapeutic regimen is being evaluated, whereas the term restaging of disease is taken to mean the period in which there is concern for new or progressive disease after completion of prior therapy. This document excludes "initial staging" and "surveillance." These appropriate use criteria (AUC) are intended to aid referring medical practitioners in the appropriate use of PET/CT for restaging of breast cancer, colorectal cancer, lymphoma, lung cancer, melanoma, sarcoma, and head and neck cancer.