PET vs. CT in Lung Cancer Surveillance: The ‘Pro’ Side from the Nuclear Medicine Perspective

A significant proportion of patients with stage I to III NSCLC or SCLC will have locoregional or distant metastases following curative-intent therapy. Studies have reported local recurrence rates of 22% to 50%, distant recurrence rates of 48% to 78%, and simultaneous local and distant recurrence rates of 3% to 20%.¹ Sites of distant recurrence include brain, bone, contralateral lung, liver, adrenal gland, and distant nodes. The American Society of Clinical Oncology recommends surveillance chest CT scans every 6 months for the first 2 years to detect recurrence and then annual surveillance CT to detect new primary lung cancers.²

¹⁸F FDG PET/CT, which combines functional and anatomic imaging, has several advantages. It may detect increased glucose metabolism at sites of tumor recurrence before there are anatomic changes on CT. The increased field of image acquisition from the skull base to mid-thighs in PET/CT scans allows detection of distant metastases not identified by chest CT.³ In addition, Post-treatment 18F FDG PET/CT has prognostic value, with improved survival noted in patients with negative results.⁴ In addition, location of imaging abnormalities on PET/CT helps identify appropriate biopsy sites.

Toba et al.⁵ found that 18F FDG PET/CT has a 97.9% sensitivity, 97.1% specificity, 92.0% positive predictive value, 99.3% negative predictive value, and 97.3% accuracy in the detection of locoregional and distant metastases in asymptomatic patients with lung cancer recurrence. 18F FDG PET/CT has a higher detection rate of postoperative recurrence than chest CT scan.⁶ When performed 3 to 6 months after completion of radiotherapy, FDG uptake in recurrent tumors is focal and intense as compared to milder diffuse uptake in post-radiation inflammatory changes. Imaging with ¹⁸F FDG PET/CT is recommended by National Comprehensive Cancer Network guidelines to differentiate tumor recurrence from benign post-treatment changes detected on surveillance chest CT scan.⁷ Increased FDG uptake in normal-sized nodes and bone marrow can identify occult tumors before anatomic changes on CT.^8,9 High FDG uptake by normal brain parenchyma, however, will obscure cerebral metastases, limiting the use of 18F FDG PET/CT in the detection of brain metastases. 

In a nationally representative cohort study of patients who underwent surveillance CT following curative-intent surgery for stage I-III NSCLC, symptomatic recurrence and distant recurrence were associated with worse survival.¹⁰ Survival duration has been reported to be longer in-patient, with recurrences detected during the asymptomatic stage.^11,12 Post-treatment 18F FDG PET/CT has been found to alter therapeutic management in 30% to 88% of patients by demonstrating unsuspected recurrence or excluding clinically suspected recurrence.¹³ With the availability of local therapeutic options for patients with oligometastatic disease recurrence and choices among chemotherapy, targeted therapy, and immunotherapy to treat metastatic disease, early detection of asymptomatic tumor recurrence is likely to prolong survival. In this era of personalized medicine, post-treatment surveillance with 18F FDG PET/CT should be considered, particularly in patients with pretreatment risk factors for locoregional and distant failures, such as locally advanced disease, unfavorable histology, and metabolic parameters predictive of early recurrence on staging 18F FDG PET/CT.

References:

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