Evaluating Positron Emission Tomography Use in Differentiated Thyroid Cancer

Abstract

Background: Using the Surveillance, Epidemiology, and End Results-Medicare database, a substantial increase was found in the use of positron emission tomography (PET) scans after 2004 in differentiated thyroid cancer (DTC) patients. The reason for the increased utilization of the PET scan was not clear based on available the data. Therefore, the indications for and outcomes of PET scans performed at an academic institution were evaluated. Methods: A retrospective cohort study was performed of DTC patients who underwent surgery at the University of Michigan Health System from 2006 to 2011. After identifying patients who underwent a PET scan, indications, rate of positive PET scans, and impact on management were evaluated. For positive scans, the location of disease was characterized, and presence of disease on other imaging was determined. Results: Of the 585 patients in the cohort, 111 (19%) patients had 200 PET scans performed for evaluation of DTC. Indications for PET scan included: elevated thyroglobulin and negative radioiodine scan in 52 scans (26.0%), thyroglobulin antibodies in 13 scans (6.5%), rising thyroglobulin in 18 scans (9.0%), evaluation of abnormality on other imaging in 22 scans (11.0%), evaluation of extent of disease in 33 scans (16.5%), followup of previous scan in 57 scans (28.5%), other indications in two scans (1.0%), and unclear indications in three scans (1.5%). The PET scan was positive in 124 studies (62.0%); positivity was identified in the thyroid bed on 25 scans, cervical or mediastinal lymph nodes on 105 scans, lung on 28 scans, bone on four scans, and other areas on 14 scans. Therapy following PET scan was surgery in 66 cases (33.0%), chemotherapy or radiation in 23 cases (11.5%), observation in 110 cases (55.0%), and palliative care in one case (0.5%). Disease was identifiable on other imaging in 66% of cases. PET scan results changed management in 59 cases (29.5%). Conclusions: In this academic medical center, the PET scan was utilized in 19% of patients. Indications for the PET scan included conventional indications, such as elevated thyroglobulin with noniodine avid disease, and more controversial uses, such as evaluation of extent of disease or abnormalities on other imaging tests. PET scan results changed management in about 30% of cases.

Impact of combined FDG-PET/CT and MRI on the detection of local recurrence and nodal metastases in thyroid cancer

“…However, it is important to note that the imaging results analyzed in this study influenced patient management in over 50 % of patients, of whom 17 (37 %) were operated. The high percentage of high-risk patients with stage 4 disease may explain the higher percentage of changes in patient management than has been recently reported in the literature with approximately 30 % [32]. However, the smaller number of patients in our study may have caused selection bias.…”

“…The rise in use of diagnostic imaging, especially of FDG-PET(/CT) in TC follow-up, leads to increased radiation exposure and associated health costs [32–34]. Unnecessary diagnosis and intervention of low-risk and clinically non-significant disease remain a legitimate concern [34].…”

“…According to Wiebel et al [32] the FDG-PET/ldCT and MRI scans were considered to impact the patient management if the “examinations identified disease that was not previously known and resulted in an intervention”, if the scans “resulted in the decision to not pursue a specific intervention”, or if the scan “changed the extent of a planned surgery because of additional disease identified” [32]. …”

Clinical utility of 18F-FDG PET/CT in the follow-up of a large cohort of patients with high-risk differentiated thyroid carcinoma

“…Patients with histological findings of aggressive DTC variants (n = 21): oncocytic (n = 3), poorly differentiated areas (n = 2), tall-cell (n = 4), diffuse sclerosing (n = 4), insular (n = 5) and solid variant (n = 3) with incomplete biochemical or structural disease. (12,14). Consequently, the remaining 36 scans were performed using LT4 (Tg/LT4).…”

ENDOCRINE TUMOURS: Imaging in the follow-up of differentiated thyroid cancer: current evidence and future perspectives for a risk-adapted approach

“…FDG PET findings lead to changes in patient management strategies (generally involving the surgical plan) in about 30% of the cases (101,102,103). As noted, however, false positivity related to inflammation is possible.…”