Is less more in 18F-FDG PET/CT staging of squamous cell carcinoma of the head and neck?

Objectives There are variable recommendations for staging of squamous cell carcinoma (SCC) of the head and neck (H&N)(1-5). Conventional staging by computed tomography (CT) includes imaging of the H&N and thorax through the level of the adrenal glands. 18F-FDGPET/CT is widely used for staging of SCC of H&N, mostly using a protocol scanning from the midbrain to midthigh. However, it was not fully demonstrated whether scanning of abdomen and pelvis can be eliminated without compromising accurate staging of SCC of H&N. We hypothesize that abdominal and pelvic scanning can be eliminated from 18F-FDG PET/CT protocol for staging of SCC of H&N, given the very low incidence of distant metastatic disease of H&N SCC in the abdomen and pelvis(6-9). We also assume that we can eliminate the conventional chest CT acquisition, as quality of CT component of the current 18F-FDGPET/CT is appropriate for staging. The objective of this study was to test our hypothesis by assessing incidence or rate of distant metastatic lesions in the abdomen and pelvis from the patients subjected to conventional 18F-FDGPET/CT scanning from midbrain to mid-thigh. Additionally, we analyzed if there was any added value of performing concurrent conventional chest CT for diagnostic imaging of H&N SCC metastases in chest when compared to chest findings on18F-FDGPET/CT studies.

Methods Institutional review board approval was obtained and informed consent was waived for this HIPAA-compliant study. A retrospective review was conducted, including reports from 154 patients who underwent 18F-FDGPET/CT for staging or restaging of H&N SCC in a midbrain to proximal thigh scanning protocol (44 patients for staging and 110 for restaging) in a 7-month period. Among these patients, eighty-five patients had conventional chest CT performed during a period of 6 months prior to or after 18F-FDGPET/CT. The reports were reviewed for findings in the abdomen and pelvis and divided into 3 categories (indeterminate, metastatic disease or nonrelated other significant findings). Findings on conventional chest CT and on chest images from the 18F-FDGPET/CT were compared. The patients’ electronic health records were reviewed for standard uptake value, in correlation to primary tumor location, size, histologic grade and TNM staging. Patient’s demographics were also noted.

Results Metastatic disease in the abdomen and pelvis was found in two restaging 18F-FDGPET/CTs, one patient in the abdomen (metastatic liver lesions, stage III at initial diagnosis) and another in the pelvis (left ischium metastasis, stage IV also at initial diagnosis), both with concomitant lung metastases, with overall incidence of 1.3%. Of the 85 patients that had concurrent conventional chest CT performed, 11 patients had suspicious chest lesions on18F-FDGPET/CT. All lesions seen on18F-FDGPET/CT were also seen on the conventional chest CT, except for a FDG avid nodule that resolved (assumed to represent an inflammatory / infectious nodule). There were no suspicious lesions seen on conventional chest CT that were not seen on 18F-FDGPET/CT.

Conclusions The finding from our study demonstrated very low incidence of metastatic disease in the abdomen and pelvis in patients with SCC of the H&N (1.3%). On the other hand, no chest lesions detected on conventional CT chest were missed in the 18F-FDGPET/CT. Our data suggest that 18F-FDGPET-CT of the abdomen and pelvis may be unnecessary for initial staging of H&N SCC and in follow up of patients below stage III. Our findings also showed that there was no need to obtain a separate conventional chest CT when FDG PET/CT is used for staging of H&N SCC. These changes should allow for reduction of scanning time, cost, and radiation dose without compromising sensitivity and specificity of using F-18 FDG PET/CT for H&N SCC staging and restaging.