Whole-body 18F-Fluorodeoxyglucose positron emission computed tomography (18F-FDG PET/CT) should be performed 30 to 90 days following treatment for sinonasal malignancies and again 18 months later, recommend radiologists at the University of Minnesota Medical Center in Minneapolis. They describe a study assessing the ideal timing for this surveillance examination in the September 2019 European Journal of Radiology.
Sinonasal malignancies represent only 3% of head and neck neoplasms, according to the authors, who stated that no commonly approved protocols on the timing and frequency of scans following curative treatment exist.
The authors studied 80 asymptomatic patients who underwent 197 post-treatment scans for sinonasal malignancy from 2009 to 2017. Thirty-six patients developed recurrences during the study period. Their median survival was 40 months, with a range of 1 to 8 years. The authors analyzed the ability of the scans to detect local recurrence, regional lymph node metastases, and distant metastases for the first and subsequent scans. From this data, they developed an optimal surveillance schedule.
Scans were categorized into 6 time interval groups: Nine performed within 30 days of treatment, 10 at 1-3 months, 31 at 3-6 months, 66 at 6-12 months, 36 at 12-18 months, and 45 after 18 months. Local recurrences were diagnosed in each interval, with most identified in the 3-6 month and 6-12 month categories. Regional lymph node metastases were diagnosed after only 90 days, and distant metastases predominantly after 6 months.
The researchers reported that diagnostic accuracy of 18F-FDG PET/CT scans was significantly inferior when scans were performed less than 30 days after treatment compared to after 30 days. They theorized that small traces of recurrent tumor may not yet be noticeable and that accurate detection of recurrent disease may be hindered by diffusely increased 18F-FDG uptake of surrounding tissue caused by inflammation. Owing to the risk of disease progression, the authors recommend that an initial post-treatment scan be performed between 30 and 90 days.
“Our study revealed that 18F-FDG PET/CT after 18 months identified recurrences in all 36 patients,” the researchers wrote. “The patients in our study obtained slightly fewer than one 18F-FDG PET/CT scan each year. Half of the true positive recurrences were identified after an initial negative scan. Even though the impact of a second scan would be significantly lower than that of the first scan, the appropriate timing of subsequent scan might be longer than 18 months after the conclusive treatment.”
“Standardized protocols and optimal timing of whole-body surveillance 18F-FDG PET/CT examinations in the post-treatment setting are essential to reduce unnecessary expenses and the radiation dose to patients while increasing the detection capability of the technique,” they concluded.
Surveillance whole-body 18F-FDG PET/CT scanning for sinonasal malignancies. Appl Radiol.