Serial positron emission tomography scans following radiation therapy of patients with head and neck cancer

Background: A single institution study was undertaken to evaluate the role of positron emission tomography (PET) scans with fluorodeoxyglucose (FDG) prior to radiation and following radiation.

Methods: Forty-five patients with head and neck cancers were evaluated with FDG-PET scans as well as either CT or MRI prior to treatment with definitive radiation (RT). These same scans were obtained following completion of RT at 1 month (36 patients), 4 months (28 patients), 12 months (19 patients), and 24 months (15 patients). Standard uptake values (SUV) normalized for blood glucose and lean body mass were calculated on the initial and 1-month post-treatment PET scans.

Results: Fifteen patients are alive without evidence of disease at 24 to 52 months following RT. Initial SUVs were calculated on the primary tumor site and ranged from 2.5 to 28.5. These values did not have any correlation with local control when examined for the entire group, primary site, or T stage. One-month post-RT SUV ranged from 1.8 to 6.24. Of the 36 1-month post-RT PET scans, six were interpreted as positive for residual disease and were confirmed by biopsy. Four of the five scans, which were interpreted as equivocal, were positive on biopsy. Seven of the 25 scans, which were interpreted as negative for tumor, were positive on biopsy. Four-month scans were more accurate for disease with disease noted in 0 of 18 negative scans, 6 of 7 positive scans, and 2 of 3 equivocal scans.

Conclusions: PET is useful for initial imaging of head and neck cancers. SUV does not appear to be useful for predicting outcome following treatment with RT. One-month post-RT scans were inaccurate for predicting the presence of cancer. Four-month post-RT scans were a better predictor for the presence of cancer.