Usefulness of open mouse position PET/CT for the evaluation of tongue cancer

Objectives To evaluate the utility of open mouse position PET scan for the purpose of reducing metallic artifact from dental implant in tongue cancer patient.

Methods Fifteen patients with untreated (n=13) and treated (m=2) tongue cancer underwent additional PET scan with open mouse position, immediately after conventional whole body PET/CT with closed mouse position. Images were acquired 60 min after administration of 185 MBq of 18F-FDG. Attenuation correction was done using CT image in both mouse position. Tumor visualization, extent of metallic artifact and SUV value of the lesion are compared in two conditions.

Results With open mouse scan, tumor visualization were improved in 40% (6/15), metallic artifact from dental implant were reduced in 46.6% (7/15) of the patients. Of those patients who showed reduced metallic artifact, 85.7% (6/7) displayed decreased SUV value (average 14%) of tumor. On the other hands, there was no significant difference in SUV value in the patient without metallic artifact. These data suggesting this is due to the effect of attenuation collection using CT. Phantom experiment showed metallic artifact decrease the measured radioactivity in 19%(4000MBq/cc) and 26% (2000MBq/cc) respectively. Larger influence was seen in the phantom of small radioactivity.

Conclusions SUV value of tongue cancer will be over estimated under the influence of metallic artifact. Open mouse PET scan is easy and useful technique to evaluate the tongue cancer and precise FDG accumulation.