Background-based Delineation of Internal Tumor Volume in Static Positron Emission Tomography in a Phantom Study.

OBJECTIVES

Considering the fact that the standardized uptake value (SUV) of a normal lung tissue is expressed as ±, +3× could be considered as the threshold value to outline the internal tumor volume (ITV) of a lung neoplasm.

METHODS

Three hollow models were filled with 55.0 kBq/mL fluorine-18 fluorodeoxyglucose (F-FDG) to represent tumors. The models were fixed to a barrel filled with 5.9 kBq/mL F-FDG to characterize normal lung tissues as a phantom. The PET/CT images of the phantom were acquired at rest. Then, the barrel was moved periodically to simulate breathing while acquiring PET/CT data. Volume recovery coefficient (VRC) was applied to evaluate the accuracy of ITVs. For statistical analysis, paired t-test and analysis of variance were applied.

RESULTS

The VRCs ranged from 0.74 to 0.98 and significantly varied among gross tumor volumes for delineating ITV (<0.01). In two-dimensional PET scans, the motion distance did not affect VRC (>0.05), whereas VRC decreased with increasing distance in three-dimensional PET scans (<0.05).

CONCLUSION

The threshold value (+3×) had the potential to delineate the ITV of cancerous tissues, surrounded by lung tissues, particularly in two-dimensional PET images.