Determine the best threshold of SUVmax of the cervical cancer with 18F-FDG PET/CT for its biological target volume

Objectives Accurately delineate the biological target volume in cervical cancer is critical for its radiotherapy, but it is still remain unclear. This study explored the best threshold of SUVmax for determining the biological target volume of the cervical cancer with 18F-FDG PET/CT.

Methods 12 patients with biopsy-proven cervical cancer were underwent 18F-FDG PET/CT before surgery. The boundary of tumor was delineated by 18F-FDG PET imaging and enhancement CT imaging respectively. After surgery, the whole tissue was cut into 5mm thickness sections. Defined the boundary of tumor in each slice and calculated the area of tumor by Photoshop, as golden standard, the pathological volume was determined by adding up areas in all sections and multiply slice thickness. The best threshold of SUVmax which PET GTV is similarly to the pathological volume can be determined. It defined as a coincidence if the difference of CT GTV, PET GTV and the pathological volume is less than 10%. Otherwise, it is an inconsistent.

Results The threshold of SUVmax is between 35% to 50%( 43.33%±3.61%). It will be well correlated with the pathological volume when define the threshold of SUVmax of tumor as 45%. CT GTV is significant difference with PET GTV or the pathological volume. 4 CT GTV is larger than pathological volume, 3 is smaller than pathological volume, all other 5 is similar with pathological volume. The radiotherapy target area for 7 patients were changed when set the threshold of SUVmax of tumor as 45%.

Conclusions PET GTV is more accurate than CT GTV comparing with pathological volume for cervical cancer if defined the threshold of SUVmax as 45%, it should be play more important role in directing radiotherapy for cervical cancer