Page 107 - 18F-FDG PET as biomarker in aggressive lymphoma; technical and clinical validation

Workflow optimization of MTV in DLBCL
each lesion), followed by automated segmentation in the tool using four separate frequently published segmentation methods:
1. 41 % of SUVmax (41%MAX)
2. A50% of SUVpeak, i.e., 50 % of SUVpeak with local background
correction [17] (A50%P)
3. fixed SUV threshold of 2.5 (SUV≥2.5)
4. fixed SUV threshold of 4.0 (SUV≥4.0).
The four segmentation methods were initiated from one single click by the observer, to avoid introduction of extra variability by repeated clicking. Moreover, the tool first calculated a robust local maximum (using a region growing method applying a 70 % threshold of the point clicked) in order to be less dependent on the exact point clicked by the observer. Generated VOIs were summed for all lesions selected by each observer to calculate MTV and TLG according to each of the four segmentation methods.
To explore the use and performance of consensus methods, two methods were added afterwards, which use the delineations found with the above four standard methods as input for a majority vote (MV) approach [18]. MV volumes were defined by all voxels included in the MTV or TLG by at least two (MV2) or three (MV3) of the input methods.
Workflow B consisted of a fully automated preselection of [18F]FDG-avid structures defined by an SUV≥4.0 and a volume threshold of ≥3 ml. These preselected regions resulted into an identical starting point for all observers but could include non-tumor regions with normal increased [18F]FDG uptake, such as the brain or bladder. From this starting point, the observers decided on the removal of non-tumor regions by using a clearing option (i.e., single click(s)) or spatial limits to reduce the analyzed field of view (e.g., using a slider option to exclude superior slices including the brain or inferior slices including the bladder); after this, only lymphoma lesions remain. Therefore, a region is defined as any preselected 3D-VOI with uptake above the SUV≥4.0 threshold, whereas a lesion is defined as a 3D-VOI identified by the observer as lymphoma.
105
5