How can I do a gamma analysis of the areas with a dose greater than 200 in both film images

The film is irradiated with an accelerator to obtain a dose distribution. The low-dose area is not the focus of our analysis, and the gamma analysis of the entire film will affect the judgment. How can I perform gamma analysis only on regions greater than 200 dose values?

The film is irradiated with an accelerator to obtain a dose distribution. The low-dose area is not the focus of our analysis, and the gamma analysis of the entire film will affect the judgment. How can I perform gamma analysis only on regions greater than 200 dose values?

You can go to Segment Editor module, add a new segment, use Threshold effect to select region that has voxel value > 200, then use this segmentation as input in the Dose comparison module.