world coordinates do not give the correct dicom coordinate

Dear all,

I want to do segmentation with itk and i would like to select a seed using
vtk with the mouse. I get the coordinates in world coordinates

                    int x = this->Interactor->GetEventPosition()[0];
                    int y = this->Interactor->GetEventPosition()[1];
                    std::cout << "(x,y) = (" << x << "," << y << ")" << std::endl;

                    seeds[0] = x;
                    seeds[1] = y;

but when i want to use it as a seed for itk i see it is the wrong place. I
tried the transformphysicalpointoindex but the result is even worst

            bool isInside =

if (isInside) {

                    ImageType::PixelType pixelValue =


Any help about the coordinates in vtk?