You are not getting it: It has nothing to do with therapy vs. detection.
The article talks about contraband of radioactive materials. I gave you examples where radioactive materials are used both in therapy (certain kinds of radiotherapy for cancer) and in medical imaging (PET and SPECT). You mentioned none of these examples.
Instead, you gave three examples (x-rays, CT scanners, chemotherapy) none of which use radioactive materials.
Thus you used completely invalid examples to illustrate a very valid point.