The use of radioactive substances as a therapy for in-stent restenosis of a coronary vessel is .

The correct answer is: Intracoronary Brachytherapy.

Explanation:

Intracoronary brachytherapy involves the usage of radioactive substances to lower the risk of lesion recurrence (also called restenosis) during percutaneous coronary intervention.

Its logic is founded on the idea that restenosis is a benign tissue proliferation process, and that locally applied radiation can reduce the amplitude of this reaction.

Brachytherapy is considered a conventional therapeutic option for selected patients with in-stent restenosis, and it is done as part of routine interventional cardiology practice.