Endovascular brachytherapy after percutaneous coronary intervention (PCI), is becoming a standard approach for the treatment and prevention of restenosis. A variety of technical approaches are currently available to deliver ionizing irradiation to the vascular target. Basically two kinds of radioactive isotopes are available that emit gamma radiation (photons) or beta radiation (electrons). The pitfalls and solutions for the optimization of dosimetry are discussed. As might be expected, the inhomogeneous dose distribution across the target volume results in recurrence by underdosage or in complications because of overdosage. Moreover, uniformization of the target definition and reporting of the dose distribution in endovascular brachytherapy is a prerequisite for comparison between the results of the various clinical trials and is absolutely necessary to improve the therapeutic efficacy of this new approach in the prevention of restenosis after coronary angioplasty with or without stenting.