33 Endovascular Brachytherapy

638 Endovascular Brachytherapy

* Remodelling. After the PTA/PTCA injury the entire artery becomes more and more constricted and may shrink significantly; this mechanism is called “unfavourable remodelling”. In contrast, the artery may expand in response to neointimal formation which is called “favourable remodelling”. Restenosis is angiographically defined as narrowing of the lumen equal to or exceeding 50% of the lumen diameter compared to the normal arterial segments. 3.2 Mechanisms of radiation for the prevention of restenosis It has been long recognised, that ionising radiation reduces cell proliferation by damaging the DNA in the nucleus through various mechanisms. For a significant time period, this paradigm formed the basic understanding of how radiotherapy works in malignant and benign disease (mechanism of action of radiotherapy). This process provided the rational for the commencement of vascular radiotherapy, which was introduced to prevent vascular restenosis after angioplasty based on knowledge of the antiproliferative effect of radiation on excessive scar formation after excision of keloids (1).

Fig 32.2: Schematic Diagram of the Process of Elastic Recoil, Neointimal Proliferation, Remodelling and the impact of radiotherapy on these processes Experimental studies in animals confirmed the first positive clinical experience, showing a significant reduction of neointimal proliferation in the irradiated arteries following different angioplasty-like procedures. Both beta and gamma radiation showed similar effectiveness in different animal models (e.g. in the iliac artery in the rabbit (12) and in the coronary artery in the pig (14)). From the