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Prevention of Heart Restenosis with Re-188
in an Angioplasty Balloon*
Richard Fox BSc W.Aust., DPhil Oxf.
Visiting Professor,
Curtin University, Western Australia
This is a scientific and technically based article. It is not intended to provide medical advice and is for information only.
If you have any health problems or questions related to your health, then please consult your doctor.
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The Need
As individuals age, their arteries become stenosed (narrowed) as a result of the ageing process.
This often first manifests by pain in the legs following exertion, since the narrowed arteries are incapable of providing sufficient blood to active muscles. However, in some cases the group of arteries radiating from the aorta that supply blood to the tissues of the heart itself become stenosed. These are the coronary arteries.
Stenosis in the coronary arteries leads to a reduced capacity to supply the heart muscle with blood, particularly during exercise when the heart rate increases. In extreme cases this leads to severe chest pain known as angina. Ultimately, damage to the heart muscle may occur as a result of the diminished blood supply. This can in turn result in a heart attack which may lead to the death of the person concerned.
Incidence of Restenosis
Cardiac disease is the major cause of death in most Western Countries and is therefore of major interest to the community.
Previous Treatment Methods
In the 1950s, surgery was introduced as a way of treating this problem by replacing diseased arteries with a vein taken from the patient’s leg. This involved a major operation that includes opening the chest and by-passing the heart during surgery. In 1977, coronary angioplasty was introduced that involved guiding a small balloon into the stenosed artery and inflating it to a pressure of 10 atmospheres to expand the artery.
This has become the preferred method of treating coronary artery disease. Unfortunately this treatment alone resulted in 20-30% of patients returning with re-stenosis of the artery. The introduction of metallic stents to hold the artery open improved matters but still a significant number had regrowth of tissue into the lumen of the stent.
In the latter half of the 1990s, it was proposed that ionising radiation may be able to halt the growth of tissue into the arterial lumen. External beam radiation would be simple to achieve but irradiation of the heart is not desirable due to the damage done to the heart muscle itself.
The Rhenium-188 Proposal
Hence localised irradiation of the artery is preferred. One such method is to fill the angioplasty balloon with a radioactive liquid which is left in the artery for a period that will deliver the required radiation dose to the wall of the artery.
Beta emitters are preferred since the activity required for a beta emitter is about 30 times less than that required for a gamma emitter and it is easier to shield a beta emitter, making radiation protection in the catheterisation laboratory (CathLab) very much easier.
One suitable radioactive material is radioactive Rhenium-188 (Re-188) which can be obtained by passing saline over a source of radioactive tungsten-188 (W-188). The latter has a half life of 69 days whereas the Re-188 has a half life of 17 hours, hence a long lived radioactive generator can be used to supply the short lived Re-188 on a daily basis.
The Rhenium-188 Procedure
Physicists at Royal Perth Hospital (RPH) used a generator purchased from Oak Ridge National Laboratory in the USA to provide the required activity of Re-188 when required by the cardiologists. The required activity of Re-188 to deliver the requested dose to the coronary arteries had been previously calculated by RPH physicists.
This radioactivity, contained in a shielded syringe, would be taken to the Catheter Laboratory in a special transport container designed by the physicists.The heavy metal container ensured that the high activity of Re-188 was always well shielded from the staff. The physicist would then monitor the area, staff and equipment to ensure that no radioactivity was spilt before or during the procedure.
Results and Present Status
Preliminary work with this technique showed that in one vulnerable group of patients the restenosis rate was reduced from an expected 60% to 15%. Hence the irradiation of coronary arteries by filling the angioplasty balloon with Re-188 had successfully reduced the incidence of coronary artery stenosis. Since then, drug eluting stents have been introduced into cardiology practice. These are simpler to use than the radioactive material and have made a substantial difference to the incidence of in-stent stenosis.
R Fox, 13 August 2019
* Intravascular brachytherapy of the coronary arteries Fox R A Phys Med Biol 2002, 47, 1-30
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