Proposal for a gamma-emitting stent for the prevention and treatment of coronary artery restenosis.
Radioactive stents have failed to prevent restenosis despite the demonstrated success of other radionuclide therapies using beta- or gamma-emitting radionuclides in the coronary arteries. This may be due to the rapid dose reduction at the end of the stent that occurs with a stent coated with 32P, which is a pure beta-emitter. A gamma-emitter will give a greater dose beyond the end of the stent and would therefore be expected to produce better results. However, it is essential that the gamma-emitter is not contaminated with beta particles of either sign nor with conversion electrons. This requirement generally demands the use of a high energy gamma-emitter, preferably with an energy greater than 500 keV. High energy gammas have other advantages, including a high radiation dose delivered per decay which reduces the total activity required and reduced dose near to the source due to electron disequilibrium. The ideal dose distribution is one that provides a uniform dose to the proliferating tissues and a reduced dose elsewhere. Although the target tissues are not well defined it is believed that the adventitia is the source of the proliferating cells. Hence the target tissue is between 0.5 and 2 mm depth into the artery. It is shown that 96Tc is a very suitable radionuclide for the production of radioactive stents giving a significantly greater dose compared with 32P both at depth and beyond the end of the stent for the same dose at the surface of the stent. Furthermore, 96Tc should be able to be made with a standard medical cyclotron and may be coated on to a stainless steel stent by a simple process that takes approximately 30 minutes to perform. Its half-life of 4.3 days will allow radioactive stents to be transported over significant distances and will result in a treatment time with a mean value of approximately 1 week. This will allow the rapid reestablishment of the endothelial layer which may be a further advantage of this radioactive stent.
Fox
R A
RA
Department of Medical Physics, Royal Perth Hospital, WA. richard.fox@health.wa.gov.au
D015906:Angioplasty, Balloon, Coronary; D023903:Coronary Restenosis / Q000517:prevention & control* / Q000532:radiotherapy / Q000628:therapy*; D005720:Gamma Rays / Q000627:therapeutic use*; D006207:Half-Life; D006801:Humans; D011853:Radiobiology; D011879:Radiotherapy Dosage; D015607:Stents; D013667:Technetium / Q000627:therapeutic use
D013667:Technetium