HIGH-DOSE-RATE BRACHYTHERAPY FOR PREVENTION OF RESTENOSIS AFTER PERCUTANEOUS TRANSLUMINAL CORONARY ANGIOPLASTY - PRELIMINARY DOSIMETRIC TESTS OF A NEW SOURCE PRESENTATION

Purpose: Balloon dilatation of coronary artery stenosis has become a s tandard treatment of atherosclerotic heart disease. Restenosis due to excessive intimal cell proliferation, which subsequently occurs in 20- 50% of patients, represents one of the major clinical problems in cont emporary cardiology, and no satisfactory method for its prevention has thus far been found. Because modest doses of radiation have proved ef fective in preventing certain types of abnormal cellular proliferation resulting from surgical trauma, and brachytherapy has already been us ed successfully after dilatation of peripheral arteries, development o f a radioactive source suitable for coronary artery applications would be of great interest. Methods and Materials: Nonradioactive flexible yttrium-89 wires (diameter of 0.15 and 0.26 mm) were activated within the thermal neutron flux of an experimental reactor. Standard angiopla sty balloons (2 cm long, 2.5 mm in diameter when inflated) were insert ed for dosimetry into a specially manufactured tissue equivalent phant om. Pour wells, drilled perpendicular to the axis of the balloon, allo wed for the insertion of thermal luminescent dosimeters (TLDs; 2 mm of diameter) and spacers. The angioplasty balloon was inflated with air or with contrast media. Radioactive yttrium-90 wires were left in the central lumen of the balloon for 2 min. Doses at the surface of the ba lloon, and at 1, 2, and 3 mm were determined from TLD readings. Result s: Doses obtained at the surface of the balloon, for a 2-min exposure for the 0.26 mm wire (balloon inflated with air) and the 0.15 mm wire (air or contrast), were 56.5 Gy, 17.8 Gy, 5.4 Gy, respectively. As exp ected for a beta emitter, the fall-off in dose as a function of depth was rapid. External irradiation from the beta source was negligible. C onclusions: Our experiments indicate that the dose rates attainable at the surface of the angioplasty balloon using this technique allow the doses necessary for the inhibition of intimal cell proliferation to b e reached within a relatively short period of time. The thin yttrium-9 0 wires are very easy to handle, and their mechanical and radioactive properties are well suited to the requirements of the catheterization procedure.