Barbara Petelenz

Post-Dilatation Intravascular Brachytherapy Trials on Hypercholesterolemic Rabbits Using 32P-Phosphate Solutions in Angioplasty Balloons

Abstract Response of peripheral arteries to post-dilatation intravascular brachytherapy (IVBT) using 32P liquid sources was studied in a rabbit model. The applied sources were angioplasty balloons filled with aqueous solutions of Na2H32PO4, NaCl and iodinated contrast. Dose distribution was calibrated by thermoluminescence dosimetry. The uncertainty of in vitro determinations of the activity–dose dependence was ± 15–30%. The animal experiments were performed on rabbits with induced hypercholesterolemia. The 32P sources were introduced into a randomly chosen (left or right) iliac artery, immediately after balloon injury. Due to the low specific activity of the applied sources, the estimated 7–49 Gy doses on the internal artery surface required 30–100 min irradiations. A symmetric, balloon-occluded but non-irradiated artery of the same animal served as control. Radiation effects were evaluated by comparing the thicknesses of various components of irradiated versus untreated artery walls of each animal. The treatment was well tolerated by the animals. The effects of various dose ranges could be distinguished although differences in individual biological reactions were large. Only the 49 Gy dose at “zero” distance (16 Gy at 1.0 mm from the balloon surface) reduced hypertrophy in every active layer of the artery wall. The cross-sectional intimal thicknesses after 7, 12, 38 and 49 Gy doses were 0.277, 0.219, 0.357 and 0.196 mm2 respectively, versus 0.114, 0.155, 0.421 and 0.256 mm2 in controls (p < 0.05). The lowest radiation dose on the intima induced the opposite effect. Edge intimal hyperplasia was not avoided, which agrees with other reports. The edge restenosis and the variability of individual response to identical treatment conditions must be considered as limitations of the post-dilatation IVBT method. Only application of highest irradiation doses was effective. The irradiation dose should be planned and calculated for adventitia.

32P liquid sources—comparison of the effectiveness of postangioplasty versus poststenting intravascular brachytherapy in hypercholesterolemic rabbits: Adjunctly implanted titanium stent does not attenuate the effect of endovascular irradiation

PURPOSE Endovascular application of ionizing radiation is a promising but still not sufficiently studied means of restenosis prevention. To test the effects of radiation on restenosis, and especially their dependence on whether the angioplasty was followed by stent implantation or not, we performed an in-stent versus no-stent intravascular brachytherapy study in an animal model. Balloon-based, continuous and self-centering, liquid 32P sources seemed the most convenient for the purpose. METHOD The radial dose distribution around angioplasty balloons filled with solutions of Na(2)H32PO(4) was calibrated by thermoluminescence dosimetry, both in the absence and presence of stents. The animal experiments were performed on rabbits with induced hypercholesterolemia. The balloons containing 32P were introduced into iliac artery immediately after stent implantation or after angioplasty alone. Radiation effects were evaluated postmortem by comparing thickness of various components of the artery wall. RESULTS In the presence of titanium stents (TTS), irradiation with 16 Gy dose at 1.0 mm from the balloon surface was no less effective in reducing hypertrophy in every active layer of the artery wall than without a stent. CONCLUSION In the animal model, IVBT basing on P(32) liquid sources was no less effective in the stented arteries than in the nonstented ones.

Thermoluminescence dosimetry of liquid 32P sources of variable size and composition

Abstract Dosimetry of liquid 32 P sources was studied in terms of their size and composition, to check how self-absorption of balloon-based intravascular brachytherapy sources may influence doses at a target point. The sources contained aqueous solutions of 32 P -phosphate, saline, and iodinated contrast media (0– 76 mg I cm −3 ). Doses were measured in Plexiglas phantoms at 1 mm radial distance, using miniature flat thermoluminescence detectors. The absolute dose rates measured for 2.0– 3.5 mm diameter range increased from 0.25 to 0.43 ( Gy min −1 )/( GBq cm −3 ) and were slightly lower than theoretical values. A 3.0 mm diameter balloon delivered 0.33, and a 3.0 mm ID Plexiglas tube 0.40 ( Gy min −1 )/( GBq cm −3 ) . A 2.7 mg titanium stent present on the balloon enhanced the dose rate at 1 mm distance, whereas an 8.2 mg one reduced it. The influence of iodine concentration was not very well pronounced. The observed increase of absolute dose rates in the clinically essential range of source diameters is an important parameter for radiotherapy planning.

Physical and chemical limitations to preparation of beta radioactive stents by direct neutron activation

Pure beta emitters are the sources of choice for intracoronary irradiations in restenosis prevention. In this work we reconsidered preparation of low activity 32P sources by ion-implantation of stable 31P into highly biocompatible pure titanium stents, followed by neutron activation. Gamma-spectrometrical analysis has shown that during activations with high thermal neutrons flux production of gamma-active long-lived contaminants is much beyond the dosimetrically acceptable limit, mainly due to the competing (n,p) reactions induced by the fast neutrons on isotopes of the bulk stent material, and to a lesser extent due to (n,gamma) reactions on chemical impurities. A potential applicability of this method for obtaining alternative beta radioactive stents is discussed.