A NOVEL SYSTEM FOR INTRACORONARY BETA-IRRADIATION - DESCRIPTION AND DOSIMETRIC RESULTS

Purpose: A dosimetric evaluation of a new device dedicated to intravas cular irradiation, associating a beta source and a centering device, w as carried out before initiation of a clinical pilot study. Methods an d Materials: A 29-mm-long Y-90 coil, coated with titanium and fixed to the end of a thrust wire, was introduced into the inner lumen of purp ose-built centering balloons of different diameters (2.5, 3, 3.5, and 4 mm). Dose homogeneity was evaluated by studying both axial and circu mferential dose variations, based on readings from thermoluminescent d osimeters (TLDs) placed on the balloon surface. Axial homogeneity was determined by comparing the readout values of dosimeters located on pe ripheral balloon segments with those located on segments adjacent to t he midpoint of the source. The centering ability of the device was stu died by comparing measurements on opposing surfaces of the balloon. Th e dose attenuation by water and contrast medium was evaluated and comp ared with that in air. The balloon contamination was studied using a c ontamination counter. The total Y-90 coil activity was measured by liq uid scintillation to relate activity to surface dose. Results: Activit y-surface dose correlation showed that for a linear coil activity of 1 mCi/mm, the mean dose rate at the surface of a 2.5-mm balloon filled with contrast medium was 8.29 Gy/min. The doses at the surface of larg er balloons (3, 3.5, and 4 mm) filled with contrast were 78%, 59%, and 47%, respectively, of the dose measured at the surface of the 2.5-mm balloon. The coefficient of variation (CV) in surface dose for 2.5-, 3 -, 3.5-, and 4-mm centering devices filled with contrast medium were 9 %, 8%, 9%, and 12%, respectively. There was no statistically significa nt difference between readouts from central and peripheral balloon seg ments or among rows of dosimeters facing each other. For a 2.5-mm ball oon, compared-with air the dose attenuation by water and contrast medi um was similar (0.70 and 0.69, respectively), but a significant differ ence was seen between the readouts of water- and contrast-filled ballo ons when the diameter was larger than 3 mm (p < 0.001). No contaminati on was found in the balloon shaft after source retrieval. Conclusion: The dosimetric tests showed very good surface dose homogeneity, demons trating satisfactory centering of the source within the centering ball oons. The achievable dose rates will permit intravascular irradiation within a short time interval. The absence of residual balloon contamin ation after source retrieval meets the requirements for a sealed sourc e used in a clinical setting. Copyright (C) 1996 Elsevier Science Inc.