A novel system for intracoronary beta-irradiation: description and dosimetric results

A dosimetric evaluation of a new device dedicated to intravascular irradiation, associating a beta source and a centering device, was carried out before initiation of a clinical pilot study.

A 29-mm-long 90Y coil, coated with titanium and fixed to the end of a thrust wire, was introduced into the inner lumen of purpose-built centering balloons of different diameters (2.5, 3, 3.5, and 4 mm). Dose homogeneity was evaluated by studying both axial and circumferential dose variations, based on readings from thermoluminescent dosimeters (TLDs) placed on the balloon surface. Axial homogeneity was determined by comparing the readout values of dosimeters located on peripheral balloon segments with those located on segments adjacent to the midpoint of the source. The centering ability of the device was studied by comparing measurements on opposing surfaces of the balloon. The dose attenuation by water and contrast medium was evaluated and compared with that in air. The balloon contamination was studied using a contamination counter. The total 90Y coil activity was measured by liquid scintillation to relate activity to surface dose.

Activity-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 larger 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 significant difference between readouts from central and peripheral balloon segments or among rows of dosimeters facing each other. For a 2.5-mm balloon, compared with air the dose attenuation by water and contrast medium was similar (0.70 and 0.69, respectively), but a significant difference was seen between the readouts of water- and contrast-filled balloons when the diameter was larger than 3 mm (p < 0.001). No contamination was found in the balloon shaft after source retrieval.

The dosimetric tests showed very good surface dose homogeneity, demonstrating satisfactory centering of the source within the centering balloons. The achievable dose rates will permit intravascular irradiation within a short time interval. The absence of residual balloon contamination after source retrieval meets the requirements for a sealed source used in a clinical setting.