A Monte Carlo investigation of the radiation dose distribution in intravascular brachytherapy

The Monte Carlo code MCNP4B was used to investigate the radiation dose distribution in several areas of intravascular brachytherapy that would be very difficult or impossible to investigate experimentally or analytically. A model for a liquid-filled balloon catheter was developed and validated by comparing the results of Monte Carlo simulations with experimental measurements made in a tissue equivalent phantom. The dose distribution in the coronary vessel wall from a liquid-filled balloon catheter containing the following radioisotopes was examined: 90Y, 188Re, 32P, 186Re, 153Sm, 111In, adn 99mTc. At 0.5 mm from the vessel surface, the beta emitters deliver a higher dose per unit cumulated activity than the gamma emitters. The gamma emitters, however, deliver a dose that is more uniform throughout the vessel wall. Eight sizes of balloon catheters were modeled and the effect of balloon catheter size on the radiation dose distribution was examined. Effects that perturb the radiation dose distribution for a liquid-filled balloon catheter were investigated. These perturbing effects were: (1) an air bubble within the balloon catheter, (2) contrast media within the balloon catheter, (3) a Palmaz-Schatz® stent surrounding the balloon catheter, and (4) the deflation of the balloon catheter. The radiation dose distribution produced from a 32P-coated Palmaz-Schatz ® stent was investigated by developing a model with 32 P deposited on the stent surface to a depth of one micron, and calculating the dose delivered to the coronary vessel wall. High dose fluctuations were observed near the surface of the stent, but these fluctuations leveled off at depth in the vessel wall. The radiation dose distribution for the case of direct injection of radioisotopes into the coronary vessel wall using the Infiltrator® angioplasty balloon catheter (IABC) was also investigated. The source distribution produced by the IABC was modeled for two configurations within the vessel wall: (1) uniform to a depth of 0.5 mm into the vessel wall, and (2) confined to discrete pools surrounding the delivery injection needles. The dose distribution for the following radioisotopes was examined: 188Re, 186Re, 153Sm, 111In, 123I, and 99mTc.