Purpose: When radioactive sources are used to treat restenosis, the blood vessels are usually curved. In catheter-based intravascular brachytherapy systems, this curvature introduces dose deviations from the idealized situation used for treatment planning, in which both blood vessels and sources are assumed to be straight. Because of the different depth characteristics of different radionuclides, it is foreseeable that the curvature effects on dosimetry might vary with the different types of radionuclides. In this study, curvature effects on dose distributions along and around a blood vessel were investigated for different gamma and beta emitters.
Materials/methods: A blood vessel was modeled as a cylinder that could be curved as a circular arc of different degrees. Dose calculations were performed on the cylindrical surfaces of the model vessel for the radioactive sources of (192)Ir, (125)I, (103)Pd, (188)Re, (32)P, and (90)Y/Sr. The radius of the vessel was assumed to be 1.0, 1.5, 2.0, and 2.5 mm, respectively. A catheter-based radiation delivery system was simulated to consist of a line source with a length of 2 cm. The dose rate at a point in space produced by the radioactive source was computed by integrating the point dose rate kernel of the corresponding radionuclide over the entire radioactive line, which was assumed to curve with the blood vessel along its central axis. Dosimetric calculations were performed for different curvature angles. The curvature effects on the dosimetry were characterized with two quantities, LDU and ADU, where LDU described the longitudinal dose uniformity (LDU) along blood vessels and ADU described the azimuthal dose uniformity (ADU) from the expected delivery dose around blood vessels.
Results: Vessel and source curvatures barely changed the LDU for the gamma emitters (within 2%). The curvature effects on the LDU were relatively larger for the beta emitters (less than 5%). The dose deviations caused by curvature around a blood vessel were more significant. Depending on the radius of the vessel and degree of curvature, the deviation could be as much as 25% for the gamma emitters and 30% for the beta emitters. The curvature effects became larger with the increase of vessel radius and, obviously, with the increase of curvature. There seemed to be no significant differences in the curvature effects among different types of gamma emitters and among different types of beta emitters.
Conclusions: Curvature-induced effects on dose distribution are similar for both the gamma and the beta emitters. The LDU along the vessels does not change significantly with curvature. The dose changes around the vessels are more pronounced and can be as high as 30%.