Dosimetric characteristics of a linear array of gamma or beta-emitting seeds in intravascular irradiation: Monte Carlo studies for the AAPM TG-43/60 formalism.
In principle, the AAPM TG-43/60 formalism for intravascular brachytherapy (IVBT) dosimetry of catheter-based sources is fully valid with a single seed of cylindrical symmetry and in the region comparable to or larger than the mean-free path of emitting radiation. However, for the geometry of a linear array of seeds within the few millimeter range of interest in IVBT, the suitability of the AAPM TG-43/60 formalism has not been fully addressed yet. We have meticulously investigated the dosimetric characteristics of catheter-based gamma (192Ir) and beta (90Sr/Y) sources using Monte Carlo methods before applying the AAPM TG-43/60 formalism. The dosimetric perturbation due to radiation interactions with neighboring seeds is at most 2% over the entire region of interest for the 192Ir source, while it increases to about 5% for the 90Sr/Y source. As the transaxial distance (y) increases beyond 3 mm, the sum of the dose contributions from neighboring seeds exceeds the dose contribution from the center seed for both sources. However, it continues to increase with the increasing y for 192Ir but is saturated beyond y = 5 mm for 9Sr/Y. Even within a few millimeters from the seeds, the dose from the low-energy betas of 192Ir is still less than 1% of the total dose. The radial dose and anisotropy functions are reformulated in reduced cylindrical coordinate with the reference point at y = 2 mm. The dose rate constant of 192Ir and the dose rate of 90Sr/Y at the reference point showed a fairly good agreement (within +/- 2%) with earlier studies and the NIST-traceable value, respectively. We conclude that the dosimetric perturbation caused by close proximity of neighboring seeds is nearly negligible so that the AAPM TG-43/60 formalism can be applied to a linear array of seeds.
Ye
Sung-Joon
SJ
Department of Radiation Oncology, Medical College of Ohio, 3000 Arlington Avenue, Toledo, Ohio 43614, USA. sye@uabmc.edu
Parsai
E Ishmael
EI
Feldmeier
John J
JJ
D000512:Alpha Particles; D001610:Beta Particles; D001918:Brachytherapy / Q000379:methods* / Q000592:standards*; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods* / Q000592:standards*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000592:standards*; D012542:Scattering, Radiation; D014481:United States; D014652:Vascular Diseases / Q000532:radiotherapy*