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Dosimetric characteristics of a linear array of γ or β‐emitting seeds in intravascular irradiation: Monte Carlo studies for the AAPM TG‐43/60 formalism
Author(s) -
Ye SungJoon,
Parsai E. Ishmael,
Feldmeier John J.
Publication year - 2003
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1538229
Subject(s) - monte carlo method , dosimetry , brachytherapy , physics , formalism (music) , anisotropy , computational physics , radiation , path length , nuclear medicine , optics , mathematics , radiation therapy , medicine , radiology , statistics , art , musical , visual arts
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‐basedγ ( 192 Ir ) andβ ( 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 the192 Ir source, while it increases to about 5% for the90Sr / 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 for192 Ir but is saturated beyond y = 5 mm for90Sr / Y . Even within a few millimeters from the seeds, the dose from the low‐energy betas of192 Ir 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 of192 Ir and the dose rate of90Sr / 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.