Report on the dosimetry of a new design 125Iodine brachytherapy source

Dosimetric measurements were performed to characterize a new I-125 source that is a variant design of an existing source, designated as MED3631-A/S, and that has application in interstitial brachytherapy. The new source, designated as MED3631-A/M, has centralized radio-opaque markers. In the original MED3631-A/S source, the radio-opaque markers are separated. Thermoluminescent dosimeters were placed in phantom to measure transverse axis and angular dose profiles over a range of distances from 0.5 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM Task Group No. 43. Tabular data evaluated in liquid water are provided for the dose-rate constant, Lambda, radial dose function, g(r), the anisotropy function, F(r, theta), the anisotropy factor, phi(an)(r), the point-source approximation anisotropy constant, <(phi)over bar>(an). The dose-rate constant was determined by an absolute method using a Cobalt-60 reference and by relative measurements using calibrated I-125 source(s). Values of the dose-rate constant are provided for both the 1985 and 1999 NIST air-kerma strength standards. The new source is comparable to both the MED3631-A/S and the model 6702 I-125 source designs, demonstrating equivalent radial dose function, g(r). Differences in the value of the dose-rate constant, Lambda, and the anisotropy of the dose distributions in phantom are discussed in light of the improved isotropy of the new design, the MED3631-A/M source, and the uncertainty involved in the dose measurement using a Cobaltd-60 reference. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)02009-X].