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Report on the dosimetry of a new design 125 Iodine brachytherapy source
Author(s) -
Wallace Robert E.,
Fan Jay J.
Publication year - 1999
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 - 10.1118/1.598737
Subject(s) - brachytherapy , dosimetry , dosimeter , imaging phantom , kerma , opacity , isotropy , anisotropy , physics , nuclear medicine , computational physics , optics , materials science , medicine , radiation therapy
Dosimetric measurements were performed to characterize a new125 I 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, Λ, radial dose function, g ( r ) , the anisotropy function, F ( r , θ ) , the anisotropy factor, φ an( r ) , the point‐source approximation anisotropy constant,φ ̄ an . The dose‐rate constant was determined by an absolute method using a Cobalt‐60 reference and by relative measurements using calibrated125 I 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 6702125 I source designs, demonstrating equivalent radial dose function, g ( r ) . Differences in the value of the dose‐rate constant, Λ, 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 Cobalt‐60 reference.