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Anisotropy functions for 103 Pd, 125 I, and 192 Ir interstitial brachytherapy sources
Author(s) -
Nath Ravinder,
Meigooni Ali S.,
Muench Philip,
Melillo Anthony
Publication year - 1993
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 - 10.1118/1.597110
Subject(s) - anisotropy , brachytherapy , dosimetry , dosimeter , imaging phantom , physics , thermoluminescence , nuclear medicine , computational physics , atomic physics , materials science , optics , radiation therapy , medicine , luminescence
Anisotropy of dose distributions around 103 Pd, 125 I, and 192 Ir sources for interstitial brachytherapy was examined. Dose rates around 125 I models 6702 and 6711 and 192 Ir sources were measured using lithium fluoride thermoluminescence dosimeters (LiF TLDs) in a water‐equivalent, solid phantom. From these measured data for 125 I and 192 Ir and the previously published measured data for 103 Pd, isodose rate contours were determined using a bivariate interpolation and smooth surface fitting algorithm. The anisotropy functions, F ( r ,θ), as defined by the Interstitial Collaborative Working Group (ICWG) for each source, were determined. Also, 4π‐averaged anisotropy factors, φ an ( r ), for use in point source approximation, have been calculated at radial distances varying from 1–10 cm for 103 Pd, 125 I, and 192 Ir sources. The anisotropy factors had average values of 0.90, 0.93, 0.95, and 0.98 for 103 Pd, 125 I model 6711, 125 I model 6702, and 192 Ir, respectively. The anisotropy factors determined from dose measurements in phantom are observed to be closer to unity than from those determined previously from in‐air measurements. This can be attributed to the smoothing of two‐dimensional dose distributions due to the presence of more scattered photons in the phantom measurements compared to in‐air measurements. Because in‐phantom measurements simulate more closely the brachytherapy patient, data from these experiments are recommended for a more accurate determination of dose distributions around clinical brachytherapy implants. In this work, we present a complete set of source data for two‐dimensional dosimetry following the ICWG formalism.