Monte Carlo dosimetric study of best industries and Alpha Omega Ir-192 brachytherapy seeds.

Ir-192 seeds are widely used in the USA for low dose rate interstitial brachytherapy. There are two commercially available models: those manufactured by Best Industries filtered with stainless steel, and those manufactured by Alpha-Omega seeds filtered with Pt. Newly developed 3D correction algorithms for brachytherapy are based on dosimetry data obtained on unbounded phantom size, allowing corrections for heterogeneities and actual tissue boundaries. Published dosimetric datasets for both seeds have been obtained under bounded conditions. The aim of the present study is to obtain dosimetric datasets for these seeds under full scatter conditions. The Monte Carlo GEANT4 code has been used to estimate air-kerma strength and dose rate in water around the Ir-192 seeds. Functions and parameters following the TG43 formalism are obtained and presented in tabular forms: the dose rate constant, the radial dose function, and the anisotropy function. Tables for the anisotropy factor have been obtained in order to apply punctual approximation. Differences between dose rate distributions for both seeds show that specific dataset must be used for each type of seed in clinical dosimetry. The data in the present study improve on published data in the following aspects: (i) dosimetric data were obtained under full scatter conditions, which affect dose values at distances greater than 4-5 cm from the source; (ii) the dose rate tables are given at greater distances from the source; and (iii) the spatial resolution in high dose gradient areas, such as those near the longitudinal source axis, has been improved.

[1]  R. Nath,et al.  Dosimetry on transverse axes of 125I and 192Ir interstitial brachytherapy sources. , 1990, Medical physics.

[2]  R. Capote,et al.  Radial dose functions for 103Pd, 125I, 169Yb and 192Ir brachytherapy sources: an EGS4 Monte Carlo study. , 2000, Physics in medicine and biology.

[3]  Kirsten Boedeker,et al.  An analysis of MCNP cross-sections and tally methods for low-energy photon emitters. , 2002, Physics in medicine and biology.

[4]  S. Chiu‐Tsao,et al.  Dose rate determination for 125I seeds. , 1990, Medical physics.

[5]  B. Clark,et al.  Experimental determination of dosimetry functions of Ir-192 sources. , 1998, Medical physics.

[6]  J. Williamson,et al.  Monte Carlo-aided dosimetry of a new high dose-rate brachytherapy source. , 1998, Medical physics.

[7]  D. Baltas,et al.  An analytical dosimetry model as a step towards accounting for inhomogeneities and bounded geometries in 192Ir brachytherapy treatment planning. , 2003, Physics in medicine and biology.

[8]  R. Nath,et al.  Anisotropy functions for 103Pd, 125I, and 192Ir interstitial brachytherapy sources. , 1993, Medical physics.

[9]  J F Williamson,et al.  Monte Carlo aided dosimetry of the microselectron pulsed and high dose-rate 192Ir sources. , 1995, Medical physics.

[10]  D Baltas,et al.  Evaluation of a TG-43 compliant analytical dosimetry model in clinical 192Ir HDR brachytherapy treatment planning and assessment of the significance of source position and catheter reconstruction uncertainties. , 2004, Physics in medicine and biology.

[11]  P. Higgins,et al.  Radial dose distribution of 192Ir and 137Cs seed sources. , 1989, Medical physics.

[12]  F Ballester,et al.  Monte Carlo dosimetric characterization of the Cs-137 selectron/LDR source: evaluation of applicator attenuation and superposition approximation effects. , 2004, Medical physics.

[13]  C. Ling,et al.  Dose parameters of 125I and 192Ir seed sources. , 1989, Medical physics.

[14]  R. Capote,et al.  Dose rate constants for 125I, 103Pd, 192Ir and 169Yb brachytherapy sources: an EGS4 Monte Carlo study. , 1998, Physics in medicine and biology.

[15]  D Granero,et al.  Phantom size in brachytherapy source dosimetric studies. , 2004, Medical physics.

[16]  R Wang,et al.  A Monte Carlo calculation of dosimetric parameters of 90Sr/90Y and 192Ir SS sources for intravascular brachytherapy. , 2000, Medical physics.

[17]  S. Chiu‐Tsao,et al.  Treatment planning dosimetric parameters for 192Ir seed at short distances: effects of air channels and neighboring seeds based on Monte Carlo study. , 2004, Medical physics.

[18]  Jose Perez-Calatayud,et al.  Monte Carlo calculation of dose rate distributions around Ir192 wires , 1997 .

[19]  L. L. Meisberger,et al.  The effective attenuation in water of the gamma rays of gold 198, iridium 192, cesium 137, radium 226, and cobalt 60. , 1968, Radiology.

[20]  J. Williamson,et al.  Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. , 2004 .

[21]  J F Williamson,et al.  Comparison of measured and calculated dose rates in water near I-125 and Ir-192 seeds. , 1991, Medical physics.

[22]  L. Anderson,et al.  Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43 , 1995 .

[23]  R. Sloboda,et al.  EGS4 dosimetry calculations for cylindrically symmetric brachytherapy sources. , 1996, Medical physics.

[24]  J Borg,et al.  Spectra and air-kerma strength for encapsulated 192Ir sources. , 1999, Medical physics.

[25]  R. Capote,et al.  Anisotropy function for 192Ir low-dose-rate brachytherapy sources: an EGS4 Monte Carlo study. , 2001, Physics in medicine and biology.

[26]  D Baltas,et al.  Dosimetry comparison of 192Ir sources. , 2002, Medical physics.

[27]  J F Williamson,et al.  Monte Carlo evaluation of kerma at a point for photon transport problems. , 1987, Medical physics.

[28]  F. Ballester,et al.  A Monte Carlo investigation of the dosimetric characteristics of the CSM11 137Cs source from CIS. , 2000, Medical physics.

[29]  M. Lindstrom,et al.  The dose distribution surrounding 192Ir and 137Cs seed sources. , 1991, Physics in medicine and biology.