E&Z BEBIG Ir192 HDR, Ir2.A85-2

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Source Description:

Dimensions for the BEBIG HDR Ir2.A85-2 source are taken from the study by Granero et al1. The source consists of a 3.50 mm long 192 Ir core with a diameter of 0.6 mm enclosed in a stainless steel capsule (AISI 316L with a density of 7.80 g/cm3) of a diameter 0.9 mm. The tip of the encapsulation is assumed to be a 0.1 mm thick conical section, with the radius of the face being 0.175 mm. The conical section is attached to a 0.5 mm long solid cylindrical section followed by a 3.62 mm long hollow section with an inner diameter of 0.7 mm. The last section of the capsule is a 0.7 mm long solid cylinder overlapped by an air cone with a height of 0.2 mm. The cable is a solid cylinder of AISI 316L stainless steel with a density of 6.90 g/cm3 a diameter of 0.9 mm and a length of 5 mm. The active length of this source is 3.5 mm.  The mean photon energy calculated on the surface of the source is 360.46 keV with statistical uncertainties < 0.002% . 


 Dose Rate Constant - Λ :

Dose rate constants, Λ, are calculated by dividing the dose to water per history in a (0.1 mm)3 voxel centered on the reference position,    (1 cm, Π/2), in the 80x80x80 cm3 water phantom, by the air-kerma strength per history factor (scored in vacuo). Air kerma per history is always calculated using a tracklength estimator in a 10x10x0.05 cm3 air voxel located in vacuo on the transverse axis 100 cm away from the source and then corrected (kr2 = 1.00217) for the lateral and thickness dimensions of the scoring voxel to give the air kerma per history on the central axis at a point 100 cm from the source’s mid-point as described in our previous study 23. Low-energy photons emitted from the source encapsulation are suppressed in the air-kerma calculations by discarding all photons with energy less than 10 keV (i.e., PCUT set to 10 keV in EGSnrc). egs_brachy uncertainties are only statistical uncertainties (k=1).

Author Method Λ (cGy h-1 U-1) Abs. Uncertainty
Safigholi et al 4 10x10x0.5 cm3 voxel at 100 cm 1.1102 0.0002
Granero et al 1 extrap 1.109 0.011
Perez_calatayud et al 5 HEBD Consensus value 1.109 0.012

Radial dose function - g(r):

The radial dose function, g(r), is calculated using both line and point source geometry functions and tabulated at 36 different radial distances ranging from 0.2 cm to 20 cm.

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radial dose function


Anisotropy function - F(r,θ):

Anisotropy functions are calculated using the line source approximation and tabulated at 12 radii from 0.25 cm to 20 cm and 47 unique polar angles with a resolution of 5°  or better. The anisotropy factor, φan (r), is calculated by integrating the solid angle weighted dose rate over 0° ≤ ϑ ≤ 180°.

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 F(1.00,θ) 
Anisotropy function
 F(5.00,θ) 
Anisotropy function
F(10.00,θ)

 

Along-Away Dose Data:

Along-away dose data are tabulated at 16 away distances from 0 cm to 20 cm and 31 along points from -20 cm to 20 cm. Doses are normalized to SK, the air kerma strength.


Primary and Scatter Separated (PSS) Dose Data: Dii (r,θ):

Primary and Scatter Separated (PSS) dose data are tabulated at 12 radii from 0.25 cm to 20 cm and 47 unique polar angles with a resolution of 5° or better. High resolution (Δr = 1 mm, ΔΘ = 1°) primary scatter dose data are also available in .csv files. For the purposes of these calculations, any photon escaping the source encapsulation is considered a primary. Only photons which scatter within the phantom are counted in the scatter tallies. Doses are normalized to the total photon energy escaping the encapsulation. The "ii" subscript labeled in the Dii(r, θ) represent the total scatter as Dto(r, θ), the primary photons as  Dpr(r, θ), the single scatter photon as  Dss(r, θ), and the multiple scatter photons as Dms (r, θ).

Dii (r,90°)*r 

Primary and Scatter Separated (PSS) Dose Data

Dii (1.00,θ) 

Primary and Scatter Separated (PSS) Dose Data

Dii (5.00,θ) 
Primary and Scatter Separated (PSS) Dose Data

Dii (10.00,θ) 
Primary and Scatter Separated (PSS) Dose Data

 
High resolution (1mm/1°) Tabulated Dii (r,θ) data in .csv format: Zipped archive

Photon Energy Spectra

Photon energy spectra generated by the source model are calculated using the egs_brachy surface count scoring option to get the spectrum on the surface of the source. The plotted values are the counts per MeV in 1 keV bins, normalized to 1 count total in the spectrum. The MC calculations have a statistical uncertainty less than 0.002% on the mean energy.  The spectrum data are available in xmgrace format below.

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Photon energy spectrum on the source surface: xmgrace 


Tabulated data:

Tabulated data are available in .xlsx format: Excel


References:

1. D. Granero, J. Pérez-Calatayud, and  F. Ballester, Monte Carlo study of the dose rate distributions for the Ir2.A85-2 and Ir2.A85-1 Ir-192 afterloading sources, Med. Phys. 35, 1280-1287, 2008. 
2. R. E. P. Taylor et al , Benchmarking BrachyDose: voxel-based EGSnrc Monte Carlo calculations of TG--43 dosimetry parameters, Med. Phys., 34 , 445 - 457, 2007
3. D. W. O. Rogers, Inverse square corrections for FACs and WAFACs, Appl. Radiat. Isot.,153 ,108638, 2019
4. H. Safigholi, M. J. P. Chamberland, R. E. P. Taylor, M. P. Martinov, D. W. O. Rogers, and R. M. Thomson, Update of the CLRP TG-43 parameter database for high-energy brachytherapy sources,  to be published (Current calculation). 
5. Perez-Calatayud et al , Dose Calculation for Photon-Emitting Brachytherapy Sources with Average Energy Higher than 50 keV: Full Report of the AAPM and ESTRO, 2012 by AAPM, ISBN: 978-1-936366-17-0


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