Source Description:
Dimensions for the generic HDR 192Ir source from the AAPM/ESTRO Working Group on MBDCA (WG-MBDCA) are taken from the study by Ballester et al 1. The generic HDR source consists of a 3.50 mm long 192Ir core with a diameter of 0.6 mm enclosed in a stainless steel capsule (AISI 316L with a density of 8.02 g/cm3). The encapsulation consists of an end weld composed of a hemisphere that is 1 mm in diameter with its center shifted 1.85 mm from the source center. The length of the capsule from the tip to the start of the cable is 5 mm. The cable is a solid cylinder of AISI 316L stainless steel with a density of 5.0 g/cm3 a diameter of 1 mm and a length of 2 mm. The active length of this source is 3.5 mm. The mean photon energy calculated on the surface of the source is 360.63 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 2,3. 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).
Note: decreasing PCUT from 10 to 1 keV increase the value of the air kerma strength by 0.066% and decrease dose-rate constant by 0.067%.
Note: DRC calculated using electron transport in phantom is 1.1115 cGy h-1 U-1 which is about 0.12% higher than the value of 1.1102 cGy h-1 U-1 without electron transport.
| Author | Method | Λ (cGy h-1 U-1) | Abs. Uncertainty |
| Safigholi et al (no e- transport) 4 | 10 x 10 x 0.05 cm3 voxel at 100 cm | 1.1102 | 0.0002 |
| Safigholi et al (with e- transport) 4 | 10 x 10 x 0.05 cm3 voxel at 100 cm | 1.1115 | 0.0017 |
| Ballester et al 1 |
0.1 x 0.1 cm2 cylindrical air cell at 10 cm (ALGEBRA code) |
1.1113 | 0.0006 |
| Ballester et al 1 | 0.1 x 0.1 cm2 cylindrical air cell at 10 cm (BrachyDose code) | 1.1100 | 0.001 |
| Ballester et al 1 | 0.1 x 0.1 cm2 cylindrical air cell at 10 cm (GEANT4 code) | 1.1104 | 0.002 |
| Ballester et al 1 | 0.1 x 0.1 cm2 cylindrical air cell at 10 cm (MCNP5 v.1.6 code) | 1.1110 | 0.0004 |
| Ballester et al 1 | 0.1 x 0.1 cm2 cylindrical air cell at 10 cm (PENELOPE2008 code) | 1.1113 | 0.0006 |
| Ballester et al 1 |
0.1 x 0.1 cm2 cylindrical air cell at 10 cm [average of multiple MC codes] |
1.1109 | 0.0004 |
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.
Note: Related to with and without e- transport.....
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Anisotropy function - F(r,θ):
Anisotropy functions are calculated using the line source approximation and tabulated at 13 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), was calculated by integrating the solid angle weighted dose rate over 0° ≤ ϑ ≤ 180°.
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F(0.50,θ)  |
F(1.00,θ)  |
F(4.00,θ)  |
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 29 along with 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 0.3 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) .
Click images for higher res versionsDii (r,90°)*r 2 |
Dii (5.00,θ) |
Dii (10.00,θ)  |
Dii (20.00,θ) |
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 spectra on the source surface: xmgrace
Tabulated Data:
Tabulated data are available in .xlsx format: Excel
References:
1. F. Ballester et al, A generic high-dose rate 192Ir brachytherapy source for evaluation of model-based dose calculations beyond the TG-43 formalism, Med. Phys. 42, 3048 -3062, 2015
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).