Source Description:
Dimensions for the VariSource VS2000 are taken from the study by Angelopoulos et al 1. The VS2000 consists of two symmetric 2.50 mm long radioactive iridium sources (density 22.42 g/cm3). Each source is made up of a 2.16 mm long cylindrical section with a 0.34 mm diameter and hemispherical ends with the same diameter. The two sources are contained in a 55.6% / 44.4% - Ni/Ti wire with a diameter of 0.59 mm (density 6.5 g/m3). The end of the wire was modelled as a hemisphere with its center shifted 3.205 mm from the center of the source. A length of wire extending 5.0 cm from the center of the source was included in this simulation. The active length of this source is 5.0 mm. The mean photon energy calculated on the surface of the source is 357.72 keV with statistical uncertainties < 0.01%.
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).
| Author | Method | Λ (cGy h-1 U-1) | Abs. Uncertainty |
| Safigholi et al 4 | 10x10x0.05 cm3 voxel at 100 cm | 1.0984 | 0.0002 |
| Taylor, Rogers 5 | 10x10x0.05 cm3 voxel at 100 cm | 1.099 | 0.002 |
| Angelopoulos et al 1 | extrap | 1.101 | 0.006 |
| Casado et al 7 | PENELOPE (extrap) | 1.10 | 0.03 |
| Perez-Calatayud et al6 | Consensus data (HEBD) | 1.100 | 0.006 |
| Papagiannis et al 7 | own code | 1.101 | 0.005 |
| Lopez et al 7 | Penelope (e- transport) | 1.096 | 0.002 |
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.
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), was calculated by integrating the solid angle weighted dose rate over 0° ≤ ϑ ≤ 180°.
Along-Away Dose Data:
Along-away dose data are tabulated at 16 away distances from 0 cm to 20 cm and 31 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: D ii (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 2  |
Dii (1.00,θ)  |
Dii (5.00,θ)  |
Dii (10.00,θ) |
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 0.01% on the mean energy. The spectrum data are available in xmgrace format below.
Photon energy spectrum on the source surface:xmgrace
Tabulated data:
Tabulated data are available in .xlsx format: Excel
References:
1. A. Angelopoulos et al , Monte Carlo dosimetry of a new 192Ir high dose rate brachytherapy source, Med. Phys., 27 , 2521--2527, 2000
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, 201
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. R. E. P. Taylor, D. W. O. Rogers, EGSnrc Monte Carlo calculated dosimetry parameters for 192Ir and 169Yb brachytherapy sources, Med. Phys., 35 , 4933 - 4944, 2008
6. 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
7. Francisco Javier Casado et al "Dosimetric characterization of an 192Ir brachytherapy source with the Monte Carlo code PENELOPE" Physica Medica, 26, 132-139, 2010.
8. P. Papagiannis et al, Dosimetry comparison of 192Ir sources Med. Phys.29 (2002) 2239 - 2246
9. J. F. A. Lopez et al, Monte Carlo dosimetry of the most commonly used 192Ir high dose rate brachytherapy sources, Rev. Fis. Med. Phys. 12, 159 -168, 2011