Source Description:
Dimensions for the microSelectron mHDR v2 revision (mHDR-v2r) are taken from the study by Granero et al 1 and Lopez et al 2. The mHDR-v2r consists of a 3.50 mm long cylindrical 192Ir core with a diameter of 0.60 mm enclosed in a 0.90 mm diameter AISI 316L stainless steel capsule (density 8.06 g/cm3) with a small layer of air around the core. The air gap thickness is 0.05 mm, 0.135 mm, and 0.065 mm around the cylinder core, and distal and proximal base of the core, respectively. The tip of the encapsulation is modelled as a 0.45 mm radius hemi-sphere with its center shifted 1.614 mm from the center of the source, which is truncated by a plan located 2.0 mm from the source center. The end of the encapsulation attached to the cable is modelled as a 0.15 mm thick conical section (half angle of 33.7o) starting 2.385 mm from the center of the source. Attached to the conical section is a 0.4 mm long and 0.7 mm diameter section of AISI 316L stainless steel cable with a density of 4.81 g/cm3. The active length of this source is 3.50 mm. The mean photon energy calculated on the surface of the source is 360.53 keV with statistical uncertainties < 0.002%.
Note: TG43 dosimetry parameters of mHDR-v2r source are very similar to previous version of this source (i.e., mHDR-v2).
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 study3,4 . 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 5 | 10x10x0.05 cm3 voxel at 100 cm | 1.1092 | 0.0003 |
| Granero et al 1 | MCNP5 | 1.1116 | 0.0004 |
| Granero et al 1 | GEANT4 (extrap) | 1.1129 | 0.0005 |
| Granero et al 1 | PENEPLOPE 2008 | 1.1119 | 0.0004 |
| Granero et al 1 | Average of three MC code | 1.1121 | 0.0008 |
| Lopez et al 2 | PENELOPE 2008 | 1.112 | 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: 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, scatter within the source is not considered and 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 (1.00,θ)  |
Dii (5.00,θ)  |
Dii (10.00,θ) |
Dii (20.00,θ)  |
High resolution (1mm/1°) Tabulated D ii (r,θ) data in .csv format: Zipped archive
Photon Energy Spectra
Photon energy spectra generated by the source model are calculated using egs_brachy surface count scoring option to get the spectrum on the surface of the source. The relative counts here are the counts per 1 keV bin 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.
Photon energy spectrum on the source surface: xmgrace
Tabulated data:
Tabulated data are available in .xlsx format: Excel
References:
1. D Granero, J Vijande, F. Ballester, and MJ Rivard, Dosimetry revisited for the HDR 192Ir brachytherapy source model mHDR-v2, Med. Phys., 38 , 486-494, 2011
2. 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
3. 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
4. D. W. O. Rogers, Inverse square corrections for FACs and WAFACs, Appl. Radiat. Isot.,153 ,108638, 2019
5. 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).