Source Description:
Source dimensions for the 6711 seed are taken from the paper by Dolan et al ^{1} which presents a more realistic geometry than was used in previous studies. The 6711 source consists of radioactive AgBr and AgI (2.5:1 molecular ratio of AgBr:AgI and a density of 6.2 g/cm^{3}) (Note: the prevoius database took 2.5:1 as the molcular ratio of AgI to AgBr) coated on a 2.8 mm long cylindrical silver rod with a 0.25 mm radius. The ends of the silver rod are conical sections bevelled at 45.0^{o} and the end faces of the rod have a radius of 0.175 mm. The radioactive coating is assumed to have a thickness of 1.75 μm over the entire surface of the rod. The silver rod is encapsulated in a 3.75 mm long titanium tube with 0.07 mm thick walls, a 0.8 mm outer diameter and 0.4 mm thick hemispherical end welds (Note: the BrachyDose model of this seed previously used 0.375 mm thick end welds, which caused a small discontinuity between the end welds and the cylindrical capsule). The overall source length is 4.55 mm and the active length is 2.8 mm. The cylindrical source element is free to move 0.835 mm along the seed axis and 0.08 mm radially from the center of the seed, however, we assume the silver rod is always centred. The mean photon energy calculated on the surface of the source is 27.34 keV with statistical uncertainties < 0.01%
DoseRate Constant  Λ :
Doserate 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 30x30x30 cm^{3 }water phantom, by the airkerma strength per history (scored in vacuo). As described in ref.2, doserate constants are provided for airkerma strength calculated using voxels of 2.66x2.66x0.05 cm^{3 }(WAFAC) and 0.1x0.1x0.05 cm^{3 }(point) located 10 cm from the source. The larger voxel size averages the airkerma per history over a region covering roughly the same solid angle subtended by the primary collimator of the WAFAC ^{3,4} at NIST used for calibrating lowenergy brachytherapy sources and is likely the most clinically relevant value. The small voxel serves to estimate the air kerma per history at a point on the transverse axis and includes a small 1/r^{2} correction (0.5%) ^{2. }egs_brachy and BrachyDose uncertainties are only statistical uncertainties (k=1).
Author  Method  Λ (cGy h^{1} U^{1})  Abs. Uncertainty 
Safigholi et al ^{5}  WAFAC 
0.932

0.0004

Safigholi et al ^{5}

Point

0.951

0.001

Taylor, Rogers ^{6}

WAFAC

0.924

0.002

Taylor, Rogers ^{6}

Point

0.942

0.003

Dolan et al ^{1}

extrap/WAFAC (PTRAN)

0.942

0.017

Dolan et al ^{1}

TLD dosimetry

0.971

0.059

Rodriguez, Rogers ^{7}

TLD (Revised Dolan)

0.915

0.057

Chen and Nath ^{8}

Photon Spectrometry

0.960

0.037

Rodriguez, Rogers ^{9}

WAFAC (BrachyDose)

0.928

0.002

Rivard et al ^{10}

TG43U1 Consensus Value

0.965



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 0.05 cm to 10 cm. Fit parameters for a modified polynomial expression are also provided ^{11}. The mean residual deviations from the actual data for the best fit were < 0.031%.
Fitting coefficients for g _{L} (r) = (a_{0} r^{2} + a_{1} r^{1} + a_{2} + a_{3}r + a_{4}r^{2} + a_{5} r^{3}) e^{a6r}  
Fit range  Coefficients  
r _{min} (cm)  r _{max} (cm)  
0.05  10.00  a_{0} / cm^{2}  (5.1+/0.6)E03 
a_{1} / cm  (2.91+/0.28)E02  
a_{2}  (1.166+/0.005)E+00  
a_{3} / cm^{1}  (4.44+/0.06)E01  
a_{4} / cm^{2}  (1.34+/0.28)E03  
a_{5} / cm^{3}  (2.68+/0.13)E03  
a_{6} / cm^{1}  (4.641+/0.024)E01 
Anisotropy function  F(r,θ):
Anisotropy functions are calculated using the line source approximation and tabulated at radii of 0.1, 0.15, 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 7.5 and 10 cm and 32 unique polar angles with a minimum resolution of 5 ^{o} . The anisotropy factor, φ _{an} (r), was calculated by integrating the solid angle weighted dose rate over 0 ^{o} ≤ ϑ ≤ 90 ^{o} .
Primary and Scatter Separated (PSS) Dose Data: D^{ii}(r, Θ):
Primary and Scatter Separated (PSS) dose data are tabulated at 24 radii from 0.1 cm to 10 cm and 24 unique polar angles with a minimum resolution of 5 ^{o }. High resolution (Δr = 1 mm, ΔΘ = 1 ^{o }) primary scatter dose data are also available in .csv files. For the purposes of these calculations, scatter within the source is not considered as scatter 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.
High resolution (1mm/1°) Tabulated D ii (r,θ) data in .csv format: Zipped archive
Click images for higher res versions
Photon Energy Spectra
Photon energy spectra generated by the source model is calculated using egs_brachy surface count scoring option to get the spectrum on the surface of the source. The relative counts is the counts per 0.1 keV bin per MeV normalized to 1 count per MeV^{1. }The MC calculations have a statistical uncertainty less than 0.0.01% on the mean energy. The spectrum data is available in xmgrace format below.
Energy weighted photon spectrum data: xmgrace
Tabulated data:
Tabulated data are available in .xlsx format: Excel
References:
1. J. Dolan et al , Monte Carlo and experimental dosimetry of an 125I brachytherapy seed, Med. Phys., 33 , 4675  4684, 2006.
2. R. E. P. Taylor et al , Benchmarking BrachyDose: voxelbased EGSnrc Monte Carlo calculations of TG43 dosimetry parameters, Med. Phys., 34 , 445  457, 2007.
3. R. Loevinger, Wideangle freeair chamber for calibration of lowenergy brachytherapy sources, Med. Phys., 20 , 907, 1993.
4. S. M Seltzer et al , New National AirKermaStrength Standards for ^{125}I and ^{103}Pd Brachytherapy Seeds, J. Res. Natl. Inst. Stand. Technol., 108 , 337  358, 2003.
5. H. Safigholi, M. J. P. Chamberland, R. E. P. Taylor, C. H. Allen, M. P. Martinov, D. W. O. Rogers, and R. M. Thomson, Updated of the CLRP TG43 parameter database for lowenergy photonemitting brachytherapy sources, to be published (Current calculation).
6. R. E. P. Taylor, D. W. O. Rogers, An EGSnrc Monte Carlocalculated database of TG43 parameters, Med. Phys., 35 , 42284241,2008. 7. M. Rodriguez and D. W. O. Rogers, Effect of improved TLD dosimetry on the determination of dose rate constants for ^{125}I and ^{103}Pd brachytherapy seeds, Med. Phys., 41, 114301, 2014. 8. Zhe (Jay) Chen and Ravinder Nath, A systematic evaluation of the doserate constant determined by photon spectrometry for 21 different models of lowenergy photonemitting brachytherapy sources, Phys. Med. Biol., 55 , 6089, 2010. 9. M. Rodriguez and D. W. O. Rogers, On determining dose rate constants spectroscopically, Med. Phys., 40, 011713, 2013.
10. M. J. Rivard et al , Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations, Med. Phys., 31 , 633  674, 2004.
11. R. E. P. Taylor, D. W. O. Rogers, More accurate fitting of ^{125}I and ^{103}Pd radial dose functions, Med. Phys., 35 , 42424250, 2008.