IsoAid, LLC, Advantage I-125, IAI-125A


Source Description:

Dimensions for the IAI-125A source  are taken from the study by  Solberg et al 2. (Note: CLRPv1 database took the source dimensions from the study by Meigooni et al 1). The IsoAid Advantage seed contains a 3 mm long silver rod with a diameter of 0.50 mm. The silver rod is coated with a 1 μm thick layer of AgI containing 125I (coating assumed to be the same thickness on the cylindrical and end face surfaces). The source is encapsulated in a titanium casing 0.05 mm thick with an outside diameter of 0.80 mm. The end welds have a maximum thickness of 0.275 mm (Note: 0.10 mm in CLRPv1 database) and are modelled using a 0.40 mm radius Ti hemisphere overlapped with a 0.350 mm radius air sphere with its center shifted by 0.20 mm (Note: 0.05 mm in CLRPv1 database) relative to the Ti sphere. The overall source length is 4.50 mm and the active length is 3.0 mm. The cylindrical source element is free to move approximately 0.948 mm (Note: 0.350 mm in CLRPv1 database) along the seed axis and 0.10 mm radially from the center of the seed, however, we assume the marker is always centred. The gas in the unoccupied space inside the source is assumed to be air. The mean photon energy calculated on the surface of the source is 27.27 keV with statistical uncertainties < 0.009%.

Dose-Rate Constant - Λ :

Dose-rate constants, Λ , are calculated by dividing the dose to water per history in a (0.1 mm)voxel centered on the reference position,        (1 cm,Π/2), in the 30x30x30 cmwater phantom, by the air-kerma strength per history (scored in vacuo). As described in ref. 3 , dose-rate constants are provided for air-kerma strength calculated using voxels of 2.66x2.66x0.05 cm3 (WAFAC) and 0.1x0.1x0.05 cm3 (point) located 10 cm from the source. The larger voxel size averages the air-kerma per history over a region covering roughly the same solid angle subtended by the primary collimator of the WAFAC 4, 5  at NIST used for calibrating low-energy 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/r2 correction (0.5%) 3. MC uncertainties are only statistical uncertainties (k=1).

Author Method Λ (cGy h-1 U-1) Abs. Uncertainty
Safigholi et al 6 WAFAC 0.9248 0.0002
Safigholi et al 6 point 0.9604 0.0015
Taylor, Rogers  7 WAFAC 0.925 0.002
Taylor, Rogers  7 point 0.959 0.002
Meigooni et al 1 point (PTRAN) 0.98 0.03
Meigooni et al 1 TLD 0.99 0.08
Solberg et al 2 point (MCNP) 0.962 0.005
Solberg et al 2 TLD 0.96 0.05
Rodriguez, Rogers 8 Revised TLD (Solberg) 0.945 0.056
Rodriguez, Rogers 8 WAFAC (BrachyDose) 0.925 0.015
Rivard et al  9 TG43U1S1 Consensus Value 0.981  ---

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  10 . The mean residual deviations from the actual data for the best fit were < 0.12%.  

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radial dose function

Fitting coefficients for g L (r) = (a0 r-2 + a1 r-1 + a2 + a3r + a4r2 + a5 r3) e-a6r
Fit range Coefficients
r min (cm) r max (cm)
0.05 10.0 a0 / cm2 (5.68+/-0.22)E-04
    a1 / cm (-1.20+/-0.04)E-02
    a2 (1.1470+/-0.0018)E+00
    a3 / cm-1 (4.465+/-0.034)E-01
    a4 / cm-2 (-3.93+/-0.20)E-03
    a5 / cm-3 (2.54+/-0.08)E-03
    a6 / cm-1 (4.591+/-0.016)E-01

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 .

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Anisotropy function
Anisotropy function
Anisotropy function

Tabulated data:

Tabulated data are available in .xlsx format: Excel


1. A. S. Meigooni et al , Experimental and theoretical determination of dosimetric characteristics of IsoAid Advantage 125I brachytherapy source, Med. Phys., 29 , 2152 - 2158, 2002 
2. T. D. Solberg et al , Dosimetric parameters of three new solid core I-125 brachytherapy sources, J. Appl. Clin. Med. Phys, 3 , 119-134, 2002 
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. R. Loevinger, Wide-angle free-air chamber for calibration of low-energy brachytherapy sources, Med. Phys., 20 , 907, 1993 
5. S. M Seltzer et al , New National Air-Kerma-Strength Standards for 125I and 103Pd Brachytherapy Seeds, J. Res. Natl. Inst. Stand. Technol., 108 , 337 - 358, 2003  
6. H. Safigholi, M. J. P. Chamberland, R. E. P. Taylor, C. H. Allen, M. P. Martinov, D. W. O. Rogers, and R. M. Thomson, Update of the CLRP TG-43 parameter database for the brachytherapy, to be published (Current calculation) 
7. R. E. P. Taylor, D. W. O. Rogers, An EGSnrc Monte Carlo-calculated database of TG-43 parameters, Med. Phys., 35 , 4228-4241, 2008
8. M. Rodriguez , D. W. O. Rogers, Effect of improved TLD dosimetry on the determination of dose rate constants for 125I and 103Pd brachytherapyseeds, Med.Phys. 41, 114301-15, 2014                                                                                                                                        9. M. J. Rivard et al, Supplement to the 2004 update of the AAPM Task Group No. 43 Report, Med. Phys., 34 , 2187 - 2205, 2007 
10. R. E. P. Taylor, D. W. O. Rogers, More accurate fitting of 125I and 103Pd radial dose functions, Med. Phys., 35 , 4242-4250, 2008

Carleton Laboratory for Radiotherapy Physics  

CLRP TG-43 Parameter Database V2
 May 5, 2020

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