Source Description:
Dimensions for the Advantage Pd-103 source 1,2 are from the study by Meigooni et al . The IsoAid Advantage 103 Pd seed contains four spherical polystyrene beads with a diameter of 0.500 mm. The 103 Pd for this source is assumed to be distributed uniformly throughout the volume of the four beads. The four beads are separated into two pairs by a cylindrical silver marker that is 0.500 mm in diameter and 1.25 mm long. The centers of the two beads within a pair are offset 0.968 mm and 1.56 mm. The source is encapsulated in a titanium casing 0.050 mm thick with an outside diameter of 0.800 mm. The end welds have a maximum thickness of 0.350 mm and are modelled using a 0.405 mm radius Ti hemisphere overlapped with a 0.890 mm radius air sphere with its center shifted by 0.840 mm relative to the Ti sphere. The overall source length is 4.50 mm and the active length is 3.62 mm. The maximum possible displacement of a source sphere is 0.459 mm along the seed axis and up to 0.070 mm in the radial direction.
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 30x30x30 cm 3 water phantom, by the air kerma strength per history (scored in vacuo ). As described in ref. 3 , dose rate constants are provided for air kerma strenth calculated using voxels of 2.7x2.7x0.05 cm 3 (WAFAC) and 0.1x0.1x0.05 cm 3 (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.
| Author | Method | Λ (cGy h-1 U-1) | Abs. Uncertainty |
| R. E. P. Taylor, D. W. O. Rogers 6 | WAFAC | 0.687 | 0.002 |
| R. E. P. Taylor, D. W. O. Rogers 6 | point | 0.687 | 0.002 |
| A. S. Meigooni et al 1 | extrap (PTRAN) | 0.70 | 0.056 |
| A. S. Meigooni et al 1 | TLD | 0.69 | 0.02 |
| K. Sowards 2 | point (PTAN) | 0.709 | 0.014 |
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 7 .
| 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 -a 6 r | ||||||||
| Fit range | Coefficients | |||||||
| r min (cm) | r max (cm) | a 0 / cm 2 | a 1 / cm | a 2 | a 3 / cm -1 | a 4 / cm -2 | a 5 / cm -3 | a 6 / cm -1 |
| 0.10 | 10.00 | -2.1916E-04 | -9.8072E-02 | 1.8342E+00 | 1.2624E-01 | -3.6875E-02 | 2.6999E-03 | 6.0320E-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° . The anisotropy factor, φan (r), was calculated by integrating the solid angle weighted dose rate over 0° ≤ ϑ ≤ 90°.
F(00.50,θ)  |
F(01.00,θ)  |
F(05.00,θ)  |
References:
1. A. S. Meigooni et al , Experimental and Monte Carlo dosimetric characterization of Advantage 103 Pd, Appl. Radiat. Isotopes, 64 , 881--887, 2006
2. K. Sowards, Monte Carlo dosimetric characterization of the IsoAid Advantage 103 Pd brachytherapy source, J. Appl. Clin. Med. Phys., 8 , 18 -- 25, 2007
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 125 I and 103 Pd Brachytherapy Seeds, J. Res. Natl. Inst. Stand. Technol., 108 , 337 -- 358, 2003
6. R. E. P. Taylor, D. W. O. Rogers, An EGSnrc Monte Carlo-calculated database of TG-43 parameters, Med. Phys., 35 , 4228--4241, 2008
7. R. E. P. Taylor, D. W. O. Rogers, More accurate fitting of 125 I and 103 Pd radial dose functions, Med. Phys., 35 , 4242--4250, 2008
Carleton Laboratory for Radiotherapy Physics
December 17 2007.