COMS 20 mm

 

Eye Plaque Description

The dimensions of the 20 mm eye plaque are available here (given in the TG129 report 1, 2). The plaque has indentations for 24 seeds within Silastic insert  (seed coordinates here) in the Modulay backing, as shown in the above figures (generated using egs_view). The 3D dose distributions for the plaque containing 125I (6711), 103Pd (200), and 131Cs (CS-1 Rev2) (Ref. 3) are provided here (normalized per unit seed air kerma strength):  

  • HOMO (24 seeds modelled under TG43 conditions) and HETERO (fully-loaded eye plaque in water) for 103Pd: Zipped archive
  • HOMO (24 seeds modelled under TG43 conditions) and HETERO (fully-loaded eye plaque in water) for 125I: Zipped archive
  • HOMO (24 seeds modelled under TG43 conditions) and HETERO (fully-loaded eye plaque in water) for 131Cs: Zipped archive

 Central axis depth dose curves

Doses along the plaque's central z-axis (CAX) for HOMO and HETERO scenarios are presented here for three radionuclides and compared with published BrachyDose 1, 4 and MCNP 5 results. Overall, HETERO doses are lower than the HOMO doses, due to the attenuation and scattering in the plaque backing and insert. For instance, HETERO/HOMO dose ratio at 0.5 cm along the CAX is 0.80, 0.87, and 0.89 for 103Pd, 125I, and 131Cs, respectively. The mean (range) percentage difference of HOMO doses along the CAX between egs_brachy and BrachyDose were 0.49% (0.19%, 0.69%) for 103Pd, 0.79% (0.43%, 1.2%) for 125I, respectively. The corresponding values between egs_brachy and MCNP were 2.9% (1.1%, 4.9%) for 103Pd, 0.93% (0.24%, 2.0%) for 125I, and 2.6% (1.9%, 3.6%) for 131Cs, respectively. The  mean (range) percentage difference of HETERO doses along the CAX  between egs_brachy and BrachyDose were -0.21% (-0.58, 0.02%) for 103Pd, 0.50% (0.27%, 0.61%) for 125I, respectively. The corresponding values between egs_brachy and MCNP were 1.2% (-0.59%, 2.7%) for 103Pd, -0.33% (-1.1%, 0.14%) for 125I, and 0.84% (0.49%, 1.3%) for 131Cs, respectively. Statistical uncertainties for egs_brachy, BrachyDose 4,  and MCNP 5 are less than  0.20%, 1.0%,  and 2.0%, respectively.  

103Pd model 200 125I model 6711 131Cs (CS-1 Rev2)
       

 

 Transverse dose profile

Transverse dose profiles (along x and y axes) at depths of z = 0.5 cm and z = 1 cm are shown for three radionuclides. These dose profiles compared to available BrachyDose results from the previous database are in good agreement (< 1.2%).

Click images for higher res versions
103Pd, x view, z =0.5 and 1 cm
 		 103Pd, y view, z =0.5 and 1 cm
 
125I, x view, z =0.5 and 1 cm
 		 125I, y view, z =0.5 and 1 cm
 
131Cs, x view, z =0.5 and 1 cm
 		   131Cs, y view, z =0.5 and 1 cm
 

 

 References

1. Chiu-Tsao ST, Astrahan MA, Finger PT, et al. Dosimetry of 125I and 103Pd COMS eye plaques for intraocular tumors: report of Task Group 129 by the AAPM and ABS. Med Phys. 39: 6161–6184, 2012.
2. M. J. Rivard, Sou-Tung Chiu-Tsao, P. T. Finger, A. S. Meigooni, C. S. Melhus, F. Mourtada,  M. E. Napolitano, D. W. O. Rogers, R. M. Thomson, R. Nath, Comparison of dose calculation methods for brachytherapy of intraocular tumors, Med. Phys. 38, 306 – 316,  2011.     
3. 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 LDR low_energy brachytherapy sources. Med Phys. 47, 4656-4669, 2020.
4. R. M. Thomson, R. E. P. Taylor, and D. W. O. Rogers, Monte Carlo dosimetry for 125I  and 103Pd eye plaque brachytherapy, Med. Phys. 35, 5530-5543, 2008.
5. C. S. Melhus and M. J. Rivard, COMS eye plaque brachytherapy dosimetry simulations for 103Pd, 125I, and 131Cs, Med. Phys. 35, 3364
-3371, 2008 
 
 


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