Short lip-acrylic (Sla)

  

Eye Plaque Description

The dimensions of the "Short-lip acrylic" (Sla)  eye plaque are available here  (given in the TG-221 report 1 and Lesperance et al study 2). The plaque has indentations for 13 seeds within acrylic 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 (13 seeds modelled under TG43 conditions) and HETERO (fully-loaded eye plaque in water) for 103Pd: Zipped archive
  • HOMO (13 seeds modelled under TG43 conditions) and HETERO (fully-loaded eye plaque in water) for 125I: Zipped archive
  • HOMO (13 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. Overall, HETERO doses are slightly lower than HOMO doses, due to the small photon attenuation and scattering in the plaque backing and insert. For instance, HETERO/HOMO dose ratio at 0.5 cm along the CAX is 0.98, 0.98, and 0.97, for 103Pd, 125I, and 131Cs, respectively.

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

 

HETERO/HOMO dose ratio along the CAX

HETERO/HOMO dose ratio along the CAX are presented here for three radionuclides. The mean values of HETERO/HOMO doses along the CAX were 0.96 for 103Pd, 0.95 for 125I,  and 0.93 for 131Cs, respectively. These corresponding values for COMS 16 mm were 0.79, 0.85, and 0.85, respectively. The mean (range) percentage difference of HETERO/HOMO doses between egs_brachy and BrachyDose1 were -0.06% (-2.4%, 1.1%) for 103Pd, -0.04% (-1.6%, 2.0%) for 125I, and -0.22 (-3.2%, -2.4%) for 131Cs, respectively. The corresponding values for COMS 16 mm  were 0.06% (-1.1%, 1.4%) for 103Pd, -0.10% (-1.3%, 0.82%) for 125I, and -0.12% (-2.2%, 2.0%) for 131Cs, respectively.  Statistical uncertainties for egs_brachy, and BrachyDose 1, 2   are less than 0.20% and 1.0%, respectively.  

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

 

 Transverse dose profile

HOMO and HETERO transverse dose profiles (along x and y axes)  at depths of z = 0.5 cm and z = 1 cm are shown for three radionuclides. 

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. R. M. Thomson et al., AAPM recommendations on medical physics practices for ocular plaque brachytherapy: Report of task group 221, Med. Phys. 46, e92-e124, 2020.
2. M. Lesperance, M. Martinov, and R. M. Thomson, Monte Carlo dosimetry for 103Pd, 125I, and 131Cs ocular brachytherapy with various plaque models using an eye phantom, Med. Phys. 41, 031706, 2014.   
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.
 
 


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