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Dosimetric Evaluation of Available I-125 High Activity Seeds for COMS Eye Plaques

L Muller

L Muller*, D Johnson , S Ahmad , T De La Fuente Herman , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


SU-I-GPD-T-26 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The radioactive eye plaque program has surged in recent years; however, the I-125 seed model 6711 is now discontinued. To preserve the flow of procedures and keep up with demand, a comparison of the dosimetry of I-125 seed models currently available was warranted to decide on a model which would agree with what was previously instated. Materials and

Methods: Treatment plans were calculated with Brachyvision (Varian) for COMS eye plaque sizes of 10, 12, 14, 16, 18, and 20mm fully loaded, and 16mm size with 12mm posterior load using I-125 seed models 6711(Oncura), AgX100(Theragenics), and IAI-125A(IsoAid). Prescription dose was 8500cGy to 7mm depth at the central axis of the plaque. For special loading case, the prescription point is shifted 2mm to the center of the “active” area. The planning software is based on TG-143U and assumes homogeneous media. The seed coordinates for 3D planning were obtained from TG-129. Five points of interest (optic disk, opposite retina, macula, and depths 7mm (prescription) and 5mm) were used for comparison.

Results: For all plaque sizes, compared to seed model 6711, doses by AgX100 and IAI-125A seeds were 1.5% and ≤2.5% different at the prescription point respectively, with equal seed activity. Greatest dose deviations occurred at the macula and the opposing retina. For AgX100, doses to macula and opposite retina were a maximum of 3.8% and 0.8% higher. For IAI 125A, doses to macula and opposite retina were a maximum of 2% and 6% higher.

Conclusion: The dosimetry of AgX100 seed geometry is closer to that of the 6711 model; nevertheless, the IAI-125A seed offers an acceptable dosimetric variation of 3% of prescription. Therefore, updating seed characteristics used in ordering forms is not necessary. The decision of which vendor to use will primarily depend on seed strength availability and quality of service.

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