Encrypted login | home

Program Information

Dosimetric Comparison of I-125, Pd-103, and Cs-131 Seed Isotopes for Slotted Plaque Radiotherapy

S Howard

S Howard1*, V Massey2 , Y Altundal3 , (1) University of Kansas Hospital, Overland Park, KS, (2) University of Kansas Cancer Center, Overland Park, KS, (3) University of Kansas Hospital, Kansas City, KS


SU-I-GPD-T-43 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Dosimetric comparison of I-125, Pd-103, and Cs-131 seed isotopes for eye plaque radiotherapy in order to evaluate dose to critical structures

Methods: Ten cases of choroidal melanoma treated with I-125 eye plaque radiotherapy were examined. Treatment plans were created using the Plaque Simulator software developed by Eye Physics. For the purpose of comparison, plans were recalculated using the Pd-103 seed and Cs-131 seed. The Cs-131 seed was added to the Plaque Simulator software using brachytherapy data from published sources. Original prescription doses (85 Gy minimum to tumor apex), plaque type and model, and seed loading configurations were maintained in the comparison plans. Analysis of the plans compared dose to critical structures including the sclera, macula, optic nerve, lens, and retina.

Results: As expected, doses to most critical structures in the eye were lower for the Pd-103 plans and higher for the Cs-131 plans compared to the original I-125 plans. The exception was for the sclera. Doses to the sclera were lower for both the Pd-103 and Cs-131 plans in seven of the cases. For the three largest tumors, scleral dose was lowest in the Cs-131 plans. Interestingly, the Pd-103 plans had the highest scleral dose for two of the three largest tumors.

Conclusion: Doses to the macula, optic nerve, lens, and retina in general are lower for Pd-103 plaque plans compared to I-125. Conversely for large tumors (area larger than 150 sq mm in our analysis), scleral dose was the lowest in the Cs-131 plans. This phenomenon could be explained by the extremely small distances to the sclera from the plaque sources. In any case these findings warrant further investigation. The use of Cs-131 may be advantageous for patients with thick tumors in eye locations where scleral atrophy or necrosis is a concern.

Contact Email: