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The Impact of Point and Line Source Models On Dose Calculation for I-125 Brachytherapy Using Eye Physics Eye Plaques

D Olek1*, K Homann2 , S Scarboro3 , (1) ,,,(2) Methodist Hospital, Houston, TX, (3) University of Virginia, Charlottesville, VA


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Evaluate the dosimetric differences between three treatment planning systems (TPS) commonly utilized for dose calculations in I-125 eye plaque brachytherapy for both point and line source models.

Methods: Three Eye Physics eye plaque types were selected and the seed positions were transcribed into BrachyVision v13.7 (BV) and Pinnacle³ v9.8 (P3) to mimic the plaque models in Plaque Simulatorᵀᴹ v6.4.7 (PS). Point and line source models were built for the IsoAid IAI-125A ¹²�I source utilizing AAPM TG-43U1S2 in both BV and P³. Calculation conditions included point sources in a homogeneous medium, line sources in a homogeneous medium, and line sources with plaque heterogeneity corrections (PS only). Source activity and implant duration were fixed; all calculations used a dose grid voxel size of 1mm. The central axis dose was evaluated from 5.0≤ r ≤15.0mm.

Results: Dose values for BV and P³ were equivalent for both the point-homo and line-homo configurations. The ratio of the PS dose to the BV/P3³ dose varied from 1.006 to 1.011 for the point-homo calculations and 0.994 to 1.004 for the line-homo calculations. The ratio of the PS-hetero to the BV/P³ point-homo calculations resulted in a range of 0.913 to 0.969; PS-hetero to BV/P³ line-homo calculations ranted from 0.908 to 0.944. Relative differences in dose increase with CAX depth when comparing PS-hetero and line/homo calculations.

Conclusion: The central axis doses reported by three TPS were in agreement with each other for the point-homo and the line-homo calculation methods. The PS-hetero calculations showed better agreement with the point-homo versus the line-homo calculations. The line-homo calculation is expected to produce more accurate results (TG43U1) but is not supported by this data. Evaluating the 85Gy prescription line, the PS calculation is 5% lower than the point-homo calculation and should be considered when utilizing Monte Carlo based system.


Brachytherapy, Dosimetry, Eye Plaques


TH- Brachytherapy: Dose optimization and planning

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