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 PinnacleÂ³ v9.8 (P3) to mimic the plaque models in Plaque Simulatoráµ€á´¹ v6.4.7 (PS). Point and line source models were built for the IsoAid IAI-125A Â¹Â²â?µI source utilizing AAPM TG-43U1S2 in both BV and PÂ³. 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 5.0â‰¤ r â‰¤15.0mm.
Results: Dose values for BV and PÂ³ were equivalent for both the point-homo and line-homo configurations. The ratio of the PS dose to the BV/P3Â³ 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/PÂ³ point-homo calculations resulted in a range of 0.913 to 0.969; PS-hetero to BV/PÂ³ 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.