Room: Exhibit Hall
Purpose: The purpose of this study is to compare optic disc dose reduction between 125I and 103Pd notched Collaborative Ocular Melanoma Study (COMS) plaques.
Methods: Optic disc dose was calculated as a function of optic disc-to-tumor margin distance (DT) for various basal dimensions (BD) for five (14mm - 22mm in diameter in 2mm increments) standard COMS plaques loaded with 125I (model IAI-125A) and 103Pd (model IAPd-103A) seeds in a validated in-house brachytherapy dose calculation program utilizing the AAPM TG-43U1 formalism with a line source approximation. A dose of 85Gy was prescribed at a central-axis depth of 5 mm. Calculations were repeated for five corresponding notched COMS plaques with one seed removed (case 1) and two seeds removed (case 2). Then for each case, optic disc dose reduction was computed by subtracting optic disc dose for notched plaques from that for standard plaques and compared between 125I and 103Pd COMS notched plaques.
Results: Optic disc dose reduction for both seeds showed similar Gaussian-like distributions except for the largest 2-3 BDs for each plaque but the maximum dose reduction was larger for 103Pd seeds than for 125I seeds. For case 1, differences in maximum dose reduction between the two seeds were 3.4Gy, 4.1Gy, 3.0Gy, 3.2Gy and 4.1Gy for 14mm, 16mm, 18mm, 20mm and 22mm, respectively. For case 2, corresponding differences were 7.7Gy, 8.7Gy, 6.3Gy, 6.2Gy, 6.9Gy. In both cases, the maximum dose reduction for both seeds occurred at the same DT.
Conclusion: The patterns of optic disc dose reduction for 125I and 103Pd notched plaques were similar but the dose reduction was larger for 103Pd plaques. The data provided in this study will allow clinicians to compare optic disc dose reduction between 125I and 103Pd notched COMS plaques and to choose adequate radionuclide seeds between the two for each own clinical case.
Not Applicable / None Entered.