Room: Exhibit Hall
Purpose: The purpose of this study is to investigate optic disc dose reduction in ocular brachytherapy using notched Collaborative Ocular Melanoma Study (COMS) plaques loaded with 125I seeds to allow clinicians to estimate optic disc dose reduction before treatment planning.
Methods: Using a validated in-house brachytherapy dose calculation program utilizing the American Association of Physicists in Medicine Task Group-43U1 formalism with a line source approximation, optic disc dose was calculated as a function of optic disc-to-tumor margin distance (DT) for various basal dimensions (BD) for six (12 mm - 22 mm in diameter in 2 mm increments) standard and notched (with one seed removed) COMS plaques loaded with 125I (model IAI-125A) seeds. A prescribed dose of 85Gy was normalized at a central-axis depth of 5 mm. Then optic disc dose reduction was computed by subtracting optic disc dose for notched plaques from that for standard plaques.
Results: First, does reduction increases with DT, reaches the maximum and then decreases with DT. For the largest 2-3 BDs for each plaque, however, dose reduction decreases with DT. Second, the maximum dose reduction (105.1Gy, 67.4Gy, 70.1Gy, 45.8Gy, 41.8Gy, 49.0Gy for 12 mm, 14 mm, 16 mm, 18 mm, 20 mm and 22 mm plaques, respectively) does not vary with BD except for that for the largest 2-3 BDs. Third, DT at which the maximum dose reduction occurs (DTmax) decreases by almost 1 mm with increasing BD by 2 mm. For the largest 2-3 BDs, on the other hand, the maximum dose reduction usually occurs at 0 mm of DT or close to 0 mm. Lastly, DTmax increases with plaque size for the same BD.
Conclusion: The data provided in this study will be beneficial in clinical practice to estimate optic disc dose reduction by notched COMS plaques before treatment planning.
Not Applicable / None Entered.