WE-D-BRB-06: Treating Ocular Melanoma with Eye Plaque Brachytherapy: COMS Or NAG Eye Plaque?

Abstract

Purpose: To compare dosimetry characteristics of Nag‐eye plaque with COMS eye plaque using I‐125 and Cs‐131 brachytherapy sources. Material and methods: Monte Carlo technique was used to generate 3D dose distributions of a 16‐mm Nag eye plaque and 16‐mm COMS eye plaque loaded with the I‐125 and Cs‐131 brachytherapy sources separately. The Nag eye plaque is a comparatively simpler eye plaque that uses fewer seeds than the COMS and does not require a Silastic seed carrier. The simulations were carried out with gold alloy plaques. A water equivalent seed carrier was used instead of the Silastic trough designed for the traditional COMS eye plaque. The Nag eye plaque used only eight sources forming two squares; the COMS eye plaque was loaded with thirteen sources forming three isocentric circles. A spherical eyeball 24.6 mm in diameter and an ellipsoid tumor 6 mm in height and 12‐mm in diameter were used to evaluate the doses delivered. Results: The doses along the eye plaque axis and the DVHs of the tumor were calculated. Our results indicated that, to achieve a prescription dose of 85 Gy at 6 mm from the inner sclera edge, the Nag eye plaque required 6.156 U/source for I‐125 and 6.82 U/source for Cs‐131; the COMS eye plaque required 4.015 U/source and 4.433 U/source for the same source types. The doses from two types of eye plaques on the central axis were almost the same at distances greater than 5 mm; the OSU‐Nag plaque gave slightly lager doses than the COMS at distances less than 5 mm. The DVHs of the tumor showed that the NAG plaque tended to create slightly more hot dose regions than the COMS. Conclusion: The dosimetric characteristic of Nag‐eye plaque is comparable to COMS in using either I‐125 or Cs‐131 source.