Dosimetry evaluation of a new 169Yb-LDR COMS plaque for treatment of intraocular tumors

Abstract

Ocular melanoma is the most common and malignant intraocular tumor with an incidence of one percent per thousand per year, which can lead to vision loss or even death. The present study investigated the dose distribution around ocular plaque containing 169Yb seeds to treat ocular melanoma. Dosimetry evaluation and comparison of the resulting isodose curve for 169Yb COMS plaque with 125I COMS plaque were performed using MCNPX code. The results of this comparison showed that with this choice, the time for ocular plaque implantation can be reduced by about 3 times for eye plaque with 20mm in diameter, which can be an important achievement for the treatment of large intraocular tumors. It was shown that for the 169Yb LDR source, a dose of 63 Gy (1.6 Gyh− 1) is equivalent to BED of 103.5 Gy and it is biologically equivalent to an 125I LDR of 85 Gy over 5 d. For critical points such as sclera the dose was minimized about %24 and 32% for tumor of apex 5 mm and 10 mm, respectively. For opposite side, it maximized only about %20 and 7% for tumor of apex 5 mm and 10 mm, respectively. Therefore, it seems that the use of 169Yb COMS plaque is better for the larger tumor apex. The results indicate that the 169Yb-LDR plaque can be suitable for treatment intraocular tumors with small basal dimension and larger in height.