Optimization of I-125 ophthalmic plaque brachytherapy

Melvin A. Astrahan,¹ Gary Luxton,¹ Gabor Jozsef,¹ Peter E. Liggett, M.D.,² and Zbigniew Petrovich, M.D.¹
Medical Physics, 17(6), pp. 1053-1057 Copyright 1990 Am.Assoc.Phys.Med.

1. Department of Radiation Oncology.
2. Department of Ophthalmology.

University of Southern California School of Medicine, Los Angeles, California, 90033, USA


Episcleral plaques containing I-125 sources are often used in the treatment of ocular melanoma. Within four years post-treatment, however, the majority of patients experience some visual loss due to radiation retinopathy. The high incidence of late complications suggests that careful treatment optimization may lead to improved outcome. The goal of optimization would be to reduce the magnitude of vision-limiting complications without compromising tumor control. We have developed a three-dimensional computer model for ophthalmic plaque therapy which permits us to explore the potential of various optimization strategies. One simple strategy which shows promise is to maximize the ratio of dose to the tumor apex (T) compared to dose to the macula (M). By modifying the parameters of source location, activity distribution, source orientation, and shielding we find that the calculated T:M ratio can be varied by a factor of 2 for a common plaque design and posterior tumor location. Margins and dose to the tumor volume remain essentially unchanged.

Key words: ophthalmic plaque, dosimetry, I-125, choroidal melanoma
(Received 26 July 1990; accepted for publication 13 August 1990)

Article: Part 1 (Introduction & Methods) | Part 2 (Results) | Part 3 (Discussion & References)

Plaque Simulator References | Guide Contents