An Interactive Treatment Planning System For Ophthalmic Plaque Radiotherapy

Melvin A. Astrahan, PH.D.,¹ Gary Luxton, PH.D.,¹ Gabor Jozsef, PH.D.,¹ Thomas D. Kampp, PH.D.,¹ Peter E. Liggett, M.D.,² Michael D. Sapozink M.D., PH.D.¹ AND Zbigniew Petrovich, M.D.¹
Int. J. Radiation Oncology, Biol, Phys., Vol. 18, pp. 679-687 Copyright 1990 Pergamon Press

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

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


Brachytherapy using removable episcleral plaques containing sealed radioisotope sources is being studied as an alternative to enucleation in the treatment of choroidal melanoma and other tumors of the eye. Encouraging early results have been reported, but late complications which lead to loss of vision continue to be a problem. A randomized national study, the Collaborative Ocular Melanoma Study (COMS) is currently in progress to evaluate the procedure. The COMS specified isotope is I-125. Precise dosimetric calculations near the plaque may correlate strongly with complications and could also be used to optimize isotope loading patterns in the plaques. A microcomputer based treatment planning system has been developed for ophthalmic plaque brachytherapy. The program incorporates an interactive, 3-dimensional, solid-surface, color-graphic interface. The program currently supports I-125 and Ir-192 seeds which are treated as anisotropic line sources. Collimation effects related to plaque structure are accounted for, permitting detailed study of shielding effectiveness near the lip of a plaque. A dose distribution matrix may be calculated in any subregion of a transverse, saggital, or coronal planar cross section of the eye, in any plane transecting the plaque and crossing the eye diametrically, or on a spherical surface within or surrounding the eye. Spherical surfaces may be displayed as 3-dimensional perspective projections or as funduscopic diagrams. Isodose contours are interpolated from the dose matrix. A pointer is also available to explicitly calculate and display dose at any location on the dosimetry surface. An interactive editing capability allows new plaque designs to be rapidly added to the system.

Key words: I-125, Plaque, Choroidal melanoma, Radiation dosimetry.
Accepted for publication 19 July 1989.

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

Plaque Simulator References | Guide Contents