A reanalysis of the Collaborative Ocular Melanoma Study Medium Tumor Trial eye plaque dosimetry.

PURPOSE To recalculate the radiation doses delivered to structures of interest within the eye, i.e., the lens, tumor apex, 5-mm point, optic disk, and macula for patients treated with eye plaque radiotherapy on the Collaborative Ocular Melanoma Study (COMS) Medium Tumor Trial, using updated dosimetric data. METHODS AND MATERIALS Using the Plaque Simulator planning system, doses were recalculated for a sampling of COMS patients for each plaque size. Dosimetry parameters incorporated into the recalculation were line source approximation, a 90% Silastic transmission factor, and a 0% gold transmission factor. Generic solutions were generated from the dose recalculations for each plaque size and structures of interest combination. Doses for the remainder of the patient population were recalculated using the generic solutions and compared with the originally reported COMS doses. RESULTS Doses to all structures of interest were reduced 7%-21%, depending on the plaque size and structure combination. The reduction in dose for the macula, optic disc, lens, tumor apex, and 5-mm point was on average 10%, 18%, 8%, 11%, and 12%, respectively. The closer the macula and optic disk were to the plaque rim, the greater the dose reduction. Incorporation of the Silastic transmission factor accounted for a large part of the dose reduction. CONCLUSIONS Incorporating anisotropy, line source approximation, and Silastic and gold shield attenuation into dose recalculations resulted in a significant and consistent reduction of doses to structures of interest within the eyes.