SU-E-T-517: Characterization of Relative Doses and Source Strengths for Various Plaque Sizes and Tumor Dimensions in the Treatment of Uveal Melanoma.

Abstract

To characterize the relative doses and source strengths for various eye plaque sizes and tumor dimensions in the treatment of uveal melanoma. Several tumors with basal diameters ranging from 6-16mm and apical height of 5-10mm were planned using the Pinnacle3 treatment planning system following the American Brachytherapy Society's recommendations. The data is based on 5-day implant to deliver 85Gy with a dose rate of 70.9cGy/hr. Choice of plaque size is based on a 2-3 mm margin on either side of the tumor. Doses to the fixed locations: sclera, center of the eye and opposite sclera were obtained. From our results we see larger source strengths needed for smaller plaques due to smaller number of sources used. The exception is with 14mm and 16mm plaques containing the same number of sources where the 16mm plaque has slightly higher source strengths. For both the inner and outer sclera, the relative dose increases with increasing height. For a 12mm plaque, the relative dose of the outer sclera increases from 4-10 times that of the Rx dose at the apex of the tumor. For a 20mm eye plaque, the relative dose of the outer sclera increases from 2-5 times that of the prescription dose at the apex of the tumor. As apical height increases, the relative dose at the center of the eye increases to about 75% of the Rx dose at 10cm depth for all plaque sizes. At the inner sclera surface opposite the center of the tumor base the relative dose is 20-22% of the Rx dose for all plaque sizes. The data provided will be a helpful tool in evaluating and predicting complications in the retina and sclera based on the tumor dimensions and selected plaque size.