Experimental validation of a new COMS-like 24 mm eye plaque for the treatment of large ocular melanoma tumors

Abstract

PurposeA new Collaborative Ocular Melanoma Study (COMS)-like 24 mm eye plaque was experimentally characterized using physical and dosimetric measurements in preparation for clinical usage. The new eye plaque will enable surgeons and radiation oncologists to accommodate patients who have larger ocular melanoma tumors. Methods and MaterialsPhysical measurement of the Modulay radius of curvature was performed using a FARO Edge, and the base thickness of the Silastic insert was measured with a depth gauge and Vernier caliper. Dosimetric measurements, using Gafchromic film, were used to determine the absolute dose as a function of the depth along the plaque's central axis, profiles as a function of polar angle, and basal coverage at the inner sclera. The measured results were compared with a theoretical model, which incorporated the plaque's heterogeneities using a modified TG-43 formalism. ResultsThe Modulay radius of curvature measured 14.7 mm (specification = 14.55 mm). The Silastic base thickness measured 0.9 mm (specification = 1.0 mm). For a 24 mm plaque fully loaded with 1.27 U 125I model 2301 seeds, the dose rate at a prescription depth of 5 mm from the inner sclera was measured to be 36 cGy U−1 hr−1. The basal coverage for the same prescription depth was 17.9 mm. The experimental measurements were in close agreement with the theoretical predictions. ConclusionsThe new 24 mm COMS-like plaque was experimentally validated for clinical use. Physical and dosimetric measurements for the 24 mm plaque agreed with nominal specifications and theoretical predictions. The 24 mm plaque provides greater basal coverage and lower surface doses than existing COMS plaques.