Evaluation of a Vision Prognostication Model for Choroidal Melanoma after Plaque Brachytherapy

Abstract

Purpose: To retrospectively evaluate and apply a vision prognostication model for patients with choroidal melanoma treated with Iodine-125 university of southern california (USC) eye physics plaque brachytherapy.

Methods: A visual nomogram was generated to predict a percentage of likely visual loss to the level of 20/200 or worse after plaque brachytherapy for choroidal melanoma by Khan et al. Gender, tumor height, and dose to macula were found to be the most significant predictors for vision loss after therapy in their nomogram.To evaluate the effectiveness of this nomogram for our patient population, we included 64 patients with primary choroidal melanomas treated with Iodine -125 eye physics plaques at USC from January 1, 1990 through December 30, 2010. Final endpoint was comparing actual vs. predicted visual acuity (VA) per the nomogram worse than or equal 20/200 at 1 year post brachytherapy. All patients with initial pre-treatment VA less than 20/200 were excluded.

Results: Of 64 patients with pre-treatment VA better than 20/200, 44 % (28) had post- treatment VA equal or worse than 20/200 and 56% (36) had post- treatment VA better than 20/200. Concordance index of 0.60 and 0.56 was calculated between actual and predicted loss of vision worse than or equal to 20/200 at 1 year at the level of 50% and 75% respectively according to the nomogram described by Khan et al. Concordance was not significantly different between the two levels. Both a threshold of 50% and 75% predicted visual loss correctly in our patients approximately 60% of the time. Lack of vision loss to the level of 20/200 or worse was predicted correctly 87% of time at the 50% threshold and 94% of time at the 75% threshold. Loss of vision to the level of 20/200 or worse was predicted correctly 12% and 5% of time at the threshold of 50% and 75% respectively.

Conclusions: The described visual prognostication model by Khan et. al. is a practical, easy to use, first step for clinicians and patients to predict vision loss after brachytherapy for choroidal melanomas. In our application of this nomogram, the prediction of vision loss to the level of 20/200 or worse was correct 60% of the time at both a predicted threshold of 50% and 75%. In our series, the nomogram predicted <lack> of vision loss more accurately than vision loss. Further research to refine the nomogram may be helpful to develop a valuable model for patients and clinicians.

Keywords: 589 melanoma • 452 choroid • 671 radiation therapy