Tumor regression after brachytherapy for choroidal melanoma: Reduction of thickness and cross-sectional area by shape and regression pattern

Abstract

Purpose. To model regression rate of thickness and cross-sectional area of choroidal melanomas after ruthenium and iodine brachytherapy by shape and regression pattern (RP). Methods. We enrolled 330 of 388 consecutive uveal melanomas from 2000 to 2008 and analyzed images from I 3 System-ABD 10-MHz B-Scan at diagnosis and during a 3-year-long follow-up. We classified tumor shape by Collaborative Ocular Melanoma Study definitions and RP according to an earlier study. We plotted regression over time and compared thickness and cross-sectional area. Results. The observed RP by thickness was classified as decrease (D) in 43%, stable (S) in 5%, increase (I) in 1%, and other in 40% of eyes; main subpatterns were decrease-stable (DS) in 16% and zigzag in 10% of eyes. The corresponding percentages by area were 42%, 3%, 1%, 45%, 16%, and 14%. Regression pattern was discordant in 34% of eyes for thickness versus area. Area reduced faster than thickness when shape was oval to dome or mushroom and ifRP was D. Pooled patterns D, DS, decrease-increase (DI), and zigzag corresponded with progressive but increasingly less pronounced regression for 3 years (56% by thickness and 69% by area), 2 years (50% and 52%), 6 months (29% and 33%), and 6 months (19% and 23%), respectively. First-order exponential decay function fitted thickness and area regression for every shape and for patterns D, DS, DI, and zigzag. Conclusions. Heterogeneity in RP, variation in shape, and tumor cross-sectional area as an alternative measure must be considered when tumor regression rate is used in outcome analysis.