Quantitative echography in primary uveal melanoma treated by proton beam therapy

Abstract

Objective: To describe the dynamics of thickness and internal reflectivity after proton beam therapy (PBT) in uveal melanoma.

Participants: One hundred and ninety-eight consecutive patients with choroidal or ciliary body melanoma treated by PBT were retrospectively considered.

Methods: The post-PBT follow-up included ophthalmologic examination, retinography, and B and A modes of standardized echography every 6 months. A total of 1393 examinations were performed. We take into account 4 tumour categories according to the seventh TNM classification.

Results: Before PBT, tumour thickness ranged from 1.5 to 12.5 mm with a mean of 5.9 mm. Its decrease after radiotherapy was best fitted by the sum of a first-order exponential decay and a constant with a decay half-life of 15 months. Based on the fit, tumour thickness stabilized on a constant value representing, on average, 47% of the initial value. Mean internal reflectivity before PBT was 68%. The dynamics of the reflectivity were best fitted by an exponential and a constant, with rise half-life of 11 months, and stability value of 87%.

Conclusions: We found that ultrasonographic dynamics of uveal melanoma treated by PBT resembles a function composed of the sum of a constant and a first-order exponential, as previously noted in studies on brachytherapy. Interestingly, after PBT, because of its shorter half-life, internal reflectivity has a faster dynamic response than thickness in large tumours, suggesting that increase of internal reflectivity is a more sensitive indicator of early response to therapy in larger tumours.