Response Evaluation of Choroidal Melanoma After Brachytherapy Using Diffusion-Weighted Magnetic Resonance Imaging (DW-MRI): Preliminary Findings

Abstract

Purpose: To evaluate the role of diffusion-weighted magnetic resonance imaging (DW-MRI) in the assessment of therapeutic response in patients with choroidal melanoma treated with brachytherapy. Materials and Methods: We performed a prospective, unicentric study which included patients with choroidal melanoma and indication for brachytherapy. Three DW-MRI examinations were proposed for each patient, one before and two after treatment. The apparent diffusion coefficient (ADC) value was calculated on DW-MRI and compared with local tumor control assessed by ophthalmologic follow-up. Results: From 07/2018 to 06/2019, 19 patients were recruited, 13 of whom underwent follow-up examinations. Patients' ages ranged from 24 to 78 years and 52.9% were male. At the ocular ultrasound, the mean tumor thickness and diameter were 6.3 and 11.5 mm, respectively. Two patients (15.4%) showed signs of tumor progression during follow-up (7 and 9 months after treatment). There was no statistically significant difference in tumor size between MR before and after treatment, however, there was a significant reduction in mean ADC in patients with progression (p = 0.02). Conclusion: DW-MRI is a promising method for monitoring patients with choroidal melanoma; reduction in the mean ADC values between pre-treatment MRI and the first post-treatment MRI may be related to the lack of response to brachytherapy and increased risk of disease progression.

Keywords: brachytherapy; diffusion magnetic resonance imaging; eye neoplasms; melanoma; response evaluation criteria in solid tumors.

Figure 1

Flowchart of selection and inclusion criteria for patients in the study.

Figure 2

Example of region of interest (ROI) placement covering the whole tumor on ADC maps.

Figure 3

A 66-year-old patient with choroidal melanoma in the left eye (upper temporal quadrant, measuring 15 × 14 × 9 mm), was treated with brachytherapy. (A–C) MR1 showing tumor with high signal at T1-weighted images, low signal at T2-weighted images, and restricted diffusion on the ADC map (mean ADC: 0.90 × 10⁻³ mm²/s). (D–F) MR2 showing that the tumor had similar morphological characteristics and dimensions, but with a slight increase in ADC values compared to the initial examination (mean ADC: 0.97 × 10-3 mm2/s). (G–I) MR3 showing a slight reduction in tumor dimensions, with further increase in ADC values (mean ADC: 1.20 × 10⁻³ mm²/s).

Figure 4

A 59-year-old patient with choroidal melanoma in the left eye (upper temporal quadrant, measuring 9 × 4 mm), was submitted to brachytherapy. Pretreatment MR images: (A) axial T2-weighted sequence and (B) axial ADC map, with mean ADC of 1.241 × 10⁻³ mm²/s. MR images collected 3 months after treatment in the same sequences demonstrate stability of lesion size (C) and decreased ADC values (D) (mean ADC: 1.007 × 10⁻³mm²/s). MR images 6 months after treatment show stability of the lesion size (E) and ADC values (F). MR images collected 9 months after treatment show an increase in lesion dimensions (G) (13 × 9 mm) and decreased ADC values (H) (mean ADC: 0.794 × 10⁻³mm²/s).