Regression of uveal melanoma after RU-106 brachytherapy and thermotherapy based on metabolic activity measured by positron emission tomography/computed tomography

Purpose: To evaluate regression rates of uveal melanoma after combined Ru-106 plaque radiotherapy and thermotherapy according to metabolic activity measured by positron emission tomography/computed tomography imaging. Methods: A retrospective medical chart review was conducted on 26 patients with uveal melanoma who underwent pretreatment whole-body positron emission tomography/computed tomography and received combined plaque radiotherapy and thermotherapy between 2006 and 2011. Tumors were classified as metabolically active and inactive based on the positron emission tomography/computed tomography imaging and compared with tumor height regression rates after treatment. Results: Before treatment, the median tumor thickness was 8.8 mm for metabolically active tumors (7 eyes) and 5.0 mm for metabolically inactive tumors (19 eyes). The median tumor thicknesses with respect to the original thickness at 3, 6, and 12 months after treatment were 88%, 78%, and 64% for metabolically active tumors and 95%, 89%, and 81% for metabolically inactive tumors, respectively. The monthly tumor regression rates during the first 3 months (4.2% vs. 1.7%, P = 0.022) and the overall monthly tumor regression rates (3.0% vs. 1.5%, P = 0.041) were significantly higher for metabolically active tumors versus inactive tumors. Two patients with positive metabolic activity developed metastatic diseases 2 years after treatment, whereas no patient with negative metabolic activity developed metastatic disease during the study period. Conclusion: Positive metabolic activity of uveal melanoma based on the positron emission tomography/computed tomography was significantly associated with rapid initial tumor regression after combined plaque radiotherapy and thermotherapy, suggesting a prognostic value for this diagnostic approach.