Malignant mucosal melanoma treated with carbon ion radiotherapy with concurrent chemotherapy: Prognostic value of pretreatment apparent diffusion coefficient (ADC)

Background and purpose: To evaluate the potential of apparent diffusion coefficient (ADC) value before carbon ion radiotherapy (C-ion RT) for malignant mucosal melanoma (MMM) to predict prognosis. Materials and methods: We recruited 37 patients with MMM in the head and neck treated by C-ion RT with concomitant chemotherapy. Univariate and multivariate analyses of minimum ADC, mean ADC, tumor volume, age, PS, and gender were performed to identify prognostic factors. Results: The 3-year local control rate, distant metastasis-free survival rate and overall survival rate of all patients were 81.1%, 37.6% and 65.3%, respectively, with a median follow-up period of 19.0 months. In univariate analyses, lower minimum ADC (≤0.6380 × 10 ^-3 mm ²/s) and lower mean ADC (≤1.1523 × 10 ^-3 mm ²/s) were unfavorable prognostic factors for distant metastasis (p = 0.029 and p = 0.014, respectively), and lower minimum ADC was an unfavorable prognostic factor for overall survival (p = 0.019). However, there was no significant prognostic factor of local control including ADC value. In multivariate analyses, only minimum ADC was selected as a prognostic factor of distant metastasis-free survival and overall survival (p = 0.015 and p = 0.006, respectively). Conclusion: Minimum ADC can be a prognostic factor of MMM in the head and neck after C-ion RT.