Predictive value of 3′-deoxy-3′-[18F]fluorothymidine positron emission tomography/computed tomography for outcome of carbon ion radiotherapy in patients with head and neck mucosal malignant melanoma

The purpose of this prospective study was to assess the prognostic value of 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) positron emission tomography/computed tomography (PET/CT) for the outcome of carbon ion radiotherapy (CIRT) in patients with mucosal malignant melanoma (MMM) of the head and neck.Thirteen patients (69 ± 13 years) with histologically proven MMM tumor were enrolled. CIRT was performed with a total dose of 57.6-64.0 gray equivalents per 16 fractions over a period of 4 weeks. FLT-PET/CT was performed before and again 1 month after CIRT. Tumor FLT uptake was quantitatively assessed using the maximum standardized uptake value (SUV(max)). FLT-PET parameters [pre-CIRT SUV(max), post-CIRT SUV(max), and the reduction rate (RR)] and clinical parameters [age, gender, tumor site, tumor status, gross tumor volume (GTV), and regional lymph node involvement] were evaluated in relation to survival estimates. The follow-up period was 16.1 ± 5.9 months for 9 deceased patients, and 36.7 ± 7.9 months for 4 survivors.Pre-CIRT SUV(max) of ≥4.3, age of ≥80 years old, sinonasal cavity tumor site, and GTV of ≥39 mL were found to be statistically significant prognostic factors for better overall survival. Pre-CIRT SUV(max) of ≥5.0, age of ≥80 years old, sinonasal cavity tumor site, and the absence of regional lymph node involvement were statistically significant prognostic factors for better metastasis-free survival. RR of ≥35 % and GTV of73 mL were predictive of better local control.The present study indicated for the first time that in patients with the head and neck MMM, FLT-PET/CT imaging was useful for predicting the therapeutic outcome of CIRT. Our results will contribute to the establishment of an effective staging system for MMM based on prognostic factors, depending on treatment choice.