Comparison of usefulness of C-11 methionine PET for predicting prognosis of patients with adenocarcinoma, adenoid cystic carcinoma and malignant melanoma in head and neck region treated by carbon ion radiotherapy

Abstract

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Objectives: The carbon ion radiotherapy (CIRT) has been introduced in our institute, and we have treated head and neck cancer using carbon ion beam. We compared the difference of MET uptake level before and after CIRT among head and neck cancers. We evaluated whether C-11 methionine (MET) uptake and its change after CIRT were the early survival factors in patients with adenocarcinoma (AC), adenoid cystic carcinoma (ACC) and malignant melanoma (MM) in head and neck region. Methods: MET-PET was performed in 87 patients with AC, ACC and MM in head and neck region before and after CIRT. There were 21 AC, 39 ACC and 27 MM. The average patient age was 59.0 years (range 15 to 84). Patients were followed for 4 to 88.6 months (mean: 38.1 months) after CIRT. Tumor MET uptake was measured with the semi-quantitative tumor to normal tissue ratio (TNR). The tumor TNR and result of prognosis were entered into Kaplan-Meire analysis on histology to histology basis. Results: TNR of MM before CIRT tended to be higher than that of AC and ACC. Mean tumor TNR before CIRT of AC, ACC and MM were 5.2, 7.0 and 9.1, respectively. There were significant difference in mean tumor TNR before CIRT between MM and AC, and also between MM and ACC. But, there was no statistically significant difference between AC and ACC in tumor TNR. Mean residual ratios of tumor TNR after CIRT of AC, ACC and MM were 82%, 60% and 51%, respectively. There were significant difference in mean residual ratios of tumor TNR between MM and others. Patients with high TNR before CIRT had a significant better survival than patients with low TNR in AC and ACC (p<0.0001). Conclusions: MM showed higher TNR before CIRT and higher residual ratios after CIRT in MET-PET than AC and ACC in head and neck region. MET uptake was a successful predictor of survival in patients with head and neck cancer treated by CIRT.