PURPOSE:Choroidal melanomas shrink slowly after radiotherapy but do not disappear completely in general. Moreover, histological evaluation after therapy cannot be made except for the case of enucleation. Therefore, another rvaluation method in addition to the measurement of tumor size is desirable. The purpose of this study is to assess the ability of Carbon-11-methionine PET (MET PET) to detect choroidal melanoma lesion and the feasibility of MET PET as an evaluation method of therapeutic effect in proton beam radiotherapy.METHOD AND MATERIALS:We studied consecutive six patients with choroidal malignant melanoma treated with proton beam therapy in 2001-2002. The mean follow up time was 22.2 months (ranged from 12 to 32 months). All patients underwent at least three MET PET scans, before therapy, one month after therapy and about six after therapy. And some patients underwent further follow up MET PET scans. Three patients underwent fourth MET PET about 12 months after therapy, and three patients underwent fifth (two patients, forth) MET PET about 24 months after therapy. MRI was performed one week within each MET PET scan. We evaluated the lesion semiquantitatively on the basis of the Tumor-To-Brain Ratio (TBR).RESULTS:No patients in this study showed tumor regrowth or local recurrence to date. Alll choroidal lesions were positive on MET PET before therapy. Mean TBR before therapy was 1.29±0.31(n=6), and did not changed at one month after therapy (p=0.987). But,mean TBR decreased to 0.77±0.23 (n=6) 6 months after therapy (p=0.003) and additionally decreased to 0.39±0.24 (n=3) 12 months after therapy (p=0.033). Mean TBR 24 months after therapy was not almost changed (0.41±0.18) compared with that 12 months after therapy. In respect of visual evaluation, all MET uptake disappeared 12 and 24 months after therapy. On the other hand, mean tumor size showed only 27.5% decrease even 24 months after therapy.CONCLUSION:Carbon-11-methionine is considered to be a useful tracer to detect choroidal melanoma. MET PET after proton beam radiotherapy may be a valuable method to evaluate the effect of proton beam radiotherapy.RSNA2004 90th Scientific Assembly and Annual Meetin
