Histological study of choroidal malignant melanoma treated by carbon ion radiotherapy.

PURPOSE

To report, we believe for the first time, a histological study of choroidal malignant melanoma treated by carbon ion beam radiotherapy.

METHODS

A 75-year-old Japanese man was diagnosed as having a choroidal melanoma after undergoing magnetic resonance imaging (MRI). Positron emission tomography (PET) revealed a hot spot in the same location as the intraocular mass seen in MRI. Carbon ion radiotherapy was performed with a total dose of 77 Gy, and the hot spot seen by PET disappeared completely. At 15 months after carbon ion therapy, the eye had to be enucleated because of uncontrollable ocular hypertension. It was examined histologically in serial sections.

RESULTS

A large tumor mass (15 x 12 mm) with high pigmentation was found in the vitreous space. Almost all tumor cells showed necrosis in every section. A small number of intact tumor cells were present at the periphery. The overlying retina did not show any necrosis, but showed mild to moderate gliosis. No intraretinal hemorrhage, lipid deposit, or protein exudate was apparent.

CONCLUSIONS

Almost all tumor cells showed necrosis after radiotherapy with a carbon ion beam. However, the effect on the adjacent tissues was determined as minimal in histological analysis.