We report a woman with malignant meningioma diagnosed 9 years after the 
treatment of a choroidal melanoma with proton beam therapy. The risk of 
secondary cancers is a well-known adverse late effect of radiation therapy, 
especially with the use of advanced techniques such as intensity-modulated 
radiation therapy. However, this risk may be less with the use of proton beam 
therapy. A 79-year-old woman presented with symptoms of enophthalmos, ptosis and 
paralysis of the left medial rectus muscle. She had previously been successfully 
treated for a choroidal melanoma of the left eye with proton beam therapy (total 
dose: 60 cobalt gray equivalents) following local resection. MRI showed a lesion 
in the left cavernous sinus with extension into the orbit and a subsequent 
biopsy revealed a papillary meningioma. The cavernous tumor was treated with 
photon radiotherapy (total dose: 54Gy) which achieved an initial partial 
response. However, 8 months later the tumor extensively metastasized to the 
skull and the spine and the patient died 1 year after the treatment. The 
incidence of secondary malignancies after proton beam therapy is low but not 
negligible, therefore, it must be taken into account when planning a treatment 
as secondary tumors may present with a highly aggressive behaviour.