Radiation treatment to a postresection primary mucoepidermoid carcinoma (MEC) of the conjunctiva with positive margins at the Tenon's fascia—A case study

Abstract The primary occurrence of mucoepidermoid carcinoma (MEC) of the conjunctiva is extremely rare, aggressive, and easily mistaken for squamous cell carcinoma. With fewer than 50 cases reported in the literature, there is no consensus on the most effective treatment. Radiation is an alternative to enucleation or orbital exenteration with the potential of eye preservation. We investigated several radiation approaches for a case with postresection positive margins at Tenon's fascia, and reported the patient's clinical course during the treatment and for a short time thereafter. An otherwise healthy 64-year-old male presented with MEC extending to the deep margin at the Tenon's fascia. Plans for 4 different radiation therapy treatment modalities (Intensity Modulated Radiation Therapy [IMRT], Volumetric Modulated Radiation Therapy [VMAT], double scattering (DS) proton, and reverse eye plaque low dose rate [LDR] ) were created and compared based on tumor coverage and normal tissue doses. The planning target volume (PTV) was too large and nonuniform for an eye plaque application. Using the largest plaque available (22 mm), the calculated minimum dose to the PTV was 57% while the dose to the skin was 1000% of the prescription. The proton plan completely spared the contralateral ocular structures and reduced the max doses to the ipsilateral macula and optic nerve, but was not clinically available at the time of treatment. The IMRT and VMAT plans produced similar dose distributions to each other, but VMAT further minimized dose to the ipsilateral eye. Due to the uniqueness of this case, a thorough study of the available radiation treatment options was deemed necessary. All of the external beam treatment techniques produced acceptable plans with VMAT producing the best available plan in this case. The patient was treated with the VMAT plan with a prescription of 6600 cGy in 30 fractions. At 5 months post-treatment, the patient is recovering from expected acute responses to radiation with follow ups scheduled.