Eye holes in a radiation mask?

Hi

I've been to have my mask fitted today and I'm very claustrophobic. I thought because the mask has holes I would be ok. However, no one said that I wouldn't be able to have my eyes open and I really struggled with that. In fact I didn't manage to get through the CT scan.

I asked if I could have eye holes cut out and they said no. Said that the accuracy wouldn't be a good. However I've been researching this and I can't see anything that says this is the case as long as the whole mask is tight. 

I'm having the right side of my face and neck treated.

Having my eyes open well make a big difference to my being able to get through the treatment.

Is this reasonable to ask for?

Thank you