Should the X in "X-ray" be capitalized?

Should the word be written as X-ray or x-ray?

Solution 1:

Wikipedia capitalizes the X. Wiktionary says that x-ray is the alternative spelling of X-ray, not the other way round. Merriam-Webster capitalizes the noun but not the verb, noting that the verb is "often capitalized", too.

Looking through the first 250 cites in the Corpus of Contemporary American English, the capitalized version is preferred by a factor of 2:1; looking through the first 250 cites in the British National Corpus, it wins by a factor of 11:1.

Solution 2:

According to the Chicago Manual of Style, 16th edition, x-ray is not capitalized. Not when it's a noun, a verb, or an adjective. This is the standard for fiction writing.

I am both a speech-language pathologist and a fiction writer.