"Trapped inside this Octavarium"
I suppose there's a link with Gates of tomorrow from Iron Maiden: we can see four occurrences of the word "trapped" in the chorus of this song just as well as here.
Besides, if you observe the other terms of the chorus, you notice the phrase "Trapped in the web" that could have influenced the song "Caught in a web" from Dream Theater, but as well as my first idea, it's just a conjecture. In the event I find any clue, I'll come back to justify my waffle ^^ (but in the end I'll just defy it ;) (cf As I am, Dream Theater).
https://www.youtube.com/watch?v=GInN6I4gWSc
https://www.youtube.com/watch?v=CgSiTNJKUr0.