Player Drawn Colliders

I'm working on a game in which the player is able to draw a line on a 2d map and have a spell cast along the line. Currently, when a user draws a line, what I'm doing is saving a point on the drawn line to a list every 0.1 seconds and, once the spell is cast, comparing every enemy to every point on the line to check if they're close enough. Obviously, not particularly efficient. I'm wondering if there's a way to take the player drawn line and create a collider around the line in basically a tube shape. This way, the colliders could handle the checking of enemies getting hit by spells, rather than checking a complicated list for every enemy.