That's the thing. The attack patterns of the first boss are quite easy and run in an obvious pattern, but I found the second time I played it I lost hardly any health as I knew the attack pattern and instead could concentrate on the gaps in the firing patterns to dodge the bullets.

As will all games of this type, without cheating the only way to progress is learning the waves and attack patterns. Those boomerang weapons are quite annoying because your shield doesn't protect you much against them.