Be careful using this cheat code because it lasts only some minutes, and then you are vulnerable again. If you are in the middle of a storm of bullets make sure to control the timers.
Nobody can kill you now! Cheat yourself with this code:
RIGHT, X, RIGHT, LEFT, RIGHT, R1, RIGHT, LEFT, X, TRIANGLE
RIGHT, A, RIGHT, LEFT, RIGHT, RB, RIGHT, LEFT, A, Y