The cause can sometimes be unknown, but very often follows after eating any fatty food (Turkey skin for instance, or even chicken fat etc) Even
a few table scraps CAN cause
Pancreatitis attacks
in susceptible dogs. And very often, when they have had one -unless they stay on a strict diet, they can get another attack in the future.
Has your vet excluded this as a possibility?
The treatment sounds harsh but is the best way to manage an attack.