I would use canned or boxed vegetable broth. It works well as a substitute.

I agree with Beverly but my vodka sauce just calls for tomatoes, vodka, and cream and we love it.

I also agree with Beverly. My vodka sauce also has no broth.

Vodka Sauce

olive oil

crushed red pepper, to taste
small onion, chopped fine

2 cans (large) tomato puree
garlic, 4-5 cloves to taste
pint heavy cream

salt
pepper

fresh parsley

parmesan cheese
Italian seasonings (basil, oregano, whatever)
3/4 cup vodka

Cover bottom of pan with oil. Add chopped onion, dash salt. Saute add garlic. Saute. Stir in your choice of seasonings, pepper. Add vodka and allow to cook a bit. Add tomatoes. Simmer for about 45 min to an hour. Add heavy cream, whisk in so it doesn't curdle. Heat on low. Toss with pasta, fresh parmesan and chopped parsley.