However, brainstorming works on stand alone situation. It's really a thinking process of coming up with as many ideas as possible and then slowly filters away the worst one and further refine the good ones.
However, let's be realistic, group brainstorming will continue to exist. You will run into it every year. Just make sure you understand that it may not be a as "effective" in large group than in small group. Prepare yourself for the real nature of the meeting to get the best use of the meeting instead of naively thinking that it's a pure brainstorming meeting. Basically you need to really assess your company's culture to determine if the terms "brainstorming" is really means what it is.