Extract string within bracket in Swift using regex

I have a scenario where i want to extract the string within bracket after each selected string

1. PS=AV_2
2. PS=AV_2(AA)
3. PS=AV_2(AA),PS=AV_20(BB,ZZ)
4. PS=AV_2,PS=AV_20
5. PS=AV_2(ZZ),PS=AV_20

eg. input will be PS=AV_2(AA),PS=AV_20(BB,ZZ) and selectedQues = AV_20 or AV_2 In above only constant part is "PS=" all other string can be anything and any format.

The function should return the string in bracket.

func getStringList(input: String, selectedQues: String ) -> [String] {

       // let pattern = "/\\((.*)\\)/"  //1. "/\(([^)]+)\)/"   //2. "/\\(([^)]+)\\)/)"  //3. "([\\w]+(?:,[\\w]+))" some tried regular expression
        let pattern = "/\(selectedQues)\\(([^)]+)\\)/g"
        let nsString = input as NSString
        let regExp = try! NSRegularExpression(pattern: pattern, options: .CaseInsensitive)
        let results = regExp.matchesInString(input, options: [], range:NSMakeRange(0, nsString.length))

        return results.map { nsString.substringWithRange($0.range)}
}

I am unable to resolve a regular expression for the same. I would be really grateful if someone can help or point to some help.