The purpose of publishing a protocol is to create an early scientific recording of your novel idea/research proposal. The results obtained out of that proposed study will be important and novel and must be published. A published protocol makes it easier to publish the eventual results as the novelty and importance of the study have already been established earlier. If your query is whether you can publish results based on a protocol published by another group, then there might be novelty concerns, and publishing such an article might be difficult. If, however, your methodology is different, even though the topic is the same, you may be able to publish such a systematic review. To stay within ethical limits, you should cite the published protocol and clearly mention how your study is different from the published protocol.