Hi, dear I have gone through your question. I can understand your concern. He has small cell cancer of lung. Treatment of choice is chemotherapy and radiotherapy. If it is localized then surgery can help. You should keep your baby away from your father while treting with radiation. Otherwise no any other problems. And at time of chemotherapy he should avoid contact of many people. Because his immune system is suppressed snd chance of infection to your father is also high. Hope I have answered your question, if you have doubt then I will be happy to answer. Thanks for using health care magic. Wish you a very good health.