Additional Study Information: The purpose of this study is to evaluate whether radiation treatment directed at liver metastases can be safely added to standard of care treatment for extensive-stage small cell lung cancer (ES-SCLC). The current standard treatment for people who have ES-SCLC is chemotherapy, called carboplatin and etoposide, that is combined with a type of immunotherapy called atezolizumab. However, patients with liver involvement of their ES-SCLC don't respond as well to this treatment. The study aims to answer whether adding radiation directed at liver metastases can improve responses to standard chemoimmunotherapy in this patient population. All study participants will get the same study intervention, which will be chemoimmunotherapy and radiation therapy.