Personalized Radiotherapy for Individualized Treatment Strategies and Monitoring (PRISM)

This study (PRISM) is developing personalized radiotherapy approaches using biological monitoring. It has two groups: one for people with extensive-stage small cell lung cancer receiving standard chemotherapy plus immunotherapy, and another for people with solid tumors that have spread to the brain (1 to 5 brain metastases). **You may be eligible if...** - (Lung group) You are 18 or older with extensive-stage small cell lung cancer, currently receiving or planned for standard chemo-immunotherapy, and your doctor agrees you could benefit from radiation to the chest - (Brain group) You are 18 or older with a solid tumor cancer that has 1 to 5 brain metastases, each measuring 2 to 5 cm **You may NOT be eligible if...** - (Lung group) You have previously received radiation to the chest - (Brain group) You have previously received whole-brain radiation - You have more than 5 brain metastases or metastases outside the allowed size range - Your overall health status does not meet study requirements Talk to your doctor to see if this trial is right for you.