Personalized Radiotherapy for Individualized Treatment Strategies and Monitoring (PRISM)

Inclusion Criteria: Cohort A: * \>=18 years old * Performance status ECOG 0-2 * Extensive stage small cell lung cancer diagnosed by tissue biopsy within 180 days of registration. * Patient must be planned for or receiving standard of care chemoimmunotherapy. * Patient must have received no more than 3 cycles by time of study enrollment. * Able and indicated according to investigator to receive thoracic radiotherapy Cohort B: * 18 years old * Diagnosis of solid tumor malignancy with MRI-defined brain metastasis lesions within 60 days of registration * Each brain metastasis lesion enrolled must be 2 - 5 cm, except brainstem lesions which may be 1.5 - 5cm in size. Cohort C: * \>=18 years old * Performance status ECOG 0-2 * Histologically confirmed surgically resectable, high grade (FNCLCC grade 2 or 3), localized soft tissue sarcoma of the trunk or extremities that measures \>5 cm in any direction as assessed by imaging * Eligible to receive immunotherapy Cohort D: * \>=18 years old * Performance status ECOG 0-2 * Pathologically proven diagnosis of squamous cell carcinoma of the oral cavity, oropharynx, larynx, or hypopharynx * Clinical stage III/IVA (AJCC 8th edition) * Disease must be deemed resectable by head and neck surgeon * Eligible to receive immunotherapy Exclusion Criteria: Cohort A: ⨀ Prior thoracic Radiotherapy Cohort B: * Prior whole brain Radiotherapy * Prior surgical resection or focal radiotherapy of a target brain metastasis * Leptomeningeal disease Cohort C: * Unresectable or metastatic (nodal or distant) disease * Synchronous malignancy requiring chemotherapy or other intensive treatment * Locally recurrent soft tissue sarcoma * Prior immunotherapy * Pregnancy or breastfeeding Cohort D: * Distant metastasis * Inability to undergo PET-CT for baseline staging * HPV-positive or p16-positive oropharyngeal cancer * Prior systemic chemotherapy for the study cancer; prior chemotherapy for a remote cancer is allowable * Prior immunotherapy for the study cancer or for a remote cancer * Prior head and neck radiotherapy