Dose-escalated Adaptive Radiotherapy of Thoracic Disease for Small Cell Lung Cancer

Inclusion Criteria: * Minimum 18 years of age * Biopsy proven, newly diagnosed, untreated SCLC * Completed standard of care staging investigations including: CT chest/abdomen/pelvis, bone scan and/or or PET-CT scan, CT head or MRI brain, or chest X-ray * Eligible for platinum doublet chemotherapy * Eligible for thoracic radiotherapy, which can also include ipsilateral supraclavicular lymph node disease * Capable of providing written, informed consent prior to participation in the study. Patient's legally authorized representative (LAR) may sign on behalf of the patient. * Able and willing to comply with protocol rules and follow-up regimen * Performance status of ECOG 0-2 * Pulmonary function tests showing FEV-1 \>1.0L and DLCO \> 50% predicted * Radiation-targetable intrathoracic disease Exclusion Criteria: * No intrathoracic disease seen to target with radiation * Thoracic disease is contiguous to extra-thoracic sites, beyond ipsilateral supraclavicular lymph nodes * Mixed histology disease * Active serious infection requiring therapy * Brain metastasis that has not been symptomatically stable on dexamethasone * 4 or more sites of extrathoracic disease, even if 2 or more of these are present in the same organ system * Previous CNS or thoracic radiotherapy * Previous chemotherapy * Ineligibility for platinum doublet chemotherapy * Life expectancy of less than 3 months * Prior thoracic surgery * History of another primary malignancy other than cutaneous basal cell carcinoma unless disease-free for at least 5 years * Pregnant or breast-feeding * In LS-SCLC, patients that are not eligible for concurrent chemoradiotherapy * In ES-SCLC, patients that are not eligible for concurrent chemoradiotherapy under the experimental arm * CT contrast allergy or kidney disease with irreversibly low creatinine clearance inadequate for IV contrast administration (for the purposes of high quality contrast enhanced CT chest and abdomen for follow-up imaging) * Lack of intrathoracic disease or intrathoracic disease spread not feasible to treat with adaptive radiotherapy * Participant in development and conduct of the research study