Active Surveillance in Early Lung Cancer

Main Cohort Inclusion Criteria: * Patient at UVMCC. * Has pathologically proven recent diagnosis (≤180 days) of solitary or multifocal Stage T1a/b/c, N0, M0 \[AJCC Staging, 8th Ed.\] non-small cell lung cancer \[NSCLC\] or carcinoid tumors. * History \& physical ≤90 days prior to enrollment. * Tumors may have a solid component of any magnitude ≤3 cm. * Age ≥65 years old. * Charlson Comorbidity Index \[CCI\] ≥6 within 90 days prior to enrollment. * Zubrod performance status of 0-3 within 90 days prior to enrollment. * Deemed unresectable or "medically inoperable" due to medical co-morbidities. Otherwise operable patients who decline surgery are considered inoperable. * Eligible to receive treatment via SABR at the discretion of the treating oncologist. * CT scan of the chest (contrast preferred) ≤90 days of enrollment with slice thickness ≤3 mm. * Whole body PET scan ≤90 days prior to enrollment. \[Preferably before biopsy performed\] Correlative Science Only Cohort Inclusion Criteria: * Patient at UVMCC. * Patients who have been followed via active surveillance \> 180 days already may enroll in the correlative science only cohort for the purpose of blood draws only, regardless of reason active surveillance was chosen. * Pathologically proven diagnosis (\>180 days prior to enrollment) of solitary or multifocal Stage T1a/b/c, N0, M0 \[AJCC Staging, 8th Ed.\] non-small cell lung cancer \[NSCLC\] or carcinoid tumors. * History \& physical ≤90 days prior to enrollment. * Any age. * Any Charlson Comorbidity Index \[CCI\]. * Zubrod performance status of 0-3 within 90 days prior to enrollment. * Can be medically operable or inoperable with any medical co-morbidities. * CT scan of the chest (contrast preferred) ≤90 days around (before or after) enrollment with slice thickness ≤3 mm. \[Frequency as deemed appropriate by managing oncologist\]. * Whole body PET/CT scan \[Not required pre-enrollment, and frequency as deemed appropriate by managing oncologist\]. Exclusion Criteria (both cohorts): * Prior radiation treatment of the study NSCLC. * Prior receipt of any systemic treatment for the study NSCLC.