Lymphocyte Depletion and Change in Lymphocyte Functionality

Inclusion Criteria:

1. Willingness and ability to provide written informed consent and to comply with the study protocol.
2. Diagnosis of biopsy confirmed non-small cell lung cancer (NSCLC) with planned treatment with SBRT as definitive therapy OR imaging confirmed lung lesion for which SBRT is planned for primary lung cancer (when clinician determines biopsy is not indicated), Registration should occur within 5 business days (before or after) of planning CT.
3. Patients must decline surgery or tumor(s) must be considered to be medically inoperable
4. Location and size of tumor- Participants must have either:

   * peripherally located tumors (\> 2 cm in all directions from the proximal bronchial tree; see Figure 2 above) as defined by RTOG 0915, OR
   * centrally located tumors (tumor size ≤ 5 cm, tumors within or touching the zone of the proximal bronchial tree or adjacent to mediastinal or pericardial pleura) as defined by RTOG 0813.
5. Patients with recurrence of prior surgically treated lung cancers are eligible if no further surgery is planned and they otherwise meet the eligibility criteria.
6. Measurable disease on chest CT, PET CT, CT simulation at diagnosis ( must be within 8 weeks of SBRT).
7. Pre- radiation therapy total lymphocyte count \> 0.5k/μL on blood count drawn within 2 weeks prior to registration.
8. In the opinion of the treating clinician, patient is medically able to tolerate the study SBRT treatment of 50-60 Gy in 5 fractions.
9. ECOG performance status of 0-2.
10. Age ≥ 18 years.
11. If participant is a woman of childbearing potential (WOCBP), agreement to adhere to contraception requirements from the time of consent through completion of SBRT.

Exclusion Criteria

1. Prior history of radiation therapy within 2 years of registration, however radiation therapy for skin cancer is allowed
2. Systemic anti-cancer therapy within the last year prior to registration or planned use during or within 6 months following SBRT.
3. Major surgery within the last 30 days before registration and/or planned before the completion of the 6 months post SBRT follow up timeframe.
4. Subject is a prisoner.
5. Subject is a pregnant woman.
6. Patient is not medically able to tolerate the study SBRT treatment of 50-60 Gy in 5 fractions or cannot comply with other aspects of the study including serial bloodwork.
7. Subject has HIV, AIDS, any type of hepatitis and/or any blood borne infectious disease for which the research lab cannot receive blood samples.