• Stage IV NSCLC. Note that patients are eligible for the study if, prior to the development of stage IV disease, they have received definitive treatment for early stage disease, presuming that they remain candidates for local ablative therapy (LAT).

• AJCC 8th Edition Stage IV disease

• Ten or less metastatic lesions (Note that this criterion includes lesions, not sites: 3 brain metastases = 3 lesions).

• o Imaging defining extent of disease should be performed within 4 weeks of ctDNA blood draw

• All lesions amenable to LAT.

• At least one site of measurable disease

• Detectable ctDNA

• ECOG Performance status 0 - 2.

• Age ≥ 18 years.

• The participant, or their legally authorized representative (LAR) are able to provide informed consent.

• Female subjects must either be of non-reproductive potential (i.e. post-menopausal by history: \>/= 60 years old and no menses for 1\> year without an alternative medical cause; OR history of hysterectomy, OR history of bilateral tubal ligation, OR history of bilateral oophorectomy) or must have a negative pregnancy test (serum) within 2 weeks or a urine pregnancy test the day of treatment.

• Adequate baseline organ function to allow SBRT to all relevant targets, as determined by the treating radiation oncologist based on lesion location, lesion size, and proximity to relevant organs at risk.

• Patient initiated their ctDNA blood draws during their first 4 cycles of first line systemic therapy +/- 3 weeks (during their first 4 cycles, or up to 3 weeks before/after they have begun/ended their first 4 cycles of systemic therapy.

• Has received at least 2 cycles of treatment, remains on first-line therapy

• No evidence of radiographic RECIST 1.1\* progression (as defined above), as measured through the following imaging modalities:

‣ 1\) PET/CT scan or CT scan of the chest/abdomen/pelvis within 4 weeks of blood draw for ctDNA analysis

⁃ 2\) MRI or CT scan of the brain at baseline, AND within 4 weeks of blood draw for ctDNA analysis (optional, per discretion of treating physician)

• NR-VAF results within 4 weeks of enrollment

• o For patients that do not have detectable ctDNA at enrollment in the monitoring phase, NR-VAF is defined as the emergence of detectable VAF on follow up blood draws

• All active lesions amenable to LAT o Note that patients who receive local therapy (radiation, surgery, or RFA) prior to enrollment for palliative purposes or to CNS lesions are eligible for enrollment if: a) all other eligibility criteria are met and b) at least one other lesion is amenable to LAT and is RECIST evaluable. All lesions treated for palliative purposes will also be counted towards the total number of lesions.