3.1 Inclusion Criteria: - Eligibility Criteria

        3.1.1 Age >/= 18 years

        3.1.2 ECOG performance status 0-1 3.1.3 Histologically proven diagnosis of a prior
        thoracic malignancy treated with thoracic external beam radiotherapy with or without
        systemic chemotherapy

        3.1.4 Pathologic or clinical diagnosis of a new or loco-regional recurrent lung
        malignancy. A reasonable attempt should be made to make a pathologic diagnosis of
        malignancy (ie. bronchoscopy, CT guided lung biopsy)

          -  Loco-regional is defined as recurrence within the region of the primary tumor or
             adjacent draining lymph node regions.

          -  The new lesion or loco-regional recurrence must be within or adjacent to the
             previously irradiated treatment volume.

        3.1.5 Imaging as follows:

          -  CT scan of the chest with IV contrast within 8 weeks of registration

          -  Whole body PET scan within 8 weeks of registration

        3.1.6 Pulmonary function test (PFTs), including diffusion capacity within 8 weeks of
        registration

        3.1.7 Negative serum pregnancy test within 2 weeks prior to registration for women of
        childbearing potential.

        3.1.6 Women of childbearing potential and male participants who are sexually active must
        agree to use a medically effective means of birth control

        3.1.7 Patients must provide study specific informed consent prior to study entry.

        Exclusion Criteria:

        - 3.2 Exclusion Criteria

        3.2.1. No previously reported thoracic radiotherapy

        3.2.2. FEV1 <20% predicted and/or DLCO <20% predicted

        3.2.2. Pregnant women or lactating women

        3.2.3 Chemotherapy within 4 weeks of the initiation of SABR

        3.2.4 Plans to administer systemic chemotherapy overlapping with radiotherapy