Multiple studies have evaluated the efficacy of SBRT in patients with early stage lung cancer. The original Indiana University phase II trial evaluating three fraction SBRT with a total dose of 60-66 Gy for T1 and T2 (\<7cm) lesions and median follow up of 50.2 months revealed a 3-year local failure rate of 5.7%. Tumor size and location did not impact tumor recurrence. \[3\]. RTOG 0236, which was a multi-institutional phase II trial evaluating the efficacy of three fraction SBRT for patients with peripherally located tumors, reported that 3-year local control rate was 98% with a median overall survival of 4 years and overall survival at 3 years of 56%. Long- term results of RTOG 0236 revealed a 5-year local failure rate of 7% and a 5-year overall survival rate of 40% \[4, 5\]. In addition, a pooled analysis of two randomized trials (Randomized study to Compare CyberKnife to Surgical Resection in Stage I Non-small Cell Lung Cancer \[STARS\] and the Trial of Either Surgery or Stereotactic Radiotherapy for Early Stage \[IA\] Lung Cancer \[ROSEL\]) comparing SBRT vs. lobectomy for operable stage I (T1-2aN0M0) NSCLC showed a 3-year overall survival for SBRT of 95% and for surgery of 79% (HR=0.14, p=0.037). There was no statistically significant difference between both groups in terms of 3-year rate of recurrence-free survival (HR = 0.69, p = 0.54) \[5\]. To evaluate the efficacy of SBRT (66 Gy in 3 fractions) compared to standard treatment (70 Gy in 35 fractions), 102 patients, with stage I inoperable NSCLC, were randomized to each treatment arm in the SPACE trial. The results were consistent with similar overall survival and progression free survival on both treatment groups. According to the TROG 09.02 CHISEL trial, stage I inoperable NSCLC patients treated with SBRT had superior local control of the primary disease (HR: 0.32) without an increase in major toxicity compared to patients treated with standard fractionation\[6\].

Pulmonary metastases frequently happen in patients with different types of cancer. Around 50% of patients who suffer from malignancy-related mortality have pulmonary metastasis at the time of autopsy \[7\]. In 1995, Hellman et al introduced the concept of oligometastases and the importance of aggressive surgical or ablative therapies to improve overall survival in this population \[8\]. As a result, SBRT technique has been widely used to treat pulmonary metastases. Multiple studies have evaluated this technique including a retrospective study evaluating 577 patients who undergo SBRT for pulmonary metastases that revealed 5-year local control of 46.3% and 5-year overall survival of 21.8% \[9\]. Based on the above findings, the researchers propose a prospective feasibility trial evaluating the combined DIBH-expiration planning and delivery technique in patients with lung tumors in close proximity to the chest wall who are candidates to receive lung SBRT per their standard care.

Based on the observed respiration dependent movement during CT simulation the study team will assign patients into two cohorts: A) Tumors with no overlap between respiratory states and B) Tumors with up to 50% overlap between respiratory states. For A, the study team will have a composite plan delivering half the dose using DIBH plan and the other half using the expiration phase plan for each fraction. For B) the radiation target will be subdivided into different zones with different zones receiving different prescriptions. The study plan will be compared to a standard plan specifically designed for the same patient. Researchers hypothesize that this technique will enable us to reduce chest wall V30 by 50% and deliver 54 Gy in 3 fractions while meeting all the dosimetric constraints. Cohorts A and B will be analyzed separately. Other dosimetric parameters will be evaluated in this trial.